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Sample records for air-water interfacial area

  1. Measuring Air-water Interfacial Area for Soils Using the Mass Balance Surfactant-tracer Method

    PubMed Central

    Araujo, Juliana B.; Mainhagu, Jon; Brusseau, Mark L.

    2015-01-01

    There are several methods for conducting interfacial partitioning tracer tests to measure air-water interfacial area in porous media. One such approach is the mass balance surfactant tracer method. An advantage of the mass-balance method compared to other tracer-based methods is that a single test can produce multiple interfacial area measurements over a wide range of water saturations. The mass-balance method has been used to date only for glass beads or treated quartz sand. The purpose of this research is to investigate the effectiveness and implementability of the mass-balance method for application to more complex porous media. The results indicate that interfacial areas measured with the mass-balance method are consistent with values obtained with the miscible-displacement method. This includes results for a soil, for which solid-phase adsorption was a significant component of total tracer retention. PMID:25950136

  2. Measuring air-water interfacial area for soils using the mass balance surfactant-tracer method.

    PubMed

    Araujo, Juliana B; Mainhagu, Jon; Brusseau, Mark L

    2015-09-01

    There are several methods for conducting interfacial partitioning tracer tests to measure air-water interfacial area in porous media. One such approach is the mass balance surfactant tracer method. An advantage of the mass-balance method compared to other tracer-based methods is that a single test can produce multiple interfacial area measurements over a wide range of water saturations. The mass-balance method has been used to date only for glass beads or treated quartz sand. The purpose of this research is to investigate the effectiveness and implementability of the mass-balance method for application to more complex porous media. The results indicate that interfacial areas measured with the mass-balance method are consistent with values obtained with the miscible-displacement method. This includes results for a soil, for which solid-phase adsorption was a significant component of total tracer retention.

  3. Novel methods for measuring air-water interfacial area in unsaturated porous media.

    PubMed

    Brusseau, Mark L; El Ouni, Asma; Araujo, Juliana B; Zhong, Hua

    2015-05-01

    Interfacial partitioning tracer tests (IPTT) are used to measure air-water interfacial area for unsaturated porous media. The standard IPTT method involves conducting tests wherein an aqueous surfactant solution is introduced into a packed column under unsaturated flow conditions. Surfactant-induced drainage has been observed to occur for this method in some cases, which can complicate data analysis and impart uncertainty to the measured values. Two novel alternative approaches for conducting IPTTs are presented herein that are designed in part to prevent surfactant-induced drainage. The two methods are termed the dual-surfactant IPTT (IPTT-DS) and the residual-air IPTT (IPTT-RA). The two methods were used to measure air-water interfacial areas for two natural porous media. System monitoring during the tests revealed no measurable surfactant-induced drainage. The measured interfacial areas compared well to those obtained with the standard IPTT method conducted in such a manner that surfactant-induced drainage was prevented. PMID:25732632

  4. Novel methods for measuring air-water interfacial area in unsaturated porous media.

    PubMed

    Brusseau, Mark L; El Ouni, Asma; Araujo, Juliana B; Zhong, Hua

    2015-05-01

    Interfacial partitioning tracer tests (IPTT) are used to measure air-water interfacial area for unsaturated porous media. The standard IPTT method involves conducting tests wherein an aqueous surfactant solution is introduced into a packed column under unsaturated flow conditions. Surfactant-induced drainage has been observed to occur for this method in some cases, which can complicate data analysis and impart uncertainty to the measured values. Two novel alternative approaches for conducting IPTTs are presented herein that are designed in part to prevent surfactant-induced drainage. The two methods are termed the dual-surfactant IPTT (IPTT-DS) and the residual-air IPTT (IPTT-RA). The two methods were used to measure air-water interfacial areas for two natural porous media. System monitoring during the tests revealed no measurable surfactant-induced drainage. The measured interfacial areas compared well to those obtained with the standard IPTT method conducted in such a manner that surfactant-induced drainage was prevented.

  5. An air-water interfacial area based variable tortuosity model for unsaturated sands

    SciTech Connect

    Khaleel, Raziuddin; Saripalli, Prasad

    2006-05-01

    Based on Kozeny-Carman equation for saturated media permeability, a new model is developed for the prediction of unsaturated hydraulic conductivity, K as a function of moisture content, ?. The K(???) estimates are obtained using laboratory measurements of moisture retention and saturated hydraulic conductivity, and a saturation-dependent tortuosity based on the immiscible fluid (air-water) interfacial area. Tortuosity (?a) for unsaturated media is defined as aaw/aaw,o (ratio of the specific air-water interfacial area of a real and the corresponding idealized porous medium). A correspondence between the real and idealized media is established by using the laboratory-measured soil moisture retention curve to calculate the interfacial area. The general trend in prediction of ?a as a function water saturation is in agreement with similar recent predictions based on diffusion theory. Unsaturated hydraulic conductivities measured for a number of coarse-textured, repacked Hanford sediments agree well with predictions based on the modified Kozeny-Carman relation. Because of the use of saturated hydraulic conductivity, a slight bias is apparent in measured and predicted K at low ?. While the modified Kozeny-Carman relation was found to be reasonably accurate in predicting K(??) for the repacked, sandy soils considered in this study, a further testing of the new model for undisturbed sediments and other soil textures would be useful.

  6. Numerical Modeling of Surfactant-Induced Flow During Laboratory Measurement of Air-Water Interfacial Area

    NASA Astrophysics Data System (ADS)

    Henry, E. J.; Costanza-Robinson, M. S.

    2010-12-01

    An understanding of the relationship between air-water interfacial area (AI) and moisture saturation (SW) is necessary for the accurate prediction of the subsurface transport of solutes that partition to the interface or are readily transferred across the interface. Interfacial areas are commonly measured in a laboratory soil column using the aqueous interfacial-partitioning tracer methodology (IPT), in which AI is calculated based on the ratio of travel times of interfacial and non-reactive tracers. IPTs are conducted in uniformly-wetted soil columns and therefore, allow the determination of AI at a particular value of SW. The interfacial tracers used are typically surfactants, such as sodium dodecyl benzene sulfonate (SDBS), which are reversibly retained the air-water interface. At the SDBS concentrations often used, the aqueous surface tension of the interfacial tracer solution is approximately 30% lower than that of the non-reactive tracer solution. Because capillary pressure gradients caused by surfactant-induced surface tension gradients can induce unsaturated flow, we used numerical modeling to examine the potential for perturbations in unsaturated flow, and thus non-uniform distributions in SW, to occur during IPT tests. We used HYDRUS 1D, modified to include concentration-dependent surfactant effects on capillary pressure, in order to simulate a typical IPT experimental configuration in which SDBS was the interfacial tracer. Linear partitioning of the tracer to the air-water interface and sorption to the solid were included as SDBS retention mechanisms. The simulation results indicated that the surface tension changes caused by SDBS were sufficient to induce significant transient unsaturated flow, which was manifested as localized drainage and wetting as the SDBS passed through the column. Average SW in the column subsequently rebounded and reached a new steady-state flow condition once SDBS had displaced resident tracer-free water. The average SW at the

  7. Study of interfacial area transport and sensitivity analysis for air-water bubbly flow

    SciTech Connect

    Kim, S.; Sun, X.; Ishii, M.; Beus, S.G.

    2000-09-01

    The interfacial area transport equation applicable to the bubbly flow is presented. The model is evaluated against the data acquired by the state-of-the-art miniaturized double-sensor conductivity probe in an adiabatic air-water co-current vertical test loop under atmospheric pressure condition. In general, a good agreement, within the measurement error of plus/minus 10%, is observed for a wide range in the bubbly flow regime. The sensitivity analysis on the individual particle interaction mechanisms demonstrates the active interactions between the bubbles and highlights the mechanisms playing the dominant role in interfacial area transport. The analysis employing the drift flux model is also performed for the data acquired. Under the given flow conditions, the distribution parameter of 1.076 yields the best fit to the data.

  8. Surfactant-Induced Flow in Unsaturated Porous Media: Implications for Air-Water Interfacial Area Determination

    NASA Astrophysics Data System (ADS)

    Costanza-Robinson, M. S.; Zheng, Z.; Estabrook, B.; Henry, E. J.; Littlefield, M. H.

    2011-12-01

    Air-water interfacial area (AI) in porous media is an important factor governing equilibrium contaminant retention, as well as the kinetics of interphase mass transfer. Interfacial-partitioning tracer (IPT) tests are a common technique for measuring AI at a given moisture saturation (SW), where AI is calculated based on the ratio of arrival times of a surfactant and a non-reactive tracer. At surfactant concentrations often used, the aqueous surface tension of the interfacial tracer solution is ~30% lower than that of the resident porewater in the system, creating transient surface tension gradients during the IPT measurement. Because surface tension gradients create capillary pressure gradients, surfactant-induced unsaturated flow may occur during IPT tests, a process that would violate fundamental assumptions of constant SW, of steady-state flow, and of nonreactive and surfactant tracers experiencing the same transport conditions. To examine the occurrence and magnitude of surfactant-induced flow, we conducted IPT tests for unsaturated systems at ~84% initial SW using surfactant input concentrations that bracket concentrations commonly used. Despite constant boundary conditions (constant inlet flux and outlet pressure), the introduction of the surfactant solution induced considerable transience in column effluent flowrate and SW. Real-time system mass measurements revealed drainage of 20-40% SW, with the amount of drainage and the maximum rate of drainage proportional to the influent surfactant concentration, as would be expected. Because AI is inversely related to SW, the use of higher surfactant concentrations should yield larger AI estimates. Measured AI values, however, showed no clear relationship to surfactant concentration or the time-averaged SW of the system. These findings cast doubt on the reliability of IPT for AI determination.

  9. Using aliphatic alcohols as gaseous tracers in determination of water contents and air-water interfacial areas in unsaturated sands

    NASA Astrophysics Data System (ADS)

    Sung, Menghau; Chen, Bi-Hsiang

    2011-11-01

    A new type of gaseous tracer utilizing nontoxic aliphatic alcohols for the determination of water content and air-water interfacial area is tested on unsaturated sands of low water content. Alcohol vapors are generated at room temperature and passed through the experimental sand column. Breakthrough curves (BTCs) of these vapors are obtained by monitoring their effluent concentrations using GC-FID. The retardation factor with respect to each vapor transport process is obtained by optimizing BTCs data using the CXTFIT program in the reverse problem mode. The water content and the interfacial area are subsequently calculated from their retardation factors by both equilibrium and nonequilibrium transport models. Experimental results indicate that the pentanol tracer is feasible in the determination of water content at conditions when the degree of water saturation is low. In the determination of air-water interfacial area, decanol is selected due to its interfacial adsorption characteristics. By comparing to interfacial areas from theoretical predictions as well as other conventional tarcer methods, the ones determined from the decanol tracer tests are found to be close to the true interfacial areas when the water content is low.

  10. Measurement of Air-Water Interfacial Areas in Unsaturated Water-Wet Sandy Porous Media Using Synchrotron X-ray Microtomography

    NASA Astrophysics Data System (ADS)

    Costanza-Robinson, M. S.; Harrold, K. H.; Brusseau, M. L.; Lieb-Lappen, R. M.

    2006-12-01

    Air-water interfacial area (Aia) is a critical parameter in porous media systems that influences equilibrium fluid and contaminant distributions, as well as mass- and energy-transfer kinetics. Despite its importance, methods for quantitative measurement of Aia are not well developed. In this work, innovative synchrotron X-ray microtomography methods were used to measure Aia for a variety of unsaturated water-wet natural silica sands and glass spheres as a function of water saturation (Sw). Individual capillary and smooth-film contributions to Aia were determined for a subset of these media using X-ray absorption edge-difference imaging techniques. Aia values were observed to decrease linearly for all porous media with increasing Sw. A linear relationship was also observed between maximum Aia values, obtained by linear extrapolation to zero water saturation, and smooth-sphere-approximated surface areas for glass spheres (r2 = 0.99) and natural silica sands (r2=0.76). The weaker correlation for natural media is likely due to grain shape variation among the sands and greater uncertainty associated with areas extracted from the more complex natural-sand images. Total measured Aia was further differentiated into individual capillary and smooth-film contributions for select media, indicating that films contribute the majority of air-water interfacial areas measured by this technique. Because the relevance of individual interfacial domains differs widely for various contaminant and remediation scenarios, the ability to experimentally distinguish these domains using X-ray microtomography represents an important advance.

  11. Implications of surfactant-induced flow for miscible-displacement estimation of air-water interfacial areas in unsaturated porous media.

    PubMed

    Costanza-Robinson, Molly S; Zheng, Zheng; Henry, Eric J; Estabrook, Benjamin D; Littlefield, Malcolm H

    2012-10-16

    Surfactant miscible-displacement experiments represent a conventional means of estimating air-water interfacial area (A(I)) in unsaturated porous media. However, changes in surface tension during the experiment can potentially induce unsaturated flow, thereby altering interfacial areas and violating several fundamental method assumptions, including that of steady-state flow. In this work, the magnitude of surfactant-induced flow was quantified by monitoring moisture content and perturbations to effluent flow rate during miscible-displacement experiments conducted using a range of surfactant concentrations. For systems initially at 83% moisture saturation (S(W)), decreases of 18-43% S(W) occurred following surfactant introduction, with the magnitude and rate of drainage inversely related to the surface tension of the surfactant solution. Drainage induced by 0.1 mM sodium dodecyl benzene sulfonate, commonly used for A(I) estimation, resulted in effluent flow rate increases of up to 27% above steady-state conditions and is estimated to more than double the interfacial area over the course of the experiment. Depending on the surfactant concentration and the moisture content used to describe the system, A(I) estimates varied more than 3-fold. The magnitude of surfactant-induced flow is considerably larger than previously recognized and casts doubt on the reliability of A(I) estimation by surfactant miscible-displacement.

  12. Interfacial structures of confined air-water two-phase bubbly flow

    SciTech Connect

    Kim, S.; Ishii, M.; Wu, Q.; McCreary, D.; Beus, S.G.

    2000-08-01

    The interfacial structure of the two-phase flows is of great importance in view of theoretical modeling and practical applications. In the present study, the focus is made on obtaining detailed local two-phase parameters in the air-water bubbly flow in a rectangular vertical duct using the double-sensor conductivity probe. The characteristic wall-peak is observed in the profiles of the interracial area concentration and the void fraction. The development of the interfacial area concentration along the axial direction of the flow is studied in view of the interfacial area transport and bubble interactions. The experimental data is compared with the drift flux model with C{sub 0} = 1.35.

  13. Interfacial characterization of Pluronic PE9400 at biocompatible (air-water and limonene-water) interfaces.

    PubMed

    Pérez-Mosqueda, Luis M; Maldonado-Valderrama, Julia; Ramírez, Pablo; Cabrerizo-Vílchez, Miguel A; Muñoz, José

    2013-11-01

    In this work, we provide an accurate characterization of non-ionic triblock copolymer Pluronic PE9400 at the air-water and limonene-water interfaces, comprising a systematic analysis of surface tension isotherms, dynamic curves, dilatational rheology and desorption profiles. The surface pressure isotherms display two different slopes of the Π-c plot suggesting the existence of two adsorption regimes for PE9400 at both interfaces. Application of a theoretical model, which assumes the coexistence of different adsorbed states characterized by their molar areas, allows quantification of the conformational changes occurring at the adsorbed layer, indentifying differences between the conformations adopted at the air-water and the limonene-water interface. The presence of two maxima in the dilatational modulus vs. interfacial pressure importantly corroborates this conformational change from a 2D flat conformation to 3D brush one. Moreover, the dilatational response provides mechanical diferences between the interfacial layers formed at the two interfaces analyzed. Dynamic surface pressure data were transformed into a dimensionless form and fitted to another model which considers the influence of the reorganization process on the adsorption dynamics. Finally, the desorption profiles reveal that Pluronic PE9400 is irreversibly adsorbed at both interfaces regardless of the interfacial conformation and nature of the interface. The systematic characterization presented in this work provides important new findings on the interfacial properties of pluronics which can be applied in the rational development of new products, such as biocompatible limonene-based emulsions and/or microemulsions.

  14. Development of Interfacial Structure in a Confined Air-Water Cap-Turbulent and Churn-Turbulent Flow

    SciTech Connect

    Xiaodong Sun; Seungjin Kim; Ling Cheng; Mamoru Ishii; Beus, Stephen G.

    2002-07-01

    The objective of the present work is to study and model the interfacial structure development of air-water two-phase flow in a confined test section. Experiments of a total of 9 flow conditions in cap-turbulent and churn-turbulent flow regimes are carried out in a vertical air-water upward two-phase flow experimental loop with a test section of 200-mm in width and 10-mm in gap. Miniaturized four-sensor conductivity probes are used to measure local two-phase parameters at three different elevations for each flow condition. The bubbles captured by the probes are categorized into two groups in view of the two-group interfacial area transport equation, i.e., spherical/distorted bubbles as Group 1 and cap/churn-turbulent bubbles as Group 2. The acquired parameters are time-averaged local void fraction, interfacial velocity, bubble number frequency, interfacial area concentration, and bubble Sauter mean diameter for both groups of bubbles. Also, the line-averaged and area-averaged data are presented and discussed. The comparisons of these parameters at different elevations demonstrate the development of interfacial structure along the flow direction due to bubble interactions. (authors)

  15. Development of Interfacial Structure in a Confined Air-Water Cap-Turbulent and Churn-Turbulent Flow

    SciTech Connect

    X. Sun; S. Kim; L. Cheng; M. Ishii; S.G. Beus

    2001-10-31

    The objective of the present work is to study and model the interfacial structure development of air-water two-phase flow in a confined test section. Experiments of a total of 9 flow conditions in a cap-turbulent and churn-turbulent flow regimes are carried out in a vertical air-water upward two-phase flow experimental loop with a test section of 20-cm in width and 1-cm in gap. The miniaturized four-sensor conductivity probes are used to measure local two-phase parameters at three different elevations for each flow condition. The bubbles captured by the probes are categorized into two groups in view of the two-group interfacial area transport equation, i.e., spherical/distorted bubbles as Group 1 and cap/churn-turbulent bubbles as Group 2. The acquired parameters are time-averaged local void fraction, interfacial velocity, bubble number frequency, interfacial area concentration, and bubble Sauter mean diameter for both groups of bubbles. Also, the line-averaged and area-averaged data are presented and discussed. The comparisons of these parameters at different elevations demonstrate the development of interfacial structure along the flow direction due to bubble interactions.

  16. Interfacial area transport in bubbly flow

    SciTech Connect

    Ishii, M.; Wu, Q.; Revankar, S.T.

    1997-12-31

    In order to close the two-fluid model for two-phase flow analyses, the interfacial area concentration needs to be modeled as a constitutive relation. In this study, the focus was on the investigation of the interfacial area concentration transport phenomena, both theoretically and experimentally. The interfacial area concentration transport equation for air-water bubbly up-flow in a vertical pipe was developed, and the models for the source and sink terms were provided. The necessary parameters for the experimental studies were identified, including the local time-averaged void fraction, interfacial area concentration, bubble interfacial velocity, liquid velocity and turbulent intensity. Experiments were performed with air-water mixture at atmospheric pressure. Double-sensor conductivity probe and hot-film probe were employed to measure the identified parameters. With these experimental data, the preliminary model evaluation was carried out for the simplest form of the developed interfacial area transport equation, i.e., the one-dimensional transport equation.

  17. Air/water interfacial formation of freestanding, stimuli-responsive, self-healing catecholamine Janus-faced microfilms.

    PubMed

    Hong, Seonki; Schaber, Clemens F; Dening, Kirstin; Appel, Esther; Gorb, Stanislav N; Lee, Haeshin

    2014-12-01

    A catecholamine freestanding film is discovered to be spontaneously formed at the air-water interface, and the film has unique properties of robust surface adhesiveness, self-healing, and stimuli-responsive properties. The interfacial film-producing procedure is a simple single step containing polyamines and catechol(amine)s. It is found that oxygen-rich regions existing at an air-water interface greatly accelerate the catecholamine crosslinking reaction. PMID:25220108

  18. Air/water interfacial formation of freestanding, stimuli-responsive, self-healing catecholamine Janus-faced microfilms.

    PubMed

    Hong, Seonki; Schaber, Clemens F; Dening, Kirstin; Appel, Esther; Gorb, Stanislav N; Lee, Haeshin

    2014-12-01

    A catecholamine freestanding film is discovered to be spontaneously formed at the air-water interface, and the film has unique properties of robust surface adhesiveness, self-healing, and stimuli-responsive properties. The interfacial film-producing procedure is a simple single step containing polyamines and catechol(amine)s. It is found that oxygen-rich regions existing at an air-water interface greatly accelerate the catecholamine crosslinking reaction.

  19. Measurement of interfacial structures in horizontal air-water bubbly flows

    SciTech Connect

    Talley, J. D.; Worosz, T.; Dodds, M. R.; Kim, S.

    2012-07-01

    In order to predict multi-dimensional phenomena in nuclear reactor systems, methods relying on computational fluid dynamics (CFD) codes are essential. However, to be applicable in assessing thermal-hydraulic safety, these codes must be able to accurately predict the development of two-phase flows. Therefore, before practical application these codes must be assessed using experimental databases that capture multi-dimensional phenomena. While a large database exists that can be employed to assess predictions in vertical flows, the available database for horizontal flows is significantly lacking. Therefore, the current work seeks to develop an additional database in air-water horizontal bubbly flow through a 38.1 mm ID test section with a total development length of approximately 250 diameters. The experimental conditions are chosen to cover a wide range of the bubbly flow regime based upon flow visualization using a high-speed video camera. A database of local time-averaged void fraction, bubble velocity, interfacial area concentration, and bubble Sauter mean diameter are acquired throughout the pipe cross-section using a four-sensor conductivity probe. To investigate the evolution of the flow, measurements are made at axial locations of 44, 116, and 244 diameters downstream of the inlet. In the current work, only measurements obtained at L/D = 244 are presented. It is found that increasing the liquid superficial velocity tends to reduce both the bubble size and the degree of bubble packing near the upper wall. However, it is observed that the position of the maximum void fraction value remains nearly constant and is located approximately one bubble diameter away from the upper wall. It is also found that the bubble velocity exhibits a power law behavior resembling a single phase liquid turbulent velocity profile. Moreover, the local bubble velocity tends to decrease as the local void fraction increases. Conversely, increasing the gas superficial velocity is found to

  20. Interfacial dynamic and dilational rheology of polyelectrolyte/surfactant two-component nanoparticle systems at air-water interface

    NASA Astrophysics Data System (ADS)

    Tong, L. J.; Bao, M. T.; Li, Y. M.; Gong, H. Y.

    2014-10-01

    The interfacial characteristics of nanoparticles and consequent inter-particle interactions at the interface are poorly understood. In this work, the interfacial dynamic and corresponding dilational surface rheology of self-assembled polyelectrolyte/surfactant nanoparticles at the air-water interface are characterized. The nanoparticles are prepared from dodecyltrimethylammonium (DTAB) and poly (sodium 4-styrene-sulfonate) (PSS) by mixing them in aqueous solution. The interfacial dynamic characteristics have been carried out by comparing the surface pressure with the dilational rheological response of these nanoparticles at interface. The results indicate that this type of nanoparticles can adsorb at the interface forming a nanoparticle monolayer, which leads to the surface tension decreased markedly. The dependence of surface pressure on time shows the instability and disassembly process of nanoparticles at the interface. On the basis of these observations, it is proposed that the nanoparticles undergo a dynamic process that interface induced nanoparticles disassembly into DTAB/PSS complexes. The presence of PSS in the subphase can promote the process of nanoparticles disassembly. A transition point in dilational elasticity and viscosity response of the nanoparticles versus oscillation frequency further validate the micro dynamic process of nanoparticles and the formation of polyelectrolyte/surfactant complex monolayer at the interface.

  1. Experimental investigation on the interfacial characteristics of stratified air-water two-phase flow in a horizontal pipe

    NASA Astrophysics Data System (ADS)

    Hudaya, Akhmad Zidni; Kuntoro, Hadiyan Yusuf; Dinaryanto, Okto; Deendarlianto, Indarto

    2016-06-01

    The interfacial wave characteristics of stratified air-water two-phase flow in a horizontal pipe were experimentally investigated by using the flush-mounted constant electric current method (CECM) sensors. The experiments were conducted in a horizontal two-phase flow loop 9.5 m long (L) consisting of transparent acrylic pipe of 26 mm i.d. (D). To obtain the stratified flow pattern, the superficial gas and liquid velocities were set to 1.02 - 3.77 m/s and 0.016 - 0.92 m/s, respectively. Several interfacial wave patterns as described by several investigators were identified. The common parameters such as liquid hold-up, probability distribution function, wave velocity and wave frequency were investigated as the function of the liquid and gas flow rates. The interfacial curvature was calculated on the basis of the liquid hold-up data from the CECM sensors and the liquid film thickness data from the image processing technique in the previous work. As a result, it was found that the mean liquid hold-up decreases with the increase of the superficial gas velocity. In the same sub flow pattern, the wave velocity increases as the superficial gas velocity increases. On the other hand, in the two-dimensional wave region, the dominant frequency decreases with the increase of the superficial liquid velocity.

  2. Effects of surface pressure on the properties of Langmuir monolayers and interfacial water at the air-water interface.

    PubMed

    Lin, Wei; Clark, Anthony J; Paesani, Francesco

    2015-02-24

    The effects of surface pressure on the physical properties of Langmuir monolayers of palmitic acid (PA) and dipalmitoylphosphatidic acid (DPPA) at the air/water interface are investigated through molecular dynamics simulations with atomistic force fields. The structure and dynamics of both monolayers and interfacial water are compared across the range of surface pressures at which stable monolayers can form. For PA monolayers at T = 300 K, the untilted condensed phase with a hexagonal lattice structure is found at high surface pressure, while the uniformly tilted condensed phase with a centered rectangular lattice structure is observed at low surface pressure, in agreement with the available experimental data. A state with uniform chain tilt but no periodic spatial ordering is observed for DPPA monolayers on a Na(+)/water subphase at both high and low surface pressures. The hydrophobic acyl chains of both monolayers pack efficiently at all surface pressures, resulting in a very small number of gauche defects. The analysis of the hydrogen-bonding structure/dynamics at the monolayer/water interface indicates that water molecules hydrogen-bonded to the DPPA head groups reorient more slowly than those hydrogen-bonded to the PA head groups, with the orientational dynamics becoming significantly slower at high surface pressure. Possible implications for physicochemical processes taking place on marine aerosols in the atmosphere are discussed.

  3. Adsorption of β-casein-surfactant mixed layers at the air-water interface evaluated by interfacial rheology.

    PubMed

    Maestro, Armando; Kotsmar, Csaba; Javadi, Aliyar; Miller, Reinhard; Ortega, Francisco; Rubio, Ramón G

    2012-04-26

    This work presents a detailed study of the dilational viscoelastic moduli of the adsorption layers of the milk protein β-casein (BCS) and a surfactant at the liquid/air interface, over a broad frequency range. Two complementary techniques have been used: a drop profile tensiometry technique and an excited capillary wave method, ECW. Two different surfactants were studied: the nonionic dodecyldimethylphosphine oxide (C12DMPO) and the cationic dodecyltrimethylammonium bromide (DoTAB). The interfacial dilational elasticity and viscosity are very sensitive to the composition of protein-surfactant mixed adsorption layers at the air/water interface. Two different dynamic processes have been observed for the two systems studied, whose characteristic frequencies are close to 0.01 and 100 Hz. In both systems, the surface elasticity was found to show a maximum when plotted versus the surfactant concentration. However, at frequencies above 50 Hz the surface elasticity of BCS + C12DMPO is higher than the one of the aqueous BCS solution over most of the surfactant concentration range, whereas for the BCS + DoTAB it is smaller for high surfactant concentrations and higher at low concentrations. The BCS-surfactant interaction modifies the BCS random coil structure via electrostatic and/or hydrophobic interactions, leading to a competitive adsorption of the BCS-surfactant complexes with the free, unbound surfactant molecules. Increasing the surfactant concentration decreases the adsorbed proteins. However, the BCS molecules are rather strongly bound to the interface due to their large adsorption energy. The results have been fitted to the model proposed by C. Kotsmar et al. ( J. Phys. Chem. B 2009 , 113 , 103 ). Even though the model describes well the concentration dependence of the limiting elasticity, it does not properly describe its frequency dependence.

  4. Experimentally probing the libration of interfacial water: the rotational potential of water is stiffer at the air/water interface than in bulk liquid.

    PubMed

    Tong, Yujin; Kampfrath, Tobias; Campen, R Kramer

    2016-07-21

    Most properties of liquid water are determined by its hydrogen-bond network. Because forming an aqueous interface requires termination of this network, one might expect the molecular level properties of interfacial water to markedly differ from water in bulk. Intriguingly, much prior experimental and theoretical work has found that, from the perspective of their time-averaged structure and picosecond structural dynamics, hydrogen-bonded OH groups at an air/water interface behave the same as hydrogen-bonded OH groups in bulk liquid water. Here we report the first experimental observation of interfacial water's libration (i.e. frustrated rotation) using the laser-based technique vibrational sum frequency spectroscopy. We find this mode has a frequency of 834 cm(-1), ≈165 cm(-1) higher than in bulk liquid water at the same temperature and similar to bulk ice. Because libration frequency is proportional to the stiffness of water's rotational potential, this increase suggests that one effect of terminating bulk water's hydrogen bonding network at the air/water interface is retarding rotation of water around intact hydrogen bonds. Because in bulk liquid water the libration plays a key role in stabilizing reaction intermediates and dissipating excess vibrational energy, we expect the ability to probe this mode in interfacial water to open new perspectives on the kinetics of heterogeneous reactions at aqueous interfaces. PMID:27339861

  5. [Interfacial area and interfacial transfer in two-phase flow

    SciTech Connect

    Ishii, M.

    1993-09-01

    A joint research program funded by the DOE/BES at Purdue University and the University of Wisconsin-Milwaukee has been underway. The main efforts of the Purdue program were concentrated on the following tasks. Development of Four Sensor Measurement Method; Experimental Study of Axial Changes of Transverse Void and Interfacial Area Profiles in Bubbly Flow; Modeling of the Probe-Particle Interaction Using Monte Carlo Numerical Simulation; and Experimental Study of the Stability of Interface of Very Large Bubbles. Highlights of these research results are reported.

  6. Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume IV. Chapters 15-19)

    SciTech Connect

    Guo, T.; Park, J.; Kojasoy, G.

    2003-03-15

    Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.

  7. Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume III. Chapters 11-14)

    SciTech Connect

    Guo, T.; Park, J.; Kojasoy, G.

    2003-03-15

    Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.

  8. Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume I. Chapters 1-5)

    SciTech Connect

    Guo, T.; Park, J.; Kojasoy, G.

    2003-03-15

    Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.

  9. The contact area dependent interfacial thermal conductance

    SciTech Connect

    Liu, Chenhan; Wei, Zhiyong; Bi, Kedong; Yang, Juekuan; Chen, Yunfei; Wang, Jian

    2015-12-15

    The effects of the contact area on the interfacial thermal conductance σ are investigated using the atomic Green’s function method. Different from the prediction of the heat diffusion transport model, we obtain an interesting result that the interfacial thermal conductance per unit area Λ is positively dependent on the contact area as the area varies from a few atoms to several square nanometers. Through calculating the phonon transmission function, it is uncovered that the phonon transmission per unit area increases with the increased contact area. This is attributed to that each atom has more neighboring atoms in the counterpart of the interface with the increased contact area, which provides more channels for phonon transport.

  10. Correlation of Oil-Water and Air-Water Contact Angles of Diverse Silanized Surfaces and Relationship to Fluid Interfacial Tensions

    SciTech Connect

    Grate, Jay W.; Dehoff, Karl J.; Warner, Marvin G.; Pittman, Jonathan W.; Wietsma, Thomas W.; Zhang, Changyong; Oostrom, Martinus

    2012-02-24

    The use of air-water, {Theta}{sub wa}, or air-liquid contact angles is customary in surface science, while oil-water contact angles {Theta}{sub ow}, are of paramount importance in subsurface multiphase flow phenomena including petroleum reocovery, nonaqueous phase liquid fate and transport, and geological carbon sequestration. In this paper we determine both the air-water and oil-water contact angles of silica surfaces modified with a diverse selection of silanes, using hexadecane as the oil. The silanes included alkylsilanes, alkylarylsilanes, and silanes with alkyl or aryl groups that are functionalized with heteroatoms such as N, O, and S. These silanes yielded surfaces with wettabilities from water-wet to oil wet, including specific silanized surfaces functionalized with heteroatoms that yield intermediate wet surfaces. The oil-water contact angles for clean and silanized surfaces, excluding one partially fluorinated surface, correlate linearly with air-water contact angles with a slope of 1.41 (R = 0.981, n = 13). These data were used to examine a previously untested theoretical treatment relating air-water and oil-water contact angles in terms of fluid interfacial energies. Plotting the cosines of these contact angles against one another, we obtain a linear relationship in excellent agreement with the theoretical treatment; the data fit cos {Theta}{sub ow} = 0.667 cos {Theta}{sub ow} + 0.384 (R = 0.981, n = 13), intercepting cos {Theta}{sub ow} = -1 at -0.284. The theoretical slope, based on the fluid interfacial tensions {Theta}{sub wa}, {Theta}{sub ow}, and {Theta}{sub oa}, is 0.67. We also demonstrate how silanes can be used to alter the wettability of the interior of a pore network micromodel device constructed in silicon/silica with a glass cover plate. Such micromodels are used to study multiphase flow phenomena. The contact angle of the resulting interior was determined in situ. An intermediate wet micromodel gave a contact angle in excellent agreement

  11. Humidity-dependent compression-induced glass transition of the air-water interfacial Langmuir films of poly(D,L-lactic acid-ran-glycolic acid) (PLGA).

    PubMed

    Kim, Hyun Chang; Lee, Hoyoung; Jung, Hyunjung; Choi, Yun Hwa; Meron, Mati; Lin, Binhua; Bang, Joona; Won, You-Yeon

    2015-07-28

    Constant rate compression isotherms of the air-water interfacial Langmuir films of poly(D,L-lactic acid-ran-glycolic acid) (PLGA) show a distinct feature of an exponential increase in surface pressure in the high surface polymer concentration regime. We have previously demonstrated that this abrupt increase in surface pressure is linked to the glass transition of the polymer film, but the detailed mechanism of this process is not fully understood. In order to obtain a molecular-level understanding of this behavior, we performed extensive characterizations of the surface mechanical, structural and rheological properties of Langmuir PLGA films at the air-water interface, using combined experimental techniques including the Langmuir film balance, X-ray reflectivity and double-wall-ring interfacial rheometry methods. We observed that the mechanical and structural responses of the Langmuir PLGA films are significantly dependent on the rate of film compression; the glass transition was induced in the PLGA film only at fast compression rates. Surprisingly, we found that this deformation rate dependence is also dependent on the humidity of the environment. With water acting as a plasticizer for the PLGA material, the diffusion of water molecules through the PLGA film seems to be the key factor in the determination of the glass transformation properties and thus the mechanical response of the PLGA film against lateral compression. Based on our combined results, we hypothesize the following mechanism for the compression-induced glass transformation of the Langmuir PLGA film; (1) initially, a humidified/non-glassy PLGA film is formed in the full surface-coverage region (where the surface pressure shows a plateau) during compression; (2) further compression leads to the collapse of the PLGA chains and the formation of new surfaces on the air side of the film, and this newly formed top layer of the PLGA film is transiently glassy in character because the water evaporation rate

  12. Humidity-dependent compression-induced glass transition of the air-water interfacial Langmuir films of poly(D,L-lactic acid-ran-glycolic acid) (PLGA).

    PubMed

    Kim, Hyun Chang; Lee, Hoyoung; Jung, Hyunjung; Choi, Yun Hwa; Meron, Mati; Lin, Binhua; Bang, Joona; Won, You-Yeon

    2015-07-28

    Constant rate compression isotherms of the air-water interfacial Langmuir films of poly(D,L-lactic acid-ran-glycolic acid) (PLGA) show a distinct feature of an exponential increase in surface pressure in the high surface polymer concentration regime. We have previously demonstrated that this abrupt increase in surface pressure is linked to the glass transition of the polymer film, but the detailed mechanism of this process is not fully understood. In order to obtain a molecular-level understanding of this behavior, we performed extensive characterizations of the surface mechanical, structural and rheological properties of Langmuir PLGA films at the air-water interface, using combined experimental techniques including the Langmuir film balance, X-ray reflectivity and double-wall-ring interfacial rheometry methods. We observed that the mechanical and structural responses of the Langmuir PLGA films are significantly dependent on the rate of film compression; the glass transition was induced in the PLGA film only at fast compression rates. Surprisingly, we found that this deformation rate dependence is also dependent on the humidity of the environment. With water acting as a plasticizer for the PLGA material, the diffusion of water molecules through the PLGA film seems to be the key factor in the determination of the glass transformation properties and thus the mechanical response of the PLGA film against lateral compression. Based on our combined results, we hypothesize the following mechanism for the compression-induced glass transformation of the Langmuir PLGA film; (1) initially, a humidified/non-glassy PLGA film is formed in the full surface-coverage region (where the surface pressure shows a plateau) during compression; (2) further compression leads to the collapse of the PLGA chains and the formation of new surfaces on the air side of the film, and this newly formed top layer of the PLGA film is transiently glassy in character because the water evaporation rate

  13. Positional isomers of linear sodium dodecyl benzene sulfonate: solubility, self-assembly, and air/water interfacial activity.

    PubMed

    Ma, Jian-Guo; Boyd, Ben J; Drummond, Calum J

    2006-10-10

    Commercial linear alkyl benzene sulfonates (ABS) are a very important class of anionic surfactants that are employed in a wide variety of applications, especially those involving wetting and detergency. Linear ABS surfactants generally consist of a complex mixture of different chain lengths and positional isomers. This diversity and level of complexity makes it difficult to develop fundamental structure-property correlations for the commercial surfactants. In this work, six monodisperse headgroup positional isomers of sodium para-dodecyl benzene sulfonate (Na-x-DBS, x = 1-6) have been studied. The influence of headgroup position and added electrolyte (NaCl) on the solubility and self-assembly (micellar and vesicular aggregation and lyotropic liquid crystalline phase behavior) in the temperature range from 10 to 90 degrees C have been investigated. Additionally, the air-aqueous solution interfacial adsorption at 25 (no added NaCl) and 50 degrees C (from 0 to 1.0 M added NaCl) has been examined. The observed physicochemical behavior is interpreted in terms of local molecular packing constraints, and in the case of the lyotropic liquid crystalline behavior global aggregate packing constraints as well.

  14. Interfacial area and interfacial transfer in two-phase systems. DOE final report

    SciTech Connect

    Ishii, Mamoru; Hibiki, T.; Revankar, S.T.; Kim, S.; Le Corre, J.M.

    2002-07-01

    In the two-fluid model, the field equations are expressed by the six conservation equations consisting of mass, momentum and energy equations for each phase. The existence of the interfacial transfer terms is one of the most important characteristics of the two-fluid model formulation. The interfacial transfer terms are strongly related to the interfacial area concentration and to the local transfer mechanisms such as the degree of turbulence near interfaces. This study focuses on the development of a closure relation for the interfacial area concentration. A brief summary of several problems of the current closure relation for the interfacial area concentration and a new concept to overcome the problem are given.

  15. Interfacial area, velocity and void fraction in two-phase slug flow

    SciTech Connect

    Kojasoy, G.; Riznic, J.R.

    1997-12-31

    The internal flow structure of air-water plug/slug flow in a 50.3 mm dia transparent pipeline has been experimentally investigated by using a four-sensor resistivity probe. Liquid and gas volumetric superficial velocities ranged from 0.55 to 2.20 m/s and 0.27 to 2.20 m/s, respectively, and area-averaged void fractions ranged from about 10 to 70%. The local distributions of void fractions, interfacial area concentration and interface velocity were measured. Contributions from small spherical bubbles and large elongated slug bubbles toward the total void fraction and interfacial area concentration were differentiated. It was observed that the small bubble void contribution to the overall void fraction was small indicating that the large slug bubble void fraction was a dominant factor in determining the total void fraction. However, the small bubble interfacial area contribution was significant in the lower and upper portions of the pipe cross sections.

  16. Modeling interfacial area transport in multi-fluid systems

    SciTech Connect

    Yarbro, S.L.

    1996-11-01

    Many typical chemical engineering operations are multi-fluid systems. They are carried out in distillation columns (vapor/liquid), liquid-liquid contactors (liquid/liquid) and other similar devices. An important parameter is interfacial area concentration, which determines the rate of interfluid heat, mass and momentum transfer and ultimately, the overall performance of the equipment. In many cases, the models for determining interfacial area concentration are empirical and can only describe the cases for which there is experimental data. In an effort to understand multiphase reactors and the mixing process better, a multi-fluid model has been developed as part of a research effort to calculate interfacial area transport in several different types of in-line static mixers. For this work, the ensemble-averaged property conservation equations have been derived for each fluid and for the mixture. These equations were then combined to derive a transport equation for the interfacial area concentration. The final, one-dimensional model was compared to interfacial area concentration data from two sizes of Kenics in-line mixer, two sizes of concurrent jet and a Tee mixer. In all cases, the calculated and experimental data compared well with the highest scatter being with the Tee mixer comparison.

  17. Experimentally Determined Interfacial Area Between Immiscible Fluids in Porous Media

    SciTech Connect

    Crandall, Dustin; Niessner, J; Hassanizadeh, S.M; Smith, Duane

    2008-01-01

    When multiple fluids flow through a porous medium, the interaction between the fluid interfaces can be of great importance. While this is widely recognized in practical applications, numerical models often disregard interactios between discrete fluid phases due to the computational complexity. And rightly so, for this level of detail is well beyond most extended Darcy Law relationships. A new model of two-phase flow including the interfacial area has been proposed by Hassarizadeh and Gray based upon thermodynamic principles. A version of this general equation set has been implemented by Nessner and Hassarizadeh. Many of the interfacial parameters required by this equation set have never been determined from experiments. The work presented here is a description of how the interfacial area, capillary pressure, interfacial velocity and interfacial permeability from two-phase flow experiments in porous media experiments can be used to determine the required parameters. This work, while on-going, has shown the possibility of digitizing images within translucent porous media and identifying the location and behavior of interfaces under dynamic conditions. Using the described methods experimentally derived interfacial functions to be used in larger scale simulations are currently being developed. In summary, the following conclusions can be drawn: (1) by mapping a pore-throat geometry onto an image of immiscible fluid flow, the saturation of fluids and the individual interfaces between the fluids can be identified; (2) the resulting saturation profiles of the low velocity drainage flows used in this study are well described by an invasion percolation fractal scaling; (3) the interfacial area between fluids has been observed to increase in a linear fashion during the initial invasion of the non-wetting fluid; and (4) the average capillary pressure within the entire cell and representative elemental volumes were observed to plateau after a small portion of the volume was

  18. Identification of Novel Fluid-Fluid Interfacial Area in Geologic Media

    NASA Astrophysics Data System (ADS)

    Araujo, J. B.; Brusseau, M. L. L.

    2015-12-01

    Pore-scale fluid processes in geological media are critical for applications such as oil and gas recovery, radioactive waste disposal, carbon sequestration, soil moisture distribution, soil and groundwater pollution, and land stability. The continued improvement of high-resolution image acquisition and processing methods has provided a means to directly measure pore-scale fluid processes for natural geomedia, and to test the usefulness of theoretical and computational models developed to simulate them. High-resolution synchrotron X-ray microtomography was used to measure air-water interfacial area at multiple wetting-phase saturations for natural sand. Analysis of the raw and processed image data with advanced visualization tools revealed the presence of air-water interface associated with macroscopic features such as pits and crevices on the surfaces of the solids. These features and respective fluid interfaces, which are not accounted for in current theoretical or computational models, may have a significant impact on accurate understanding and simulation of multi-phase flow, energy, heat, and mass transfer, and contaminant transport.

  19. Characterizing Fluid/Fluid Interfacial Areas for Non-Wetting/Wetting Fluid Pairs in Natural Porous Media

    NASA Astrophysics Data System (ADS)

    Narter, M.; Brusseau, M. L.; Araujo, J. B.; Marble, J. C.; Schnaar, G. A.

    2011-12-01

    The interface between fluids in the subsurface mediates a number of pore-scale processes affecting contaminant transport and fate. These processes include multiphase flow, mass transfer, sorption, and bioavailability. The objective of this study was to characterize the interfacial area between pairs of non-wetting and wetting fluids in a variety of natural porous media. Synchrotron X-ray microtomography was used to obtain high-resolution, three-dimensional images of multi-phase porous media systems. Four porous media, comprising a range of physical properties, were used in the study. The three pairs of non-wetting/wetting fluids used were organic-liquid/water, air/organic-liquid, and air/water. Tetrachloroethene and hexadecane were used as the model organic liquids. The results show that for each fluid pair, total (capillary + film) interfacial areas increased linearly with decreasing non-wetting fluid saturation. The maximum specific interfacial area (Am) was determined to quantify the magnitude of interfacial area associated with a given porous medium. The value of Am did not vary significantly between fluid-pairs for a given porous medium.

  20. Measurement of Interfacial Area Production and Permeability within Porous Media

    SciTech Connect

    Crandall, Dustin; Ahmadi, Goodarz; Smith, Duane H.

    2010-01-01

    An understanding of the pore-level interactions that affect multi-phase flow in porous media is important in many subsurface engineering applications, including enhanced oil recovery, remediation of dense non-aqueous liquid contaminated sites, and geologic CO2 sequestration. Standard models of two-phase flow in porous media have been shown to have several shortcomings, which might partially be overcome using a recently developed model based on thermodynamic principles that includes interfacial area as an additional parameter. A few static experimental studies have been previously performed, which allowed the determination of static parameters of the model, but no information exists concerning the interfacial area dynamic parameters. A new experimental porous flow cell that was constructed using stereolithography for two-phase gas-liquid flow studies was used in conjunction with an in-house analysis code to provide information on dynamic evolution of both fluid phases and gas-liquid interfaces. In this paper, we give a brief introduction to the new generalized model of two-phase flow model and describe how the stereolithography flow cell experimental setup was used to obtain the dynamic parameters for the interfacial area numerical model. In particular, the methods used to determine the interfacial area permeability and production terms are shown.

  1. The Interfacial-Area-Based Relative Permeability Function

    SciTech Connect

    Zhang, Z. F.; Khaleel, Raziuddin

    2009-09-25

    CH2M Hill Plateau Remediation Company (CHPRC) requested the services of the Pacific Northwest National Laboratory (PNNL) to provide technical support for the Remediation Decision Support (RDS) activity within the Soil & Groundwater Remediation Project. A portion of the support provided in FY2009, was to extend the soil unsaturated hydraulic conductivity using an alternative approach. This alternative approach incorporates the Brooks and Corey (1964), van Genuchten (1980), and a modified van Genuchten water-retention models into the interfacial-area-based relative permeability model presented by Embid (1997). The general performance of the incorporated models is shown using typical hydraulic parameters. The relative permeability models for the wetting phase were further examined using data from literature. Results indicate that the interfacial-area-based model can describe the relative permeability of the wetting phase reasonably well.

  2. Direct, Dynamic Measurement of Interfacial Area within Porous Media

    SciTech Connect

    Crandall, Dustin; Ahmadi, Goodarz; Smith, Duane H.; Bromhal, Grant

    2010-01-01

    Standard models of two-phase flow in porous media have been shown to exhibit several shortcomings that might be partially overcome with a recently developed model based on thermodynamic principles (Hassanizadeh and Gray, 1990). This alternative two-phase flow model contains a set of new and non-standard parameters, including specific interfacial area. By incorporating interfacial area production, destruction, and propagation into functional relationships that describe the capillary pressure and saturation, a more physical model has been developed. Niessner and Hassanizadeh (2008) have examined this model numerically and have shown that the model captures saturation hysteresis with drainage/imbibition cycles. Several static experimental studies have been performed to examine the validity of this new thermodynamically based approach; these allow the determination of static parameters of the model. To date, no experimental studies have obtained information about the dynamic parameters required for the model. A new experimental porous flow cell has been constructed using stereolithography to study two-phase flow phenomena (Crandall et al. 2008). A novel image analysis tool was developed for an examination of the evolution of flow patterns during displacement experiments (Crandall et al. 2009). This analysis tool enables the direct quantification of interfacial area between fluids by matching known geometrical properties of the constructed flow cell with locations identified as interfaces from images of flowing fluids. Numerous images were obtained from two-phase experiments within the flow cell. The dynamic evolution of the fluid distribution and the fluid-fluid interface locations were determined by analyzing these images. In this paper, we give a brief introduction to the thermodynamically based two-phase flow model, review the properties of the stereolithography flow cell, and show how the image analysis procedure has been used to obtain dynamic parameters for the

  3. INTERFACIAL AREA TRANSPORT AND REGIME TRANSITION IN COMBINATORIAL CHANNELS

    SciTech Connect

    Seugjin Kim

    2011-01-28

    . This study investigates the geometric effects of 90-degree vertical elbows and flow configurations in two-phase flow. The study shows that the elbows make a significant effect on the transport characteristics of two-phase flow, which includes the changes in interfacial structures, bubble interaction mechanisms and flow regime transition. The effect of the elbows is characterized for global and local two-phase flow parameters. The global two-phase flow parameters include two-phase pressure, interfacial structures and flow regime transition. In order to characterize the frictional pressure drop and minor loss across the vertical elbows, pressure measurements are obtained across the test section over a wide range of flow conditions in both single-phase and two-phase flow conditions. A two-phase pressure drop correlation analogous to Lockhart-Martinelli correlation is proposed to predict the minor loss across the elbows. A high speed camera is employed to perform extensive flow visualization studies across the elbows in vertical upward, horizontal and vertical downward sections and modified flow regime maps are proposed. It is found that modified flow regime maps immediately downstream of the vertical upward elbow deviate significantly from the conventional flow regime map. A qualitative assessment of the counter-current flow limitation characteristics specific to the current experimental facility is performed. A multi-sensor conductivity probe is used to measure local two-phase flow parameters such as: void fraction, bubble velocity, interfacial area concentration and bubble frequency. The local measurements are obtained for six different flow conditions at ten measurement locations along axial direction of the test section. Both the vertical-upward and vertical-downward elbows have a significant impact on bubble distribution, resulting in, a bimodal distribution along the horizontal radius of the tube cross-section and migration of bubbles towards the inside of the

  4. Salinity Influence on Interfacial Area, Wettability, and NAPL Recovery

    NASA Astrophysics Data System (ADS)

    Zhong, L.; Valenta, M. M.

    2007-12-01

    Wettability, the tendency of rock or sediment particle surfaces to be preferentially wet by one fluid phase, has a strong influence on the distribution and flow of immiscible fluids in oil reservoirs or aquifers. The efficiency of oil and non-aqueous phase liquid (NAPL) recovery processes and the displacement and production of oil/NAPL by fluids injected into the reservoir or aquifer depend on the wetting properties of the rock/sediment particle surfaces. Effects of salinity on wettability and residual oil saturation during water flooding are of particular interest in the petroleum industry with some reservoirs. It was indicated that the residual oil saturation may be reduced significantly by flooding with low salinity water instead of seawater or brine. This observation may be also true in NAPL recovery from contaminated aquifers. NAPL recovery enhancement may be achieved by manipulating the salinity of the remedial fluid. Two sets of 8 core-flooding column experiments have been completed, using decane and Alaska North Slope (ANS) crude oil as surrogate NAPLs. Unconsolidated sand packs were used as representative porous media. NAPL removal was conducted by flushing column at residual NAPL saturation using water with salinity ranging from 0% to 8% wt of NaCl. The NAPL-water interfacial area (anw, cm-1) was measured and used as an indicator for the wettability characteristics of the packed sand. Sodium Dodecyl Benzene Sulfonate (SDBS) was used as an interfacial partitioning tracer and Pentafluoro Benzoic acid (PFBA) was used as a non-reactive and non-partitioning tracer. NAPL was imbibed into an initially water saturated column, using positive displacement methods. NAPL was then flushed out using water at certain salinity. When the column attained a residual NAPL saturation after each water flushing displacement, the partitioning and conservative tracer experiments were conducted separately, to characterize the specific NAPL-water interfacial areas, and the

  5. Interfacial area transport of steam-water two-phase flow in a vertical annulus at elevated pressures

    NASA Astrophysics Data System (ADS)

    Ozar, Basar

    Analysis of accident scenarios in nuclear reactors are done by using codes such as TRACE and RELAP5. Large oscillations in the core void fraction are observed in calculations of advanced passive light water reactors (ALWRs), especially during the low pressure long-term cooling phase. These oscillations are attributed to be numerical in nature and served to limit the accuracy as well as the credibility of the calculations. One of the root causes of these unphysical oscillations is determined to be flow regime transitions caused by the usage of static flow regime maps. The interfacial area transport equation was proposed earlier in order to address these issues. Previous research successfully developed the foundation of the interfacial area transport equation and the experimental techniques needed for the measurement of interfacial area, bubble diameters and velocities. In the past, an extensive database has been then generated for adiabatic air-water conditions in vertical upward and downward bubbly-churn turbulent flows in pipes. Using this database, mechanistic models for the creation (bubble breakup) and destruction (bubble coalescence) of interfacial area have been developed for the bubblyslug flow regime transition. However, none of these studies investigated the effect of phase change. To address this need, a heated annular test section was designed and constructed. The design relied on a three level scaling approach: geometric scaling; hydrodynamic scaling; thermal scaling. The test section consisted of a heated and unheated section in order to study the sub-cooled boiling and bulk condensation/flashing and evaporation phenomena, respectively. Steam-water two-phase flow tests were conducted under sub-cooled boiling conditions in the heated section and with sub-cooled/super-heated bulk liquid in the unheated section. The modeling of interfacial area transport equation with phase change effects was introduced and discussed. Constitutive relations, which took

  6. X-ray Microtomography Determination of Air−Water Interfacial Area−Water Saturation Relationships in Sandy Porous Media

    SciTech Connect

    Costanza-Robinson, Molly S.; Harrold, Katherine H.; Lieb-Lappen, Ross M.

    2008-08-06

    In this work, total smooth air-water interfacial areas were measured for a series of nine natural and model sandy porous media as a function of water saturation using synchrotron X-ray microtomography. Interfacial areas decreased linearly with water saturation, while the estimated maximum interfacial area compared favorably to the media geometric surface areas. Importantly, relative interfacial area (i.e., normalized by geometric surface area) versus water saturation plots for all media collapsed into a single linear cluster (r{sup 2} = 0.93), suggesting that geometric surface area is an important, and perhaps sufficient, descriptor of sandy media that governs total smooth interfacial area?water saturation relationships. Measured relationships were used to develop an empirical model for estimating interfacial area-water saturation relationships for sandy porous media. Model-based interfacial area estimates for independent media were generally slightly higher than interfacial areas measured using aqueous-phase interfacial tracer methods, which may indicate that microtomography captures regions of the air-water interface that are not accessible to aqueous-phase interfacial tracers. The empirical model presented here requires only average particle diameter and porosity as input parameters and can be used to readily estimate air-water interfacial area?water saturation relationships for sandy porous media.

  7. Lattice-Boltzmann modeling of experimental fluid displacement patterns, interfacial area and capillary trapped CO2

    NASA Astrophysics Data System (ADS)

    Porter, M. L.; Kang, Q.; Tarimala, S.; Abdel-Fattah, A.; Backhaus, S.; Carey, J. W.

    2010-12-01

    Successful sequestration of CO2 into deep saline aquifers presents an enormous challenge that requires fundamental understanding of reactive-multiphase flow and transport across many temporal and spatial scales. Of critical importance is accurately predicting the efficiency of CO2 trapping mechanisms. At the pore scale (e.g., microns to millimeters) the interfacial area between CO2 and brine, as well as CO2 and the solid phase, directly influences the amount of CO2 trapped due to capillary forces, dissolution and mineral precipitation. In this work, we model immiscible displacement micromodel experiments using the lattice-Boltzmann (LB) method. We focus on quantifying interfacial area as a function of capillary numbers and viscosity ratios typically encountered in CO2 sequestration operations. We show that the LB model adequately predicts the steady-state experimental flow patterns and interfacial area measurements. Based on the steady-state agreement, we use the LB model to investigate interfacial dynamics (e.g., fluid-fluid interfacial velocity and the rate of production of fluid-fluid interfacial area). In addition, we quantify the amount of interfacial area and the interfacial dynamics associated with the capillary trapped nonwetting phase. This is expected to be important for predicting the amount of nonwetting phase subsequently trapped due to dissolution and mineral precipitation.

  8. Laser Ablation Increases PEM/Catalyst Interfacial Area

    NASA Technical Reports Server (NTRS)

    Whitacre, Jay; Yalisove, Steve

    2009-01-01

    An investigational method of improving the performance of a fuel cell that contains a polymer-electrolyte membrane (PEM) is based on the concept of roughening the surface of the PEM, prior to deposition of a thin layer of catalyst, in order to increase the PEM/catalyst interfacial area and thereby increase the degree of utilization of the catalyst. The roughening is done by means of laser ablation under carefully controlled conditions. Next, the roughened membrane surface is coated with the thin layer of catalyst (which is typically platinum), then sandwiched between two electrode/catalyst structures to form a membrane/ele c t - rode assembly. The feasibility of the roughening technique was demonstrated in experiments in which proton-conducting membranes made of a perfluorosulfonic acid-based hydrophilic, protonconducting polymer were ablated by use of femtosecond laser pulses. It was found that when proper combinations of the pulse intensity, pulse-repetition rate, and number of repetitions was chosen, the initially flat, smooth membrane surfaces became roughened to such an extent as to be converted to networks of nodules interconnected by filaments (see Figure 1). In further experiments, electrochemical impedance spectroscopy (EIS) was performed on a pristine (smooth) membrane and on two laser-roughened membranes after the membranes were coated with platinum on both sides. Some preliminary EIS data were interpreted as showing that notwithstanding the potential for laser-induced damage, the bulk conductivities of the membranes were not diminished in the roughening process. Other preliminary EIS data (see Figure 2) were interpreted as signifying that the surface areas of the laser-roughened membranes were significantly greater than those of the smooth membrane. Moreover, elemental analyses showed that the sulfur-containing molecular groups necessary for proton conduction remained intact, even near the laser-roughened surfaces. These preliminary results can be taken

  9. Comparison of fluid-fluid interfacial areas measured with X-ray microtomography and interfacial partitioning tracer tests for the same samples

    NASA Astrophysics Data System (ADS)

    McDonald, Kieran; Carroll, Kenneth C.; Brusseau, Mark L.

    2016-07-01

    Two different methods are currently used for measuring interfacial areas between immiscible fluids within 3-D porous media, high-resolution microtomographic imaging and interfacial partitioning tracer tests (IPTT). Both methods were used in this study to measure nonwetting/wetting interfacial areas for a natural sand. The microtomographic imaging was conducted on the same packed columns that were used for the IPTTs. This is in contrast to prior studies comparing the two methods, for which in all cases different samples were used for the two methods. In addition, the columns were imaged before and after the IPTTs to evaluate the potential impacts of the tracer solution on fluid configuration and attendant interfacial area. The interfacial areas measured using IPTT are ˜5 times larger than the microtomographic-measured values, which is consistent with previous work. Analysis of the image data revealed no significant impact of the tracer solution on NAPL configuration or interfacial area. Other potential sources of error were evaluated, and all were demonstrated to be insignificant. The disparity in measured interfacial areas between the two methods is attributed to the limitation of the microtomography method to characterize interfacial area associated with microscopic surface roughness due to resolution constraints.

  10. Measurement and Estimation of Organic-Liquid/Water Interfacial Areas for Several Natural Porous Media

    SciTech Connect

    Brusseau, M.L.; Narter, M.; Schnaar, G.; Marble, J.

    2009-06-01

    The objective of this study was to quantitatively characterize the impact of porous-medium texture on interfacial area between immiscible organic liquid and water residing within natural porous media. Synchrotron X-ray microtomography was used to obtain high-resolution, three-dimensional images of solid and liquid phases in packed columns. The image data were processed to generate quantitative measurements of organic-liquid/water interfacial area and of organic-liquid blob sizes. Ten porous media, comprising a range of median grain sizes, grain-size distributions, and geochemical properties, were used to evaluate the impact of porous-medium texture on interfacial area. The results show that fluid-normalized specific interfacial area (A{sub f}) and maximum specific interfacial area (A{sub m}) correlate very well to inverse median grain diameter. These functionalities were shown to result from a linear relationship between effective organic-liquid blob diameter and median grain diameter. These results provide the basis for a simple method for estimating specific organic-liquid/water interfacial area as a function of fluid saturation for a given porous medium. The availability of a method for which the only parameter needed is the simple-to-measure median grain diameter should be of great utility for a variety of applications.

  11. Interfacial Area Transport of Bubbly Flow in a Small Diameter Pipe Under Microgravity Environment

    SciTech Connect

    Tatsuya Hazuku; Tomoji Takamasa; Takashi Hibiki; Mamoru Ishii

    2002-07-01

    Axial developments of one-dimensional void fraction, bubble number density, interfacial area concentration, and Sauter mean diameter of adiabatic nitrogen-water bubbly flows in a 9-mm-diameter pipe were measured under a microgravity environment using an image-processing method. The interfacial area transport mechanism was determined based on visual observation. Marked bubble coalescence occurred when fast-moving bubbles near the channel center overtook and swept up slower-moving bubbles in the vicinity of the channel wall (velocity profile entrainment). Negligible bubble breakup was observed because of weak turbulence under tested flow conditions. Axial changes of measured interfacial area concentrations were compared with the interfacial area transport equation considering the bubble expansion and wake entrainment as observed under a normal gravity environment. The velocity profile entrainment effect under microgravity was likely to be comparable to the wake entrainment effect under normal gravity in the tested flow conditions. This apparently led to insignificant differences between measured interfacial area concentrations and those predicted by the interfacial area transport equation with the wake entrainment model under normal gravity. Possible bubble coalescence mechanisms would differ, however, between normal gravity and microgravity conditions. (authors)

  12. PREDICTION OF INTERFACIAL AREAS DURING IMBIBITION IN SIMPLE POROUS MEDIA. (R827116)

    EPA Science Inventory

    The interfacial area between wetting (W-) and non-wetting (NW-) phases is one of the crucial parameters in several flow and transport processes in porous media. This paper gives predictions of such areas during imbibition (displacement of NW-phase by W) in simple porous media....

  13. Air/Water Purification

    NASA Technical Reports Server (NTRS)

    1992-01-01

    After 18 years of research into air/water pollution at Stennis Space Center, Dr. B. C. Wolverton formed his own company, Wolverton Environmental Services, Inc., to provide technology and consultation in air and water treatment. Common houseplants are used to absorb potentially harmful materials from bathrooms and kitchens. The plants are fertilized, air is purified, and wastewater is converted to clean water. More than 100 U.S. communities have adopted Wolverton's earlier water hyacinth and artificial marsh applications. Catfish farmers are currently evaluating the artificial marsh technology as a purification system.

  14. Two-Fluid Models and Interfacial Area Transport in Microgravity Condition

    NASA Technical Reports Server (NTRS)

    Ishii, Mamoru; Sun, Xiao-Dong; Vasavada, Shilp

    2004-01-01

    The objective of the present study is to develop a two-fluid model formulation with interfacial area transport equation applicable for microgravity conditions. The new model is expected to make a leapfrog improvement by furnishing the constitutive relations for the interfacial interaction terms with the interfacial area transport equation, which can dynamically model the changes of the interfacial structures. In the first year of this three-year project supported by the U.S. NASA, Office of Biological and Physics Research, the primary focus is to design and construct a ground-based, microgravity two-phase flow simulation facility, in which two immiscible fluids with close density will be used. In predicting the two-phase flow behaviors in any two-phase flow system, the interfacial transfer terms are among the most essential factors in the modeling. These interfacial transfer terms in a two-fluid model specify the rate of phase change, momentum exchange, and energy transfer at the interface between the two phases. For the two-phase flow under the microgravity condition, the stability of the fluid particle interface and the interfacial structures are quite different from those under normal gravity condition. The flow structure may not reach an equilibrium condition and the two fluids may be loosely coupled such that the inertia terms of each fluid should be considered separately by use of the two-fluid model. Previous studies indicated that, unless phase-interaction terms are accurately modeled in the two-fluid model, the complex modeling does not necessarily warrant an accurate solution.

  15. Interfacial Area Estimates for a NAPL-Water System and Their Effect on Predicting Groundwater Remediation Efficiency

    NASA Astrophysics Data System (ADS)

    Wildenschild, D.; Bradford, S. A.

    2005-12-01

    In mass transfer relationships pertaining to immiscible contaminant clean-up, NAPL-water interfacial area is in many cases substituted by the total NAPL-blob surface area because the latter is much easier to measure with various imaging techniques. Apart from results obtained indirectly with interfacial tracer techniques, data on the NAPL-water interfacial area has been difficult to obtain. We have used high-resolution micro-tomography to image NAPL (Soltrol) and water distribution, and quantity, in a system of sintered glass beads. The interfacial areas between NAPL and water and for the total NAPL surface were calculated using various image processing techniques and the results show a significant difference between the NAPL-water and total NAPL interfacial areas. Using the total NAPL area as a proxy for the NAPL-water interfacial area results in an order of magnitude overestimation at low saturations and a factor 5 overestimation at high saturations. This has serious implications for modeled predictions pertaining to clean-up efficiency and resulting concentrations removed during a pump-and-treat clean-up scenario. We have incorporated the different interfacial area estimates in a numerical model (MISER) and simulated NAPL dissolution in a realistic porous medium to illustrate the magnitude of the potential error introduced by using the total NAPL area as a proxy for the NAPL-water interfacial area.

  16. Interfacial Area per Volume: The link between capillary pressure and saturation

    NASA Astrophysics Data System (ADS)

    Chen, D.; Cheng, J.; Nolte, D. D.; Giordano, N.; Pyrak-Nolte, L. J.

    2004-12-01

    Measurements were performed on micro-models to quantify interfacial area per volume for a known pore geometry as a function of fluid pressure and saturation. The micro-models are completely transparent and measure 600 µm x 600 µm with an aperture of 1.08 µm. Because the micro-models are transparent, full visualization and quantification of the fluid distributions is possible. Initially the micro-models are saturated with decane (wetting phase). Nitrogen (non-wetting phase) is invaded into the system by the application of pressure in increments. At each increment, the system is allowed to equilibrate and then digital images of fluid distributions within the pore structure are acquired. The images are analyzed to determined fluid saturations, interfacial areas per volume and curvature of the interfaces. The curvatures of the interfaces are calculated using level set methods Pressure measurements are also made with pressure transducers during the experiment. From the data, we have established that the interfacial area per volume between non-wetting and wetting fluids lifts the ambiguity associated with the hysteretic relationship between capillary pressure and saturation in porous media. The interface between the non-wetting and wetting phases is composed of two subsets: one with a unique curvature determined by the capillary pressure, and the other with a distribution of curvatures dominated by disjoining pressure. This work provides experimental support for theoretical predictions that the capillary-dominated subset plays a role analogous to a state variable. Any comprehensive description of multiphase flow properties must include this interfacial area with the traditional variables of pressure and fluid saturation. Research is continuing to examine the role of pore structure on the relationship among capillary pressure, saturation and interfacial area per volume. Acknowledgments: Geosciences Research Program, Office of Basic Energy Sciences US Department of

  17. Tortuosity of Immiscible Fluids in Porous Media based on Phase Interfacial Areas: A New Definition and its Applications to Unsaturated Flow and Transport

    NASA Astrophysics Data System (ADS)

    Saripalli, K. P.; Serne, R. J.; Khaleel, R.

    2003-04-01

    Tortuosity is the single most important characteristic of flow through porous media that determines several flow and transport phenomena. Currently available definitions of tortuosity are empirical, and do not lend themselves to direct and independent measurement. We present a new definition for the tortuosity factor of saturated media as the ratio of specific surface of real porous medium to that of an idealized capillary bundle. For unsaturated media, tortuosity factor is defined as the ratio of the specific air-water interfacial area of real and the corresponding idealized porous medium. This tortuosity factor is suitably measured using sorptive tracers (e.g., nitrogen adsorption method) for saturated media and interfacial tracers for unsaturated media. New models based on this approach are presented for the prediction of several fundamental phenomena in unsaturated porous media, such as diffusion, unsaturated water flow and anisotropy, that are influenced by changes in tortuosity with a changing water content. Diffusion coefficients and diffusive resistances measured in a number of saturated and unsaturated granular porous media agree well with the predictions of the model. Trends in the prediction of tortuosity as a function water saturation are in agreement with similar recent predictions based on diffusion theory (Moldrup et al., 2001). Unsaturated hydraulic conductivities measured for a number of coarse-textured sediments agree well with predictions based on a modified Kozeny-Carman relation. Results indicate that the alternative definition of tortuosity is useful to the understanding and prediction of multiphase flow and transport. By defining the tortuosity factor as the phase interfacial area ratio, one overcomes the need to base its definition on the length dimensions of flow through the idealized capillary bundles, which is the most serious deficiency in the tortuosity-based approaches to modeling flow through porous media (Dullien, 1979; Epstein, 1989).

  18. Establishing a quantitative functional relationship between capillary pressure, saturation and interfacial area. 1997 annual progress report

    SciTech Connect

    Montemagno, C.D.

    1997-01-01

    'There is a fundamental knowledge gap associated with the in situ remediation of non-aqueous phase pollutants. Currently it is not possible to accurately determine the interfacial surface area of non-aqueous contaminants. As a result it is impossible to (1) accurately establish the health and environmental risk associated with the pollution: (2) precisely quantify and evaluate the potential efficacy of various in situ treatment technologies; and (3) conduct reliable performance assessments of the applied remediation technology during and after the clean-up. The global goal of this investigation is to try to remedy these shortcomings through the development of a formalized functional relationship between interfacial area (a), phase saturation (S) and capillary pressure (P). The development of this relationship will allow the direct determination of the fluid-fluid interfacial area from field measurements. Quantitative knowledge of the surface area of the non-aqueous phase pollutant facilitates accurate predictions of both the rate of dissolution and the contact area available for treatment. In addition. if saturation and capillary pressure measurements are made during the remediation process. both the spatial and temporal effectiveness of the remediation technology can be quantified. This information can then be used to optimize the restoration program. The project objective will be achieved through an integrated and focused research program that is comprised of theoretical computational and experimental efforts. These efforts are organized into a framework of four tasks: (1) improve on newly developed laboratory techniques to quantify and directly measure the functional relationship between phase interfacial area (a), saturation (S) and capillary pressure (P). (2) Develop new computational algorithms in conjunction with laboratory measurements to predict P, S and a. (3) Test existing theory and develop new theory to describe the relationship between P, S and a at

  19. Molecular dynamics study of contact mechanics: contact area and interfacial separation from small to full contact

    NASA Astrophysics Data System (ADS)

    Yang, Chunyan; Persson, Bo

    2008-03-01

    We report a molecular dynamics study of the contact between a rigid solid with a randomly rough surface and an elastic block with a flat surface. We study the contact area and the interfacial separation from small contact (low load) to full contact (high load). For small load the contact area varies linearly with the load and the interfacial separation depends logarithmically on the load [1-4]. For high load the contact area approaches to the nominal contact area (i.e., complete contact), and the interfacial separation approaches to zero. The present results may be very important for soft solids, e.g., rubber, or for very smooth surfaces, where complete contact can be reached at moderate high loads without plastic deformation of the solids. References: [1] C. Yang and B.N.J. Persson, arXiv:0710.0276, (to appear in Phys. Rev. Lett.) [2] B.N.J. Persson, Phys. Rev. Lett. 99, 125502 (2007) [3] L. Pei, S. Hyun, J.F. Molinari and M.O. Robbins, J. Mech. Phys. Sol. 53, 2385 (2005) [4] M. Benz, K.J. Rosenberg, E.J. Kramer and J.N. Israelachvili, J. Phy. Chem. B.110, 11884 (2006)

  20. Influence of interfacial area on the rheological behavior of heavy oil emulsions

    NASA Astrophysics Data System (ADS)

    Soto, Enrique; Ramírez-González, Patsy V.; de la Torre, Rocío G.; Guadarrama-Cetina, José M.; Quiñones-Cisneros, Sergio H.

    2014-03-01

    Experimental observations of the rheological behavior of heavy oil emulsions ARE presented. The emulsions were prepared from mixtures of the oil and brine in different rations and controlled mixing conditions. It was observed that the oil is the continuous phase and the brine the dispersed one. The drop size distribution and water fraction were measured from digital images obtained by a camera and a microscopy. The viscosity of the emulsions increases, when the drop size decreases and The interfacial area increases. The fluid exhibits a shear thinning and elastic rheological behavior below a critical drop size and concentration. The emulsions are stable for long periods of time. The increase in viscosity and non Newtonian behavior are strongly related to the interfacial area.

  1. On the prediction of horizontal bubbly flows using the interfacial area transport equation

    SciTech Connect

    Talley, J. D.; Kim, S.

    2012-07-01

    To solve the two-fluid model utilized in current nuclear reactor system analysis codes, the interfacial area concentration (a i) is estimated through flow regime dependent correlations that rely on static regime transition criteria. This approach does not capture the continuous evolution of the interfacial structures, and thus, it can pose numerical issues near the transition boundaries. The interfacial area transport equation (IATE) can help address these shortcomings by providing a dynamic prediction of a a{sub i} through mechanistic source and sink terms that account for bubble coalescence and breakup. Most of the previous work for this approach has focused on vertical two-phase flow. However, relatively few studies have been performed for horizontal two-phase flows, where buoyancy strongly affects the phase distribution. To develop a one-dimensional, area-averaged form of the IATE for adiabatic, horizontal bubbly flows the following considerations are necessary: (1) pressure drop estimation, (2) bubble velocity/void fraction estimation, (3) determination of bubble interaction mechanisms, and (4) treatment of the asymmetric phase distribution. In the current work, treatment of the asymmetric phase distribution is presented. (authors)

  2. Thermocapillary migration of a drop: an exact solution with Newtonian interfacial rheology and stretching/shrinkage of interfacial area elements for small Marangoni numbers

    NASA Technical Reports Server (NTRS)

    Balasubramaniam, R.; Subramanian, R. Shankar

    2004-01-01

    In this paper we analyze the effects of the following phenomena associated with the thermocapillary migration of a drop. The first is the influence of Newtonian surface rheology of the interface and the second is that of the energy changes associated with stretching and shrinkage of the interfacial area elements, when the drop is in motion. The former occurs because of dissipative processes in the interfacial region, such as when surfactant molecules are adsorbed at the interface in sufficient concentration. The interface is typically modeled in this instance by ascribing to it a surface viscosity. This is a different effect from that of interfacial tension gradients arising from surfactant concentration gradients. The stretching and shrinkage of interfacial area elements leads to changes in the internal energy of these elements that affects the transport of energy in the fluids adjoining the interface. When an element on the interface is stretched, its internal energy increases because of the increase in its area. This energy is supplied by the neighboring fluids that are cooled as a consequence. Conversely, when an element on the interface shrinks, the adjoining fluids are warmed. In the case of a moving drop, elements of interfacial area are stretched in the forward half of the drop, and are shrunk in the rear half. Consequently, the temperature variation on the surface of the drop and its migration speed are modified. The analysis of the motion of a drop including these effects was first performed by LeVan in 1981, in the limit when convective transport of momentum and energy are negligible. We extend the analysis of LeVan to include the convective transport of momentum by demonstrating that an exact solution of the momentum equation is obtained for an arbitrary value of the Reynolds number. This solution is then used to calculate the slightly deformed shape of the drop from a sphere.

  3. Thermodynamic Model for Fluid-Fluid Interfacial Areas in Porous Media for Arbitrary Drainage-Imbibition Sequences

    SciTech Connect

    Schroth, Martin H.; Oostrom, Mart; Dobson, Richard; Zeyer, Josef

    2008-08-01

    Fluid/fluid interfacial areas are important in controlling the rate of mass and energy transfer between fluid phases in porous media. We present a modified thermodynamically based model (TBM) to predict fluid/fluid interfacial areas in porous media for arbitrary drainage/imbibition sequences. The TBM explicitly distinguishes between interfacial areas associated with continuous (free) and isolated (entrapped) nonwetting fluids. The model is restricted to two-fluid systems in which (1) no significant conversion of mechanical work into heat occurs, (2) the wetting fluid completely wets the porous medium’s solid surfaces, and (3) no changes in interfacial area due to mass transfer between phases occur. We show example calculations for two different drainage/imbibition sequences in two porous media: a highly uniform silica sand and a well-graded silt. The TBM’s predictions for interfacial area associated with free nonwetting-fluid are identical to those of a previously published geometry-based model (GBM). However, predictions for interfacial area associated with entrapped nonwetting-fluid are consistently larger in the TBM than in the GBM. Although a comparison of model predictions with experimental data is currently only possible to a limited extent, good general agreement was found for the TBM. As required model parameters are commonly used as inputs for or tracked during multifluid-flow simulations, the modified TBM may be easily incorporated in numerical codes.

  4. Gas and liquid measurements in air-water bubbly flows

    SciTech Connect

    Zhou, X.; Doup, B.; Sun, X.

    2012-07-01

    Local measurements of gas- and liquid-phase flow parameters are conducted in an air-water two-phase flow loop. The test section is a vertical pipe with an inner diameter of 50 mm and a height of 3.2 m. The measurements are performed at z/D = 10. The gas-phase measurements are performed using a four-sensor conductivity probe. The data taken from this probe are processed using a signal processing program to yield radial profiles of the void fraction, bubble velocity, and interfacial area concentration. The velocity measurements of the liquid-phase are performed using a state-of-the-art Particle Image Velocimetry (PIV) system. The raw PIV images are acquired using fluorescent particles and an optical filtration device. Image processing is used to remove noise in the raw PIV images. The statistical cross correlation is introduced to determine the axial velocity field and turbulence intensity of the liquid-phase. Measurements are currently being performed at z/D = 32 to provide a more complete data set. These data can be used for computational fluid dynamic model development and validation. (authors)

  5. Interfacial solvation thermodynamics.

    PubMed

    Ben-Amotz, Dor

    2016-10-19

    Previous studies have reached conflicting conclusions regarding the interplay of cavity formation, polarizability, desolvation, and surface capillary waves in driving the interfacial adsorptions of ions and molecules at air-water interfaces. Here we revisit these questions by combining exact potential distribution results with linear response theory and other physically motivated approximations. The results highlight both exact and approximate compensation relations pertaining to direct (solute-solvent) and indirect (solvent-solvent) contributions to adsorption thermodynamics, of relevance to solvation at air-water interfaces, as well as a broader class of processes linked to the mean force potential between ions, molecules, nanoparticles, proteins, and biological assemblies. PMID:27545849

  6. Interfacial solvation thermodynamics

    NASA Astrophysics Data System (ADS)

    Ben-Amotz, Dor

    2016-10-01

    Previous studies have reached conflicting conclusions regarding the interplay of cavity formation, polarizability, desolvation, and surface capillary waves in driving the interfacial adsorptions of ions and molecules at air-water interfaces. Here we revisit these questions by combining exact potential distribution results with linear response theory and other physically motivated approximations. The results highlight both exact and approximate compensation relations pertaining to direct (solute-solvent) and indirect (solvent-solvent) contributions to adsorption thermodynamics, of relevance to solvation at air-water interfaces, as well as a broader class of processes linked to the mean force potential between ions, molecules, nanoparticles, proteins, and biological assemblies.

  7. Hybrid multiphase CFD simulation for liquid-liquid interfacial area prediction in annular centrifugal contactors

    SciTech Connect

    Wardle, K.E.

    2013-07-01

    Liquid-liquid contacting equipment used in solvent extraction processes has the dual purpose of mixing and separating two immiscible fluids. Consequently, such devices inherently encompass a wide variety of multiphase flow regimes. A hybrid multiphase computational fluid dynamics (CFD) solver which combines the Eulerian multi-fluid method with VOF (volume of fluid) sharp interface capturing has been developed for application to annular centrifugal contactors. This solver has been extended to enable prediction of mean droplet size and liquid-liquid interfacial area through a single moment population balance method. Simulations of liquid-liquid mixing in a simplified geometry and a model annular centrifugal contactor are reported with droplet breakup/coalescence models being calibrated versus available experimental data. Quantitative comparison is made for two different housing vane geometries and it is found that the predicted droplet size is significantly smaller for vane geometries which result in higher annular liquid holdup.

  8. Behaviors of bovine serum albumin and rapeseed proteins at the air/water interface after grafting aliphatic or aromatic chains.

    PubMed

    Gerbanowski, Alice; Rabiller, Claude; Guéguen, Jacques

    2003-06-15

    The influence of grafting aliphatic or aromatic groups on the behaviors of bovine serum albumin (BSA) and rapeseed proteins (napin and cruciferin) at the air/water interface is studied. From compression isotherms, it is shown that the chemical modification induces an increase in the interfacial molecular areas of the three proteins. The more hydrophobic the groups grafted, the more important this increase is. The dilatational modulus clearly emphasized that the grafting of hydrophobic groups also leads to an increase of the collapse pressure, demonstrating a higher cohesiveness and resistance to pressure of the interfacial films. These results are discussed on the basis of the physicochemical changes due to these chemical modifications, especially the conformation, the surface hydrophobicity, and the flexibility of the modified proteins. The improvement of surface properties obtained by grafting aliphatic or aromatic chains onto these proteins looks very promising in regard to emulsifying and foaming properties.

  9. Bubble size and gas-liquid interfacial area measurements using molten paraffin waxes in bubble columns

    SciTech Connect

    Bukur, D.B.; Patel, S.A.; Daly, J.G.; Raphael, M.L.

    1987-01-01

    Experiments were conducted in 0.05 m ID and 0.23 m ID by 3 m tall bubble columns with different types of molten waxes as the liquid medium and nitrogen as the gas, under processing conditions typical or Fischer-Tropsch synthesis over iron catalysts (i.e. gas velocities up to 0.15 m s, and temperatures between 200 and 270/sup 0/C) to estimate gas liquid interfacial area from measured values of average gas hold-up and Sauter mean bubble diameter. The gas hold-up was estimated from visual observations of the expanded and static liquid heights, and the Sauter was estimated from bubble size measurements obtained by photography and dynamic gas disengagement. The paraffin wax (FT-300) used in the authors' studies is non-coalescing and has a tendency to foam. The amount of foam is greater for runs conducted in the order of increasing gas velocities, than in runs with decreasing velocities. Thus, two values of hold-up are possible and the start-up procedure determines which one will be attained. At higher gas velocities (> 0.05 m/s) the foam disappears and a transition to the slug flow, churn-turbulent regime takes place. Reactor waxes are coalescing in nature and do not produce foam. Despite similar hold-ups for the different waxes at higher gas velocities, the Sauters are significantly different and this is reflected in the specific gas-liquid interfacial areas, with larger values obtained with the paraffin wax compared to values with reactor waxes.

  10. Interfacial area and two-phase flow structure development measured by a double-sensor probe

    SciTech Connect

    Leung, Waihung; Revankar, S.T.; Ishii, Yoshihiko; Ishii, Mamoru.

    1992-06-01

    In this report, we studied the local phasic characters of dispersed flow regime both at the entrance and at the fully developed regions. Since the dispersed phase is distributed randomly in the medium and enclosed in relatively small interfaces, the phasic measurement becomes difficult to obtain. Local probe must be made with a miniaturized sensor in order to reduce the interface distortion. The double-sensor resistivity probe has been widely used in local void fraction and interface velocity measurements because the are small in comparison with the interfaces. It has been tested and proved to be an accurate local phasic measurement tool. In these experiments, a double-sensor probe was employed to measure the local void fraction and interface velocity in an air-water system. The test section was flow regime can be determined by visualization. Furthermore, local phasic measurements can be verified by photographic studies. We concentrated our study on the bubbly flow regime only. The local measurements were conducted at two axial locations, L/D = 8 and 60, in which the first measurement represents the entrance region where the flow develops, and the second measurement represents the fully developed flow region where the radial profile does not change as the flow moves along the axial direction. Four liquid flow rates were chosen in combination with four different gas injection rates. The superficial liquid velocities were j{sub t} = 1.0, 0.6,0.4, and 0.1 m/s and superficial gas velocities were j{sub g} = 0.0965, 0.0696, 0.0384, and 0.0192 m/s. These combinations put the two-phase flow well in the bubbly flow regime. In this sequence of phenomenological studies, the local void fraction, interface area concentration, sauter mean diameter, bubble velocity and bubble frequency were measured.

  11. Measurements of interfacial area concentration in two-phase bubbly flow

    SciTech Connect

    Wu, Q.; Kim, S.; McCreary, D.; Ishii, M.; Beus, S.G.

    1997-12-31

    Interfacial area concentration is an important parameter in the two-fluid model for two-phase flow analysis, which is defined as the total interface area per unit mixture volume and has the following local time-averaged expression: {bar a}{sup t} = 1/{Delta}T {Sigma}{sub j}(1/{vert_bar}V{sub i} {center_dot} n{sub i}{vert_bar}){sub j}, where j denotes the j-th interface that passes the point of interest in a time interval {Delta}T. V{sub i} and n{sub i} refer to the bubble interface velocity and surface normal vector, respectively. To measure this parameter, the double-sensor probe technique is commonly used. Due to the influences of the bubble lateral motions, however, the measurement results should be interpreted via a certain statistic approach. Recently, to take into account the effects of the probe spacing, Wu and Ishii provided the following new formula to correlate the measurable values to the interfacial area concentration: {bar a}{sub i}{sup t} = 2N{sub b}/{Delta}T ({Delta}{bar t}/{Delta}s) [2 + (1.2{sigma}{sub {Delta}t}/{Delta}{bar t}){sup 2.25}], for D = 1.2 {approximately} 2.8 {Delta}s, where N{sub b} refers to the number of the bubbles that hit the probe front tip during time interval {Delta}T, {Delta}s denotes the distance between the two probe tips, D is the bubble diameter, {Delta}{bar t} represents the measured average time interval for an interface to travel through the two probe tips, and {sigma}{sub {Delta}t} is the standard deviation of {Delta}t. The theoretical accuracy of this formula is within {+-} 5% if the sample size is sufficiently large. The purpose of this study is to evaluate this method experimentally using an image processing method.

  12. ISSUES IN SIMULATING ELEMENTAL MERCURY AIR/WATER EXCHANGE AND AQUEOUS MONOMETHYLMERCURY SPECIATION

    EPA Science Inventory

    This presentation focuses on two areas relevant to assessing the global fate and bioavailability of mercury: elemental mercury air/water exchange and aqueous environmental monomethylmercury speciation.

  13. A CSF-SPH method for simulating drainage and imbibition at pore-scale resolution while tracking interfacial areas

    NASA Astrophysics Data System (ADS)

    Sivanesapillai, Rakulan; Falkner, Nadine; Hartmaier, Alexander; Steeb, Holger

    2016-09-01

    We present a conservative smoothed particle hydrodynamics (SPH) model to study the flow of multiple, immiscible fluid phases in porous media using direct pore-scale simulations. Particular focus is put on continuously tracking the evolution of interfacial areas, which are considered to be important morphological quantities affecting multiphase transport in porous media. In addition to solving the Navier-Stokes equations, the model accounts for the effects of capillarity at interfaces and contact lines. This is done by means of incorporating the governing interfacial mass and momentum balances using the continuum surface force (CSF) method, thus rendering model calibration routines unnecessary and minimizing the set of constitutive and kinematic assumptions. We address the application of boundary conditions at rigid solid surfaces and study the predictive capability of the model as well as optimal choices for numerical parameters using an extensive model validation procedure. We demonstrate the applicability of the model to simulate multiphase flows involving partial wettability, dynamic effects, large density ratios (up to 1000), large viscosity ratios (up to 100), as well as fragmentation and coalescence of fluid phases. The model is used to study the evolution of fluid-fluid interfacial areas during saturation-controlled primary drainage and main imbibition of heterogeneous pore spaces at low capillary numbers. A variety of pore-scale effects, such as wetting phase entrapment and fragmentation due to snap-off, are observed. Specific fluid-fluid interfacial area is observed to monotonically increase during primary drainage and hysteretic effects are apparent during main imbibition.

  14. Effects of the conjugation of whey proteins with gellan polysaccharides on surfactant-induced competitive displacement from the air-water interface.

    PubMed

    Cai, B; Ikeda, S

    2016-08-01

    Whey proteins can be used to stabilize foams and emulsions against coalescence because of their ability to form viscoelastic films at the interface that resist film rupture on collision between colloidal particles. However, whey proteins are competitively displaced from the interface if small-molecule surfactants are added, leading to destabilization of the entire system. This is because surfactants are more effective in molecular packing at the interface, and they lower interfacial tension to a greater degree than whey proteins do, but their interfacial films are poor in viscoelasticity. We hypothesized that whey proteins would become more resistant to surfactant-induced competitive displacement if they were conjugated with network-forming polysaccharides. The protein moiety of the conjugate would be expected to enable its adsorption to the interface, and the polysaccharide moiety would be expected to form self-assembled networks, strengthening the interfacial film as a whole. In this study, whey proteins were conjugated with gellan polysaccharides using the Maillard reaction. Atomic force microscopy images of interfacial films formed by the whey protein-gellan conjugate at the air-water interface and transferred onto mica sheets using the Langmuir-Blodgett method revealed that gellan did form self-assembled networks at the interface and that interfacial films also contained a large number of unconjugated whey protein molecules. Following the addition of a small-molecule surfactant (Tween 20) to the sub-phase, surface pressure increased, indicating spontaneous adsorption of surfactants to the interface. Atomic force microscopy images showed decreases in interfacial area coverage by whey proteins as surface pressure increased. At a given surface pressure, the interfacial area coverage by whey protein-gellan conjugates was greater than coverage by unconjugated whey proteins, confirming that whey proteins became more resistant to surfactant-induced displacement after

  15. Surface activity of saponin from Quillaja bark at the air/water and oil/water interfaces.

    PubMed

    Wojciechowski, Kamil

    2013-08-01

    Surface activity of Sigma's Quillaja bark saponin (QBS) was studied by means of dynamic interfacial tension and surface dilational rheology at three fluid/fluid interfaces with the polarity of the non-aqueous phase increasing in the order: air/water, tetradecane/water and olive oil/water. The equilibrium interfacial tension isotherms were fitted to the generalized Frumkin model with surface compressibility for the air/water and tetradecane/water interfaces, whereas the isotherm for the third interface displays a more complex shape. Upon fast compression of a drop of concentrated "Sigma" QBS solution immersed in olive oil, a clearly visible and durable skin was formed. On the other hand, no skin formation was noticed at the air/water interface, and only a little at the tetradecane/water interface. Addition of a fatty acid, however, improved slightly the skin-formation ability of the QBS at the latter interface. The surface behavior of the QBS from Sigma was compared with that from Desert King, Int. ("Supersap"), employed in a recent study by Stanimirova et al. [22]. The two products exhibit different areas per molecule in the saturated adsorbed layer (0.37nm(2) vs. 1.19nm(2) for "Sigma" and "Supersap", respectively). Also their surface rheology is different: although both QBSs form predominantly elastic layers, for "Sigma" the surface storage modulus, εr=103mNm(-1), while for "Supersap" εr=73mNm(-1) at 10(-3)moll(-1) (i.e., around their cmc). The two saponin products exhibit also different ionic character, as proven by the acid-base titration of their aqueous solutions: QBS from Sigma is an ionic surfactant, while the "Supersap" from Desert King is a non-ionic one. PMID:23524082

  16. Surface activity of saponin from Quillaja bark at the air/water and oil/water interfaces.

    PubMed

    Wojciechowski, Kamil

    2013-08-01

    Surface activity of Sigma's Quillaja bark saponin (QBS) was studied by means of dynamic interfacial tension and surface dilational rheology at three fluid/fluid interfaces with the polarity of the non-aqueous phase increasing in the order: air/water, tetradecane/water and olive oil/water. The equilibrium interfacial tension isotherms were fitted to the generalized Frumkin model with surface compressibility for the air/water and tetradecane/water interfaces, whereas the isotherm for the third interface displays a more complex shape. Upon fast compression of a drop of concentrated "Sigma" QBS solution immersed in olive oil, a clearly visible and durable skin was formed. On the other hand, no skin formation was noticed at the air/water interface, and only a little at the tetradecane/water interface. Addition of a fatty acid, however, improved slightly the skin-formation ability of the QBS at the latter interface. The surface behavior of the QBS from Sigma was compared with that from Desert King, Int. ("Supersap"), employed in a recent study by Stanimirova et al. [22]. The two products exhibit different areas per molecule in the saturated adsorbed layer (0.37nm(2) vs. 1.19nm(2) for "Sigma" and "Supersap", respectively). Also their surface rheology is different: although both QBSs form predominantly elastic layers, for "Sigma" the surface storage modulus, εr=103mNm(-1), while for "Supersap" εr=73mNm(-1) at 10(-3)moll(-1) (i.e., around their cmc). The two saponin products exhibit also different ionic character, as proven by the acid-base titration of their aqueous solutions: QBS from Sigma is an ionic surfactant, while the "Supersap" from Desert King is a non-ionic one.

  17. Experimentally Measured Interfacial Area during Gas Injection into Saturated Porous Media: An Air Sparging Analogy

    SciTech Connect

    Crandall, Dustin; Ahmadi, Goodarz; Smith, Duane H., Bromhal, Grant

    2010-01-01

    The amount of interfacial area (awn) between air and subsurface liquids during air-sparging can limit the rate of site remediation. Lateral movement within porous media could be encountered during air-sparging operations when air moves along the bottom of a low-permeability lens. This study was conducted to directly measure the amount of awn between air and water flowing within a bench-scale porous flow cell during the lateral movement of air along the upper edge of the cell during air injections into an initially water-saturated flow cell. Four different cell orientations were used to evaluate the effect of air injection rates and porous media geometries on the amount of awn between fluids. Air was injected at flow rates that varied by three orders of magnitude, and for each flow cellover this range of injection rates little change in awn was noted. A wider variation in awn was observed when air moved through different regions for the different flow cell orientations. These results are in good agreement with the experimental findings of Waduge et al. (2007), who performed experiments in a larger sand-pack flow cell, and determined that air-sparging efficiency is nearly independent of flow rate but highly dependent on the porous structure. By directly measuring the awn, and showing that awn does not vary greatly with changes in injection rate, we show that the lack of improvement to remediation rates is because there is a weak dependence of the awn on the air injection rate.

  18. Air-water flow in subsurface systems

    NASA Astrophysics Data System (ADS)

    Hansen, A.; Mishra, P.

    2013-12-01

    Groundwater traces its roots to tackle challenges of safe and reliable drinking water and food production. When the groundwater level rises, air pressure in the unsaturated Vadose zone increases, forcing air to escape from the ground surface. Abnormally high and low subsurface air pressure can be generated when the groundwater system, rainfall, and sea level fluctuation are favorably combined [Jiao and Li, 2004]. Through this process, contamination in the form of volatile gases may diffuse from the ground surface into residential areas, or possibly move into groundwater from industrial waste sites. It is therefore crucial to understand the combined effects of air-water flow in groundwater system. Here we investigate theoretically and experimentally the effects of air and water flow in groundwater system.

  19. Surface pressure affects B-hordein network formation at the air-water interface in relation to gastric digestibility.

    PubMed

    Yang, Jingqi; Huang, Jun; Zeng, Hongbo; Chen, Lingyun

    2015-11-01

    Protein interfacial network formation under mechanical pressure and its influence on degradation was investigated at molecular level using Langmuir-Blodgett B-hordein monolayer as a 2D model. Surface properties, such as surface pressure, dilatational and shear rheology and the surface pressure--area (π-A) isotherm, of B-hordein at air-water interface were analyzed by tensiometer, rheometer and a Langmuir-Blodgett trough respectively. B-Hordein conformation and orientation under different surface pressures were determined by polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS). The interfacial network morphology was observed by atomic force microscopy (AFM). B-Hordein could reduce the air-water surface tension rapidly to ∼ 45 mN/m and form a solid-like network with high rheological elasticity and compressibility at interface, which could be a result of interactions developed by intermolecular β-sheets. The results also revealed that B-hordein interfacial network switched from an expanded liquid phase to a solid-like film with increasing compression pressure. The orientation of B-hordein was parallel to the surface when in expended liquid phase, whereas upon compression, the hydrophobic repetitive region tilted away from water phase. When compressed to 30 mN/m, a strong elastic network was formed at the interface, and it was resistant to a harsh gastric-like environment of low pH and pepsin. This work generated fundamental knowledge, which suggested the potential to design B-hordein stabilized emulsions and encapsulations with controllable digestibility for small intestine targeted delivery of bioactive compounds.

  20. The two-phase flow IPTT method for measurement of nonwetting-wetting liquid interfacial areas at higher nonwetting saturations in natural porous media

    NASA Astrophysics Data System (ADS)

    Zhong, Hua; El Ouni, Asma; Lin, Dan; Wang, Bingguo; Brusseau, Mark L.

    2016-07-01

    Interfacial areas between nonwetting-wetting (NW-W) liquids in natural porous media were measured using a modified version of the interfacial partitioning tracer test (IPTT) method that employed simultaneous two-phase flow conditions, which allowed measurement at NW saturations higher than trapped residual saturation. Measurements were conducted over a range of saturations for a well-sorted quartz sand under three wetting scenarios of primary drainage (PD), secondary imbibition (SI), and secondary drainage (SD). Limited sets of experiments were also conducted for a model glass-bead medium and for a soil. The measured interfacial areas were compared to interfacial areas measured using the standard IPTT method for liquid-liquid systems, which employs residual NW saturations. In addition, the theoretical maximum interfacial areas estimated from the measured data are compared to specific solid surface areas measured with the N2/BET method and estimated based on geometrical calculations for smooth spheres. Interfacial areas increase linearly with decreasing W-phase (water) saturation over the range of saturations employed. The maximum interfacial areas determined for the glass beads, which have no surface roughness, are 32 ± 4 and 36 ± 5 cm-1 for PD and SI cycles, respectively. The values are similar to the geometric specific solid surface area (31 ± 2 cm-1) and the N2/BET solid surface area (28 ± 2 cm-1). The maximum interfacial areas are 274 ± 38, 235 ± 27, and 581 ± 160 cm-1 for the sand for PD, SI, and SD cycles, respectively, and ˜7625 cm-1 for the soil for PD and SI. The maximum interfacial areas for the sand and soil are significantly larger than the estimated smooth-sphere specific solid surface areas (107 ± 8 cm-1 and 152 ± 8 cm-1, respectively), but much smaller than the N2/BET solid surface area (1387 ± 92 cm-1 and 55224 cm-1, respectively). The NW-W interfacial areas measured with the two-phase flow method compare well to values measured using the

  1. The criterion of subscale sufficiency and its application to the relationship between static capillary pressure, saturation and interfacial areas

    NASA Astrophysics Data System (ADS)

    Kurzeja, Patrick

    2016-05-01

    Modern imaging techniques, increased simulation capabilities and extended theoretical frameworks, naturally drive the development of multiscale modelling by the question: which new information should be considered? Given the need for concise constitutive relationships and efficient data evaluation; however, one important question is often neglected: which information is sufficient? For this reason, this work introduces the formalized criterion of subscale sufficiency. This criterion states whether a chosen constitutive relationship transfers all necessary information from micro to macroscale within a multiscale framework. It further provides a scheme to improve constitutive relationships. Direct application to static capillary pressure demonstrates usefulness and conditions for subscale sufficiency of saturation and interfacial areas.

  2. Cleaning verification by air/water impingement

    NASA Technical Reports Server (NTRS)

    Jones, Lisa L.; Littlefield, Maria D.; Melton, Gregory S.; Caimi, Raoul E. B.; Thaxton, Eric A.

    1995-01-01

    This paper will discuss how the Kennedy Space Center intends to perform precision cleaning verification by Air/Water Impingement in lieu of chlorofluorocarbon-113 gravimetric nonvolatile residue analysis (NVR). Test results will be given that demonstrate the effectiveness of the Air/Water system. A brief discussion of the Total Carbon method via the use of a high temperature combustion analyzer will also be given. The necessary equipment for impingement will be shown along with other possible applications of this technology.

  3. A Pore Network Model Evaluation of the Types of Fluid/Fluid Interfacial Area Measured by Static and Dynamic Water-Phase Tracer Methods

    NASA Astrophysics Data System (ADS)

    Kibbey, T. C.; Chen, L.

    2010-12-01

    Tracer methods have gained acceptance for measuring fluid/fluid interfacial areas in porous media, and have been applied in both laboratory and field settings. Tracer methods make use of chemicals (typically surfactants or other surface-active chemicals) which adsorb to fluid/fluid interfaces, leading to changes (retardation of transport, depletion of solution concentration, or mobilization of fluid) which can be used to calculate the amount of interfacial area. Advantages of tracer methods include that they are inexpensive to use, don’t require specialized equipment, and can potentially be applied in field settings. The primary disadvantages include uncertainty about the types of interfacial area measured, and questions about whether the tracers themselves produce interfacial area changes. Interfacial areas in porous media containing multiple fluids are often categorized as capillary area (area corresponding to fluids held by capillary forces) and film area (area corresponding to molecular films of the wetting phase on porous medium surfaces). Total area is a measure of area that includes both capillary and film area. The focus of this work was on examining the types of interfacial area measured by both static and dynamic water-phase advective transport tracer methods. Static advective transport methods were introduced in the late 1990s (e.g., Kim et al., Water Resour. Res., 1997, 33, 2705-2711), and involve measuring the retardation of a tracer passed through a porous medium maintained at a preset degree of saturation (interfaces are presumed to be static). Dynamic advective transport methods were introduced in 2006 (Chen and Kibbey, Langmuir, 2006, 22, 6874-6880), and involve measuring depletion of tracer during drainage from a specially-constructed low volume soil cell. As new interfacial area is formed during drainage, tracer adsorbs to the interface, depleting the bulk solution; mass balance calculations are used to determine interfacial area as a function

  4. Proton Transfers at the Air-Water Interface

    NASA Astrophysics Data System (ADS)

    Mishra, Himanshu

    Proton transfer reactions at the interface of water with hydrophobic media, such as air or lipids, are ubiquitous on our planet. These reactions orchestrate a host of vital phenomena in the environment including, for example, acidification of clouds, enzymatic catalysis, chemistries of aerosol and atmospheric gases, and bioenergetic transduction. Despite their importance, however, quantitative details underlying these interactions have remained unclear. Deeper insight into these interfacial reactions is also required in addressing challenges in green chemistry, improved water quality, self-assembly of materials, the next generation of micro-nanofluidics, adhesives, coatings, catalysts, and electrodes. This thesis describes experimental and theoretical investigation of proton transfer reactions at the air-water interface as a function of hydration gradients, electrochemical potential, and electrostatics. Since emerging insights hold at the lipid-water interface as well, this work is also expected to aid understanding of complex biological phenomena associated with proton migration across membranes. Based on our current understanding, it is known that the physicochemical properties of the gas-phase water are drastically different from those of bulk water. For example, the gas-phase hydronium ion, H3O +(g), can protonate most (non-alkane) organic species, whereas H 3O+(aq) can neutralize only relatively strong bases. Thus, to be able to understand and engineer water-hydrophobe interfaces, it is imperative to investigate this fluctuating region of molecular thickness wherein the 'function' of chemical species transitions from one phase to another via steep gradients in hydration, dielectric constant, and density. Aqueous interfaces are difficult to approach by current experimental techniques because designing experiments to specifically sample interfacial layers (< 1 nm thick) is an arduous task. While recent advances in surface-specific spectroscopies have provided

  5. Properties of diphytanoyl phospholipids at the air-water interface.

    PubMed

    Yasmann, Anthony; Sukharev, Sergei

    2015-01-01

    Diphytanoylphosphatidyl choline (DPhPC) is a synthetic ester lipid with methylated tails found in archaeal ether lipids. Because of the stability of DPhPC bilayers and the absence of phase transitions over a broad range of temperatures, the lipid is used as an artificial membrane matrix for the reconstitution of channels, pumps, and membrane-active peptides. We characterized monomolecular films made of DPhPC and its natural ether analog DOPhPC at the air-water interface. We measured compression isotherms and dipole potentials of films made of DPhPC, DPhPE, and DOPhPC. We determined that at 40 mN/m the molecular area of DPhPC is 81.2 Å(2), consistent with X-ray and neutron scattering data obtained in liposomes. This indicates that 40 mN/m is the monolayer-bilayer equivalence pressure for this lipid. At this packing density, the compressibility modulus (Cs(-1 )= 122 ± 7 mN/m) and interfacial dipole potential (V = 355 ± 16 mV) were near their maximums. The molecular dipole moment was estimated to be 0.64 ± 0.02 D. The ether DOPhPC compacted to 70.4 Å(2)/lipid at 40 mN/m displaying a peak compressibility similar to that of DPhPC. The maximal dipole potential of the ether lipid was about half of that for DPhPC at this density, and the elemental dipole moment was about a quarter. The spreading of DPhPC and DOPhPC liposomes reduced the surface tension of the aqueous phase by 46 and 49 mN/m, respectively. This corresponds well to the monolayer collapse pressure. The equilibration time shortened as the temperature increased from 20 to 60 °C, but the surface pressure at equilibrium did not change. The data illustrates the properties of branched chains and the contributions of ester bonds in setting the mechanical and electrostatic parameters of diphytanoyl lipids. These properties determine an environment in which reconstituted voltage- or mechano-activated proteins may function. Electrostatic properties are important in the preparation of asymmetric folded bilayers

  6. Non-contact microrheology at the air-water interface

    NASA Astrophysics Data System (ADS)

    Boatwright, Thomas; Shlomovitz, Roie; Levine, Alex; Dennin, Michael

    2012-02-01

    Mechanical properties of biological interfaces, such as cell membranes, have the potential to be measured with optical tweezers. We report on an approach to measure air-water interfacial properties through microrheology of particles near, but not contacting, the surface. An inverted optical tweezer traps beads of micron size or greater in the bulk, and can then translate them perpendicular to the interface. Through the measurement of thermally driven fluctuations, the mobility of the particle is found to vary as a function of submerged depth and the boundary conditions at the interface. Near a rigid wall, the mobility is confirmed to decrease in a way consistent with Faxèn's law. Very close to the free air-water interface, the mobility changes with the opposite sign, increasing by about 30% at the surface, consistent with recent calculations by Shlomovitz and Levine. In addition, the presence of a Langmuir monolayer at the interface is found to significantly change the mobility of the particle close to the interface. With an accurate theory, it should be possible to infer the shear modulus of a monolayer from the fluctuations of the particle beneath the interface. Since particles are not embedded in the monolayer, this technique avoids impacting the system of study.

  7. Protein interfacial structure and nanotoxicology

    NASA Astrophysics Data System (ADS)

    White, John W.; Perriman, Adam W.; McGillivray, Duncan J.; Lin, Jhih-Min

    2009-02-01

    Here we briefly recapitulate the use of X-ray and neutron reflectometry at the air-water interface to find protein structures and thermodynamics at interfaces and test a possibility for understanding those interactions between nanoparticles and proteins which lead to nanoparticle toxicology through entry into living cells. Stable monomolecular protein films have been made at the air-water interface and, with a specially designed vessel, the substrate changed from that which the air-water interfacial film was deposited. This procedure allows interactions, both chemical and physical, between introduced species and the monomolecular film to be studied by reflectometry. The method is briefly illustrated here with some new results on protein-protein interaction between β-casein and κ-casein at the air-water interface using X-rays. These two proteins are an essential component of the structure of milk. In the experiments reported, specific and directional interactions appear to cause different interfacial structures if first, a β-casein monolayer is attacked by a κ-casein solution compared to the reverse. The additional contrast associated with neutrons will be an advantage here. We then show the first results of experiments on the interaction of a β-casein monolayer with a nanoparticle titanium oxide sol, foreshadowing the study of the nanoparticle "corona" thought to be important for nanoparticle-cell wall penetration.

  8. Two-phase flow interfacial structures in a rod bundle geometry

    NASA Astrophysics Data System (ADS)

    Paranjape, Sidharth S.

    Interfacial structure of air-water two-phase flow in a scaled nuclear reactor rod bundle geometry was studied in this research. Global and local flow regimes were obtained for the rod bundle geometry. Local two-phase flow parameters were measured at various axial locations in order to understand the transport of interfacial structures. A one-dimensional two-group interfacial area transport model was evaluated using the local parameter database. Air-water two-phase flow experiments were performed in an 8 X 8 rod bundle test section to obtain flow regime maps at various axial locations. Area averaged void fraction was measured using parallel plate type impedance void meters. The cumulative probability distribution functions of the signals from the impedance void meters were used along with a self organizing neural network to identify flow regimes. Local flow regime maps revealed the cross-sectional distribution of flow regimes in the bundle. Local parameters that characterize interfacial structure, that is, void fraction alpha, interfacial area concentration, ai, bubble Sauter mean diameter, DSm and bubble velocity, vg were measured using four sensor conductivity probe technique. The local data revealed the distribution of the interfacial structure in the radial direction, as well as its development in the axial direction. In addition to this, the effect of spacer grid on the flow structure at different gas and liquid velocities was revealed by local parameter measurements across the spacer grids. A two-group interfacial area transport equation (IATE) specific to rod bundle geometry was derived. The derivation of two-group IATE required certain assumption on the bubble shapes in the subchannels and the bubbles spanning more than a subchannel. It was found that the geometrical relationship between the volume and the area of a cap bubble distorted by rods was similar to the one derived for a confined channel under a specific geometrical transformation. The one

  9. Understanding the structure of hydrophobic surfactants at the air/water interface from molecular level.

    PubMed

    Zhang, Li; Liu, Zhipei; Ren, Tao; Wu, Pan; Shen, Jia-Wei; Zhang, Wei; Wang, Xinping

    2014-11-25

    Understanding the behavior of fluorocarbon surfactants at the air/water interface is crucial for many applications, such as lubricants, paints, cosmetics, and fire-fighting foams. In this study, molecular dynamics (MD) simulations were employed to investigate the microscopic properties of non-ionic fluorocarbon surfactants at the air/water interface. Several properties, including the distribution of head groups, the distribution probability of the tilt angle between hydrophobic tails with respect to the xy plane, and the order parameter of surfactants, were computed to probe the structure of hydrophobic surfactants at the air/water interface. The effects of the monomer structure on interfacial phenomena of non-ionic surfactants were investigated as well. It is observed that the structure of fluorocarbon surfactants at the air/water interface is more ordered than that of hydrocarbons, which is dominated by the van der Waals interaction between surfactants and water molecules. However, replacing one or two CF2 with one or two CH2 group does not significantly influence the interfacial structure, suggesting that hydrocarbons may be promising alternatives to perfluorinated surfactants.

  10. Measurement of the Surface Dilatational Viscosity of an Insoluble Surfactant Monolayer at the Air/Water Interface Using a Pendant Drop Apparatus

    NASA Technical Reports Server (NTRS)

    Lorenzo, Jose; Couzis, Alex; Maldarelli, Charles; Singh, Bhim S. (Technical Monitor)

    2000-01-01

    When a fluid interface with surfactants is at rest, the interfacial stress is isotropic (as given by the equilibrium interfacial tension), and is described by the equation of state which relates the surface tension to the surfactant surface concentration. When surfactants are subjected to shear and dilatational flows, flow induced interaction of the surfactants; can create interfacial stresses apart from the equilibrium surface tension. The simplest relationship between surface strain rate and surface stress is the Boussinesq-Scriven constitutive equation completely characterized by three coefficients: equilibrium interfacial tension, surface shear viscosity, and surface dilatational viscosity Equilibrium interfacial tension and surface shear viscosity measurements are very well established. On the other hand, surface dilatational viscosity measurements are difficult because a flow which change the surface area also changes the surfactant surface concentration creating changes in the equilibrium interfacial tension that must be also taken into account. Surface dilatational viscosity measurements of existing techniques differ by five orders of magnitude and use spatially damped surface waves and rapidly expanding bubbles. In this presentation we introduce a new technique for measuring the surface dilatational viscosity by contracting an aqueous pendant drop attached to a needle tip and having and insoluble surfactant monolayer at the air-water interface. The isotropic total tension on the surface consists of the equilibrium surface tension and the tension due to the dilation. Compression rates are undertaken slow enough so that bulk hydrodynamic stresses are small compared to the surface tension force. Under these conditions we show that the total tension is uniform along the surface and that the Young-Laplace equation governs the drop shape with the equilibrium surface tension replaced by the constant surface isotropic stress. We illustrate this technique using

  11. Role of mixed boundaries on flow in open capillary channels with curved air-water interfaces.

    PubMed

    Zheng, Wenjuan; Wang, Lian-Ping; Or, Dani; Lazouskaya, Volha; Jin, Yan

    2012-09-01

    Flow in unsaturated porous media or in engineered microfluidic systems is dominated by capillary and viscous forces. Consequently, flow regimes may differ markedly from conventional flows, reflecting strong interfacial influences on small bodies of flowing liquids. In this work, we visualized liquid transport patterns in open capillary channels with a range of opening sizes from 0.6 to 5.0 mm using laser scanning confocal microscopy combined with fluorescent latex particles (1.0 μm) as tracers at a mean velocity of ∼0.50 mm s(-1). The observed velocity profiles indicate limited mobility at the air-water interface. The application of the Stokes equation with mixed boundary conditions (i.e., no slip on the channel walls and partial slip or shear stress at the air-water interface) clearly illustrates the increasing importance of interfacial shear stress with decreasing channel size. Interfacial shear stress emerges from the velocity gradient from the adjoining no-slip walls to the center where flow is trapped in a region in which capillary forces dominate. In addition, the increased contribution of capillary forces (relative to viscous forces) to flow on the microscale leads to increased interfacial curvature, which, together with interfacial shear stress, affects the velocity distribution and flow pattern (e.g., reverse flow in the contact line region). We found that partial slip, rather than the commonly used stress-free condition, provided a more accurate description of the boundary condition at the confined air-water interface, reflecting the key role that surface/interface effects play in controlling flow behavior on the nanoscale and microscale.

  12. Interfacial characteristic measurements in horizontal bubbly two-phase flow

    NASA Astrophysics Data System (ADS)

    Wang, Z.; Huang, W. D.; Srinivasmurthy, S.; Kocamustafaogullari, G.

    1990-10-01

    Advances in the study of two-phase flow increasingly require detailed internal structure information upon which theoretical models can be formulated. The void fraction and interfacial area are two fundamental parameters characterizing the internal structure of two-phase flow. However, little information is currently available on these parameters, and it is mostly limited to vertical flow configurations. In view of the above, the internal phase distribution of concurrent, air-water bubbly flow in a 50.3 mm diameter transparent pipeline has been experimentally investigated by using a double-sensor resistivity probe. Liquid and gas volumetric superficial velocities ranged from 3.74 to 5.60 m/s and 0.25 to 1.59 m/s, respectively, and average void fractions ranged from 2.12 to 22.5 percent. The local values of void fractions, interfacial area concentration, mean bubble diameter, bubble interface velocity, bubble chord-length and bubble frequency distributions were measured. The experimental results indicate that the void fraction interfacial area concentration and bubble frequency have local maxima near the upper pipe wall, and the profiles tend to flatten with increasing void fraction. The observed peak void fraction can reach 0.65, the peak interfacial area can go up to 900 approximately 1000 sq m/cu m, and the bubble frequency can reach a value of 2200 per s. These ranges of values have never been reported for vertical bubbly flow. It is found that either decreasing the liquid flow rate or increasing the gas flow would increase the local void fraction, the interfacial area concentration and the bubble frequency.

  13. Toward mechanistic understanding of nuclear reprocessing chemistries by quantifying lanthanide solvent extraction kinetics via microfluidics with constant interfacial area and rapid mixing.

    PubMed

    Nichols, Kevin P; Pompano, Rebecca R; Li, Liang; Gelis, Artem V; Ismagilov, Rustem F

    2011-10-01

    The closing of the nuclear fuel cycle is an unsolved problem of great importance. Separating radionuclides produced in a nuclear reactor is useful both for the storage of nuclear waste and for recycling of nuclear fuel. These separations can be performed by designing appropriate chelation chemistries and liquid-liquid extraction schemes, such as in the TALSPEAK process (Trivalent Actinide-Lanthanide Separation by Phosphorus reagent Extraction from Aqueous Komplexes). However, there are no approved methods for the industrial scale reprocessing of civilian nuclear fuel in the United States. One bottleneck in the design of next-generation solvent extraction-based nuclear fuel reprocessing schemes is a lack of interfacial mass transfer rate constants obtained under well-controlled conditions for lanthanide and actinide ligand complexes; such rate constants are a prerequisite for mechanistic understanding of the extraction chemistries involved and are of great assistance in the design of new chemistries. In addition, rate constants obtained under conditions of known interfacial area have immediate, practical utility in models required for the scaling-up of laboratory-scale demonstrations to industrial-scale solutions. Existing experimental techniques for determining these rate constants suffer from two key drawbacks: either slow mixing or unknown interfacial area. The volume of waste produced by traditional methods is an additional, practical concern in experiments involving radioactive elements, both from disposal cost and experimenter safety standpoints. In this paper, we test a plug-based microfluidic system that uses flowing plugs (droplets) in microfluidic channels to determine absolute interfacial mass transfer rate constants under conditions of both rapid mixing and controlled interfacial area. We utilize this system to determine, for the first time, the rate constants for interfacial transfer of all lanthanides, minus promethium, plus yttrium, under TALSPEAK

  14. Toward mechanistic understanding of nuclear reprocessing chemistries by quantifying lanthanide solvent extraction kinetics via microfluidics with constant interfacial area and rapid mixing.

    PubMed

    Nichols, Kevin P; Pompano, Rebecca R; Li, Liang; Gelis, Artem V; Ismagilov, Rustem F

    2011-10-01

    The closing of the nuclear fuel cycle is an unsolved problem of great importance. Separating radionuclides produced in a nuclear reactor is useful both for the storage of nuclear waste and for recycling of nuclear fuel. These separations can be performed by designing appropriate chelation chemistries and liquid-liquid extraction schemes, such as in the TALSPEAK process (Trivalent Actinide-Lanthanide Separation by Phosphorus reagent Extraction from Aqueous Komplexes). However, there are no approved methods for the industrial scale reprocessing of civilian nuclear fuel in the United States. One bottleneck in the design of next-generation solvent extraction-based nuclear fuel reprocessing schemes is a lack of interfacial mass transfer rate constants obtained under well-controlled conditions for lanthanide and actinide ligand complexes; such rate constants are a prerequisite for mechanistic understanding of the extraction chemistries involved and are of great assistance in the design of new chemistries. In addition, rate constants obtained under conditions of known interfacial area have immediate, practical utility in models required for the scaling-up of laboratory-scale demonstrations to industrial-scale solutions. Existing experimental techniques for determining these rate constants suffer from two key drawbacks: either slow mixing or unknown interfacial area. The volume of waste produced by traditional methods is an additional, practical concern in experiments involving radioactive elements, both from disposal cost and experimenter safety standpoints. In this paper, we test a plug-based microfluidic system that uses flowing plugs (droplets) in microfluidic channels to determine absolute interfacial mass transfer rate constants under conditions of both rapid mixing and controlled interfacial area. We utilize this system to determine, for the first time, the rate constants for interfacial transfer of all lanthanides, minus promethium, plus yttrium, under TALSPEAK

  15. A study on the characteristics of upward air-water two-phase flow in a large diameter pipe

    SciTech Connect

    Shen, Xiuzhong; Saito, Yasushi; Mishima, Kaichiro; Nakamura, Hideo

    2006-10-15

    An adiabatic upward co-current air-water two-phase flow in a vertical large diameter pipe (inner diameter, D: 0.2m, ratio of pipe length to diameter, L/D: 60.5) was experimentally investigated under various inlet conditions. Flow regimes were visually observed, carefully analyzed and classified into five, i.e. undisturbed bubbly, agitated bubbly, churn bubbly, churn slug and churn froth. Void fraction, bubble frequency, Sauter mean diameter, interfacial area concentration (IAC) and interfacial direction were measured with four-sensor optical probes. Both the measured void fraction and the measured IAC demonstrated radial core-peak distributions in most of the flow regimes and radial wall peak in the undisturbed bubbly flow only. The bubble frequency also showed a wall-peak radial distribution only when the bubbles were small in diameter and the flow was in the undisturbed bubbly flow. The Sauter mean diameter of bubbles did not change much in the radial direction in undisturbed bubbly, agitated bubbly and churn bubbly flows and showed a core-peak radial distribution in the churn slug flow due to the existence of certain amount of large and deformed bubbles in this flow regime. The measurements of interfacial direction showed that the main and the secondary bubbly flow could be displayed by the main flow peak and the secondary flow peak, respectively, in the probability density function (PDF) of the interfacial directional angle between the interfacial direction and the z-axis, {eta}{sub zi}. The local average {eta}{sub zi }at the bubble front or rear hemisphere ({eta}{sub zi}{sup F} and {eta}{sub zi}{sup R}) reflected the local bubble movement and was in direct connection with the flow regimes. Based on the analysis, the authors classified the flow regimes in the vertical large diameter pipe quantitatively by the cross-sectional area-averaged {eta}{sub zi }at bubbly front hemisphere ({eta}{sub zi}{sup F}-bar). Bubbles in the undisturbed bubbly flow moved in a

  16. Anisotropic orientational motion of molecular adsorbates at the air-water interface

    SciTech Connect

    Zimdars, D.; Dadap, J.I.; Eisenthal, K.B.; Heinz, T.F.

    1999-04-29

    The ultrafast orientational motions of coumarin 314 (C314) adsorbed at the air/water interface were investigated by time-resolved surface second harmonic generation (TRSHG). The theory and method of using TRSHG to detect both out-of-plane and in-plane orientational motions are discussed. The interfacial solute motions were found to be anisotropic, with differing out-of-plane and in-plane reorientation time constants. This report presents the first direct observation of in-plane orientational motion of a molecule (C314) at the air/water interface using TRSHG. The in-plane reorientation time constant is 600 {+-} 40 ps. The out-of-plane reorientation time constant is 350 {+-} 20 ps. The out-of-plane orientational motion of C314 is similar to the previous results on rhodamine 6G at the air/water interface which indicated increased interfacial friction compared with bulk aqueous solution. The surface reorientation times are 2--3 times slower than the bulk isotropic orientational diffusion time.

  17. Hydrodynamics of a self-propelled camphor boat at the air-water interface

    NASA Astrophysics Data System (ADS)

    Akella, Sathish; Singh, Dhiraj; Singh, Ravi; Bandi, Mahesh

    2015-11-01

    A camphor tablet, when placed at the air-water interface undergoes sublimation and camphor vapour spreads radially outwards across the surface due to Marangoni forces. This steady camphor influx from tablet onto the air-water interface is balanced by the camphor outflux due to evaporation. When spontaneous fluctuations in evaporation break the axial symmetry of Marangoni force acting radially outwards, the camphor tablet is propelled like a boat along the water surface. We report experiments on the hydrodynamics of a self-propelled camphor boat at air-water interfaces. We observe three different modes of motion, namely continuous, harmonic and periodic, due to the volatile nature of camphor. We explain these modes in terms of ratio of two time-scales: the time-scale over which viscous forces are dominant over the Marangoni forces (τη) and the time-scale over which Marangoni forces are dominant over the viscous forces (τσ). The continuous, harmonic and periodic motions are observed when τη /τσ ~ 1 , τη /τσ >= 1 and τη /τσ >> 1 respectively. Experimentally, the ratio of the time scales is varied by changing the interfacial tension of the air-water interface using Sodium Dodecyl Sulfate. This work was supported by the Collective Interactions Unit, OIST Graduate University.

  18. Formation, disruption and mechanical properties of a rigid hydrophobin film at an air-water interface

    NASA Astrophysics Data System (ADS)

    Walker, Lynn; Kirby, Stephanie; Anna, Shelley; CMU Team

    Hydrophobins are small, globular proteins with distinct hydrophilic and hydrophobic regions that make them extremely surface active. The behavior of hydrophobins at surfaces has raised interest in their potential industrial applications, including use in surface coatings, food foams and emulsions, and as dispersants. Practical use of hydrophobins requires an improved understanding of the interfacial behavior of these proteins, both individually and in the presence of surfactants. Cerato-ulmin (CU) is a hydrophobin that has been shown to strongly stabilize air bubbles and oil droplets through the formation of a persistent protein film at the interface. In this work, we characterize the adsorption behavior of CU at air/water interfaces by measuring the surface tension and interfacial rheology as a function of adsorption time. CU is found to strongly, irreversibly adsorb at air/water interfaces; the magnitude of the dilatational modulus increases with adsorption time and surface pressure, until the CU eventually forms a rigid film. The persistence of this film is tested through the addition of SDS, a strong surfactant, to the bulk. SDS is found to co-adsorb to interfaces pre-coated with a CU film. At high concentrations, the addition of SDS significantly decreases the dilatational modulus, indicating disruption and displacement of CU. These results lend insight into the complex interfacial interactions between hydrophobins and surfactants. Funding from GoMRI.

  19. Proton Transfers at the Air-Water Interface

    NASA Astrophysics Data System (ADS)

    Mishra, Himanshu

    Proton transfer reactions at the interface of water with hydrophobic media, such as air or lipids, are ubiquitous on our planet. These reactions orchestrate a host of vital phenomena in the environment including, for example, acidification of clouds, enzymatic catalysis, chemistries of aerosol and atmospheric gases, and bioenergetic transduction. Despite their importance, however, quantitative details underlying these interactions have remained unclear. Deeper insight into these interfacial reactions is also required in addressing challenges in green chemistry, improved water quality, self-assembly of materials, the next generation of micro-nanofluidics, adhesives, coatings, catalysts, and electrodes. This thesis describes experimental and theoretical investigation of proton transfer reactions at the air-water interface as a function of hydration gradients, electrochemical potential, and electrostatics. Since emerging insights hold at the lipid-water interface as well, this work is also expected to aid understanding of complex biological phenomena associated with proton migration across membranes. Based on our current understanding, it is known that the physicochemical properties of the gas-phase water are drastically different from those of bulk water. For example, the gas-phase hydronium ion, H3O +(g), can protonate most (non-alkane) organic species, whereas H 3O+(aq) can neutralize only relatively strong bases. Thus, to be able to understand and engineer water-hydrophobe interfaces, it is imperative to investigate this fluctuating region of molecular thickness wherein the 'function' of chemical species transitions from one phase to another via steep gradients in hydration, dielectric constant, and density. Aqueous interfaces are difficult to approach by current experimental techniques because designing experiments to specifically sample interfacial layers (< 1 nm thick) is an arduous task. While recent advances in surface-specific spectroscopies have provided

  20. Interfacial growth of large-area single-layer metal-organic framework nanosheets

    PubMed Central

    Makiura, Rie; Konovalov, Oleg

    2013-01-01

    The air/liquid interface is an excellent platform to assemble two-dimensional (2D) sheets of materials by enhancing spontaneous organizational features of the building components and encouraging large length scale in-plane growth. We have grown 2D molecularly-thin crystalline metal-organic-framework (MOF) nanosheets composed of porphyrin building units and metal-ion joints (NAFS-13) under operationally simple ambient conditions at the air/liquid interface. In-situ synchrotron X-ray diffraction studies of the formation process performed directly at the interface were employed to optimize the NAFS-13 growth protocol leading to the development of a post-injection method –post-injection of the metal connectors into the water subphase on whose surface the molecular building blocks are pre-oriented– which allowed us to achieve the formation of large-surface area morphologically-uniform preferentially-oriented single-layer nanosheets. The growth of such large-size high-quality sheets is of interest for the understanding of the fundamental physical/chemical properties associated with ultra-thin sheet-shaped materials and the realization of their use in applications. PMID:23974345

  1. Local Interfacial Structure in Downward Two-Phase Bubbly Flow

    SciTech Connect

    Hiroshi Goda; Seungjin Kim; Paranjape, Sidharth S.; Finch, Joshua P.; Mamoru Ishii; Uhle, Jennifer

    2002-07-01

    The local interfacial structure for vertical air-water co-current downward two-phase flow was investigated under adiabatic conditions. A multi-sensor conductivity probe was utilized in order to acquire the local two-phase flow parameters. The present experimental loop consisted of 25.4 mm and 50.8 mm ID round tubes as test sections. The measurement was performed at three axial locations: L/D = 13, 68 and 133 for the 25.4 mm ID loop and L/D 7, 34, 67 for the 50.8 mm ID loop, in order to study the axial development of the flow. A total of 7 and 10 local measurement points along the tube radius were chosen for the 25.4 mm ID loop and the 50.8 mm ID loop, respectively. The experimental flow conditions were determined within bubbly flow regime. The acquired local parameters included the void fraction, interfacial area concentration, bubble interface frequency, bubble Sauter mean diameter, and interfacial velocity. (authors)

  2. Tailored interfacial rheology for gastric stable adsorption layers.

    PubMed

    Scheuble, N; Geue, T; Windhab, E J; Fischer, P

    2014-08-11

    Human lipid digestion begins at the interface of oil and water by interfacial adsorption of lipases. Tailoring the available surface area for lipase activity can lead to specific lipid sensing in the body, thus, tailored satiety hormone release. In this study we present biopolymer layers at the MCT-oil/water interface with different stabilities under human gastric environment (37 °C, pH 2, pepsin). Physicochemical changes and enzymatic degradation of interfacial layers were monitored online by interfacial shear rheology. We show the weakening of β-lactoglobulin (β-lg) layers at body temperature and acidification and their hydrolysis by pepsin. If sufficient concentrations of nanocrystalline cellulose (NCC) are given to an existing β-lg layer, this weakening is buffered and the proteolysis delayed. A synergistic, composite layer is formed by adding methylated NCC to the β-lg layer. This layer thermogels at body temperature and resists hydrolysis by pepsin. Coexistence of these two emulsifiers at the air/water interface is evidenced by neutron reflectometry measurements, where morphological information are extracted. The utilized layers and their analysis provide knowledge of physicochemical changes during in vitro digestion of interfaces, which promote functional food formulations. PMID:25029559

  3. Ligand interaction with the purified serotonin transporter in solution and at the air/water interface

    SciTech Connect

    Faivre, V.; Manivet, P.; Callaway, J.C.; Morimoto, H.; Airaksinen, M.M.; Baszkin, A.; Launay, J.M.; Rosilio, V.

    2000-06-01

    The purified serotonin transporter (SERT) was spread at the air/water interface and the effects both of its surface density and of the temperature on its interfacial behavior were studied. The recorded isotherms evidenced the existence of a stable monolayer undergoing a lengthy rearrangement. SERT/ligand interactions appeared to be dependent on the nature of the studied molecules. Whereas an unrelated drug (chlorcyclizine) did not bind to the spread SERT, it interacted with its specific ligands. Compared to heterocyclic drugs, for which binding appeared to be concentration-dependent, a 'two-site' mechanism was evidenced for pinoline and imipramine.

  4. Study of Interfacial Structures: Bubbly Flow in 1.27 cm Diameter Pipe

    SciTech Connect

    Paranjape, S.; Kim, S.; Ishii, M.; Uhle, J.

    2002-07-01

    The objective of the present research is to study the flow regime map, the detailed interfacial structures, and the bubble transport in an adiabatic air-water two-phase flow mixture, flowing upward through a vertical round pipe having 1.27 cm. inner diameter. The flow regime map is obtained by processing the characteristic signals acquired from an impedance void meter, using a self-organized neural network. The local two-phase flow parameters are measured by the state-of-the-art four-sensor conductivity probe at three axial locations in the pipe. The measured local parameters include void fraction ({alpha}), interfacial area concentration (a{sub i}), bubble frequency (f{sub b}), bubble velocity (U{sub b}) and bubble Sauter mean diameter (D{sub sm}). The radial profiles of these parameters and their development along the axial direction reveals the structure of the two phase mixture and the bubble interaction mechanisms. (authors)

  5. Role of specific interfacial area in controlling properties of immiscible blends of biodegradable polylactide and poly[(butylene succinate)-co-adipate].

    PubMed

    Ojijo, Vincent; Sinha Ray, Suprakas; Sadiku, Rotimi

    2012-12-01

    Binary blends of two biodegradable polymers: polylactide (PLA), which has high modulus and strength but is brittle, and poly[(butylene succinate)-co-adipate] (PBSA), which is flexible and tough, were prepared through batch melt mixing. The PLA/PBSA compositions were 100/0, 90/10, 70/30, 60/40, 50/50, 40/60, 30/70, 10/90, and 0/100. Fourier-transform infrared measurements revealed the absence of any chemical interaction between the two polymers, resulting in a phase-separated morphology as shown by scanning electron microscopy (SEM). SEM micrographs showed that PLA-rich blends had smaller droplet sizes when compared to the PBSA-rich blends, which got smaller with the reduction in PBSA content due to the differences in their melt viscosities. The interfacial area of PBSA droplets per unit volume of the blend reached a maximum in the 70PLA/30PBSA blend. Thermal stability and mechanical properties were not only affected by the composition of the blend, but also by the interfacial area between the two polymers. Through differential scanning calorimetry, it was shown that molten PBSA enhanced crystallization of PLA while the stiff PLA hindered cold crystallization of PBSA. Optimal synergies of properties between the two polymers were found in the 70PLA/30PBSA blend because of the maximum specific interfacial area of the PBSA droplets.

  6. On the inclusion of the interfacial area between phases in the physical and mathematical description of subsurface multiphase flow. 1998 annual progress report

    SciTech Connect

    Gray, W.G.; Tompson, A.; Soll, W.E.

    1998-06-01

    'Improved capabilities for modeling multiphase flow in the subsurface requires that several aspects of the system which impact the flow and transport processes be more properly accounted for. A distinguishing feature of multiphase flow in comparison to single phase flow is the existence of interfaces between fluids. At the microscopic (pore) scale, these interfaces are known to influence system behavior by supporting non-zero stresses such that the pressures in adjacent phases are not equal. In problems of interphase transport at the macroscopic (core) scale, knowledge of the total amount of interfacial area in the system provides a clue to the effectiveness of the communication between phases. Although interfacial processes are central to multiphase flow physics, their treatment in traditional porous-media theories has been implicit rather than explicit; and no attempts have been made to systematically account for the evolution of the interfacial area in dynamic systems or to include the dependence of constitutive functions, such as capillary pressure, on the interfacial area. This project implements a three-pronged approach to assessing the importance of various features of multiphase flow to its description. The research contributes to the improved understanding and precise physical description of multiphase subsurface flow by combining: (1) theoretical derivation of equations, (2) lattice Boltzmann modeling of hydrodynamics to identify characteristics and parameters, and (3) solution of the field-scale equations using a discrete numerical method to assess the advantages and disadvantages of the complete theory. This approach includes both fundamental scientific inquiry and a path for inclusion of the scientific results obtained in a technical tool that will improve assessment capabilities for multiphase flow situations that have arisen due to the introduction of organic materials in the natural environment. This report summarizes work after 1.5 years of a 3

  7. Effect of glycyrrhetinic acid on lipid raft model at the air/water interface.

    PubMed

    Sakamoto, Seiichi; Uto, Takuhiro; Shoyama, Yukihiro

    2015-02-01

    To investigate an interfacial behavior of the aglycon of glycyrrhizin (GC), glycyrrhetinic acid (GA), with a lipid raft model consisting of equimolar ternary mixtures of N-palmitoyl sphingomyelin (PSM), dioleoylphosphatidylcholine (DOPC), and cholesterol (CHOL), Langmuir monolayer techniques were systematically conducted. Surface pressure (π)-molecular area (A) and surface potential (ΔV)-A isotherms showed that the adsorbed GA at the air/water interface was desorbed into the bulk upon compression of the lipid monolayer. In situ morphological analysis by Brewster angle microscopy and fluorescence microscopy revealed that the raft domains became smaller as the concentrations of GA in the subphase (CGA) increased, suggesting that GA promotes the formation of fluid networks related to various cellular processes via lipid rafts. In addition, ex situ morphological analysis by atomic force microscopy revealed that GA interacts with lipid raft by lying down at the surface. Interestingly, the distinctive striped regions were formed at CGA=5.0 μM. This phenomenon was observed to be induced by the interaction of CHOL with adsorbed GA and is involved in the membrane-disrupting activity of saponin and its aglycon. A quantitative comparison of GA with GC (Sakamoto et al., 2013) revealed that GA interacts more strongly with the raft model than GC in the monolayer state. Various biological activities of GA are known to be stronger than those of GC. This fact allows us to hypothesize that differences in the interactions of GA/GC with the model monolayer correlate to their degree of exertion for numerous activities.

  8. Ligand Shell Composition-Dependent Effects on the Apparent Hydrophobicity and Film Behavior of Gold Nanoparticles at the Air-Water Interface.

    PubMed

    Bradford, Stephen M; Fisher, Elizabeth A; Meli, M-Vicki

    2016-09-27

    Nanoparticles with well-defined interfacial energy and wetting properties are needed for a broad range of applications involving nanoparticle self-assembly including the formation of superlattices, stability of Pickering emulsions, and for the control of nanoparticle interactions with biological membranes. Theoretical, simulated, and recent experimental studies have found nanometer-scale chemical heterogeneity to have important effects on hydrophobic interactions. Here we report the study of 4 nm gold nanoparticles with compositionally well-defined mixed ligand shells of hydroxyl-(OH) and methyl-(CH3) terminated alkylthiols as Langmuir films. Compositions ranging from 0-25% hydroxyl were examined and reveal nonmonotonic changes in particle hydrophobicity at the air-water interface. Unlike nanoparticles capped exclusively with a methyl-terminated alkylthiol, extensive particle aggregation is found for ligand shells containing <2% hydroxyl-terminated chains. This aggregation was lessened upon increasing the quantity of OH-terminated chains. Nanoparticles capped with 25% OH yield films of well-separated nanoparticles exhibiting a fluid-phase regime in the surface pressure vs area isotherm. Compression-expansion hysteresis, monolayer collapse, and mean nanoparticle area measurements support the TEM-observed changes in film morphology. Such clear changes in the hydrophobicity of nanoparticles based on very small changes in the ligand shell composition are shown to impact the process of interfacial nanoparticle self-assembly and are an important demonstration of nanoscale wetting with consequences in both materials and biological applications of nanoparticles that require tunable hydrophobicity. PMID:27594307

  9. Probing Shear Thinning Behaviors of IgG Molecules at the Air-Water Interface via Rheological Methods.

    PubMed

    Gleason, Camille; Yee, Chanel; Masatani, Peter; Middaugh, C Russell; Vance, Aylin

    2016-01-19

    Shear thinning behavior, often observed in shear viscosity tests of IgG therapeutic molecules, could lead to significant disparities in the projections for the viscosity profile of a molecule. Despite its importance, molecular determinants of sheer thinning in protein suspensions are largely unknown. To better understand the factors influencing sheer thinning, viscosity profiles of IgG1 and IgG2 molecules were monitored over a wide range of bulk concentrations (0.007-70 mg/mL). The degree of shear-thinning of 70 and 0.007 mg/mL samples was minimal in comparison to the 0.7 mg/mL solution for both IgG molecules. These observations suggest that bulk concentration alone does not determine the degree of sheer thinning, and additional factors play a role. Additional data reveals, within a threshold range of concentrations, that a strong correlation exists between the degree of shear thinning and the surface area to volume (SA:V) ratio of an IgG sample exposed to the interface. The influence of the interface, however, diminishes when the bulk concentration falls outside this concentration window. Also revealed by interfacial oscillatory rheological testing, both IgG molecules showed solid-like behavior (G'i) at the air-water interface at 0.7 mg/mL, whereas liquid-like behavior (G″i) was dominant at 0.007 and 70 mg/mL concentrations. These observations imply that the lack of solid-like behavior was due to the absence of a network structure. Likewise the addition of polysorbate 20 (PS20) to the 0.7 mg/mL solutions decreased the degree of shear thinning by disrupting the network structure at the interface. Taken together, the results presented here suggest that, although shear thinning behavior is a manifestation of an interfacial, rather than a bulk, phenomenon, the extent of it depends on how susceptible the surface molecules are to the air-water interface, where the surface molecular structures are influenced by the bulk properties.

  10. Hydrodynamics of a fixed camphor boat at the air-water interface

    NASA Astrophysics Data System (ADS)

    Singh, Dhiraj; Akella, Sathish; Singh, Ravi; Mandre, Shreyas; Bandi, Mahesh

    2015-11-01

    A camphor tablet, when introduced at the air-water interface undergoes sublimation and the camphor vapour spreads radially outwards across the surface. This radial spreading of camphor is due to Marangoni forces setup by the camphor concentration gradient. We report experiments on the hydrodynamics of this process for a camphor tablet held fixed at the air-water interface. During the initial transient, the time-dependent spread radius R (t) of camphor scales algebraically with time t (R (t) ~t 1 / 2) in agreement with empirical scalings reported for spreading of volatile oils on water surface. But unlike surfactants, the camphor stops spreading when the influx of camphor from the tablet onto the air-water interface is balanced by the outflux of camphor due to evaporation, and a steady-state condition is reached. The spreading camphor however, shears the underlying fluid and sets up bulk convective flow. We explain the coupled steady-state dynamics between the interfacial camphor spreading and bulk convective flow with a boundary layer approximation, supported by experimental evidence. This work was supported by the Collective Interactions Unit, OIST Graduate University.

  11. Measuring NAPL-Water Interfacial Areas to Evaluate the Effectiveness of In-Situ Chemical Oxidation for DNAPL-Contaminated Source Zones: A Two-Dimensional Flow Cell Study

    NASA Astrophysics Data System (ADS)

    Li, M.; Brusseau, M. L. L.; Yan, N.; Wan, L.

    2015-12-01

    In-situ chemical oxidation (ISCO) using persulfate was employed to remediate a flow cell contaminated with a model dense nonaqueous-phase liquid (DNAPL), trichloroethene (TCE). The flow cell was packed homogeneously with 359 μm diameter natural sand. Dyed TCE DNAPL was naturally distributed in the flow cell. Fe2+-activated persulfate (5 mM) was used for ISCO. Interfacial partitioning tracer tests (IPTT) were conducted before and after ISCO to measure NAPL-water interfacial area, using sodium dodecyl benzenesulfonate (SDBS, 35mg/L) as the tracer. The change in interfacial area was examined as influenced by ISCO remediation. The interfacial areas measured for this two-dimensional system are compared to previously reported values obtained from one-dimensional column experiments.

  12. Influence of phase connectivity on the relationship among capillary pressure, fluid saturation, and interfacial area in two-fluid-phase porous medium systems

    DOE PAGES

    McClure, James E.; Berrill, Mark A.; Gray, William G.; Miller, Cass T.

    2016-09-02

    Here, multiphase flow in porous medium systems is typically modeled using continuum mechanical representations at the macroscale in terms of averaged quantities. These models require closure relations to produce solvable forms. One of these required closure relations is an expression relating fluid pressures, fluid saturations, and, in some cases, the interfacial area between the fluid phases, and the Euler characteristic. An unresolved question is whether the inclusion of these additional morphological and topological measures can lead to a non-hysteretic closure relation compared to the hysteretic forms that are used in traditional models, which typically do not include interfacial areas, ormore » the Euler characteristic. We develop a lattice-Boltzmann (LB) simulation approach to investigate the equilibrium states of a two-fluid-phase porous medium system, which include disconnected now- wetting phase features. The proposed approach is applied to a synthetic medium consisting of 1,964 spheres arranged in a random, non-overlapping, close-packed manner, yielding a total of 42,908 different equilibrium points. This information is evaluated using a generalized additive modeling approach to determine if a unique function from this family exists, which can explain the data. The variance of various model estimates is computed, and we conclude that, except for the limiting behavior close to a single fluid regime, capillary pressure can be expressed as a deterministic and non-hysteretic function of fluid saturation, interfacial area between the fluid phases, and the Euler characteristic. This work is unique in the methods employed, the size of the data set, the resolution in space and time, the true equilibrium nature of the data, the parameterizations investigated, and the broad set of functions examined. The conclusion of essentially non-hysteretic behavior provides support for an evolving class of two-fluid-phase flow in porous medium systems models.« less

  13. Methylglyoxal at the Air-Water Interface

    NASA Astrophysics Data System (ADS)

    Wren, S. N.; Gordon, B. P.; McWilliams, L.; Valley, N. A.; Richmond, G.

    2014-12-01

    Recently, it has been suggested that aqueous-phase processing of atmospheric α-dicarbonyl compounds such as methylglyoxal (MG) could constitute an important source of secondary organic aerosol (SOA). The uptake of MG to aqueous particles is higher than expected due to the fact that its carbonyl moieties can hydrate to form diols, as well as the fact that MG can undergo aldol condensation reactions to form larger oligomers in solution. MG is known to be surface active but an improved description of its surface behaviour is crucial to understanding MG-SOA formation, in addition to understanding its gas-to-particle partitioning and cloud forming potential. Here, we employ a combined experimental and theoretical approach involving vibrational sum frequency generation spectroscopy (VSFS), surface tensiometry, molecular dynamics simulations, and density functional theory calculations to study MG's surface adsorption, in both the presence and absence of salts. We are particularly interested in determining MG's hydration state at the surface. Our experimental results indicate that MG slowly adsorbs to the air-water interface and strongly perturbs the water structure there. This perturbation is enhanced in the presence of NaCl. Together our experimental and theoretical results suggest that singly-hydrated MG is the dominant form of MG at the surface.

  14. Surface Wave Driven Air-Water Plasmas

    NASA Astrophysics Data System (ADS)

    Tatarova, Elena; Henriques, Julio; Ferreira, Carlos

    2013-09-01

    The performance of a surface wave driven air-water plasma source operating at atmospheric pressure and 2.45 GHz has been analyzed. A 1D model has been developed in order to describe in detail the creation and loss processes of active species of interest and to provide a complete characterization of the axial structure of the source, including the discharge and the afterglow zones. The main electron creation channel was found to be the associative ionization process N +O -->NO+ + e. The NO(X) relative density in the afterglow plasma jet ranges from 1.2% to 1.6% depending on power and water percentage according to the model predictions and the measurements. Other types of species such as NO2 and nitrous acid HNO2 have also been detected by mass and FT-IR spectroscopy. Furthermore, high densities of O2(a1Δg) singlet delta oxygen molecules and OH radicals (1% and 5%, respectively) can be achieved in the discharge zone. In the late afterglow the O2(a1Δg) density is about 0.1% of the total density. The plasma source has a flexible operation and potential for channeling the energy in ways that maximize the density of active species of interest. This study was funded by the Foundation for Science and Technology, Portuguese Ministry of Education and Science, under the research contract PTDC/FIS/108411/2008.

  15. Emulsions for interfacial filtration.

    SciTech Connect

    Grillet, Anne Mary; Bourdon, Christopher Jay; Souza, Caroline Ann; Welk, Margaret Ellen; Hartenberger, Joel David; Brooks, Carlton, F.

    2006-11-01

    We have investigated a novel emulsion interfacial filter that is applicable for a wide range of materials, from nano-particles to cells and bacteria. This technology uses the interface between the two immiscible phases as the active surface area for adsorption of targeted materials. We showed that emulsion interfaces can effectively collect and trap materials from aqueous solution. We tested two aqueous systems, a bovine serum albumin (BSA) solution and coal bed methane produced water (CBMPW). Using a pendant drop technique to monitor the interfacial tension, we demonstrated that materials in both samples were adsorbed to the liquid-liquid interface, and did not readily desorb. A prototype system was built to test the emulsion interfacial filter concept. For the BSA system, a protein assay showed a progressive decrease in the residual BSA concentration as the sample was processed. Based on the initial prototype operation, we propose an improved system design.

  16. Interfacial structure of sugar beet pectin studied by atomic force microscopy.

    PubMed

    Gromer, A; Kirby, A R; Gunning, A P; Morris, V J

    2009-07-21

    Unlike pectins from other origins, sugar beet pectin (SBP) acts as an emulsifier, a property which has been correlated to its more hydrophobic character and high protein content. In this work, we have investigated the structure of SBP at interfaces by atomic force microscopy (AFM). Three situations were studied: the mica/water, graphite/water, and air/water interface. For the latter, the interfacial film was transferred onto mica using the Langmuir-Blodgett method. While the adsorption of individual pectin chains on mica requires the addition of divalent cations, on graphite a thin layer containing amorphous areas and rodlike chains forms spontaneously. We suggest that the layer contains proteins and pectin chains which are bound to the graphite via CH-pi interactions. SBP adsorbed at the air/water interface forms an elastic layer, as evidenced by pendant drop and surface shear rheology measurements. AFM Images reveal the layer is crippled with holes and contains rodlike chains, suggesting that the pectin chains prevent the formation of a densely packed protein layer. Nevertheless, we show that the interfacial pectin film is more resistant to displacement by surfactants than a pure protein film, possibly because of the formation of linkages between the pectin chains. In contrast, alkali treatment of the pectin appears to remove the pectin chains from the air/water interface and leaves a film that behaves similarly to pure protein. This work gives a new insight into the nanoscale organization of polysaccharides and polysaccharide-protein mixtures at macroscopic surfaces. The results gathered from the different interfaces studied permit a better understanding of the likely structure of SBP at the interface of emulsion droplets. Such knowledge might be used to modify rationally the pectin in order to improve its emulsifying properties, leading to broader commercial applications.

  17. Formation of a Rigid Hydrophobin Film and Disruption by an Anionic Surfactant at an Air/Water Interface.

    PubMed

    Kirby, Stephanie M; Zhang, Xujun; Russo, Paul S; Anna, Shelley L; Walker, Lynn M

    2016-06-01

    Hydrophobins are amphiphilic proteins produced by fungi. Cerato-ulmin (CU) is a hydrophobin that has been associated with Dutch elm disease. Like other hydrophobins, CU stabilizes air bubbles and oil droplets through the formation of a persistent protein film at the interface. The behavior of hydrophobins at surfaces has raised interest in their potential applications, including use in surface coatings, food foams, and emulsions and as dispersants. The practical use of hydrophobins requires an improved understanding of the interfacial behavior of these proteins, alone and in the presence of added surfactants. In this study, the adsorption behavior of CU at air/water interfaces is characterized by measuring the surface tension and interfacial rheology as a function of adsorption time. CU is found to adsorb irreversibly at air/water interfaces. The magnitude of the dilatational modulus increases with adsorption time and surface pressure until CU eventually forms a rigid film. The persistence of this film is tested through the sequential addition of strong surfactant sodium dodecyl sulfate (SDS) to the bulk liquid adjacent to the interface. SDS is found to coadsorb to interfaces precoated with a CU film. At high concentrations, the addition of SDS significantly decreases the dilatational modulus, indicating disruption and displacement of CU by SDS. Sequential adsorption results in mixed layers with properties not observed in interfaces generated from complexes formed in the bulk. These results lend insight to the complex interfacial interactions between hydrophobins and surfactants. PMID:27164189

  18. Investigation of the interfacial adhesion of the transparent conductive oxide films to large-area flexible polymer substrates using laser-induced thermo-mechanical stresses

    NASA Astrophysics Data System (ADS)

    Park, Jin-Woo; Lee, Seung-Ho; Yang, Chan-Woo

    2013-08-01

    In this study, we investigated the interfacial adhesion strength (σint) of transparent conductive oxide (TCO) coatings on polymer substrates using a nanosecond Nd:YAG pulsed laser. We compared our results with those achieved using conventional testing methods such as bending and fragmentation tests as well as theoretical calculations. In the fragmentation and bending tests, mechanical compressive stress is induced in the film due to mismatches in Poisson's ratio and Young's modulus between the substrate and film. But, the incident laser makes the film under compression due to the mismatch in thermal expansion between the TCO and the polymer substrate. With a pulse incident to the substrate, the TCO rapidly expands by laser-induced instant heating while the transparent polymer does little, which causes the TCO to buckle and delaminate over the critical pulse energy. The critical compressive stress that scales with σint was calculated using simple equations, which agreed well with the results from previous theoretical calculations. Because the films preferentially delaminate at the defects and grain boundaries, this technique also provided useful information regarding the interface microstructures. Moreover, because the laser can scan over large areas, this method is suitable for flexible substrates that are produced by a roll-to-roll process. Nevertheless, the mechanical stress introduced by the bending and fragmentation tests causes the TCO to buckle without interfacial delamination. Hence, the stresses at the buckling disagreed with the results obtained from the laser test and the theoretical calculations.

  19. Thermodynamics of iodide adsorption at the instantaneous air-water interface

    NASA Astrophysics Data System (ADS)

    Stern, Abraham C.; Baer, Marcel D.; Mundy, Christopher J.; Tobias, Douglas J.

    2013-03-01

    We performed molecular dynamics simulations using both polarizable and non-polarizable force fields to study the adsorption of iodide to the air-water interface. A novel aspect of our analysis is that the progress of ion adsorption is measured as the distance from the instantaneous interface, which is defined by a coarse-graining scheme proposed recently by Willard and Chandler ["Instantaneous liquid interfaces," J. Phys. Chem. B 114, 1954-1958 (2010), 10.1021/jp909219k]. Referring structural and thermodynamic quantities to the instantaneous interface unmasks molecular-scale details that are obscured by thermal fluctuations when the same quantities are referred to an average measure of the position of the interface, such as the Gibbs dividing surface. Our results suggest that an ion adsorbed at the interface resides primarily in the topmost water layer, and the interfacial location of the ion is favored by enthalpy and opposed by entropy.

  20. Mechanical Stability of Polystyrene and Janus Particle Monolayers at the Air/Water Interface.

    PubMed

    Lenis, Jessica; Razavi, Sepideh; Cao, Kathleen D; Lin, Binhua; Lee, Ka Yee C; Tu, Raymond S; Kretzschmar, Ilona

    2015-12-16

    The compressional instability of particle-laden air/water interfaces is investigated with plain and surface-anisotropic (Janus) particles. We hypothesize that the amphiphilic nature of Janus particles leads to both anisotropic particle-particle and particle-interface interactions that can yield particle films with unique collapse mechanisms. Analysis of Langmuir isotherms and microstructural characterization of the homogeneous polystyrene particle films during compression reveal an interfacial buckling instability followed by folding, which is in good agreement with predictions from classical elasticity theory. In contrast, Janus particle films exhibit a different behavior during compression, where the collapse mode occurs through the subduction of the Janus particle film. Our results suggest that particle-laden films comprised of surface-anisotropic particles can be engineered to evolve new material properties. PMID:26588066

  1. Propensity of Hydrated Excess Protons and Hydroxide Anions for the Air-Water Interface.

    PubMed

    Tse, Ying-Lung Steve; Chen, Chen; Lindberg, Gerrick E; Kumar, Revati; Voth, Gregory A

    2015-10-01

    Significant effort has been undertaken to better understand the molecular details governing the propensity of ions for the air-water interface. Facilitated by computationally efficient reactive molecular dynamics simulations, new and statistically conclusive molecular-scale results on the affinity of the hydrated excess proton and hydroxide anion for the air-water interface are presented. These simulations capture the dynamic bond breaking and formation processes (charge defect delocalization) that are important for correctly describing the solvation and transport of these complex species. The excess proton is found to be attracted to the interface, which is correlated with a favorable enthalpic contribution and consistent with reducing the disruption in the hydrogen bond network caused by the ion complex. However, a recent refinement of the underlying reactive potential energy function for the hydrated excess proton shows the interfacial attraction to be weaker, albeit nonzero, a result that is consistent with the experimental surface tension measurements. The influence of a weak hydrogen bond donated from water to the protonated oxygen, recently found to play an important role in excess hydrated proton transport in bulk water, is seen to also be important for this study. In contrast, the hydroxide ion is found to be repelled from the air-water interface. This repulsion is characterized by a reduction of the energetically favorable ion-water interactions, which creates an enthalpic penalty as the ion approaches the interface. Finally, we find that the fluctuation in the coordination number around water sheds new light on the observed entropic trends for both ions. PMID:26366480

  2. Molecular Adsorption Steers Bacterial Swimming at the Air/Water Interface

    PubMed Central

    Morse, Michael; Huang, Athena; Li, Guanglai; Maxey, Martin R.; Tang, Jay X.

    2013-01-01

    Microbes inhabiting Earth have adapted to diverse environments of water, air, soil, and often at the interfaces of multiple media. In this study, we focus on the behavior of Caulobacter crescentus, a singly flagellated bacterium, at the air/water interface. Forward swimming C. crescentus swarmer cells tend to get physically trapped at the surface when swimming in nutrient-rich growth medium but not in minimal salt motility medium. Trapped cells move in tight, clockwise circles when viewed from the air with slightly reduced speed. Trace amounts of Triton X100, a nonionic surfactant, release the trapped cells from these circular trajectories. We show, by tracing the motion of positively charged colloidal beads near the interface that organic molecules in the growth medium adsorb at the interface, creating a high viscosity film. Consequently, the air/water interface no longer acts as a free surface and forward swimming cells become hydrodynamically trapped. Added surfactants efficiently partition to the surface, replacing the viscous layer of molecules and reestablishing free surface behavior. These findings help explain recent similar studies on Escherichia coli, showing trajectories of variable handedness depending on media chemistry. The consistent behavior of these two distinct microbial species provides insights on how microbes have evolved to cope with challenging interfacial environments. PMID:23823220

  3. Semifluorinated Alkanes at the Air-Water Interface: Tailoring Structure and Rheology at the Molecular Scale.

    PubMed

    Theodoratou, Antigoni; Jonas, Ulrich; Loppinet, Benoit; Geue, Thomas; Stangenberg, Rene; Keller, Rabea; Li, Dan; Berger, Rüdiger; Vermant, Jan; Vlassopoulos, Dimitris

    2016-04-01

    Semifluorinated alkanes form monolayers with interesting properties at the air-water interface due to their pronounced amphi-solvophobic nature and the stiffness of the fluorocarbons. In the present work, using a combination of structural and dynamic probes, we investigated how small molecular changes can be used to control the properties of such an interface, in particular its organization, rheology, and reversibility during compression-expansion cycles. Starting from a reference system perfluor(dodecyl)dodecane, we first retained the linear structure but changed the linkage groups between the alkyl chains and the fluorocarbons, by introducing either a phenyl group or two oxygens. Next, the molecular structure was changed from linear to branched, with four side chains (two fluorocarbons and two hydrocarbons) connected to extended aromatic cores. Neutron reflectivity at the air-water interface and scanning force microscopy on deposited films show how the changes in the molecular structure affect molecular arrangement relative to the interface. Rheological and compression-expansion measurements demonstrate the significant consequences of these changes in molecular structure and interactions on the interfacial properties. Remarkably, even with these simple molecules, a wide range of surface rheological behaviors can be engineered, from viscous over viscoelastic to brittle solids, for very similar values of the surface pressure.

  4. Use of Surfactants to Decrease Air-Water Interfacial Tension During Sparging (OKC, OK)

    EPA Science Inventory

    Air sparging is a remediation procedure of injecting air into polluted ground water. The primary intention of air sparging is to promote biodegradation of volatile organic compounds (VOCs) in the groundwater passing through the treatment sector. Sparging treatment efficiency dep...

  5. Use of Surfactants to Decrease Air-Water Interfacial Tension During Sparging

    EPA Science Inventory

    Air sparging is a remediation procedure of injecting air into polluted ground water. The primary intention of air sparging is to promote biodegradation of volatile organic compounds (VOCs) in the groundwater passing through the treatment sector. Sparging treatment efficiency dep...

  6. Spectroscopic analysis of total-internal-reflection stimulated Raman scattering from the air/water interface under the strong focusing condition

    NASA Astrophysics Data System (ADS)

    Yui, Hiroharu; Fujiwara, Hideyuki; Sawada, Tsuguo

    2002-07-01

    Anomalous enhancement of stimulated Raman scattering (SRS) derived from the OH stretching vibration of interfacial water molecules is observed when excess electrons are generated at an air/water interface by focusing an intense pulsed beam under a total internal reflection configuration. The characteristic SRS peak appears at 3200 cm-1 and is attributed to the water molecules being in an ice-like hydrogen-bonding environment at the interface. The mechanism of the SRS enhancement is discussed in terms of the enhancement of the nonlinear polarizability of the interfacial water by the large electrostatic fields induced by the transiently generated excess electrons at the interface.

  7. Mechanical properties of protein adsorption layers at the air/water and oil/water interface: a comparison in light of the thermodynamical stability of proteins.

    PubMed

    Mitropoulos, Varvara; Mütze, Annekathrin; Fischer, Peter

    2014-04-01

    Over the last decades numerous studies on the interfacial rheological response of protein adsorption layers have been published. The comparison of these studies and the retrieval of a common parameter to compare protein interfacial activity are hampered by the fact that different boundary conditions (e.g. physico-chemical, instrumental, interfacial) were used. In the present work we review previous studies and attempt a unifying approach for the comparison between bulk protein properties and their adsorption films. Among many common food grade proteins we chose bovine serum albumin, β-lactoglobulin and lysozyme for their difference in thermodynamic stability and studied their adsorption at the air/water and limonene/water interface. In order to achieve this we have i) systematically analyzed protein adsorption kinetics in terms of surface pressure rise using a drop profile analysis tensiometer and ii) we addressed the interfacial layer properties under shear stress using an interfacial shear rheometer under the same experimental conditions. We could show that thermodynamically less stable proteins adsorb generally faster and yield films with higher shear rheological properties at air/water interface. The same proteins showed an analog behavior when adsorbing at the limonene/water interface but at slower rates. PMID:24332621

  8. Mechanical properties of protein adsorption layers at the air/water and oil/water interface: a comparison in light of the thermodynamical stability of proteins.

    PubMed

    Mitropoulos, Varvara; Mütze, Annekathrin; Fischer, Peter

    2014-04-01

    Over the last decades numerous studies on the interfacial rheological response of protein adsorption layers have been published. The comparison of these studies and the retrieval of a common parameter to compare protein interfacial activity are hampered by the fact that different boundary conditions (e.g. physico-chemical, instrumental, interfacial) were used. In the present work we review previous studies and attempt a unifying approach for the comparison between bulk protein properties and their adsorption films. Among many common food grade proteins we chose bovine serum albumin, β-lactoglobulin and lysozyme for their difference in thermodynamic stability and studied their adsorption at the air/water and limonene/water interface. In order to achieve this we have i) systematically analyzed protein adsorption kinetics in terms of surface pressure rise using a drop profile analysis tensiometer and ii) we addressed the interfacial layer properties under shear stress using an interfacial shear rheometer under the same experimental conditions. We could show that thermodynamically less stable proteins adsorb generally faster and yield films with higher shear rheological properties at air/water interface. The same proteins showed an analog behavior when adsorbing at the limonene/water interface but at slower rates.

  9. Influence of phase connectivity on the relationship among capillary pressure, fluid saturation, and interfacial area in two-fluid-phase porous medium systems

    NASA Astrophysics Data System (ADS)

    McClure, James E.; Berrill, Mark A.; Gray, William G.; Miller, Cass T.

    2016-09-01

    Multiphase flows in porous medium systems are typically modeled at the macroscale by applying the principles of continuum mechanics to develop models that describe the behavior of averaged quantities, such as fluid pressure and saturation. These models require closure relations to produce solvable forms. One of these required closure relations is an expression relating the capillary pressure to fluid saturation and, in some cases, other topological invariants such as interfacial area and the Euler characteristic (or average Gaussian curvature). The forms that are used in traditional models, which typically consider only the relationship between capillary pressure and saturation, are hysteretic. An unresolved question is whether the inclusion of additional morphological and topological measures can lead to a nonhysteretic closure relation. Relying on the lattice Boltzmann (LB) method, we develop an approach to investigate equilibrium states for a two-fluid-phase porous medium system, which includes disconnected nonwetting phase features. A set of simulations are performed within a random close pack of 1964 spheres to produce a total of 42 908 distinct equilibrium configurations. This information is evaluated using generalized additive models to quantitatively assess the degree to which functional relationships can explain the behavior of the equilibrium data. The variance of various model estimates is computed, and we conclude that, except for the limiting behavior close to a single fluid regime, capillary pressure can be expressed as a deterministic and nonhysteretic function of fluid saturation, interfacial area between the fluid phases, and the Euler characteristic. To our knowledge, this work is unique in the methods employed, the size of the data set, the resolution in space and time, the true equilibrium nature of the data, the parametrizations investigated, and the broad set of functions examined. The conclusion of essentially nonhysteretic behavior provides

  10. Interfacial reactivity of block copolymers: understanding the amphiphile-to-hydrophile transition.

    PubMed

    Napoli, Alessandro; Bermudez, Harry; Hubbell, Jeffrey A

    2005-09-27

    Block copolymers offer an interesting platform to study chemically triggered transitions in self-assembled structures. We have previously reported the oxidative degradation of vesicles made of poly(propylene sulfide)-poly(ethylene glycol) (PPS-PEG) copolymers. Here we propose a mechanism for vesicle degradation deduced from copolymer conformational changes occurring at the air/water interface in a Langmuir trough together with a reactive subphase. The hydrophobic PPS block is converted into hydrophilic poly(propylene sulfoxide) and poly(propylene sulfone) by oxidation upon exposure to 1% aqueous H(2)O(2) subphase. As a result, a dramatic increase in area per molecule at constant surface pressure (Pi) was observed, followed by an apparent decrease (recorded as decrease in area at constant Pi) due to copolymer dissolution. For monolayers at the air/water surface, the large interfacial tensions present suppress increases in local curvature for alleviating the increased hydrophilicity of the copolymer chains. By contrast, vesicles can potentially rearrange molecules in their bilayers to accommodate a changing hydrophilic-lipophilic balance (HLB). Similar time scales for monolayer rearrangement and vesicle degradation imply a common copolymer chain solubilization mechanism, which in vesicles lead to an eventual transition to aggregates of higher curvature, such as cylindrical and spherical micelles. Subtle differences in response to the applied surface pressure for the diblock compared to the triblock suggest an effect of the different chain mobility. PMID:16171345

  11. Understand the limitations of air/water testing of distillation equipment

    SciTech Connect

    Bennett, D.L.; Ludwig, K.A. )

    1994-04-01

    Distillation continues to be a unit operation of major importance--and a dynamic area for technical development. The designs of trays and packings are rapidly evolving, and the application of equipment also is changing. As chemical processes are pushed to become more efficient and lower cost, a general reduction in the traditional values for equipment safety factors are being seen. The net results is that one now has a greater need for a more thorough and fundamental understanding of distillation equipment. One technique to improve the understanding of distillation equipment is air/water testing. Such testing of distillation trays has become very common, and air/water test results for packed columns also are being reported. In this article, the authors will provide some guidance on how to assess the validity of such tests to industrial applications. In addition, they will discuss several possible approaches to test--and develop confidence in--the design of distillation equipment.

  12. Interaction between graphene oxide and Pluronic F127 at the air-water interface.

    PubMed

    Li, Shanghao; Guo, Jingru; Patel, Ravi A; Dadlani, Anup L; Leblanc, Roger M

    2013-05-14

    Triblock copolymer Pluronic F127 (PF127) has previously been demonstrated to disperse graphene oxide (GO) in electrolyte solution and block the hydrophobic interaction between GO and l-tryptophan and l-tyrosine. However, the nature of this interaction between PF127 and GO remains to be characterized and elucidated. In the present study, we aimed to characterize and understand the interaction between GO and PF127 using a 2-dimensional Langmuir monolayer methodology at the air-water interface by surface pressure-area isotherm measurement, stability, adsorption, and atomic force microscopy (AFM) imaging. Based on the observation of surface pressure-area isotherms, adsorption, and stability of PF127 and PF127/GO mixture at the air-water interface, GO is suggested to change the conformation of PF127 at the air-water interface and also drag PF127 from the interface to the bulk subphase. Atomic force microscopy (AFM) image supports this assumption, as GO and PF127 can be observed by spreading the subphase solution outside the compressing barriers, as shown in the TOC graphic.

  13. Properties of amphiphilic oligonucleotide films at the air/water interface and after film transfer.

    PubMed

    Keller, R; Kwak, M; de Vries, J W; Sawaryn, C; Wang, J; Anaya, M; Müllen, K; Butt, H-J; Herrmann, A; Berger, R

    2013-11-01

    The self-assembly of amphiphilic hybrid materials containing an oligonucleotide sequence at the air/water interface was investigated by means of pressure-molecular area (Π-A) isotherms. In addition, films were transferred onto solid substrates and imaged using scanning force microscopy. We used oligonucleotide molecules with lipid tails, which consisted of a single stranded oligonucleotide 11 mer containing two hydrophobically modified 5-(dodec-1-ynyl)uracil nucleobases (dU11) at the 5'-end of the oligonucleotide sequence. The air/water interface was used as confinement for the self-assembling process of dU11. Scanning force microscopy of films transferred via Langmuir-Blodgett technique revealed mono-, bi- (Π ≥ 2 mN/m) and multilayer formation (Π ≥ 30 mN/m). The first layer was 1.6 ± 0.1 nm thick. It was oriented with the hydrophilic oligonucleotide moiety facing the hydrophilic substrate while the hydrophobic alkyl chains faced air. In the second layer the oligonucleotide moiety was found to face the air. The second layer was found to cover up to 95% of the sample area. Our measurements indicated that the rearrangement of the molecules into bi- and multiple bilayers happened already at the air/water interface. Similar results were obtained with a second type of oligonucleotide amphiphile, an oligonucleotide block copolymer, which was composed of an oligonucleotide 11 mer covalently attached at the terminus to polypropyleneoxide (PPO).

  14. Mechanism of vibrational energy dissipation of free OH groups at the air-water interface.

    PubMed

    Hsieh, Cho-Shuen; Campen, R Kramer; Okuno, Masanari; Backus, Ellen H G; Nagata, Yuki; Bonn, Mischa

    2013-11-19

    Interfaces of liquid water play a critical role in a wide variety of processes that occur in biology, a variety of technologies, and the environment. Many macroscopic observations clarify that the properties of liquid water interfaces significantly differ from those of the bulk liquid. In addition to interfacial molecular structure, knowledge of the rates and mechanisms of the relaxation of excess vibrational energy is indispensable to fully understand physical and chemical processes of water and aqueous solutions, such as chemical reaction rates and pathways, proton transfer, and hydrogen bond dynamics. Here we elucidate the rate and mechanism of vibrational energy dissipation of water molecules at the air-water interface using femtosecond two-color IR-pump/vibrational sum-frequency probe spectroscopy. Vibrational relaxation of nonhydrogen-bonded OH groups occurs at a subpicosecond timescale in a manner fundamentally different from hydrogen-bonded OH groups in bulk, through two competing mechanisms: intramolecular energy transfer and ultrafast reorientational motion that leads to free OH groups becoming hydrogen bonded. Both pathways effectively lead to the transfer of the excited vibrational modes from free to hydrogen-bonded OH groups, from which relaxation readily occurs. Of the overall relaxation rate of interfacial free OH groups at the air-H2O interface, two-thirds are accounted for by intramolecular energy transfer, whereas the remaining one-third is dominated by the reorientational motion. These findings not only shed light on vibrational energy dynamics of interfacial water, but also contribute to our understanding of the impact of structural and vibrational dynamics on the vibrational sum-frequency line shapes of aqueous interfaces.

  15. Propagation of density disturbances in air-water flow

    NASA Technical Reports Server (NTRS)

    Nassos, G. P.

    1969-01-01

    Study investigated the behavior of density waves propagating vertically in an atmospheric pressure air-water system using a technique based on the correlation between density change and electric resistivity. This information is of interest to industries working with heat transfer systems and fluid power and control systems.

  16. External exposure to radionuclides in air, water, and soil

    SciTech Connect

    Eckerman, K.F.; Ryman, J.C.

    1996-05-01

    Federal Guidance Report No. 12 tabulates dose coefficients for external exposure to photons and electrons emitted by radionuclides distributed in air, water, and soil. The dose coefficients are intended for use by Federal Agencies in calculating the dose equivalent to organs and tissues of the body.

  17. Structure of Air-Water Bubbly Flow in a Vertical Annulus

    SciTech Connect

    Rong Situ; Takashi Hibiki; Ye Mi; Mamoru Ishii; Michitsugu Mori

    2002-07-01

    Local measurements of flow parameters were performed for vertical upward bubbly flows in an annulus. The annulus channel consisted of an inner rod with a diameter of 19.1 mm and an outer round tube with an inner diameter of 38.1 mm, and the hydraulic equivalent diameter was 19.1 mm. Double-sensor conductivity probe was used for measuring void fraction, interfacial area concentration, and interfacial velocity, and Laser Doppler anemometer was utilized for measuring liquid velocity and turbulence intensity. The mechanisms to form the radial profiles of local flow parameters were discussed in detail. The constitutive equations for distribution parameter and drift velocity in the drift-flux model, and the semi-theoretical correlation for Sauter mean diameter namely interfacial area concentration, which were proposed previously, were validated by local flow parameters obtained in the experiment using the annulus. (authors)

  18. Catechol oxidation by ozone and hydroxyl radicals at the air-water interface.

    PubMed

    Pillar, Elizabeth A; Camm, Robert C; Guzman, Marcelo I

    2014-12-16

    Anthropogenic emissions of aromatic hydrocarbons promptly react with hydroxyl radicals undergoing oxidation to form phenols and polyphenols (e.g., catechol) typically identified in the complex mixture of humic-like substances (HULIS). Because further processing of polyphenols in secondary organic aerosols (SOA) can continue mediated by a mechanism of ozonolysis at interfaces, a better understanding about how these reactions proceed at the air-water interface is needed. This work shows how catechol, a molecular probe of the oxygenated aromatic hydrocarbons present in SOA, can contribute interfacial reactive species that enhance the production of HULIS under atmospheric conditions. Reactive semiquinone radicals are quickly produced upon the encounter of 40 ppbv-6.0 ppmv O3(g) with microdroplets containing [catechol] = 1-150 μM. While the previous pathway results in the instantaneous formation of mono- and polyhydroxylated aromatic rings (PHA) and chromophoric mono- and polyhydroxylated quinones (PHQ), a different channel produces oxo- and dicarboxylic acids of low molecular weight (LMW). The cleavage of catechol occurs at the 1,2 carbon-carbon bond at the air-water interface through the formation of (1) an ozonide intermediate, (2) a hydroperoxide, and (3) cis,cis-muconic acid. However, variable [catechol] and [O3(g)] can affect the ratio of the primary products (cis,cis-muconic acid and trihydroxybenzenes) and higher order products observed (PHA, PHQ, and LMW oxo- and dicarboxylic acids). Secondary processing is confirmed by mass spectrometry, showing the production of crotonic, maleinaldehydic, maleic, glyoxylic, and oxalic acids. The proposed pathway can contribute precursors to aqueous SOA (AqSOA) formation, converting aromatic hydrocarbons into polyfunctional species widely found in tropospheric aerosols with light-absorbing brown carbon.

  19. Catechol oxidation by ozone and hydroxyl radicals at the air-water interface.

    PubMed

    Pillar, Elizabeth A; Camm, Robert C; Guzman, Marcelo I

    2014-12-16

    Anthropogenic emissions of aromatic hydrocarbons promptly react with hydroxyl radicals undergoing oxidation to form phenols and polyphenols (e.g., catechol) typically identified in the complex mixture of humic-like substances (HULIS). Because further processing of polyphenols in secondary organic aerosols (SOA) can continue mediated by a mechanism of ozonolysis at interfaces, a better understanding about how these reactions proceed at the air-water interface is needed. This work shows how catechol, a molecular probe of the oxygenated aromatic hydrocarbons present in SOA, can contribute interfacial reactive species that enhance the production of HULIS under atmospheric conditions. Reactive semiquinone radicals are quickly produced upon the encounter of 40 ppbv-6.0 ppmv O3(g) with microdroplets containing [catechol] = 1-150 μM. While the previous pathway results in the instantaneous formation of mono- and polyhydroxylated aromatic rings (PHA) and chromophoric mono- and polyhydroxylated quinones (PHQ), a different channel produces oxo- and dicarboxylic acids of low molecular weight (LMW). The cleavage of catechol occurs at the 1,2 carbon-carbon bond at the air-water interface through the formation of (1) an ozonide intermediate, (2) a hydroperoxide, and (3) cis,cis-muconic acid. However, variable [catechol] and [O3(g)] can affect the ratio of the primary products (cis,cis-muconic acid and trihydroxybenzenes) and higher order products observed (PHA, PHQ, and LMW oxo- and dicarboxylic acids). Secondary processing is confirmed by mass spectrometry, showing the production of crotonic, maleinaldehydic, maleic, glyoxylic, and oxalic acids. The proposed pathway can contribute precursors to aqueous SOA (AqSOA) formation, converting aromatic hydrocarbons into polyfunctional species widely found in tropospheric aerosols with light-absorbing brown carbon. PMID:25423038

  20. Vibrational sum-frequency generation spectroscopy of ionic liquid 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate at the air-water interface

    NASA Astrophysics Data System (ADS)

    Saha, Ankur; SenGupta, Sumana; Kumar, Awadhesh; Choudhury, Sipra; Naik, Prakash D.

    2016-08-01

    The structure and orientation of room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate [PF3(C2F5)3], commonly known as [bmim][fap], have been investigated at the air-[bmim][fap] and air-water interfaces, employing vibrational sum-frequency generation (VSFG) spectroscopy. The VSFG spectra in the CH stretch region suggest presence of the [bmim] cation at the interfaces. Studies reveal that the butyl chain protrudes out into air, and the imidazolium ring lies almost planar to the interface. The CH stretch intensities get enhanced at the air-water interface, mainly because of polar orientation of imidazolium cation induced by interfacial water molecules. The OH stretch intensities are also enhanced at the air-water interface due to polar orientation of interfacial water molecules induced by [bmim][fap]. The Brewster angle microscopy suggests self aggregation of [bmim][fap] in the presence of water, and the aggregation becomes extensive showing dense surface domains with time. However, the surface pressure is almost unaffected due to aggregation.

  1. Forced convection heat transfer to air/water vapor mixtures

    NASA Technical Reports Server (NTRS)

    Richards, D. R.; Florschuetz, L. W.

    1986-01-01

    Heat transfer coefficients were measured using both dry air and air/water vapor mixtures in the same forced convection cooling test rig (jet array impingement configurations) with mass ratios of water vapor to air up to 0.23. The primary objective was to verify by direct experiment that selected existing methods for evaluation of viscosity and thermal conductivity of air/water vapor mixtures could be used with confidence to predict heat transfer coefficients for such mixtures using as a basis heat transfer data for dry air only. The property evaluation methods deemed most appropriate require as a basis a measured property value at one mixture composition in addition to the property values for the pure components.

  2. Thermodynamic and transport properties of air/water mixtures

    NASA Technical Reports Server (NTRS)

    Fessler, T. E.

    1981-01-01

    Subroutine WETAIR calculates properties at nearly 1,500 K and 4,500 atmospheres. Necessary inputs are assigned values of combinations of density, pressure, temperature, and entropy. Interpolation of property tables obtains dry air and water (steam) properties, and simple mixing laws calculate properties of air/water mixture. WETAIR is used to test gas turbine engines and components operating in relatively humid air. Program is written in SFTRAN and FORTRAN.

  3. Surface pressure-induced layer growth of a monolayer at the air-water interface

    SciTech Connect

    Fang, J.Y.; Uphaus, R.A. )

    1994-04-01

    Spread monolayers containing a nematic liquid crystal and stearic acid were characterized at various mole fractions by determination of surface pressure-area isotherms at the air-water interface. The surface-composition phase diagrams indicate that compression induces a new phase transition in the films, which changes from a mixed monolayer to a supermonomolecular system. X-ray diffraction and optical absorption spectra demonstrate that the supermolecular array consists of an island liquid crystal monolayer and a uniform stearic acid monolayer. 12 refs., 7 figs.

  4. Organization of tethered polyoxazoline polymer brushes at the air/water interface

    NASA Astrophysics Data System (ADS)

    Gutberlet, T.; Wurlitzer, A.; Dietrich, U.; Politsch, E.; Cevc, G.; Steitz, R.; Lösche, M.

    2000-06-01

    Surface monolayers of short chain poly(methyl oxazoline) (PMeOx) attached to diacylglycerol have been investigated by X-ray and neutron reflectivity in pure systems and in binary mixtures with the unmodified phospholipid DMPC at the air/water interface. Reflectivity curves of pure PMeOx and its mixtures with DMPC indicate an extended conformation of the polymer independent of the available lateral area and pressure. An almost linear increase in the thickness of the polymer layer is found with increasing lateral pressure π. The thickness of the hydrophobic slab within the surface monolayers decreases continuously upon addition of PMeOx to DMPC.

  5. Toward a unified picture of the water self-ions at the air-water interface: a density functional theory perspective.

    PubMed

    Baer, Marcel D; Kuo, I-Feng W; Tobias, Douglas J; Mundy, Christopher J

    2014-07-17

    The propensities of the water self-ions, H3O(+) and OH(-), for the air-water interface have implications for interfacial acid-base chemistry. Despite numerous experimental and computational studies, no consensus has been reached on the question of whether or not H3O(+) and/or OH(-) prefer to be at the water surface or in the bulk. Here we report a molecular dynamics simulation study of the bulk vs interfacial behavior of H3O(+) and OH(-) that employs forces derived from density functional theory with a generalized gradient approximation exchange-correlation functional (specifically, BLYP) and empirical dispersion corrections. We computed the potential of mean force (PMF) for H3O(+) as a function of the position of the ion in the vicinity of an air-water interface. The PMF suggests that H3O(+) has equal propensity for the interface and the bulk. We compare the PMF for H3O(+) to our previously computed PMF for OH(-) adsorption, which contains a shallow minimum at the interface, and we explore how differences in solvation of each ion at the interface vs in the bulk are connected with interfacial propensity. We find that the solvation shell of H3O(+) is only slightly dependent on its position in the water slab, while OH(-) partially desolvates as it approaches the interface, and we examine how this difference in solvation behavior is manifested in the electronic structure and chemistry of the two ions.

  6. 14 CFR 1274.926 - Clean Air-Water Pollution Control Acts.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 5 2011-01-01 2010-01-01 true Clean Air-Water Pollution Control Acts. 1274... AGREEMENTS WITH COMMERCIAL FIRMS Other Provisions and Special Conditions § 1274.926 Clean Air-Water Pollution Control Acts. Clean Air-Water Pollution Control Acts July 2002 If this cooperative agreement or...

  7. Ultrafast Reorientational Dynamics of Leucine at the Air-Water Interface.

    PubMed

    Donovan, Michael A; Yimer, Yeneneh Y; Pfaendtner, Jim; Backus, Ellen H G; Bonn, Mischa; Weidner, Tobias

    2016-04-27

    Ultrafast dynamics of protein side chains are involved in important biological processes such as ligand binding, protein folding, and hydration. In addition, the dynamics of a side chain can report on local environments within proteins. While protein side chain dynamics have been probed for proteins in solution with nuclear magnetic resonance and infrared methods for decades, information about side chain dynamics at interfaces is lacking. At the same time, the dynamics and motions of side chains can be particularly important for interfacial binding and protein-driven surface manipulation. We here demonstrate that ultrafast reorientation dynamics of leucine amino acids at interfaces can be recorded in situ and in real time using polarization- and time-resolved pump-probe sum frequency generation (SFG). Combined with molecular dynamics simulations, time-resolved SFG was used to probe the reorientation of the isopropyl methyl groups of l-leucine at the air-water interface. The data show that the methyl units reorient diffusively at an in plane rate of Dφ = 0.07 rad(2)/ps and an out of plane rate of Dθ = 0.05 rad(2)/ps. PMID:27057584

  8. Air-Water Exchange of Legacy and Emerging Organic Pollutants across the Great Lakes

    NASA Astrophysics Data System (ADS)

    Lohmann, R.; Ruge, Z.; Khairy, M.; Muir, D.; Helm, P.

    2014-12-01

    Organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) are transported to great water bodies via long-range atmospheric transport and released from the surface water as air concentrations continue to diminish. As the largest fresh water bodies in North America, the Great Lakes have both the potential to accumulate and serve as a secondary source of persistent bioaccumulative toxins. OCP and PCB concentrations were sampled at 30+ sites across Lake Superior, Ontario and Erie in the summer of 2011. Polyethylene passive samplers (PEs) were simultaneously deployed in surface water and near surface atmosphere to determine air-water gaseous exchange of OCPs and PCBs. In Lake Superior, surface water and atmospheric concentrations were dominated by α-HCH (average 250 pg/L and 4.2 pg/m3, respectively), followed by HCB (average 17 pg/L and 89 pg/m3, respectively). Air-water exchange varied greatly between sites and individual OCPs, however α-endosulfan was consistently deposited into the surface water (average 19 pg/m2/day). PCBs in the air and water were characterized by penta- and hexachlorobiphenyls with distribution along the coast correlated with proximity to developed areas. Air-water exchange gradients generally yielded net volatilization of PCBs out of Lake Superior. Gaseous concentrations of hexachlorobenzene, dieldrin and chlordanes were significantly higher (p < 0.05) at Lake Erie than Lake Ontario. A multiple linear regression that incorporated meteorological, landuse and population data was used to explain variability in the atmospheric concentrations. Results indicated that landuse (urban and/or cropland) greatly explained the variability in the data. Freely dissolved concentrations of OCPs (

  9. Forced convective flow and heat transfer of upward cocurrent air-water slug flow in vertical plain and swirl tubes

    SciTech Connect

    Chang, Shyy Woei; Yang, Tsun Lirng

    2009-10-15

    This experimental study comparatively examined the two-phase flow structures, pressured drops and heat transfer performances for the cocurrent air-water slug flows in the vertical tubes with and without the spiky twisted tape insert. The two-phase flow structures in the plain and swirl tubes were imaged using the computerized high frame-rate videography with the Taylor bubble velocity measured. Superficial liquid Reynolds number (Re{sub L}) and air-to-water mass flow ratio (AW), which were respectively in the ranges of 4000-10000 and 0.003-0.02 were selected as the controlling parameters to specify the flow condition and derive the heat transfer correlations. Tube-wise averaged void fraction and Taylor bubble velocity were well correlated by the modified drift flux models for both plain and swirl tubes at the slug flow condition. A set of selected data obtained from the plain and swirl tubes was comparatively examined to highlight the impacts of the spiky twisted tape on the air-water interfacial structure and the pressure drop and heat transfer performances. Empirical heat transfer correlations that permitted the evaluation of individual and interdependent Re{sub L} and AW impacts on heat transfer in the developed flow regions of the plain and swirl tubes at the slug flow condition were derived. (author)

  10. Surface rheology of PEO-PPO-PEO triblock copolymers at the air-water interface: comparison of spread and adsorbed layers.

    PubMed

    Blomqvist, B Rippner; Wärnheim, T; Claesson, P M

    2005-07-01

    The dilatational rheological properties of monolayers of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)-type block copolymers at the air-water interface have been investigated by employing an oscillating ring trough method. The properties of adsorbed monolayers were compared to spread layers over a range of surface concentrations. The studied polymers were PEO26-PPO39-PEO26 (P85), PEO103-PPO40-PEO103 (F88), and PEO99-PPO65-PEO99 (F127). Thus, two of the polymers have similar PPO block size and two of them have similar PEO block size, which allows us to draw conclusions about the relationship between molecular structure and surface dilatational rheology. The dilatational properties of adsorbed monolayers were investigated as a function of time and bulk solution concentration. The time dependence was found to be rather complex, reflecting structural changes in the layer. When the dilatational modulus measured at different concentrations was replotted as a function of surface pressure, one unique master curve was obtained for each polymer. It was found that the dilatational behavior of spread (Langmuir) and adsorbed (Gibbs) monolayers of the same polymer is close to identical up to surface concentrations of approximately 0.7 mg/m2. At higher coverage, the properties are qualitatively alike with respect to dilatational modulus, although some differences are noticeable. Relaxation processes take place mainly within the interfacial layers by a redistribution of polymer segments. Several conformational transitions were shown to occur as the area per molecule decreased. PEO desorbs significantly from the interface at segmental areas below 20 A(2), while at higher surface coverage, we propose that segments of PPO are forced to leave the interface to form a mixed sublayer in the aqueous region. PMID:15982044

  11. Air/water oxydesulfurization of coal: laboratory investigation

    SciTech Connect

    Warzinski, R. P.; Friedman, S.; Ruether, J. A.; LaCount, R. B.

    1980-08-01

    Air/water oxidative desulfurization has been demonstrated in autoclave experiments at the Pittsburgh Energy Technology Center for various coals representative of the major US coal basins. This experimentation has shown that the reaction proceeds effectively for pulverized coals at temperatures of 150 to 200/sup 0/C with air at a total system pressure of 500 to 1500 psig. Above 200/sup 0/C, the loss of coal and product heating value increases due to oxidative consumption of carbon and hydrogen. The pyritic sulfur solubilization reactions are typically complete (95 percent removal) within 15 to 40 minutes at temperature; however, significant apparent organic sulfur removal requires residence times of up to 60 minutes at the higher temperatures. The principal products of the reaction are sulfuric acid, which can be neutralized with limestone, and iron oxide. Under certain conditions, especially for high pyritic sulfur coals, the precipitation of sulfur-containing compounds from the products of the pyrite reaction may cause anomalous variations in the sulfur form data. The influence of various parameters on the efficiency of sulfur removal from coal by air/water oxydesulfurization has been studied.

  12. Interfacial and oil/water emulsions characterization of potato protein isolates.

    PubMed

    Romero, Alberto; Beaumal, Valérie; David-Briand, Elisabeth; Cordobés, Felipe; Guerrero, Antonio; Anton, Marc

    2011-09-14

    Interfacial and emulsifying properties of potato protein isolate (PPI) have been studied to evaluate its potential application to stabilize oil/water emulsions at two pH values (2 and 8). The amount, type, and solubility of proteins and the size of aggregates have been determined in aqueous dispersion. Air-water and oil-water interfacial properties (adsorption, spreading, and viscoelastic properties) have been determined as a function of concentration and pH using soluble phases of PPI. The behavior of PPI stabilized oil/water emulsions has been then analyzed by droplet size distribution measurements and interfacial concentration. PPI exhibits low solubility over a wide range of pH values, with the presence of submicrometer aggregates. The pH value exerts a negligible effect on interfacial tension (oil-water) or surface pressure (air-water) but displays very important differences in viscoelastic properties of the interfacial films formed between oil and water. In this sense, pH 8 provides a major elastic response at oil-water interfaces as compared to pH 2. In relation with this result, a much higher ability to produce fine and stable emulsions is noticed at pH 8 as compared to pH 2. Consequently, there is an evident relationship between the rheological properties of the oil-water interfacial films and the macroscopic emulsion behavior.

  13. Tunable Interfacial Thermal Conductance by Molecular Dynamics

    NASA Astrophysics Data System (ADS)

    Shen, Meng

    We study the mechanism of tunable heat transfer through interfaces between solids using a combination of non-equilibrium molecular dynamics simulation (NEMD), vibrational mode analysis and wave packet simulation. We investigate how heat transfer through interfaces is affected by factors including pressure, interfacial modulus, contact area and interfacial layer thickness, with an overreaching goal of developing fundamental knowledge that will allow one to tailor thermal properties of interfacial materials. The role of pressure and interfacial stiffness is unraveled by our studies on an epitaxial interface between two Lennard-Jones (LJ) crystals. The interfacial stiffness is varied by two different methods: (i) indirectly by applying pressure which due to anharmonic nature of bonding, increases interfacial stiffness, and (ii) directly by changing the interfacial bonding strength by varying the depth of the potential well of the LJ potential. When the interfacial bonding strength is low, quantitatively similar behavior to pressure tuning is observed when the interfacial thermal conductance is increased by directly varying the potential-well depth parameter of the LJ potential. By contrast, when the interfacial bonding strength is high, thermal conductance is almost pressure independent, and even slightly decreases with increasing pressure. This decrease can be explained by the change in overlap between the vibrational densities of states of the two crystalline materials. The role of contact area is studied by modeling structures comprised of Van der Waals junctions between single-walled nanotubes (SWCNT). Interfacial thermal conductance between SWCNTs is obtained from NEMD simulation as a function of crossing angle. In this case the junction conductance per unit area is essentially a constant. By contrast, interfacial thermal conductance between multiwalled carbon nanotubes (MWCNTs) is shown to increase with diameter of the nanotubes by recent experimental studies [1

  14. Tunable Interfacial Thermal Conductance by Molecular Dynamics

    NASA Astrophysics Data System (ADS)

    Shen, Meng

    We study the mechanism of tunable heat transfer through interfaces between solids using a combination of non-equilibrium molecular dynamics simulation (NEMD), vibrational mode analysis and wave packet simulation. We investigate how heat transfer through interfaces is affected by factors including pressure, interfacial modulus, contact area and interfacial layer thickness, with an overreaching goal of developing fundamental knowledge that will allow one to tailor thermal properties of interfacial materials. The role of pressure and interfacial stiffness is unraveled by our studies on an epitaxial interface between two Lennard-Jones (LJ) crystals. The interfacial stiffness is varied by two different methods: (i) indirectly by applying pressure which due to anharmonic nature of bonding, increases interfacial stiffness, and (ii) directly by changing the interfacial bonding strength by varying the depth of the potential well of the LJ potential. When the interfacial bonding strength is low, quantitatively similar behavior to pressure tuning is observed when the interfacial thermal conductance is increased by directly varying the potential-well depth parameter of the LJ potential. By contrast, when the interfacial bonding strength is high, thermal conductance is almost pressure independent, and even slightly decreases with increasing pressure. This decrease can be explained by the change in overlap between the vibrational densities of states of the two crystalline materials. The role of contact area is studied by modeling structures comprised of Van der Waals junctions between single-walled nanotubes (SWCNT). Interfacial thermal conductance between SWCNTs is obtained from NEMD simulation as a function of crossing angle. In this case the junction conductance per unit area is essentially a constant. By contrast, interfacial thermal conductance between multiwalled carbon nanotubes (MWCNTs) is shown to increase with diameter of the nanotubes by recent experimental studies [1

  15. Surface Mechanical and Rheological Behaviors of Biocompatible Poly((D,L-lactic acid-ran-glycolic acid)-block-ethylene glycol) (PLGA-PEG) and Poly((D,L-lactic acid-ran-glycolic acid-ran-ε-caprolactone)-block-ethylene glycol) (PLGACL-PEG) Block Copolymers at the Air-Water Interface.

    PubMed

    Kim, Hyun Chang; Lee, Hoyoung; Khetan, Jawahar; Won, You-Yeon

    2015-12-29

    Air-water interfacial monolayers of poly((D,L-lactic acid-ran-glycolic acid)-block-ethylene glycol) (PLGA-PEG) exhibit an exponential increase in surface pressure under high monolayer compression. In order to understand the molecular origin of this behavior, a combined experimental and theoretical investigation (including surface pressure-area isotherm, X-ray reflectivity (XR) and interfacial rheological measurements, and a self-consistent field (SCF) theoretical analysis) was performed on air-water monolayers formed by a PLGA-PEG diblock copolymer and also by a nonglassy analogue of this diblock copolymer, poly((D,L-lactic acid-ran-glycolic acid-ran-caprolactone)-block-ethylene glycol) (PLGACL-PEG). The combined results of this study show that the two mechanisms, i.e., the glass transition of the collapsed PLGA film and the lateral repulsion of the PEG brush chains that occur simultaneously under lateral compression of the monolayer, are both responsible for the observed PLGA-PEG isotherm behavior. Upon cessation of compression, the high surface pressure of the PLGA-PEG monolayer typically relaxes over time with a stretched exponential decay, suggesting that in this diblock copolymer situation, the hydrophobic domain formed by the PLGA blocks undergoes glass transition in the high lateral compression state, analogously to the PLGA homopolymer monolayer. In the high PEG grafting density regime, the contribution of the PEG brush chains to the high monolayer surface pressure is significantly lower than what is predicted by the SCF model because of the many-body attraction among PEG segments (referred to in the literature as the "n-cluster" effects). The end-grafted PEG chains were found to be protein resistant even under the influence of the "n-cluster" effects.

  16. Conformational changes of a calix[8]arene derivative at the air-water interface.

    PubMed

    de Miguel, Gustavo; Pedrosa, José M; Martín-Romero, María T; Muñoz, Eulogia; Richardson, Tim H; Camacho, Luis

    2005-03-10

    The particular behavior of a p-tert-butyl calix[8]arene derivative (C8A) has been studied at the air-water interface using surface pressure-area isotherms, surface potential-area isotherms, film relaxation measurements, Brewster angle microscopy (BAM), and infrared spectroscopy for Langmuir-Blodgett films. Thus, it is observed that the properties of the film, for example, isotherms, domain formation, and FTIR spectra, recorded during the first compression cycle differ appreciably from those during the second compression and following cycles. The results obtained are interpreted on the basis of the conformational changes of the C8A molecules by surface pressure, allowing us to inquire into the inter- and intramolecular interactions (hydrogen bonds) of those molecules. Thus, the compression induces changes in the kind of hydrogen bonds from intra- and intermolecular with other C8A molecules to hydrogen bonds with water molecules. PMID:16851456

  17. Conformational changes of a calix[8]arene derivative at the air-water interface.

    PubMed

    de Miguel, Gustavo; Pedrosa, José M; Martín-Romero, María T; Muñoz, Eulogia; Richardson, Tim H; Camacho, Luis

    2005-03-10

    The particular behavior of a p-tert-butyl calix[8]arene derivative (C8A) has been studied at the air-water interface using surface pressure-area isotherms, surface potential-area isotherms, film relaxation measurements, Brewster angle microscopy (BAM), and infrared spectroscopy for Langmuir-Blodgett films. Thus, it is observed that the properties of the film, for example, isotherms, domain formation, and FTIR spectra, recorded during the first compression cycle differ appreciably from those during the second compression and following cycles. The results obtained are interpreted on the basis of the conformational changes of the C8A molecules by surface pressure, allowing us to inquire into the inter- and intramolecular interactions (hydrogen bonds) of those molecules. Thus, the compression induces changes in the kind of hydrogen bonds from intra- and intermolecular with other C8A molecules to hydrogen bonds with water molecules.

  18. Disruption of viscoelastic beta-lactoglobulin surface layers at the air-water interface by nonionic polymeric surfactants.

    PubMed

    Rippner Blomqvist, B; Ridout, M J; Mackie, A R; Wärnheim, T; Claesson, P M; Wilde, P

    2004-11-01

    Nonequilibrium interfacial layers formed by competitive adsorption of beta-lactoglobulin and the nonionic triblock copolymer PEO99-PPO65-PEO99 (F127) to the air-water interface were investigated in order to explain the influence of polymeric surfactants on protein film surface rheology and foam stability. Surface dilatational and shear rheological methods, surface tension measurements, dynamic thin-film measurements, diffusion measurements (from fluorescence recovery after photo bleaching), and determinations of foam stability were used as methods. The high surface viscoelasticity, both the shear and dilatational, of the protein films was significantly reduced by coadsorption of polymeric surfactant. The drainage rate of single thin films, in the presence of beta-lactoglobulin, increased with the amount of added F127, but equilibrium F127 films were found to be thicker than beta-lactoglobulin films, even at low concentration of the polymeric surfactant. It is concluded that the effect of the nonionic triblock copolymer on the interfacial rheology of beta-lactoglobulin layers is similar to that of low molecular weight surfactants. They differ however in that F127 increases the thickness of thin liquid films. In addition, the significant destabilizing effect of low molecular weight surfactants on protein foams is not found in the investigated system. This is explained as due to long-range steric forces starting to stabilize the foam films at low concentrations of F127. PMID:15518507

  19. Disruption of viscoelastic beta-lactoglobulin surface layers at the air-water interface by nonionic polymeric surfactants.

    PubMed

    Rippner Blomqvist, B; Ridout, M J; Mackie, A R; Wärnheim, T; Claesson, P M; Wilde, P

    2004-11-01

    Nonequilibrium interfacial layers formed by competitive adsorption of beta-lactoglobulin and the nonionic triblock copolymer PEO99-PPO65-PEO99 (F127) to the air-water interface were investigated in order to explain the influence of polymeric surfactants on protein film surface rheology and foam stability. Surface dilatational and shear rheological methods, surface tension measurements, dynamic thin-film measurements, diffusion measurements (from fluorescence recovery after photo bleaching), and determinations of foam stability were used as methods. The high surface viscoelasticity, both the shear and dilatational, of the protein films was significantly reduced by coadsorption of polymeric surfactant. The drainage rate of single thin films, in the presence of beta-lactoglobulin, increased with the amount of added F127, but equilibrium F127 films were found to be thicker than beta-lactoglobulin films, even at low concentration of the polymeric surfactant. It is concluded that the effect of the nonionic triblock copolymer on the interfacial rheology of beta-lactoglobulin layers is similar to that of low molecular weight surfactants. They differ however in that F127 increases the thickness of thin liquid films. In addition, the significant destabilizing effect of low molecular weight surfactants on protein foams is not found in the investigated system. This is explained as due to long-range steric forces starting to stabilize the foam films at low concentrations of F127.

  20. Microscopic dynamics of nanoparticle monolayers at air-water interface.

    PubMed

    Bhattacharya, R; Basu, J K

    2013-04-15

    We present results of surface mechanical and particle tracking measurements of nanoparticles trapped at the air-water interface as a function of their areal density. We monitor both the surface pressure (Π) and isothermal compression modulus (ϵ) as well as the dynamics of nanoparticle clusters, using fluorescence confocal microscopy while they are compressed to very high density near the two dimensional close packing density Φ∼0.82. We observe non-monotonic variation in both ϵ and the dynamic heterogeneity, characterized by the dynamical susceptibility χ4 with Φ, in such high density monolayers. We provide insight into the underlying nature of such transitions in close packed high density nanoparticle monolayers in terms of the morphology and flexibility of these soft colloidal particles. We discuss the significance our results in the context of related studies on two dimensional granular or colloidal systems. PMID:23411354

  1. Powder wettability at a static air-water interface.

    PubMed

    Dupas, Julien; Forny, Laurent; Ramaioli, Marco

    2015-06-15

    The reconstitution of a beverage from a dehydrated powder involves several physical mechanisms that determine the practical difficulty to obtain a homogeneous drink in a convenient way and within an acceptable time for the preparation of a beverage. When pouring powder onto static water, the first hurdle to overcome is the air-water interface. We propose a model to predict the percentage of powder crossing the interface in 45 s, namely the duration relevant for this application. We highlight theoretically the determinant role of the contact angle and of the particle size distribution. We validate experimentally the model for single spheres and use it to predict the wettability performance of commercial food powders for different contact angles and particles sizes. A good agreement is obtained when comparing the predictions and the wettability of the tested powders. PMID:25721855

  2. Measurement and computation of hydrodynamic coupling at an air/water interface with an insoluble monolayer

    NASA Astrophysics Data System (ADS)

    Hirsa, Amir H.; Lopez, Juan M.; Miraghaie, Reza

    2001-09-01

    The coupling between a bulk vortical flow and a surfactant-influenced air/water interface has been examined in a canonical flow geometry through experiments and computations. The flow in an annular region bounded by stationary inner and outer cylinders is driven by the constant rotation of the floor and the free surface is initially covered by a uniformly distributed insoluble monolayer. When driven slowly, this geometry is referred to as the deep-channel surface viscometer and the flow is essentially azimuthal. The only interfacial property that affects the flow in this regime is the surface shear viscosity, [mu]s, which is uniform on the surface due to the vanishingly small concentration gradient. However, when operated at higher Reynolds number, secondary flow drives the surfactant film towards the inner cylinder until the Marangoni stress balances the shear stress on the bulk fluid. In general, the flow can be influenced by the surface tension, [sigma], and the surface dilatational viscosity, [kappa]s, as well as [mu]s. However, because of the small capillary number of the present flow, the effects of surface tension gradients dominate the surface viscosities in the radial stress balance, and the effect of [mu]s can only come through the azimuthal stress. Vitamin K1 was chosen for this study since it forms a well-behaved insoluble monolayer on water and [mu]s is essentially zero in the range of concentration on the surface, c, encountered. Thus the effect of Marangoni elasticity on the interfacial stress could be isolated. The flow near the interface was measured in an optical channel using digital particle image velocimetry. Steady axisymmetric flow was observed at the nominal Reynolds number of 8500. A numerical model has been developed using the axisymmetric Navier Stokes equations to examine the details of the coupling between the bulk and the interface. The nonlinear equation of state, [sigma](c), for the vitamin K1 monolayer was measured and utilized in

  3. Interfacial adsorption and aggregation of amphiphilic proteins

    NASA Astrophysics Data System (ADS)

    Cheung, David

    2012-02-01

    The adsorption and aggregation on liquid interfaces of proteins is important in many biological contexts, such as the formation of aerial structures, immune response, and catalysis. Likewise the adsorption of proteins onto interfaces has applications in food technology, drug delivery, and in personal care products. As such there has been much interest in the study of a wide range of biomolecules at liquid interfaces. One class of proteins that has attracted particular attention are hydrophobins, small, fungal proteins with a distinct, amphiphilic surface structure. This makes these proteins highly surface active and they recently attracted much interest. In order to understand their potential applications a microscopic description of their interfacial and self-assembly is necessary and molecular simulation provides a powerful tool for providing this. In this presentation I will describe some recent work using coarse-grained molecular dynamics simulations to study the interfacial and aggregation behaviour of hydrophobins. Specifically this will present the calculation of their adsorption strength at oil-water and air-water interfaces, investigate the stability of hydrophobin aggregates in solution and their interaction with surfactants.

  4. Simulating Urban Tree Effects on Air, Water, and Heat Pollution Mitigation: iTree-Hydro Model

    NASA Astrophysics Data System (ADS)

    Yang, Y.; Endreny, T. A.; Nowak, D.

    2011-12-01

    Urban and suburban development changes land surface thermal, radiative, porous, and roughness properties and pollutant loading rates, with the combined effect leading to increased air, water, and heat pollution (e.g., urban heat islands). In this research we present the USDA Forest Service urban forest ecosystem and hydrology model, iTree Eco and Hydro, used to analyze how tree cover can deliver valuable ecosystem services to mitigate air, water, and heat pollution. Air pollution mitigation is simulated by dry deposition processes based on detected pollutant levels for CO, NO2, SO2, O3 and atmospheric stability and leaf area indices. Water quality mitigation is simulated with event mean concentration loading algorithms for N, P, metals, and TSS, and by green infrastructure pollutant filtering algorithms that consider flow path dispersal areas. Urban cooling considers direct shading and indirect evapotranspiration. Spatially distributed estimates of hourly tree evapotranspiration during the growing season are used to estimate human thermal comfort. Two main factors regulating evapotranspiration are soil moisture and canopy radiation. Spatial variation of soil moisture is represented by a modified urban topographic index and radiation for each tree is modified by considering aspect, slope and shade from surrounding buildings or hills. We compare the urban cooling algorithms used in iTree-Hydro with the urban canopy and land surface physics schemes used in the Weather Research and Forecasting model. We conclude by identifying biophysical feedbacks between tree-modulated air and water quality environmental services and how these may respond to urban heating and cooling. Improvements to this iTree model are intended to assist managers identify valuable tree services for urban living.

  5. Harmonization of environmental quality objectives for air, water and soil

    SciTech Connect

    Plassche, E.J. van de

    1994-12-31

    Environmental quality objectives (EQO) are often derived for single compartments only. However, concentrations at or below EQO level for one compartment may lead to exceeding of the EQO in another compartment due to intermedia transport of the chemical. Hence, achieving concentrations lower than the EQO in e.g. air does not necessarily mean that a ``safe`` concentration in soil can be maintained because of deposition from air to soil. This means that EQOs for air, water and soil must be harmonized in such a way that they meet a coherence criterion. This criterion implies that a EQO for one compartment has to be set at a level that full protection to organisms living in other compartments is ensured. In The Netherlands a project has been started to derive harmonized EQOs for a large number of chemicals. First, EQ0s are derived for all compartments based on ecotoxicological data for single species applying extrapolation methods. Secondly, these independently derived EQOs are harmonized. For harmonization of EQOs for water, sediment and soil the equilibrium partitioning method is used. For harmonization of EQOs for water and soil with the E00s for air a procedure is used applying computed steady state concentration ratios rather than equilibrium partitioning. The model SimpleBox is used for these computations. Some results of the project mentioned above will be presented. Attention will be paid to the derivation of independent EQ0s as well as the harmonization procedures applied.

  6. Air-water gas exchange by waving vegetation stems

    NASA Astrophysics Data System (ADS)

    Foster-Martinez, M. R.; Variano, E. A.

    2016-07-01

    Exchange between wetland surface water and the atmosphere is driven by a variety of motions, ranging from rainfall impact to thermal convection and animal locomotion. Here we examine the effect of wind-driven vegetation movement. Wind causes the stems of emergent vegetation to wave back and forth, stirring the water column and facilitating air-water exchange. To understand the magnitude of this effect, a gas transfer velocity (k600 value) was measured via laboratory experiments. Vegetation waving was studied in isolation by mechanically forcing a model canopy to oscillate at a range of frequencies and amplitudes matching those found in the field. The results show that stirring due to vegetation waving produces k600 values from 0.55 cm/h to 1.60 cm/h. The dependence of k600 on waving amplitude and frequency are evident from the laboratory data. These results indicate that vegetation waving has a nonnegligible effect on gas transport; thus, it can contribute to a mechanistic understanding of the fluxes underpinning biogeochemical processes.

  7. The Effect of Rain on Air-Water Gas Exchange

    NASA Technical Reports Server (NTRS)

    Ho, David T.; Bliven, Larry F.; Wanninkhof, Rik; Schlosser, Peter

    1997-01-01

    The relationship between gas transfer velocity and rain rate was investigated at NASA's Rain-Sea Interaction Facility (RSIF) using several SF, evasion experiments. During each experiment, a water tank below the rain simulator was supersaturated with SF6, a synthetic gas, and the gas transfer velocities were calculated from the measured decrease in SF6 concentration with time. The results from experiments with IS different rain rates (7 to 10 mm/h) and 1 of 2 drop sizes (2.8 or 4.2 mm diameter) confirm a significant and systematic enhancement of air-water gas exchange by rainfall. The gas transfer velocities derived from our experiment were related to the kinetic energy flux calculated from the rain rate and drop size. The relationship obtained for mono-dropsize rain at the RSIF was extrapolated to natural rain using the kinetic energy flux of natural rain calculated from the Marshall-Palmer raindrop size distribution. Results of laboratory experiments at RSIF were compared to field observations made during a tropical rainstorm in Miami, Florida and show good agreement between laboratory and field data.

  8. 14 CFR 1274.926 - Clean Air-Water Pollution Control Acts.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 5 2013-01-01 2013-01-01 false Clean Air-Water Pollution Control Acts...-Water Pollution Control Acts. Clean Air-Water Pollution Control Acts July 2002 If this cooperative... 91-604) and section 308 of the Federal Water Pollution Control Act, as amended (33 U.S.C. 1251 et...

  9. 14 CFR 1274.926 - Clean Air-Water Pollution Control Acts.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 5 2010-01-01 2010-01-01 false Clean Air-Water Pollution Control Acts...-Water Pollution Control Acts. Clean Air-Water Pollution Control Acts July 2002 If this cooperative... 91-604) and section 308 of the Federal Water Pollution Control Act, as amended (33 U.S.C. 1251 et...

  10. 14 CFR 1274.926 - Clean Air-Water Pollution Control Acts.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 5 2012-01-01 2012-01-01 false Clean Air-Water Pollution Control Acts...-Water Pollution Control Acts. Clean Air-Water Pollution Control Acts July 2002 If this cooperative... 91-604) and section 308 of the Federal Water Pollution Control Act, as amended (33 U.S.C. 1251 et...

  11. 14 CFR § 1274.926 - Clean Air-Water Pollution Control Acts.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 5 2014-01-01 2014-01-01 false Clean Air-Water Pollution Control Acts. Â...-Water Pollution Control Acts. Clean Air-Water Pollution Control Acts July 2002 If this cooperative... 91-604) and section 308 of the Federal Water Pollution Control Act, as amended (33 U.S.C. 1251 et...

  12. Static and dynamic evanescent wave light scattering studies of diblock copolymers adsorbed at the air/water interface

    NASA Astrophysics Data System (ADS)

    Lin, Binhua; Rice, Stuart A.; Weitz, D. A.

    1993-11-01

    We report the results of static and dynamic evanescent wave light scattering studies of a monolayer of a diblock copolymer, polystyrene-b-polymethylmethacrylate (PS-b-PMMA) with weight averaged molecular weights (Mw) of 880 000:290 000 supported at the air/water interface. Our studies probe the interfacial structural and dynamic properties of the monolayer on a length scale which is a fraction of the wavelength of light. The static light scattering studies were carried out as a function of polymer surface coverage and temperature; we also report some preliminary data for the dependence of the static structure function on the relative molecular weights of the PS and PMMA blocks. The complementary dynamic light scattering studies were carried out only as a function of surface coverage. Our data suggest that, upon spreading in the air/water interface, PS-b-PMMA (880:290 K) copolymers form thin disklike aggregates containing about 240 molecules. These data are consistent with a model in which each such aggregate is a ``furry disk'' with a dense core consisting of a layer of collapsed PS blocks atop a thin layer of extended PMMA blocks on the water surface and a brushlike boundary of extended PMMA blocks. The data show that the furry disks diffuse freely when the surface coverage is small, but when the surface coverage is large, they are immobile. Our data also suggest that the furry disks can aggregate to form even larger ``islands'' of disks with an extension greater than 20 μm. The static structure function of the assembly of furry disks is well described, over a wide range of surface coverage, by the structure factor of a two-dimensional hard disk fluid modulated by a two-dimensional hard disk form factor.

  13. Precision cleaning verification of fluid components by air/water impingement and total carbon analysis

    NASA Technical Reports Server (NTRS)

    Barile, Ronald G.; Fogarty, Chris; Cantrell, Chris; Melton, Gregory S.

    1994-01-01

    NASA personnel at Kennedy Space Center's Material Science Laboratory have developed new environmentally sound precision cleaning and verification techniques for systems and components found at the center. This technology is required to replace existing methods traditionally employing CFC-113. The new patent-pending technique of precision cleaning verification is for large components of cryogenic fluid systems. These are stainless steel, sand cast valve bodies with internal surface areas ranging from 0.2 to 0.9 sq m. Extrapolation of this technique to components of even larger sizes (by orders of magnitude) is planned. Currently, the verification process is completely manual. In the new technique, a high velocity, low volume water stream impacts the part to be verified. This process is referred to as Breathing Air/Water Impingement and forms the basis for the Impingement Verification System (IVS). The system is unique in that a gas stream is used to accelerate the water droplets to high speeds. Water is injected into the gas stream in a small, continuous amount. The air/water mixture is then passed through a converging/diverging nozzle where the gas is accelerated to supersonic velocities. These droplets impart sufficient energy to the precision cleaned surface to place non-volatile residue (NVR) contaminants into suspension in the water. The sample water is collected and its NVR level is determined by total organic carbon (TOC) analysis at 880 C. The TOC, in ppm carbon, is used to establish the NVR level. A correlation between the present gravimetric CFC113 NVR and the IVS NVR is found from experimental sensitivity factors measured for various contaminants. The sensitivity has the units of ppm of carbon per mg/sq ft of contaminant. In this paper, the equipment is described and data are presented showing the development of the sensitivity factors from a test set including four NVRs impinged from witness plates of 0.05 to 0.75 sq m.

  14. Precision Cleaning Verification of Fluid Components by Air/Water Impingement and Total Carbon Analysis

    NASA Technical Reports Server (NTRS)

    Barile, Ronald G.; Fogarty, Chris; Cantrell, Chris; Melton, Gregory S.

    1995-01-01

    NASA personnel at Kennedy Space Center's Material Science Laboratory have developed new environmentally sound precision cleaning and verification techniques for systems and components found at the center. This technology is required to replace existing methods traditionally employing CFC-113. The new patent-pending technique of precision cleaning verification is for large components of cryogenic fluid systems. These are stainless steel, sand cast valve bodies with internal surface areas ranging from 0.2 to 0.9 m(exp 2). Extrapolation of this technique to components of even larger sizes (by orders of magnitude) is planned. Currently, the verification process is completely manual. In the new technique, a high velocity, low volume water stream impacts the part to be verified. This process is referred to as Breathing Air/Water Impingement and forms the basis for the Impingement Verification System (IVS). The system is unique in that a gas stream is used to accelerate the water droplets to high speeds. Water is injected into the gas stream in a small, continuous amount. The air/water mixture is then passed through a converging-diverging nozzle where the gas is accelerated to supersonic velocities. These droplets impart sufficient energy to the precision cleaned surface to place non-volatile residue (NVR) contaminants into suspension in the water. The sample water is collected and its NVR level is determined by total organic carbon (TOC) analysis at 880 C. The TOC, in ppm carbon, is used to establish the NVR level. A correlation between the present gravimetric CFC-113 NVR and the IVS NVR is found from experimental sensitivity factors measured for various contaminants. The sensitivity has the units of ppm of carbon per mg-ft(exp 2) of contaminant. In this paper, the equipment is described and data are presented showing the development of the sensitivity factors from a test set including four NVR's impinged from witness plates of 0.05 to 0.75 m(exp 2).

  15. Reorientation of the ‘free OH’ group in the top-most layer of air/water interface of sodium fluoride aqueous solution probed with sum-frequency generation vibrational spectroscopy

    SciTech Connect

    Feng, Ran-Ran; Guo, Yuan; Wang, Hongfei

    2014-09-17

    Many experimental and theoretical studies have established the specific anion, as well as cation effects on the hydrogen-bond structures at the air/water interface of electrolyte solutions. However, the ion effects on the top-most layer of the air/water interface, which is signified by the non-hydrogen-bonded so-called ‘free O-H’ group, has not been discussed or studied. In this report, we present the measurement of changes of the orientational angle of the ‘free O-H’ group at the air/water interface of the sodium fluoride (NaF) solutions at different concentrations using the interface selective sum-frequency generation vibrational spectroscopy (SFG-VS) in the ssp and ppp polarizations. The polarization dependent SFG-VS results show that the average tilt angle of the ‘free O-H’ changes from about 35.3 degrees ± 0.5 degrees to 43.4 degrees ± 2.1degrees as the NaF concentration increase from 0 to 0.94M (nearly saturated). Such tilt angle change is around the axis of the other O-H group of the same water molecule at the top-most layer at the air/water interface that is hydrogen-bonded to the water molecules below the top-most layer. These results provide quantitative molecular details of the ion effects of the NaF salt on the structure of the water molecules at the top-most layer of the air/water interfacial, even though both the Na+ cation and the F- anion are believed to be among the most excluded ions from the air/water interface.

  16. Air-water oxygen exchange in a large whitewater river

    USGS Publications Warehouse

    Hall, Robert O.; Kennedy, Theodore A.; Rosi-Marshall, Emma J.

    2012-01-01

    Air-water gas exchange governs fluxes of gas into and out of aquatic ecosystems. Knowing this flux is necessary to calculate gas budgets (i.e., O2) to estimate whole-ecosystem metabolism and basin-scale carbon budgets. Empirical data on rates of gas exchange for streams, estuaries, and oceans are readily available. However, there are few data from large rivers and no data from whitewater rapids. We measured gas transfer velocity in the Colorado River, Grand Canyon, as decline in O2 saturation deficit, 7 times in a 28-km segment spanning 7 rapids. The O2 saturation deficit exists because of hypolimnetic discharge from Glen Canyon Dam, located 25 km upriver from Lees Ferry. Gas transfer velocity (k600) increased with slope of the immediate reach. k600 was -1 in flat reaches, while k600 for the steepest rapid ranged 3600-7700 cm h-1, an extremely high value of k600. Using the rate of gas exchange per unit length of water surface elevation (Kdrop, m-1), segment-integrated k600 varied between 74 and 101 cm h-1. Using Kdrop we scaled k600 to the remainder of the Colorado River in Grand Canyon. At the scale corresponding to the segment length where 80% of the O2 exchanged with the atmosphere (mean length = 26.1 km), k600 varied 4.5-fold between 56 and 272 cm h-1 with a mean of 113 cm h-1. Gas transfer velocity for the Colorado River was higher than those from other aquatic ecosystems because of large rapids. Our approach of scaling k600 based on Kdrop allows comparing gas transfer velocity across rivers with spatially heterogeneous morphology.

  17. Soy milk oleosome behaviour at the air-water interface.

    PubMed

    Waschatko, Gustav; Junghans, Ann; Vilgis, Thomas A

    2012-01-01

    Soy milk is a highly stable emulsion mainly due to the presence of oleosomes, which are oil bodies and function as lipid storage organelles in plants, e.g., in seeds. Oleosomes are micelle-like structures with an outer phospholipid monolayer, an interior filled with triacylglycerides (TAGs), and oleosins anchored hairpin-like into the structure with their hydrophilic parts remaining outside the oleosomes, completely covering their surface (K. Hsieh and A. H. C. Huang, Plant Physiol., 2004, 136, 3427-3434). Oleosins are alkaline proteins of 15-26 kDa (K. Hsieh and A. H. C. Huang, Plant Physiol., 2004, 136, 3427-3434) which are expressed during seed development and maturation and play a major role in the stability of oil bodies. Additionally, the oil bodies of seeds seem to have the highest impact on coalescence, probably due to the required protection against environmental stress during dormancy and germination compared to, e.g., vertebrates' lipoproteins. Surface pressure investigations and Brewster angle microscopy of oleosomes purified from raw soy milk were executed to reveal their diffusion to the air-water interface, rupture, adsorption and structural modification over time at different subphase conditions. Destroying the surface portions of the oleosins by tryptic digestion induced coalescence of oleosomes (J. Tzen and A. Huang, J. Cell. Biol., 1992, 117, 327-335) and revealed severe changes in their adsorption kinetics. Such investigations will help to determine the effects behind oleosome stability and are necessary for a better understanding of the principal function of oleosins and their interactions with phospholipids.

  18. Development of a numerical workflow based on μ-CT imaging for the determination of capillary pressure-saturation-specific interfacial area relationship in 2-phase flow pore-scale porous-media systems: a case study on Heletz sandstone

    NASA Astrophysics Data System (ADS)

    Peche, Aaron; Halisch, Matthias; Bogdan Tatomir, Alexandru; Sauter, Martin

    2016-05-01

    In this case study, we present the implementation of a finite element method (FEM)-based numerical pore-scale model that is able to track and quantify the propagating fluid-fluid interfacial area on highly complex micro-computed tomography (μ-CT)-obtained geometries. Special focus is drawn to the relationship between reservoir-specific capillary pressure (pc), wetting phase saturation (Sw) and interfacial area (awn). The basis of this approach is high-resolution μ-CT images representing the geometrical characteristics of a georeservoir sample. The successfully validated 2-phase flow model is based on the Navier-Stokes equations, including the surface tension force, in order to consider capillary effects for the computation of flow and the phase-field method for the emulation of a sharp fluid-fluid interface. In combination with specialized software packages, a complex high-resolution modelling domain can be obtained. A numerical workflow based on representative elementary volume (REV)-scale pore-size distributions is introduced. This workflow aims at the successive modification of model and model set-up for simulating, such as a type of 2-phase problem on asymmetric μ-CT-based model domains. The geometrical complexity is gradually increased, starting from idealized pore geometries until complex μ-CT-based pore network domains, whereas all domains represent geostatistics of the REV-scale core sample pore-size distribution. Finally, the model can be applied to a complex μ-CT-based model domain and the pc-Sw-awn relationship can be computed.

  19. Detachment of deposited colloids by advancing and receding air-water interfaces.

    PubMed

    Aramrak, Surachet; Flury, Markus; Harsh, James B

    2011-08-16

    Moving air-water interfaces can detach colloidal particles from stationary surfaces. The objective of this study was to quantify the effects of advancing and receding air-water interfaces on colloid detachment as a function of interface velocity. We deposited fluorescent, negatively charged, carboxylate-modified polystyrene colloids (diameter of 1 μm) into a cylindrical glass channel. The colloids were hydrophilic with an advancing air-water contact angle of 60° and a receding contact angle of 40°. After colloid deposition, two air bubbles were sequentially introduced into the glass channel and passed through the channel at different velocities (0.5, 7.7, 72, 982, and 10,800 cm/h). The passage of the bubbles represented a sequence of receding and advancing air-water interfaces. Colloids remaining in the glass channel after each interface passage were visualized with confocal microscopy and quantified by image analysis. The advancing air-water interface was significantly more effective in detaching colloids from the glass surface than the receding interface. Most of the colloids were detached during the first passage of the advancing air-water interface, while the subsequent interface passages did not remove significant amounts of colloids. Forces acting on the colloids calculated from theory corroborate our experimental results, and confirm that the detachment forces (surface tension forces) during the advancing air-water interface movement were stronger than during the receding movement. Theory indicates that, for hydrophilic colloids, the advancing interface movement generally exerts a stronger detachment force than the receding, except when the hysteresis of the colloid-air-water contact angle is small and that of the channel-air-water contact angle is large.

  20. Universal nanopatternable interfacial bonding.

    PubMed

    Ding, Yuzhe; Garland, Shaun; Howland, Michael; Revzin, Alexander; Pan, Tingrui

    2011-12-01

    A nanopatternable polydimethylsiloxane (PDMS) oligomer layer is demonstrated as an interfacial adhesive for its intrinsic transferability and universal adhesiveness. Utilizing the well-established surface modification and bonding techniques of PDMS surfaces, irreversible bonding is formed (up to 400 kPa) between a wide range of substrate pairs, representing ones within and across different materials categories, including metals, ceramics, thermoset, and thermoplastic polymers.

  1. Structural properties and organization of hexadecanol isomers at the air/water interface

    NASA Astrophysics Data System (ADS)

    Walker, Robert; Can, Süleyman; Mago, Deesha

    2006-03-01

    A wealth of experimental data and theoretical modeling has led to well-honed intuition about the surface properties and structure of symmetric amphiphiles adsorbed to liquid surfaces. Less clear is how asymmetric amphiphiles organize in two dimensions at different surface coverages. We have studied the structure and two dimensional phase behavior of hexadecanol isomers adsorbed to the air/water interface. These isomers include the linear, n-hexadecanol as well structures with the alcohol functional group in the 2-, 3-, and 4- positions. Surface pressure methods are employed to study thermodynamic behavior of these insoluble monolayers, and vibrational sum frequency generation -- a vibrational spectroscopy with surface specificity -- is used to probe the molecular conformation and orientation of molecules within films. At their equilibrium spreading pressures, both 1- and 2- hexadecanol form very compact films having a high degree of conformational order and molecular areas of 19 and 28 sq. Angstroms/molecule in the tightly packed limit. In contrast, monolayers formed by 3-hexadecanol and 4-hexadecanol are much more disordered - but very similar to each other - and occupy much larger areas/molecule (75 sq. Angstroms/molec) in the tightly packed limit.

  2. A CRITICAL ASSESSMENT OF ELEMENTAL MERCURY AIR/WATER EXCHANGE PARTNERS

    EPA Science Inventory

    Although evasion of elemental mercury from aquatic systems can significantly deplete net mercury accumulation resulting from atmospheric deposition, the current ability to model elemental mercury air/water exchange is limited by uncertainties in our understanding of all gaseous a...

  3. Capillary forces between sediment particles and an air-water interface.

    PubMed

    Chatterjee, Nirmalya; Lapin, Sergey; Flury, Markus

    2012-04-17

    In the vadose zone, air-water interfaces play an important role in particle fate and transport, as particles can attach to the air-water interfaces by action of capillary forces. This attachment can either retard or enhance the movement of particles, depending on whether the air-water interfaces are stationary or mobile. Here we use three standard PTFE particles (sphere, circular cylinder, and tent) and seven natural mineral particles (basalt, granite, hematite, magnetite, mica, milky quartz, and clear quartz) to quantify the capillary forces between an air-water interface and the different particles. Capillary forces were determined experimentally using tensiometry, and theoretically assuming volume-equivalent spherical, ellipsoidal, and circular cylinder shapes. We experimentally distinguished between the maximum capillary force and the snap-off force when the air-water interface detaches from the particle. Theoretical and experimental values of capillary forces were of similar order of magnitude. The sphere gave the smallest theoretical capillary force, and the circular cylinder had the largest force due to pinning of the air-water interface. Pinning was less pronounced for natural particles when compared to the circular cylinder. Ellipsoids gave the best agreement with measured forces, suggesting that this shape can provide a reasonable estimation of capillary forces for many natural particles.

  4. Reaction of a phospholipid monolayer with gas-phase ozone at the air-water interface: measurement of surface excess and surface pressure in real time.

    PubMed

    Thompson, Katherine C; Rennie, Adrian R; King, Martin D; Hardman, Samantha J O; Lucas, Claire O M; Pfrang, Christian; Hughes, Brian R; Hughes, Arwel V

    2010-11-16

    The reaction between gas-phase ozone and monolayers of the unsaturated lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, POPC, on aqueous solutions has been studied in real time using neutron reflection and surface pressure measurements. The reaction between ozone and lung surfactant, which contains POPC, leads to decreased pulmonary function, but little is known about the changes that occur to the interfacial material as a result of oxidation. The results reveal that the initial reaction of ozone with POPC leads to a rapid increase in surface pressure followed by a slow decrease to very low values. The neutron reflection measurements, performed on an isotopologue of POPC with a selectively deuterated palmitoyl strand, reveal that the reaction leads to loss of this strand from the air-water interface, suggesting either solubilization of the product lipid or degradation of the palmitoyl strand by a reactive species. Reactions of (1)H-POPC on D(2)O reveal that the headgroup region of the lipids in aqueous solution is not dramatically perturbed by the reaction of POPC monolayers with ozone supporting degradation of the palmitoyl strand rather than solubilization. The results are consistent with the reaction of ozone with the oleoyl strand of POPC at the air-water interface leading to the formation of OH radicals. The highly reactive OH radicals produced can then go on to react with the saturated palmitoyl strands leading to the formation of oxidized lipids with shorter alkyl tails.

  5. Comparison of the influence of fluorocarbon and hydrocarbon surfactants on the adsorptions of SDS, DTAB and C12E8 at the air/water interface by MD simulation

    NASA Astrophysics Data System (ADS)

    Pang, Jinyu; Xu, Guiying

    2012-06-01

    Adsorptions of sodium dodecylsulfate (SDS), dodecyltrimethylammonium bromide (DTAB) and octaethylene glycol monododecyl ether (C12E8) at the air/water interface in the presence of hydrocarbon and fluorocarbon surfactants (HCEP and FCEP) were investigated by molecular dynamics (MD) simulation. With the addition of HCEP or FCEP, the monolayer is more organized than in individual surfactant systems. Extremely expanded C12E8 chain in a smaller tilt angle is discovered in C12E8/HCEP system. In SDS or DTAB systems, relatively small tilt angle of surfactants is observed in the presence of FCEP. Their analog, a silicone surfactant DSEP shows a favorable effect on interfacial properties with DTAB.

  6. Effect of grafted polymer species on particle monolayer structure at the air-water interface.

    PubMed

    Mouri, Emiko; Okazaki, Yoshitaka; Komune, Seishu; Yoshinaga, Kohji

    2011-03-01

    We have studied poly(methyl methacrylate)-grafted(PMMA) particle monolayer systems at the air-water interface. In previous papers, we reported that PMMA chains grafted from particles (silica particle and polystyrene latex) were extended on water surfaces. Through observing deposited particle monolayers on substrates using SEM, we have confirmed that PMMA of large molecular weights were either dispersed or arrayed in structure with long inter-particle distances approximately 500 nm. In contrast, low molecular weight PMMA were observed to aggregate upon deposition. We speculated that the difference in morphology in deposited particle monolayers would be attributed to the affinity between the grafted polymer and the substrate. To examine the effect of this affinity three new polymer-grafted silica particles were synthesized with a fairly high graft density of about 0.14 approximately 0.43 nm(-2). As well as PMMA-grafted silica particles (SiO2-PMMA), poly(2-hydroxyethyl methacrylate) and poly(t-butyl methacrylate)--grafted silica particles (SiO2-PHEMA and SiO2-PtBuMA) were also prepared and subjected to pi-A isotherm measurements and SEM observations. These pi-A isotherms indicated that polymer-grafted silica formed monolayer at the air-water interface, and the onset area of increasing surface pressure suggests that the polymer chains are extended on a water surface. However, the morphology of the deposited monolayer is highly dependent on polymer species: SiO2-PHEMA showed that the dispersed particle monolayer structure was independent of grafted molecular weight while SiO2-tBuMA showed an aggregated structure that was also independent of grafted moleculer weight. SiO2-PMMA showed intermediate tendencies: dispersed structure was observed with high grafted molecular weight and aggregated structure was observed with low grafted molecule weight. The morphology on glass substrate would be explaiened by hydrophilic interaction between grafted polymer and hydrophilic glass

  7. Iridium Interfacial Stack (IRIS)

    NASA Technical Reports Server (NTRS)

    Spry, David James (Inventor)

    2015-01-01

    An iridium interfacial stack ("IrIS") and a method for producing the same are provided. The IrIS may include ordered layers of TaSi.sub.2, platinum, iridium, and platinum, and may be placed on top of a titanium layer and a silicon carbide layer. The IrIS may prevent, reduce, or mitigate against diffusion of elements such as oxygen, platinum, and gold through at least some of its layers.

  8. Dynamic interfacial properties of human tear-lipid films and their interactions with model-tear proteins in vitro.

    PubMed

    Svitova, Tatyana F; Lin, Meng C

    2016-07-01

    This review summarizes the current state of knowledge regarding interfacial properties of very complex biological colloids, specifically, human meibum and tear lipids, and their interactions with proteins similar to the proteins found in aqueous part of human tears. Tear lipids spread as thin films over the surface of tear-film aqueous and play crucial roles in tear-film stability and overall ocular-surface health. The vast majority of papers published to date report interfacial properties of meibum-lipid monolayers spread on various aqueous sub-phases, often containing model proteins, in Langmuir trough. However, it is well established that natural human ocular tear lipids exist as multilayered films with a thickness between 30 and 100nm, that is very much disparate from 1 to 2nm thick meibum monolayers. We employed sessile-bubble tensiometry to study the dynamic interfacial and rheological properties of reconstituted multilayered human tear-lipid films. Small amounts (0.5-1μg) of human tear lipids were deposited on an air-bubble surface to produce tear-lipid films in thickness range 30-100nm corresponding to ocular lipid films. Thus, we were able to overcome major Langmuir-trough method limitations because ocular tear lipids can be safely harvested only in minute, sub-milligram quantities, insufficient for Langmuir through studies. Sessile-bubble method is demonstrated to be a versatile tool for assessing conventional synthetic surfactants adsorption/desorption dynamics at an air-aqueous solution interface. (Svitova T., Weatherbee M., Radke C.J. Dynamics of surfactant sorption at the air/water interface: continuous-flow tensiometry. J. Colloid Interf. Sci. 2003;261:1170-179). The augmented flow-sessile-bubble setup, with step-strain relaxation module for dynamic interfacial rheological properties and high-precision syringe pump to generate larger and slow interfacial area expansions-contractions, was developed and employed in our studies. We established that

  9. Gold Nanoparticle Monolayers from Sequential Interfacial Ligand Exchange and Migration in a Three-Phase System

    PubMed Central

    Yang, Guang; Hallinan, Daniel T.

    2016-01-01

    Using a three-phase system, centimeter-scale monolayer gold nanoparticle (Au NP) films have been prepared that have long-range order and hydrophobic ligands. The system contains an interface between an aqueous phase containing Au NPs and an oil phase containing one of various types of amine ligands, and a water/air interface. As the Au NPs diffuse to the water/oil interface, ligand exchange takes place which temporarily traps them at the water/oil interface. The ligand-exchanged particles then spontaneously migrate to the air/water interface, where they self-assemble, forming a monolayer under certain conditions. The spontaneous formation of the NP film at the air/water interface was due to the minimization of the system Helmholtz free energy. However, the extent of surface functionalization was dictated by kinetics. This decouples interfacial ligand exchange from interfacial self-assembly, while maintaining the simplicity of a single system. The interparticle center-to-center distance was dictated by the amine ligand length. The Au NP monolayers exhibit tunable surface plasma resonance and excellent spatial homogeneity, which is useful for surface-enhanced Raman scattering. The “air/water/oil” self-assembly method developed here not only benefits the fundamental understanding of NP ligand conformations, but is also applicable to the manufacture of plasmonic nanoparticle devices with precisely designed optical properties. PMID:27762394

  10. Interfacial Bubble Deformations

    NASA Astrophysics Data System (ADS)

    Seymour, Brian; Shabane, Parvis; Cypull, Olivia; Cheng, Shengfeng; Feitosa, Klebert

    Soap bubbles floating at an air-water experience deformations as a result of surface tension and hydrostatic forces. In this experiment, we investigate the nature of such deformations by taking cross-sectional images of bubbles of different volumes. The results show that as their volume increases, bubbles transition from spherical to hemispherical shape. The deformation of the interface also changes with bubble volume with the capillary rise converging to the capillary length as volume increases. The profile of the top and bottom of the bubble and the capillary rise are completely determined by the volume and pressure differences. James Madison University Department of Physics and Astronomy, 4VA Consortium, Research Corporation for Advancement of Science.

  11. Duolayers at the Air/Water Interface: Improved Lifetime through Ionic Interactions.

    PubMed

    Prime, Emma L; Solomon, David H; Dagley, Ian J; Qiao, Greg G

    2016-08-01

    Ionic interactions to stabilize Langmuir films at the air/water interface have been used to develop improved duolayer films. Two-component mixtures of octadecanoic (stearic) acid and poly(diallyldimethylammonium chloride) (polyDADMAC) with different ratios were prepared and applied to the water surface. Surface pressure isotherm cycles demonstrated a significant improvement in film stability with the inclusion of the polymer. Viscoelastic properties were measured using canal viscometry and oscillating barriers, with both methods showing that the optimum ratio for improved properties was four octadecanoic acid molecules to one DADMAC unit (1:0.25). At this ratio it is expected multiple strong ionic interactions are formed along each polymer chain. Brewster angle microscopy showed decreased domain size with increased ratios of polyDADMAC, indicating that the polymer is interspersed across the surface. This new method to stabilize and increase the viscoelastic properties of charged monolayer films, using a premixed composition, will have application in areas such as water evaporation mitigation, optical devices, and foaming. PMID:27420341

  12. Spread Films of Human Serum Albumin at the Air-Water Interface: Optimization, Morphology, and Durability.

    PubMed

    Campbell, Richard A; Ang, Joo Chuan; Sebastiani, Federica; Tummino, Andrea; White, John W

    2015-12-22

    It has been known for almost one hundred years that a lower surface tension can be achieved at the air-water interface by spreading protein from a concentrated solution than by adsorption from an equivalent total bulk concentration. Nevertheless, the factors that control this nonequilibrium process have not been fully understood. In the present work, we apply ellipsometry, neutron reflectometry, X-ray reflectometry, and Brewster angle microscopy to elaborate the surface loading of human serum albumin in terms of both the macroscopic film morphology and the spreading dynamics. We show that the dominant contribution to the surface loading mechanism is the Marangoni spreading of protein from the bulk of the droplets rather than the direct transfer of their surface films. The films can be spread on a dilute subphase if the concentration of the spreading solution is sufficient; if not, dissolution of the protein occurs, and only a textured adsorbed layer slowly forms. The morphology of the spread protein films comprises an extended network with regions of less textured material or gaps. Further, mechanical cycling of the surface area of the spread films anneals the network into a membrane that approach constant compressibility and has increased durability. Our work provides a new perspective on an old problem in colloid and interface science. The scope for optimization of the surface loading mechanism in a range of systems leading to its exploitation in deposition-based technologies in the future is discussed.

  13. Role of the interfacial area for structure and dynamics in polymer nanocomposites: molecular dynamics simulations of polystyrene with silica nanoparticles of different shapes

    NASA Astrophysics Data System (ADS)

    Liu, Shengyuan; Böhm, Michael C.; Müller-Plathe, Florian

    2016-10-01

    Polystyrene nanocomposites containing a fraction of silica nanoparticles of different geometries (sphere, cube and regular tetrahedron) have been investigated by coarse-grained molecular dynamics simulations. Structural and dynamic properties of the polymer chains in the presence of the nanoparticles have been analyzed as a function of the nanoparticle mass fraction and geometrical shape. It has been found that the dimension of the polymer chains in the interphase expands due to the polymer–nanoparticle interaction. Their global dimension (averaged over the whole sample), however, shrinks when increasing the total surface area of the nanoparticles. The conformational changes of polymer chains in the interphase are monitored by a chain orientation parameter. The profiles of the chain dimension and orientation as a function of their distance from the nanoparticle center of mass show that the interphase thickness is roughly equal to the radius of gyration of the polymer chains. Moreover, the dynamic behavior of the polymer chains in nanocomposites is analyzed by the center of mass diffusion coefficient, the relaxation time of the chain end-to-end vector and the characteristic escape time of the polymer chains from the interphase. Compared with neat polymers, both the global and local chain dynamics in nanocomposites are hindered with an increasing nanoparticle mass fraction and with an increasing surface area. The local chain dynamics in the interphase is stronger affected by the surface area of the nanoparticles than the global one. Specifically, the global diffusion coefficient of polymer chains is almost linearly reduced with the total surface area of the nanoparticles, whereas the global relaxation time of the chain end-to-end vector increases almost linearly with it. The interphase relaxation time of the polymer chains increases superlinearly with the surface area of an individual nanoparticle. Additionally, the characteristic escape time of polymer chains from

  14. Highly Enhanced Electromechanical Stability of Large-Area Graphene with Increased Interfacial Adhesion Energy by Electrothermal-Direct Transfer for Transparent Electrodes.

    PubMed

    Kim, Jangheon; Kim, Gi Gyu; Kim, Soohyun; Jung, Wonsuk

    2016-09-01

    Graphene, a two-dimensional sheet of carbon atoms in a hexagonal lattice structure, has been extensively investigated for research and industrial applications as a promising material with outstanding electrical, mechanical, and chemical properties. To fabricate graphene-based devices, graphene transfer to the target substrate with a clean and minimally defective surface is the first step. However, graphene transfer technologies require improvement in terms of uniform transfer with a clean, nonfolded and nontorn area, amount of defects, and electromechanical reliability of the transferred graphene. More specifically, uniform transfer of a large area is a key challenge when graphene is repetitively transferred onto pretransferred layers because the adhesion energy between graphene layers is too low to ensure uniform transfer, although uniform multilayers of graphene have exhibited enhanced electrical and optical properties. In this work, we developed a newly suggested electrothermal-direct (ETD) transfer method for large-area high quality monolayer graphene with less defects and an absence of folding or tearing of the area at the surface. This method delivers uniform multilayer transfer of graphene by repetitive monolayer transfer steps based on high adhesion energy between graphene layers and the target substrate. To investigate the highly enhanced electromechanical stability, we conducted mechanical elastic bending experiments and reliability tests in a highly humid environment. This ETD-transferred graphene is expected to replace commercial transparent electrodes with ETD graphene-based transparent electrodes and devices such as a touch panels with outstanding electromechanical stability. PMID:27564120

  15. Surface relaxations as a tool to distinguish the dynamic interfacial properties of films formed by normal and diseased meibomian lipids.

    PubMed

    Georgiev, Georgi As; Yokoi, Norihiko; Ivanova, Slavyana; Tonchev, Vesselin; Nencheva, Yana; Krastev, Rumen

    2014-08-14

    The surface properties of human meibomian lipids (MGS), the major constituent of the tear film (TF) lipid layer, are of key importance for TF stability. The dynamic interfacial properties of films by MGS from normal eyes (nMGS) and eyes with meibomian gland dysfunction (dMGS) were studied using a Langmuir surface balance. The behavior of the samples during dynamic area changes was evaluated by surface pressure-area isotherms and isocycles. The surface dilatational rheology of the films was examined in the frequency range 10(-5) to 1 Hz by the stress-relaxation method. A significant difference was found, with dMGS showing slow viscosity-dominated relaxation at 10(-4) to 10(-3) Hz, whereas nMGS remained predominantly elastic over the whole range. A Cole-Cole plot revealed two characteristic processes contributing to the relaxation, fast (on the scale of characteristic time τ < 5 s) and slow (τ > 100 s), the latter prevailing in dMGS films. Brewster angle microscopy revealed better spreading of nMGS at the air-water interface, whereas dMGS layers were non-uniform and patchy. The distinctions in the interfacial properties of the films in vitro correlated with the accelerated degradation of meibum layer pattern at the air-tear interface and with the decreased stability of TF in vivo. These results, and also recent findings on the modest capability of meibum to suppress the evaporation of the aqueous subphase, suggest the need for a re-evaluation of the role of MGS. The probable key function of meibomian lipids might be to form viscoelastic films capable of opposing dilation of the air-tear interface. The impact of temperature on the meibum surface properties is discussed in terms of its possible effect on the normal structure of the film.

  16. On the challenges of measuring interfacial characteristics of three-phase fluid flow with x-ray microtomography.

    PubMed

    Brown, K; Schlüter, S; Sheppard, A; Wildenschild, D

    2014-03-01

    Synchrotron-based x-ray computed microtomography contributes high-resolution, three-dimensional observations to investigations of multiphase fluid transport in porous media. Pore-scale observations are valuable to the development and validation of new theory, as well as numerical models. Computed microtomography has been used previously to measure fluid content and interfacial areas in systems containing two fluids (air-water, oil-water) and to a limited extent to measure fluid content and entrapped fluid morphology in systems containing three fluids (air-oil-water). This study addresses challenges that arise when imaging three-phase flow in spreading systems. The first challenge is related to wettability alteration. Observations reported herein suggest that the wettability of solid surfaces changed over the course of a three-fluid phase flow experiment, a phenomenon that has not been observed in similar, previously conducted two-fluid phase experiments. Follow-up experiments showed that wettability alteration is significant when oil-solid contact is combined with x-ray exposure, and is not reversed with a conventional cleaning procedure. The second challenge arises in segmenting three-phase images, and thereby obtaining data from which various measures can be quantified with sufficient accuracy. Partial volume effects and blur often cause the grey-scale values of different fluids to overlap and appropriate steps must be taken to avoid ambiguity at phase boundaries. A comparison of images collected at standard resolution (10.6 microns voxel(-1) ) to those collected at a higher resolution (5.3 microns voxel(-1) ) showed that saturation measurements are within 5% of each other, but interfacial areas for three-phase systems may be underestimated at standard resolution by as much as 25%.

  17. Estimating pH at the Air/Water Interface with a Confocal Fluorescence Microscope.

    PubMed

    Yang, Haiya; Imanishi, Yasushi; Harata, Akira

    2015-01-01

    One way to determine the pH at the air/water interface with a confocal fluorescence microscope has been proposed. The relation between the pH at the air/water interface and that in a bulk solution has been formulated in connection with the adsorption equilibrium and the dissociation equilibrium of the dye adsorbed. Rhodamine B (RhB) is used as a surface-active fluorescent pH probe. The corrected fluorescence spectrum of RhB molecules at the air/water interface with the surface density of 1.0 nmol m(-2) level shows pH-dependent shifts representing an acid-base equilibrium. Two ways to determine the unknown acid-base equilibrium constant of RhB molecules at the air/water interface have been discussed. With surface-tension measurements, the adsorption properties, maximum surface density, and adsorption equilibrium constants were estimated for both cationic and zwitterionic forms of RhB molecules at the air/water interface.

  18. The impact of transitions between two-fluid and three-fluid phases on fluid configuration and fluid-fluid interfacial area in porous media

    NASA Astrophysics Data System (ADS)

    Carroll, Kenneth C.; McDonald, Kieran; Marble, Justin; Russo, Ann E.; Brusseau, Mark L.

    2015-09-01

    Multiphase-fluid distribution and flow is inherent in numerous areas of hydrology. Yet pore-scale characterization of transitions between two and three immiscible fluids is limited. The objective of this study was to examine the impact of such transitions on the pore-scale configuration of organic liquid in a multifluid system comprising natural porous media. Three-dimensional images of an organic liquid (trichloroethene) in two-phase (organic-liquid/water) and three-phase (air/organic-liquid/water) systems were obtained using X-ray microtomography before and after drainage and imbibition. Upon transition from a two-phase to a three-phase system, a significant portion of the organic liquid (intermediate wetting fluid) was observed to exist as lenses and films in contact with air (nonwetting fluid). In these cases, the air was either encased by or contiguous to the organic liquid. The presence of air resulted in an increase in the surface-area-to-volume ratios for the organic-liquid blobs. Upon imbibition, the air was displaced downgradient, and concomitantly, the morphology of the organic-liquid blobs no longer in contact with air reverted to that characteristic of a two-phase distribution (i.e., more spherical blobs and ganglia). This change in morphology resulted in a reduction in the surface-area-to-volume ratio. These results illustrate the impact of transitions between two-phase and three-phase conditions on fluid configuration, and they demonstrate the malleable nature of fluid configuration under dynamic, multiphase-flow conditions. The results have implications for characterizing and modeling pore-scale flow and mass transfer processes.

  19. Characerization of photosynthetic reaction centres from Rhodobacter sphaeroides at the air-water interface and in Langmuir-Blodgett films

    SciTech Connect

    Fang, J.Y.; Gaul, D.F.; Chumanov, G.; Cotton, T.M.; Uphaus, R.A. |

    1995-11-01

    Monolayers of the reaction center complex from Rhodobacter sphaeroides were prepared from dodecyl {Beta}-maltoside suspensions at an air-water interface. The stability of these monolayers was determined. A value of 28 nm{sup 2} per complex was obtained for the cross-sectional area from the equilibrium surface pressure-area isotherms. Multilayer films of alternating arachidic acid-reaction center monolayers were constructed on quartz slides by the Langmuir-Blodgett technique. Absorption spectroscopy was used to confirm the structural integrity of the complex and to determine the transfer ratio. Low-angle X-ray diffraction measurements were performed on these multilayers. A value of 64 A was obtained for the thickness of the reaction center monolayer in the multilayer film. This novel approach can be used to study multilayers of other membrane-bound proteins. 20 refs., 9 figs.

  20. Langmuir structure of poly (2-vinylpyridine-b-hexyl isocyanate) rod-coil diblock copolymers at the air/water Interface

    NASA Astrophysics Data System (ADS)

    Ahmad, Farhan

    2005-03-01

    We conducted a systematic interfacial study for the complete range (5%-90% of rod mole percentage) of an amphiphilic rod-coil system, poly (hexyl isocyanate)-b-(2-vinylpyridine) at the air/water and air/solid interface. We applied Langmuir balance technique, scanning probe microscopy (SPM), transmission electron microscopy (TEM) and X-ray reflectivity for the complete characterization of the monolayer at the interfaces. The phase isotherms showed the well amphiphilic balance for the diblock copolymers, and the formation of stable monolayers. With the increasing rod content, the consistent increase in the monolayer packing density was observed by the phase isotherms and supported by X-ray reflectivity. SPM and TEM characterization showed their interesting surface morphology according to the varying rod mole percentage in the rod-coil system. Rod mole percentage 5%-15% showed micellar morphology. Rod mole percentage 23%-32% showed distinct and dispersed rods, whereas rod mole percentage 70%-90% showed well packed structure similar to lamella phase. We found the tendency of the diblock system to adopt a packed monomolecular structure has increased by the increasing rod content. This lead us to conclude that it is the hexyl-isocyanate (rod part) that governs mostly the interfacial behavior of rod-coil block copolymers.

  1. Interfacial behavior of perchlorate versus chloride ions in saturated aqueous salt solutions

    SciTech Connect

    Ghosal, S; Kuo, I W; Baer, M D; Bluhm, H

    2009-04-14

    In recent years combination of theoretical and experimental work have presented a novel view of the aqueous interface wherein hard and/or multiply charged ions are excluded from the interface, but large polarizable anions show interfacial enhancement relative to the bulk. The observed trend in the propensity of anions to adsorb at the air/water interface appears to be reverse of the Hofmeister series for anions. This study focuses on experimental and theoretical examination of the partitioning behavior of perchlorate (ClO{sub 4}{sup -}) and chloride (Cl{sup -}) ions at the air/water interface. We have used ambient pressure X-ray photoelectron spectroscopy technique to directly probe the interfacial concentrations of ClO{sub 4}{sup -} and Cl{sup -} ions in sodium perchlorate and sodium chloride solutions, respectively. Experimental observations are compared with first principles molecular dynamics simulations. Both experimental and simulation results show enhancement of ClO{sub 4}{sup -} ion at the interface, compared with the absence of such enhancement in the case of Cl{sup -} ion. These observations are in agreement with the expected trend in the interfacial propensity of anions based on the Hofmeister series.

  2. Two-phase air-water stratified flow measurement using ultrasonic techniques

    SciTech Connect

    Fan, Shiwei; Yan, Tinghu; Yeung, Hoi

    2014-04-11

    In this paper, a time resolved ultrasound system was developed for investigating two-phase air-water stratified flow. The hardware of the system includes a pulsed wave transducer, a pulser/receiver, and a digital oscilloscope. The time domain cross correlation method is used to calculate the velocity profile along ultrasonic beam. The system is able to provide velocities with spatial resolution of around 1mm and the temporal resolution of 200μs. Experiments were carried out on single phase water flow and two-phase air-water stratified flow. For single phase water flow, the flow rates from ultrasound system were compared with those from electromagnetic flow (EM) meter, which showed good agreement. Then, the experiments were conducted on two-phase air-water stratified flow and the results were given. Compared with liquid height measurement from conductance probe, it indicated that the measured velocities were explainable.

  3. Surface behavior of malonic acid adsorption at the air/water interface.

    PubMed

    Blower, Patrick G; Shamay, Eric; Kringle, Loni; Ota, Stephanie T; Richmond, Geraldine L

    2013-03-28

    The presence of organic materials adsorbed to the surfaces of aerosol particles has been demonstrated to be a determining factor in relevant atmospheric processes. Malonic acid is a small, water-soluble organic acid that is common in aerosols and is surface-active. A comprehensive investigation of the adsorption of malonic acid to the air/water interface was accomplished using vibrational sum frequency spectroscopy (VSFS) and surface tension measurements as functions of concentration and pH. Malonic acid was found to be weakly solvated at the air/water interface, and its orientation as a function of concentration was explored through different VSFS polarization schemes. pH-dependent experiments revealed that the surface-active species is the fully protonated species. Computational analyses were used to obtain depth-specific geometries of malonic acid at the air/water interface that confirm and enrich the experimental results. PMID:23384061

  4. LIF measurements of oxygen concentration gradients along flat and wavy air-water interfaces

    NASA Astrophysics Data System (ADS)

    Woodrow, Philip T., Jr.; Duke, Steve R.

    Instantaneous spatially-varying measurements of concentration gradients occurring during aeration for flat, stagnant air-water interfaces and for interfaces with mechanically-generated waves are presented. Measurements were obtained in a laboratory wave tank using a laser-induced fluorescence (LIF) technique that images planar oxygen concentration fields near air-water interfaces. Pulsed nitrogen laser light focused to a thin sheet induces the fluorescence of pyrene butyric acid (in micromolar concentration) in deoxygenated water. The PBA fluorescence is quenched by dissolved oxygen. A high-resolution CCD camera images in two dimensions the intensities of the fluorescence field, providing spatial measurements of oxygen concentration with magnification of 7 μm per pixel. The concentration fields, gradients, and boundary layer thicknesses along the flat and wavy air-water interfaces are quantified and compared to previous measurements associated with sheared gas-liquid interfaces and with wind-generated waves.

  5. Towards a unified picture of the water self-ions at the air-water interface: a density functional theory perspective

    SciTech Connect

    Baer, Marcel D.; Kuo, I-F W.; Tobias, Douglas J.; Mundy, Christopher J.

    2014-07-17

    The propensities of the water self ions, H3O+ and OH- , for the air-water interface has implications for interfacial acid-base chemistry. Despite numerous experimental and computational studies, no consensus has been reached on the question of whether or not H3O+ and/or OH- prefer to be at the water surface or in the bulk. Here we report a molecular dynamics simulation study of the bulk vs. interfacial behavior of H3O+ and OH- that employs forces derived from density functional theory with a generalized gradient approximation exchangecorrelation functional (specifically, BLYP) and empirical dispersion corrections. We computed the potential of mean force (PMF) for H3O+ as a function of the position of the ion in a 215-molecule water slab. The PMF is flat, suggesting that H3O+ has equal propensity for the air-water interface and the bulk. We compare the PMF for H3O+ to our previously computed PMF for OH- adsorption, which contains a shallow minimum at the interface, and we explore how differences in solvation of each ion at the interface vs. the bulk are connected with interfacial propensity. We find that the solvation shell of H3O+ is only slightly dependent on its position in the water slab, while OH- partially desolvates as it approaches the interface, and we examine how this difference in solvation behavior is manifested in the electronic structure and chemistry of the two ions. DJT was supported by National Science Foundation grant CHE-0909227. CJM was supported by the U.S. Department of Energy‘s (DOE) Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences. Pacific Northwest National Laboratory (PNNL) is operated for the Department of Energy by Battelle. The potential of mean force required resources of the Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DEAC05-00OR22725. The remaining simulations

  6. Effect of nanoscale patterned interfacial roughness on interfacial toughness.

    SciTech Connect

    Zimmerman, Jonathan A.; Moody, Neville Reid; Mook, William M.; Kennedy, Marian S.; Bahr, David F.; Zhou, Xiao Wang; Reedy, Earl David, Jr.

    2007-09-01

    The performance and the reliability of many devices are controlled by interfaces between thin films. In this study we investigated the use of patterned, nanoscale interfacial roughness as a way to increase the apparent interfacial toughness of brittle, thin-film material systems. The experimental portion of the study measured the interfacial toughness of a number of interfaces with nanoscale roughness. This included a silicon interface with a rectangular-toothed pattern of 60-nm wide by 90-nm deep channels fabricated using nanoimprint lithography techniques. Detailed finite element simulations were used to investigate the nature of interfacial crack growth when the interface is patterned. These simulations examined how geometric and material parameter choices affect the apparent toughness. Atomistic simulations were also performed with the aim of identifying possible modifications to the interfacial separation models currently used in nanoscale, finite element fracture analyses. The fundamental nature of atomistic traction separation for mixed mode loadings was investigated.

  7. Does colloid shape affect detachment of colloids by a moving air-water interface?

    PubMed

    Aramrak, Surachet; Flury, Markus; Harsh, James B; Zollars, Richard L; Davis, Howard P

    2013-05-14

    Air-water interfaces interact strongly with colloidal particles by capillary forces. The magnitude of the interaction force depends on, among other things, the particle shape. Here, we investigate the effects of particle shape on colloid detachment by a moving air-water interface. We used hydrophilic polystyrene colloids with four different shapes (spheres, barrels, rods, and oblong disks), but otherwise identical surface properties. The nonspherical shapes were created by stretching spherical microspheres on a film of polyvinyl alcohol (PVA). The colloids were then deposited onto the inner surface of a glass channel. An air bubble was introduced into the channel and passed through, thereby generating a receding followed by an advancing air-water interface. The detachment of colloids by the air-water interfaces was visualized with a confocal microscope, quantified by image analysis, and analyzed statistically to determine significant differences. For all colloid shapes, the advancing air-water interface caused pronounced colloid detachment (>63%), whereas the receding interface was ineffective in colloid detachment (<1.5%). Among the different colloid shapes, the barrels were most readily removed (94%) by the advancing interface, followed by the spheres and oblong disks (80%) and the rods (63%). Colloid detachment was significantly affected by colloid shape. The presence of an edge, as it occurs in a barrel-shaped colloid, promoted colloid detachment because the air-water interface is being pinned at the edge of the colloid. This suggests that the magnitude of colloid mobilization and transport in porous media is underestimated for edged particles and overestimated for rodlike particles when a sphere is used as a model colloid.

  8. Large-scale recrystallization of the S-layer of Bacillus coagulans E38-66 at the air/water interface and on lipid films.

    PubMed Central

    Pum, D; Weinhandl, M; Hödl, C; Sleytr, U B

    1993-01-01

    S-layer protein isolated from Bacillus coagulans E38-66 could be recrystallized into large-scale coherent monolayers at an air/water interface and on phospholipid films spread on a Langmuir-Blodgett trough. Because of the asymmetry in the physiochemical surface properties of the S-layer protein, the subunits were associated with their more hydrophobic outer face with the air/water interface and oriented with their negatively charged inner face to the zwitterionic head groups of the dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylethanolamine (DPPE) monolayer films. The dynamic crystal growth at both types of interfaces was first initiated at several distant nucleation points. The individual monocrystalline areas grew isotropically in all directions until the front edge of neighboring crystals was met. The recrystallized S-layer protein and the S-layer-DPPE layer could be chemically cross-linked from the subphase with glutaraldehyde. Images PMID:8478338

  9. The interaction of eugenol with cell membrane models at the air-water interface is modulated by the lipid monolayer composition.

    PubMed

    Gonçalves, Giulia E G; de Souza, Fernanda S; Lago, João Henrique G; Caseli, Luciano

    2015-12-01

    Eugenol, a natural phenylpropanoid derivative with possible action in biological surfaces as microbicide, anesthetic and antioxidant, was incorporated in lipid monolayers of selected lipids at the air-water interface, representing cell membrane models. Interaction of eugenol with the lipids dipalmitoylphosphatidylcholine (DPPC), dioctadecyldimethylammonium bromide (DODAB), and dipalmitoylphosphatidylserine (DPPS) could be inferred by means of surface pressure-area isotherms and Polarization-Modulation Reflection-Absorption Spectroscopy. The interaction showed different effects on the different lipids. A higher monolayer expansion was observed for DPPS and DODAB, while more significant effects on the polar groups of the lipids were observed for DPPS and DPPC. These results pointed to the fact that the interaction of eugenol with lipid monolayers at the air-water interface is modulated by the lipid composition, which may be important to comprehend at the molecular level the interaction of this drug with biological surfaces.

  10. Direct impact of nonequilibrium aggregates on the structure and morphology of Pdadmac/SDS layers at the air/water interface.

    PubMed

    Campbell, Richard A; Yanez Arteta, Marianna; Angus-Smyth, Anna; Nylander, Tommy; Noskov, Boris A; Varga, Imre

    2014-07-29

    We discuss different nonequilibrium mechanisms by which bulk aggregates directly modify, and can even control, the interfacial structure and morphology of an oppositely charged polyelectrolyte/surfactant (P/S) mixture. Samples are categorized at the air/water interface with respect to the dynamic changes in the bulk phase behavior, the bulk composition, and the sample history using complementary surface-sensitive techniques. First, we show that bulk aggregates can spontaneously interact with the adsorption layer and are retained in it and that this process occurs most readily for positively charged aggregates with an expanded structure. In this case, key nonequilibrium issues of aggregate dissociation and spreading of surface-active material at the interface have a marked influence on the macroscopic interfacial properties. In a second distinct mechanism, aggregates inherently become trapped at the interface during its creation and lateral flocculation occurs. This irreversible process is most pronounced for aggregates with the lowest charge. A third mechanism involves the deposition of aggregates at interfaces due to their transport under gravity. The specificity of this process at an interface depends on its location and is mediated by density effects in the bulk. The prevalence of each mechanism critically depends on a number of different factors, which are outlined systematically here for the first time. This study highlights the sheer complexity by which aggregates can directly impact the interfacial properties of a P/S mixture. Our findings offer scope for understanding seemingly mysterious irreproducible effects which can compromise the performance of formulations in wide-ranging applications from foams to emulsions and lubricants.

  11. Surface adsorption of oppositely charged C14TAB-PAMPS mixtures at the air/water interface and the impact on foam film stability.

    PubMed

    Fauser, Heiko; von Klitzing, Regine; Campbell, Richard A

    2015-01-01

    We have studied the oppositely charged polyelectrolyte/surfactant mixture of poly(acrylamidomethylpropanesulfonate) sodium salt (PAMPS) and tetradecyl trimethylammonium bromide (C14TAB) using a combination of neutron reflectivity and ellipsometry measurements. The interfacial composition was determined using three different analysis methods involving the two techniques for the first time. The bulk surfactant concentration was fixed at a modest value while the bulk polyelectrolyte concentration was varied over a wide range. We reveal complex changes in the surface adsorption behavior. Mixtures with low bulk PAMPS concentrations result in the components interacting synergistically in charge neutral layers at the air/water interface. At the bulk composition where PAMPS and C14TAB are mixed in an equimolar charge ratio in the bulk, we observe a dramatic drop in the surfactant surface excess to leave a large excess of polyelectrolyte at the interface, which we infer to have loops in its interfacial structure. Further increase of the bulk PAMPS concentration leads to a more pronounced depletion of material from the surface. Mixtures containing a large excess of PAMPS in the bulk showed enhanced adsorption, which is attributed to the large increase in total ionic strength of the system and screening of the surfactant headgroup charges. The data are compared to our former results on PAMPS/C14TAB mixtures [Kristen et al. J. Phys. Chem. B, 2009, 23, 7986]. A peak in the surface tension is rationalized in terms of the changing surface adsorption and, unlike in more concentrated systems, is unrelated to bulk precipitation. Also, a comparison between the determined interfacial composition with zeta potential and foam film stability data shows that the highest film stability occurs when there is enhanced synergistic adsorption of both components at the interface due to charge screening when the total ionic strength of the system is highest. The additional contribution to the

  12. Surface pressure and elasticity of hydrophobin HFBII layers on the air-water interface: rheology versus structure detected by AFM imaging.

    PubMed

    Stanimirova, Rumyana D; Gurkov, Theodor D; Kralchevsky, Peter A; Balashev, Konstantin T; Stoyanov, Simeon D; Pelan, Eddie G

    2013-05-21

    Here, we combine experiments with Langmuir trough and atomic force microscopy (AFM) to investigate the reasons for the special properties of layers from the protein HFBII hydrophobin spread on the air-water interface. The hydrophobin interfacial layers possess the highest surface dilatational and shear elastic moduli among all investigated proteins. The AFM images show that the spread HFBII layers are rather inhomogeneous, (i.e., they contain voids, monolayer and multilayer domains). A continuous compression of the layer leads to filling the voids and transformation of a part of the monolayer into a trilayer. The trilayer appears in the form of large surface domains, which can be formed by folding and subduction of parts from the initial monolayer. The trilayer appears also in the form of numerous submicrometer spots, which can be obtained by forcing protein molecules out of the monolayer and their self-assembly into adjacent pimples. Such structures are formed because not only the hydrophobic parts, but also the hydrophilic parts of the HFBII molecules can adhere to each other in the water medium. If a hydrophobin layer is subjected to oscillations, its elasticity considerably increases, up to 500 mN/m, which can be explained with compaction. The relaxation of the layer's tension after expansion or compression follows the same relatively simple law, which refers to two-dimensional diffusion of protein aggregates within the layer. The characteristic diffusion time after compression is longer than after expansion, which can be explained with the impedence of diffusion in the more compact interfacial layer. The results shed light on the relation between the mesoscopic structure of hydrophobin interfacial layers and their unique mechanical properties that find applications for the production of foams and emulsions of extraordinary stability; for the immobilization of functional molecules at surfaces, and as coating agents for surface modification.

  13. Gas exchange rates across the sediment-water and air-water interfaces in south San Francisco Bay

    USGS Publications Warehouse

    Hartman, Blayne; Hammond, Douglas E.

    1984-01-01

    Radon 222 concentrations in the water and sedimentary columns and radon exchange rates across the sediment-water and air-water interfaces have been measured in a section of south San Francisco Bay. Two independent methods have been used to determine sediment-water exchange rates, and the annual averages of these methods agree within the uncertainty of the determinations, about 20%. The annual average of benthic fluxes from shoal areas is nearly a factor of 2 greater than fluxes from the channel areas. Fluxes from the shoal and channel areas exceed those expected from simple molecular diffusion by factors of 4 and 2, respectively, apparently due to macrofaunal irrigation. Values of the gas transfer coefficient for radon exchange across the air-water interface were determined by constructing a radon mass balance for the water column and by direct measurement using floating chambers. The chamber method appears to yield results which are too high. Transfer coefficients computed using the mass balance method range from 0.4 m/day to 1.8 m/day, with a 6-year average of 1.0 m/day. Gas exchange is linearly dependent upon wind speed over a wind speed range of 3.2–6.4 m/s, but shows no dependence upon current velocity. Gas transfer coefficients predicted from an empirical relationship between gas exchange rates and wind speed observed in lakes and the oceans are within 30% of the coefficients determined from the radon mass balance and are considerably more accurate than coefficients predicted from theoretical gas exchange models.

  14. Charge and pressure-tuned surface patterning of surfactant-encapsulated polyoxometalate complexes at the air-water interface.

    PubMed

    Xu, Miao; Li, Haolong; Zhang, Liying; Wang, Yizhan; Yuan, Yuan; Zhang, Jianming; Wu, Lixin

    2012-10-16

    In this paper, four organic-inorganic hybrid complexes were prepared using a cationic surfactant dimethyldioctadecylammonium (DODA) to replace the counter cations of four Keggin-type polyoxometalate (POM) clusters with gradually increased negative charges, PW(12)O(40)(3-), SiW(12)O(40)(4-), BW(12)O(40)(5-), and CoW(12)O(40)(6-). The formed surfactant-encapsulated POM (SEP) complexes showed typical amphiphilic properties and can be spread onto the air-water interface to form Langmuir monolayers. The interfacial behavior of the SEP monolayer films was systemically studied by multiple in situ and ex situ characterization methods including Brewster angle microscopy (BAM), atomic force microscopy (AFM), reflection-absorption infrared (RAIR), and X-ray photoelectron spectroscopy (XPS). We found that the increasing alkyl chain density of SEPs leads to an enhanced stability and a higher collapse pressure of SEP Langmuir monolayers. Moreover, a second layer evolved as patterns from the initial monolayers of all the SEPs, when the surface pressures approached the collapse values. The rational combination of alkyl chain density and surface pressure can precisely control the size and the morphology of SEP patterns transforming from disk-like to leaf-like structures on a micrometer scale. The pattern formation was demonstrated to be driven by the self-optimized surface energy of SEP monolayers. This finding can direct a new strategy for the fabrication of POM-hybrid films with controllable patterns, which should be instructive for designing POM-based thin film devices. PMID:22991980

  15. Charge and pressure-tuned surface patterning of surfactant-encapsulated polyoxometalate complexes at the air-water interface.

    PubMed

    Xu, Miao; Li, Haolong; Zhang, Liying; Wang, Yizhan; Yuan, Yuan; Zhang, Jianming; Wu, Lixin

    2012-10-16

    In this paper, four organic-inorganic hybrid complexes were prepared using a cationic surfactant dimethyldioctadecylammonium (DODA) to replace the counter cations of four Keggin-type polyoxometalate (POM) clusters with gradually increased negative charges, PW(12)O(40)(3-), SiW(12)O(40)(4-), BW(12)O(40)(5-), and CoW(12)O(40)(6-). The formed surfactant-encapsulated POM (SEP) complexes showed typical amphiphilic properties and can be spread onto the air-water interface to form Langmuir monolayers. The interfacial behavior of the SEP monolayer films was systemically studied by multiple in situ and ex situ characterization methods including Brewster angle microscopy (BAM), atomic force microscopy (AFM), reflection-absorption infrared (RAIR), and X-ray photoelectron spectroscopy (XPS). We found that the increasing alkyl chain density of SEPs leads to an enhanced stability and a higher collapse pressure of SEP Langmuir monolayers. Moreover, a second layer evolved as patterns from the initial monolayers of all the SEPs, when the surface pressures approached the collapse values. The rational combination of alkyl chain density and surface pressure can precisely control the size and the morphology of SEP patterns transforming from disk-like to leaf-like structures on a micrometer scale. The pattern formation was demonstrated to be driven by the self-optimized surface energy of SEP monolayers. This finding can direct a new strategy for the fabrication of POM-hybrid films with controllable patterns, which should be instructive for designing POM-based thin film devices.

  16. Langmuir nanoarchitectonics: one-touch fabrication of regularly sized nanodisks at the air-water interface.

    PubMed

    Mori, Taizo; Sakakibara, Keita; Endo, Hiroshi; Akada, Misaho; Okamoto, Ken; Shundo, Atsuomi; Lee, Michael V; Ji, Qingmin; Fujisawa, Takuya; Oka, Kenichiro; Matsumoto, Mutsuyoshi; Sakai, Hideki; Abe, Masahiko; Hill, Jonathan P; Ariga, Katsuhiko

    2013-06-18

    In this article, we propose a novel methodology for the formation of monodisperse regularly sized disks of several nanometer thickness and with diameters of less than 100 nm using Langmuir monolayers as fabrication media. An amphiphilic triimide, tri-n-dodecylmellitic triimide (1), was spread as a monolayer at the air-water interface with a water-soluble macrocyclic oligoamine, 1,4,7,10-tetraazacyclododecane (cyclen), in the subphase. The imide moieties of 1 act as hydrogen bond acceptors and can interact weakly with the secondary amine moieties of cyclen as hydrogen bond donors. The monolayer behavior of 1 was investigated through π-A isotherm measurements and Brewster angle microscopy (BAM). The presence of cyclen in the subphase significantly shifted isotherms and induced the formation of starfish-like microstructures. Transferred monolayers on solid supports were analyzed by reflection absorption FT-IR (FT-IR-RAS) spectroscopy and atomic force microscopy (AFM). The Langmuir monolayer transferred onto freshly cleaved mica by a surface touching (i.e., Langmuir-Schaefer) method contained disk-shaped objects with a defined height of ca. 3 nm and tunable diameter in the tens of nanometers range. Several structural parameters such as the disk height, molecular aggregation numbers in disk units, and 2D disk density per unit surface area are further discussed on the basis of AFM observations together with aggregate structure estimation and thermodynamic calculations. It should be emphasized that these well-defined structures are produced through simple routine procedures such as solution spreading, mechanical compression, and touching a substrate at the surface. The controlled formation of defined nanostructures through easy macroscopic processes should lead to unique approaches for economical, energy-efficient nanofabrication.

  17. More About Measuring Interfacial Tension Between Liquids

    NASA Technical Reports Server (NTRS)

    Rashidnia, Nasser; Balasubramaniam, R.; Del Signore, David M.

    1995-01-01

    Report presents additional discussion of technique for measuring interfacial tension between two immiscible liquids. Technique described in "Measuring Interfacial Tension Between Immiscible Liquids" (LEW-15855).

  18. Specific effects of Ca(2+) ions and molecular structure of β-lactoglobulin interfacial layers that drive macroscopic foam stability.

    PubMed

    Braunschweig, Björn; Schulze-Zachau, Felix; Nagel, Eva; Engelhardt, Kathrin; Stoyanov, Stefan; Gochev, Georgi; Khristov, Khr; Mileva, Elena; Exerowa, Dotchi; Miller, Reinhard; Peukert, Wolfgang

    2016-07-01

    β-Lactoglobulin (BLG) adsorption layers at air-water interfaces were studied in situ with vibrational sum-frequency generation (SFG), tensiometry, surface dilatational rheology and ellipsometry as a function of bulk Ca(2+) concentration. The relation between the interfacial molecular structure of adsorbed BLG and the interactions with the supporting electrolyte is additionally addressed on higher length scales along the foam hierarchy - from the ubiquitous air-water interface through thin foam films to macroscopic foam. For concentrations <1 mM, a strong decrease in SFG intensity from O-H stretching bands and a slight increase in layer thickness and surface pressure are observed. A further increase in Ca(2+) concentrations above 1 mM causes an apparent change in the polarity of aromatic C-H stretching vibrations from interfacial BLG which we associate to a charge reversal at the interface. Foam film measurements show formation of common black films at Ca(2+) concentrations above 1 mM due to considerable decrease of the stabilizing electrostatic disjoining pressure. These observations also correlate with a minimum in macroscopic foam stability. For concentrations >30 mM Ca(2+), micrographs of foam films show clear signatures of aggregates which tend to increase the stability of foam films. Here, the interfacial layers have a higher surface dilatational elasticity. In fact, macroscopic foams formed from BLG dilutions with high Ca(2+) concentrations where aggregates and interfacial layers with higher elasticity are found, showed the highest stability with much smaller bubble sizes.

  19. Molecular modeling directed by an interfacial test apparatus for the evaluation of protein and polymer ingredient function in situ.

    PubMed

    Collins, George W; Patel, Avani; Dilley, Alan; Sarker, Dipak K

    2008-05-28

    A simplified apparatus is described that measures the damping of a suspended measuring device. The movement of the device (bob) is damped by the properties of the air-water surface adsorbed material. Its value lies in describing the surface chemomechanical properties of ingredients and excipients used in food, nutraceutical, cosmetic (cosmeceutical), and natural drug-food product formulations that traverse the food sciences. Two surfactants, two food and drug-grade polymers, and five naturally occurring food and serum proteins were tested and used to estimate and model interfacial viscoelasticity. Equilibration times of >15 min were found to give sufficiently stable interfaces for routine assessment. The viscoelasticity of the air-water interface was estimated with reference to model solutions. These model solutions and associated self-assembled interfacial nanostructured adsorbed layers were fabricated using a preliminary screening process with the aid of a specialized foaming apparatus ( C(300) values), surface tension measurements (23-73 mN/m), and referential surface shear and dilation experiments. The viscoelasticity measured as a percentage of surface damping ( D) of a pendulum was found to range from 1.0 to 22.4% across the samples tested, and this represented interfacial viscosities in the range of 0-4630 microNs/m. The technique can distinguish between interfacial compositions and positions itself as an easily accessible valuable addition to tensiometric and analytical biochemistry-based techniques.

  20. The Equilibria of Diosgenin-Phosphatidylcholine and Diosgenin-Cholesterol in Monolayers at the Air/Water Interface.

    PubMed

    Janicka, Katarzyna; Jastrzebska, Izabella; Petelska, Aneta Dorota

    2016-08-01

    Diosgenin (Dio) has shown many treatment properties, but the most important property is cytotoxic activity in cancer cells. In this study, we investigated monolayers of Dio, cholesterol (Ch), and phosphatidylcholine (PC) at the air/water interface. The measurements were carried with a Langmuir Teflon trough and a Nima 9000 tensiometer program. The surface tension values of pure and mixed monolayers were used to calculate π-A isotherms and determine molecular surface areas. We were able to demonstrate the formation of complexes between Dio and PC and Dio and Ch molecules also. We considered the equilibrium between individual components and the formed complexes. In addition, we established that diosgenin and the lipids formed highly stable 1:1 complexes. PMID:27350149

  1. Supramolecular 1-D polymerization of DNA origami through a dynamic process at the 2-dimensionally confined air-water interface.

    PubMed

    Yonamine, Yusuke; Cervantes-Salguero, Keitel; Minami, Kosuke; Kawamata, Ibuki; Nakanishi, Waka; Hill, Jonathan P; Murata, Satoshi; Ariga, Katsuhiko

    2016-05-14

    In this study, a Langmuir-Blodgett (LB) system has been utilized for the regulation of polymerization of a DNA origami structure at the air-water interface as a two-dimensionally confined medium, which enables dynamic condensation of DNA origami units through variation of the film area at the macroscopic level (ca. 10-100 cm(2)). DNA origami sheets were conjugated with a cationic lipid (dioctadecyldimethylammonium bromide, 2C18N(+)) by electrostatic interaction and the corresponding LB-film was prepared. By applying dynamic pressure variation through compression-expansion processes, the lipid-modified DNA origami sheets underwent anisotropic polymerization forming a one-dimensionally assembled belt-shaped structure of a high aspect ratio although the thickness of the polymerized DNA origami was maintained at the unimolecular level. This approach opens up a new field of mechanical induction of the self-assembly of DNA origami structures. PMID:27091668

  2. Effects of flow on insulin fibril formation at an air/water interface

    NASA Astrophysics Data System (ADS)

    Posada, David; Heldt, Caryn; Sorci, Mirco; Belfort, Georges; Hirsa, Amir

    2009-11-01

    The amyloid fibril formation process, which is implicated in several diseases such as Alzheimer's and Huntington's, is characterized by the conversion of monomers to oligomers and then to fibrils. Besides well-studied factors such as pH, temperature and concentration, the kinetics of this process are significantly influenced by the presence of solid or fluid interfaces and by flow. By studying the nucleation and growth of a model system (insulin fibrils) in a well-defined flow field with an air/water interface, we can identify the flow conditions that impact protein aggregation kinetics both in the bulk solution and at the air/water interface. The present flow system (deep-channel surface viscometer) consists of an annular region bounded by stationary inner and outer cylinders, an air/water interface, and a floor driven at constant rotation. We show the effects of Reynolds number on the kinetics of the fibrillation process both in the bulk solution and at the air/water interface, as well as on the structure of the resultant amyloid aggregates.

  3. THE EFFECT OF SALINITY ON RATES OF ELEMENTAL MERCURY AIR/WATER EXCHANGE

    EPA Science Inventory

    The U.S. EPA laboratory in Athens, Georgia i spursuing the goal of developing a model for describing toxicant vapor phase air/water exchange under all relevant environmental conditions. To date, the two-layer exchange model (suitable for low wind speed conditions) has been modif...

  4. Physicochemical Study of Viral Nanoparticles at the Air/Water Interface.

    PubMed

    Torres-Salgado, Jose F; Comas-Garcia, Mauricio; Villagrana-Escareño, Maria V; Durán-Meza, Ana L; Ruiz-García, Jaime; Cadena-Nava, Ruben D

    2016-07-01

    The assembly of most single-stranded RNA (ssRNA) viruses into icosahedral nucleocapsids is a spontaneous process driven by protein-protein and RNA-protein interactions. The precise nature of these interactions results in the assembly of extremely monodisperse and structurally indistinguishable nucleocapsids. In this work, by using a ssRNA plant virus (cowpea chlorotic mottle virus [CCMV]) as a charged nanoparticle we show that the diffusion of these nanoparticles from the bulk solution to the air/water interface is an irreversible adsorption process. By using the Langmuir technique, we measured the diffusion and adsorption of viral nucleocapsids at the air/water interface at different pH conditions. The pH changes, and therefore in the net surface charge of the virions, have a great influence in the diffusion rate from the bulk solution to the air/water interface. Moreover, assembly of mesoscopic and microscopic viral aggregates at this interface depends on the net surface charge of the virions and the surface pressure. By using Brewster's angle microscopy we characterized these structures at the interface. Most common structures observed were clusters of virions and soap-frothlike micron-size structures. Furthermore, the CCMV films were compressed to form monolayers and multilayers from moderate to high surface pressures, respectively. After transferring the films from the air/water interface onto mica by using the Langmuir-Blodgett technique, their morphology was characterized by atomic force microscopy. These viral monolayers showed closed-packing nano- and microscopic arrangements.

  5. The behavior of NaOH at the air-water interface, a computational study

    SciTech Connect

    Wick, Collin D.; Dang, Liem X.

    2010-07-14

    Molecular dynamics simulations with a polarizable multi-state empirical valence bond model were carried out to investigate NaOH dissociation and pairing in water bulk and at the air-water interface. It was found that NaOH readily dissociates in the bulk, and the effect of the air-water interface on NaOH dissociation is fairly minor. Also, NaOH complexes were found to be strongly repelled from the air-water interface, which is consistent with surface tension measurements. At the same time, a very strong preference for the hydroxide anion to be oriented towards the air was found that persisted a few angstroms towards the liquid from the Gibbs dividing surface of the air-water interface. This was due to a preference for the hydroxide anion to have its hydrogen pointing towards the air, and the fact that the sodium ion was more likely to be found near the hydroxide oxygen than hydrogen. As a consequence, the simulation results show that surfaces of NaOH solutions should be negatively charged, in agreement with experimental observations, but also that the hydroxide has little surface affinity. This provides the possibility that the surface of water can be devoid of hydroxide anions, but still have a strong negative charge. This work was supported by the US Department of Energy Basic Energy Sciences' Chemical Sciences, Geosciences & Biosciences Division. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

  6. It's Alive!: Students Observe Air-Water Interface Samples Rich with Organisms

    ERIC Educational Resources Information Center

    Avant, Thomas

    2002-01-01

    This article describes an experiment, designed by Cindy Henk, manager of the Socolofsky Microscopy Center at Louisiana State University (LSU), that involved collecting and viewing microorganisms in the air-water interface. The experiment was participated by Leesville High School microbiology students. The students found that the air-water…

  7. Mesoscale Interfacial Dynamics in Magnetoelectric Nanocomposites

    SciTech Connect

    Shashank, Priya

    2009-12-14

    Biphasic composites are the key towards achieving enhanced magnetoelectric response. In order understand the control behavior of the composites and resultant symmetry of the multifunctional product tensors, we need to synthesized model material systems with the following features (i) interface formation through either deposition control or natural decomposition; (ii) a very high interphase-interfacial area, to maximize the ME coupling; and (iii) an equilibrium phase distribution and morphology, resulting in preferred crystallographic orientation relations between phases across the interphase-interfacial boundaries. This thought process guided the experimental evolution in this program. We initiated the research with the co-fired composites approach and then moved on to the thin film laminates deposited through the rf-magnetron sputtering and pulsed laser deposition process

  8. Insect flight on fluid interfaces: a chaotic interfacial oscillator

    NASA Astrophysics Data System (ADS)

    Mukundarajan, Haripriya; Prakash, Manu

    2013-11-01

    Flight is critical to the dominance of insect species on our planet, with about 98 percent of insect species having wings. How complex flight control systems developed in insects is unknown, and arboreal or aquatic origins have been hypothesized. We examine the biomechanics of aquatic origins of flight. We recently reported discovery of a novel mode of ``2D flight'' in Galerucella beetles, which skim along an air-water interface using flapping wing flight. This unique flight mode is characterized by a balance between capillary forces from the interface and biomechanical forces exerted by the flapping wings. Complex interactions on the fluid interface form capillary wave trains behind the insect, and produce vertical oscillations at the surface due to non-linear forces arising from deformation of the fluid meniscus. We present both experimental observations of 2D flight kinematics and a dynamic model explaining the observed phenomena. Careful examination of this interaction predicts the chaotic nature of interfacial flight and takeoff from the interface into airborne flight. The role of wingbeat frequency, stroke plane angle and body angle in determining transition between interfacial and fully airborne flight is highlighted, shedding light on the aquatic theory of flight evolution.

  9. Detachment of colloids from a solid surface by a moving air-water interface.

    PubMed

    Sharma, Prabhakar; Flury, Markus; Zhou, Jun

    2008-10-01

    Colloid attachment to liquid-gas interfaces is an important process used in industrial applications to separate suspended colloids from the fluid phase. Moving gas bubbles can also be used to remove colloidal dust from surfaces. Similarly, moving liquid-gas interfaces lead to colloid mobilization in the natural subsurface environment, such as in soils and sediments. The objective of this study was to quantify the effect of moving air-water interfaces on the detachment of colloids deposited on an air-dried glass surface, as a function of colloidal properties and interface velocity. We selected four types of polystyrene colloids (positive and negative surface charge, hydrophilic and hydrophobic). The colloids were deposited on clean microscope glass slides using a flow-through deposition chamber. Air-water interfaces were passed over the colloid-deposited glass slides, and we varied the number of passages and the interface velocity. The amounts of colloids deposited on the glass slides were visualized using confocal laser scanning microscopy and quantified by image analysis. Our results showed that colloids attached under unfavorable conditions were removed in significantly greater amounts than those attached under favorable conditions. Hydrophobic colloids were detached more than hydrophilic colloids. The effect of the air-water interface on colloid removal was most pronounced for the first two passages of the air-water interface. Subsequent passages of air-water interfaces over the colloid-deposited glass slides did not cause significant additional colloid removal. Increasing interface velocity led to decreased colloid removal. The force balances, calculated from theory, supported the experimental findings, and highlight the dominance of detachment forces (surface tension forces) over the attachment forces (DLVO forces).

  10. Charge dependent condensation of macro-ions at air-water interfaces

    NASA Astrophysics Data System (ADS)

    Bera, Mrinal; Antonio, Mark

    2015-03-01

    Ordering of ions at and near air-water interfaces is a century old problem for researchers and has implications on a host of physical, chemical and biological processes. The dynamic nature of water surface and the surface fluctuations created by thermally excited capillary waves have always limited measurement of near surface ionic-distributions. We demonstrate that this limitation can be overcome by using macro-ions of sizes larger than the capillary wave roughness ~3Å. Our attempts to measure distributions of inorganic macro-ions in the form of Keggin heteropolyanions (HPAs) of sizes ~10Å have unraveled novel charge-dependent condensation of macro-ions beneath air-water interfaces. Our results demonstrate that HPAs with -3 charges condense readily beneath air-water interfaces. This is in contrast to the absence of surface preference for HPAs with -4 charges. The similarity of HPA-HPA separations near air-water interfaces and in bulk crystal structures suggests the presence of the planar Zundel ions (H5O2+), which interact with HPAs and the water surface to facilitate the charge dependent condensation beneath the air-water interfaces.This work and the use of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility at Argonne National Laboratory, is based upon work supported by the U.S. DOE, Office of Science, Office of Basic Energy Science, Division of Chemical Sciences, Biosciences and Geosciences, under contract No DE-AC02-06CH11357.

  11. Modeling interfacial fracture in Sierra.

    SciTech Connect

    Brown, Arthur A.; Ohashi, Yuki; Lu, Wei-Yang; Nelson, Stacy A. C.; Foulk, James W.,; Reedy, Earl David,; Austin, Kevin N.; Margolis, Stephen B.

    2013-09-01

    This report summarizes computational efforts to model interfacial fracture using cohesive zone models in the SIERRA/SolidMechanics (SIERRA/SM) finite element code. Cohesive surface elements were used to model crack initiation and propagation along predefined paths. Mesh convergence was observed with SIERRA/SM for numerous geometries. As the funding for this project came from the Advanced Simulation and Computing Verification and Validation (ASC V&V) focus area, considerable effort was spent performing verification and validation. Code verification was performed to compare code predictions to analytical solutions for simple three-element simulations as well as a higher-fidelity simulation of a double-cantilever beam. Parameter identification was conducted with Dakota using experimental results on asymmetric double-cantilever beam (ADCB) and end-notched-flexure (ENF) experiments conducted under Campaign-6 funding. Discretization convergence studies were also performed with respect to mesh size and time step and an optimization study was completed for mode II delamination using the ENF geometry. Throughout this verification process, numerous SIERRA/SM bugs were found and reported, all of which have been fixed, leading to over a 10-fold increase in convergence rates. Finally, mixed-mode flexure experiments were performed for validation. One of the unexplained issues encountered was material property variability for ostensibly the same composite material. Since the variability is not fully understood, it is difficult to accurately assess uncertainty when performing predictions.

  12. High temperature interfacial superconductivity

    SciTech Connect

    Bozovic, Ivan; Logvenov, Gennady; Gozar, Adrian Mihai

    2012-06-19

    High-temperature superconductivity confined to nanometer-scale interfaces has been a long standing goal because of potential applications in electronic devices. The spontaneous formation of a superconducting interface in bilayers consisting of an insulator (La.sub.2CuO.sub.4) and a metal (La.sub.1-xSr.sub.xCuO.sub.4), neither of which is superconducting per se, is described. Depending upon the layering sequence of the bilayers, T.sub.c may be either .about.15 K or .about.30 K. This highly robust phenomenon is confined to within 2-3 nm around the interface. After exposing the bilayer to ozone, T.sub.c exceeds 50 K and this enhanced superconductivity is also shown to originate from a 1 to 2 unit cell thick interfacial layer. The results demonstrate that engineering artificial heterostructures provides a novel, unconventional way to fabricate stable, quasi two-dimensional high T.sub.c phases and to significantly enhance superconducting properties in other superconductors. The superconducting interface may be implemented, for example, in SIS tunnel junctions or a SuFET.

  13. Morphological and structural characteristics of diazo dyes at the air-water interface: in situ Brewster angle microscopy and polarized UV/vis analysis.

    PubMed

    Yamaki, Sahori B; Andrade, Acácio A; Mendonça, Cléber R; Oliveira, Osvaldo N; Atvars, Teresa D Z

    2005-03-15

    A morphological analysis is presented for Langmuir films of the diazo dyes Sudan 4 (S4), Sudan 3 (S3), and Sudan red (SR), using Brewster angle microscopy. Stable nonmonomolecular structures are formed at the air-water interface denoted as a plateau in the pressure-area isotherms. Monolayer domains are evident by the contrastless image even before the pressure onset, which grow in size until it reached a condensed monolayer. This behavior resembles that of Langmuir films from simple aromatic fatty acids. Films from all the azo dyes display similar features, according to the surface potential isotherms and in situ polarized UV/vis spectroscopy except for the larger area per molecule occupied by S4 and SR. This is attributed to the presence of CH(3) groups that cause steric hindrance modifying the organization of diazo dye molecules at the air-water interface. UV/vis polarized absorption spectroscopy showed preferential orientation of S4 and S3 on the water surface, while SR molecules lie isotropically. For these three diazo dyes, film absorption was negligible at very large areas per molecule, becoming nonzero only at a critical area coinciding with the onset of surface potential. The critical area is ascribed to the formation of a H-bonded network between water molecules and diazo dye headgroups. PMID:15721920

  14. Smart nanogels at the air/water interface: structural studies by neutron reflectivity.

    PubMed

    Zielińska, Katarzyna; Sun, Huihui; Campbell, Richard A; Zarbakhsh, Ali; Resmini, Marina

    2016-03-01

    The development of effective transdermal drug delivery systems based on nanosized polymers requires a better understanding of the behaviour of such nanomaterials at interfaces. N-Isopropylacrylamide-based nanogels synthesized with different percentages of N,N'-methylenebisacrylamide as cross-linker, ranging from 10 to 30%, were characterized at physiological temperature at the air/water interface, using neutron reflectivity (NR), with isotopic contrast variation, and surface tension measurements; this allowed us to resolve the adsorbed amount and the volume fraction of nanogels at the interface. A large conformational change for the nanogels results in strong deformations at the interface. As the percentage of cross-linker incorporated in the nanogels becomes higher, more rigid matrices are obtained, although less deformed, and the amount of adsorbed nanogels is increased. The data provide the first experimental evidence of structural changes of nanogels as a function of the degree of cross-linking at the air/water interface. PMID:26697736

  15. Structure of phospholipid monolayers containing poly(ethylene glycol) lipids at the air-water interface

    SciTech Connect

    Majewski, J.; Smith, G.S.; Kuhl, T.L.; Israelachvili, J.N.; Gerstenberg, M.C.

    1997-04-17

    The density distribution of a lipid monolayer at the air-water interface mixed with varying amounts of lipid with poly(ethylene glycol)polymer headgroups (polymer-lipid or PEG-lipid) was measured using neutron reflectometry. The structure of the monolayer at the interface was greatly perturbed by the presence of the bulky polymer-lipid headgroups resulting in a large increase in the thickness of the headgroup region normal to the interface and a systematic roughening of the interface with increasing polymer-lipid content. These results show how bulky hydrophilic moieties cause significant deformations and out-of-place protrusions of phospholipid monolayers and presumably bilayers, vesicles and biological membranes. In terms of polymer physics, very short polymer chains tethered to the air-water interface follow scaling behavior with a mushroom to brush transition with increasing polymer grafting density. 34 refs., 9 figs., 1 tab.

  16. WETAIR: A computer code for calculating thermodynamic and transport properties of air-water mixtures

    NASA Technical Reports Server (NTRS)

    Fessler, T. E.

    1979-01-01

    A computer program subroutine, WETAIR, was developed to calculate the thermodynamic and transport properties of air water mixtures. It determines the thermodynamic state from assigned values of temperature and density, pressure and density, temperature and pressure, pressure and entropy, or pressure and enthalpy. The WETAIR calculates the properties of dry air and water (steam) by interpolating to obtain values from property tables. Then it uses simple mixing laws to calculate the properties of air water mixtures. Properties of mixtures with water contents below 40 percent (by mass) can be calculated at temperatures from 273.2 to 1497 K and pressures to 450 MN/sq m. Dry air properties can be calculated at temperatures as low as 150 K. Water properties can be calculated at temperatures to 1747 K and pressures to 100 MN/sq m. The WETAIR is available in both SFTRAN and FORTRAN.

  17. Physicochemical Study of Viral Nanoparticles at the Air/Water Interface.

    PubMed

    Torres-Salgado, Jose F; Comas-Garcia, Mauricio; Villagrana-Escareño, Maria V; Durán-Meza, Ana L; Ruiz-García, Jaime; Cadena-Nava, Ruben D

    2016-07-01

    The assembly of most single-stranded RNA (ssRNA) viruses into icosahedral nucleocapsids is a spontaneous process driven by protein-protein and RNA-protein interactions. The precise nature of these interactions results in the assembly of extremely monodisperse and structurally indistinguishable nucleocapsids. In this work, by using a ssRNA plant virus (cowpea chlorotic mottle virus [CCMV]) as a charged nanoparticle we show that the diffusion of these nanoparticles from the bulk solution to the air/water interface is an irreversible adsorption process. By using the Langmuir technique, we measured the diffusion and adsorption of viral nucleocapsids at the air/water interface at different pH conditions. The pH changes, and therefore in the net surface charge of the virions, have a great influence in the diffusion rate from the bulk solution to the air/water interface. Moreover, assembly of mesoscopic and microscopic viral aggregates at this interface depends on the net surface charge of the virions and the surface pressure. By using Brewster's angle microscopy we characterized these structures at the interface. Most common structures observed were clusters of virions and soap-frothlike micron-size structures. Furthermore, the CCMV films were compressed to form monolayers and multilayers from moderate to high surface pressures, respectively. After transferring the films from the air/water interface onto mica by using the Langmuir-Blodgett technique, their morphology was characterized by atomic force microscopy. These viral monolayers showed closed-packing nano- and microscopic arrangements. PMID:26999022

  18. New Mechanistic Pathways for Criegee-Water Chemistry at the Air/Water Interface.

    PubMed

    Zhu, Chongqin; Kumar, Manoj; Zhong, Jie; Li, Lei; Francisco, Joseph S; Zeng, Xiao Cheng

    2016-09-01

    Understanding Criegee chemistry has become one of central topics in atmospheric research recently. The reaction of Criegee intermediates with gas-phase water clusters has been widely viewed as a key Criegee reaction in the troposphere. However, the effect of aerosols or clouds on Criegee chemistry has received little attention. In this work, we have investigated the reaction between the smallest Criegee intermediate, CH2OO, and water clusters in the gas phase, as well as at the air/water surface using ab initio quantum chemical calculations and adaptive buffered force quantum mechanics/molecular mechanics (QM/MM) dynamics simulations. Our simulation results show that the typical time scale for the reaction of CH2OO with water at the air/water interface is on the order of a few picoseconds, 2-3 orders of magnitude shorter than that in the gas phase. Importantly, the adbf-QM/MM dynamics simulations suggest several reaction pathways for the CH2OO + water reaction at the air/water interface, including the loop-structure-mediated mechanism and the stepwise mechanism. Contrary to the conventional gas-phase CH2OO reaction, the loop-structure is not a prerequisite for the stepwise mechanism. For the latter, a water molecule and the CH2OO at the air/water interface, upon their interaction, can result in the formation of (H3O)(+) and (OH)CH2(OO)(-). Thereafter, a hydrogen bond can be formed between (H3O)(+) and the terminal oxygen atom of (OH)CH2(OO)(-), leading to direct proton transfer and the formation of α-hydroxy methylperoxide, HOCH2OOH. The mechanistic insights obtained from this simulation study should motivate future experimental studies of the effect of water clouds on Criegee chemistry.

  19. Revised parameters for modeling the transport of PCB components across an air water interface

    SciTech Connect

    Bopp, R.F.

    1983-03-20

    A number of revisions of the data base and conceptualizations utilized in air-water transport models for PCB components are suggested. The most significant of these involves the assignment of physical chemical properties on the basis of degree of chlorination. the effect of temperature on the rate of transport is also discussed. The revised model is tested on a number of natural situations and compared with available data.

  20. New Mechanistic Pathways for Criegee-Water Chemistry at the Air/Water Interface.

    PubMed

    Zhu, Chongqin; Kumar, Manoj; Zhong, Jie; Li, Lei; Francisco, Joseph S; Zeng, Xiao Cheng

    2016-09-01

    Understanding Criegee chemistry has become one of central topics in atmospheric research recently. The reaction of Criegee intermediates with gas-phase water clusters has been widely viewed as a key Criegee reaction in the troposphere. However, the effect of aerosols or clouds on Criegee chemistry has received little attention. In this work, we have investigated the reaction between the smallest Criegee intermediate, CH2OO, and water clusters in the gas phase, as well as at the air/water surface using ab initio quantum chemical calculations and adaptive buffered force quantum mechanics/molecular mechanics (QM/MM) dynamics simulations. Our simulation results show that the typical time scale for the reaction of CH2OO with water at the air/water interface is on the order of a few picoseconds, 2-3 orders of magnitude shorter than that in the gas phase. Importantly, the adbf-QM/MM dynamics simulations suggest several reaction pathways for the CH2OO + water reaction at the air/water interface, including the loop-structure-mediated mechanism and the stepwise mechanism. Contrary to the conventional gas-phase CH2OO reaction, the loop-structure is not a prerequisite for the stepwise mechanism. For the latter, a water molecule and the CH2OO at the air/water interface, upon their interaction, can result in the formation of (H3O)(+) and (OH)CH2(OO)(-). Thereafter, a hydrogen bond can be formed between (H3O)(+) and the terminal oxygen atom of (OH)CH2(OO)(-), leading to direct proton transfer and the formation of α-hydroxy methylperoxide, HOCH2OOH. The mechanistic insights obtained from this simulation study should motivate future experimental studies of the effect of water clouds on Criegee chemistry. PMID:27509207

  1. Interfacial Micellar Structures from Novel Amphiphilic Star Polymers

    SciTech Connect

    Genson, Kirsten L.; Hoffman, Joshua; Teng, Jing; Zubarev, Eugene R.; Vaknin, David; Tsukruk, Vladimir V.

    2010-11-10

    An amphiphilic heteroarm star polymer containing 12 alternating hydrophobic/hydrophilic arms of polystyrene (PS) and poly(acrylic acid) (PAA) connected to a well-defined rigid aromatic core was studied at the air-water and the air-solid interfaces. At the air-water interface, the molecules spontaneously form pancakelike micellar aggregates which measure up to several microns in diameter and 5 nm in thickness. Upon reduction of the surface area per molecule to 7 nm2, the two-dimensional micelles merged into a dense monolayer. We suggest that confined phase separation of dissimilar polymer arms occurred upon their segregation on the opposite sides of the rigid disklike aromatic core, forcing the rigid cores to adopt a face-on orientation with respect to the interface. Upon transfer onto solid supports the PS chains face the air-film interface making it completely hydrophobic, and the PAA chains were found to collapse and form a thin flattened underlayer. This study points toward new strategies to create large 2D microstructures with facial amphiphilicity and suggests a profound influence of star molecular architecture on the self-assembly of amphiphiles at the air-water interface.

  2. Flow-induced 2D protein crystallization: characterization of the coupled interfacial and bulk flows.

    PubMed

    Young, James E; Posada, David; Lopez, Juan M; Hirsa, Amir H

    2015-05-14

    Two-dimensional crystallization of the protein streptavidin, crystallizing below a biotinylated lipid film spread on a quiescent air-water interface is a well studied phenomenon. More recently, 2D crystallization induced by a shearing interfacial flow has been observed at film surface pressures significantly lower than those required in a quiescent system. Here, we quantify the interfacial and bulk flow associated with 2D protein crystallization through numerical modeling of the flow along with a Newtonian surface model. Experiments were conducted over a wide range of conditions resulting in a state diagram delineating the flow strength required to induce crystals for various surface pressures. Through measurements of the velocity profile at the air-water interface, we found that even in the cases where crystals are formed, the macroscopic flow at the interface is well described by the Newtonian model. However, the results show that even in the absence of any protein in the system, the viscous response of the biotinylated lipid film is complicated and strongly dependent on the strength of the flow. This observation suggests that the insoluble lipid film plays a key role in flow-induced 2D protein crystallization.

  3. Effects of Temperature, Oxygen Level, Ionic Strength, and pH on the Reaction of Benzene with Hydroxyl Radicals at the Air-Water Interface in Comparison to the Bulk Aqueous Phase.

    PubMed

    Heath, Aubrey A; Valsaraj, Kalliat T

    2015-08-01

    Atmospheric aerosols (e.g., fog droplets) are complex, multiphase mediums. Depending on location, time of day, and/or air mass source, there can be considerable variability within these droplets, relating to temperature, pH, and ionic strength. Due to the droplets' inherently small size, the reactions that occur within these droplets are determined by bulk aqueous phase and air-water interfacial conditions. In this study, the reaction of benzene and hydroxyl radicals is examined kinetically in a thin-film flow-tube reactor. By varying the aqueous volume (e.g., film thickness) along the length of the reactor, both bulk and interfacial reaction rates are measured from a single system. Temperature, pH, and ionic strength are varied to model conditions typical of fog events. Oxygen-poor conditions are measured to study oxygen's overall effect on the reaction pathway. Initial rate activation energies and the bulk aqueous phase and interfacial contributions to the overall rate constant are also obtained. PMID:26158391

  4. Effects of Temperature, Oxygen Level, Ionic Strength, and pH on the Reaction of Benzene with Hydroxyl Radicals at the Air-Water Interface in Comparison to the Bulk Aqueous Phase.

    PubMed

    Heath, Aubrey A; Valsaraj, Kalliat T

    2015-08-01

    Atmospheric aerosols (e.g., fog droplets) are complex, multiphase mediums. Depending on location, time of day, and/or air mass source, there can be considerable variability within these droplets, relating to temperature, pH, and ionic strength. Due to the droplets' inherently small size, the reactions that occur within these droplets are determined by bulk aqueous phase and air-water interfacial conditions. In this study, the reaction of benzene and hydroxyl radicals is examined kinetically in a thin-film flow-tube reactor. By varying the aqueous volume (e.g., film thickness) along the length of the reactor, both bulk and interfacial reaction rates are measured from a single system. Temperature, pH, and ionic strength are varied to model conditions typical of fog events. Oxygen-poor conditions are measured to study oxygen's overall effect on the reaction pathway. Initial rate activation energies and the bulk aqueous phase and interfacial contributions to the overall rate constant are also obtained.

  5. Solvent-dependent properties of poly(vinylidene fluoride) monolayers at the air-water interface.

    PubMed

    Zhu, Huie; Matsui, Jun; Yamamoto, Shunsuke; Miyashita, Tokuji; Mitsuishi, Masaya

    2015-03-14

    The present work addresses the solvent-dependent properties of Langmuir films of poly(vinylidene fluoride) (PVDF) and amphiphilic poly(N-dodecylacrylamide) (pDDA) at different mixing ratios. After introducing pDDA nanosheets, PVDF Langmuir films obtain a tremendously enhanced modulus as well as high transfer ratios using the vertical dipping method caused by the support of the pDDA two-dimensional hydrogen bonding network. Brewster angle microscopy (BAM) was used to investigate PVDF monolayers at the air-water interface in situ. Spreading from different solvents, the PVDF molecules take completely different aggregation states at the air-water interface. The PVDF molecules aggregate to become large domains when spread from N-methyl-2-pyrrolidone (NMP). However, the volatile and low-polarity methylethyl ketone (MEK) made the PVDF molecules more dispersive on the water surface. This study also discovers a versatile crystallization control of PVDF homopolymer from complete β phase (NMP) to complete α phase (MEK) at the air-water interface, thereby eliciting useful information for further manipulation of film morphologies and film applications. PMID:25622932

  6. Demonstration of adaptive optics for mitigating laser propagation through a random air-water interface

    NASA Astrophysics Data System (ADS)

    Land, Phillip; Majumdar, Arun K.

    2016-05-01

    This paper describes a new concept of mitigating signal distortions caused by random air-water interface using an adaptive optics (AO) system. This is the first time the concept of using an AO for mitigating the effects of distortions caused mainly by a random air-water interface is presented. We have demonstrated the feasibility of correcting the distortions using AO in a laboratory water tank for investigating the propagation effects of a laser beam through an airwater interface. The AO system consisting of a fast steering mirror, deformable mirror, and a Shack-Hartmann Wavefront Sensor for mitigating surface water distortions has a unique way of stabilizing and aiming a laser onto an object underneath the water. Essentially the AO system mathematically takes the complex conjugate of the random phase caused by air-water interface allowing the laser beam to penetrate through the water by cancelling with the complex conjugates. The results show the improvement of a number of metrics including Strehl ratio, a measure of the quality of optical image formation for diffraction limited optical system. These are the first results demonstrating the feasibility of developing a new sensor system such as Laser Doppler Vibrometer (LDV) utilizing AO for mitigating surface water distortions.

  7. Interfacial force microscopy: Application to polymer surfaces

    SciTech Connect

    HOUSTON,JACK E.; WINTER,R.M.

    2000-05-16

    Scanning-probe microscopies (SPM) are presently widely used in remarkably diverse applications and, as evidenced by this symposium these techniques are rapidly expanding into the important areas of polymer surfaces and interfaces. The Atomic Force Microscope (AFM) is presently the most widely used of the scanning-probe techniques. However, the AFM's range of application suffers from an inherent mechanical instability in its deflection force sensor. The instability problem has been overcome by the development of the Interfacial Force Microscope (IFM), which utilizes a force-feedback sensor concept. In the following, the authors present several examples of polymer applications to illustrate the utility of the IFM sensor concept.

  8. Photophysical behavior in spread monolayers. Dansyl fluorescence as a probe for polarity at the air-water interface. [N-(5-(dimethylamino)naphthalene-1-sulfonyl)dihexadecylamine

    SciTech Connect

    Grieser, F.; Thistlethwaite, P.; Urquhart, R.; Patterson, L.K.

    1987-09-24

    The emission spectrum of N-(5-(dimethylamino)naphthalene-1-sulfonyl)dihexadecylamine (dansyldihexadecylamine) in monolayers at the air-water interface has been studied. In some cases sudden shifts in the dansyl emission can be correlated with particular features of the surface pressure-area isotherms. These spectral shifts can be explained in terms of a change in the conformation of the head group on the surface and with aggregation of the dansyldihexadecylamine. In other cases the dansyl emission shows a blue shift with increasing compression that can be associated with reduced head-group hydration.

  9. Charged Surfaces and Interfacial Ions.

    PubMed

    Kallay; Zalac

    2000-10-01

    Interfacial charge in a solid/liquid system is due to interactions of ions with surface sites affected by the electrostatic potential that is a consequence of their accumulation. The present theoretical approach is based on the so-called Surface Complexation Model that has several modifications known as either the 1-pK, the 2-pK, or the "MUSIC" model. These models assume different surface reactions and their equilibrium constants, taking into account electrostatic interactions. For that purpose the relationships between potentials affecting the state of interfacial ions and their surface densities need to be known, so that a certain model of the electrical interfacial layer should be introduced. The complexity of the problem results in the use of a variety of different theoretical approaches that cannot be distinguished experimentally. This article discusses several aspects of the problem, such as counterion association, structure of the electrical interfacial layer, potential-charge relationships, surface potentials, the zero charge condition, enthalpy of surface reactions, and the influence of the interfacial ionic equilibrium on the colloid stability. Copyright 2000 Academic Press. PMID:10998282

  10. Mixed layers of β-lactoglobulin and SDS at air-water interfaces with tunable intermolecular interactions.

    PubMed

    Engelhardt, Kathrin; Weichsel, Ulrike; Kraft, Elena; Segets, Doris; Peukert, Wolfgang; Braunschweig, Björn

    2014-04-17

    Mixtures of β-lactoglobulin (BLG) and sodium dodecyl sulfate (SDS) were studied at pH 3.8 and 6.7 under equilibrium conditions. At these pH conditions, BLG carries either a positive or a negative net charge, respectively, which enables tunable electrostatic interactions between anionic SDS surfactants and BLG proteins. For pH 3.8, vibrational sum-frequency generation (SFG) and ellipsometry indicate strong BLG-SDS complex formation at air-water interfaces that is caused by attractive electrostatic interactions. The latter complexes are already formed in the bulk solution which was confirmed by a thermodynamic study of BLG-SDS mixtures using isothermal titration calorimetry (ITC). For acidic conditions we determine from our ITC data an exothermal binding enthalpy of -40 kJ mol(-1). Increasing SDS/BLG molar ratios above 10 leads to a surface excess of SDS and thus to a charge reversal from a positive net charge with BLG as the dominating surface adsorbed species to a negatively charged layer with SDS as the dominating surface species. The latter is evidenced by a pronounced minimum in SFG intensities that is also accompanied by a phase change of O-H stretching bands due to a reorientation of H2O within the local electric field. This phase change which occurs at SDS/BLG molar ratio between 1 and 10 causes a polarity change in SFG intensities from BLG aromatic C-H stretching vibrations. Conclusions from SFG spectra are corroborated by ellipsometry which shows a dramatic increase in layer thicknesses at molar ratios where a charge reversal occurs. The formation of interfacial multilayers comprising SDS-BLG complexes is, thus, caused by cancellation of electrostatic interactions which leads to agglomeration at the interface. In contrast to pH 3.8, behavior of BLG-SDS mixtures at pH 6.7 is different due to repulsive electrostatic interactions between SDS and BLG which lead to a significantly reduced binding enthalpy of -17 kJ mol(-1). Finally, it has to be mentioned that

  11. Interfacial welding of dynamic covalent network polymers

    NASA Astrophysics Data System (ADS)

    Yu, Kai; Shi, Qian; Li, Hao; Jabour, John; Yang, Hua; Dunn, Martin L.; Wang, Tiejun; Qi, H. Jerry

    2016-09-01

    Dynamic covalent network (or covalent adaptable network) polymers can rearrange their macromolecular chain network by bond exchange reactions (BERs) where an active unit replaces a unit in an existing bond to form a new bond. Such macromolecular events, when they occur in large amounts, can attribute to unusual properties that are not seen in conventional covalent network polymers, such as shape reforming and surface welding; the latter further enables the important attributes of material malleability and powder-based reprocessing. In this paper, a multiscale modeling framework is developed to study the surface welding of thermally induced dynamic covalent network polymers. At the macromolecular network level, a lattice model is developed to describe the chain density evolution across the interface and its connection to bulk stress relaxation due to BERs. The chain density evolution rule is then fed into a continuum level interfacial model that takes into account surface roughness and applied pressure to predict the effective elastic modulus and interfacial fracture energy of welded polymers. The model yields particularly accessible results where the moduli and interfacial strength of the welded samples as a function of temperature and pressure can be predicted with four parameters, three of which can be measured directly. The model identifies the dependency of surface welding efficiency on the applied thermal and mechanical fields: the pressure will affect the real contact area under the consideration of surface roughness of dynamic covalent network polymers; the chain density increment on the real contact area of interface is only dependent on the welding time and temperature. The modeling approach shows good agreement with experiments and can be extended to other types of dynamic covalent network polymers using different stimuli for BERs, such as light and moisture etc.

  12. Two-dimensional crystallization of catalase on a monolayer film of poly(1-benzyl-L-histidine) spread at the air/water interface.

    PubMed

    Sato, A; Furuno, T; Toyoshima, C; Sasabe, H

    1993-03-01

    Two-dimensional (2D) crystals of beef liver catalase were prepared by adsorption to a film of synthetic polypeptide, poly(1-benzyl-L-histidine) (PBLH), spread at the air/water interface. The crystallization experiments were carried out in the pH range of 4.8-6.4 for catalase solutions at low concentration (10 micrograms/ml). The pH-dependence suggested an electrostatic interaction in the binding of catalase to the PBLH film. At lower pH, small crystals were formed at a low binding rate, and at higher pH the binding was rapid and densely-packed 2D arrays with poor crystallinity were formed. To stimulate crystal growth, a thermal treatment was applied. One-shot heating of the interfacial catalase-PBLH film to 35-40 degrees C was remarkably effective to form larger 2D crystals. The structure of catalase 2D crystals has been analyzed by Fourier filtering of the transmission electron micrographs. The crystal form is a new one, containing four catalase molecules in the unit cell with lattice parameters of alpha = 187 A, b = 225 A and gamma = 92.8 degrees.

  13. Interfacial activity of polymer-coated gold nanoparticles.

    PubMed

    Borrell, Marcos; Leal, L Gary

    2007-12-01

    A systematic study of the interfacial activity of polymer-coated gold nanoparticles was performed with the use of a computer-controlled four-roll mill. The nanoparticle locality within the polymeric domains (bulk or interface) was controlled by means of a mixture of polymeric ligands grafted to the gold nanoparticle core. The bulk polymers were polybutadiene (PBd) and polydimethylsiloxane (PDMS). Monoterminated PDMS and PBd ligands were synthesized on the basis of the esterification of reactive groups (such as hydroxyl or amino groups) with lipoic acid anhydride. The formation of polymer-coated nanoparticles using these lipoic acid-functionalized polymers was confirmed via transmission electron microscopy (TEM), and their interfacial activity was manifested as a reduction of the interfacial tension and in the enhanced stability of thin films (as seen via the inhibition of coalescence). The nanoparticles showed an equal, if not superior, ability to reduce the interfacial tension when compared to previous studies on the effect of insoluble surfactants; however, these particles proved not to be as effective at inhibiting coalescence as their surfactant counterpart. We suggest that this effect may be caused by an increase in the attractive van der Waals forces created by the presence of metal-core nanoparticles. Experimental measurements using the four-roll mill allow us to explore the relationship between nanoparticle concentration at the interface and interfacial tension. In particular, we have found evidence that the interface concentration can be increased relative to the equilibrium value achieved by diffusion alone, and thus the interfacial tension can be systematically reduced if the interfacial area is increased temporarily via drop deformation or breakup followed by recoalescence. PMID:17973410

  14. Spatial Distribution, Air-Water Fugacity Ratios and Source Apportionment of Polychlorinated Biphenyls in the Lower Great Lakes Basin.

    PubMed

    Khairy, Mohammed; Muir, Derek; Teixeira, Camilla; Lohmann, Rainer

    2015-12-01

    Polychlorinated biphenyls (PCBs) continue to be contaminants of concern across the Great Lakes. It is unclear whether current concentrations are driven by ongoing primary emissions from their original uses, or whether ambient PCBs are dominated by their environmental cycling. Freely dissolved PCBs in air and water were measured using polyethylene passive samplers across Lakes Erie and Ontario during summer and fall, 2011, to investigate their spatial distribution, determine and apportion their sources and to asses their air-water exchange gradients. Average gaseous and freely dissolved ∑29 PCB concentrations ranged from 5.0 to 160 pg/m(3) and 2.0 to 55 pg/L respectively. Gaseous concentrations were significantly correlated (R(2) = 0.80) with the urban area within a 3-20 km radius. Fugacity ratios indicated that the majority of PCBs are volatilizing from the water thus acting as a secondary source for the atmosphere. Dissolved PCBs were probably linked to PCB emissions from contaminated sites and areas of concern. Positive matrix factorization indicated that although volatilized Aroclors (gaseous PCBs) and unaltered Aroclors (dissolved PCBs) dominate in some samples, ongoing non-Aroclor sources such as paints/pigments (PCB 11) and coal/wood combustion showed significant contributions across the lower Great Lakes. Accordingly, control strategies should give further attention to PCBs emitted from current use sources. PMID:25915412

  15. Spatial Distribution, Air-Water Fugacity Ratios and Source Apportionment of Polychlorinated Biphenyls in the Lower Great Lakes Basin.

    PubMed

    Khairy, Mohammed; Muir, Derek; Teixeira, Camilla; Lohmann, Rainer

    2015-12-01

    Polychlorinated biphenyls (PCBs) continue to be contaminants of concern across the Great Lakes. It is unclear whether current concentrations are driven by ongoing primary emissions from their original uses, or whether ambient PCBs are dominated by their environmental cycling. Freely dissolved PCBs in air and water were measured using polyethylene passive samplers across Lakes Erie and Ontario during summer and fall, 2011, to investigate their spatial distribution, determine and apportion their sources and to asses their air-water exchange gradients. Average gaseous and freely dissolved ∑29 PCB concentrations ranged from 5.0 to 160 pg/m(3) and 2.0 to 55 pg/L respectively. Gaseous concentrations were significantly correlated (R(2) = 0.80) with the urban area within a 3-20 km radius. Fugacity ratios indicated that the majority of PCBs are volatilizing from the water thus acting as a secondary source for the atmosphere. Dissolved PCBs were probably linked to PCB emissions from contaminated sites and areas of concern. Positive matrix factorization indicated that although volatilized Aroclors (gaseous PCBs) and unaltered Aroclors (dissolved PCBs) dominate in some samples, ongoing non-Aroclor sources such as paints/pigments (PCB 11) and coal/wood combustion showed significant contributions across the lower Great Lakes. Accordingly, control strategies should give further attention to PCBs emitted from current use sources.

  16. Interaction between heterogeneous environmental quality domains (air, water, land, socio-demographic and built environment) on preterm birth.

    EPA Science Inventory

    Environmental exposures are often measured individually, though many occur in tandem. To address aggregate exposures, a county-level Environmental Quality Index (EQI) representing five environmental domains (air, water, land, built and sociodemographic) was constructed. Recent st...

  17. Influence of eutrophication on air-water exchange, vertical fluxes, and phytoplankton concentrations of persistent organic pollutants

    SciTech Connect

    Dachs, J.; Eisenreich, S.J.; Hoff, R.M.

    2000-03-15

    The influence of eutrophication on the biogeochemical cycles of persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs) is largely unknown. In this paper, the application of a dynamic air-water-phytoplankton exchange model to Lake Ontario is used as a framework to study the influence of eutrophication on air-water exchange, vertical fluxes, and phytoplankton concentrations of POPs. The results of these simulations demonstrate that air-water exchange controls phytoplankton concentrations in remote aquatic environments with little influence from land-based sources of pollutants and supports levels in even historically contaminated systems. Furthermore, eutrophication or high biomass leads to a disequilibrium between the gas and dissolved phase, enhanced air-water exchange, and vertical sinking fluxes of PCBs. Increasing biomass also depletes the water concentrations leading to lower than equilibrium PCB concentrations in phytoplankton. Implications to future trends in PCB pollution in Lake Ontario are also discussed.

  18. Using the Langmuir-Schaefer technique to fabricate large-area dense SERS-active Au nanoprism monolayer films.

    PubMed

    Lee, Yih Hong; Lee, Choon Keong; Tan, Baorui; Rui Tan, Joel Ming; Phang, In Yee; Ling, Xing Yi

    2013-07-21

    Interfacial self-assembly of nanoparticles is capable of creating large-area close-packed structures for a variety of applications. However, monolayers of hydrophilic cetyltrimethylammonium bromide (CTAB)-coated Au nanoparticles are challenging to assemble via interfacial self-assembly. This report presents a facile and scalable process to fabricate large-area monolayer films of ultrathin CTAB-coated Au nanoprisms at the air-water interface using the Langmuir-Schaefer technique. This is first achieved by a one-step functionalization of Au nanoprisms with poly(vinylpyrrolidone) (PVP). PVP functionalization is completed within a short time without loss of nanoprisms due to aggregation. Uniform and near close-packed monolayers of the Au nanoprisms formed over large areas (∼1 cm(2)) at the air-water interface can be transferred to substrates with different wettabilities. The inter-prism gaps are tuned qualitatively through the introduction of dodecanethiol and oleylamine. The morphological integrity of the nanoprisms is maintained throughout the entire assembly process, without truncation of the nanoprism tips. The near close-packed arrangement of the nanoprism monolayers generates large numbers of hot spots in the 2D arrays in the tip-to-tip and edge-to-edge inter-particle regions, giving rise to strong surface-enhanced Raman scattering (SERS) signals. When deposited on an Au mirror film, additional hotspots are created in the 3(rd) dimension in the gaps between the 2D nanoprism monolayers and the Au film. SERS enhancement factors reaching 10(4) for non-resonant probe molecules are achieved.

  19. Real-time investigation of protein unfolding at an air-water interface at the 1 s time scale.

    PubMed

    Yano, Yohko F; Arakawa, Etsuo; Voegeli, Wolfgang; Matsushita, Tadashi

    2013-11-01

    Protein unfolding at an air-water interface has been demonstrated such that the X-ray reflectivity can be measured with an acquisition time of 1 s using a recently developed simultaneous multiple-angle-wavelength-dispersive X-ray reflectometer. This has enabled the electron density profile of the adsorbed protein molecules to be obtained in real time. A globular protein, lysozyme, adsorbed at the air-water interface is found to unfold into a flat shape within 1 s.

  20. Environmental Applications of Interfacial Materials with Special Wettability.

    PubMed

    Wang, Zhangxin; Elimelech, Menachem; Lin, Shihong

    2016-03-01

    Interfacial materials with special wettability have become a burgeoning research area in materials science in the past decade. The unique surface properties of materials and interfaces generated by biomimetic approaches can be leveraged to develop effective solutions to challenging environmental problems. This critical review presents the concept, mechanisms, and fabrication techniques of interfacial materials with special wettability, and assesses the environmental applications of these materials for oil-water separation, membrane-based water purification and desalination, biofouling control, high performance vapor condensation, and atmospheric water collection. We also highlight the most promising properties of interfacial materials with special wettability that enable innovative environmental applications and discuss the practical challenges for large-scale implementation of these novel materials.

  1. Quantitative morphological characterization of bicontinuous Pickering emulsions via interfacial curvatures

    NASA Astrophysics Data System (ADS)

    Reeves, Matthew; Stratford, Kevin; Thijssen, Job H. J.

    Bicontinuous Pickering emulsions (bijels) are a physically interesting class of soft materials with many potential applications including catalysis, microfluidics and tissue engineering. They are created by arresting the spinodal decomposition of a partially-miscible liquid with a (jammed) layer of interfacial colloids. Porosity $L$ (average interfacial separation) of the bijel is controlled by varying the radius ($r$) and volume fraction ($\\phi$) of the colloids ($L \\propto r/\\phi$). However, to optimize the bijel structure with respect to other parameters, e.g. quench rate, characterizing by $L$ alone is insufficient. Hence, we have used confocal microscopy and X-ray CT to characterize a range of bijels in terms of local and area-averaged interfacial curvatures. In addition, the curvatures of bijels have been monitored as a function of time, which has revealed an intriguing evolution up to 60 minutes after bijel formation, contrary to previous understanding.

  2. First-Principles Prediction of Liquid/Liquid Interfacial Tension.

    PubMed

    Andersson, M P; Bennetzen, M V; Klamt, A; Stipp, S L S

    2014-08-12

    The interfacial tension between two liquids is the free energy per unit surface area required to create that interface. Interfacial tension is a determining factor for two-phase liquid behavior in a wide variety of systems ranging from water flooding in oil recovery processes and remediation of groundwater aquifers contaminated by chlorinated solvents to drug delivery and a host of industrial processes. Here, we present a model for predicting interfacial tension from first principles using density functional theory calculations. Our model requires no experimental input and is applicable to liquid/liquid systems of arbitrary compositions. The consistency of the predictions with experimental data is significant for binary, ternary, and multicomponent water/organic compound systems, which offers confidence in using the model to predict behavior where no data exists. The method is fast and can be used as a screening technique as well as to extend experimental data into conditions where measurements are technically too difficult, time consuming, or impossible.

  3. Formation of H-type liquid crystal dimer at air-water interface

    SciTech Connect

    Karthik, C. Gupta, Adbhut Joshi, Aditya Manjuladevi, V. Gupta, Raj Kumar; Varia, Mahesh C.; Kumar, Sandeep

    2014-04-24

    We have formed the Langmuir monolayer of H-shaped Azo linked liquid crystal dimer molecule at the air-water interface. Isocycles of the molecule showed hysteresis suggesting the ir-reversible nature of the monolayer formed. The thin film deposited on the silicon wafer was characterized using Atomic Force Microscopy (AFM) and Field Emission Scanning Electron Microscopy (FESEM). The images showed uniform domains of the dimer molecule. We propose that these molecules tend to take book shelf configuration in the liquid phase.

  4. Sensitivity study of poisson corruption in tomographic measurements for air-water flows

    SciTech Connect

    Munshi, P. ); Vaidya, M.S. )

    1993-01-01

    An application of computerized tomography (CT) for measuring void fraction profiles in two-phase air-water flows was reported earlier. Those attempts involved some special radial methods for tomographic reconstruction and the popular convolution backprojection (CBP) method. The CBP method is capable of reconstructing void profiles for nonsymmetric flows also. In this paper, we investigate the effect of corrupted CT data for gamma-ray sources and aCBP algorithm. The corruption in such a case is due to the statistical (Poisson) nature of the source.

  5. A Thermodynamic Study of Dopant Interfacial Segregation Effect on Nanostability and Mechanical Properties

    NASA Astrophysics Data System (ADS)

    Wu, Longjia

    Nanoparticles, with great surface area and high surface to volume ratio, have been widely applied in many applications due to their unique size related effects. However, this high surface area character of nanoparticles also brings great excess energy to the whole system, making the system unstable and even causing the failure of nanoparticles, especially at higher temperatures. In order to maintain nanocrystalline structure of the materials, nanostability enhancement is of great significance in nanotechnology. It is well known that the global driving force for particles growth is to eliminate the excess energy brought by surface and grain boundary. Therefore, interfacial energetics has a great influence on the nanostability of the materials. And according to previous studies, dopant interfacial segregation could be a potential way to control the interfacial energetics of the nanoparticles and possibly lead to an improved nanostability. Furthermore, the interfacial energetics even can affect mechanical properties of nano-grain ceramic materials based on recent research. The main goals of the present work were to experimentally measure the interfacial energies of nanoparticles as well as nano-grain ceramics, modify the interfacial energetics through dopant segregation effect and engineer the nanostability and mechanical properties of the nanocrystalline materials through interfacial energetics modification. To achieve this goal, Mn cation has been chosen to introduce Mn interfacial segregation on ceria nanoparticles, and La cation has been added to 12 mol% yttria stabilized zirconia (12YSZ) and magnesium aluminate spinel (MAO) two-phase nano-grain ceramics to cause La interfacial segregation. Both of the dopant segregation phenomena were directly proved by electron energy loss spectroscopy (EELS). To quantify the dopant segregation effect on the interfacial energies, high-temperature oxide melt drop solution calorimetry, water adsorption calorimetry and differential

  6. Interfacial rheology in complex flow

    NASA Astrophysics Data System (ADS)

    Martin, Jeffrey; Hudson, Steven

    2009-03-01

    Multiphase liquid systems are omnipresent in and essential to everyday life, e.g. foods, pharmaceutics, cosmetics, paints, oil recovery, etc. The morphology and stability of such systems depend on dynamic interfacial properties and processes. Typical methods utilized to measure such interfacial properties often employ drops that are much larger and flows that are much simpler than those encountered in typical processing applications. A microfluidic approach is utilized to measure dynamic structure and kinetics in multiphase systems with drop sizes comparable to those encountered in applications and flow complexity that is easily adjustable. The internal circulation and deformation of an aqueous droplet in clear mineral oil is measured using particle tracers and a detailed shape analysis, which is capable of measuring sub-micron deviations in drop shape. Deformation dynamics, detailed drop shape, interfacial tension, and internal circulation patterns and velocities are measured in Poiseuille and transient elongational flows. Flow kinematics are adjusted by varying the microchannel geometry, relative drop size, and drop height. The effects of confinement on interfacial dynamics and circulation patterns and velocities are also explored.

  7. Determination and comparison of how the chain number and chain length of a lipid affects its interactions with a phospholipid at an air/water interface.

    PubMed

    Ngyugen, Hang; McNamee, Cathy E

    2014-06-01

    We determined how the number of chains in a lipid and its chain length affects its interactions with a phospholipid model membrane, and whether the number of chains or the chain length of lipids affects their interactions with the phospholipids more. This was achieved by using a Langmuir trough and a fluorescence microscope to study the interactions of mono-, di-, and triglycerides with a phospholipid monolayer at an air/water interface. The effect of the number of chains in a lipid on its interactions with phospholipids at air/water interfaces was shown by surface pressure-area per molecule isotherms and their thermodynamic analysis to worsen as the number of alkyl chains was increased to be greater than one. An increase in the packing density decreased the mixing ability of the lipids with the phospholipids, resulting in the formation of aggregates in the mixed monolayer. The aggregation was explained by the intermolecular hydrophobic and van der Waals attractions between the lipid molecules. Fluorescence microscopy revealed partial mixing without aggregation for monoglycerides, but the presence of lipid aggregation for diglycerides and triglycerides. The effect of decreasing the chain length of triglycerides from a long chain to a medium chain caused the interactions of the lipids with the phospholipid molecules at the air/water interface to significantly improve. Decreasing the chain length of monoglycerides from a long chain to a medium chain worsened their interaction with the phospholipid molecules. The effect of decreasing the triglyceride chain length on their interactions with phospholipids was much greater than the effect of decreasing the number of alkyl chains in the lipid.

  8. In situ studies of metal coordinations and molecular orientations in monolayers of amino-acid-derived Schiff bases at the air-water interface.

    PubMed

    Liu, Huijin; Zheng, Haifu; Miao, Wangen; Du, Xuezhong

    2009-03-01

    The surface behaviors of monolayers of amino-acid-derived Schiff bases, namely, 4-(4-(hexadecyloxy)benzylideneamino)benzoic acid (HBA), at the air-water interface on pure water and ion-containing subphases (Cu2+, Ca2+, and Ba2+) have been clarified by a combination of surface pressure-area isotherms and surface plasmon resonance (SPR) technique, and the metal coordinations and molecular orientations in the monolayers have been investigated using in situ infrared reflection absorption spectroscopy (IRRAS). The presence of metal ions gives rise to condensation of the monolayers (Cu2+, pH 6.1; Ca2+, pH 11; Ba2+, pH 10), even leading to the formation of three-dimensional structures of the compressed monolayer in the case of Ba2+ (pH 12). The metal coordinations with the carboxyl groups at the interface depend on the type of metal ions and pH of the aqueous subphase. The orientations of the aromatic Schiff base segments with surface pressure are elaborately described. The spectral behaviors of the Schiff base segments with incidence angle in the case of Ba2+ (pH 12) have so far presented an excellent example for the selection rule of IRRAS at the air-water interface for p-polarization with vibrational transition moments perpendicular to the water surface. The chain orientations in the monolayers are quantitatively determined on the assumption that the thicknesses of the HBA monolayers at the air-water interface are composed of the sublayers of alkyl chains and Schiff base segments. PMID:19437705

  9. Effects of cholesterol component on molecular interactions between paclitaxel and phospholipid within the lipid monolayer at the air-water interface.

    PubMed

    Zhao, Lingyun; Feng, Si-Shen

    2006-08-01

    Cholesterol is a main component of the cell membrane and could have significant effects on drug-cell membrane interactions and thus the therapeutic efficacy of the drug. It also plays an important role in liposomal formulation of drugs for controlled and targeted delivery. In this research, Langmuir film technique, atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR) are employed for a systematic investigation on the effects of cholesterol component on the molecular interactions between a prototype antineoplastic drug (paclitaxel) and 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) within the cell membrane by using the lipid monolayer at the air-water interface as a model of the lipid bilayer membrane and the biological cell membrane. Analysis of the measured surface pressure (pi) versus molecular area (a) isotherms of the mixed DPPC/paclitaxel/cholesterol monolayers at various molar ratios shows that DPPC, paclitaxel and cholesterol can form a non-ideal miscible system at the air-water interface. Cholesterol enhances the intermolecular forces between paclitaxel and DPPC, produces an area-condensing effect and thus makes the mixed monolayer more stable. Investigation of paclitaxel penetration into the mixed DPPC/cholesterol monolayer shows that the existence of cholesterol in the DPPC monolayer can considerably restrict the drug penetration into the monolayer, which may have clinical significance for diseases of high cholesterol. FTIR and AFM investigation on the mixed monolayer deposited on solid surface confirmed the obtained results.

  10. Interfacial behavior of polymer electrolytes

    SciTech Connect

    Kerr, John; Kerr, John B.; Han, Yong Bong; Liu, Gao; Reeder, Craig; Xie, Jiangbing; Sun, Xiaoguang

    2003-06-03

    Evidence is presented concerning the effect of surfaces on the segmental motion of PEO-based polymer electrolytes in lithium batteries. For dry systems with no moisture the effect of surfaces of nano-particle fillers is to inhibit the segmental motion and to reduce the lithium ion transport. These effects also occur at the surfaces in composite electrodes that contain considerable quantities of carbon black nano-particles for electronic connection. The problem of reduced polymer mobility is compounded by the generation of salt concentration gradients within the composite electrode. Highly concentrated polymer electrolytes have reduced transport properties due to the increased ionic cross-linking. Combined with the interfacial interactions this leads to the generation of low mobility electrolyte layers within the electrode and to loss of capacity and power capability. It is shown that even with planar lithium metal electrodes the concentration gradients can significantly impact the interfacial impedance. The interfacial impedance of lithium/PEO-LiTFSI cells varies depending upon the time elapsed since current was turned off after polarization. The behavior is consistent with relaxation of the salt concentration gradients and indicates that a portion of the interfacial impedance usually attributed to the SEI layer is due to concentrated salt solutions next to the electrode surfaces that are very resistive. These resistive layers may undergo actual phase changes in a non-uniform manner and the possible role of the reduced mobility polymer layers in dendrite initiation and growth is also explored. It is concluded that PEO and ethylene oxide-based polymers are less than ideal with respect to this interfacial behavior.

  11. Interaction of N-myristoylethanolamine with cholesterol investigated in a Langmuir film at the air-water interface.

    PubMed

    Kamlekar, Ravi Kanth; Chandra, M Sharath; Radhakrishnan, T P; Swamy, Musti J

    2009-01-01

    The dramatic increase in the content of N-acylethanolamines (NAEs) having different acyl chains in various tissues when subjected to stress has resulted in significant interest in investigations on these molecules. Previous studies suggested that N-myristoylethanolamine (NMEA) and cholesterol interact to form a 1:1 (mol/mol) complex. In studies reported here, pressure-area isotherms of Langmuir films at the air-water interface have shown that at low fractions of cholesterol, the average area per molecule is lower than that predicted for ideal mixing, whereas at high cholesterol content the observed molecular area is higher, with a cross-over point at the equimolar composition. A plausible model that can explain these observations is the following: addition of small amounts of cholesterol to NMEA results in a reorientation of the NMEA molecules from the tilted disposition in the crystalline state to the vertical and stabilization of the intermolecular interactions, leading to the formation of a compact monolayer film, whereas at the other end of the composition diagram, addition of small amounts of NMEA to cholesterol leads to a tilting of the cholesterol molecules resulting in an increase in the average area per molecule. In Brewster angle microscopy experiments, a stable and bright homogeneous condensed phase was observed at a relatively low applied pressure of 2 mN.m(-1) for the NMEA:Chol. (1:1, mol/mol) mixture, whereas all other samples required significantly higher pressures (>10 mN.m(-1)) to form a homogeneous condensed phase. These observations are consistent with the formation of a 1:1 stoichiometric complex between NMEA and cholesterol and suggest that increase in the content of NAEs under stress may modulate the composition and dynamics of lipid rafts in biological membranes, resulting in alterations in signaling events involving them, which may be relevant to the putative cytoprotective and stress-combating ability of NAEs.

  12. Concentrations, Trends, and Air-Water Exchange of PAHs and PBDEs Derived from Passive Samplers in Lake Superior in 2011.

    PubMed

    Ruge, Zoe; Muir, Derek; Helm, Paul; Lohmann, Rainer

    2015-12-01

    Polycyclic aromatic hydrocarbons (PAHs) and polybrominated diphenylethers (PBDEs) are both currently released into the environment from anthropogenic activity. Both are hence primarily associated with populated or industrial areas, although wildfires can be an important source of PAHs, as well. Polyethylene passive samplers (PEs) were simultaneously deployed in surface water and near surface atmosphere to determine spatial trends and air-water gaseous exchange of 21 PAHs and 11 PBDEs at 19 sites across Lake Superior in 2011. Surface water and atmospheric PAH concentrations were greatest at urban sites (up to 65 ng L(-1) and 140 ng m(-3), respectively, averaged from June to October). Near populated regions, PAHs displayed net air-to-water deposition, but were near equilibrium off-shore. Retene, probably depositing following major wildfires in the region, dominated dissolved PAH concentrations at most Lake Superior sites. Atmospheric and dissolved PBDEs were greatest near urban and populated sites (up to 6.8 pg L(-1) and 15 pg m(-3), respectively, averaged from June to October), dominated by BDE-47. At most coastal sites, there was net gaseous deposition of BDE-47, with less brominated congeners contributing to Sault Ste. Marie and eastern open lake fluxes. Conversely, the central open lake and Eagle Harbor sites generally displayed volatilization of PBDEs into the atmosphere, mainly BDE-47. PMID:26436513

  13. Self-Assembly and Lipid Interactions of Diacylglycerol Lactone Derivatives Studied at the Air/Water Interface

    PubMed Central

    Philosof-Mazor, Liron; Volinsky, Roman; Comin, Maria J.; Lewin, Nancy E.; Kedei, Noemi; Blumberg, Peter M.; Marquez, Victor E.; Jelinek, Raz

    2009-01-01

    Synthetic diacylglycerol lactones (DAG-lactones) have been shown to be effective modulators of critical cellular signaling pathways. The biological activity of these amphiphilic molecules depends in part upon their lipid interactions within the cellular plasma membrane. This study explores the thermodynamic and structural features of DAG-lactone derivatives and their lipid interactions at the air/water interface. Surface-pressure/area isotherms and Brewster angle microscopy revealed the significance of specific side-groups attached to the terminus of a very rigid 4-(2-phenylethynyl) benzoyl chain of the DAG-lactones, which affected both the self-assembly of the molecules and their interactions with phospholipids. The experimental data highlight the formation of different phases within mixed DAG-lactone/phospholipid monolayers and underscore the relationship between the two components in binary mixtures of different mole ratios. Importantly, the results suggest that DAG-lactones are predominantly incorporated within fluid phospholipid phases rather than in the condensed phases that form, for example, by cholesterol. Moreover, the size and charge of the phospholipid headgroups do not seem to affect DAG-lactone interactions with lipids. PMID:18788772

  14. Effect of perfluoroalkyl chain length on monolayer behavior of partially fluorinated oleic acid molecules at the air-water interface.

    PubMed

    Baba, Teruhiko; Takai, Katsuki; Takagi, Toshiyuki; Kanamori, Toshiyuki

    2013-01-01

    A series of oleic acid (OA) analogs containing terminal perfluoroalkyl groups (CF3, C2F5, n-C3F7, n-C4F9 or n-C8F17) was synthesized to clarify how the fluorinated chain length affects the stability and molecular packing of liquid-expanded OA monolayers at the air-water interface. Although the substitution of terminal CF3 group for CH3 in OA had no effect on monolayer stability, further fluorination led to a gradual increase in monolayer stability at 25 °C. Surface pressure-area isotherm revealed that partially fluorinated OA analogs form more expanded monolayers than OA at low surface pressures, and that the monolayer behavior of OA analogs with the even-carbon numbered fluorinated chain is almost the same as that of OA upon monolayer compression, whereas the behavior of OA analogs with the odd-carbon numbered fluorinated chain significantly differs from that of OA. These results indicate: (i) the terminal short part (at least C2 residue) in OA predominantly determines the liquid-expanded monolayer stability; (ii) the molecular packing state of OA may be perturbed by the substitution of a short odd-carbon numbered fluorinated chain; (iii) hence, OA analogs with even-carbon numbered chain are considered to be preferable as hydrophobic building blocks for the synthesis of fluorinated phospholipids.

  15. Reversible self-association of ovalbumin at air-water interfaces and the consequences for the exerted surface pressure.

    PubMed

    Kudryashova, Elena V; Visser, Antonie J W G; De Jongh, Harmen H J

    2005-02-01

    In this study the relation between the ability of protein self-association and the surface properties at air-water interfaces is investigated using a combination of spectroscopic techniques. Three forms of chicken egg ovalbumin were obtained with different self-associating behavior: native ovalbumin, heat-treated ov-albumin-being a cluster of 12-16 predominantly noncovalently bound proteins, and succinylated ovalbumin, as a form with diminished aggregation properties due to increased electrostatic repulsion. While the bulk diffusion of aggregated protein is clearly slower compared to monomeric protein, the efficiency of transport to the interface is increased, just like the efficiency of sticking to rather than bouncing from the interface. On a timescale of hours, the aggregated protein dissociates and adopts a conformation comparable to that of native protein adsorbed to the interface. The exerted surface pressure is higher for aggregated material, most probably because the deformability of the particle is smaller. Aggregated protein has a lower ability to desorb from the interface upon compression of the surface layer, resulting in a steadily increasing surface pressure upon reducing the available area for the surface layer. This observation is opposite to what is observed for succinylated protein that may desorb more easily and thereby suppresses the buildup of a surface pressure. Generally, this work demonstrates that modulating the ability of proteins to self-associate offers a tool to control the rheological properties of interfaces.

  16. Biogenic amine – surfactant interactions at the air-water interface.

    PubMed

    Penfold, J; Thomas, R K; Li, P X

    2015-07-01

    The strong interaction between polyamines and anionic surfactants results in pronounced adsorption at the air-water interface and can lead to the formation of layered surface structures. The transition from monolayer adsorption to more complex surface structures depends upon solution pH, and the structure and molecular weight of the polyamine. The effects of manipulating the polyamine molecular weight and structure on the adsorption of the anionic surfactant sodium dodecyl sulphate at the air-water interface are investigated using neutron reflectivity and surface tension, for the biogenic amines putrescine, spermidine and spermine. The results show how changing the number of amine groups and the spacing between the amine groups impacts upon the surface adsorption. At lower pH, 3-7, and for the higher molecular weight polyamines, spermidine and spermine, ordered multilayer structures are observed. For putrescine at all pH and for spermidine and spermine at high pH, monolayer adsorption with enhanced surfactant adsorption compared to the pure surfactant is observed. The data for the biogenic amines, when compared with similar data for the polyamines ethylenediamine, diethylenetriamine and triethylenetetramine, indicate that the spacing between amines groups is more optimal for the formation of ordered surface multilayer structures.

  17. Air-water ‘tornado’-type microwave plasmas applied for sugarcane biomass treatment

    NASA Astrophysics Data System (ADS)

    Bundaleska, N.; Tatarova, E.; Dias, F. M.; Lino da Silva, M.; Ferreira, C. M.; Amorim, J.

    2014-02-01

    The production of cellulosic ethanol from sugarcane biomass is an attractive alternative to the use of fossil fuels. Pretreatment is needed to separate the cellulosic material, which is packed with hemicellulose and lignin in cell wall of sugarcane biomass. A microwave ‘tornado’-type air-water plasma source operating at 2.45 GHz and atmospheric pressure has been applied for this purpose. Samples of dry and wet biomass (˜2 g) have been exposed to the late afterglow plasma stream. The experiments demonstrate that the air-water highly reactive plasma environment provides a number of long-lived active species able to destroy the cellulosic wrapping. Scanning electron microscopy has been applied to analyse the morphological changes occurring due to plasma treatment. The effluent gas streams have been analysed by Fourier-transform infrared spectroscopy (FT-IR). Optical emission spectroscopy and FT-IR have been applied to determine the gas temperature in the discharge and late afterglow plasma zones, respectively. The optimal range of the operational parameters is discussed along with the main active species involved in the treatment process. Synergistic effects can result from the action of singlet O2(a 1Δg) oxygen, NO2, nitrous acid HNO2 and OH hydroxyl radical.

  18. Mechanisms of Polyelectrolyte Enhanced Surfactant Adsorption at the Air-Water Interface

    PubMed Central

    Stenger, Patrick C.; Palazoglu, Omer A.; Zasadzinski, Joseph A.

    2009-01-01

    Chitosan, a naturally occurring cationic polyelectrolyte, restores the adsorption of the clinical lung surfactant Survanta to the air-water interface in the presence of albumin at much lower concentrations than uncharged polymers such as polyethylene glycol. This is consistent with the positively charged chitosan forming ion pairs with negative charges on the albumin and lung surfactant particles, reducing the net charge in the double-layer, and decreasing the electrostatic energy barrier to adsorption to the air-water interface. However, chitosan, like other polyelectrolytes, cannot perfectly match the charge distribution on the surfactant, which leads to patches of positive and negative charge at net neutrality. Increasing the chitosan concentration further leads to a reduction in the rate of surfactant adsorption consistent with an over-compensation of the negative charge on the surfactant and albumin surfaces, which creates a new repulsive electrostatic potential between the now cationic surfaces. This charge neutralization followed by charge inversion explains the window of polyelectrolyte concentration that enhances surfactant adsorption; the same physical mechanism is observed in flocculation and re-stabilization of anionic colloids by chitosan and in alternate layer deposition of anionic and cationic polyelectrolytes on charged colloids. PMID:19366599

  19. Photosensitized Formation of Secondary Organic Aerosols above the Air/Water Interface.

    PubMed

    Bernard, F; Ciuraru, R; Boréave, A; George, C

    2016-08-16

    In this study, we evaluated photosensitized chemistry at the air-sea interface as a source of secondary organic aerosols (SOA). Our results show that, in addition to biogenic emissions, abiotic processes could also be important in the marine boundary layer. Photosensitized production of marine secondary organic aerosol was studied in a custom-built multiphase atmospheric simulation chamber. The experimental chamber contained water, humic acid (1-10 mg L(-1)) as a proxy for dissolved organic matter, and nonanoic acid (0.1-10 mM), a fatty acid proxy which formed an organic film at the air-water interface. Dark secondary reaction with ozone after illumination resulted in SOA particle concentrations in excess of 1000 cm(-3), illustrating the production of unsaturated compounds by chemical reactions at the air-water interface. SOA numbers via photosensitization alone and in the absence of ozone did not exceed background levels. From these results, we derived a dependence of SOA numbers on nonanoic acid surface coverage and dissolved organic matter concentration. We present a discussion on the potential role of the air-sea interface in the production of atmospheric organic aerosol from photosensitized origins. PMID:27434860

  20. Spectroscopic signatures of ozone at the air-water interface and photochemistry implications.

    PubMed

    Anglada, Josep M; Martins-Costa, Marilia; Ruiz-López, Manuel F; Francisco, Joseph S

    2014-08-12

    First-principles simulations suggest that additional OH formation in the troposphere can result from ozone interactions with the surface of cloud droplets. Ozone exhibits an affinity for the air-water interface, which modifies its UV and visible light spectroscopic signatures and photolytic rate constant in the troposphere. Ozone cross sections on the red side of the Hartley band (290- to 350-nm region) and in the Chappuis band (450-700 nm) are increased due to electronic ozone-water interactions. This effect, combined with the potential contribution of the O3 + hν → O((3)P) + O2(X(3)Σg(-)) photolytic channel at the interface, leads to an enhancement of the OH radical formation rate by four orders of magnitude. This finding suggests that clouds can influence the overall oxidizing capacity of the troposphere on a global scale by stimulating the production of OH radicals through ozone photolysis by UV and visible light at the air-water interface.

  1. Predicting Air-Water Geysers and Their Implications on Reducing Combined Sewer Overflows

    NASA Astrophysics Data System (ADS)

    Choi, Y.; Leon, A.; Apte, S.

    2014-12-01

    An air-water geyser in a closed conduit system is characterized by an explosive jetting of a mixture of air and water through drop-shafts. In this study, three scenarios of geysers are numerically simulated using a 3D computational fluid dynamics (CFD) model. The three tested scenarios are comprised of a drop shaft that is closed at its bottom and partially or fully open at the top. Initially, the lower section of the drop shaft is filled with pressurized air, the middle section with stagnant water and the upper section with air at atmospheric pressure. The pressure and volume of the pressurized air, and hence the stored energy, is different for all three test cases. The volume of the stagnant water and the air at atmospheric pressure are kept constant in the tests. The numerical simulations aim to identify the correlation between dimensionless energy stored in the pressurized air pocket and dimensionless maximum pressure reached at the outlet. This dimensionless correlation could be used to determine the energy threshold that does not produce air-water geyser, which in turn could be used in the design of combined sewer systems for minimizing geysers.

  2. Free Energies of Cavity and Noncavity Hydrated Electrons Near the Instantaneous Air/Water Interface.

    PubMed

    Casey, Jennifer R; Schwartz, Benjamin J; Glover, William J

    2016-08-18

    The properties of the hydrated electron at the air/water interface are computed for both a cavity and a noncavity model using mixed quantum/classical molecular dynamics simulation. We take advantage of our recently developed formalism for umbrella sampling with a restrained quantum expectation value to calculate free-energy profiles of the hydrated electron's position relative to the water surface. We show that it is critical to use an instantaneous description of the air/water interface rather than the Gibbs' dividing surface to obtain accurate potentials of mean force. We find that noncavity electrons, which prefer to encompass several water molecules, avoid the interface where water molecules are scarce. In contrast, cavity models of the hydrated electron, which prefer to expel water, have a local free-energy minimum near the interface. When the cavity electron occupies this minimum, its absorption spectrum is quite red-shifted, its binding energy is significantly lowered, and its dynamics speed up quite a bit compared with the bulk, features that have not been found by experiment. The surface activity of the electron therefore serves as a useful test of cavity versus noncavity electron solvation. PMID:27479028

  3. Spatial Distribution and Air-Water Exchange of Organic Flame Retardants in the Lower Great Lakes.

    PubMed

    McDonough, Carrie A; Puggioni, Gavino; Helm, Paul A; Muir, Derek; Lohmann, Rainer

    2016-09-01

    Organic flame retardants (OFRs) such as polybrominated diphenyl ethers (PBDEs) and novel halogenated flame retardants (NHFRs) are ubiquitous, persistent, and bioaccumulative contaminants that have been used in consumer goods to slow combustion. In this study, polyethylene passive samplers (PEs) were deployed throughout the lower Great Lakes (Lake Erie and Lake Ontario) to measure OFRs in air and water, calculate air-water exchange fluxes, and investigate spatial trends. Dissolved Σ12BDE was greatest in Lake Ontario near Toronto (18 pg/L), whereas gaseous Σ12BDE was greatest on the southern shoreline of Lake Erie (11 pg/m(3)). NHFRs were generally below detection limits. Air-water exchange was dominated by absorption of BDEs 47 and 99, ranging from -964 pg/m(2)/day to -30 pg/m(2)/day. Σ12BDE in air and water was significantly correlated with surrounding population density, suggesting that phased-out PBDEs continued to be emitted from population centers along the Great Lakes shoreline in 2012. Correlation with dissolved Σ12BDE was strongest when considering population within 25 km while correlation with gaseous Σ12BDE was strongest when using population within 3 km to the south of each site. Bayesian kriging was used to predict dissolved Σ12BDE over the lakes, illustrating the utility of relatively highly spatially resolved measurements in identifying potential hot spots for future study.

  4. Spatial Distribution and Air-Water Exchange of Organic Flame Retardants in the Lower Great Lakes.

    PubMed

    McDonough, Carrie A; Puggioni, Gavino; Helm, Paul A; Muir, Derek; Lohmann, Rainer

    2016-09-01

    Organic flame retardants (OFRs) such as polybrominated diphenyl ethers (PBDEs) and novel halogenated flame retardants (NHFRs) are ubiquitous, persistent, and bioaccumulative contaminants that have been used in consumer goods to slow combustion. In this study, polyethylene passive samplers (PEs) were deployed throughout the lower Great Lakes (Lake Erie and Lake Ontario) to measure OFRs in air and water, calculate air-water exchange fluxes, and investigate spatial trends. Dissolved Σ12BDE was greatest in Lake Ontario near Toronto (18 pg/L), whereas gaseous Σ12BDE was greatest on the southern shoreline of Lake Erie (11 pg/m(3)). NHFRs were generally below detection limits. Air-water exchange was dominated by absorption of BDEs 47 and 99, ranging from -964 pg/m(2)/day to -30 pg/m(2)/day. Σ12BDE in air and water was significantly correlated with surrounding population density, suggesting that phased-out PBDEs continued to be emitted from population centers along the Great Lakes shoreline in 2012. Correlation with dissolved Σ12BDE was strongest when considering population within 25 km while correlation with gaseous Σ12BDE was strongest when using population within 3 km to the south of each site. Bayesian kriging was used to predict dissolved Σ12BDE over the lakes, illustrating the utility of relatively highly spatially resolved measurements in identifying potential hot spots for future study. PMID:27458653

  5. A Mechanism for the Entrapment of DNA at an Air-Water Interface

    PubMed Central

    Eickbush, Thomas H.; Moudrianakis, Evangelos N.

    1977-01-01

    Addition of the intercalating dye quinacrine to a low ionic strength solution of DNA in quantities sufficient to saturate the high affinity sites in the DNA will result in the accumulation of the DNA at the solution interface. This entrapment of DNA at the air-water interface has been assayed by the adsorption of DNA to untreated carbon-coated electron microscope grids touched to the solution surface. Other intercalating dyes can also bring about this entrapment, if they possess a side arm large enough to occupy one of the DNA grooves when the dye is intercalated into the DNA. The extension and unwinding of the DNA helix brought about by the intercalating chromophore of the dye molecules are not requirements for the entrapment process. Spermidine, a simple polyamine that will bind to the DNA minor groove but that has no intercalating chromophore, was found to bring about this entrapment. Even simple mono- and divalent cations in the absence of the above ligands were found to promote a low level of surface entrapment. A model for the entrapment of DNA at the air-water interface is proposed in which one (or both) of the hydrophobic grooves of the DNA becomes a surface-active agent as a consequence of the association of various ligands and charge neutralization. ImagesFIGURE 1FIGURE 6 PMID:890027

  6. Aggregation behaviors of gelatin with cationic gemini surfactant at air/water interface.

    PubMed

    Wu, Dan; Xu, Guiying; Feng, Yujun; Li, Yiming

    2007-03-10

    The dilational rheological properties of gelatin with cationic gemini surfactant 1,2-ethane bis(dimethyl dodecyl ammonium bromide) (C(12)C(2)C(12)) at air/water interface were investigated using oscillating barriers method at low frequency (0.005-0.1 Hz), which was compared with single-chain surfactant dodecyltrimethyl ammonium bromide (DTAB). The results indicate that the maximum dilational modulus and the film stability of gelatin-C(12)C(2)C(12) are higher than those of gelatin-DTAB. At high concentration of C(12)C(2)C(12) or DTAB, the dilational modulus of gelatin-surfactant system becomes close to that corresponding to pure surfactant, suggesting gelatin at interface is replaced by surfactant. This replacement is also observed by surface tension measurement. However, it is found that gelatin-C(12)C(2)C(12) system has two obvious breaks but gelatin-DTAB has not in surface tension isotherms. These phenomena are ascribed to the double charges and strong hydrophobicity of C(12)C(2)C(12). Based on these experimental results, a mechanism of gelatin-surfactant interaction at air/water interface is proposed.

  7. Air-water gas exchange and CO2 flux in a mangrove-dominated estuary

    USGS Publications Warehouse

    Ho, David T.; Ferrón, Sara; Engel, Victor C.; Larsen, Laurel G.; Barr, Jordan G.

    2014-01-01

    Mangrove forests are highly productive ecosystems, but the fate of mangrove-derived carbon remains uncertain. Part of that uncertainty stems from the fact that gas transfer velocities in mangrove-surrounded waters are not well determined, leading to uncertainty in air-water CO2 fluxes. Two SF6 tracer release experiments were conducted to determine gas transfer velocities (k(600) = 8.3 ± 0.4 and 8.1 ± 0.6 cm h−1), along with simultaneous measurements of pCO2 to determine the air-water CO2 fluxes from Shark River, Florida (232.11 ± 23.69 and 171.13 ± 20.28 mmol C m−2 d−1), an estuary within the largest contiguous mangrove forest in North America. The gas transfer velocity results are consistent with turbulent kinetic energy dissipation measurements, indicating a higher rate of turbulence and gas exchange than predicted by commonly used wind speed/gas exchange parameterizations. The results have important implications for carbon fluxes in mangrove ecosystems.

  8. Photosensitized Formation of Secondary Organic Aerosols above the Air/Water Interface.

    PubMed

    Bernard, F; Ciuraru, R; Boréave, A; George, C

    2016-08-16

    In this study, we evaluated photosensitized chemistry at the air-sea interface as a source of secondary organic aerosols (SOA). Our results show that, in addition to biogenic emissions, abiotic processes could also be important in the marine boundary layer. Photosensitized production of marine secondary organic aerosol was studied in a custom-built multiphase atmospheric simulation chamber. The experimental chamber contained water, humic acid (1-10 mg L(-1)) as a proxy for dissolved organic matter, and nonanoic acid (0.1-10 mM), a fatty acid proxy which formed an organic film at the air-water interface. Dark secondary reaction with ozone after illumination resulted in SOA particle concentrations in excess of 1000 cm(-3), illustrating the production of unsaturated compounds by chemical reactions at the air-water interface. SOA numbers via photosensitization alone and in the absence of ozone did not exceed background levels. From these results, we derived a dependence of SOA numbers on nonanoic acid surface coverage and dissolved organic matter concentration. We present a discussion on the potential role of the air-sea interface in the production of atmospheric organic aerosol from photosensitized origins.

  9. Phase diagram, design of monolayer binary colloidal crystals, and their fabrication based on ethanol-assisted self-assembly at the air/water interface.

    PubMed

    Dai, Zhengfei; Li, Yue; Duan, Guotao; Jia, Lichao; Cai, Weiping

    2012-08-28

    Flexible structural design and accurate controlled fabrication with structural tunability according to need for binary or multicomponent colloidal crystals have been expected. However, it is still a challenge. In this work, the phase diagram of monolayer binary colloidal crystals (bCCs) is established on the assumption that both large and small polystyrene (PS) colloidal spheres can stay at the air/water interface, and the range diagram for the size ratio and number ratio of small to large colloidal spheres is presented. From this phase diagram, combining the range diagram, we can design and relatively accurately control fabrication of the bCCs with specific structures (or patterns) according to need, including single or mixed patterns with the given relative content. Further, a simple and facile approach is presented to fabricate large-area (more than 10 cm(2)) monolayer bCCs without any surfactants, using differently sized PS spheres, based on ethanol-assisted self-assembly at the air/water interface. bCCs with different patterns and stoichiometries are thus designed from the established phase diagram and then successfully fabricated based on the volume ratios (V(S/L)) of the small to large PS suspensions using the presented colloidal self-assembling method. Interestingly, these monolayer bCCs can be transferred to any desired substrates using water as the medium. This study allows us to design desired patterns of monolayer bCCs and to more accurately control their structures with the used V(S/L).

  10. Current status of persistent organic pesticides residues in air, water, and soil, and their possible effect on neighboring countries: a comprehensive review of India.

    PubMed

    Yadav, Ishwar Chandra; Devi, Ningombam Linthoingambi; Syed, Jabir Hussain; Cheng, Zhineng; Li, Jun; Zhang, Gan; Jones, Kevin C

    2015-04-01

    Though the use of pesticides has offered significant economic benefits by enhancing the production and yield of food and fibers and the prevention of vector-borne diseases, evidence suggests that their use has adversely affected the health of human populations and the environment. Pesticides have been widely distributed and their traces can be detected in all areas of the environment (air, water and soil). Despite the ban of DDT and HCH in India, they are still in use, both in domestic and agricultural settings. In this comprehensive review, we discuss the production and consumption of persistent organic pesticides, their maximum residual limit (MRL) and the presence of persistent organic pesticides in multicomponent environmental samples (air, water and soil) from India. In order to highlight the global distribution of persistent organic pesticides and their impact on neighboring countries and regions, the role of persistent organic pesticides in Indian region is reviewed. Based on a review of research papers and modeling simulations, it can be concluded that India is one of the major contributors of global persistent organic pesticide distribution. This review also considers the health impacts of persistent organic pesticides, the regulatory measures for persistent organic pesticides, and the status of India's commitment towards the elimination of persistent organic pesticides.

  11. Mechanism of Action of Thymol on Cell Membranes Investigated through Lipid Langmuir Monolayers at the Air-Water Interface and Molecular Simulation.

    PubMed

    Ferreira, João Victor N; Capello, Tabata M; Siqueira, Leonardo J A; Lago, João Henrique G; Caseli, Luciano

    2016-04-01

    A major challenge in the design of biocidal drugs is to identify compounds with potential action on microorganisms and to understand at the molecular level their mechanism of action. In this study, thymol, a monoterpenoid found in the oil of leaves of Lippia sidoides with possible action in biological surfaces, was incorporated in lipid monolayers at the air-water interface that represented cell membrane models. The interaction of thymol with dipalmitoylphosphatidylcholine (DPPC) at the air-water interface was investigated by means of surface pressure-area isotherms, Brewster angle microscopy (BAM), polarization-modulation reflection-absorption spectroscopy (PM-IRRAS), and molecular dynamics simulation. Thymol expands DPPC monolayers, decreases their surface elasticity, and changes the morphology of the lipid monolayer, which evidence the incorporation of this compound in the lipid Langmuir film. Such incorporation could be corroborated by PM-IRRAS since some specific bands for DPPC were changed upon thymol incorporation. Furthermore, potential of mean force obtained by molecular dynamics simulations indicates that the most stable position of the drug along the lipid film is near the hydrophobic regions of DPPC. These results may be useful to understand the interaction between thymol and cell membranes during biochemical phenomena, which may be associated with its pharmaceutical properties at the molecular level.

  12. Supramolecular interfacial architectures for biosensing

    NASA Astrophysics Data System (ADS)

    Yu, Fang; Yao, Danfeng; Christensen, Danica; Neumann, Thomas; Sinner, Eva-Kathrin; Knoll, Wolfgang

    2004-12-01

    This contribution summarizes some of our efforts in designing, assembling and functionally characterizing supramolecular interfacial architectures for bio-affinity studies and for biosensor development. All the surface interaction studies will be based on the recently introduced novel sensor platforms involving surface plasmon fluorescence spectroscopy (SPFS) and -microscopy (SPFM). Emphasis will be put on documenting the distance-dependence of fluorescence intensity at the metal-dielectric interface and utilizing this principle to optimize the conformation/orientation of the interfacial supra-molecular sensor coatings. This is exemplified by a number of examples, including a layer-by-layer assembly system, antibody-antigen interactions, oligonucleotide-oligonucleotide, and oligonucleotide-PCR amplicon hybridization. For practical sensing purposes, a three-dimensionally extended surface coating is then employed to overcome the fluorescence quenching problem on a planar matrix. A commercial dextran layer is shown to be an optimized matrix for SPFS, with an example of a protein-binding study.

  13. Mechanics of interfacial composite materials.

    PubMed

    Subramaniam, Anand Bala; Abkarian, Manouk; Mahadevan, L; Stone, Howard A

    2006-11-21

    Recent experiments and simulations have demonstrated that particle-covered fluid/fluid interfaces can exist in stable nonspherical shapes as a result of the steric jamming of the interfacially trapped particles. The jamming confers the interface with solidlike properties. We provide an experimental and theoretical characterization of the mechanical properties of these armored objects, with attention given to the two-dimensional granular state of the interface. Small inhomogeneous stresses produce a plastic response, while homogeneous stresses produce a weak elastic response. Shear-driven particle-scale rearrangements explain the basic threshold needed to obtain the near-perfect plastic deformation that is observed. Furthermore, the inhomogeneous stress state of the interface is exhibited experimentally by using surfactants to destabilize the particles on the surface. Since the interfacially trapped particles retain their individual characteristics, armored interfaces can be recognized as a kind of composite material with distinct chemical, structural, and mechanical properties.

  14. Investigation of the interfacial tension of complex coacervates using field-theoretic simulations

    NASA Astrophysics Data System (ADS)

    Riggleman, Robert A.; Kumar, Rajeev; Fredrickson, Glenn H.

    2012-01-01

    Complex coacervation, a liquid-liquid phase separation that occurs when two oppositely charged polyelectrolytes are mixed in a solution, has the potential to be exploited for many emerging applications including wet adhesives and drug delivery vehicles. The ultra-low interfacial tension of coacervate systems against water is critical for such applications, and it would be advantageous if molecular models could be used to characterize how various system properties (e.g., salt concentration) affect the interfacial tension. In this article we use field-theoretic simulations to characterize the interfacial tension between a complex coacervate and its supernatant. After demonstrating that our model is free of ultraviolet divergences (calculated properties converge as the collocation grid is refined), we develop two methods for calculating the interfacial tension from field-theoretic simulations. One method relies on the mechanical interpretation of the interfacial tension as the interfacial pressure, and the second method estimates the change in free energy as the area between the two phases is changed. These are the first calculations of the interfacial tension from full field-theoretic simulation of which we are aware, and both the magnitude and scaling behaviors of our calculated interfacial tension agree with recent experiments.

  15. Investigation of the interfacial tension of complex coacervates using field-theoretic simulations

    SciTech Connect

    Kumar, Rajeev

    2012-01-01

    Complex coacervation, a liquid-liquid phase separation that occurs when two oppositely charged polyelectrolytes are mixed in a solution, has the potential to be exploited for many emerging applications including wet adhesives and drug delivery vehicles. The ultra-low interfacial tension of coacervate systems against water is critical for such applications, and it would be advantageous if molecular models could be used to characterize how various system properties (e.g., salt concentration) affect the interfacial tension. In this article we use field-theoretic simulations to characterize the interfacial tension between a complex coacervate and its supernatant. After demonstrating that our model is free of ultraviolet divergences (calculated properties converge as the collocation grid is refined), we develop two methods for calculating the interfacial tension from field-theoretic simulations. One method relies on the mechanical interpretation of the interfacial tension as the interfacial pressure, and the second method estimates the change in free energy as the area between the two phases is changed. These are the first calculations of the interfacial tension from full field theoretic simulation of which we are aware, and both the magnitude and scaling behaviors of our calculated interfacial tension agree with recent experiments.

  16. Self-Assembly of Single-Sized and Binary Colloidal Particles at Air/Water Interface by Surface Confinement and Water Discharge.

    PubMed

    Lotito, Valeria; Zambelli, Tomaso

    2016-09-20

    We present an innovative apparatus allowing self-assembly at air/water interface in a smooth and reproducible way. The combination of water discharge and surface confinement of the area over which self-assembly takes place allows transfer of the assembled monolayer without any risk of damage to the colloidal crystal. As we demonstrate, the designed approach offers remarkable advantages in terms of cost and robustness compared to state-of-the art methods and is suitable for the fabrication of highly ordered monolayers even for more challenging assembly experiments such as transfer on rough substrates or assembly of binary colloids. Hence, our apparatus represents a significant headway toward high scale production of large area colloidal crystals. For the binary colloid assembly experiments, we also report the first experimental demonstration of a morphology based on the alternation of three and four small particles in the interstices between large particles. PMID:27574790

  17. Self-Assembly of Single-Sized and Binary Colloidal Particles at Air/Water Interface by Surface Confinement and Water Discharge.

    PubMed

    Lotito, Valeria; Zambelli, Tomaso

    2016-09-20

    We present an innovative apparatus allowing self-assembly at air/water interface in a smooth and reproducible way. The combination of water discharge and surface confinement of the area over which self-assembly takes place allows transfer of the assembled monolayer without any risk of damage to the colloidal crystal. As we demonstrate, the designed approach offers remarkable advantages in terms of cost and robustness compared to state-of-the art methods and is suitable for the fabrication of highly ordered monolayers even for more challenging assembly experiments such as transfer on rough substrates or assembly of binary colloids. Hence, our apparatus represents a significant headway toward high scale production of large area colloidal crystals. For the binary colloid assembly experiments, we also report the first experimental demonstration of a morphology based on the alternation of three and four small particles in the interstices between large particles.

  18. Liquid Surface X-ray Studies of Gold Nanoparticle-Phospholipid Films at the Air/Water Interface.

    PubMed

    You, Siheng Sean; Heffern, Charles T R; Dai, Yeling; Meron, Mati; Henderson, J Michael; Bu, Wei; Xie, Wenyi; Lee, Ka Yee C; Lin, Binhua

    2016-09-01

    Amphiphilic phospholipids and nanoparticles functionalized with hydrophobic capping ligands have been extensively investigated for their capacity to self-assemble into Langmuir monolayers at the air/water interface. However, understanding of composite films consisting of both nanoparticles and phospholipids, and by extension, the complex interactions arising between nanomaterials and biological membranes, remains limited. In this work, dodecanethiol-capped gold nanoparticles (Au-NPs) with an average core diameter of 6 nm were incorporated into 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayers with surface densities ranging from 0.1 to 20% area coverage at a surface pressure of 30 mN/m. High resolution liquid surface X-ray scattering studies revealed a phase separation of the DPPC and Au-NP components of the composite film, as confirmed with atomic force microscopy after the film was transferred to a substrate. At low Au-NP content, the structural organization of the phase-separated film is best described as a DPPC film containing isolated islands of Au-NPs. However, increasing the Au-NP content beyond 5% area coverage transforms the structural organization of the composite film to a long-range interconnected network of Au-NP strands surrounding small seas of DPPC, where the density of the Au-NP network increases with increasing Au-NP content. The observed phase separation and structural organization of the phospholipid and nanoparticle components in these Langmuir monolayers are useful for understanding interactions of nanoparticles with biological membranes. PMID:27459364

  19. Atmospheric photochemistry at a fatty acid–coated air-water interface

    NASA Astrophysics Data System (ADS)

    Rossignol, Stéphanie; Tinel, Liselotte; Bianco, Angelica; Passananti, Monica; Brigante, Marcello; Donaldson, D. James; George, Christian

    2016-08-01

    Although fatty acids are believed to be photochemically inert in the actinic region, complex volatile organic compounds are produced during illumination of an air-water interface coated solely with a monolayer of carboxylic acid. When aqueous solutions containing nonanoic acid (NA) at bulk concentrations that give rise to just over a monolayer of NA coverage are illuminated with actinic radiation, saturated and unsaturated aldehydes are seen in the gas phase, and more highly oxygenated products appear in the aqueous phase. This chemistry is probably initiated by triplet-state NA molecules excited by direct absorption of actinic light at the water surface. Because fatty acids–covered interfaces are ubiquitous in the environment, such photochemical processing will have a substantial impact on local ozone and particle formation.

  20. Linear and nonlinear microrheology of lysozyme layers forming at the air-water interface.

    PubMed

    Allan, Daniel B; Firester, Daniel M; Allard, Victor P; Reich, Daniel H; Stebe, Kathleen J; Leheny, Robert L

    2014-09-28

    We report experiments studying the mechanical evolution of layers of the protein lysozyme adsorbing at the air-water interface using passive and active microrheology techniques to investigate the linear and nonlinear rheological response, respectively. Following formation of a new interface, the linear shear rheology, which we interrogate through the Brownian motion of spherical colloids at the interface, becomes viscoelastic with a complex modulus that has approximately power-law frequency dependence. The power-law exponent characterizing this frequency dependence decreases steadily with increasing layer age. Meanwhile, the nonlinear microrheology, probed via the rotational motion of magnetic nanowires at the interface, reveals a layer response characteristic of a shear-thinning power-law fluid with a flow index that decreases with age. We discuss two possible frameworks for understanding this mechanical evolution: gelation and the formation of a soft glass phase. PMID:24969505

  1. Compositions of surface layers formed on amalgams in air, water, and saline.

    PubMed

    Hanawa, T; Gnade, B E; Ferracane, J L; Okabe, T; Watari, F

    1993-12-01

    The surface layers formed on both a zinc-free and a zinc-containing dental amalgam after polishing and aging in air, water, or saline, were characterized using x-ray photoelectron spectroscopy (XPS) to determine the compositions of the surface layers which might govern the release of mercury from amalgam. The XPS data revealed that the formation of the surface layer on the zinc-containing amalgam was affected by the environment in which the amalgam was polished and aged, whereas that on the zinc-free amalgam was not affected. In addition, among the elements contained in amalgam, zinc was the most reactive with the environment, and was preferentially dissolved from amalgam into water or saline. Mercury atoms existed in the metallic state in the surface layer.

  2. Entropy of adsorption of mixed surfactants from solutions onto the air/water interface

    USGS Publications Warehouse

    Chen, L.-W.; Chen, J.-H.; Zhou, N.-F.

    1995-01-01

    The partial molar entropy change for mixed surfactant molecules adsorbed from solution at the air/water interface has been investigated by surface thermodynamics based upon the experimental surface tension isotherms at various temperatures. Results for different surfactant mixtures of sodium dodecyl sulfate and sodium tetradecyl sulfate, decylpyridinium chloride and sodium alkylsulfonates have shown that the partial molar entropy changes for adsorption of the mixed surfactants were generally negative and decreased with increasing adsorption to a minimum near the maximum adsorption and then increased abruptly. The entropy decrease can be explained by the adsorption-orientation of surfactant molecules in the adsorbed monolayer and the abrupt entropy increase at the maximum adsorption is possible due to the strong repulsion between the adsorbed molecules.

  3. Thermodynamics of Iodide Adsorption at the Instantaneous Air-Water Interface.

    SciTech Connect

    Stern, Abraham C.; Baer, Marcel D.; Mundy, Christopher J.; Tobias, Douglas J.

    2013-03-21

    We perform simulations using both polarizable and non-polarizable force fields to study the adsorption of iodide to the air-water interface. A novel aspect of our analysis is that the progress of the adsorption is measured as the distance from the instantaneous interface, which is defined by a coarse-graining scheme proposed recently by Willard and Chandler.\\cite{chandler1} Referring structural and thermodynamic quantities to the instantaneous interface unmasks molecular-scale details that are obscured by thermal fluctuations when the same quantities are referred to an average measure of the position of the interface, such as the Gibbs dividing surface. Our results suggest that an ion adsorbed at the interface resides primarily in the topmost layer water.

  4. Near-surface physics during convection affecting air-water gas transfer

    NASA Astrophysics Data System (ADS)

    Fredriksson, S. T.; Arneborg, L.; Nilsson, H.; Handler, R. A.

    2016-05-01

    The gas flux at the water surface is affected by physical processes including turbulence from wind shear, microscale wave breaking, large-scale breaking, and convection due to heat loss at the surface. The main route in the parameterizations of the gas flux has been to use the wind speed as a proxy for the gas flux velocity, indirectly taking into account the dependency of the wind shear and the wave processes. The interest in the contributions from convection processes has increased as the gas flux from inland waters (with typically lower wind and sheltered conditions) now is believed to play a substantial role in the air-water gas flux budget. The gas flux is enhanced by convection through the mixing of the mixed layer as well as by decreasing the diffusive boundary layer thickness. The direct numerical simulations performed in this study are shown to be a valuable tool to enhance the understanding of this flow configuration often present in nature.

  5. Turbulent heat and mass transfers across a thermally stratified air-water interface

    NASA Technical Reports Server (NTRS)

    Papadimitrakis, Y. A.; Hsu, Y.-H. L.; Wu, J.

    1986-01-01

    Rates of heat and mass transfer across an air-water interface were measured in a wind-wave research facility, under various wind and thermal stability conditions (unless otherwise noted, mass refers to water vapor). Heat fluxes were obtained from both the eddy correlation and the profile method, under unstable, neutral, and stable conditions. Mass fluxes were obtained only under unstable stratification from the profile and global method. Under unstable conditions the turbulent Prandtl and Schmidt numbers remain fairly constant and equal to 0.74, whereas the rate of mass transfer varies linearly with bulk Richardson number. Under stable conditions the turbulent Prandtl number rises steadily to a value of 1.4 for a bulk Richardson number of about 0.016. Results of heat and mass transfer, expressed in the form of bulk aerodynamic coefficients with friction velocity as a parameter, are also compared with field data.

  6. Trapping of Sodium Dodecyl Sulfate at the Air-Water Interface of Oscillating Bubbles.

    PubMed

    Corti, Mario; Pannuzzo, Martina; Raudino, Antonio

    2015-06-16

    We report that at very low initial bulk concentrations, a couple of hundred times below the critical micellar concentration (CMC), anionic surfactant sodium dodecyl sulfate (SDS) adsorbed at the air-water interface of a gas bubble cannot be removed, on the time scale of the experiment (hours), when the surrounding solution is gently replaced by pure water. Extremely sensitive interferometric measurements of the resonance frequency of the bubble-forced oscillations give precise access to the concentration of the surfactant monolayer. The bulk-interface dynamic exchange of SDS molecules is shown to be inhibited below a concentration which we believe refers to a kind of gas-liquid phase transition of the surface monolayer. Above this threshold we recover the expected concentration-dependent desorption. The experimental observations are interpreted within simple energetic considerations supported by molecular dynamics (MD) calculations. PMID:26039913

  7. Phospholipid surface bilayers at the air-water interface. II. Water permeability of dimyristoylphosphatidylcholine surface bilayers.

    PubMed Central

    Ginsberg, L; Gershfeld, N L

    1985-01-01

    Dispersions of dimyristoylphosphatidylcholine (DMPC) in water have been reported to form a structure at 29 degrees C at the equilibrium air/water surface with a molecular density equal to that of a typical bilayer. In this study, the water permeability of this structure has been evaluated by measuring the rate of water evaporation from DMPC dispersions in water in the temperature range where the surface film density exceeds that of a monolayer. Evaporation rates for the lipid dispersions did not deviate from those for lipid-free systems throughout the entire temperature range examined (20-35 degrees C) except at 29 degrees C, where a barrier to evaporation was detected. This strengthens the view that the structure that forms at this temperature has the properties of a typical bilayer. PMID:3978199

  8. Atmospheric photochemistry at a fatty acid-coated air-water interface

    NASA Astrophysics Data System (ADS)

    Rossignol, Stéphanie; Tinel, Liselotte; Bianco, Angelica; Passananti, Monica; Brigante, Marcello; Donaldson, D. James; George, Christian

    2016-08-01

    Although fatty acids are believed to be photochemically inert in the actinic region, complex volatile organic compounds are produced during illumination of an air-water interface coated solely with a monolayer of carboxylic acid. When aqueous solutions containing nonanoic acid (NA) at bulk concentrations that give rise to just over a monolayer of NA coverage are illuminated with actinic radiation, saturated and unsaturated aldehydes are seen in the gas phase, and more highly oxygenated products appear in the aqueous phase. This chemistry is probably initiated by triplet-state NA molecules excited by direct absorption of actinic light at the water surface. Because fatty acids-covered interfaces are ubiquitous in the environment, such photochemical processing will have a substantial impact on local ozone and particle formation.

  9. Reversible monolayer-to-crystalline phase transition in amphiphilic silsesquioxane at the air-water interface

    DOE PAGES

    Banerjee, R.; Sanyal, M. K.; Bera, M. K.; Gibaud, A.; Lin, B.; Meron, M.

    2015-02-17

    We report on the counter intuitive reversible crystallisation of two-dimensional monolayer of Trisilanolisobutyl Polyhedral Oligomeric SilSesquioxane (TBPOSS) on water surface using synchrotron x-ray scattering measurements. Amphiphilic TBPOSS form rugged monolayers and Grazing Incidence X-ray Scattering (GIXS) measurements reveal that the in-plane inter-particle correlation peaks, characteristic of two-dimensional system, observed before transition is replaced by intense localized spots after transition. The measured x-ray scattering data of the non-equilibrium crystalline phase on the air-water interface could be explained with a model that assumes periodic stacking of the TBPOSS dimers. These crystalline stacking relaxes upon decompression and the TBPOSS layer retains its initialmore » monolayer state. The existence of these crystals in compressed phase is confirmed by atomic force microscopy measurements by lifting the materials on a solid substrate.« less

  10. Atmospheric photochemistry at a fatty acid-coated air-water interface.

    PubMed

    Rossignol, Stéphanie; Tinel, Liselotte; Bianco, Angelica; Passananti, Monica; Brigante, Marcello; Donaldson, D James; George, Christian

    2016-08-12

    Although fatty acids are believed to be photochemically inert in the actinic region, complex volatile organic compounds are produced during illumination of an air-water interface coated solely with a monolayer of carboxylic acid. When aqueous solutions containing nonanoic acid (NA) at bulk concentrations that give rise to just over a monolayer of NA coverage are illuminated with actinic radiation, saturated and unsaturated aldehydes are seen in the gas phase, and more highly oxygenated products appear in the aqueous phase. This chemistry is probably initiated by triplet-state NA molecules excited by direct absorption of actinic light at the water surface. Because fatty acids-covered interfaces are ubiquitous in the environment, such photochemical processing will have a substantial impact on local ozone and particle formation. PMID:27516601

  11. Reversible monolayer-to-crystalline phase transition in amphiphilic silsesquioxane at the air-water interface

    SciTech Connect

    Banerjee, R.; Sanyal, M. K.; Bera, M. K.; Gibaud, A.; Lin, B.; Meron, M.

    2015-02-17

    We report on the counter intuitive reversible crystallisation of two-dimensional monolayer of Trisilanolisobutyl Polyhedral Oligomeric SilSesquioxane (TBPOSS) on water surface using synchrotron x-ray scattering measurements. Amphiphilic TBPOSS form rugged monolayers and Grazing Incidence X-ray Scattering (GIXS) measurements reveal that the in-plane inter-particle correlation peaks, characteristic of two-dimensional system, observed before transition is replaced by intense localized spots after transition. The measured x-ray scattering data of the non-equilibrium crystalline phase on the air-water interface could be explained with a model that assumes periodic stacking of the TBPOSS dimers. These crystalline stacking relaxes upon decompression and the TBPOSS layer retains its initial monolayer state. The existence of these crystals in compressed phase is confirmed by atomic force microscopy measurements by lifting the materials on a solid substrate.

  12. Linear and nonlinear microrheology of lysozyme layers forming at the air-water interface.

    PubMed

    Allan, Daniel B; Firester, Daniel M; Allard, Victor P; Reich, Daniel H; Stebe, Kathleen J; Leheny, Robert L

    2014-09-28

    We report experiments studying the mechanical evolution of layers of the protein lysozyme adsorbing at the air-water interface using passive and active microrheology techniques to investigate the linear and nonlinear rheological response, respectively. Following formation of a new interface, the linear shear rheology, which we interrogate through the Brownian motion of spherical colloids at the interface, becomes viscoelastic with a complex modulus that has approximately power-law frequency dependence. The power-law exponent characterizing this frequency dependence decreases steadily with increasing layer age. Meanwhile, the nonlinear microrheology, probed via the rotational motion of magnetic nanowires at the interface, reveals a layer response characteristic of a shear-thinning power-law fluid with a flow index that decreases with age. We discuss two possible frameworks for understanding this mechanical evolution: gelation and the formation of a soft glass phase.

  13. A criterion for the onset of slugging in horizontal stratified air-water countercurrent flow

    SciTech Connect

    Chun, Moon-Hyun; Lee, Byung-Ryung; Kim, Yang-Seok

    1995-09-01

    This paper presents an experimental and theoretical investigation of wave height and transition criterion from wavy to slug flow in horizontal air-water countercurrent stratified flow conditions. A theoretical formula for the wave height in a stratified wavy flow regime has been developed using the concept of total energy balance over a wave crest to consider the shear stress acting on the interface of two fluids. From the limiting condition of the formula for the wave height, a necessary criterion for transition from a stratified wavy flow to a slug flow has been derived. A series of experiments have been conducted changing the non-dimensional water depth and the flow rates of air in a horizontal pipe and a duct. Comparisons between the measured data and the predictions of the present theory show that the agreement is within {plus_minus}8%.

  14. Real-time imaging of crystallization in polylactide enantiomeric monolayers at the air-water interface.

    PubMed

    Kim, Young Shin; Snively, Christopher M; Liu, Yujuan; Rabolt, John F; Chase, D Bruce

    2008-10-01

    A newly developed planar array infrared reflection-absorption spectrograph (PA-IRRAS) offers significant advantages over conventional approaches including fast acquisition speed, excellent compensation for water vapor, and an excellent capacity for large infrared accessories, e.g., a water trough. In this study, the origin of stereocomplexation in a polylactide enantiomeric monolayer at the air-water interface was investigated using PA-IRRAS. PA-IRRAS was used as a probe to follow the real-time conformational changes associated with intermolecular interactions of polymer chains during the compression of the monolayers. It was found that a mixture of poly(D-lactic acid) (PDLA) and poly(L-lactic acid) (PLLA) (D/L) formed a stereocomplex when the two-dimensional monolayer developed at the air-water interface before film compression, indicating that there is no direct correlation between film compression and stereocomplexation. PA-IRRAS spectra of the stereocomplex exhibited distinct band shifts in crystalline sensitive components, e.g., the vas(C-O-C, h) mode, as well as amorphous-dependent components, e.g., the vs(C-O-C) mode, when compared with the spectra of PLLA alone. On the other hand, time-resolved PA-IRRAS spectra, which were obtained as the films were being compressed, revealed that both monolayers of PLLA and mixed PLLA/PDLA stereocomplex were crystallized into a 10(3)-helix and a 3(1)-helix, respectively, with a distinct band shift in crystalline sensitive components only. Fourier self-deconvolution of the spectra demonstrated that the band shift in crystalline sensitive components is correlated with the intermolecular interaction of polymer chains. PMID:18781784

  15. Air/water oxidative desulfurization of coal and sulfur-containing compounds

    NASA Astrophysics Data System (ADS)

    Warzinski, R. P.; Freidman, S.; LaCount, R. B.

    1981-02-01

    Air/water Oxydesulfurization has been demonstrated in autoclave experiments at the Pittsburgh Energy Technology Center for various coals representative of the major U. S. coal basins. The applicability at present of this treatment for producing an environmentally acceptable coal has been restricted by recently proposed SO2 emission standards for utility boilers. The product would, however, be attractive to the many smaller industrial coal users who cannot afford to operate and maintain flue gas desulfurization systems. It is also possible that the utility industry could realize a benefit by using chemically cleaned coal with partial flue gas scrubbing. The higher cost of the cleaned coal would be offset by the reduction in capital and operating costs resulting from decreased FGD requirements. The susceptibility of sulfur in coal to oxidative removal varies with the nature of the sulfur-containing species. The inorganic sulfur compounds, primarily pyrite, marcasite, and iron sulfate, are more amenable to treatment than the organically bound sulfur which exhibits varying degrees of resistance depending on its chemical environment. Air/water Oxydesulfurization consistently removes in excess of 90 percent of the pyritic sulfur; the extent and efficiency of organic sulfur removal however, depends on the type of coal and severity of treatment used. In general, the organic sulfur of the higher rank coals exhibits more resistance to treatment than that of the lower rank coals; however, the accompanying heating value is greater for the latter. Similar treatment of sulfur-containing model compounds further illustrates the relative susceptibilities of different chemical species to oxidation. Application of these data to the understanding of the complex chemistry involved in the treatment of coal is a preliminary step toward improving the efficiency of Oxydesulfurization.

  16. Impact of interfacial tension on residual CO2 clusters in porous sandstone

    NASA Astrophysics Data System (ADS)

    Jiang, Fei; Tsuji, Takeshi

    2015-03-01

    We develop a numerical simulation that uses the lattice Boltzmann method to directly calculate the characteristics of residual nonwetting-phase clusters to quantify capillary trapping mechanisms in real sandstone. For this purpose, a digital-rock-pore model reconstructed from micro-CT-scanned images of Berea sandstone is filtered and segmented into a binary file. The residual-cluster distribution is generated following simulation of the drainage and imbibition processes. The characteristics of the residual cluster in terms of size distribution, major length, interfacial area, and sphericity are investigated under conditions of different interfacial tension (IFT). Our results indicate that high interfacial tension increases the residual saturation and leads to a large size distribution of residual clusters. However, low interfacial tension results in a larger interfacial area, which is beneficial for dissolution and reaction processes during geological carbon storage. Analysis of the force balance acting on the residual clusters demonstrates that trapping stability is higher in high interfacial tension case, and the interfacial tension should be a controlling factor for the trapping stability in addition to the pore geometry and connectivity. The proposed numerical method can handle the complex displacement of multicomponent systems in porous media. By using this method, we can obtain residual-cluster distributions under different conditions for optimizing the storage capacity of carbon-storage projects.

  17. Measuring Interfacial Tension Between Immiscible Liquids

    NASA Technical Reports Server (NTRS)

    Rashidnia, Nasser; Balasubramaniam, R.; Delsignore, David M.

    1995-01-01

    Glass capillary tube technique measures interfacial tension between two immiscible liquids. Yields useful data over fairly wide range of interfacial tensions, both for pairs of liquids having equal densities and pairs of liquids having unequal densities. Data on interfacial tensions important in diverse industrial chemical applications, including enhanced extraction of oil; printing; processing foods; and manufacture of paper, emulsions, foams, aerosols, detergents, gel encapsulants, coating materials, fertilizers, pesticides, and cosmetics.

  18. Interfacial reactions between titanium and borate glass

    SciTech Connect

    Brow, R.K.; Saha, S.K.; Goldstein, J.I.

    1992-12-31

    Interfacial reactions between melts of several borate glasses and titanium have been investigated by analytical scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS). A thin titanium boride interfacial layer is detected by XPS after short (30 minutes) thermal treatments. ASEM analyses after longer thermal treatments (8--120 hours) reveal boron-rich interfacial layers and boride precipitates in the Ti side of the interface.

  19. Interfacial thermodynamics of water and six other liquid solvents.

    PubMed

    Pascal, Tod A; Goddard, William A

    2014-06-01

    We examine the thermodynamics of the liquid-vapor interface by direct calculation of the surface entropy, enthalpy, and free energy from extensive molecular dynamics simulations using the two-phase thermodynamics (2PT) method. Results for water, acetonitrile, cyclohexane, dimethyl sulfoxide, hexanol, N-methyl acetamide, and toluene are presented. We validate our approach by predicting the interfacial surface tensions (IFT--excess surface free energy per unit area) in excellent agreement with the mechanical calculations using Kirkwood-Buff theory. Additionally, we evaluate the temperature dependence of the IFT of water as described by the TIP4P/2005, SPC/Ew, TIP3P, and mW classical water models. We find that the TIP4P/2005 and SPC/Ew water models do a reasonable job of describing the interfacial thermodynamics; however, the TIP3P and mW are quite poor. We find that the underprediction of the experimental IFT at 298 K by these water models results from understructured surface molecules whose binding energies are too weak. Finally, we performed depth profiles of the interfacial thermodynamics which revealed long tails that extend far into what would be considered bulk from standard Gibbs theory. In fact, we find a nonmonotonic interfacial free energy profile for water, a unique feature that could have important consequences for the absorption of ions and other small molecules.

  20. Time-Dependent Interfacial Properties and DNAPL Mobility

    SciTech Connect

    Tuck, D.M.

    1999-03-10

    Interfacial properties play a major role in governing where and how dense nonaqueous phase liquids (DNAPLs) move in the subsurface. Interfacial tension and contact angle measurements were obtained for a simple, single component DNAPL (tetrachloroethene, PCE), complex laboratory DNAPLs (PCE plus Sudan IV dye), and a field DNAPL from the Savannah River Site (SRS) M-Area DNAPL (PCE, trichloroethene [TCE], and maching oils). Interfacial properties for complex DNAPLs were time-dependent, a phenomenon not observed for PCE alone. Drainage capillary pressure-saturation curves are strongly influenced by interfacial properties. Therefore time-dependence will alter the nature of DNAPL migration and penetration. Results indicate that the time-dependence of PCE with relatively high Sudan IV dye concentrations is comparable to that of the field DNAPL. Previous DNAPL mobility experiments in which the DNAPL was dyed should be reviewed to determine whether time-dependent properties influenced the resutls. Dyes appear to make DNAPL more complex, and therefore a more realistic analog for field DNAPLs than single component DNAPLs.

  1. The Hydrophobic Effect in Solute Partitioning and Interfacial Tension

    PubMed Central

    Jackson, Meyer B.

    2016-01-01

    Studies of the partitioning of hydrophobic solutes between water and nonpolar solvents provide estimates for the energy cost of creating hydrophobic-water contacts. This energy is a factor of three lower than the work of adhesion derived from interfacial tension measurements. This discrepancy noted by Tanford in 1979 is widely viewed as a serious challenge to our understanding of hydrophobic interactions. However, the interfacial energy of a water-alkane interface depends on chain length. A simple analysis of published data shows that the loss of rotational freedom of an alkane chain at an interface accounts quantitatively for the length-dependent contribution to interfacial tension, leaving a length-independent contribution very close to the free energy of transfer per unit of solvent accessible surface area. This analysis thus clarifies the discrepancy between the thermodynamic and interfacial tension measurements of hydrophobic interaction energy. Alkanes do not loose rotational freedom when transferred between two different liquid phases but they do at an interface. This reconciles the difference between microscopic and macroscopic measurements. Like the partitioning free energy, the work of adhesion also has a large entropy and small enthalpy at 20 oC. PMID:26813712

  2. Structural and topographical characteristics of adsorbed WPI and monoglyceride mixed monolayers at the air-water interface.

    PubMed

    Patino, Juan M Rodríguez; Fernández, Marta Cejudo

    2004-05-25

    In this work we have analyzed the structural and topographical characteristics of mixed monolayers formed by an adsorbed whey protein isolate (WPI) and a spread monoglyceride monolayer (monopalmitin or monoolein) on the previously adsorbed protein film. Measurements of the surface pressure (pi)-area (A) isotherm were obtained at 20 degrees C and at pH 7 for protein-adsorbed films from water in a Wilhelmy-type film balance. Since the surface concentration (1/A) is actually unknown for the adsorbed monolayer, the values were derived by assuming that the A values for adsorbed and spread monolayers were equal at the collapse point of the mixed film. The pi-A isotherm deduced for adsorbed WPI monolayer in this work is practically the same as that obtained directly by spreading. For WPI-monoglyceride mixed films, the pi-A isotherms for adsorbed and spread monolayers at pi higher than the equilibrium surface pressure of WPI are practically coincident, a phenomenon which may be attributed to the protein displacement by the monoglyceride from the interface. At lower surface pressures, WPI and monoglyceride coexist at the interface and the adsorbed and spread pi-A isotherms (i.e., the monolayer structure of the mixed films) are different. Monopalmitin has a higher capacity than monoolein for the displacement of protein from the air-water interface. However, some degree of interactions exists between proteins and monoglycerides and these interactions are higher for adsorbed than for spread films. The topography of the monolayer corroborates these conclusions.

  3. Strong improvement of interfacial properties can result from slight structural modifications of proteins: the case of native and dry-heated lysozyme.

    PubMed

    Desfougères, Yann; Saint-Jalmes, Arnaud; Salonen, Anniina; Vié, Véronique; Beaufils, Sylvie; Pezennec, Stéphane; Desbat, Bernard; Lechevalier, Valérie; Nau, Françoise

    2011-12-20

    Identification of the key physicochemical parameters of proteins that determine their interfacial properties is still incomplete and represents a real stake challenge, especially for food proteins. Many studies have thus consisted in comparing the interfacial behavior of different proteins, but it is difficult to draw clear conclusions when the molecules are completely different on several levels. Here the adsorption process of a model protein, the hen egg-white lysozyme, and the same protein that underwent a thermal treatment in the dry state, was characterized. The consequences of this treatment have been previously studied: net charge and hydrophobicity increase and lesser protein stability, but no secondary and tertiary structure modification (Desfougères, Y.; Jardin, J.; Lechevalier, V.; Pezennec, S.; Nau, F. Biomacromolecules 2011, 12, 156-166). The present study shows that these slight modifications dramatically increase the interfacial properties of the protein, since the adsorption to the air-water interface is much faster and more efficient (higher surface pressure). Moreover, a thick and strongly viscoelastic multilayer film is created, while native lysozyme adsorbs in a fragile monolayer film. Another striking result is that completely different behaviors were observed between two molecular species, i.e., native and native-like lysozyme, even though these species could not be distinguished by usual spectroscopic methods. This suggests that the air-water interface could be considered as a useful tool to reveal very subtle differences between protein molecules. PMID:22040020

  4. Molecular recognition of 7-(2-octadecyloxycarbonylethyl)guanine to cytidine at the air/water interface and LB film studied by Fourier transform infrared spectroscopy.

    PubMed

    Miao, Wangen; Luo, Xuzhong; Liang, Yingqiu

    2003-03-15

    Monolayer behavior of a nucleolipid amphiphile, 7-(2-octadecyloxycarbonylethyl)guanine (ODCG), on aqueous cytidine solution was investigated by means of surface-molecular area (pi-A) isotherms. It indicates that molecular recognition by hydrogen bonding is present between ODCG monolayer and the cytidine in subphase. The Fourier transform infrared (FTIR) transmission spectroscopic result indicates that the cytidine molecules in the subphase can be transferred onto solid substrates by Langmuir-Blodgett (LB) technique as a result of the formation of Watson-Crick base-pairing at the air/water interface. Investigation by rotating polarized FTIR transmission also suggests that the headgroup recognition of this amphiphile to the dissolved cytidine influence the orientation of the tailchains.

  5. Wind driven vertical transport in a vegetated, wetland water column with air-water gas exchange

    NASA Astrophysics Data System (ADS)

    Poindexter, C.; Variano, E. A.

    2010-12-01

    Flow around arrays of cylinders at low and intermediate Reynolds numbers has been studied numerically, analytically and experimentally. Early results demonstrated that at flow around randomly oriented cylinders exhibits reduced turbulent length scales and reduced diffusivity when compared to similarly forced, unimpeded flows (Nepf 1999). While horizontal dispersion in flows through cylinder arrays has received considerable research attention, the case of vertical dispersion of reactive constituents has not. This case is relevant to the vertical transfer of dissolved gases in wetlands with emergent vegetation. We present results showing that the presence of vegetation can significantly enhance vertical transport, including gas transfer across the air-water interface. Specifically, we study a wind-sheared air-water interface in which randomly arrayed cylinders represent emergent vegetation. Wind is one of several processes that may govern physical dispersion of dissolved gases in wetlands. Wind represents the dominant force for gas transfer across the air-water interface in the ocean. Empirical relationships between wind and the gas transfer coefficient, k, have been used to estimate spatial variability of CO2 exchange across the worlds’ oceans. Because wetlands with emergent vegetation are different from oceans, different model of wind effects is needed. We investigated the vertical transport of dissolved oxygen in a scaled wetland model built inside a laboratory tank equipped with an open-ended wind tunnel. Plastic tubing immersed in water to a depth of approximately 40 cm represented emergent vegetation of cylindrical form such as hard-stem bulrush (Schoenoplectus acutus). After partially removing the oxygen from the tank water via reaction with sodium sulfite, we used an optical probe to measure dissolved oxygen at mid-depth as the tank water re-equilibrated with the air above. We used dissolved oxygen time-series for a range of mean wind speeds to estimate the

  6. Synthesis and electrochemical properties of polyaniline nanofibers by interfacial polymerization.

    PubMed

    Manuel, James; Ahn, Jou-Hyeon; Kim, Dul-Sun; Ahn, Hyo-Jun; Kim, Ki-Won; Kim, Jae-Kwang; Jacobsson, Per

    2012-04-01

    Polyaniline nanofibers were prepared by interfacial polymerization with different organic solvents such as chloroform and carbon tetrachloride. Field emission scanning electron microscopy and transmission electron microscopy were used to study the morphological properties of polyaniline nanofibers. Chemical characterization was carried out using Fourier transform infrared spectroscopy, UV-Vis spectroscopy, and X-ray diffraction spectroscopy and surface area was measured using BET isotherm. Polyaniline nanofibers doped with lithium hexafluorophosphate were prepared and their electrochemical properties were evaluated.

  7. Convection and interfacial mass exchange

    NASA Astrophysics Data System (ADS)

    Colinet, P.; Legros, J. C.; Dauby, P. C.; Lebon, G.; Bestehorn, M.; Stephan, P.; Tadrist, L.; Cerisier, P.; Poncelet, D.; Barremaecker, L.

    2005-10-01

    Mass-exchange through fluid interfaces is ubiquitous in many natural and industrial processes. Yet even basic phase-change processes such as evaporation of a pure liquid are not fully understood, in particular when coupled with fluid motions in the vicinity of the phase-change interface, or with microscopic physical phenomena in the vicinity of a triple line (where the interface meets a solid). Nowadays, many industries recognise that this lack of fundamental knowledge is hindering the optimisation of existing processes. Their modelling tools are too dependent on empirical correlations with a limited - and often unknown - range of applicability. In addition to the intrinsic multiscale nature of the phenomena involved in typical industrial processes linked to interfacial mass exchange, their study is highly multi-disciplinary, involving tools and techniques belonging to physical chemistry, chemical engineering, fluid dynamics, non-linear physics, non-equilibrium thermodynamics, chemistry and statistical physics. From the experimental point of view, microgravity offers a unique environment to obtain valuable data on phase-change processes, greatly reducing the influence of body forces and allowing the detailed and accurate study of interfacial dynamics. In turn, such improved understanding leads to optimisation of industrial processes and devices involving phase-change, both for space and ground applications.

  8. Sinusoidal Forcing of Interfacial Films

    NASA Astrophysics Data System (ADS)

    Rasheed, Fayaz; Raghunandan, Aditya; Hirsa, Amir; Lopez, Juan

    2015-11-01

    Fluid transport, in vivo, is accomplished via pumping mechanisms of the heart and lungs, which results in biological fluids being subjected to oscillatory shear. Flow is known to influence biological macromolecules, but predicting the effect of shear is incomplete without also accounting for the influence of complex interfaces ubiquitous throughout the body. Here, we investigated the oscillatory response of the structure of aqueous interfacial films using a cylindrical knife edge viscometer. Vitamin K1 was used as a model monolayer because its behaviour has been thoroughly quantified and it doesn't show any measurable hysteresis. The monolayer was subjected to sinusoidal forcing under varied conditions of surface concentrations, periodic frequencies, and knife edge amplitudes. Particle Image Velocimetry(PIV) data was collected using Brewster Angle Microscopy(BAM), revealing the influence of oscillatory interfacial shear stress on the monolayer. Insights were gained as to how the velocity profile dampens at specific distances from the knife edge contact depending on the amplitude, frequency, and concentration of Vitamin K1. Supported by NNX13AQ22G, National Aeronautics and Space Administration.

  9. The AirWaterGas Teacher Professional Development Program: Lessons Learned by Pairing Scientists and Teachers to Develop Curriculum on Global Climate Change and Regional Unconventional Oil and Gas Development

    NASA Astrophysics Data System (ADS)

    Gardiner, L. S.; Hatheway, B.; Rogers, J. D.; Casey, J. G.; Lackey, G.; Birdsell, D.; Brown, K.; Polmear, M.; Capps, S.; Rosenblum, J.; Sitterley, K.; Hafich, K. A.; Hannigan, M.; Knight, D.

    2015-12-01

    The AirWaterGas Teacher Professional Development Program, run by the UCAR Center for Science Education, brought together scientists and secondary science teachers in a yearlong program culminating in the development of curriculum related to the impacts of unconventional oil and gas development. Graduate students and research scientists taught about their research area and its relationship to oil and gas throughout three online courses during the 2015-16 school year, during which teachers and scientists engaged in active online discussions. Topics covered included climate change, oil and gas infrastructure, air quality, water quality, public health, and practices and policies relating to oil and gas development. Building upon their initial online interactions and a face-to-face meeting in March, teachers were paired with appropriate AirWaterGas team members as science advisors during a month-long residency in Boulder, Colorado. During the residency, graduate student scientists provided resources and feedback as teachers developed curriculum projects in collaboration with each other and UCAR science educators. Additionally, teachers and AirWaterGas researchers shared experiences on an oil and gas well site tour, and a short course on drilling methods with a drilling rig simulator. Here, we share lessons learned from both sides of the aisle, including initial results from program assessment conducted with the participating teachers.

  10. Logarithmic finite-size effects on interfacial free energies: phenomenological theory and Monte Carlo studies.

    PubMed

    Schmitz, Fabian; Virnau, Peter; Binder, Kurt

    2014-07-01

    The computation of interfacial free energies between coexisting phases (e.g., saturated vapor and liquid) by computer simulation methods is still a challenging problem due to the difficulty of an atomistic identification of an interface and interfacial fluctuations on all length scales. The approach to estimate the interfacial tension from the free-energy excess of a system with interfaces relative to corresponding single-phase systems does not suffer from the first problem but still suffers from the latter. Considering d-dimensional systems with interfacial area L(d-1) and linear dimension L(z) in the direction perpendicular to the interface, it is argued that the interfacial fluctuations cause logarithmic finite-size effects of order ln(L)/L(d-1) and order ln(L(z))/L(d-1), in addition to regular corrections (with leading-order const/L(d-1)). A phenomenological theory predicts that the prefactors of the logarithmic terms are universal (but depend on the applied boundary conditions and the considered statistical ensemble). The physical origin of these corrections are the translational entropy of the interface as a whole, "domain breathing" (coupling of interfacial fluctuations to the bulk order parameter fluctuations of the coexisting domains), and capillary waves. Using a new variant of the ensemble switch method, interfacial tensions are found from Monte Carlo simulations of d = 2 and d = 3 Ising models and a Lennard-Jones fluid. The simulation results are fully consistent with the theoretical predictions.

  11. Wind variability and sheltering effects on measurements and modeling of air-water exchange for a small lake

    NASA Astrophysics Data System (ADS)

    Markfort, Corey D.; Resseger, Emily; Porté-Agel, Fernando; Stefan, Heinz

    2014-05-01

    Lakes with a surface area of less than 10 km2 account for over 50% of the global cumulative lake surface water area, and make up more than 99% of the total number of global lakes, ponds, and wetlands. Within the boreal regions as well as some temperate and tropical areas, a significant proportion of land cover is characterized by lakes or wetlands, which can have a dramatic effect on land-atmosphere fluxes as well as the local and regional energy budget. Many of these small water bodies are surrounded by complex terrain and forest, which cause the wind blowing over a small lake or wetland to be highly variable. Wind mixing of the lake surface layer affects thermal stratification, surface temperature and air-water gas transfer, e.g. O2, CO2, and CH4. As the wind blows from the land to the lake, wake turbulence behind trees and other shoreline obstacles leads to a recirculation zone and enhanced turbulence. This wake flow results in the delay of the development of wind shear stress on the lake surface, and the fetch required for surface shear stress to fully develop may be ~O(1 km). Interpretation of wind measurements made on the lake is hampered by the unknown effect of wake turbulence. We present field measurements designed to quantify wind variability over a sheltered lake. The wind data and water column temperature profiles are used to evaluate a new method to quantify wind sheltering of lakes that takes into account lake size, shape and the surrounding landscape features. The model is validated against field data for 36 Minnesota lakes. Effects of non-uniform sheltering and lake shape are also demonstrated. The effects of wind sheltering must be included in lake models to determine the effect of wind-derived energy inputs on lake stratification, surface gas transfer, lake water quality, and fish habitat. These effects are also important for correctly modeling momentum, heat, moisture and trace gas flux to the atmosphere.

  12. Interfacial material for solid oxide fuel cell

    DOEpatents

    Baozhen, Li; Ruka, Roswell J.; Singhal, Subhash C.

    1999-01-01

    Solid oxide fuel cells having improved low-temperature operation are disclosed. In one embodiment, an interfacial layer of terbia-stabilized zirconia is located between the air electrode and electrolyte of the solid oxide fuel cell. The interfacial layer provides a barrier which controls interaction between the air electrode and electrolyte. The interfacial layer also reduces polarization loss through the reduction of the air electrode/electrolyte interfacial electrical resistance. In another embodiment, the solid oxide fuel cell comprises a scandia-stabilized zirconia electrolyte having high electrical conductivity. The scandia-stabilized zirconia electrolyte may be provided as a very thin layer in order to reduce resistance. The scandia-stabilized electrolyte is preferably used in combination with the terbia-stabilized interfacial layer. The solid oxide fuel cells are operable over wider temperature ranges and wider temperature gradients in comparison with conventional fuel cells.

  13. Orientation-controlled parallel assembly at the air-water interface

    NASA Astrophysics Data System (ADS)

    Park, Kwang Soon; Hao Hoo, Ji; Baskaran, Rajashree; Böhringer, Karl F.

    2012-10-01

    This paper presents an experimental and theoretical study with statistical analysis of a high-yield, orientation-specific fluidic self-assembly process on a preprogrammed template. We demonstrate self-assembly of thin (less than few hundred microns in thickness) parts, which is vital for many applications in miniaturized platforms but problematic for today's pick-and-place robots. The assembly proceeds row-by-row as the substrate is pulled up through an air-water interface. Experiments and analysis are presented with an emphasis on the combined effect of controlled surface waves and magnetic force. For various gap values between a magnet and Ni-patterned parts, magnetic force distributions are generated using Monte Carlo simulation and employed to predict assembly yield. An analysis of these distributions shows that a gradual decline in yield following the probability density function can be expected with degrading conditions. The experimentally determined critical magnetic force is in good agreement with a derived value from a model of competing forces acting on a part. A general set of design guidelines is also presented from the developed model and experimental data.

  14. Estimating Riverine Air-Water Gas Exchange and Metabolism from Long Oxygen Time Series

    NASA Astrophysics Data System (ADS)

    Hall, R. O., Jr.; Appling, A.; Yackulic, C. B.; Arroita, M.

    2015-12-01

    To accurately depict the role of streams and rivers in carbon cycling requires estimating air- water gas exchange, productivity, and respiration. It is possible to estimate gas exchange and metabolism (gross primary production and ecosystem respiration) simultaneously from oxygen data themselves, but estimates from any single day often contain a substantial (and unknown) amount of parameter error. Here we developed a statistical method to leverage the extra information in a long time series to better estimate daily rates of gas exchange and metabolism. Such time series are ubiquitous in water quality monitoring programs, and these data are readily available over broad spatial scales. We developed a hierarchical model that estimates gas exchange as a function of discharge for a year-long time series of dissolved oxygen data. Gas exchange, and therefore metabolism, had much lower temporal variability than if we estimated parameters on separate days. Rates of gas exchange were positively related with discharge, but the relationship was river specific and often nonlinear. Our approach provides a robust means to estimate gas exchange and metabolism from the many rivers that have oxygen time series collected as part of water quality monitoring.

  15. Hydration, Orientation, and Conformation of Methylglyoxal at the Air-Water Interface.

    PubMed

    Wren, Sumi N; Gordon, Brittany P; Valley, Nicholas A; McWilliams, Laura E; Richmond, Geraldine L

    2015-06-18

    Aqueous-phase processing of methylglyoxal (MG) has been suggested to constitute an important source of secondary organic aerosol (SOA). The uptake of MG to aqueous particles is higher than expected because its carbonyl moieties can hydrate to form geminal diols, as well as because MG and its hydration products can undergo aldol condensation reactions to form larger oligomers in solution. MG is known to be surface active, but an improved description of its surface behavior is crucial to understanding MG-SOA formation. These studies investigate MG adsorption, focusing on its hydration state at the air-water interface, using a combined experimental and theoretical approach that involves vibrational sum frequency spectroscopy, molecular dynamics simulations, and density functional theory calculations. Together, the experimental and theoretical data show that MG exists predominantly in a singly hydrated state (diol) at the interface, with a diol-tetrol ratio at the surface higher than that for the bulk. In addition to exhibiting a strong surface activity, we find that MG significantly perturbs the water structure at the interface. The results have implications for understanding the atmospheric fate of methylglyoxal.

  16. Air - water temperature relationships in the trout streams of southeastern Minnesota’s carbonate - sandstone landscape

    USGS Publications Warehouse

    Krider, Lori A.; Magner, Joseph A.; Perry, Jim; Vondracek, Bruce C.; Ferrington, Leonard C.

    2013-01-01

    Carbonate-sandstone geology in southeastern Minnesota creates a heterogeneous landscape of springs, seeps, and sinkholes that supply groundwater into streams. Air temperatures are effective predictors of water temperature in surface-water dominated streams. However, no published work investigates the relationship between air and water temperatures in groundwater-fed streams (GWFS) across watersheds. We used simple linear regressions to examine weekly air-water temperature relationships for 40 GWFS in southeastern Minnesota. A 40-stream, composite linear regression model has a slope of 0.38, an intercept of 6.63, and R2 of 0.83. The regression models for GWFS have lower slopes and higher intercepts in comparison to surface-water dominated streams. Regression models for streams with high R2 values offer promise for use as predictive tools for future climate conditions. Climate change is expected to alter the thermal regime of groundwater-fed systems, but will do so at a slower rate than surface-water dominated systems. A regression model of intercept vs. slope can be used to identify streams for which water temperatures are more meteorologically than groundwater controlled, and thus more vulnerable to climate change. Such relationships can be used to guide restoration vs. management strategies to protect trout streams.

  17. Influence of the air-water interface on hydrosol lidar operation.

    PubMed

    Kokhanenko, Grigorii P; Krekova, Margarita M; Penner, Loganes E; Shamanaev, Vitalii S

    2005-06-10

    The results of seawater sensing by use of an airborne lidar with a changeable field of view (FOV) are presented, together with the results of numerical simulation of lidar operation by the Monte Carlo method. It is demonstrated that multiple scattering and wind-driven sea waves have opposite effects on the measured attenuation coefficient. At small FOVs the wind-driven sea waves cause the lidar signal decay rate to increase compared with the size of the plane surface and hence result in an overestimation of the retrieved attenuation coefficient. Inefficient operation of lidars with small FOVs is caused by strong fluctuations of lidar signal power that cannot be described by a normal distribution. Specific features of the fluctuations can be interpreted as manifestations of the well-known effect of backscattered signal amplification caused by the double passage of radiation through the same inhomogeneities. As for the plane air-water interface, multiple scattering is significant for large FOVs and compensates for the effect of wind-driven sea waves. The applicability of simple sea-surface models to a description of lidar signal power fluctuations is discussed.

  18. Surface shear rheology of WPI-monoglyceride mixed films spread at the air-water interface.

    PubMed

    Carrera Sánchez, Cecilio; Rodríguez Patino, Juan M

    2004-07-01

    Surface shear viscosity of food emulsifiers may contribute appreciably to the long-term stability of food dispersions (emulsions and foams). In this work we have analyzed the structural, topographical, and shear characteristics of a whey protein isolate (WPI) and monoglyceride (monopalmitin and monoolein) mixed films spread on the air-water interface at pH 7 and at 20 degrees C. The surface shear viscosity (etas) depend on the surface pressure and on the composition of the mixed film. The surface shear viscosity varies greatly with the surface pressure. In general, the greater the surface pressure, the greater are the values of etas. The values of etas for the mixed WPI-monoolein monolayer were more than one order of magnitude lower than those for a WPI-monopalmitin mixed film, especially at the higher surface pressures. At higher surface pressures, collapsed WPI residues may be displaced from the interface by monoglyceride molecules with important repercussions on the shear characteristics of the mixed films. A shear-induced change in the topography and a segregation between domains of the film forming components were also observed. The displacement of the WPI by the monoglycerides is facilitates under shear conditions, especially for WPI-monoolein mixed films.

  19. Dynamic mechanical properties of a polyelectrolyte adsorbed insoluble lipid monolayer at the air-water interface.

    PubMed

    Park, Chang Young; Kim, Mahn Won

    2015-04-23

    Polymers have been used to stabilize interfaces or to tune the mechanical properties of interfaces in various contexts, such as in oil emulsions or biological membranes. Although the structural properties of these systems are relatively well-studied, instrumental limitations continue to make it difficult to understand how the addition of polymer affects the dynamic mechanical properties of thin and soft films. We have solved this challenge by developing a new instrument, an optical-tweezer-based interface shear microrheometer (ISMR). With this technique, we observed that the interface shear modulus, G*, of a dioctadecyldimethylammonium chloride (DODAC) monolayer at the air-water interface significantly increased with adsorption of polystyrenesulfonate (PSS). In addition, the viscous film (DODAC monolayer) became a viscoelastic film with PSS adsorption. At a low salt concentration, 10 mM of NaCl in the subphase, the viscoelasticity of the DODAC/PSS composite was predominantly determined by a particular property of PSS, that is, it behaves as a Gaussian chain in a θ-solvent. At a high salt concentration, 316 mM of NaCl, the thin film behaved as a polymer melt excluding water molecules. PMID:25826703

  20. Mechanistic Insights on the Photosensitized Chemistry of a Fatty Acid at the Air/Water Interface

    PubMed Central

    2016-01-01

    Interfaces are ubiquitous in the environment and many atmospheric key processes, such as gas deposition, aerosol, and cloud formation are, at one stage or another, strongly impacted by physical and chemical processes occurring at interfaces. Here, the photoinduced chemistry of an air/water interface coated with nonanoic acid—a fatty acid surfactant we use as a proxy for chemically complex natural aqueous surface microlayers—was investigated as a source of volatile and semivolatile reactive organic species. The carboxylic acid coating significantly increased the propensity of photosensitizers, chosen to mimic those observed in real environmental waters, to partition to the interface and enhance reactivity there. Photochemical formation of functionalized and unsaturated compounds was systematically observed upon irradiation of these coated surfaces. The role of a coated interface appears to be critical in providing a concentrated medium allowing radical–radical reactions to occur in parallel with molecular oxygen additions. Mechanistic insights are provided from extensive analysis of products observed in both gas and aqueous phases by online switchable reagent ion-time of flight-mass spectrometry and by off-line ultraperformance liquid chromatography coupled to a Q Exactive high resolution mass spectrometer through heated electrospray ionization, respectively. PMID:27611489

  1. Bifurcations of a creeping air-water flow in a conical container

    NASA Astrophysics Data System (ADS)

    Balci, Adnan; Brøns, Morten; Herrada, Miguel A.; Shtern, Vladimir N.

    2016-04-01

    This numerical study describes the eddy emergence and transformations in a slow steady axisymmetric air-water flow, driven by a rotating top disk in a vertical conical container. As water height Hw and cone half-angle β vary, numerous flow metamorphoses occur. They are investigated for β =30°, 45°, and 60°. For small Hw , the air flow is multi-cellular with clockwise meridional circulation near the disk. The air flow becomes one cellular as Hw exceeds a threshold depending on β . For all β , the water flow has an unbounded number of eddies whose size and strength diminish as the cone apex is approached. As the water level becomes close to the disk, the outmost water eddy with clockwise meridional circulation expands, reaches the interface, and induces a thin layer with anticlockwise circulation in the air. Then this layer expands and occupies the entire air domain. The physical reasons for the flow transformations are provided. The results are of fundamental interest and can be relevant for aerial bioreactors.

  2. Substrateless Welding of Self-Assembled Silver Nanowires at Air/Water Interface.

    PubMed

    Hu, Hang; Wang, Zhongyong; Ye, Qinxian; He, Jiaqing; Nie, Xiao; He, Gufeng; Song, Chengyi; Shang, Wen; Wu, Jianbo; Tao, Peng; Deng, Tao

    2016-08-10

    Integrating connected silver nanowire networks with flexible polymers has appeared as a popular way to prepare flexible electronics. To reduce the contact resistance and enhance the connectivity between silver nanowires, various welding techniques have been developed. Herein, rather than welding on solid supporting substrates, which often requires complicated transferring operations and also may pose damage to heat-sensitive substrates, we report an alternative approach to prepare easily transferrable conductive networks through welding of self-assembled silver nanowires at the air/water interface using plasmonic heating. The intriguing welding behavior of partially aligned silver nanowires was analyzed with combined experimental observation and theoretical modeling. The underlying water not only physically supports the assembled silver nanowires but also buffers potential overheating during the welding process, thereby enabling effective welding within a broad range of illumination power density and illumination duration. The welded networks could be directly integrated with PDMS substrates to prepare high-performance stable flexible heaters that are stretchable, bendable, and can be easily patterned to explore selective heating applications. PMID:27437907

  3. Field observations of turbulent dissipation rate profiles immediately below the air-water interface

    NASA Astrophysics Data System (ADS)

    Wang, Binbin; Liao, Qian

    2016-06-01

    Near surface profiles of turbulence immediately below the air-water interface were measured with a free-floating Particle Image Velocimetry (PIV) system on Lake Michigan. The surface-following configuration allowed the system to measure the statistics of the aqueous-side turbulence in the topmost layer immediately below the water surface (z≈0˜15 cm, z points downward with 0 at the interface). Profiles of turbulent dissipation rate (ɛ) were investigated under a variety of wind and wave conditions. Various methods were applied to estimate the dissipation rate. Results suggest that these methods yield consistent dissipation rate profiles with reasonable scattering. In general, the dissipation rate decreases from the water surface following a power law relation in the top layer, ɛ˜z-0.7, i.e., the slope of the decrease was lower than that predicted by the wall turbulence theory, and the dissipation was considerably higher in the top layer for cases with higher wave ages. The measured dissipation rate profiles collapse when they were normalized with the wave speed, wave height, water-side friction velocity, and the wave age. This scaling suggests that the enhanced turbulence may be attributed to the additional source of turbulent kinetic energy (TKE) at the "skin layer" (likely due to micro-breaking), and its downward transport in the water column.

  4. Amyloid fibril formation at a uniformly sheared air/water interface

    NASA Astrophysics Data System (ADS)

    Posada, David; Hirsa, Amir

    2013-11-01

    Amyloid fibril formation is a process by which protein molecules in solution form nuclei and aggregate into fibrils. Amyloid fibrils have long been associated with several common diseases such as Parkinson's disease and Alzheimer's. More recently, fibril protein deposition has been implicated in uncommon disorders leading to the failure of various organs including the kidneys, heart, and liver. Fibrillization can also play a detrimental role in biotherapeutic production. Results from previous studies show that a hydrophobic interface, such air/water, can accelerate fibrillization. Studies also show that agitation accelerates fibrillization. When attempting to elucidate fundamental mechanisms of fibrillization and distinguish the effects of interfaces and flow, it can be helpful to experiment with uniformly sheared interfaces. A new Taylor-Couette device is introduced for in situ, real-time high resolution microscopy. With a sub-millimeter annular gap, surface tension acts as the channel floor, permitting a stable meniscus to be placed arbitrarily close to a microscope to study amyloid fibril formation over long periods.

  5. Dipolar interactions between domains in lipid monolayers at the air-water interface.

    PubMed

    Rufeil-Fiori, Elena; Wilke, Natalia; Banchio, Adolfo J

    2016-05-25

    A great variety of biologically relevant monolayers present phase coexistence characterized by domains formed by lipids in an ordered phase state dispersed in a continuous, disordered phase. From the difference in surface densities between these phases, inter-domain dipolar interactions arise. These interactions are relevant for the determination of the spacial distribution of domains as well as their dynamics. In this work, we propose a novel way of estimating the dipolar repulsion using a passive method that involves the analysis of images of the monolayer with phase coexistence. This method is based on the comparison of the pair correlation function obtained from experiments with that obtained from Brownian dynamics simulations of a model system. As an example, we determined the difference in dipolar density of a binary monolayer of DSPC/DMPC at the air-water interface from the analysis of the radial distribution of domains, and the results are compared with those obtained by surface potential determinations. A systematic analysis for the experimentally relevant parameter range is given, which may be used as a working curve for obtaining the dipolar repulsion in different systems. PMID:27139819

  6. Substrateless Welding of Self-Assembled Silver Nanowires at Air/Water Interface.

    PubMed

    Hu, Hang; Wang, Zhongyong; Ye, Qinxian; He, Jiaqing; Nie, Xiao; He, Gufeng; Song, Chengyi; Shang, Wen; Wu, Jianbo; Tao, Peng; Deng, Tao

    2016-08-10

    Integrating connected silver nanowire networks with flexible polymers has appeared as a popular way to prepare flexible electronics. To reduce the contact resistance and enhance the connectivity between silver nanowires, various welding techniques have been developed. Herein, rather than welding on solid supporting substrates, which often requires complicated transferring operations and also may pose damage to heat-sensitive substrates, we report an alternative approach to prepare easily transferrable conductive networks through welding of self-assembled silver nanowires at the air/water interface using plasmonic heating. The intriguing welding behavior of partially aligned silver nanowires was analyzed with combined experimental observation and theoretical modeling. The underlying water not only physically supports the assembled silver nanowires but also buffers potential overheating during the welding process, thereby enabling effective welding within a broad range of illumination power density and illumination duration. The welded networks could be directly integrated with PDMS substrates to prepare high-performance stable flexible heaters that are stretchable, bendable, and can be easily patterned to explore selective heating applications.

  7. Reliable quantification of phthalates in environmental matrices (air, water, sludge, sediment and soil): a review.

    PubMed

    Net, Sopheak; Delmont, Anne; Sempéré, Richard; Paluselli, Andrea; Ouddane, Baghdad

    2015-05-15

    Because of their widespread application, phthalates or phthalic acid esters (PAEs) are ubiquitous in the environment. Their presence has attracted considerable attention due to their potential impacts on ecosystem functioning and on public health, so their quantification has become a necessity. Various extraction procedures as well as gas/liquid chromatography and mass spectrometry detection techniques are found as suitable for reliable detection of such compounds. However, PAEs are ubiquitous in the laboratory environment including ambient air, reagents, sampling equipment, and various analytical devices, that induces difficult analysis of real samples with a low PAE background. Therefore, accurate PAE analysis in environmental matrices is a challenging task. This paper reviews the extensive literature data on the techniques for PAE quantification in natural media. Sampling, sample extraction/pretreatment and detection for quantifying PAEs in different environmental matrices (air, water, sludge, sediment and soil) have been reviewed and compared. The concept of "green analytical chemistry" for PAE determination is also discussed. Moreover useful information about the material preparation and the procedures of quality control and quality assurance are presented to overcome the problem of sample contamination and these encountered due to matrix effects in order to avoid overestimating PAE concentrations in the environment. PMID:25723871

  8. Impact of artificial monolayer application on stored water quality at the air-water interface.

    PubMed

    Pittaway, P; Martínez-Alvarez, V; Hancock, N; Gallego-Elvira, B

    2015-01-01

    Evaporation mitigation has the potential to significantly improve water use efficiency, with repeat applications of artificial monolayer formulations the most cost-effective strategy for large water storages. Field investigations of the impact of artificial monolayers on water quality have been limited by wind and wave turbulence, and beaching. Two suspended covers differing in permeability to wind and light were used to attenuate wind turbulence, to favour the maintenance of a condensed monolayer at the air/water interface of a 10 m diameter tank. An octadecanol formulation was applied twice-weekly to one of two covered tanks, while a third clean water tank remained uncovered for the 14-week duration of the trial. Microlayer and subsurface water samples were extracted once a week to distinguish impacts associated with the installation of covers, from the impact of prolonged monolayer application. The monolayer was selectively toxic to some phytoplankton, but the toxicity of hydrocarbons leaching from a replacement liner had a greater impact. Monolayer application did not increase water temperature, humified dissolved organic matter, or the biochemical oxygen demand, and did not reduce dissolved oxygen. The impact of an octadecanol monolayer on water quality and the microlayer may not be as detrimental as previously considered. PMID:26398042

  9. Gaseous exchange of polycyclic aromatic hydrocarbons across the air-water interface of lower Chesapeake Bay

    SciTech Connect

    Gustafson, K.E.; Dickhut, R.M.

    1995-12-31

    The gaseous exchange fluxes of polycyclic aromatic hydrocarbons (PAHs) across the air-water interface of lower Chesapeake Bay were determined using a modified two-film exchange model. Sampling covered the period January 1994 to June 1995 for five sites on lower Chesapeake Bay ranging from rural to urban and highly industrialized. Simultaneous air and water samples were collected and the atmospheric gas phase and water column dissolved phase analyzed via GC/MS for 17 PAHs. The direction and magnitude of flux for each PAH was calculated using Henry`s law constants, hydrological and meteorological parameters, Temperature was observed to be an important environmental factor in determining both the direction and magnitude of PAH gas exchange. Nonetheless, wind speed significantly impacts mass transfer coefficients, and therefore was found to control the magnitude of flux. Spatial and temporal variation of PAH gaseous exchange fluxes were examined. Fluxes were determined to be both into and out of Chesapeake Bay. The range of gas exchange fluxes ({minus}560 to 600{micro}g/M{sup 2}*Mo) is of the same order to 10X greater than atmospheric wet and dry depositional fluxes to lower Chesapeake Bay. The results of this study support the hypothesis that gas exchange is a major transport process affecting the net loadings of PAHs in lower Chesapeake Bay.

  10. Surface modification of gold nanoparticles and their monolayer behavior at the air/water interface

    NASA Astrophysics Data System (ADS)

    Hsu, Chaio-Ling; Wang, Ke-Hsuan; Chang, Chien-Hsiang; Hsu, Wen-Ping; Lee, Yuh-Lang

    2011-01-01

    Gold nanoparticles were prepared by two different methods. The first method was chemically grafting the particles with different lengths of alkylthiol (C6SH, C12SH and C18SH). For the second method, the Au particles were surface modified first by mercaptosuccinic acid (MSA) to render a surface with carboxylic acid groups which play a role to physically adsorb cationic surfactant in chloroform. This method was termed physical/chemical method. In the first method, the effects of alkyl chain length and dispersion solvent on the monolayer behavior of surface modified gold nanoparticles was evaluated. The gold nanoparticles prepared by 1-hexanthiol demonstrated the narrowest size distribution. Most of them showed narrower particle size distributions in chloroform than in hexane. For the physical/chemical method, the particles can spread more uniformly on the water surface which is attributed to the amphiphilic character of the particles at the air/water interface. However, the particles cannot pack closely due to the relatively weak particle-particle interaction. The effect of alkyl chain length was also assessed for the second method.

  11. Bifurcations of a creeping air-water flow in a conical container

    NASA Astrophysics Data System (ADS)

    Balci, Adnan; Brøns, Morten; Herrada, Miguel A.; Shtern, Vladimir N.

    2016-10-01

    This numerical study describes the eddy emergence and transformations in a slow steady axisymmetric air-water flow, driven by a rotating top disk in a vertical conical container. As water height Hw and cone half-angle β vary, numerous flow metamorphoses occur. They are investigated for β =30°, 45°, and 60°. For small Hw, the air flow is multi-cellular with clockwise meridional circulation near the disk. The air flow becomes one cellular as Hw exceeds a threshold depending on β . For all β , the water flow has an unbounded number of eddies whose size and strength diminish as the cone apex is approached. As the water level becomes close to the disk, the outmost water eddy with clockwise meridional circulation expands, reaches the interface, and induces a thin layer with anticlockwise circulation in the air. Then this layer expands and occupies the entire air domain. The physical reasons for the flow transformations are provided. The results are of fundamental interest and can be relevant for aerial bioreactors.

  12. Equation of state and adsorption dynamics of soft microgel particles at an air-water interface.

    PubMed

    Deshmukh, Omkar S; Maestro, Armando; Duits, Michel H G; van den Ende, Dirk; Stuart, Martien Cohen; Mugele, Frieder

    2014-09-28

    Understanding the adsorption dynamics of soft microgel particles is a key step in designing such particles for potential applications as stimuli-responsive Pickering stabilizers for foams or emulsions. In this study we experimentally determine an equation of state (EOS) for poly (N-isopropylacrylamide) (PNIPAM) microgel particles adsorbed onto an air-water interface using a Langmuir film balance. We detect a finite surface pressure at very low surface concentration of particles, for which standard theories based on hard disk models predict negligible pressures, implying that the particles must deform strongly upon adsorption to the interface. Furthermore, we study the evolution of the surface pressure due to the adsorption of PNIPAM particles as a function of time using pendant drop tensiometry. The equation of state determined in the equilibrium measurements allows us to extract the adsorbed amount as a function of time. We find a mixed-kinetic adsorption that is initially controlled by the diffusion of particles towards the interface. At later stages, a slow exponential relaxation indicates the presence of a coverage-dependent adsorption barrier related to crowding of particles at the interface. PMID:24954112

  13. Kinetics of trans-cis isomerization in azobenzene dimers at an air-water interface

    SciTech Connect

    Kumar, Bharat; Suresh, K. A.

    2009-08-15

    We have studied the kinetics of trans to cis isomerization under the illumination of ultraviolet light, in the Langmuir monolayer of mesogenic azobenzene dimer, bis-[5-(4{sup '}-n-dodecyloxy benzoyloxy)-2-(4{sup ''}-methylphenylazo)phenyl] adipate, at an air-water interface. We find that the trans to cis isomerization reaction of the molecules in the monolayer shows deviation from the first-order kinetics unlike those reported on Langmuir monolayers of azobenzene molecules. We attribute the deviation from first-order kinetics to the simultaneous photoisomerization of trans isomers to form cis isomers and the reverse thermal isomerization of cis isomers to form trans isomers. Our analysis of the rate of change of mole fraction of trans isomers to form cis isomers indicates a first-order kinetics for trans to cis photoisomerization reaction and a second-order kinetics for cis to trans thermal isomerization reaction. This second-order kinetics mechanism is similar to the Lindemann-Hinshelwood mechanism for the unimolecular reactions at low concentration of reactants. The formation of the activated cis isomer by collisions is a slow process as compared to the decay of the activated cis isomer to trans isomer in the liquid expanded phase. This results in the second-order kinetics for the thermal isomerization of cis isomers.

  14. Dipolar interactions between domains in lipid monolayers at the air-water interface.

    PubMed

    Rufeil-Fiori, Elena; Wilke, Natalia; Banchio, Adolfo J

    2016-05-25

    A great variety of biologically relevant monolayers present phase coexistence characterized by domains formed by lipids in an ordered phase state dispersed in a continuous, disordered phase. From the difference in surface densities between these phases, inter-domain dipolar interactions arise. These interactions are relevant for the determination of the spacial distribution of domains as well as their dynamics. In this work, we propose a novel way of estimating the dipolar repulsion using a passive method that involves the analysis of images of the monolayer with phase coexistence. This method is based on the comparison of the pair correlation function obtained from experiments with that obtained from Brownian dynamics simulations of a model system. As an example, we determined the difference in dipolar density of a binary monolayer of DSPC/DMPC at the air-water interface from the analysis of the radial distribution of domains, and the results are compared with those obtained by surface potential determinations. A systematic analysis for the experimentally relevant parameter range is given, which may be used as a working curve for obtaining the dipolar repulsion in different systems.

  15. Interfacial instabilities in vibrated fluids

    NASA Astrophysics Data System (ADS)

    Porter, Jeff; Laverón-Simavilla, Ana; Tinao Perez-Miravete, Ignacio; Fernandez Fraile, Jose Javier

    2016-07-01

    Vibrations induce a range of different interfacial phenomena in fluid systems depending on the frequency and orientation of the forcing. With gravity, (large) interfaces are approximately flat and there is a qualitative difference between vertical and horizontal forcing. Sufficient vertical forcing produces subharmonic standing waves (Faraday waves) that extend over the whole interface. Horizontal forcing can excite both localized and extended interfacial phenomena. The vibrating solid boundaries act as wavemakers to excite traveling waves (or sloshing modes at low frequencies) but they also drive evanescent bulk modes whose oscillatory pressure gradient can parametrically excite subharmonic surface waves like cross-waves. Depending on the magnitude of the damping and the aspect ratio of the container, these locally generated surfaces waves may interact in the interior resulting in temporal modulation and other complex dynamics. In the case where the interface separates two fluids of different density in, for example, a rectangular container, the mass transfer due to vertical motion near the endwalls requires a counterflow in the interior region that can lead to a Kelvin-Helmholtz type instability and a ``frozen wave" pattern. In microgravity, the dominance of surface forces favors non-flat equilibrium configurations and the distinction between vertical and horizontal applied forcing can be lost. Hysteresis and multiplicity of solutions are more common, especially in non-wetting systems where disconnected (partial) volumes of fluid can be established. Furthermore, the vibrational field contributes a dynamic pressure term that competes with surface tension to select the (time averaged) shape of the surface. These new (quasi-static) surface configurations, known as vibroequilibria, can differ substantially from the hydrostatic state. There is a tendency for the interface to orient perpendicular to the vibrational axis and, in some cases, a bulge or cavity is induced

  16. Interfacial behaviours of smart composites

    NASA Astrophysics Data System (ADS)

    Poon, Chi-Kin

    The success of conventional fiber reinforced composites (FRC) relies on the quality of bonding between fibers and matrix. A review of literatures shows that there is a lack of theoretical models and experimental findings on the interfacial behaviours of the SMA-composites. In the past, the operation limit as well as the ideal actuation condition of SMA inclusions could not be predicted accurately during the design stage and the SMA-composite structures may therefore suffer a potential risk of sudden failure due to overloading or over-actuation. The theoretical models developed in this research provide a study basis for the prediction of internal stresses and interfacial strength of the SMA-composites. Martensite volume fraction is considered as a critical parameter which determines the material properties and shape memory effect (SME) of the SMA inclusions. The proposed model reproduce the SMA behaviour inside a substrate, evolutions of martensite volume fraction and elastic modulus of SMA, and the internal stresses along the embedded length in different loading and actuation scenarios. The concepts of 'constant martensite volume fraction region (CMR)' and 'constant axial stress region (CASR)' are proposed to justify the desired SMA actuation. In addition, substantial improvement of the initial debond stress is predicted with the increase of the actuation temperature. The 'Optimum Actuation Condition (OAC)' that ensures the reinforcement of SMA composite but avoids the failure of composite interface due to over-actuation is also defined to optimize the application of SME in the composite structure within a safety actuation limit. A simplified OAC (SOAC) is also developed to provide an analytical solution of OAC and thus the ideal actuation temperature for achieving such specific actuation condition can be estimated more easily. Single fiber pullout test and finite element analysis (FEA) are employed to evaluate the interfacial behaviours and analyze the stress

  17. THE ROLE OF AQUEOUS THIN FILM EVAPORATIVE COOLING ON RATES OF ELEMENTAL MERCURY AIR-WATER EXCHANGE UNDER TEMPERATURE DISEQUILIBRIUM CONDITIONS

    EPA Science Inventory

    The technical conununity has only recently addressed the role of atmospheric temperature variations on rates of air-water vapor phase toxicant exchange. The technical literature has documented that: 1) day time rates of elemental mercury vapor phase air-water exchange can exceed ...

  18. Hydrated interfacial ions and electrons.

    PubMed

    Abel, Bernd

    2013-01-01

    Charged particles such as hydrated ions and transient hydrated electrons, the simplest anionic reducing agents in water, and the special hydronium and hydroxide ions at water interfaces play an important role in many fields of science, such as atmospheric chemistry, radiation chemistry, and biology, as well as biochemistry. This article focuses on these species near hydrophobic interfaces of water, such as the air or vacuum interface of water or water protein/membrane interfaces. Ions at interfaces as well as solvated electrons have been reviewed frequently during the past decade. Although all species have been known for some time with seemingly familiar features, recently the picture in all cases became increasingly diffuse rather than clearer. The current account gives a critical state-of-the art overview of what is known and what remains to be understood and investigated about hydrated interfacial ions and electrons.

  19. Interfacial adhesion: Theory and experiment

    NASA Technical Reports Server (NTRS)

    Ferrante, John; Bozzolo, Guillermo H.; Finley, Clarence W.; Banerjea, Amitava

    1988-01-01

    Adhesion, the binding of different materials at an interface, is of general interest to many branches of technology, e.g., microelectronics, tribology, manufacturing, construction, etc. However, there is a lack of fundamental understanding of such diverse interfaces. In addition, experimental techniques generally have practical objectives, such as the achievement of sufficient strength to sustain mechanical or thermal effects and/or have the proper electronic properties. In addition, the theoretical description of binding at interfaces is quite limited, and a proper data base for such theoretical analysis does not exist. This presentation will review both experimental and theoretical aspects of adhesion in nonpolymer materials. The objective will be to delineate the critical parameters needed, governing adhesion testing along with an outline of testing objectives. A distinction will be made between practical and fundamental objectives. Examples are given where interfacial bonding may govern experimental consideration. The present status of theory is presented along wiith recommendations for future progress and needs.

  20. Interfacial adhesion - Theory and experiment

    NASA Technical Reports Server (NTRS)

    Ferrante, John; Banerjea, Amitava; Bozzolo, Guillermo H.; Finley, Clarence W.

    1988-01-01

    Adhesion, the binding of different materials at an interface, is of general interest to many branches of technology, e.g., microelectronics, tribology, manufacturing, construction, etc. However, there is a lack of fundamental understanding of such diverse interfaces. In addition, experimental techniques generally have practical objectives, such as the achievement of sufficient strength to sustain mechanical or thermal effects and/or have the proper electronic properties. In addition, the theoretical description of binding at interfaces is quite limited, and a proper data base for such theoretical analysis does not exist. This presentation will review both experimental and theoretical aspects of adhesion in nonpolymer materials. The objective will be to delineate the critical parameters needed, governing adhesion testing along with an outline of testing objectives. A distinction will be made between practical and fundamental objectives. Examples are given where interfacial bonding may govern experimental consideration. The present status of theory is presented along with recommendations for future progress and needs.

  1. Interfacial instabilities and Kapitsa pendula

    NASA Astrophysics Data System (ADS)

    Krieger, Madison

    2015-11-01

    Determining the critera for onset and amplitude growth of instabilities is one of the central problems of fluid mechanics. We develop a parallel between the Kapitsa effect, in which a pendulum subject to high-frequency low-amplitude vibrations becomes stable in the inverted position, and interfaces separating fluids of different density. It has long been known that such interfaces can be stabilized by vibrations, even when the denser fluid is on top. We demonstrate that the stability diagram for these fluid interfaces is identical to the stability diagram for an appopriate Kapitsa pendulum. We expand the robust, ``dictionary''-type relationship between Kapitsa pendula and interfacial instabilities by considering the classical Rayleigh-Taylor, Kelvin-Helmholtz and Plateau instabilities, as well as less-canonical examples ranging in scale from the micron to the width of a galaxy.

  2. Interfacial Bioorthogonal Cross-Linking

    PubMed Central

    2015-01-01

    Described herein is interfacial bioorthogonal cross-linking, the use of bioorthogonal chemistry to create and pattern biomaterials through diffusion-controlled gelation at the liquid-gel interface. The basis is a rapid (k2 284000 M–1 s–1) reaction between strained trans-cyclooctene (TCO) and tetrazine (Tz) derivatives. Syringe delivery of Tz-functionalized hyaluronic acid (HA-Tz) to a bath of bis-TCO cross-linker instantly creates microspheres with a cross-linked shell through which bis-TCO diffuses freely to introduce further cross-linking at the interface. Tags can be introduced with 3D resolution without external triggers or templates. Water-filled hydrogel channels were prepared by simply reversing the order of addition. Prostate cancer cells encapsulated in the microspheres have 99% viability, proliferate readily, and form aggregated clusters. This process is projected to be useful in the fabrication of cell-instructive matrices for in vitro tissue models. PMID:25177528

  3. Topology-generating interfacial pattern formation during liquid metal dealloying

    PubMed Central

    Geslin, Pierre-Antoine; McCue, Ian; Gaskey, Bernard; Erlebacher, Jonah; Karma, Alain

    2015-01-01

    Liquid metal dealloying has emerged as a novel technique to produce topologically complex nanoporous and nanocomposite structures with ultra-high interfacial area and other unique properties relevant for diverse material applications. This process is empirically known to require the selective dissolution of one element of a multicomponent solid alloy into a liquid metal to obtain desirable structures. However, how structures form is not known. Here we demonstrate, using mesoscale phase-field modelling and experiments, that nano/microstructural pattern formation during dealloying results from the interplay of (i) interfacial spinodal decomposition, forming compositional domain structures enriched in the immiscible element, and (ii) diffusion-coupled growth of the enriched solid phase and the liquid phase into the alloy. We highlight how those two basic mechanisms interact to yield a rich variety of topologically disconnected and connected structures. Moreover, we deduce scaling laws governing microstructural length scales and dealloying kinetics. PMID:26582248

  4. Topology-generating interfacial pattern formation during liquid metal dealloying

    DOE PAGES

    Geslin, Pierre -Antoine; McCue, Ian; Gaskey, Bernard; Erlebacher, Jonah; Karma, Alain

    2015-11-19

    Liquid metal dealloying has emerged as a novel technique to produce topologically complex nanoporous and nanocomposite structures with ultra-high interfacial area and other unique properties relevant for diverse material applications. This process is empirically known to require the selective dissolution of one element of a multicomponent solid alloy into a liquid metal to obtain desirable structures. However, how structures form is not known. Here we demonstrate, using mesoscale phase-field modelling and experiments, that nano/microstructural pattern formation during dealloying results from the interplay of (i) interfacial spinodal decomposition, forming compositional domain structures enriched in the immiscible element, and (ii) diffusion-coupled growthmore » of the enriched solid phase and the liquid phase into the alloy. We highlight how those two basic mechanisms interact to yield a rich variety of topologically disconnected and connected structures. Furthermore, we deduce scaling laws governing microstructural length scales and dealloying kinetics.« less

  5. Topology-generating interfacial pattern formation during liquid metal dealloying

    SciTech Connect

    Geslin, Pierre -Antoine; McCue, Ian; Gaskey, Bernard; Erlebacher, Jonah; Karma, Alain

    2015-11-19

    Liquid metal dealloying has emerged as a novel technique to produce topologically complex nanoporous and nanocomposite structures with ultra-high interfacial area and other unique properties relevant for diverse material applications. This process is empirically known to require the selective dissolution of one element of a multicomponent solid alloy into a liquid metal to obtain desirable structures. However, how structures form is not known. Here we demonstrate, using mesoscale phase-field modelling and experiments, that nano/microstructural pattern formation during dealloying results from the interplay of (i) interfacial spinodal decomposition, forming compositional domain structures enriched in the immiscible element, and (ii) diffusion-coupled growth of the enriched solid phase and the liquid phase into the alloy. We highlight how those two basic mechanisms interact to yield a rich variety of topologically disconnected and connected structures. Furthermore, we deduce scaling laws governing microstructural length scales and dealloying kinetics.

  6. Reliability assessment on interfacial failure of thermal barrier coatings

    NASA Astrophysics Data System (ADS)

    Guo, Jin-Wei; Yang, Li; Zhou, Yi-Chun; He, Li-Min; Zhu, Wang; Cai, Can-Ying; Lu, Chun-Sheng

    2016-08-01

    Thermal barrier coatings (TBCs) usually exhibit an uncertain lifetime owing to their scattering mechanical properties and severe service conditions. To consider these uncertainties, a reliability assessment method is proposed based on failure probability analysis. First, a limit state equation is established to demarcate the boundary between failure and safe regions, and then the failure probability is calculated by the integration of a probability density function in the failure area according to the first- or second-order moment. It is shown that the parameters related to interfacial failure follow a Weibull distribution in two types of TBC. The interfacial failure of TBCs is significantly affected by the thermal mismatch of material properties and the temperature drop in service.

  7. Interfacial assignment of branched-alkyl benzene sulfonates: A molecular simulation

    NASA Astrophysics Data System (ADS)

    Liu, Zi-Yu; Wei, Ning; Wang, Ce; Zhou, He; Zhang, Lei; Liao, Qi; Zhang, Lu

    2015-11-01

    A molecular dynamics simulation was conducted to analyze orientations of sodium branched-alkyl benzene sulfonates molecules at nonane/water interface, which is helpful to design optimal surfactant structures to achieve ultralow interfacial tension (IFT). Through the two dimensional density profiles, monolayer collapses are found when surfactant concentration continues to increase. Thus the precise scope of monolayer is certain and orientation can be analyzed. Based on the simulated results, we verdict the interfacial assignment of branched-alkyl benzene sulfonates at the oil-water interface, and discuss the effect of hydrophobic tail structure on surfactant assignment. Bigger hydrophobic size can slow the change rate of surfactant occupied area as steric hindrance, and surfactant meta hydrophobic tails have a stronger tendency to stretch to the oil phase below the collapsed concentration. Furthermore, an interfacial model with reference to collapse, increasing steric hindrance and charge repulsive force between interfacial surfactant molecules, responsible for effecting of surfactant concentration and structure has been supposed.

  8. Mass Transfer in Slag Refining of Silicon with Mechanical Stirring: Transient Interfacial Phenomena

    NASA Astrophysics Data System (ADS)

    White, Jesse F.; Sichen, Du

    2013-12-01

    Experiments have been carried out to study the rates of mass transfer between liquid silicon and CaO-SiO2 slag with impeller stirring at 1823 K (1550 °C). The occurrence of transient interfacial phenomena related to the mass transfer of calcium has been observed; the evidence suggests that the reduction of calcium oxide at the interface leads to a rapid, temporary drop in the apparent interfacial tension. At low apparent interfacial tension, mechanical agitation facilitates the dispersion of metal into the slag phase, which dramatically increases the interfacial area; here, it has been estimated to increase by at least one order of magnitude. As the reaction rate slows down, the apparent interfacial tension increases and the metal recoalesces. The incidental transfer of calcium very likely promotes the transfer of boron by increasing the interfacial area. Mechanical mixing appears to be an extremely effective means to increase the reaction rate of boron extraction and could feasibly be implemented in the industrial slag refining of silicon to improve reaction rates.

  9. Interfacial tension of aluminum in cryolite melts

    NASA Astrophysics Data System (ADS)

    Utigard, T.; Toguri, J. M.

    1985-06-01

    The interfacial tension between aluminum and cryolite melts containing different salt additions has been measured based on a combination of the sessile drop and X-ray radiographie technique. A computer program was used to calculate the interfacial tension from approximately twenty randomly measured coordinate points of the drop profile. Aluminum and salt mixtures containing different amounts of Na3AlF6, A1F3, NaF, A12O3, CaF2, KF, LiF, and NaCl were melted in a graphite or alumina crucible in a graphite resistor furnace under an argon atmosphere. The interfacial tension was found to be strongly dependent on the NaF/AlF3 ratio. At the cryolite composition the interfacial tension was 481 mN/m at 1304 K, while it was 650 mN/m when the NaF/AlF3 ratio was equal to 1.5. The change in interfacial tension with composition is explained by sodium enrichment of the Al/melt interface. Additions of A12O3 increased the interfacial tension for a given NaF/AlF3 ratio. KF was found to be surface active, while CaF2, LiF, and NaCl slightly increased the interfacial tension by decreasing the sodium activity.

  10. Miscibility behavior of two-component monolayers at the air-water interface: perfluorocarboxylic acids and DMPE.

    PubMed

    Yokoyama, Hiroki; Nakahara, Hiromichi; Nakagawa, Takahiro; Shimono, Satoshi; Sueishi, Kunihiko; Shibata, Osamu

    2009-09-01

    Surface pressure (pi)-molecular area (A) and surface potential (DeltaV)-A isotherms have been measured for two-component monolayers of four different perfluorocarboxylic acids [FCn; perfluorododecanoic acid (FC12), perfluorotetradecanoic acid (FC14), perfluorohexadecanoic acid (FC16), and perfluorooctadecanoic acid (FC18)] and dimyristoylphosphatidylethanolamine (DMPE) on 0.15M NaCl (pH 2) at 298.2K. The present study is focused on the miscibility and the interfacial behavior for the binary DMPE/FCn monolayers upon compression. From the isotherms, the miscibility has been elucidated in terms of the additivity rule, the interaction parameter, and the interaction energy. The interaction parameter (or energy) is compared with that for the previous dipalmitoylphosphatidylcholine (DPPC)/FCn systems [Colloids Surf. B 41 (2005) 285-298] to understand the effect of phospholipids' polar headgroup on the binary miscibility. Furthermore, the phase behavior of the DMPE/FCn systems has been morphologically examined using fluorescence microscopy (FM) and atomic force microscopy (AFM). These images reveal the different interaction modes among the four systems; DMPE can be miscible with FC12 and FC14 and immiscible with FC16 and FC18 in the monolayer state. These systematic examinations indicate that the miscibility of perfluorocarboxylic acids and phospholipids depends on combination of hydrocarbon and fluorocarbon chain lengths and on phospholipids' polar headgroups within a monolayer.

  11. Advances in simulating radiance signatures for dynamic air/water interfaces

    NASA Astrophysics Data System (ADS)

    Goodenough, Adam A.; Brown, Scott D.; Gerace, Aaron

    2015-05-01

    The air-water interface poses a number of problems for both collecting and simulating imagery. At the surface, the magnitude of observed radiance can change by multiple orders of magnitude at high spatiotemporal frequency due to glinting effects. In the volume, similarly high frequency focusing of photons by a dynamic wave surface significantly changes the reflected radiance of in-water objects and the scattered return of the volume itself. These phenomena are often manifest as saturated pixels and artifacts in collected imagery (often enhanced by time delays between neighboring pixels or interpolation between adjacent filters) and as noise and greater required computation times in simulated imagery. This paper describes recent advances made to the Digital Image and Remote Sensing Image Generation (DIRSIG) model to address the simulation issues to better facilitate an understanding of a multi/hyper-spectral collection. Glint effects are simulated using a dynamic height field that can be driven by wave frequency models and generates a sea state at arbitrary time scales. The volume scattering problem is handled by coupling the geometry representing the surface (facetization by the height field) with the single scattering contribution at any point in the water. The problem is constrained somewhat by assuming that contributions come from a Snell's window above the scattering point and by assuming a direct source (sun). Diffuse single scattered and multiple scattered energy contributions are handled by Monte Carlo techniques employed previously. The model is compared to existing radiative transfer codes where possible, with the objective of providing a robust movel of time-dependent absolute radiance at many wavelengths.

  12. 20 Years of Air-Water Gas Exchange Observations for Pesticides in the Western Arctic Ocean.

    PubMed

    Jantunen, Liisa M; Wong, Fiona; Gawor, Anya; Kylin, Henrik; Helm, Paul A; Stern, Gary A; Strachan, William M J; Burniston, Deborah A; Bidleman, Terry F

    2015-12-01

    The Arctic has been contaminated by legacy organochlorine pesticides (OCPs) and currently used pesticides (CUPs) through atmospheric transport and oceanic currents. Here we report the time trends and air-water exchange of OCPs and CUPs from research expeditions conducted between 1993 and 2013. Compounds determined in both air and water were trans- and cis-chlordanes (TC, CC), trans- and cis-nonachlors (TN, CN), heptachlor exo-epoxide (HEPX), dieldrin (DIEL), chlorobornanes (ΣCHBs and toxaphene), dacthal (DAC), endosulfans and metabolite endosulfan sulfate (ENDO-I, ENDO-II, and ENDO SUL), chlorothalonil (CHT), chlorpyrifos (CPF), and trifluralin (TFN). Pentachloronitrobenzene (PCNB and quintozene) and its soil metabolite pentachlorothianisole (PCTA) were also found in air. Concentrations of most OCPs declined in surface water, whereas some CUPs increased (ENDO-I, CHT, and TFN) or showed no significant change (CPF and DAC), and most compounds declined in air. Chlordane compound fractions TC/(TC + CC) and TC/(TC + CC + TN) decreased in water and air, while CC/(TC + CC + TN) increased. TN/(TC + CC + TN) also increased in air and slightly, but not significantly, in water. These changes suggest selective removal of more labile TC and/or a shift in chlordane sources. Water-air fugacity ratios indicated net volatilization (FR > 1.0) or near equilibrium (FR not significantly different from 1.0) for most OCPs but net deposition (FR < 1.0) for ΣCHBs. Net deposition was shown for ENDO-I on all expeditions, while the net exchange direction of other CUPs varied. Understanding the processes and current state of air-surface exchange helps to interpret environmental exposure and evaluate the effectiveness of international protocols and provides insights for the environmental fate of new and emerging chemicals. PMID:26196214

  13. 20 Years of Air-Water Gas Exchange Observations for Pesticides in the Western Arctic Ocean.

    PubMed

    Jantunen, Liisa M; Wong, Fiona; Gawor, Anya; Kylin, Henrik; Helm, Paul A; Stern, Gary A; Strachan, William M J; Burniston, Deborah A; Bidleman, Terry F

    2015-12-01

    The Arctic has been contaminated by legacy organochlorine pesticides (OCPs) and currently used pesticides (CUPs) through atmospheric transport and oceanic currents. Here we report the time trends and air-water exchange of OCPs and CUPs from research expeditions conducted between 1993 and 2013. Compounds determined in both air and water were trans- and cis-chlordanes (TC, CC), trans- and cis-nonachlors (TN, CN), heptachlor exo-epoxide (HEPX), dieldrin (DIEL), chlorobornanes (ΣCHBs and toxaphene), dacthal (DAC), endosulfans and metabolite endosulfan sulfate (ENDO-I, ENDO-II, and ENDO SUL), chlorothalonil (CHT), chlorpyrifos (CPF), and trifluralin (TFN). Pentachloronitrobenzene (PCNB and quintozene) and its soil metabolite pentachlorothianisole (PCTA) were also found in air. Concentrations of most OCPs declined in surface water, whereas some CUPs increased (ENDO-I, CHT, and TFN) or showed no significant change (CPF and DAC), and most compounds declined in air. Chlordane compound fractions TC/(TC + CC) and TC/(TC + CC + TN) decreased in water and air, while CC/(TC + CC + TN) increased. TN/(TC + CC + TN) also increased in air and slightly, but not significantly, in water. These changes suggest selective removal of more labile TC and/or a shift in chlordane sources. Water-air fugacity ratios indicated net volatilization (FR > 1.0) or near equilibrium (FR not significantly different from 1.0) for most OCPs but net deposition (FR < 1.0) for ΣCHBs. Net deposition was shown for ENDO-I on all expeditions, while the net exchange direction of other CUPs varied. Understanding the processes and current state of air-surface exchange helps to interpret environmental exposure and evaluate the effectiveness of international protocols and provides insights for the environmental fate of new and emerging chemicals.

  14. Microwave plasma source operating with atmospheric pressure air-water mixtures

    NASA Astrophysics Data System (ADS)

    Tatarova, E.; Henriques, J. P.; Felizardo, E.; Lino da Silva, M.; Ferreira, C. M.; Gordiets, B.

    2012-11-01

    The overall performance of a surface wave driven air-water plasma source operating at atmospheric pressure and 2.45 GHz has been analyzed. A 1D model previously developed has been improved in order to describe in detail the creation and loss processes of active species of interest. This model provides a complete characterization of the axial structure of the source, including the discharge and the afterglow zones. The main electron creation channel was found to be the associative ionization process N + O → NO+ + e. The NO(X) relative density in the afterglow plasma jet ranges from 1.2% to 1.6% depending on power and water percentage, according to the model predictions and the measurements. Other types of species such as NO2 and nitrous acid HNO2 have also been detected by mass and Fourier Transform Infrared spectroscopy. The relative population density of O(3P) ground state atoms increases from 8% to 10% in the discharge zone when the input microwave power increases from 200 to 400 W and the water percentage from 1% to 10%. Furthermore, high densities of O2(a1Δg) singlet delta oxygen molecules and OH radicals (1% and 5%, respectively) can be achieved in the discharge zone. In the late afterglow the O2(a1Δg) density is about 0.1% of the total density. This plasma source has a flexible operation and potential for channeling the energy in ways that maximize the density of active species of interest.

  15. Application of a laser Doppler vibrometer for air-water to subsurface signature detection

    NASA Astrophysics Data System (ADS)

    Land, Phillip; Roeder, James; Robinson, Dennis; Majumdar, Arun

    2015-05-01

    There is much interest in detecting a target and optical communications from an airborne platform to a platform submerged under water. Accurate detection and communications between underwater and aerial platforms would increase the capabilities of surface, subsurface, and air, manned and unmanned vehicles engaged in oversea and undersea activities. The technique introduced in this paper involves a Laser Doppler Vibrometer (LDV) for acousto-optic sensing for detecting acoustic information propagated towards the water surface from a submerged platform inside a 12 gallon water tank. The LDV probes and penetrates the water surface from an aerial platform to detect air-water surface interface vibrations caused by an amplifier to a speaker generating a signal generated from underneath the water surface (varied water depth from 1" to 8"), ranging between 50Hz to 5kHz. As a comparison tool, a hydrophone was used simultaneously inside the water tank for recording the acoustic signature of the signal generated between 50Hz to 5kHz. For a signal generated by a submerged platform, the LDV can detect the signal. The LDV detects the signal via surface perturbations caused by the impinging acoustic pressure field; proving a technique of transmitting/sending information/messages from a submerged platform acoustically to the surface of the water and optically receiving the information/message using the LDV, via the Doppler Effect, allowing the LDV to become a high sensitivity optical-acoustic device. The technique developed has much potential usage in commercial oceanography applications. The present work is focused on the reception of acoustic information from an object located underwater.

  16. Air-water CO2 outgassing in the Lower Lakes (Alexandrina and Albert, Australia) following a millennium drought.

    PubMed

    Li, Siyue; Bush, Richard T; Ward, Nicholas J; Sullivan, Leigh A; Dong, Fangyong

    2016-01-15

    Lakes are an important source and sink of atmospheric CO2, and thus are a vital component of the global carbon cycle. However, with scarce data on potentially important subtropical and tropical areas for whole continents such as Australia, the magnitude of large-scale lake CO2 emissions is unclear. This study presents spatiotemporal changes of dissolved inorganic carbon and water - to - air interface CO2 flux in the two of Australia's largest connected, yet geomorphically different freshwater lakes (Lake Alexandrina and Lake Albert, South Australia), during drought (2007 to September-2010) and post-drought (October 2010 to 2013). Lake levels in the extreme drought were on average approximately 1m lower than long-term average (0.71 m AHD). Drought was associated with an increase in the concentrations of dissolved inorganic species, organic carbon, nitrogen, Chl-a and major ions, as well as water acidification as a consequence of acid sulfate soil (ASS) exposure, and hence, had profound effects on lake pCO2 concentrations. Lakes Alexandrina and Albert were a source of CO2 to the atmosphere during the drought period, with efflux ranging from 0.3 to 7.0 mmol/m(2)/d. The lake air-water CO2 flux was negative in the post-drought, ranging between -16.4 and 0.9 mmol/m(2)/d. The average annual CO2 emission was estimated at 615.5×10(6) mol CO2/y during the drought period. These calculated emission rates are in the lower range for lakes, despite the potential for drought conditions that shift the lakes from sink to net source for atmospheric CO2. These observations have significant implications in the context of predicted increasing frequency and intensity of drought as a result of climate change. Further information on the spatial and temporal variability in CO2 flux from Australian lakes is urgently warranted to revise the global carbon budget for lakes. PMID:26520269

  17. Air-water CO2 outgassing in the Lower Lakes (Alexandrina and Albert, Australia) following a millennium drought.

    PubMed

    Li, Siyue; Bush, Richard T; Ward, Nicholas J; Sullivan, Leigh A; Dong, Fangyong

    2016-01-15

    Lakes are an important source and sink of atmospheric CO2, and thus are a vital component of the global carbon cycle. However, with scarce data on potentially important subtropical and tropical areas for whole continents such as Australia, the magnitude of large-scale lake CO2 emissions is unclear. This study presents spatiotemporal changes of dissolved inorganic carbon and water - to - air interface CO2 flux in the two of Australia's largest connected, yet geomorphically different freshwater lakes (Lake Alexandrina and Lake Albert, South Australia), during drought (2007 to September-2010) and post-drought (October 2010 to 2013). Lake levels in the extreme drought were on average approximately 1m lower than long-term average (0.71 m AHD). Drought was associated with an increase in the concentrations of dissolved inorganic species, organic carbon, nitrogen, Chl-a and major ions, as well as water acidification as a consequence of acid sulfate soil (ASS) exposure, and hence, had profound effects on lake pCO2 concentrations. Lakes Alexandrina and Albert were a source of CO2 to the atmosphere during the drought period, with efflux ranging from 0.3 to 7.0 mmol/m(2)/d. The lake air-water CO2 flux was negative in the post-drought, ranging between -16.4 and 0.9 mmol/m(2)/d. The average annual CO2 emission was estimated at 615.5×10(6) mol CO2/y during the drought period. These calculated emission rates are in the lower range for lakes, despite the potential for drought conditions that shift the lakes from sink to net source for atmospheric CO2. These observations have significant implications in the context of predicted increasing frequency and intensity of drought as a result of climate change. Further information on the spatial and temporal variability in CO2 flux from Australian lakes is urgently warranted to revise the global carbon budget for lakes.

  18. Characterization of composite phthalocyanine-fatty acid films from the air/water interface to solid supports.

    PubMed

    Giancane, G; Manno, D; Serra, A; Sgobba, V; Valli, L

    2011-12-22

    A commercial vanadyl 2,9,16,23-tetraphenoxy-29H,31H-phthalocyanine (VOPc) was dissolved in chloroform and spread on ultrapure water subphase in a Langmuir trough. The floating film was thoroughly characterized at the air-water interface by means of the Langmuir isotherm, Brewster angle microscopy, UV-vis reflection spectroscopy, and infrared measurements carried out directly at the air-water interface. All the results showed the formation of a non-uniform and aggregated floating layer, too rigid to be transferred by the Langmuir-Blodgett (LB) method. For this reason, a mixture of arachidic acid and VOPc was realized, characterized, and transferred by the LB technique on solid substrates. Interface measurements and atomic force microscopy analysis suggested the formation of a uniform arachidic acid film and a superimposed VOPc placed in prone configuration.

  19. Bromine and heavy halide chemistry at the air/water and air/ice interfaces: a computational approach

    NASA Astrophysics Data System (ADS)

    Gladich, I.; Shepson, P. B.; Szleifer, I.; Carignano, M.

    2010-12-01

    The air-water and air-ice interfaces are critically important surfaces, with respect to the physical and chemical properties of the Earth's atmosphere. In particular chloride, bromide and iodide ions are strongly involved in the reactions occurring at aerosol surfaces that are hydrated and at the air-ice interface in the polar boundary layer. Unfortunately, experimental access to these interfaces are quite problematic and the computational approach, based on molecular dynamic simulations and quantum mechanic calculations, is an interesting alternative approach. In this work, molecular dynamic (MD) simulations are used to study the halide enhancements at the air-water interface in the case of a dilute mixture of iodide, bromide and chloride ions. The MD results show how the air- water halide enhancement is different in the case of mixtures from the case of binary solutions (i.e. anions plus counter-positive ions) and how the presence of these halides at the interfaces depends from their relative concentrations in solution. In detail, heavy halides are strongly enhanced at the interfaces even if they are minor constituents in the bulk. Furthermore the enhancement of the larger halide ions, like bromide, at the surface is greater if lighter halides, like chloride, are in greater excess in the bulk. The applications of this last result on some real system, like sea-water, and the importance of bromide ions in the polar chemistry of ozone depletion events suggest a combined approach, MD and quantum mechanism (QM) calculation, to investigate the ozonation reaction of bromide (Br-+O3 → BrO-+O2 ) in the ice-QLL and in bulk water. The study of the reaction constants suggests how the different environments can affect the kinetics of such reaction. These results can help to understand the complex chemistry occurring at the air-water interface of hydrated aerosol and at the air-ice interface in the polar boundary layer.

  20. Capillarity-induced directed self-assembly of patchy hexagram particles at the air-water interface.

    PubMed

    Kang, Sung-Min; Choi, Chang-Hyung; Kim, Jongmin; Yeom, Su-Jin; Lee, Daeyeon; Park, Bum Jun; Lee, Chang-Soo

    2016-07-01

    Directed self-assembly can produce ordered or organized superstructures from pre-existing building blocks through pre-programmed interactions. Encoding desired information into building blocks with specific directionality and strength, however, poses a significant challenge for the development of self-assembled superstructures. Here, we demonstrate that controlling the shape and patchiness of particles trapped at the air-water interface can represent a powerful approach for forming ordered macroscopic complex structures through capillary interactions. We designed hexagram particles using a micromolding method that allowed for precise control over the shape and, more importantly, the chemical patchiness of the particles. The assembly behaviors of these hexagram particles at the air-water interface were strongly affected by chemical patchiness. In particular, two-dimensional millimeter-scale ordered structures could be formed by varying the patchiness of the hexagram particles, and we attribute this effect to the delicate balance between the attractive and repulsive interactions among the patchy hexagram particles. Our results provide important clues for encoding information into patchy particles to achieve macroscopic assemblies via a simple molding technique and potentially pave a new pathway for the programmable assembly of particles at the air-water interface.

  1. Capillarity-induced directed self-assembly of patchy hexagram particles at the air-water interface.

    PubMed

    Kang, Sung-Min; Choi, Chang-Hyung; Kim, Jongmin; Yeom, Su-Jin; Lee, Daeyeon; Park, Bum Jun; Lee, Chang-Soo

    2016-07-01

    Directed self-assembly can produce ordered or organized superstructures from pre-existing building blocks through pre-programmed interactions. Encoding desired information into building blocks with specific directionality and strength, however, poses a significant challenge for the development of self-assembled superstructures. Here, we demonstrate that controlling the shape and patchiness of particles trapped at the air-water interface can represent a powerful approach for forming ordered macroscopic complex structures through capillary interactions. We designed hexagram particles using a micromolding method that allowed for precise control over the shape and, more importantly, the chemical patchiness of the particles. The assembly behaviors of these hexagram particles at the air-water interface were strongly affected by chemical patchiness. In particular, two-dimensional millimeter-scale ordered structures could be formed by varying the patchiness of the hexagram particles, and we attribute this effect to the delicate balance between the attractive and repulsive interactions among the patchy hexagram particles. Our results provide important clues for encoding information into patchy particles to achieve macroscopic assemblies via a simple molding technique and potentially pave a new pathway for the programmable assembly of particles at the air-water interface. PMID:27328067

  2. Physicochemically functional ultrathin films by interfacial polymerization

    DOEpatents

    Lonsdale, H.K.; Babcock, W.C.; Friensen, D.T.; Smith, K.L.; Johnson, B.M.; Wamser, C.C.

    1990-08-14

    Interfacially-polymerized ultrathin films containing physicochemically functional groups are disclosed, both with and without supports. Various applications are disclosed, including membrane electrodes, selective membranes and sorbents, biocompatible materials, targeted drug delivery, and narrow band optical absorbers. 3 figs.

  3. Physicochemically functional ultrathin films by interfacial polymerization

    DOEpatents

    Lonsdale, Harold K.; Babcock, Walter C.; Friensen, Dwayne T.; Smith, Kelly L.; Johnson, Bruce M.; Wamser, Carl C.

    1990-01-01

    Interfacially-polymerized ultrathin films containing physicochemically functional groups are disclosed, both with and without supports. Various applications are disclsoed, including membrane electrodes, selective membranes and sorbents, biocompatible materials, targeted drug delivery, and narrow band optical absorbers.

  4. Interfacial adhesion for microelectronics and MEMS devices

    NASA Astrophysics Data System (ADS)

    Kennedy, Marian Siobhan

    2007-12-01

    test methods is not the same. Both test methods were used to test both reliability of metal-dielectrcs and the adhesion between metal-polymers and metal-metal interfaces. In Au/Si interfaces, competing mechanisms of stress corrosion cracking and diffusion control the evolution of interface toughness (Chapter 6). A separate study of roughness using W/Si showed quantitatively that increasing the surface area fraction of the well adhered layers increases the interfacial fracture energy (Chapter 7). For polymer-metal interfaces, the control of surface contaminants affected adhesion much more than metal-dielectric interfaces (Chapter 8).

  5. Interfacial Materials for Organic Solar Cells: Recent Advances and Perspectives

    PubMed Central

    Yin, Zhigang; Wei, Jiajun

    2016-01-01

    Organic solar cells (OSCs) have shown great promise as low‐cost photovoltaic devices for solar energy conversion over the past decade. Interfacial engineering provides a powerful strategy to enhance efficiency and stability of OSCs. With the rapid advances of interface layer materials and active layer materials, power conversion efficiencies (PCEs) of both single‐junction and tandem OSCs have exceeded a landmark value of 10%. This review summarizes the latest advances in interfacial layers for single‐junction and tandem OSCs. Electron or hole transporting materials, including metal oxides, polymers/small‐molecules, metals and metal salts/complexes, carbon‐based materials, organic‐inorganic hybrids/composites, and other emerging materials, are systemically presented as cathode and anode interface layers for high performance OSCs. Meanwhile, incorporating these electron‐transporting and hole‐transporting layer materials as building blocks, a variety of interconnecting layers for conventional or inverted tandem OSCs are comprehensively discussed, along with their functions to bridge the difference between adjacent subcells. By analyzing the structure–property relationships of various interfacial materials, the important design rules for such materials towards high efficiency and stable OSCs are highlighted. Finally, we present a brief summary as well as some perspectives to help researchers understand the current challenges and opportunities in this emerging area of research. PMID:27812480

  6. Quantitative morphological characterization of bicontinuous Pickering emulsions via interfacial curvatures.

    PubMed

    Reeves, Matthew; Stratford, Kevin; Thijssen, Job H J

    2016-05-14

    Bicontinuous Pickering emulsions (bijels) are a physically interesting class of soft materials with many potential applications including catalysis, microfluidics and tissue engineering. They are created by arresting the spinodal decomposition of a partially-miscible liquid with a (jammed) layer of interfacial colloids. Porosity L (average interfacial separation) of the bijel is controlled by varying the radius (r) and volume fraction (ϕ) of the colloids (L∝r/ϕ). However, to optimize the bijel structure with respect to other parameters, e.g. quench rate, characterizing by L alone is insufficient. Hence, we have used confocal microscopy and X-ray CT to characterize a range of bijels in terms of local and area-averaged interfacial curvatures; we further demonstrate that bijels are bicontinuous using an image-analysis technique known as 'region growing'. In addition, the curvatures of bijels have been monitored as a function of time, which has revealed an intriguing evolution up to 60 minutes after bijel formation, contrary to previous understanding. PMID:27035101

  7. Penetration of surfactin into phospholipid monolayers: nanoscale interfacial organization.

    PubMed

    Eeman, M; Berquand, A; Dufrêne, Y F; Paquot, M; Dufour, S; Deleu, M

    2006-12-19

    Atomic force microscopy (AFM) combined with surface pressure-area isotherms were used to probe the interfacial behavior of phospholipid monolayers following penetration of surfactin, a cyclic lipopeptide produced by Bacillus subtilis strains. Prior to penetration experiments, interfacial behavior of different surfactin molecules (cyclic surfactins with three different aliphatic chain lengths--S13, S14, and S15--and a linear surfactin obtained by chemical cleavage of the cycle of the surfactin S15) has been investigated. A more hydrophobic aliphatic chain induces greater surface-active properties of the lipopeptide. The opening of the peptide ring reduces the surface activity. The effect of phospholipid acyl chain length (dimyristoylphosphatidylcholine, dipalmitoylphosphatidylcholine- (DPPC), and distearoylphosphatidylcholine) and phospholipid polar head (DPPC, dipalmitoylphosphatidylethanolamine and dipalmitoylphosphatidylserine) on monolayer penetration properties of the surfactin S15 has been explored. Results showed that while the lipid monolayer thickness and the presence of electrostatic repulsions from the interfacial film do not significantly influence surfactin insertion, these parameters strongly modulate the ability of the surfactin to alter the nanoscale organization of the lipid films. We also probed the effect of surfactin structure (influence of the aliphatic chain length and of the cyclic structure of the peptide ring) on the behavior of DPPC monolayers. AFM images and isotherms showed that surfactin penetration is promoted by longer lipopeptide chain length and a cyclic polar head. This indicates that hydrophobic interactions are of main importance for the penetration power of surfactin molecules.

  8. Quantitative morphological characterization of bicontinuous Pickering emulsions via interfacial curvatures.

    PubMed

    Reeves, Matthew; Stratford, Kevin; Thijssen, Job H J

    2016-05-14

    Bicontinuous Pickering emulsions (bijels) are a physically interesting class of soft materials with many potential applications including catalysis, microfluidics and tissue engineering. They are created by arresting the spinodal decomposition of a partially-miscible liquid with a (jammed) layer of interfacial colloids. Porosity L (average interfacial separation) of the bijel is controlled by varying the radius (r) and volume fraction (ϕ) of the colloids (L∝r/ϕ). However, to optimize the bijel structure with respect to other parameters, e.g. quench rate, characterizing by L alone is insufficient. Hence, we have used confocal microscopy and X-ray CT to characterize a range of bijels in terms of local and area-averaged interfacial curvatures; we further demonstrate that bijels are bicontinuous using an image-analysis technique known as 'region growing'. In addition, the curvatures of bijels have been monitored as a function of time, which has revealed an intriguing evolution up to 60 minutes after bijel formation, contrary to previous understanding.

  9. Electric Field Induced Interfacial Instabilities

    NASA Technical Reports Server (NTRS)

    Kusner, Robert E.; Min, Kyung Yang; Wu, Xiao-Lun; Onuki, Akira

    1996-01-01

    The study of the interface in a charge-free, nonpolar, critical and near-critical binary fluid in the presence of an externally applied electric field is presented. At sufficiently large fields, the interface between the two phases of the binary fluid should become unstable and exhibit an undulation with a predefined wavelength on the order of the capillary length. As the critical point is approached, this wavelength is reduced, potentially approaching length-scales such as the correlation length or critical nucleation radius. At this point the critical properties of the system may be affected. In zero gravity, the interface is unstable at all long wavelengths in the presence of a field applied across it. It is conjectured that this will cause the binary fluid to break up into domains small enough to be outside the instability condition. The resulting pattern formation, and the effects on the critical properties as the domains approach the correlation length are of acute interest. With direct observation, laser light scattering, and interferometry, the phenomena can be probed to gain further understanding of interfacial instabilities and the pattern formation which results, and dimensional crossover in critical systems as the critical fluctuations in a particular direction are suppressed by external forces.

  10. Interfacial adsorption in ternary alloys

    SciTech Connect

    Huang, C.; Cruz, M.O. de la; Voorhees, P.W.

    1999-11-26

    Interfaces of A-B-C ternary alloys decomposed into two and three phases are studied. The effect of the gradient energy coefficients {bar {kappa}}{sub II}, I = A, B, C, on the interface composition profiles of ternary alloys is examined. The adsorption of component C in ternary alloys is obtained numerically by finding steady-state solutions of the nonlinear Cahn-Hilliard equations and by solving the two Euler-Lagrange equations resulting from minimizing the interfacial energy, and analytically near the critical point. It is found that the solutions from both numerical methods are identical for a two-phase system. In symmetric ternary systems (equal interaction energy between each pair of components) with a minority component C, the gradient energy coefficient of C, {bar {kappa}}{sub CC}, can have a very strong influence on the degree of adsorption. In the {alpha} and {beta} two-phase regions, where {alpha} and {beta} are the phases rich in the majority components A and B, respectively, as {bar {kappa}}{sub CC} increases, the adsorption of the minority component C in the {alpha} and {beta} interfaces decreases. Near a critical point, however, the degree of adsorption of minority component C is independent of the gradient energy coefficient.

  11. Interfacial engineering for silica nanocapsules.

    PubMed

    Wibowo, David; Hui, Yue; Middelberg, Anton P J; Zhao, Chun-Xia

    2016-10-01

    Silica nanocapsules have attracted significant interest due to their core-shell hierarchical structure. The core domain allows the encapsulation of various functional components such as drugs, fluorescent and magnetic nanoparticles for applications in drug delivery, imaging and sensing, and the silica shell with its unique properties including biocompatibility, chemical and physical stability, and surface-chemistry tailorability provides a protection layer for the encapsulated cargo. Therefore, significant effort has been directed to synthesize silica nanocapsules with engineered properties, including size, composition and surface functionality, for various applications. This review provides a comprehensive overview of emerging methods for the manufacture of silica nanocapsules, with a special emphasis on different interfacial engineering strategies. The review starts with an introduction of various manufacturing approaches of silica nanocapsules highlighting surface engineering of the core template nanomaterials (solid nanoparticles, liquid droplets, and gas bubbles) using chemicals or biomolecules which are able to direct nucleation and growth of silica at the boundary of two-phase interfaces (solid-liquid, liquid-liquid, and gas-liquid). Next, surface functionalization of silica nanocapsules is presented. Furthermore, strategies and challenges of encapsulating active molecules (pre-loading and post-loading approaches) in these capsular systems are critically discussed. Finally, applications of silica nanocapsules in controlled release, imaging, and theranostics are reviewed. PMID:27522646

  12. Relative Order of Sulfuric Acid, Bisulfate, Hydronium, and Cations at the Air-Water Interface.

    PubMed

    Hua, Wei; Verreault, Dominique; Allen, Heather C

    2015-11-01

    Sulfuric acid (H2SO4), bisulfate (HSO4(-)), and sulfate (SO4(2-)) are among the most abundant species in tropospheric and stratospheric aerosols due to high levels of atmospheric SO2 emitted from biomass burning and volcanic eruptions. The air/aqueous interfaces of sulfuric acid and bisulfate solutions play key roles in heterogeneous reactions, acid rain, radiative balance, and polar stratospheric cloud nucleation. Molecular-level knowledge about the interfacial distribution of these inorganic species and their perturbation of water organization facilitates a better understanding of the reactivity and growth of atmospheric aerosols and of the aerosol surface charge, thus shedding light on topics of air pollution, climate change, and thundercloud electrification. Here, the air/aqueous interface of NaHSO4, NH4HSO4, and Mg(HSO4)2 salt solutions as well as H2SO4 and HCl acid solutions are investigated by means of vibrational sum frequency generation (VSFG) and heterodyne-detected (HD) VSFG spectroscopy. VSFG spectra of all acid solutions show higher SFG response in the OH-bonded region relative to neat water, with 1.1 M H2SO4 being more enhanced than 1.1 M HCl. In addition, VSFG spectra of bisulfate salt solutions highly resemble that of the dilute H2SO4 solution (0.26 M) at a comparable pH. HD-VSFG (Im χ((2))) spectra of acid and bisulfate salt solutions further reveal that hydrogen-bonded water molecules are oriented preferentially toward the bulk liquid phase. General agreement between Im χ((2)) spectra of 1.1 M H2SO4 and 1.1 M HCl acid solutions indicate that HSO4(-) ions have a similar surface preference as that of chloride (Cl(-)) ions. By comparing the direction and magnitude of the electric fields arising from the interfacial ion distributions and the concentration of each species, the most reasonable relative surface preference that can be deduced from a simplified model follows the order H3O(+) > HSO4(-) > Na(+), NH4(+), Mg(2+) > SO4(2-). Interestingly

  13. Relative Order of Sulfuric Acid, Bisulfate, Hydronium, and Cations at the Air-Water Interface.

    PubMed

    Hua, Wei; Verreault, Dominique; Allen, Heather C

    2015-11-01

    Sulfuric acid (H2SO4), bisulfate (HSO4(-)), and sulfate (SO4(2-)) are among the most abundant species in tropospheric and stratospheric aerosols due to high levels of atmospheric SO2 emitted from biomass burning and volcanic eruptions. The air/aqueous interfaces of sulfuric acid and bisulfate solutions play key roles in heterogeneous reactions, acid rain, radiative balance, and polar stratospheric cloud nucleation. Molecular-level knowledge about the interfacial distribution of these inorganic species and their perturbation of water organization facilitates a better understanding of the reactivity and growth of atmospheric aerosols and of the aerosol surface charge, thus shedding light on topics of air pollution, climate change, and thundercloud electrification. Here, the air/aqueous interface of NaHSO4, NH4HSO4, and Mg(HSO4)2 salt solutions as well as H2SO4 and HCl acid solutions are investigated by means of vibrational sum frequency generation (VSFG) and heterodyne-detected (HD) VSFG spectroscopy. VSFG spectra of all acid solutions show higher SFG response in the OH-bonded region relative to neat water, with 1.1 M H2SO4 being more enhanced than 1.1 M HCl. In addition, VSFG spectra of bisulfate salt solutions highly resemble that of the dilute H2SO4 solution (0.26 M) at a comparable pH. HD-VSFG (Im χ((2))) spectra of acid and bisulfate salt solutions further reveal that hydrogen-bonded water molecules are oriented preferentially toward the bulk liquid phase. General agreement between Im χ((2)) spectra of 1.1 M H2SO4 and 1.1 M HCl acid solutions indicate that HSO4(-) ions have a similar surface preference as that of chloride (Cl(-)) ions. By comparing the direction and magnitude of the electric fields arising from the interfacial ion distributions and the concentration of each species, the most reasonable relative surface preference that can be deduced from a simplified model follows the order H3O(+) > HSO4(-) > Na(+), NH4(+), Mg(2+) > SO4(2-). Interestingly

  14. Understanding the interfacial layer dynamics of polymer nanocomposites from broadband dielectric spectroscopy

    NASA Astrophysics Data System (ADS)

    Carroll, Robert; Cheng, Shiwang; Sokolov, Alexei

    Polymer nanocomposites show many advanced mechanical, thermal, optical, and transport properties mainly due to the vast interfacial area between the polymer matrix and nanoparticles. Recent studies show that there is an interfacial polymer layer with structure and dynamics that are different from the bulk polymer, and that contributes to the advanced macroscopic properties. It has been shown that broadband dielectric spectroscopy provides good method to study the interfacial dynamics in nanocomposites. However, current dielectric spectroscopy studies ignore the heterogeneous nature of polymer nanocomposites. Models based on a simple superposition of bulk polymer and interfacial layer spectra, or those that assume the interfacial layer is dynamically ``dead'' are inaccurate. In this talk, the prevailing methods in the literature will be compared with an accurate method accounting for the heterogeneity of the nanocomposites. Different nanocomposites with well-dispersed nanoparticles will be used as examples. The analysis clearly shows that the width and the amplitude of the relaxation peaks are affected by the data analysis. Thus accurate quantitative conclusions on properties and thickness of the interfacial layer can be achieved only using heterogeneous models.

  15. Hydrogen bonding and orientation effects on the accommodation of methylamine at the air-water interface

    NASA Astrophysics Data System (ADS)

    Hoehn, Ross D.; Carignano, Marcelo A.; Kais, Sabre; Zhu, Chongjing; Zhong, Jie; Zeng, Xiao C.; Francisco, Joseph S.; Gladich, Ivan

    2016-06-01

    Methylamine is an abundant amine compound detected in the atmosphere which can affect the nature of atmospheric aerosol surfaces, changing their chemical and optical properties. Molecular dynamics simulation results show that methylamine accommodation on water is close to unity with the hydrophilic head group solvated in the interfacial environment and the methyl group pointing into the air phase. A detailed analysis of the hydrogen bond network indicates stronger hydrogen bonds between water and the primary amine group at the interface, suggesting that atmospheric trace gases will likely react with the methyl group instead of the solvated amine site. These findings suggest new chemical pathways for methylamine acting on atmospheric aerosols in which the methyl group is the site of orientation specific chemistry involving its conversion into a carbonyl site providing hydrophilic groups for uptake of additional water. This conversion may explain the tendency of aged organic aerosols to form cloud condensation nuclei. At the same time, formation of NH2 radical and formaldehyde is suggested to be a new source for NH2 radicals at aerosol surfaces, other than by reaction of absorbed NH3. The results have general implications for the chemistry of other amphiphilic organics, amines in particular, at the surface of atmospherically relevant aerosols.

  16. Adsorption of egg phosphatidylcholine to an air/water and triolein/water bubble interface: use of the 2-dimensional phase rule to estimate the surface composition of a phospholipid/triolein/water surface as a function of surface pressure.

    PubMed

    Mitsche, Matthew A; Wang, Libo; Small, Donald M

    2010-03-11

    Phospholipid monolayers play a critical role in the structure and stabilization of biological interfaces, including all membranes, the alveoli of the lungs, fat droplets in adipose tissue, and lipoproteins. The behavior of phospholipids in bilayers and at an air-water interface is well understood. However, the study of phospholipids at oil-water interfaces is limited due to technical challenges. In this study, egg phosphatidylcholine (EPC) was deposited from small unilamellar vesicles onto a bubble of either air or triolein (TO) formed in a low-salt buffer. The surface tension (gamma) was measured using a drop tensiometer. We observed that EPC binds irreversibly to both interfaces and at equilibrium exerts approximately 12 and 15 mN/m of pressure (Pi) at an air and TO interface, respectively. After EPC was bound to the interface, the unbound EPC was washed out of the cuvette, and the surface was compressed to study the Pi/area relationship. To determine the surface concentration (Gamma), which cannot be measured directly, compression isotherms from a Langmuir trough and drop tensiometer were compared. The air-water interfaces had identical characteristics using both techniques; thus, Gamma on the bubble can be determined by overlaying the two isotherms. Both TO and EPC are surface-active, so in a mixed TO/EPC monolayer, both molecules will be exposed to water. Since TO is less surface-active than EPC, as Pi increases, the TO is progressively ejected. To understand the Pi/area isotherm of EPC on a TO bubble, a variety of TO-EPC mixtures were spread at the air-water interface. The isotherms show an abrupt break in the curve caused by the ejection of TO from the monolayer into a new bulk phase. By overlaying the compression isotherm above the ejection point with a TO bubble compression isotherm, Gamma can be estimated. This allows determination of Gamma of EPC on a TO bubble as a function of Pi.

  17. The effect of filler-polymer interfacial adhesion on the rheological behavior of filled polymers

    NASA Astrophysics Data System (ADS)

    Rucker, Derek Peck

    1997-11-01

    Current applications for filled polymers require small particle, high surface area fillers as well as extremely specific flow behavior. It has long been suspected that filler-polymer interfacial adhesion affects the rheological properties of filled polymers. Only recently, however, have filler surface areas become so large and fine control of rheological behavior become so important that these effects must be considered. Several predictions exist for the effect of interfacial adhesion on filled polymer rheological behavior. When there is strong interfacial adhesion, the filler particles may act as cross-link sites, or may increase their effective size by trapping polymer on their surface. Either effect would result in an increase in the solid-like character of the material with increasing adhesion. If the interfacial adhesion is weaker, the material may behave much like a traditional colloid, with an increase in the liquid-like behavior with increasing particle stability, or in this case, increasing interfacial adhesion. The goal of this research was to use a model system of surface treated silica in polyethylene and poly (methyl methacrylate) to investigate the effect of interfacial adhesion on oscillatory rheological behavior. Frequency sweep experiments were primarily used in this work to prevent the breakdown of interfacial adhesion induced structure. The two polymers were chosen for their non-polar and polar surface characteristics, respectively, yielding a wide range of adhesion behavior with surface modified silica. The relative storage modulus behavior for the different systems was compared, and a normalized plot was developed as a function of work of adhesion. The relative storage modulus of these systems was shown to decrease with increasing work of adhesion for all filler volume fractions and over all frequencies. This suggests that the traditional colloidal model for interfacial adhesion effects is appropriate for the adhesion range studied in this work

  18. Spider-web amphiphiles as artificial lipid clusters: design, synthesis, and accommodation of lipid components at the air-water interface.

    PubMed

    Ariga, Katsuhiko; Urakawa, Toshihiro; Michiue, Atsuo; Kikuchi, Jun-ichi

    2004-08-01

    As a novel category of two-dimensional lipid clusters, dendrimers having an amphiphilic structure in every unit were synthesized and labeled "spider-web amphiphiles". Amphiphilic units based on a Lys-Lys-Glu tripeptide with hydrophobic tails at the C-terminal and a polar head at the N-terminal are dendrically connected through stepwise peptide coupling. This structural design allowed us to separately introduce the polar head and hydrophobic tails. Accordingly, we demonstrated the synthesis of the spider-web amphiphile series in three combinations: acetyl head/C16 chain, acetyl head/C18 chain, and ammonium head/C16 chain. All the spider-web amphiphiles were synthesized in satisfactory yields, and characterized by 1H NMR, MALDI-TOFMS, GPC, and elemental analyses. Surface pressure (pi)-molecular area (A) isotherms showed the formation of expanded monolayers except for the C18-chain amphiphile at 10 degrees C, for which the molecular area in the condensed phase is consistent with the cross-sectional area assigned for all the alkyl chains. In all the spider-web amphiphiles, the molecular areas at a given pressure in the expanded phase increased in proportion to the number of units, indicating that alkyl chains freely fill the inner space of the dendritic core. The mixing of octadecanoic acid with the spider-web amphiphiles at the air-water interface induced condensation of the molecular area. From the molecular area analysis, the inclusion of the octadecanoic acid bears a stoichiometric characteristic; i.e., the number of captured octadecanoic acids in the spider-web amphiphile roughly agrees with the number of branching points in the spider-web amphiphile.

  19. Interfacial and near interfacial crack growth phenomena in metal bonded alumina

    SciTech Connect

    Kruzic, Jamie Joseph

    2002-03-01

    Metal/ceramic interfaces can be found in many engineering applications including microelectronic packaging, multi-layered films, coatings, joints, and composite materials. In order to design reliable engineering systems that contain metal/ceramic interfaces, a comprehensive understanding of interfacial and near interfacial failure mechanisms is necessary.

  20. Spectroscopic [correction of eSpectroscopic] and structural properties of valine gramicidin A in monolayers at the air-water interface.

    PubMed Central

    Lavoie, Hugo; Blaudez, Daniel; Vaknin, David; Desbat, Bernard; Ocko, Benjamin M; Salesse, Christian

    2002-01-01

    Monomolecular films of valine gramicidin A (VGA) were investigated in situ at the air-water interface by x-ray reflectivity and x-ray grazing incidence diffraction as well as polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). These techniques were combined to obtain information on the secondary structure and the orientation of VGA and to characterize the shoulder observed in its pi-A isotherm. The thickness of the film was obtained by x-ray reflectivity, and the secondary structure of VGA was monitored using the frequency position of the amide I band. The PM-IRRAS spectra were compared with the simulated ones to identify the conformation adopted by VGA in monolayer. At large molecular area, VGA shows a disordered secondary structure, whereas at smaller molecular areas, VGA adopts an anti-parallel double-strand intertwined beta(5.6) helical conformation with 30 degrees orientation with respect to the normal with a thickness of 25 A. The interface between bulk water and the VGA monolayer was investigated by x-ray reflectivity as well as by comparing the experimental and the simulated PM-IRRAS spectra on D(2)O and H(2)O, which suggested the presence of oriented water molecules between the bulk and the monolayer. PMID:12496123

  1. Spatial trends, sources, and air-water exchange of organochlorine pesticides in the Great Lakes basin using low density polyethylene passive samplers.

    PubMed

    Khairy, Mohammed; Muir, Derek; Teixeira, Camilla; Lohmann, Rainer

    2014-08-19

    Polyethylene passive samplers were deployed during summer and fall of 2011 in the lower Great Lakes to assess the spatial distribution and sources of gaseous and freely dissolved organochlorine pesticides (OCPs) and their air-water exchange. Average gaseous OCP concentrations ranged from nondetect to 133 pg/m(3). Gaseous concentrations of hexachlorobenzene, dieldrin, and chlordanes were significantly greater (Mann-Whitney test, p < 0.05) at Lake Erie than Lake Ontario. A multiple linear regression implied that both cropland and urban areas within 50 and 10 km buffer zones, respectively, were critical parameters to explain the total variability in atmospheric concentrations. Freely dissolved OCP concentrations (nondetect to 114 pg/L) were lower than previously reported. Aqueous half-lives generally ranged from 1.7 to 6.7 years. Nonetheless, concentrations of p,p'-DDE and chlordanes were higher than New York State Ambient Water Quality Standards for the protection of human health from the consumption of fish. Spatial distributions of freely dissolved OCPs in both lakes were influenced by loadings from areas of concern and the water circulation patterns. Flux calculations indicated net deposition of γ-hexachlorocyclohexane, heptachlor-epoxide, and α- and β-endosulfan (-0.02 to -33 ng/m(2)/day) and net volatilization of heptachlor, aldrin, trans-chlordane, and trans-nonachlor (0.0 to 9.0 ng/m(2)/day) in most samples.

  2. An excellent candidate for largely reducing interfacial thermal resistance: a nano-confined mass graded interface

    NASA Astrophysics Data System (ADS)

    Zhou, Yanguang; Zhang, Xiaoliang; Hu, Ming

    2016-01-01

    Pursuing extremely low interfacial thermal resistance has long been the task of many researchers in the area of nano-scale heat transfer, in particular pertaining to improve heat dissipation performance in electronic cooling. While it is well known and documented that confining a macroscopic third layer between two dissimilar materials usually increases the overall interfacial thermal resistance, no research has realized the fundamental decrease in resistance so far. By performing nonequilibrium molecular dynamics simulations, we report that the overall interfacial thermal resistance can be reduced by 6 fold by confining mass graded materials with thickness of the order of nanometers. As comparison we also studied the thermal transport across the perfectly abrupt interface and the widely used alloyed (rough) interface, which shows an opposing and significantly large increase in the overall thermal resistance. With the help of frequency dependent interfacial thermal conductance and wave packet dynamics simulation, different mechanisms governing the heat transfer across these three types of interfaces are identified. It is found that for the rough interface there are two different regimes of interfacial heat transfer, which originates from the competition between phonon scattering and the thickness of the interface. The mechanism of dramatically improved interfacial heat transfer across the nano-confined mass graded interface resides in the minor phonon reflection when the phonons first reach the mass graded area and the rare occurrence of phonon scattering in the subsequent interior region. The phonons are found to be gradually truncated by the geometric interfaces and can travel through the mass graded layer with a high transmission coefficient, benefited from the small mass mismatch between two neighboring layers in the interfacial region. Our findings provide deep insight into the phonon transport across nano-confined mass graded layers and also offer significant

  3. Conversion of Iodide to Hypoiodous Acid and Molecular Iodine at the Air-Water Interface

    NASA Astrophysics Data System (ADS)

    Pillar, E. A.; Guzman, M. I.

    2013-12-01

    Sea spray aerosols continuously transfer a significant amount of halides to the marine boundary layer, where they play a major role in the depletion of tropospheric ozone. The reactivity of iodide is of special interest in sea spray aerosols, where this species is enriched relative to chloride and bromide in surface seawater. This work presents laboratory experiments that provide mechanistic information to understand the reactivity of halides in atmospheric aerosols. Pneumatically assisted electrospray is used to aerosolize solutions of sodium iodide (0.01-100 μM), which are rapidly (~3 μs) oxidized by ozone at 25 °C. Reaction products include HIO, IO2-, IO3-, I2, HI2O-, and I3-, all identified by mass spectrometry. The distribution of products varies along two different reaction pathways, one favoring the production of I2 and HIO for typical tropospheric ozone levels (~50 ppbv), and another one directed to the production of IO3- at higher oxidizer concentrations. The formation of products increases exponentially with rising concentrations of initial sodium iodide, [NaI]0. The process is determined to be pH independent for the pH range 6-8 representative of surface waters. The substitution of aqueous solutions by organic solvents, such as methanol or acetonitrile, causes a decrease in the surface tension and lifetime of the droplets, leading to larger I2 production. The presence of surface active organic compounds, which alter the structure of the interfacial region, promote the pathway of I2 formation over IO3-. In conclusion, this presentation will show how the oxidation of iodide in aqueous microdroplets can release reactive gas-phase species, such as I2 and HIO, capable to affect tropospheric ozone globally. Normalized intensity of products observed during the ozonolysis of iodide solutions at 130 ppbv ozone. Cone voltage = 70 V, needle voltage = 2.5 kV.

  4. Ecosystem Metabolism and Air-Water Fluxes of Greenhouse Gases in High Arctic Wetland Ponds

    NASA Astrophysics Data System (ADS)

    Lehnherr, I.; Venkiteswaran, J.; St. Louis, V. L.; Emmerton, C.; Schiff, S. L.

    2012-12-01

    Freshwater lakes and wetlands can be very productive systems on the Arctic landscape compared to terrestrial tundra ecosystems and provide valuable resources to many organisms, including waterfowl, fish and humans. Rates of ecosystem productivity dictate how much energy flows through food webs, impacting the abundance of higher-level organisms (e.g., fish), as well as the net carbon balance, which determines whether a particular ecosystem is a source or sink of carbon. Climate change is predicted to result in warmer temperatures, increased precipitation and permafrost melting in the Arctic and is already altering northern ecosystems at unprecedented rates; however, it is not known how freshwater systems are responding to these changes. To predict how freshwater systems will respond to complex environmental changes, it is necessary to understand the key processes, such as primary production and ecosystem respiration, that are driving these systems. We sampled wetland ponds (n=8) and lakes (n=2) on northern Ellesmere Island (81° N, Nunavut, Canada) during the open water season for a suite of biogeochemical parameters, including concentrations of dissolved gases (O2, CO2, CH4, N2O) as well as stable-isotope ratios of dissolved inorganic carbon (δ13C-DIC), dissolved oxygen (δ18O-DO), and water (δ18O-H2O). We will present rates of primary production and ecosystem respiration, modeled from the concentration and stable isotope ratios of DIC and DO, as well as air-water gas exchange of greenhouse gases in these high Arctic ponds and lakes. Preliminary results demonstrate that ecosystem metabolism in these ponds was high enough to result in significant deviations in the isotope ratios of DIC and DO from atmospheric equilibrium conditions. In other words ecosystem rates of primary production and respiration were faster than gas exchange even in these small, shallow, well-mixed ponds. Furthermore, primary production was elevated enough at all sites except Lake Hazen, a

  5. Determination of interfacial tension of binary mixtures from perturbative approaches

    NASA Astrophysics Data System (ADS)

    Martínez-Ruiz, F. J.; Blas, F. J.

    2015-05-01

    We determine the interfacial properties of mixtures of spherical Lennard-Jones molecules from direct simulation of the vapour-liquid interface. We consider mixtures with same molecular size but different dispersive energy parameter values. We use the extensions of the improved version of the inhomogeneous long-range corrections of Janeček, presented recently by MacDowell and Blas and Martínez-Ruiz et al., to deal with the interaction energy and microscopic components of the pressure tensor. We have performed Monte Carlo simulations in the canonical ensemble to obtain the interfacial properties of mixtures of Lennard-Jones molecules with a cut-off distance rc = 3σ in combination with the inhomogeneous long-range corrections. The pressure tensor is obtained using the mechanical (virial) and thermodynamic route. The vapour-liquid interfacial tension is also evaluated using three different procedures, the Irving-Kirkwood method, the difference between the macroscopic components of the pressure tensor, and the test-area methodology. This allows to check the validity of the recent extensions presented to deal with the contributions due to long-range corrections for intermolecular energy and pressure tensor in the case of binary mixtures. In addition to the pressure tensor and the surface tension, we also obtain density profiles, coexistence densities, and interfacial thickness as functions of pressure, at a given temperature. According to our results, the main effect of increasing the ratio between the dispersive energy parameters of the mixture, ε22/ε11, is to sharpen the vapour-liquid interface and to increase the width of the biphasic coexistence region. Particularly interesting is the presence of a relative maximum in the density profiles of the less volatile component at the interface. This maximum is related with adsorption or accumulation of these molecules at the interface, a direct consequence of stronger attractive interactions between these molecules in

  6. The Silver-Nickel Interfacial Enthalpy Determined by Magnetic and Calorimetric Measurements.

    NASA Astrophysics Data System (ADS)

    Zolla, Howard Gordon

    1995-01-01

    A new method for the determination of the average interfacial enthalpy, sigma_sp{A -B}{H}, between unlike phases is presented. A differential scanning calorimeter is used to measure the heat released during precipitation of a superparamagnetic phase from a supersaturated solid solution. The volume fraction distribution of the precipitated phase is determined by maximum entropy modeling of the magnetization, measured to ultra-high fields, as a linear superposition of Langevin functions. Transmission electron microscopy is used to determine the aspect ratios of the precipitates, which is combined with the volume fraction distributions to calculate the total interfacial area in each specimen. The saturation magnetization is used to determine the total amount of the precipitated phase in each sample. The changes in enthalpy, interfacial area, and amount precipitated are used in a thermodynamic and kinetic model to calculate the interfacial enthalpy and heat of mixing. This method is applied to Ag-(5-10)at.% Ni alloys, produced in thin-film form by electron-beam co-evaporation. The average interfacial enthalpy between Ag and Ni, sigma_sp {Ag-Ni} {H}, and the heat of mixing are found to be, respectively, 0.779 +/- 0.076 J/m^2 and 3.59 +/- 0.03 kJ/mol for the average alloy composition of 6.89 at.% Ni.

  7. Air-water fluxes of N₂O and CH₄ during microalgae (Staurosira sp.) cultivation in an open raceway pond.

    PubMed

    Ferrón, Sara; Ho, David T; Johnson, Zackary I; Huntley, Mark E

    2012-10-01

    The industrial-scale production of biofuels from cultivated microalgae has gained considerable interest in the last several decades. While the climate benefits of microalgae cultivation that result from the capture of atmospheric CO(2) are known, the counteracting effect from the potential emission of other greenhouse gases has not been well quantified. Here, we report the results of a study conducted at an industrial pilot facility in Hawaii to determine the air-water fluxes of N(2)O and CH(4) from open raceway ponds used to grow the marine diatom Staurosira sp. as a feedstock for biofuel. Dissolved O(2), CH(4), and N(2)O concentrations were measured over a 24 h cycle. During this time, four SF(6) tracer release experiments were conducted to quantify gas transfer velocities in the ponds, and these were then used to calculate air-water fluxes. Our results show that pond waters were consistently supersaturated with CH(4) (up to 725%) resulting in an average emission of 19.9 ± 5.6 μmol CH(4) m(-2) d(-1). Upon NO(3)(-) depletion, the pond shifted from being a source to being a sink of N(2)O, with an overall net uptake during the experimental period of 3.4 ± 3.5 μmol N(2)O m(-2) d(-1). The air-water fluxes of N(2)O and CH(4) expressed as CO(2) equivalents of global warming potential were 2 orders of magnitude smaller than the overall CO(2) uptake by the microalgae.

  8. Towards Organized Hybrid Nanomaterials at the Air/Water Interface Based on Liquid-Crystal/ZnO Nanocrystals.

    PubMed

    Paczesny, Jan; Wolska-Pietkiewicz, Małgorzata; Binkiewicz, Ilona; Wróbel, Zbigniew; Wadowska, Monika; Matuła, Kinga; Dzięcielewski, Igor; Pociecha, Damian; Smalc-Koziorowska, Julita; Lewiński, Janusz; Hołyst, Robert

    2015-11-16

    The ability to self-assemble nanosized ligand-stabilized metal oxide or semiconductor materials offers an intriguing route to engineer nanomaterials with new tailored properties from the disparate components. We describe a novel one-pot two-step organometallic approach to prepare ZnO nanocrystals (NCs) coated with deprotonated 4-(dodecyloxy)benzoic acid (i.e., an X-type liquid-crystalline ligand) as a model LC system (termed ZnO-LC1 NCs). Langmuir and Langmuir-Blodgett films of the resulting hybrids are investigated. The observed behavior of the ZnO NCs at the air/water interface is rationalized by invoking a ZnO-interdigitation process mediated by the anchored liquid-crystalline shell. The ordered superstructures form according to mechanism based on a ZnO-interdigitation process mediated by liquid crystals (termed ZIP-LC). The external and directed force applied upon compression at the air/water interface and the packing of the ligands that stabilize the ZnO cores drives the formation of nanorods of ordered internal structure. To study the process in detail, we follow a nontraditional protocol of thin-film investigation. We collect the films from the air/water interface in powder form (ZnO-LC1 LB), resuspend the powder in organic solvents and utilize otherwise unavailable experimental techniques. The structural and physical properties of the resulting superlattices were studied by using electron microscopy, atomic force microscopy, X-ray studies, dynamic light scattering, thermogravimetric analysis, UV/Vis absorption, and photoluminescence spectroscopy.

  9. Application of LIF to investigate gas transfer near the air-water interface in a grid-stirred tank

    NASA Astrophysics Data System (ADS)

    Herlina; Jirka, G. H.

    The interaction between oxygen absorption into liquids and bottom shear-induced turbulence was investigated in a grid-stirred tank using a laser-induced fluorescence (LIF) technique. The LIF technique enabled visualization as well as quantification of planar concentration fields of the dissolved oxygen (DO) near the air-water interface. Qualitative observation of the images provided more insight into the physical mechanism controlling the gas transfer process. The high data resolution is an advantage for revealing the concentration distribution within the boundary layer, which is a few hundreds of a micrometer thick. Mean and turbulent fluctuation characteristics were obtained and compared with previous results.

  10. OH-Radical Oxidation of Surface-Active cis-Pinonic Acid at the Air-Water Interface.

    PubMed

    Enami, Shinichi; Sakamoto, Yosuke

    2016-05-26

    Gaseous biogenic volatile organic compounds (BVOCs) are immediately oxidized by gaseous oxidants to form BVOC-acids that rapidly condense onto aqueous aerosol phase and thus contribute to the growth of atmospheric particles. Because BVOC-acids are highly hydrophobic and hence surface-active in nature, it seems critical to study the oxidation by gaseous hydroxyl radical (·OH(g)) at the air-water interface. Here we report on the fast (≤10 μs) oxidation of aqueous cis-pinonic acid (C10H16O3, CPA, cis-pinonate anion's m/z = 183), a representative BVOC-acid, by ·OH(g) at the air-water interface for the first time. We find that cis-pinonate anion is more enriched at the air-water interface by ∼4 and ∼14 times than n-octanoate anion at 10 and 100 μM, respectively, as revealed by an interface-specific mass spectrometry of the equimolar mixture of microjets. Exposure of aqueous CPA microjets to ·OH(g) pulses from the 266 nm laser photolysis of O3(g)/O2(g)/H2O(g)/N2(g) mixtures yields pinonic peroxyl radicals (m/z = 214) that lead to the functionalization products carbonyls (m/z = 197), alcohols (m/z = 199), and pinonic hydroperoxides (m/z = 215) in addition to smaller-mass products including carbonyls (m/z = 155 and 157). We confirmed the formation of the corresponding alcohols, aldehydes, and hydroperoxides in experiments performed in D2O solvent. The analysis of total mass balance implies a significant amount (>70%) of products would be emitted into the gas-phase during the heterogeneous ·OH-oxidations. Our results suggest ·OH-oxidations of amphiphilic BVOC-acids at the air-water interface may play a far more significant role in photochemical aging process of aqueous aerosols than previously assumed. PMID:27098046

  11. Interfacial Properties of a Hydrophobic Dye in the Tetrachloroethylene-Water-Glass Systems

    SciTech Connect

    Tuck, D.M.

    1999-02-23

    condition at the highest dye concentration. The contact angle, measured through the aqueous phase, changed from 58 degrees for undyed PCE to 93 degrees at a dye concentration of 5.08 g/L. Complete reversal of the wettability is likely given the short equilibration time used in this study (approximately five minutes) together with literature indications that hundreds to thousands of hours may be required to reach equilibrium during contact angle measurements. Observations suggesting changing wetting relationships were also noted between PCE, water, and the platinum-iridium surface used in the standard du No/374y ring method for measuring interfacial tension.Observations of the dyed-PCE-water interface behavior during du No/374y ring interfacial tension measurements were similar to observations noted previously during measurements of the interfacial tension between the Savannah River Site (SRS) M-Area Settling Basin DNAPL (M-Area DNAPL) and water. This observation suggests that the M-Area DNAPL may contain surface active components. If this proves to be the case, it would have significant implications for how the M-Area DNAPL is distributed and moves in the SRS subsurface.

  12. Microfluidic ultralow interfacial tensiometry with magnetic particles.

    PubMed

    Tsai, Scott S H; Wexler, Jason S; Wan, Jiandi; Stone, Howard A

    2013-01-01

    We describe a technique that measures ultralow interfacial tensions using paramagnetic spheres in a co-flow microfluidic device designed with a magnetic section. Our method involves tuning the distance between the co-flowing interface and the magnet's center, and observing the behavior of the spheres as they approach the liquid-liquid interface-the particles either pass through or are trapped by the interface. Using threshold values of the magnet-to-interface distance, we make estimates of the two-fluid interfacial tension. We demonstrate the effectiveness of this technique for measuring very low interfacial tensions, O(10(-6)-10(-5)) N m(-1), by testing solutions of different surfactant concentrations, and we show that our results are comparable with measurements made using a spinning drop tensiometer. PMID:23154819

  13. Investigation of oil recovery improvement by coupling an interfacial tension agent and a mobility control agent in light oil reservoirs. Annual report, October 1992--September 1993

    SciTech Connect

    Pitts, M.J.

    1994-06-01

    Investigation of Oil Recovery Improvement by Coupling and Interfacial Tension Agent and a Mobility Control Agent in Light Oil Reservoirs will study two major areas concerning co-injecting an interfacial tension reduction agent(s) and a mobility control agent. The first area defines the interactions of alkaline agent, surfactants, and polymers on a fluid-fluid and fluid-rock basis. The second area concerns the economic improvement of the combined technology. This report examines the interactions of different alkaline agents, surfactants, and polymer combinations on a fluid-fluid basis. Alkali and surfactant combine to reduce the interfacial tension between a low acid number, 42 API gravity crude oil and the aqueous solution to values lower than either agent alone. Surfactant structure can vary from linear chain sulfonates to alkyl aryl sulfonates to produce low interfacial tension values when combined with alkali. However as a class, the alkyl aryl sulfonates were the most effective surfactants. Surfactant olefinic character appears to be critical in developing low interfacial tensions. For the 42 API gravity crude oil, surfactants with molecular weights ranging from 370 to 450 amu are more effective in lowering interfacial tension. Ultra low interfacial tensions were achieved with all of the alkaline agents evaluated when combined with appropriate surfactants. Different interfacial tension reduction characteristics with the various alkali types indicates alkali interacts synergistically with the surfactants to develop interfacial tension reduction. The solution pH is not a determining factor in lowering interfacial tension. Surfactant is the dominant agent for interfacial tension reduction.

  14. Surface characteristics of phosphatidylglycerol phosphate from the extreme halophile Halobacterium cutirubrum compared with those of its deoxy analogue, at the air/water interface.

    PubMed

    Quinn, P J; Kates, M; Tocanne, J F; Tomoaia-Cotişel, M

    1989-07-15

    The relationship between area per molecule and surface pressure of monolayers of phosphatidylglycerol phosphate from extreme halophile Halobacterium cutrirubrum and its deoxy analogue, deoxyphosphatidylglycerol phosphate, spread at an air/water interface was examined. The effect of ionization of the primary and secondary acidic functions of the phosphate groups of the two lipids on surface characteristics of compression isotherms was determined by spreading monolayers on subphases with pH values ranging from below the apparent pKa of the primary ionization (pH 0) to greater than that of secondary ionization (pH 10.9). The limiting molecular area increases with decreasing pH below 2. Ionization of the primary phosphate functions of both phospholipids (with bulk pK1 values close to 4) is associated with a marked expansion of the films, as judged by values of limiting molecular area. Ionization of the secondary phosphate functions causes further expansion of the films, with the apparent pK2 of deoxyphosphatidylglycerol phosphate slightly less than that indicated for phosphatidylglycerol phosphate. Values of surface-compressibility modulus calculated from the surface characteristics of the phosphatidylglcerol phosphate monolayers showed that films spread on subphases with a pH of about the apparent pK1 of the primary phosphate functions were the least compressible. Increasing or decreasing subphase pH caused an increase in compressibility; this effect on compressibility was much less with monolayers of deoxyphosphatidylglycerol phosphate at high pH. The effect of inorganic counter-ions on monolayer characteristics of phosphatidylglycerol phosphate was examined by using subphases of NaCl concentrations varying from 0.01 to 1 M. The limiting molecular area was found to increase exponentially with respect to the subphase NaCl concentration.

  15. Assessment of measurement techniques to determine the interfacial properties of bilayer dental ceramics

    NASA Astrophysics Data System (ADS)

    Anunmana, Chuchai

    The clinical success of all-ceramic dental restorations depends on the quality of interfacial bonding between ceramic layers. In addition, the residual stress in the structure that developed during ceramic processing is one of the important factors that contributes to the quality of the bond. Because all-ceramic restorations are usually fabricated as bilayer or trilayer structures and failures of all-ceramic restorations have been frequently reported as chipping or delamination of the veneer layers, the interfacial quality of bilayer dental ceramic restorations was investigated. However, most of the published bond test data reflect strength values that are inversely related to cross-sectional areas and failure locations are frequently disregarded or bond strength values are misinterpreted. In addition, residual tensile stresses that develop in the structures because of thermal expansion/contraction mismatches may also adversely affect interfacial fracture resistance. The first objective of this study was to determine the interfacial toughness of bonded bilayer ceramics using two different approaches. The results indicate that the short-bar chevron-notch test and a controlled-flaw microtensile test can induce interfacial failure that represents true bonding quality. The second objective of this study was to test the hypothesis that residual stresses estimated from an indentation technique are not significantly different from residual stresses that are calculated based on fractography and flexural strength. The indentation technique may be useful as a simplified method to determine residual stresses in bilayer dental ceramics. The results of this study demonstrate that there is no significant difference in mean residual stresses determined from the two techniques. Because of relationship between residual stresses and apparent interfacial toughness, estimates of residual stresses can now be estimated more rapidly by measuring the apparent interfacial toughness of

  16. A swarm of Stokeslets with interfacial tension

    NASA Astrophysics Data System (ADS)

    Nitsche, Ludwig C.; Schaflinger, Uwe

    2001-06-01

    A formal analogy between sedimenting drops in Stokes flow and a swarm of Stokeslets [Machu et al., J. Fluid Mech. (in press)] is extended to include interfacial tension. Using a cohesive potential, mean curvature is extended as a meaningful quantity off the interface, allowing the boundary-integral formulation to be rewritten in volumetric form. A prescription for assigning forces to the Stokeslets comprising the swarm incorporates the action of interfacial tension without having to identify a boundary surface. Numerical simulations agree with linear small-deformation theory, and reproduce the spontaneous coalescense of two touching drops.

  17. Monitoring of interfacial tensions by drop counting

    SciTech Connect

    Duerksen, W.K.; Boring, C.P.; McLaughlin, J.F.; Harless, D.P.

    1988-11-01

    A capillary tube device was shown to provide a rapid means of measuring the interfacial tension between water and Freon-113. The measurement technique is based on counting the number of drops that form when a fixed volume of water passes through the capillary tube into the bulk Freon. The interfacial tension is predicted to be proportional to the number of drops to the negative 2/3 power. Calibration curves were obtained for Freon-water samples containing known concentrations of a surfactant. A standard Gibbs adsorption curve was obtained. 5 refs., 3 figs., 2 tabs.

  18. Surface interactions, thermodynamics and topography of binary monolayers of Insulin with dipalmitoylphosphatidylcholine and 1-palmitoyl-2-oleoylphosphatidylcholine at the air/water interface.

    PubMed

    Grasso, E J; Oliveira, R G; Maggio, B

    2016-02-15

    The molecular packing, thermodynamics and surface topography of binary Langmuir monolayers of Insulin and DPPC (dipalmitoylphosphatidylcholine) or POCP (1-palmitoyl-2-oleoylphosphatidylcholine) at the air/water interface on Zn(2+) containing solutions were studied. Miscibility and interactions were ascertained by the variation of surface pressure-mean molecular area isotherms, surface compressional modulus and surface (dipole) potential with the film composition. Brewster Angle Microscopy was used to visualize the surface topography of the monolayers. Below 20mN/m Insulin forms stable homogenous films with DPPC and POPC at all mole fractions studied (except for films with XINS=0.05 at 10mN/m where domain coexistence was observed). Above 20mN/m, a segregation process between mixed phases occurred in all monolayers without squeezing out of individual components. Under compression the films exhibit formation of a viscoelastic or kinetically trapped organization leading to considerable composition-dependent hysteresis under expansion that occurs with entropic-enthalpic compensation. The spontaneously unfavorable interactions of Insulin with DPPC are driven by favorable enthalpy that is overcome by unfavorable entropic ordering; in films with POPC both the enthalpic and entropic effects are unfavorable. The surface topography reveals domain coexistence at relatively high pressure showing a striped appearance. The interactions of Insulin with two major membrane phospholipids induces composition-dependent and long-range changes of the surface organization that ought to be considered in the context of the information-transducing capabilities of the hormone for cell functioning.

  19. Combined effect of synthetic protein, Mini-B, and cholesterol on a model lung surfactant mixture at the air-water interface.

    PubMed

    Chakraborty, Aishik; Hui, Erica; Waring, Alan J; Dhar, Prajnaparamita

    2016-04-01

    The overall goal of this work is to study the combined effects of Mini-B, a 34 residue synthetic analog of the lung surfactant protein SP-B, and cholesterol, a neutral lipid, on a model binary lipid mixture containing dipalmitolphosphatidylcholine (DPPC) and palmitoyl-oleoyl-phosphatidylglycerol (POPG), that is often used to mimic the primary phospholipid composition of lung surfactants. Using surface pressure vs. mean molecular area isotherms, fluorescence imaging and analysis of lipid domain size distributions; we report on changes in the structure, function and stability of the model lipid-protein films in the presence and absence of varying composition of cholesterol. Our results indicate that at low cholesterol concentrations, Mini-B can prevent cholesterol's tendency to lower the line tension between lipid domain boundaries, while maintaining Mini-B's ability to cause reversible collapse resulting in the formation of surface associated reservoirs. Our results also show that lowering the line tension between domains can adversely impact monolayer folding mechanisms. We propose that small amounts of cholesterol and synthetic protein Mini-B can together achieve the seemingly opposing requirements of efficient LS: fluid enough to flow at the air-water interface, while being rigid enough to oppose irreversible collapse at ultra-low surface tensions. PMID:26775740

  20. Surface interactions, thermodynamics and topography of binary monolayers of Insulin with dipalmitoylphosphatidylcholine and 1-palmitoyl-2-oleoylphosphatidylcholine at the air/water interface.

    PubMed

    Grasso, E J; Oliveira, R G; Maggio, B

    2016-02-15

    The molecular packing, thermodynamics and surface topography of binary Langmuir monolayers of Insulin and DPPC (dipalmitoylphosphatidylcholine) or POCP (1-palmitoyl-2-oleoylphosphatidylcholine) at the air/water interface on Zn(2+) containing solutions were studied. Miscibility and interactions were ascertained by the variation of surface pressure-mean molecular area isotherms, surface compressional modulus and surface (dipole) potential with the film composition. Brewster Angle Microscopy was used to visualize the surface topography of the monolayers. Below 20mN/m Insulin forms stable homogenous films with DPPC and POPC at all mole fractions studied (except for films with XINS=0.05 at 10mN/m where domain coexistence was observed). Above 20mN/m, a segregation process between mixed phases occurred in all monolayers without squeezing out of individual components. Under compression the films exhibit formation of a viscoelastic or kinetically trapped organization leading to considerable composition-dependent hysteresis under expansion that occurs with entropic-enthalpic compensation. The spontaneously unfavorable interactions of Insulin with DPPC are driven by favorable enthalpy that is overcome by unfavorable entropic ordering; in films with POPC both the enthalpic and entropic effects are unfavorable. The surface topography reveals domain coexistence at relatively high pressure showing a striped appearance. The interactions of Insulin with two major membrane phospholipids induces composition-dependent and long-range changes of the surface organization that ought to be considered in the context of the information-transducing capabilities of the hormone for cell functioning. PMID:26624532

  1. Combined effect of synthetic protein, Mini-B, and cholesterol on a model lung surfactant mixture at the air-water interface.

    PubMed

    Chakraborty, Aishik; Hui, Erica; Waring, Alan J; Dhar, Prajnaparamita

    2016-04-01

    The overall goal of this work is to study the combined effects of Mini-B, a 34 residue synthetic analog of the lung surfactant protein SP-B, and cholesterol, a neutral lipid, on a model binary lipid mixture containing dipalmitolphosphatidylcholine (DPPC) and palmitoyl-oleoyl-phosphatidylglycerol (POPG), that is often used to mimic the primary phospholipid composition of lung surfactants. Using surface pressure vs. mean molecular area isotherms, fluorescence imaging and analysis of lipid domain size distributions; we report on changes in the structure, function and stability of the model lipid-protein films in the presence and absence of varying composition of cholesterol. Our results indicate that at low cholesterol concentrations, Mini-B can prevent cholesterol's tendency to lower the line tension between lipid domain boundaries, while maintaining Mini-B's ability to cause reversible collapse resulting in the formation of surface associated reservoirs. Our results also show that lowering the line tension between domains can adversely impact monolayer folding mechanisms. We propose that small amounts of cholesterol and synthetic protein Mini-B can together achieve the seemingly opposing requirements of efficient LS: fluid enough to flow at the air-water interface, while being rigid enough to oppose irreversible collapse at ultra-low surface tensions.

  2. Thermodynamic, morphological and structural properties of dissociated fatty acid monolayers at the air-water interface

    NASA Astrophysics Data System (ADS)

    Johann, Robert

    2001-10-01

    Research on monolayers of amphiphilic lipids on aqueous solution is of basic importance in surface science. Due to the applicability of a variety of surface sensitive techniques, floating insoluble monolayers are very suitable model systems for the study of order, structure formation and material transport in two dimensions or the interactions of molecules at the interface with ions or molecules in the bulk (headword 'molecular recognition'). From the behavior of monolayers conclusions can be drawn on the properties of lipid layers on solid substrates or in biological membranes. This work deals with specific and fundamental interactions in monolayers both on the molecular and on the microscopic scale and with their relation to the lattice structure, morphology and thermodynamic behavior of monolayers at the air-water interface. As model system especially monolayers of long chain fatty acids are used, since there the molecular interactions can be gradually adjusted by varying the degree of dissociation by means of the suphase pH value. For manipulating the molecular interactions besides the subphase composition also temperature and monolayer composition are systematically varied. The change in the monolayer properties as a function of an external parameter is analyzed by means of isotherm and surface potential measurements, Brewster-angle microscopy, X-ray diffraction at grazing incidence and polarization modulated infrared reflection absorption spectroscopy. For this a quantitative measure for the molecular interactions and for the chain conformational order is derived from the X-ray data. The most interesting results of this work are the elucidation of the origin of regular polygonal and dendritic domain shapes, the various effects of cholesterol on molecular packing and lattice order of long chain amphiphiles, as well as the detection of an abrupt change in the head group bonding interactions, the chain conformational order and the phase transition pressure

  3. Multi-scale modeling of mycosubtilin lipopeptides at the air/water interface: structure and optical second harmonic generation.

    PubMed

    Loison, Claire; Nasir, Mehmet Nail; Benichou, Emmanuel; Besson, Françoise; Brevet, Pierre-François

    2014-02-01

    Monolayers of the lipopeptide mycosubtilin are studied at the air/water interface. Their structure is investigated using molecular dynamics simulations. All-atom models suggest that the lipopeptide is flexible and aggregates at the interface. To achieve simulation times of several microseconds, a coarse-grained (CG) model based on the MARTINI force field was also used. These CG simulations describe the formation of half-micelles at the interface for surface densities up to 1 lipopeptide per nm(2). In these aggregates, the tyrosine side chain orientation is found to be constrained: on average, its main axis, as defined along the C-OH bond, aligns along the interface normal and points towards the air side. The origin of the optical second harmonic generation (SHG) from mycosubtilin monolayers at the air/water interface is also investigated. The molecular hyperpolarizability of the lipopeptide is obtained from quantum chemistry calculations. The tyrosine side chain contribution to the hyperpolarizability is found to be dominant. The orientation distribution of tyrosine, associated with a dominant hyperpolarizability component along the C-OH bond of the tyrosine, yields a ratio of the susceptibility elements χ((2))(ZZZ)/χ((2))(ZXX) consistent with the experimental measurements recently reported by M. N. Nasir et al. [Phys. Chem. Chem. Phys., 2013, 15, 19919].

  4. Polystyrene-poly(ethylene oxide) diblock copolymer: the effect of polystyrene and spreading concentration at the air/water interface.

    PubMed

    Glagola, Cameron P; Miceli, Lia M; Milchak, Marissa A; Halle, Emily H; Logan, Jennifer L

    2012-03-20

    Polystyrene-block-poly(ethylene oxide) (PS-PEO) is an amphiphilic diblock copolymer that undergoes microphase separation when spread at the air/water interface, forming nanosized domains. In this study, we investigate the impact of PS by examining a series of PS-PEO samples containing constant PEO (~17,000 g·mol(-1)) and variable PS (from 3600 to 200,000 g·mol(-1)) through isothermal characterization and atomic force microscopy (AFM). The polymers separated into two categories: predominantly hydrophobic and predominantly hydrophilic with a weight percent of PEO of ~20% providing the boundary between the two. AFM results indicated that predominantly hydrophilic PS-PEO forms dots while more hydrophobic samples yield a mixture of dots and spaghetti with continent-like structures appearing at ~7% PEO or less. These structures reflect a blend of polymer spreading, entanglement, and vitrification as the solvent evaporates. Changing the spreading concentration provides insight into this process with higher concentrations representing earlier kinetic stages and lower concentrations demonstrating later ones. Comparison of isothermal results and AFM analysis shows how polymer behavior at the air/water interface correlates with the observed nanostructures. Understanding the impact of polymer composition and spreading concentration is significant in leading to greater control over the nanostructures obtained through PS-PEO self-assembly and their eventual application as polymer templates.

  5. Surface Partitioning and Stability of Mixed Films of Fluorinated Alcohols and Acids at the Air- Water Interface

    NASA Astrophysics Data System (ADS)

    Rontu, N. A.; Vaida, V.

    2007-05-01

    The production of fluorinated compounds over the past 50 years has had numerous industrial applications. For example, perfluorinated carboxylic acids are used in the synthesis of polymers and fire retardants, perfluoroalkyl sulfonates act as surface protectors, and fluorotelomer alcohols are incorporated into products such as paints, coatings, polymers, and adhesives. Fluorotelomer alcohols (FTOHs) are linear polyfluorinated alcohols with the formula CF3(CF2)nCH2CH2OH (n=1,3,5,...). They have been suggested as possible precursors for perfluorinated carboxylic acids and detected in the troposphere over several North American sites. Perfluorocarboxylic acids have even been detected in the arctic food chain, human blood, tissues of animals and environmental waters. We report the surface activity of fluorotelomer alcohols and perfluorinated carboxylic acids at the air-water interface by using a Langmuir trough. Isotherms of the pure compounds along with mixed films with other organic carboxylic acids were collected. The main objective of these experiments was to understand their heterogeneous chemistry by characterizing the pure and mixed films, which serves as a representative model for organic films on atmospheric surfaces such as those found on oceans and aqueous aerosols. Film properties and behavior, notably stabilization, evaporation from the subphase, and miscibility in the single-component mixtures as well as in the mixed films will be discussed. An important consequence of FTOHs and perfluorocarboxylic acids being found to partition to the air-water interface is the possibility of their transport and widespread distribution and deposition using atmospheric aerosols.

  6. Interpreting Vibrational Sum-frequency Spectra of Sulfur Dioxide at the Air/Water Interface: A Comprehensive Molecular Dynamics Study

    SciTech Connect

    Baer, Marcel; Mundy, Christopher J.; Chang, Tsun-Mei; Tao, Fu-Ming; Dang, Liem X.

    2010-06-01

    We investigated the solvation and spectroscopic properties of SO2 at the air/water interface using molecular simulation techniques. Molecular interactions from both Kohn-Sham (KS) density functional theory (DFT) and classical polarizable models were utilized to understand the properties of SO2:(H2O)x complexes in the vicinity of the air/water interface. The KS-DFT was included to allow comparisons with sum-frequency generation spectroscopy through the identification of surface SO2:(H2O)x complexes. Using our simulation results, we were able to develop a much more detailed picture for the surface structure of SO2 that is consistent with the spectroscopic data obtained Richmond and coworkers (J. Am. Chem. Soc. 127, 16806 (2005)). We also found many similarities and differences between to the two interaction potentials, including a noticeable weakness of the classical potential model in reproducing the asymmetric hydrogen bonding of water with SO2 due to its inability to account for SO2 resonance structures. This work was supported by the US Department of Energy Basic Energy Sciences' Chemical Sciences, Geosciences & Biosciences Division. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

  7. Gas exchange in wetlands with emergent vegetation: The effects of wind and thermal convection at the air-water interface

    NASA Astrophysics Data System (ADS)

    Poindexter, Cristina M.; Variano, Evan A.

    2013-07-01

    Methane, carbon dioxide, and oxygen are exchanged between wetlands and the atmosphere through multiple pathways. One of these pathways, the hydrodynamic transport of dissolved gas through the surface water, is often underestimated in importance. We constructed a model wetland in the laboratory with artificial emergent plants to investigate the mechanisms and magnitude of this transport. We measured gas transfer velocities, which characterize the near-surface stirring driving air-water gas transfer, while varying two stirring processes important to gas exchange in other aquatic environments: wind and thermal convection. To isolate the effects of thermal convection, we identified a semiempirical model for the gas transfer velocity as a function of surface heat loss. The laboratory results indicate that thermal convection will be the dominant mechanism of air-water gas exchange in marshes with emergent vegetation. Thermal convection yielded peak gas transfer velocities of 1 cm h-1. Because of the sheltering of the water surface by emergent vegetation, gas transfer velocities for wind-driven stirring alone are likely to exceed this value only in extreme cases.

  8. Electrochemical Surface Potential due to Classical Point Charge Models Drives Anion Adsorption to the Air-Water Interface

    SciTech Connect

    Baer, Marcel D.; Stern, Abraham C.; Levin, Yan; Tobias, Douglas J.; Mundy, Christopher J.

    2012-06-07

    Herein, we present research that suggests that the underlying physics that drive simple empirical models of anions (e.g. point charge, no polarization) to the air-water interface, with water described by SPC/E, or related partial charge models is different than when both ions and water are modeled with quantum mechanical based interactions. Specifically, we will show that the driving force of ions to the air-water interface for point charge models results from both cavitation and the negative electrochemical surface potential. We will demonstrate that we can fully characterize the role of the free energy due to the electrochemical surface potential computed from simple empirical models and its role in ionic adsorption within the context of dielectric continuum theory (DCT). Our research suggests that a significant part of the electrochemical surface potential in empirical models appears to be an artifact of the failure of point charge models in the vicinity of a broken symmetry. This work was supported by the U.S. Department of Energy‘s (DOE) Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences. Pacific Northwest National Laboratory (PNNL) is operated for the Department of Energy by Battelle.

  9. Ellipsometric characterization of ethylene oxide-butylene oxide diblock copolymer adsorption at the air-water interface.

    PubMed

    Blomqvist, B Rippner; Benjamins, J-W; Nylander, T; Arnebrant, T

    2005-05-24

    Ellipsometry was used to determine the adsorbed layer thickness (d) and the surface excess (adsorbed amount, Gamma) of a nonionic diblock copolymer, E(106)B(16), of poly(ethylene oxide) (E) and poly(butylene oxide) (B) at the air-water interface. The results were obtained (i) by the conventional ellipsometric evaluation procedure using the change of both ellipsometric angles Psi and Delta and (ii) by using the change of Delta only and assuming values of the layer thickness. It was demonstrated that the calculated surface excesses from the different methods were in close agreement, independent of the evaluation procedure, with a plateau adsorption of about 2.5 mg/m(2) (400 A(2)/molecule). Furthermore, the amount of E(106)B(16) adsorbed at the air-water interface was found to be almost identical to that adsorbed from aqueous solution onto a hydrophobic solid surface. In addition, the possibility to use combined measurements with H(2)O or D(2)O as substrates to calculate values of d and Gamma was investigated and discussed. We also briefly discuss within which limits the Gibbs equation can be used to determine the surface excess of polydisperse block copolymers. PMID:15896051

  10. Multi-scale modeling of mycosubtilin lipopeptides at the air/water interface: structure and optical second harmonic generation.

    PubMed

    Loison, Claire; Nasir, Mehmet Nail; Benichou, Emmanuel; Besson, Françoise; Brevet, Pierre-François

    2014-02-01

    Monolayers of the lipopeptide mycosubtilin are studied at the air/water interface. Their structure is investigated using molecular dynamics simulations. All-atom models suggest that the lipopeptide is flexible and aggregates at the interface. To achieve simulation times of several microseconds, a coarse-grained (CG) model based on the MARTINI force field was also used. These CG simulations describe the formation of half-micelles at the interface for surface densities up to 1 lipopeptide per nm(2). In these aggregates, the tyrosine side chain orientation is found to be constrained: on average, its main axis, as defined along the C-OH bond, aligns along the interface normal and points towards the air side. The origin of the optical second harmonic generation (SHG) from mycosubtilin monolayers at the air/water interface is also investigated. The molecular hyperpolarizability of the lipopeptide is obtained from quantum chemistry calculations. The tyrosine side chain contribution to the hyperpolarizability is found to be dominant. The orientation distribution of tyrosine, associated with a dominant hyperpolarizability component along the C-OH bond of the tyrosine, yields a ratio of the susceptibility elements χ((2))(ZZZ)/χ((2))(ZXX) consistent with the experimental measurements recently reported by M. N. Nasir et al. [Phys. Chem. Chem. Phys., 2013, 15, 19919]. PMID:24346061

  11. Adsorption, Ordering, and Local Environments of Surfactant-Encapsulated Polyoxometalate Ions Probed at the Air-Water Interface.

    PubMed

    Doughty, Benjamin; Yin, Panchao; Ma, Ying-Zhong

    2016-08-16

    The continued development and application of surfactant-encapsulated polyoxometalates (SEPs) relies on understanding the ordering and organization of species at their interface and how these are impacted by the various local environments to which they are exposed. Here, we report on the equilibrium properties of two common SEPs adsorbed to the air-water interface and probed with surface-specific vibrational sum-frequency generation (SFG) spectroscopy. These results reveal clear shifts in vibrational band positions, the magnitude of which scales with the charge of the SEP core, which is indicative of a static field effect on the surfactant coating and the associated local chemical environment. This static field also induces ordering in surrounding water molecules that is mediated by charge screening via the surface-bound surfactants. From these SFG measurements, we are able to show that Mo132-based SEPs are more polar than Mo72V30 SEPs. Disorder in the surfactant chain packing at the highly curved SEP surfaces is attributed to large conic volumes that can be sampled without interactions with neighboring chains. Measurements of adsorption isotherms yield free energies of adsorption to the air-water interface of -46.8 ± 0.4 and -44.8 ± 1.2 kJ/mol for the Mo132 and Mo72V30 SEPs, respectively, indicating a strong propensity for the fluid surface. The influence of intermolecular interactions on the surface adsorption energies is discussed. PMID:27452922

  12. Image processing analysis on the air-water slug two-phase flow in a horizontal pipe

    NASA Astrophysics Data System (ADS)

    Dinaryanto, Okto; Widyatama, Arif; Majid, Akmal Irfan; Deendarlianto, Indarto

    2016-06-01

    Slug flow is a part of intermittent flow which is avoided in industrial application because of its irregularity and high pressure fluctuation. Those characteristics cause some problems such as internal corrosion and the damage of the pipeline construction. In order to understand the slug characteristics, some of the measurement techniques can be applied such as wire-mesh sensors, CECM, and high speed camera. The present study was aimed to determine slug characteristics by using image processing techniques. Experiment has been carried out in 26 mm i.d. acrylic horizontal pipe with 9 m long. Air-water flow was recorded 5 m from the air-water mixer using high speed video camera. Each of image sequence was processed using MATLAB. There are some steps including image complement, background subtraction, and image filtering that used in this algorithm to produce binary images. Special treatments also were applied to reduce the disturbance effect of dispersed bubble around the bubble. Furthermore, binary images were used to describe bubble contour and calculate slug parameter such as gas slug length, gas slug velocity, and slug frequency. As a result the effect of superficial gas velocity and superficial liquid velocity on the fundamental parameters can be understood. After comparing the results to the previous experimental results, the image processing techniques is a useful and potential technique to explain the slug characteristics.

  13. Verification and Validation of Numerical Models for Air/Water Flow on Coastal and Navigation Fluid-Structure Interaction Applications

    NASA Astrophysics Data System (ADS)

    Kees, C. E.; Farthing, M.; Dimakopoulos, A.; DeLataillade, T.

    2015-12-01

    Performance analysis and optimization of coastal and navigation structures is becoming feasible due to recent improvements in numerical methods for multiphase flows and the steady increase in capacity and availability of high performance computing resources. Now that the concept of fully three-dimensional air/water flow modelling for real world engineering analysis is achieving acceptance by the wider engineering community, it is critical to expand careful comparative studies on verification,validation, benchmarking, and uncertainty quantification for the variety of competing numerical methods that are continuing to evolve. Furthermore, uncertainty still remains about the relevance of secondary processes such as surface tension, air compressibility, air entrainment, and solid phase (structure) modelling so that questions about continuum mechanical theory and mathematical analysis of multiphase flow are still required. Two of the most popular and practical numerical approaches for large-scale engineering analysis are the Volume-Of-Fluid (VOF) and Level Set (LS) approaches. In this work we will present a publically available verification and validation test set for air-water-structure interaction problems as well as computational and physical model results including a hybrid VOF-LS method, traditional VOF methods, and Smoothed Particle Hydrodynamics (SPH) results. The test set repository and test problem formats will also be presented in order to facilitate future comparative studies and reproduction of scientific results.

  14. Dissecting the Molecular Structure of the Air/Water Interface from Quantum Simulations of the Sum-Frequency Generation Spectrum.

    PubMed

    Medders, Gregory R; Paesani, Francesco

    2016-03-23

    The molecular characterization of the air/water interface is a key step in understanding fundamental multiphase phenomena ranging from heterogeneous chemical processes in the atmosphere to the hydration of biomolecules. The apparent simplicity of the air/water interface, however, masks an underlying complexity associated with the dynamic nature of the water hydrogen-bond network that has so far hindered an unambiguous characterization of its microscopic properties. Here, we demonstrate that the application of quantum many-body molecular dynamics, which enables spectroscopically accurate simulations of water from the gas to the condensed phase, leads to a definitive molecular-level picture of the interface region. For the first time, excellent agreement is obtained between the simulated vibrational sum-frequency generation spectrum and the most recent state-of-the-art measurements, without requiring any empirical frequency shift or ad hoc scaling of the spectral intensity. A systematic dissection of the spectral features demonstrates that a rigorous representation of nuclear quantum effects as well as of many-body energy and electrostatic contributions is necessary for a quantitative reproduction of the experimental data. The unprecedented accuracy of the simulations presented here indicates that quantum many-body molecular dynamics can enable predictive studies of aqueous interfaces, which by complementing analogous experimental measurements will provide unique molecular insights into multiphase and heterogeneous processes of relevance in chemistry, biology, materials science, and environmental research. PMID:26943730

  15. Degradation and rearrangement of a lung surfactant lipid at the air-water interface during exposure to the pollutant gas ozone.

    PubMed

    Thompson, Katherine C; Jones, Stephanie H; Rennie, Adrian R; King, Martin D; Ward, Andrew D; Hughes, Brian R; Lucas, Claire O M; Campbell, Richard A; Hughes, Arwel V

    2013-04-01

    The presence of unsaturated lipids in lung surfactant is important for proper respiratory function. In this work, we have used neutron reflection and surface pressure measurements to study the reaction of the ubiquitous pollutant gas-phase ozone, O3, with pure and mixed phospholipid monolayers at the air-water interface. The results reveal that the reaction of the unsaturated lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, POPC, with ozone leads to the rapid loss of the terminal C9 portion of the oleoyl strand of POPC from the air-water interface. The loss of the C9 portion from the interface is accompanied by an increase in the surface pressure (decrease in surface tension) of the film at the air-water interface. The results suggest that the portion of the oxidized oleoyl strand that is still attached to the lipid headgroup rapidly reverses its orientation and penetrates the air-water interface alongside the original headgroup, thus increasing the surface pressure. The reaction of POPC with ozone also leads to a loss of material from the palmitoyl strand, but the loss of palmitoyl material occurs after the loss of the terminal C9 portion from the oleoyl strand of the molecule, suggesting that the palmitoyl material is lost in a secondary reaction step. Further experiments studying the reaction of mixed monolayers composed of unsaturated lipid POPC and saturated lipid dipalmitoyl-sn-glycero-3-phosphocholine, DPPC, revealed that no loss of DPPC from the air-water interface occurs, eliminating the possibility that a reactive species such as an OH radical is formed and is able to attack nearby lipid chains. The reaction of ozone with the mixed films does cause a significant change in the surface pressure of the air-water interface. Thus, the reaction of unsaturated lipids in lung surfactant changes and impairs the physical properties of the film at the air-water interface.

  16. The Constrained Vapor Bubble Experiment - Interfacial Flow Region

    NASA Technical Reports Server (NTRS)

    Kundan, Akshay; Wayner, Peter C., Jr.; Plawsky, Joel L.

    2015-01-01

    Internal heat transfer coefficient of the CVB correlated to the presence of the interfacial flow region. Competition between capillary and Marangoni flow caused Flooding and not a Dry-out region. Interfacial flow region growth is arrested at higher power inputs. 1D heat model confirms the presence of interfacial flow region. 1D heat model confirms the arresting phenomena of interfacial flow region Visual observations are essential to understanding.

  17. Spread mixed monolayers of deoxycholic and dehydrocholic acids at the air-water interface, effect of subphase pH. Characterization by axisymmetric drop shape analysis.

    PubMed

    Messina, Paula V; Fernández-Leyes, Marcos D; Prieto, Gerardo; Ruso, Juan M; Sarmiento, Félix; Schulz, Pablo C

    2008-01-01

    Bile acids (deoxycholic and dehydrocholic acids) spread mixed monolayers behavior at the air/water interface were studied as a function of subphase pH using a constant surface pressure penetration Langmuir balance based on the Axisymmetric Drop Shape Analysis (ADSA). We examined the influence of electrostatic, hydrophobic and hydration forces on the interaction between amphiphilic molecules at the interface by the collapse area values, the thermodynamic parameters and equation of state virial coefficients analysis. The obtained results showed that at neutral (pH=6.7) or basic (pH=10) subphase conditions the collapse areas values are similar to that of cholanoic acid and consistent with the cross-sectional area of the steroid nucleus (approximately 40 A(2)). The Gibbs energy of mixing values (DeltaG(mix)<0) and the first virial coefficients of the equation of state (b(0)<1) indicated that a miscible monolayer with laterally structured microdomains existed. The aggregation number (1/b(0)) was estimated within the order of 6 (pH=6.7) and 3 (pH=10). At pH=3.2, acidic subphase conditions, no phase separation occurs (DeltaG(mix)<0) but a high expanded effect of the monolayer could be noted. The mixed monolayer behavior was no ideal and no aggregates were formed (b(0)> or =1). Such behavior indicates that the polar groups of the molecules interacts each other more strongly by repulsive electrostatic forces than with the more hydrophobic part of the molecule.

  18. New flange correction formula applied to interfacial resistance measurements of ohmic contacts to GaAs

    NASA Technical Reports Server (NTRS)

    Lieneweg, Udo; Hannaman, David J.

    1987-01-01

    A quasi-two-dimensional analytical model is developed to account for vertical and horizontal current flow in and adjacent to a square ohmic contact between a metal and a thin semiconducting strip which is wider than the contact. The model includes side taps to the contact area for voltage probing and relates the 'apparent' interfacial resistivity to the (true) interfacial resistivity, the sheet resistance of the semiconducting layer, the contact size, and the width of the 'flange' around the contact. This relation is checked against numerical simulations. With the help of the model, interfacial resistivities of ohmic contacts to GaAs were extracted and found independent of contact size in the range of 1.5-10 microns.

  19. Fiber reinforced solids possessing great fracture toughness: The role of interfacial strength

    NASA Technical Reports Server (NTRS)

    Atkins, A. G.

    1974-01-01

    The high tensile strength characteristic of strong interfacial filament/matrix bonding can be combined with the high fracture toughness of weak interfacial bonding, when the filaments are arranged to have alternate sections of high and low shear stress (and low and high toughness). Such weak and strong areas can be achieved by appropriate intermittent coating of the fibers. An analysis is presented for toughness and strength which demonstrates, in broad terms, the effects of varying the coating parameters of concern. Results show that the toughness of interfaces is an important parameter, differences in which may not be shown up in terms of interfacial strength. Some observations are made upon methods of measuring the components of toughness in composites.

  20. Interfacial shear rheology of DPPC under physiologically relevant conditions.

    PubMed

    Hermans, Eline; Vermant, Jan

    2014-01-01

    Lipids, and phosphatidylcholines in particular, are major components in cell membranes and in human lung surfactant. Their ability to encapsulate or form stable layers suggests a significant role of the interfacial rheological properties. In the present work we focus on the surface rheological properties of dipalmitoylphosphatidylcholine (DPPC). Literature results are confusing and even contradictory; viscosity values have been reported differ by several orders of magnitude. Moreover, even both purely viscous and gel-like behaviours have been described. Assessing the literature critically, a limited experimental window has been explored correctly, which however does not yet include conditions relevant for the physiological state of DPPC in vivo. A complete temperature and surface pressure analysis of the interfacial shear rheology of DPPC is performed, showing that the monolayer behaves as a viscoelastic liquid with a domain structure. At low frequencies and for a thermally structured monolayer, the interaction of the molecules within the domains can be probed. The low frequency limit of the complex viscosity is measured over a wide range of temperatures and surface pressures. The effects of temperature and surface pressure on the low frequency viscosity can be analysed in terms of the effects of free molecular area. However, at higher frequencies or following a preshear at high shear rates, elasticity becomes important; most probably elasticity due to defects at the edge of the domains in the layer is probed. Preshearing refines the structure and induces more defects. As a result, disagreeing interfacial rheology results in various publications might be due to different pre-treatments of the interface. The obtained dataset and scaling laws enable us to describe the surface viscosity, and its dependence under physiological conditions of DPPC. The implications on functioning of lung surfactants and lung surfactant replacements will be discussed. PMID:24651838

  1. Interfacial Assembly of Graphene Oxide Films

    NASA Astrophysics Data System (ADS)

    Valtierrez, Cain; Ismail, Issam; Macosko, Christopher; Stottrup, Benjamin

    Controlled assembly of monolayer graphene-oxide (GO) films at the air/water interface is of interest for the development of transparent conductive thin films of chemically-derived graphene. We present experimental results from investigations of the assembly of polydisperse GO sheets at the air-water interface. GO nanosheets with lateral dimensions of greater than 10 microns were created using a modified Tour synthesis (Dimiev and Tour, 2014). GO films were generated with conventional Langmuir trough techniques to control lateral packing density. Film morphology was characterized in situ with Brewster angle microscopy. Films were transferred unto a substrate via the Langmuir-Blodgett deposition technique and imaged with fluorescence quenching microscopy. Through pH modulation of the aqueous subphase, it was found that GO's intrinsic surface activity to the interface increased with increasing subphase acidity. Finally, we found a dominant elastic contribution during uniaxial film deformation as measured by anisotropic pressure measurements. A. M. Dimiev, and J. M. Tour, ``Mechanism of GO Formation,'' ACS Nano, 8, (2014)

  2. Recent Advances in Colloidal and Interfacial Phenomena Involving Liquid Crystals

    PubMed Central

    Bai, Yiqun; Abbott, Nicholas L.

    2011-01-01

    This article describes recent advances in several areas of research involving the interfacial ordering of liquid crystals (LCs). The first advance revolves around the ordering of LCs at bio/chemically functionalized surfaces. Whereas the majority of past studies of surface-induced ordering of LCs have involved surfaces of solids that present a limited diversity of chemical functional groups (surfaces at which van der Waals forces dominate surface-induced ordering), recent studies have moved to investigate the ordering of LCs on chemically complex surfaces. For example, surfaces decorated with biomolecules (e.g. oligopeptides and proteins) and transition metal ions have been investigated, leading to an understanding of the roles that metal-ligand coordination interactions, electrical double-layers, acid-base interactions, and hydrogen bonding can have on the interfacial ordering of LCs. The opportunity to create chemically-responsive LCs capable of undergoing ordering transitions in the presence of targeted molecular events (e.g., ligand exchange around a metal center) has emerged from these fundamental studies. A second advance has focused on investigations of the ordering of LCs at interfaces with immiscible isotropic fluids, particularly water. In contrast to prior studies of surface-induced ordering of LCs on solid surfaces, LC- aqueous interfaces are deformable and molecules at these interfaces exhibit high levels of mobility and thus can reorganize in response to changes in interfacial environment. A range of fundamental investigations involving these LC-aqueous interfaces have revealed that (i) the spatial and temporal characteristics of assemblies formed from biomolecular interactions can be reported by surface-driven ordering transitions in the LCs, (ii) the interfacial phase behaviour of molecules and colloids can be coupled to (and manipulated via) the ordering (and nematic elasticity) of LCs, and (iii) confinement of LCs leads to unanticipated size

  3. Apparent interfacial fracture toughness of resin/ceramic systems.

    PubMed

    Della Bona, A; Anusavice, K J; Mecholsky, J J

    2006-11-01

    We suggest that the apparent interfacial fracture toughness (K(A)) may be estimated by fracture mechanics and fractography. This study tested the hypothesis that the K(A) of the adhesion zone of resin/ceramic systems is affected by the ceramic microstructure. Lithia disilicate-based (Empress2-E2) and leucite-based (Empress-E1) ceramics were surface-treated with hydrofluoric acid (HF) and/or silane (S), followed by an adhesive resin. Microtensile test specimens (n = 30; area of 1 +/- 0.01 mm(2)) were indented (9.8 N) at the interface and loaded to failure in tension. We used tensile strength (sigma) and the critical crack size (c) to calculate K(A) (K(A) = Ysigmac(1/2)) (Y = 1.65). ANOVA and Weibull analyses were used for statistical analyses. Mean K(A) (MPa.m(1/2)) values were: (E1HF) 0.26 +/- 0.06; (E1S) 0.23 +/- 0.06; (E1HFS) 0.30 +/- 0.06; (E2HF) 0.31 +/- 0.06; (E2S) 0.13 +/- 0.05; and (E2HFS) 0.41 +/- 0.07. All fractures originated from indentation sites. Estimation of interfacial toughness was feasible by fracture mechanics and fractography. The K(A) for the systems tested was affected by the ceramic microstructure and surface treatment. PMID:17062746

  4. Effect of microstructure on Au/sapphire interfacial thermal resistance

    SciTech Connect

    Xu Yibin; Kato, Ryozo; Goto, Masahiro

    2010-11-15

    We deposit Au films on single crystal sapphire substrates by sputtering and evaporation methods. The microstructure characteristics such as crystal textures, grain sizes, and fraction of contacted area of the films are examined by x-ray diffraction and transmission electron microscopy. The sputtered films have an average grain size of about 200 nm and perfectly attach to the substrates; the as-evaporated films partially attach to the substrate; the grain size varies from 10 to 30 nm, and after annealing, increases to 50 nm. Au{sub 2}Al phase is observed in the annealed samples. The interfacial thermal resistance is measured by a frequency domain thermoreflectance method. The thermal resistance of the sputtered Au/sapphire interfaces is 35.5x10{sup -9} m{sup 2} K W{sup -1}, and those of the evaporated samples are up to three times as large as this value. The change in interfacial thermal resistance is explained by the effect of detachment using a parallel arranged thermal resistance model, the effect of grain size, and the influence of chemical bonding at the interfaces.

  5. Characterisation and applications of microcapsules obtained by interfacial polycondensation.

    PubMed

    Zhang, Yufen; Rochefort, Dominic

    2012-01-01

    This review highlights the materials, mechanisms and applications of microencapsulation by interfacial polycondensation in different areas. This technology entraps active ingredients inside microcapsules/microspheres, having an average diameter ranging from nanosize to several 100 µ. Polycondensation reactions take place at the boundary of two phases to form the shells of microcapsules or matrix microspheres. The emulsion can be classified into three types: water-in-oil, oil-in-water and oil-in-oil. According to the hydrophilic-lipophilic property of core phase, different active substances, such as proteins, enzymes, insecticides, herbicides, vitamins, catalysts, drugs, essential oils, dyes and phase change materials, have been successfully incorporated into different microcapsules/microspheres. Based on the shell-forming materials, this technology is capable of preparing polyamine, polyurea, polyurethane, polythiourea, polyester, polyepoxide, polyacrylamide and polysiloxane microcapsules. Over the past two decades, microcapsules prepared by interfacial polycondensation have been widely used in carbonless paper, cosmetics, pharmacy, agriculture, energy storage/transfer, thermal insulation/regulation and information and magnetic recording. PMID:22494033

  6. A modeling procedure to evaluate the coherence of independently derived environmental quality objectives for air, water and soil

    SciTech Connect

    Meent, D. van de . Lab. for Ecotoxicology); Bruijn, J.H.M. de . Directorate for Chemicals, Safety and Radiation Protection)

    1995-01-01

    Sets of independently derived environmental quality objectives (EQOs) for air, water, and soil may not be coherent in that maintaining the concentration at EQO level in one compartment may lead to exceeding EQO levels in other compartments. A methodology to evaluate this coherence is suggested. Starting from a steady concentration in the compartment of focus (the primary compartment), steady-state concentrations in the adjacent (secondary) compartments are estimated using a multimedia fate model. If air is the primary compartment, steady-state concentrations in water and soil close to the equilibrium concentrations can be expected, and coherence of EQOs can be evaluated easily by means of an extended equilibrium partitioning procedure. If water or soil is the primary compartment, the steady-state concentrate in air is usually well below the equilibrium concentration. Subequilibrium steady-state concentrations are sensitive to assumed model parameters. The procedure is illustrated with the results of a coherence analysis for seven chemicals for The Netherlands.

  7. Influence of current velocity and wind speed on air-water gas exchange in a mangrove estuary

    NASA Astrophysics Data System (ADS)

    Ho, David T.; Coffineau, Nathalie; Hickman, Benjamin; Chow, Nicholas; Koffman, Tobias; Schlosser, Peter

    2016-04-01

    Knowledge of air-water gas transfer velocities and water residence times is necessary to study the fate of mangrove derived carbon exported into surrounding estuaries and ultimately to determine carbon balances in mangrove ecosystems. For the first time, the 3He/SF6 dual tracer technique, which has been proven to be a powerful tool to determine gas transfer velocities in the ocean, is applied to Shark River, an estuary situated in the largest contiguous mangrove forest in North America. The mean gas transfer velocity was 3.3 ± 0.2 cm h-1 during the experiment, with a water residence time of 16.5 ± 2.0 days. We propose a gas exchange parameterization that takes into account the major sources of turbulence in the estuary (i.e., bottom generated shear and wind stress).

  8. A Designed A. vinelandii-S. elongatus Coculture for Chemical Photoproduction from Air, Water, Phosphate, and Trace Metals.

    PubMed

    Smith, Matthew J; Francis, Matthew B

    2016-09-16

    Microbial mutualisms play critical roles in a diverse number of ecosystems and have the potential to improve the efficiency of bioproduction for desirable chemicals. We investigate the growth of a photosynthetic cyanobacterium, Synechococcus elongatus PCC 7942, and a diazotroph, Azotobacter vinelandii, in coculture. From initial studies of the coculture grown in media with glutamate, we proposed a model of cross-feeding between these organisms. We then engineer a new microbial mutualism between Azotobacter vinelandii AV3 and cscB Synechococcus elongatus that grows in the absence of fixed carbon or nitrogen. The coculture cannot grow in the absence of a sucrose-exporting S. elongatus, and neither organism can grow alone without fixed carbon or nitrogen. This new system has the potential to produce industrially relevant products, such as polyhydroxybutyrate (PHB) and alginate, from air, water, phosphate, trace metals, and sunlight. We demonstrate the ability of the coculture to produce PHB in this work. PMID:27232890

  9. Synthesis of a Two-Dimensional Covalent Organic Monolayer through Dynamic Imine Chemistry at the Air/Water Interface.

    PubMed

    Dai, Wenyang; Shao, Feng; Szczerbiński, Jacek; McCaffrey, Ryan; Zenobi, Renato; Jin, Yinghua; Schlüter, A Dieter; Zhang, Wei

    2016-01-01

    A two-dimensional covalent organic monolayer was synthesized from simple aromatic triamine and dialdehyde building blocks by dynamic imine chemistry at the air/water interface (Langmuir-Blodgett method). The obtained monolayer was characterized by optical microscopy, scanning electron microscopy, and atomic force microscopy, which unambiguously confirmed the formation of a large (millimeter range), unimolecularly thin aromatic polyimine sheet. The imine-linked chemical structure of the obtained monolayer was characterized by tip-enhanced Raman spectroscopy, and the peak assignment was supported by spectra simulated by density functional theory. Given the modular nature and broad substrate scope of imine formation, the work reported herein opens up many new possibilities for the synthesis of customizable 2D polymers and systematic studies of their structure-property relationships.

  10. Introducing high-quality planar defects into colloidal crystals via self-assembly at the air/water interface

    NASA Astrophysics Data System (ADS)

    Zhong, Kuo; Demeyer, Pieter-Jan; Zhou, Xingping; Kruglova, Olga; Verellen, Niels; Moshchalkov, Victor V.; Song, Kai; Clays, Koen

    2015-02-01

    We demonstrate a facile method for fabrication of colloidal crystals containing a planar defect by using PS@SiO2 core-shell spheres as building blocks. A monolayer of solid spheres was embedded in core-shell colloidal crystals serving as the defect layer, which formed by means of self-assembly at the air/water interface. Compared with previous methods, this fabrication method results in pronounced passbands in the band gaps of the colloidal photonic crystal. The FWHM of the obtained passband is only ~16nm, which is narrower than the previously reported results. The influence of the defect layer thickness on the optical properties of these sandwiched structures was also investigated. No high-cost processes or specific equipment is needed in our approach. Inverse opals with planar defects can be obtained via calcination of the PS cores, without the need of infiltration. The experimental results are in good agreement with simulations performed using the FDTD method.

  11. Ordered mesoporous materials based on interfacial assembly and engineering.

    PubMed

    Li, Wei; Yue, Qin; Deng, Yonghui; Zhao, Dongyuan

    2013-10-01

    Ordered mesoporous materials have inspired prominent research interest due to their unique properties and functionalities and potential applications in adsorption, separation, catalysis, sensors, drug delivery, energy conversion and storage, and so on. Thanks to continuous efforts over the past two decades, great achievements have been made in the synthesis and structural characterization of mesoporous materials. In this review, we summarize recent progresses in preparing ordered mesoporous materials from the viewpoint of interfacial assembly and engineering. Five interfacial assembly and synthesis are comprehensively highlighted, including liquid-solid interfacial assembly, gas-liquid interfacial assembly, liquid-liquid interfacial assembly, gas-solid interfacial synthesis, and solid-solid interfacial synthesis, basics about their synthesis pathways, princples and interface engineering strategies.

  12. Turbulence at the Air-Water Interface in Lakes of Different Sizes: Consequences for Gas Transfer Coefficients

    NASA Astrophysics Data System (ADS)

    MacIntyre, S.; Crowe, A. T.; Amaral, J. H.; Arneborg, L.; Bastviken, D.; Forsberg, B. R.; Melack, J. M.; Tota, J.; Tedford, E. W.; Karlsson, J.; Podgrajsek, E.; Andersson, A.; Rutgersson, A.

    2014-12-01

    Similarity scaling predicts that wind induced shear will be the dominant source of turbulence near the air-water interface in lakes with low to moderate wind forcing. Turbulence is expected to be enhanced with wave activity; results are conflicting on the effects of heating and cooling. We measured turbulence with an acoustic Doppler velocimeter (ADV) and / or a temperature-gradient microstructure profiler and obtained correlative time series measurements of meteorology and water column temperature in a 800 m2 arctic pond, a 1 ha boreal lake, and a large tropical reservoir. Turbulence measurements with both instruments corroborated those calculated from similarity scaling in the boreal lake. Within the arctic pond, dissipation rates obtained with the ADV were in agreement with those from similarity scaling when winds exceeded ~1.5 m/s with a greater frequency of measurable dissipation rates when surface waves were present. Dissipation rates in the tropical reservoir reached and often exceeded 10-6 m2 s-3 in the upper meter under light winds and decreased by an order of magnitude with cooling or rainfall. Under cooling, dissipation rates were at least an order of magnitude higher in the uppermost 25 cm bin than in the water column below. Gas transfer coefficients calculated from concurrent measurements of greenhouse gas fluxes with floating chambers and the surface renewal model using the estimates of turbulence were in agreement. These results support the predictions of Monin-Obuhov similarity scaling in that shear dominates turbulence production near the air-water interface under heating and cooling, illustrate spatial variability in turbulence production in small water bodies due to the intermittency of wind interacting with the water's surface, are in agreement with prior oceanic observations that shear and associated turbulence can be intensified in shallow mixing layers under heating with light winds, and illustrate the utility of similarity scaling for

  13. On the coefficients of small eddy and surface divergence models for the air-water gas transfer velocity

    NASA Astrophysics Data System (ADS)

    Wang, Binbin; Liao, Qian; Fillingham, Joseph H.; Bootsma, Harvey A.

    2015-03-01

    Recent studies suggested that under low to moderate wind conditions without bubble entraining wave breaking, the air-water gas transfer velocity k+ can be mechanistically parameterized by the near-surface turbulence, following the small eddy model (SEM). Field measurements have supported this model in a variety of environmental forcing systems. Alternatively, surface divergence model (SDM) has also been shown to predict the gas transfer velocity across the air-water interface in laboratory settings. However, the empirically determined model coefficients (α in SEM and c1 in SDM) scattered over a wide range. Here we present the first field measurement of the near-surface turbulence with a novel floating PIV system on Lake Michigan, which allows us to evaluate the SEM and SDM in situ in the natural environment. k+ was derived from the CO2 flux that was measured simultaneously with a floating gas chamber. Measured results indicate that α and c1 are not universal constants. Regression analysis showed that α˜log>(ɛ>) while the near-surface turbulence dissipation rate ɛ is approximately greater than 10-6 m2 s-3 according to data measured for this study as well as from other published results measured in similar environments or in laboratory settings. It also showed that α scales linearly with the turbulent Reynolds number. Similarly, coefficient c1 in the SDM was found to linearly scale with the Reynolds number. These findings suggest that larger eddies are also important parameters, and the dissipation rate in the SEM or the surface divergence β' in the SDM alone may not be adequate to determine k+ completely.

  14. Reactivity of aldehydes at the air-water interface. Insights from molecular dynamics simulations and ab initio calculations.

    PubMed

    Martins-Costa, Marilia T C; García-Prieto, Francisco F; Ruiz-López, Manuel F

    2015-02-14

    Understanding the influence of solute-solvent interactions on chemical reactivity has been a subject of intense research in the last few decades. Theoretical studies have focused on bulk solvation phenomena and a variety of models and methods have been developed that are now widely used by both theoreticians and experimentalists. Much less attention has been paid, however, to processes that occur at liquid interfaces despite the important role such interfaces play in chemistry and biology. In this study, we have carried out sequential molecular dynamics simulations and quantum mechanical calculations to analyse the influence of the air-water interface on the reactivity of formaldehyde, acetaldehyde and benzaldehyde, three simple aldehydes of atmospheric interest. The calculated free-energy profiles exhibit a minimum at the interface, where the average reactivity indices may display large solvation effects. The study emphasizes the role of solvation dynamics, which are responsible for large fluctuations of some molecular properties. We also show that the photolysis rate constant of benzaldehyde in the range 290-308 nm increases by one order of magnitude at the surface of a water droplet, from 2.7 × 10(-5) s(-1) in the gas phase to 2.8 × 10(-4) s(-1) at the air-water interface, and we discuss the potential impact of this result on the chemistry of the troposphere. Experimental data in this domain are still scarce and computer simulations like those presented in this work may provide some insights that can be useful to design new experiments.

  15. Polymerization of a diacetylenic phospholipid monolayer at the air-water interface

    NASA Astrophysics Data System (ADS)

    Bourdieu, L.; Chatenay, D.; Daillant, J.; Luzet, D.

    1994-01-01

    Monolayers of a polymerizable phospholipid on water have been studied both before and after polymerization. Before polymerization, the phase diagram is established by isotherm measurements and optical microscopy (epifluorescence and direct observation between crossed polarizer and analyzer). This allows us to bring into evidence a coexistence region between a condensed and an expanded phase, above a triple point temperature T_t = 20 ^{circ}C. The dramatic influence of impurities on the size of coexistence domains between the condensed phase and the expanded one is clearly demonstrated, even at a very low concentration of impurities. Structural and morphological modifications during the polymerization where investigated using X-ray surface scattering together with atomic force microscopy. Whatever the polymerization conditions (constant area or constant pressure), X-ray reflectivity clearly shows the reorientation of the diacetylenic links. Only constant area polymerization leads to a viscoelastic behavior of the film, as shown by talcum decoration. The topochemical nature of the polymerization of diacetylenic groups induces strong constraints on the monolayers and, when the polymerization is achieved at constant area, leads to the collapse of the films evidenced by both techniques.

  16. Interfacial Binding of Divalent Cations to Calixarene-Based Langmuir Monolayers

    SciTech Connect

    Tulli, Ludovico G.; Wang, Wenjie; Lindemann, William R.; Kuzmenko, Ivan; Meier, Wolfgang; Vaknin, David; Shahgaldian, Patrick

    2015-02-20

    The interactions of Langmuir monolayers produced through the self-assembly of an amphiphilic p-carboxycalix[4]arene (1) with a series of divalent, fourth-period transition metals, at the air-water interface, were investigated. Changes in the interfacial behavior of 1 in response to the presence of CuCl2, CoCl2, MnCl2, and NiCl2 were studied by means of Langmuir compression isotherms and Brewster angle microscopy (BAM). The measurements revealed that the self-assembly properties of 1 are significantly affected by Cu2+ ions. The interactions of 1-based monolayers with Co2+ and Cu2+ ions were further investigated by means of synchrotron radiation-based X-ray reflectivity (XRR), X-ray near-total-reflection fluorescence (XNTRF), and grazing incidence X-ray diffraction (GIXD). XNTRF and XRR analyses revealed that the monolayer of 1 binds more strongly to Cu2+ than Co2+ ions. In the presence of relatively high concentrations of Cu2+ ions in the subphase (1.4 × 10-3 M), XNTRF exhibited anomalous depth profile behavior and GIXD measurements showed considerably strong diffuse scattering. Both measurements suggest the formation of Cu2+ clusters contiguous to the monolayer of 1.

  17. Interfacial binding of divalent cations to calixarene-based Langmuir monolayers.

    PubMed

    Tulli, Ludovico G; Wang, Wenjie; Lindemann, William R; Kuzmenko, Ivan; Meier, Wolfgang; Vaknin, David; Shahgaldian, Patrick

    2015-03-01

    The interactions of Langmuir monolayers produced through the self-assembly of an amphiphilic p-carboxycalix[4]arene (1) with a series of divalent, fourth-period transition metals, at the air-water interface, were investigated. Changes in the interfacial behavior of 1 in response to the presence of CuCl2, CoCl2, MnCl2, and NiCl2 were studied by means of Langmuir compression isotherms and Brewster angle microscopy (BAM). The measurements revealed that the self-assembly properties of 1 are significantly affected by Cu(2+) ions. The interactions of 1-based monolayers with Co(2+) and Cu(2+) ions were further investigated by means of synchrotron radiation-based X-ray reflectivity (XRR), X-ray near-total-reflection fluorescence (XNTRF), and grazing incidence X-ray diffraction (GIXD). XNTRF and XRR analyses revealed that the monolayer of 1 binds more strongly to Cu(2+) than Co(2+) ions. In the presence of relatively high concentrations of Cu(2+) ions in the subphase (1.4 × 10(-3) M), XNTRF exhibited anomalous depth profile behavior and GIXD measurements showed considerably strong diffuse scattering. Both measurements suggest the formation of Cu(2+) clusters contiguous to the monolayer of 1.

  18. Interfacial behavior of pulmonary surfactant preparations containing egg yolk lecithin.

    PubMed

    Nakahara, Hiromichi; Shibata, Osamu

    2014-01-01

    Mammalian lungs are covered with lipid-protein complexes or pulmonary surfactants. In this work, which aimed towards the less expensive production of artificial pulmonary surfactants, we produced surfactants composed of egg yolk lecithin (eggPC), palmitic acid, and hexadecanol (= 0.30/0.35/0.35, mol/mol/mol ) containing different amounts of Hel 13-5 (NH2-KLLKLLLKLWLKLLKLLL-COOH) as a substitute for the proteins in native pulmonary surfactants. Surface pressure (π)-molecular area (A) and surface potential (DV)-A isotherms of the mixtures were measured via the Wilhelmy and ionizing (241)Am electrode methods, respectively. The interactions between the lipid components and Hel 13-5 led to variations in the surface pressure caused by the expulsion of fluid components from the surface. Furthermore, the π-A and DV-A isotherms featured large hysteresis loops for the surfactant that contained a small amount of Hel 13-5 during compression and successive expansion cycling. To elucidate the morphology, the phase behavior was visualized in situ at the air-water interface by means of fluorescence microscopy; the images suggested less effective interactions between Hel 13-5 and the unsaturated PC in eggPC despite the similarity of their monolayer properties.

  19. Water temperature effect on upward air-water flow in a vertical pipe: Local measurements database using four-sensor conductivity probes and LDA

    NASA Astrophysics Data System (ADS)

    Monrós-Andreu, G.; Chiva, S.; Martínez-Cuenca, R.; Torró, S.; Juliá, J. E.; Hernández, L.; Mondragón, R.

    2013-04-01

    Experimental work was carried out to study the effects of temperature variation in bubbly, bubbly to slug transition. Experiments were carried out in an upward air-water flow configuration. Four sensor conductivity probes and LDA techniques was used together for the measurement of bubble parameters. The aim of this paper is to provide a bubble parameter experimental database using four-sensor conductivity probes and LDA technique for upward air-water flow at different temperatures and also show transition effect in different temperatures under the boiling point.

  20. Interfacial Rheology of Hydrogen-Bonded Polymer Multilayers Assembled at Liquid Interfaces: Influence of Anchoring Energy and Hydrophobic Interactions.

    PubMed

    Le Tirilly, Sandrine; Tregouët, Corentin; Reyssat, Mathilde; Bône, Stéphane; Geffroy, Cédric; Fuller, Gerald; Pantoustier, Nadège; Perrin, Patrick; Monteux, Cécile

    2016-06-21

    We study the 2D rheological properties of hydrogen-bonded polymer multilayers assembled directly at dodecane-water and air-water interfaces using pendant drop/bubble dilation and the double-wall ring method for interfacial shear. We use poly(vinylpyrrolidone) (PVP) as a proton acceptor and a series of polyacrylic acids as proton donors. The PAA series of chains with varying hydrophobicity was fashioned from poly(acrylic acid), (PAA), polymethacrylic acid (PMAA), and a homemade hydrophobically modified polymer. The latter consisted of a PAA backbone covalently grafted with C12 moieties at 1% mol (referred to as PAA-1C12). Replacing PAA with the more hydrophobic PMAA provides a route for combining hydrogen bonding and hydrophobic interactions to increase the strength and/or the number of links connecting the polyacid chains to PVP. This systematic replacement allows for control of the ability of the monomer units inside the absorbed polymer layer to reorganize as the interface is sheared or compressed. Consequently, the interplay of hydrogen bonding and hydrophobic interactions leads to control of the resistance of the polymer multilayers to both shear and dilation. Using PAA-1C12 as the first layer improves the anchoring energy of a few monomers of the chain without changing the strength of the monomer-monomer contact in the complex layer. In this way, the layer does not resist shear but resists compression. This strategy provides the means for using hydrophobicity to control the interfacial dynamics of the complexes adsorbed at the interface of the bubbles and droplets that either elongate or buckle upon compression. Moreover, we demonstrate the pH responsiveness of these interfacial multilayers by adding aliquots of NaOH to the acidic water subphase surrounding the bubbles and droplets. Subsequent pH changes can eventually break the polymer complex, providing opportunities for encapsulation/release applications. PMID:27176147

  1. Frontiers of interfacial water research :workshop report.

    SciTech Connect

    Cygan, Randall Timothy; Greathouse, Jeffery A.

    2005-10-01

    Water is the critical natural resource of the new century. Significant improvements in traditional water treatment processes require novel approaches based on a fundamental understanding of nanoscale and atomic interactions at interfaces between aqueous solution and materials. To better understand these critical issues and to promote an open dialog among leading international experts in water-related specialties, Sandia National Laboratories sponsored a workshop on April 24-26, 2005 in Santa Fe, New Mexico. The ''Frontiers of Interfacial Water Research Workshop'' provided attendees with a critical review of water technologies and emphasized the new advances in surface and interfacial microscopy, spectroscopy, diffraction, and computer simulation needed for the development of new materials for water treatment.

  2. Interfacial geometry dictates cancer cell tumorigenicity

    NASA Astrophysics Data System (ADS)

    Lee, Junmin; Abdeen, Amr A.; Wycislo, Kathryn L.; Fan, Timothy M.; Kilian, Kristopher A.

    2016-08-01

    Within the heterogeneous architecture of tumour tissue there exists an elusive population of stem-like cells that are implicated in both recurrence and metastasis. Here, by using engineered extracellular matrices, we show that geometric features at the perimeter of tumour tissue will prime a population of cells with a stem-cell-like phenotype. These cells show characteristics of cancer stem cells in vitro, as well as enhanced tumorigenicity in murine models of primary tumour growth and pulmonary metastases. We also show that interfacial geometry modulates cell shape, adhesion through integrin α5β1, MAPK and STAT activity, and initiation of pluripotency signalling. Our results for several human cancer cell lines suggest that interfacial geometry triggers a general mechanism for the regulation of cancer-cell state. Similar to how a growing tumour can co-opt normal soluble signalling pathways, our findings demonstrate how cancer can also exploit geometry to orchestrate oncogenesis.

  3. Interfacial transport in lithium-ion conductors

    NASA Astrophysics Data System (ADS)

    Shaofei, Wang; Liquan, Chen

    2016-01-01

    Physical models of ion diffusion at different interfaces are reviewed. The use of impedance spectroscopy (IS), nuclear magnetic resonance (NMR), and secondary ion mass spectrometry (SIMS) techniques are also discussed. The diffusion of ions is fundamental to the operation of lithium-ion batteries, taking place not only within the grains but also across different interfaces. Interfacial ion transport usually contributes to the majority of the resistance in lithium-ion batteries. A greater understanding of the interfacial diffusion of ions is crucial to improving battery performance. Project supported by the Beijing S&T Project, China (Grant No. Z13111000340000), the National Natural Science Foundation of China (Grant Nos. 51325206 and 11234013) and the National Basic Research Program of China (Grant No. 2012CB932900).

  4. Scaling for interfacial tensions near critical endpoints.

    PubMed

    Zinn, Shun-Yong; Fisher, Michael E

    2005-01-01

    Parametric scaling representations are obtained and studied for the asymptotic behavior of interfacial tensions in the full neighborhood of a fluid (or Ising-type) critical endpoint, i.e., as a function both of temperature and of density/order parameter or chemical potential/ordering field. Accurate nonclassical critical exponents and reliable estimates for the universal amplitude ratios are included naturally on the basis of the "extended de Gennes-Fisher" local-functional theory. Serious defects in previous scaling treatments are rectified and complete wetting behavior is represented; however, quantitatively small, but unphysical residual nonanalyticities on the wetting side of the critical isotherm are smoothed out "manually." Comparisons with the limited available observations are presented elsewhere but the theory invites new, searching experiments and simulations, e.g., for the vapor-liquid interfacial tension on the two sides of the critical endpoint isotherm for which an amplitude ratio -3.25+/-0.05 is predicted.

  5. Simulation of direct contact condensation of steam jets based on interfacial instability theories

    NASA Astrophysics Data System (ADS)

    Heinze, David; Schulenberg, Thomas; Class, Andreas; Behnke, Lars

    2014-11-01

    A simulation model for the direct contact condensation of steam in subcooled water is presented that allows to determine major parameters of the process such as the jet penetration length. Entrainment of water by the steam jet is modeled based on the Kelvin-Helmholtz and Rayleigh-Taylor instability theories. Primary atomization due to acceleration of interfacial waves and secondary atomization due to aerodynamic forces account for the initial size of entrained droplets. The resulting steam-water two-phase flow is simulated based on a one-dimensional two-fluid model. An interfacial area transport equation is used to track changes of the interfacial area density due to droplet entrainment and steam condensation. Interfacial heat and mass transfer rates during condensation are calculated using the two-resistance model. The resulting two-phase flow equations constitute a system of ordinary differential equations which is discretized by means of an explicit Runge-Kutta method. The simulation results are in good agreement with published experimental data over a wide range of pool temperatures and mass flow rates. funded by RWE Power AG.

  6. Interfacial chemistry in solvent extraction systems

    SciTech Connect

    Neuman, R.D.

    1993-01-01

    Research this past year continued to emphasize characterization of the physicochemical nature of the microscopic interfaces, i.e., reversed micelles and other association microstructures, which form in both practical and simplified acidic organophosphorus extraction systems associated with Ni, Co, and Na in order to improve on the model for aggregation of metal-extractant complexes. Also, the macroscopic interfacial behavior of model extractant (surfactant) molecules was further investigated. 1 fig.

  7. Interfacial chemistry in solvent extraction systems

    SciTech Connect

    Neuman, R.D.

    1992-01-01

    Research last year emphasized the nature of microscopic interfaces, i. e., reversed micelles and other association microstructures, which form in both practical and simplified acidic organophosphorus extraction systems associated with Ni, Co and Na in order to improve on a recently proposed model for aggregation of metal-extractant complexes. Also, the macroscopic interfacial behavior of extractant molecules and their interactions with metal ions which occur in hydrometallurgical solvent extraction systems were further investigated.

  8. Intrinsic interfacial phenomena in manganite heterostructures

    NASA Astrophysics Data System (ADS)

    Vaz, C. A. F.; Walker, F. J.; Ahn, C. H.; Ismail-Beigi, S.

    2015-04-01

    We review recent advances in our understanding of interfacial phenomena that emerge when dissimilar materials are brought together at atomically sharp and coherent interfaces. In particular, we focus on phenomena that are intrinsic to the interface and review recent work carried out on perovskite manganites interfaces, a class of complex oxides whose rich electronic properties have proven to be a useful playground for the discovery and prediction of novel phenomena.

  9. Interfacial microfluidic transport on micropatterned superhydrophobic textile.

    PubMed

    Xing, Siyuan; Jiang, Jia; Pan, Tingrui

    2013-05-21

    Textile-enabled interfacial microfluidics, utilizing fibrous hydrophilic yarns (e.g., cotton) to guide biological reagent flows, has been extended to various biochemical analyses recently. The restricted capillary-driving mechanism, however, persists as a major challenge for continuous and facilitated biofluidic transport. In this paper, we have first introduced a novel interfacial microfluidic transport principle to drive three-dimensional liquid flows on a micropatterned superhydrophobic textile (MST) platform in a more autonomous and controllable manner. Specifically, the MST system utilizes the surface tension-induced Laplace pressure to facilitate the liquid motion along the hydrophilic yarn, in addition to the capillarity present in the fibrous structure. The fabrication of MST is simply accomplished by stitching hydrophilic cotton yarn into a superhydrophobic fabric substrate (contact angle 140 ± 3°), from which well-controlled wetting patterns are established for interfacial microfluidic operations. The geometric configurations of the stitched micropatterns, e.g., the lengths and diameters of the yarn and bundled arrangement, can all influence the transport process, which is investigated both experimentally and theoretically. Two operation modes, discrete and continuous transport, are also presented in detail. In addition, the gravitational effect as well as the droplet removal process have been also considered and quantitatively analysed during the transport process. As a demonstration, an MST design has been implemented on an artificial skin surface to collect and remove sweat in a highly efficient and facilitated means. The results have illustrated that the novel interfacial transport on the textile platform can be potentially extended to a variety of biofluidic collection and removal applications.

  10. Interfacial chemistry and structure in ceramic composites

    SciTech Connect

    Jones, R.H.; Saenz, N.T.; Schilling, C.H.

    1990-09-01

    The interfacial chemistry and structure of ceramic matrix composites (CMCs) play a major role in the properties of these materials. Fiber-matrix interfaces chemistries are vitally important in the fracture strength, fracture toughness, and fracture resistance of ceramic composites because they influence fiber loading and fiber pullout. Elevated-temperature properties are also linked to the interfacial characteristics through the chemical stability of the interface in corrosive environments and the creep/pullout behavior of the interface. Physical properties such as electrical and thermal conductivity are also dependent on the interface. Fiber-matrix interfaces containing a 1-{mu}m-thick multilayered interface with amorphous and graphitic C to a 1-nm-thick SiO{sub 2} layer can result from sintering operations for some composite systems. Fibers coated with C, BN, C/BC/BN, and Si are also used to produce controlled interface chemistries and structures. Growth interfaces within the matrix resulting from processing of CMCs can also be crucial to the behavior of these materials. Evaluation of the interfacial chemistry and structure of CMCs requires the use of a variety of analytical tools, including optical microscopy, scanning electron microscopy, Auger electron spectroscopy, and transmission electron microscopy coupled with energy dispersive x-ray analysis. A review of the interfacial chemistry and structure of SiC whisker- and fiber-reinforced Si{sub 3}N{sub 4} and SiC/SiC materials is presented. Where possible, correlations with fracture properties and high-temperature stability are made. 94 refs., 10 figs.

  11. Microstructural Evolution Based on Fundamental Interfacial Properties

    SciTech Connect

    A. D. Rollett; D. J. Srolovitz; A. Karma

    2003-07-11

    This first CMSN project has been operating since the summer of 1999. The main achievement of the project was to bring together a community of materials scientists, physicists and mathematicians who share a common interest in the properties of interfaces and the impact of those properties on microstructural evolution. Six full workshops were held at Carnegie Mellon (CMU), Northwestern (NWU), Santa Fe, Northeastern University (NEU), National Institute for Standards and Technology (NIST), Ames Laboratory, and at the University of California in San Diego (UCSD) respectively. Substantial scientific results were obtained through the sustained contact between the members of the project. A recent issue of Interface Science (volume 10, issue 2/3, July 2002) was dedicated to the output of the project. The results include: the development of methods for extracting anisotropic boundary energy and mobility from molecular dynamics simulations of solid/liquid interfaces in nickel; the extraction of anisotropic energies and mobilities in aluminum from similar MD simulations; the application of parallel computation to the calculation of interfacial properties; the development of a method to extract interfacial properties from the fluctuations in interface position through consideration of interfacial stiffness; the use of anisotropic interface properties in studies of abnormal grain growth; the discovery of abnormal grain growth from random distributions of orientation in subgrain networks; the direct comparison at the scale of individual grains between experimentally observed grain growth and simulations, which confirmed the importance of including anisotropic interfacial properties in the simulations; the classification of a rich variety of dendritic morphologies based on slight variations in the anisotropy of the solid-liquid interface; development of phase field methods that permit both solidification and grain growth to be simulated within the same framework.

  12. Interfacial Symmetry Control of Emergent Ferromagnetism

    NASA Astrophysics Data System (ADS)

    Grutter, Alexander; Borchers, Julie; Kirby, Brian; He, Chunyong; Arenholz, Elke; Vailionis, Arturas; Flint, Charles; Suzuki, Yuri

    Atomically precise complex oxide heterostructures provide model systems for the discovery of new emergent phenomena since their magnetism, structure and electronic properties are strongly coupled. Octahedral tilts and rotations have been shown to alter the magnetic properties of complex oxide heterostructures, but typically induce small, gradual magnetic changes. Here, we demonstrate sharp switching between ferromagnetic and antiferromagnetic order at the emergent ferromagnetic interfaces of CaRuO3/CaMnO3 superlattices. Through synchrotron X-ray diffraction and neutron reflectometry, we show that octahedral distortions in superlattices with an odd number of CaMnO3 unit cells in each layer are symmetry mismatched across the interface. In this case, the rotation symmetry switches across the interface, reducing orbital overlap, suppressing charge transfer from Ru to Mn, and disrupting the interfacial double exchange. This disruption switches half of the interfaces from ferromagnetic to antiferromagnetic and lowers the saturation magnetic of the superlattice from 1.0 to 0.5 μB/interfacial Mn. By targeting a purely interfacial emergent magnetic system, we achieve drastic alterations to the magnetic ground state with extremely small changes in layer thickness.

  13. Interfacial Studies of Sized Carbon Fiber

    SciTech Connect

    Shahrul, S. N.; Hartini, M. N.; Hilmi, E. A.; Nizam, A.

    2010-03-11

    This study was performed to investigate the influence of sizing treatment on carbon fiber in respect of interfacial adhesion in composite materials, Epolam registered 2025. Fortafil unsized carbon fiber was used to performed the experiment. The fiber was commercially surface treated and it was a polyacrylonitrile based carbon fiber with 3000 filament per strand. Epicure registered 3370 was used as basic sizing chemical and dissolved in two types of solvent, ethanol and acetone for the comparison purpose. The single pull out test has been used to determine the influence of sizing on carbon fiber. The morphology of carbon fiber was observed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The apparent interfacial strength IFSS values determined by pull out test for the Epicure registered 3370/ethanol sized carbon fiber pointed to a good interfacial behaviour compared to the Epicure registered 3370/acetone sized carbon fiber. The Epicure registered 3370/ethanol sizing agent was found to be effective in promoting adhesion because of the chemical reactions between the sizing and Epolam registered 2025 during the curing process. From this work, it showed that sized carbon fiber using Epicure registered 3370 with addition of ethanol give higher mechanical properties of carbon fiber in terms of shear strength and also provided a good adhesion between fiber and matrix compared to the sizing chemical that contain acetone as a solvent.

  14. Investigation of interfacial rheology & foam stability.

    SciTech Connect

    Yaklin, Melissa A.; Cote, Raymond O.; Grillet, Anne Mary; Walker, Lynn M.; Koehler, Timothy P.; Reichert, Matthew D.; Castaneda, Jaime N.; Mondy, Lisa Ann; Brooks, Carlton, F.

    2010-05-01

    The rheology at gas-liquid interfaces strongly influences the stability and dynamics of foams and emulsions. Several experimental techniques are employed to characterize the rheology at liquid-gas interfaces with an emphasis on the non-Newtonian behavior of surfactant-laden interfaces. The focus is to relate the interfacial rheology to the foamability and foam stability of various aqueous systems. An interfacial stress rheometer (ISR) is used to measure the steady and dynamic rheology by applying an external magnetic field to actuate a magnetic needle suspended at the interface. Results are compared with those from a double wall ring attachment to a rotational rheometer (TA Instruments AR-G2). Micro-interfacial rheology (MIR) is also performed using optical tweezers to manipulate suspended microparticle probes at the interface to investigate the steady and dynamic rheology. Additionally, a surface dilatational rheometer (SDR) is used to periodically oscillate the volume of a pendant drop or buoyant bubble. Applying the Young-Laplace equation to the drop shape, a time-dependent surface tension can be calculated and used to determine the effective dilatational viscosity of an interface. Using the ISR, double wall ring, SDR, and MIR, a wide range of sensitivity in surface forces (fN to nN) can be explored as each experimental method has different sensitivities. Measurements will be compared to foam stability.

  15. Interfacial gauge methods for incompressible fluid dynamics.

    PubMed

    Saye, Robert

    2016-06-01

    Designing numerical methods for incompressible fluid flow involving moving interfaces, for example, in the computational modeling of bubble dynamics, swimming organisms, or surface waves, presents challenges due to the coupling of interfacial forces with incompressibility constraints. A class of methods, denoted interfacial gauge methods, is introduced for computing solutions to the corresponding incompressible Navier-Stokes equations. These methods use a type of "gauge freedom" to reduce the numerical coupling between fluid velocity, pressure, and interface position, allowing high-order accurate numerical methods to be developed more easily. Making use of an implicit mesh discontinuous Galerkin framework, developed in tandem with this work, high-order results are demonstrated, including surface tension dynamics in which fluid velocity, pressure, and interface geometry are computed with fourth-order spatial accuracy in the maximum norm. Applications are demonstrated with two-phase fluid flow displaying fine-scaled capillary wave dynamics, rigid body fluid-structure interaction, and a fluid-jet free surface flow problem exhibiting vortex shedding induced by a type of Plateau-Rayleigh instability. The developed methods can be generalized to other types of interfacial flow and facilitate precise computation of complex fluid interface phenomena. PMID:27386567

  16. Interfacial gauge methods for incompressible fluid dynamics

    PubMed Central

    Saye, Robert

    2016-01-01

    Designing numerical methods for incompressible fluid flow involving moving interfaces, for example, in the computational modeling of bubble dynamics, swimming organisms, or surface waves, presents challenges due to the coupling of interfacial forces with incompressibility constraints. A class of methods, denoted interfacial gauge methods, is introduced for computing solutions to the corresponding incompressible Navier-Stokes equations. These methods use a type of “gauge freedom” to reduce the numerical coupling between fluid velocity, pressure, and interface position, allowing high-order accurate numerical methods to be developed more easily. Making use of an implicit mesh discontinuous Galerkin framework, developed in tandem with this work, high-order results are demonstrated, including surface tension dynamics in which fluid velocity, pressure, and interface geometry are computed with fourth-order spatial accuracy in the maximum norm. Applications are demonstrated with two-phase fluid flow displaying fine-scaled capillary wave dynamics, rigid body fluid-structure interaction, and a fluid-jet free surface flow problem exhibiting vortex shedding induced by a type of Plateau-Rayleigh instability. The developed methods can be generalized to other types of interfacial flow and facilitate precise computation of complex fluid interface phenomena. PMID:27386567

  17. Interfacial Studies of Sized Carbon Fiber

    NASA Astrophysics Data System (ADS)

    Shahrul, S. N.; Hartini, M. N.; Hilmi, E. A.; Nizam, A.

    2010-03-01

    This study was performed to investigate the influence of sizing treatment on carbon fiber in respect of interfacial adhesion in composite materials, Epolam® 2025. Fortafil unsized carbon fiber was used to performed the experiment. The fiber was commercially surface treated and it was a polyacrylonitrile based carbon fiber with 3000 filament per strand. Epicure® 3370 was used as basic sizing chemical and dissolved in two types of solvent, ethanol and acetone for the comparison purpose. The single pull out test has been used to determine the influence of sizing on carbon fiber. The morphology of carbon fiber was observed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The apparent interfacial strength IFSS values determined by pull out test for the Epicure® 3370/ethanol sized carbon fiber pointed to a good interfacial behaviour compared to the Epicure® 3370/acetone sized carbon fiber. The Epicure® 3370/ethanol sizing agent was found to be effective in promoting adhesion because of the chemical reactions between the sizing and Epolam® 2025 during the curing process. From this work, it showed that sized carbon fiber using Epicure® 3370 with addition of ethanol give higher mechanical properties of carbon fiber in terms of shear strength and also provided a good adhesion between fiber and matrix compared to the sizing chemical that contain acetone as a solvent.

  18. Supramolecular Systems Behavior at the Air-Water Interface. Molecular Dynamic Simulation Study.

    NASA Astrophysics Data System (ADS)

    Sandoval, C.; Saavedra, M.; Gargallo, L.; Radić, D.

    2008-08-01

    Atomistic molecular dynamics simulation (MDS) was development to investigate the structural and dynamic properties of a monolayer of supramolecular systems. The simulations were performed at room temperature, on inclusion complexes (ICs) of α-cyclodextrin (CD) with poly(ethylene-oxide)(PEO), poly(ɛ-caprolactone)(PEC) and poly(tetrahydrofuran)(PTHF). The simulations were carried out for a surface area of 30Å. The trajectories of the MDS show that the system more stable was IC-PEC, being the less stable IC-PEO. The disordered monolayer for the systems was proved by the orientation correlation function and the radial distribution function between the polar groups of ICs and the water molecules. We found that the system IC-PEC was more stable that the systems IC-PTHF and IC-PEO.

  19. SUPRAMOLECULAR SYSTEMS BEHAVIOR AT THE AIR-WATER INTERFACE. MOLECULAR DYNAMIC SIMULATION STUDY

    SciTech Connect

    Sandoval, C.; Saavedra, M.; Gargallo, L.; Radic, D.

    2008-08-28

    Atomistic molecular dynamics simulation (MDS) was development to investigate the structural and dynamic properties of a monolayer of supramolecular systems. The simulations were performed at room temperature, on inclusion complexes (ICs) of {alpha}-cyclodextrin (CD) with poly(ethylene-oxide)(PEO), poly({epsilon}-caprolactone)(PEC) and poly(tetrahydrofuran)(PTHF). The simulations were carried out for a surface area of 30A ring . The trajectories of the MDS show that the system more stable was IC-PEC, being the less stable IC-PEO. The disordered monolayer for the systems was proved by the orientation correlation function and the radial distribution function between the polar groups of ICs and the water molecules. We found that the system IC-PEC was more stable that the systems IC-PTHF and IC-PEO.

  20. Determination of chain orientation in the monolayers of amino-acid-derived schiff base at the air-water interface using in situ infrared reflection absorption spectroscopy.

    PubMed

    Liu, Huijin; Miao, Wangen; Du, Xuezhong

    2007-10-23

    The chain orientation in the monolayers of amino-acid-derived Schiff base, 4-(4-dodecyloxy)-2-hydroxybenzylideneamino)benzoic acid (DSA), at the air-water interface has been determined using infrared reflection absorption spectroscopy (IRRAS). On pure water, a condensed monolayer is formed with the long axes of Schiff base segments almost perpendicular to the water surface. In the presence of metal ions (Ca2+, Co2+, Zn2+, Ni2+, and Cu2+) in the subphase, the monolayer is expanded and the long axes of the Schiff base segments are inclined with respect to the monolayer normal depending on metal ion. The monolayer thickness, which is an important parameter for quantitative determination of orientation of hydrocarbon chains, is composed of alkyl chains and salicylideneaniline portions for the DSA monolayers. The effective thickness of the Schiff base portions is roughly estimated in the combination of the IRRAS results and surface pressure-area isotherms for computer simulation, since the only two observable p- and s-polarized reflectance-absorbance (RA) values can be obtained. The alkyl chains with almost all-trans conformations are oriented at an angle of about 10 degrees for H2O, 15 degrees for Ca2+, 30 degrees for Co2+, 35 degrees -40 degrees for Zn2+, and 35 degrees -40 degrees for Ni2+ with respect to the monolayer normal. The chain segments linked with gauche conformers in the case of Cu2+ are estimated to be 40 degrees -50 degrees away from the normal. PMID:17902721

  1. Interfacial fracture between highly crosslinked polymer networks and a solid surface: Effect of interfacial bond density

    SciTech Connect

    STEVENS,MARK J.

    2000-03-23

    For highly crosslinked, polymer networks bonded to a solid surface, the effect of interfacial bond density as well as system size on interfacial fracture is studied molecular dynamics simulations. The correspondence between the stress-strain curve and the sequence of molecular deformations is obtained. The failure strain for a fully bonded surface is equal to the strain necessary to make taut the average minimal path through the network from the bottom solid surface to the top surface. At bond coverages less than full, nanometer scale cavities form at the surface yielding an inhomogeneous strain profile. The failure strain and stress are linearly proportional to the number of bonds at the interface unless the number of bonds is so few that van der Waals interactions dominate. The failure is always interfacial due to fewer bonds at the interface than in the bulk.

  2. Effect of cation enrichment on dipalmitoylphosphatidylcholine (DPPC) monolayers at the air-water interface.

    PubMed

    Adams, Ellen M; Casper, Clayton B; Allen, Heather C

    2016-09-15

    The effect of highly concentrated salt solutions of marine-relevant cations (Na(+), K(+), Mg(2+), and Ca(2+)) on Langmuir monolayers of dipalmitoylphosphatidylcholine (DPPC) was investigated by means of surface pressure-area isotherms, Brewster angle microscopy (BAM), and infrared reflection-absorption spectroscopy (IRRAS). It was found that monovalent cations and Mg(2+) have similar phase behavior, causing DPPC monolayers to expand, while Ca(2+) induces condensation. All cations disrupted the surface morphology at high cation concentration, resulting in decreased reflectivity from the monolayer. Monolayer refractive index was calculated from BAM image intensity in the liquid condensed phase and decreased with increasing cation concentration, which suggests that orientation of the alkyl chains change. Monovalent ions increase ordering of the alkyl chains, more than divalents, yet have little interaction with the DPPC headgroup. Mg(2+) induces gauche defects in the alkyl chain and increases headgroup hydration at low lipid coverage but increases chain ordering and dehydrates the headgroup at high lipid coverage. Ca(2+) orders alkyl chains and dehydrates the phosphate moiety, independent of lipid phase. At the highest salt concentration investigated, significant narrowing of the asymmetric PO2(-) vibrational mode occurs and is attributed to considerable dehydration of the DPPC headgroup. PMID:27322949

  3. Evaluation of Natural Radioactivity in Subsurface Air, Water and Soil in Western Japan

    SciTech Connect

    Fukui, Masami

    2008-08-07

    Surveys of radon concentrations in western Japan were carried out to estimate the contents not only of waters in the environment but also in soil gas. The maximum concentration measured for drinking water as public supply exceeded the 1991 United States Environmental Protection Agency-recommended limit for drinking water (11 Bq L{sup -1}) but did not exceed that of several European countries (100 Bq L{sup -1}). Overall, the concentrations of radon in subsurface water ranged from 1 to 100 Bq L{sup -1} and those in surface water were below 1 Bq L{sup -1} in a residential area. Fifty nine samples in soil gas at 4 Prefectures of the Kinki district were analyzed together with 19 samples of interest due to karst and uranium mining sites from another two Prefectures to compare with the above samples. The cumulative frequency of the {sup 222}Rn-concentrations both in environmental water and soil gas showed a log-normal distribution. Surveys of natural radioactivity in soils were also carried out with a Ge(Li) detector to determine the concentrations.

  4. Behavior of lysozyme adsorbed onto biological liquid crystal lipid monolayer at the air/water interface

    NASA Astrophysics Data System (ADS)

    Lu, Xiaolong; Shi, Ruixin; Hao, Changchun; Chen, Huan; Zhang, Lei; Li, Junhua; Xu, Guoqing; Sun, Runguang

    2016-09-01

    The interaction between proteins and lipids is one of the basic problems of modern biochemistry and biophysics. The purpose of this study is to compare the penetration degree of lysozyme into 1,2-diapalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoethano-lamine (DPPE) by analyzing the data of surface pressure-area (π-A) isotherms and surface pressure-time (π-T) curves. Lysozyme can penetrate into both DPPC and DPPE monolayers because of the increase of surface pressure at an initial pressure of 15 mN/m. However, the changes of DPPE are larger than DPPC, indicating stronger interaction of lysozyme with DPPE than DPPC. The reason may be due to the different head groups and phase state of DPPC and DPPE monolayers at the surface pressure of 15 mN/m. Atomic force microscopy reveals that lysozyme was absorbed by DPPC and DPPE monolayers, which leads to self-aggregation and self-assembly, forming irregular multimers and conical multimeric. Through analysis, we think that the process of polymer formation is similar to the aggregation mechanism of amyloid fibers. Project supported by the National Natural Science Foundation of China (Grant Nos. 21402114 and 11544009), the Natural Science Basic Research Plan in Shaanxi Province of China (Grant No. 2016JM2010), the Fundamental Research Funds for the Central Universities of China (Grant No. GK201603026), and the National University Science and Technology Innovation Project of China (Grant No. 201610718013).

  5. Weighing graphene with QCM to monitor interfacial mass changes

    NASA Astrophysics Data System (ADS)

    Kakenov, Nurbek; Balci, Osman; Salihoglu, Omer; Hur, Seung Hyun; Balci, Sinan; Kocabas, Coskun

    2016-08-01

    In this Letter, we experimentally determined the mass density of graphene using quartz crystal microbalance (QCM) as a mechanical resonator. We developed a transfer printing technique to integrate large area single-layer graphene on QCM. By monitoring the resonant frequency of an oscillating quartz crystal loaded with graphene, we were able to measure the mass density of graphene as ˜118 ng/cm2, which is significantly larger than the ideal graphene (˜76 ng/cm2) mainly due to the presence of wrinkles and organic/inorganic residues on graphene sheets. High sensitivity of the quartz crystal resonator allowed us to determine the number of graphene layers in a particular sample. Additionally, we extended our technique to probe interfacial mass variation during adsorption of biomolecules on graphene surface and plasma-assisted oxidation of graphene.

  6. Air-water greenhouse gases exchange in two coastal systems in Cadiz Bay (SW Spain)

    NASA Astrophysics Data System (ADS)

    Burgos, Macarena; Ortega, Teodora; Forja, Jesús

    2014-05-01

    Coastal areas are subject to a great anthropogenic pressure because more than half of the world's population lives in its vicinity, causing organic matter inputs, which intensifies greenhouse gas emissions into the atmosphere. Water surface greenhouse gas concentrations (CH4 and N2O) have been estimated in two aquatic systems of Cadiz Bay Natural Park: Rio San Pedro Creek and Sancti Petri Channel Water renewal in Rio San Pedro Creek is tidally controlled. Due to its little freshwater input, the Creek is essentially a marine system. Several fish farms are distributed on its banks discharging effluents without previous treatment. Nine sampling stations are distributed along this system 12 Km length. Sancti Petri Channel is a flow channel-ebb tides extending from the inner Cadiz Bay to the Atlantic Ocean along 17 Km. Organic matter pollution sources in this environment are straggly. There exist anthropogenic inputs such as aquaculture effluents and sewage discharges coming through the Iro River, which flows into the Channel central part. In addition there are natural organic matter inputs from surrounding marshes. It has been established 11 sampling stations crossing this system. Sampling was conducted seasonally during 2013. CH4 and N2O concentrations were obtained though a gas chromatograph connected to an equilibration system. Greenhouse gas values vary between 24 and 295 nM and 16 and 27 nM for CH4 and N2O, respectively. Gas concentrations increase close to the fish farm effluent in Rio San Pedro Creek, and next to Iro River's mouth in Sancti Petri tidal Channel. Both environments act as greenhouse gas sources into the atmosphere, showing seasonal variations. It has been estimated mean fluxes of 75.3 μmol m-2 d-1 of CH4 and 31.9 μmol m-2 d-1 of N2O for both systems.

  7. Behavior of lysozyme adsorbed onto biological liquid crystal lipid monolayer at the air/water interface

    NASA Astrophysics Data System (ADS)

    Lu, Xiaolong; Shi, Ruixin; Hao, Changchun; Chen, Huan; Zhang, Lei; Li, Junhua; Xu, Guoqing; Sun, Runguang

    2016-09-01

    The interaction between proteins and lipids is one of the basic problems of modern biochemistry and biophysics. The purpose of this study is to compare the penetration degree of lysozyme into 1,2-diapalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoethano-lamine (DPPE) by analyzing the data of surface pressure–area (π–A) isotherms and surface pressure–time (π–T) curves. Lysozyme can penetrate into both DPPC and DPPE monolayers because of the increase of surface pressure at an initial pressure of 15 mN/m. However, the changes of DPPE are larger than DPPC, indicating stronger interaction of lysozyme with DPPE than DPPC. The reason may be due to the different head groups and phase state of DPPC and DPPE monolayers at the surface pressure of 15 mN/m. Atomic force microscopy reveals that lysozyme was absorbed by DPPC and DPPE monolayers, which leads to self-aggregation and self-assembly, forming irregular multimers and conical multimeric. Through analysis, we think that the process of polymer formation is similar to the aggregation mechanism of amyloid fibers. Project supported by the National Natural Science Foundation of China (Grant Nos. 21402114 and 11544009), the Natural Science Basic Research Plan in Shaanxi Province of China (Grant No. 2016JM2010), the Fundamental Research Funds for the Central Universities of China (Grant No. GK201603026), and the National University Science and Technology Innovation Project of China (Grant No. 201610718013).

  8. Simulating the Vapour Phase Air/Water Exchange of p,p′-DDE, p,p′-DDT, Lindane, and 2,3,7,8-Tetrachlorodibenzodioxin

    EPA Science Inventory

    Uncertainties in our understanding of gaseous air/water exchange have emerged as major sources of concern in efforts to construct global and regional mass balances of both the green house gas carbon dioxide and semi-volatile persistent, bioaccumulative and toxic chemicals. Hoff e...

  9. DIFFUSIVE EXCHANGE OF GASEOUS POLYCYCLIC AROMATIC HYDROCARBONS AND POLYCHLORINATED BIPHENYLS ACROSS THE AIR-WATER INTERFACE OF THE CHESAPEAKE BAY. (R825245)

    EPA Science Inventory

    Dissolved and gas-phase concentrations of nine polycyclic aromatic hydrocarbons and 46 polychlorinated biphenyl congeners were measured at eight sites on the Chesapeake Bay at four different times of the year to estimate net diffusive air-water gas exchange rates. Gaseous PAHs ar...

  10. A Narrow Amide I Vibrational Band Observed by Sum Frequency Generation Spectroscopy Reveals Highly Ordered Structures of a Biofilm Protein at the Air/Water Interface†

    PubMed Central

    Wang, Zhuguang; Morales-Acosta, M. Daniela; Li, Shanghao; Liu, Wei; Kanai, Tapan; Liu, Yuting; Chen, Ya-Na; Walker, Frederick J.; Ahn, Charles H.; Leblanc, Roger M.

    2016-01-01

    We characterized BslA, a bacterial biofilm protein, at the air/water interface using vibrational sum frequency generation spectroscopy and observed one of the sharpest amide I band ever reported. Combining methods of surface pressure measurements, thin film X-ray reflectivity, and atomic force microscopy, we showed extremely ordered BslA at the interface. PMID:26779572

  11. Nanostructure and salt effect of zwitterionic carboxybetaine brush at the air/water interface.

    PubMed

    Matsuoka, Hideki; Yamakawa, Yuta; Ghosh, Arjun; Saruwatari, Yoshiyuki

    2015-05-01

    Zwitterionic amphiphilic diblock copolymer, poly(ethylhexyl acrylate)-b-poly(carboxybetaine) (PEHA-b-PGLBT), was synthesized by the reversible addition-fragmentation chain transfer (RAFT) method with precise control of block length and polydispersity. The polymers thus obtained were spread onto the water surface to form a polymer monolayer. The fundamental property and nanostructure of the block copolymer monolayer were systematically studied by the surface pressure-molecular area (π-A) isotherm, Brewster angle microscopy (BAM), and X-ray reflectivity (XR) techniques. The π values of the monolayer increased by compression in relatively larger A regions. After showing a large plateau region by compression, the π value sharply increased at very small A regions, suggesting the formation of poly(GLBT) brush formation just beneath the water surface. The domain structure of μm size was observed by BAM in the plateau region. XR profiles for the monolayer at higher surface pressure regions clearly showed the PGLBT brush formation in addition to PGLBT carpet layer formation under the hydrophobic PEHA layer on the water surface, as was observed for both anionic and cationic brush layer in the water surface monolayer studied previously. The critical brush density, where the PGLBT brush is formed, was estimated to be about 0.30 chains/nm(2) for the (EHA)45-b-(GLBT)60 monolayer, which is relatively large compared to other ionic brushes. This observation is consistent with the fact that the origin of brush formation is mainly steric hindrance between brush chains. The brush thickness increased by compression and also by salt addition, unlike the normal ionic brush (anionic and cationic), whose thickness tended to decrease, i.e., shrink, by salt addition. This might be a character unique to the zwitterionic brush, and its origin is thought to be transition to an ionic nature from the almost nonionic inner salt caused by salt addition since both the cation and anion of the

  12. Mercury in the Air, Water and Biota at the Great Salt Lake (Utah, USA)

    NASA Astrophysics Data System (ADS)

    Peterson, C.; Gustin, M. S.

    2008-12-01

    The Great Salt Lake, Utah (USA), is the fourth largest terminal lake on Earth and a stop-over location for 35 million birds on the Pacific Flyway. Recently, the Utah Department of Health and Utah Division of Wildlife Resources issued tissue mercury (Hg) consumption advisories for several species of birds that consume the lake's brine shrimp. Sources of Hg to the lake are the watershed and the atmosphere, and we hypothesized that the chemistry of the air above the Great Salt Lake would facilitate atmospheric deposition of Hg to the water. Because little information was available on Hg at the Great Salt Lake, and to begin to test this hypothesis, we measured atmospheric elemental (Hg0) and reactive gaseous mercury (RGM) concentrations as well as Hg concentrations in water and brine shrimp five times over a year. Surrogate surfaces and a dry deposition model were applied to estimate the amount of Hg that could be input to the lake surface. We found that atmospheric Hg0 and RGM concentrations were comparable to global ambient background values and those measured in rural areas (respectively). Both Hg0 and RGM exhibited regular diel variability, and no consistent seasonal periods of depleted or elevated values were observed. Based on these findings, local factors are thought to be important in generating elevated RGM concentrations that could be deposited to the lake. Model estimated deposition velocities for RGM to the lake ranged from 0.9 to 3.0 cm sec-1, with an estimated 19 kg of Hg deposited annually. Total Hg and methyl Hg concentrations in surface waters of the lake were consistent throughout the year (3.8 ± 0.8 ng L- 1 and 0.93 ± 0.59 ng L-1, respectively) and not significantly elevated relative to natural waters; however, the percent methyl Hg to total Hg was high (25 to 50%). Brine shrimp Hg concentrations were 384 ppb and had a statistically significant increase from early summer to fall. Based on modeled dry deposition and estimated wet deposition, the

  13. Phase Characteristics of 1-Monopalmitoyl-rac-glycerol Monolayers at the Air/Water Interface.

    PubMed

    Vollhardt, D; Brezesinski, G

    2016-07-26

    1-Monopalmitoyl-rac-glycerol is omnipresent in numerous biological and applied systems. Systematic GIXD measurements of 1-monopalmitoyl-rac-glycerol monolayers are carried out over a large pressure interval at 5, 10, and 15 °C to construct the phase diagram on the basis of reliable 2D lattice structures. These studies are complemented by other monolayer characteristics, such as π-A isotherms and mesoscopic domain topographies. A phase transition is found between the two orthorhombic structures with NN and NNN tilted alkyl chains at low temperatures (5 and 10 °C). It increases linearly with increasing temperature. With a further increase in temperature to 15 °C, only NN-tilted orthorhombic lattices are observed in the whole pressure region. The cross-sectional area, A0, is less affected by surface pressure and temperature and amounts to values of between 19.7 and 19.8 Å(2), as expected for a rotator phase at the lower limit. The tilt angle t with respect to the surface normal decreases with increasing pressure and is only slightly influenced by the temperature. The transition pressure to untilted alkyl chains, as determined by the extrapolation of 1/cos(t) to zero tilt angle, is >50 mN/m for all temperatures. The results of lattice distortion d versus sin 2(t) suggest for 10 and 15 °C the tilt of the aliphatic chains as the reason for the monolayer lattice distortion whereas at 5 °C the nonzero-tilt-angle intercept d0 could be an indication of the prevention of hexagonal packing. The generic π-T phase diagram of racemic monoacylglycerol monolayers is constructed on the basis of the phase diagrams of 1-monopalmitoyl-rac-glycerol and 1-monostearoyl-rac-glycerol, which shows that for 1-monopalmitoyl-rac-glycerol monolayers the oblique phase can occur only close to and below 0 °C. The possible phase behavior of other racemic monoacylglycerol monolayers with alkyl chain lengths of C14 and C20 is discussed on the basis of the generic phase diagram. PMID:27351635

  14. Phases, line tension and pattern formation in molecularly thin films at the air-water interface

    NASA Astrophysics Data System (ADS)

    Mandal, Pritam

    A Langmuir film, which is a molecularly thin insoluble film on a liquid substrate, is one practical realization of a quasi-two dimensional matter. The major advantages of this system for the study of phase separation and phase co-existence are (a) it allows accurate control of the components and molecular area of the film and (b) it can be studied by various methods that require very flat films. Phase separation in molecularly thin films plays an important role in a range of systems from biomembranes to biosensors. For example, phase-separated lipid nano-domains in biomembranes are thought to play crucial roles in membrane function. I use Brewster Angel Microscopy (BAM) coupled with Fluorescence Microscopy (FM) and static Light Scattering Microscopy (LSM) to image phases and patterns within Langmuir films. The three microscopic techniques --- BAM, FM and LSM --- are complimentary to each other, providing distinct sets of information. They allow direct comparison with literature results in lipid systems. I have quantitatively validated the use of detailed hydrodynamic simulations to determine line tension in monolayers. Line tension decreases as temperature rises. This decrease gives us information on the entropy associated with the line, and thus about line structure. I carefully consider the thermodynamics of line energy and entropy to make this connection. In the longer run, LSM will be exploited to give us further information about line structure. I have also extended the technique by testing it on domains within the curved surface of a bilayer vesicle. I also note that in the same way that the presence of surface-active agents, known as surfactants, affects surface energy, the addiction of line active agents alters the inter-phase line energy. Thus my results set to stage to systematically study the influence of line active agents ---'linactants' --- on the inter-phase line energy. Hierarchal self-assembled chiral patterns were observed as a function of

  15. Gaseous and Freely-Dissolved PCBs in the Lower Great Lakes Based on Passive Sampling: Spatial Trends and Air-Water Exchange.

    PubMed

    Liu, Ying; Wang, Siyao; McDonough, Carrie A; Khairy, Mohammed; Muir, Derek C G; Helm, Paul A; Lohmann, Rainer

    2016-05-17

    Polyethylene passive sampling was performed to quantify gaseous and freely dissolved polychlorinated biphenyls (PCBs) in the air and water of Lakes Erie and Ontario during 2011-2012. In view of differing physical characteristics and the impacts of historical contamination by PCBs within these lakes, spatial variation of PCB concentrations and air-water exchange across these lakes may be expected. Both lakes displayed statistically similar aqueous and atmospheric PCB concentrations. Total aqueous concentrations of 29 PCBs ranged from 1.5 pg L(-1) in the open lake of Lake Erie (site E02) in 2011 spring to 105 pg L(-1) in Niagara (site On05) in 2012 summer, while total atmospheric concentrations were 7.7-634 pg m(-3) across both lakes. A west-to-east gradient was observed for aqueous PCBs in Lake Erie. River discharge and localized influences (e.g., sediment resuspension and regional alongshore transport) likely dominated spatial trends of aqueous PCBs in both lakes. Air-water exchange fluxes of Σ7PCBs ranged from -2.4 (±1.9) ng m(-2) day(-1) (deposition) in Sheffield (site E03) to 9.0 (±3.1) ng m(-2) day(-1) (volatilization) in Niagara (site On05). Net volatilization of PCBs was the primary trend across most sites and periods. Almost half of variation in air-water exchange fluxes was attributed to the difference in aqueous concentrations of PCBs. Uncertainty analysis in fugacity ratios and mass fluxes in air-water exchange of PCBs indicated that PCBs have reached or approached equilibrium only at the eastern Lake Erie and along the Canadian shore of Lake Ontario sites, where air-water exchange fluxes dominated atmospheric concentrations.

  16. Gaseous and Freely-Dissolved PCBs in the Lower Great Lakes Based on Passive Sampling: Spatial Trends and Air-Water Exchange.

    PubMed

    Liu, Ying; Wang, Siyao; McDonough, Carrie A; Khairy, Mohammed; Muir, Derek C G; Helm, Paul A; Lohmann, Rainer

    2016-05-17

    Polyethylene passive sampling was perf