Effect of Surface Tension Anisotropy and Welding Parameters on Initial Instability Dynamics During Solidification: A Phase-Field Study

NASA Astrophysics Data System (ADS)

Yu, Fengyi; Wei, Yanhong

2018-05-01

The effects of surface tension anisotropy and welding parameters on initial instability dynamics during gas tungsten arc welding of an Al-alloy are investigated by a quantitative phase-field model. The results show that the surface tension anisotropy and welding parameters affect the initial instability dynamics in different ways during welding. The surface tension anisotropy does not influence the solute diffusion process but does affect the stability of the solid/liquid interface during solidification. The welding parameters affect the initial instability dynamics by varying the growth rate and thermal gradient. The incubation time decreases, and the initial wavelength remains stable as the welding speed increases. When welding power increases, the incubation time increases and the initial wavelength slightly increases. Experiments were performed for the same set of welding parameters used in modeling, and the results of the experiments and simulations were in good agreement.

Dynamics of a camphoric acid boat at the air-water interface

NASA Astrophysics Data System (ADS)

Akella, V. S.; Singh, Dhiraj K.; Mandre, Shreyas; Bandi, M. M.

2018-05-01

We report experiments on an agarose gel tablet loaded with camphoric acid (c-boat) spontaneously set into motion by surface tension gradients on the water surface. We observe three distinct modes of c-boat motion: harmonic mode where the c-boat speed oscillates sinusoidally in time, a steady mode where the c-boat maintains constant speed, and an intermittent mode where the c-boat maintains near-zero speed between sudden jumps in speed. Whereas all three modes have been separately reported before in different systems, controlled release of Camphoric Acid (CA) from the agarose gel matrix allowed the observation of all the three modes in the same system. These three modes are a result of a competition between the driving (surface tension gradients) and drag forces acting on the c-boat. Moreover we suggest that there exist two time scales corresponding to spreading of CA and boat motion and the mismatch of these two time scales give rise to the three modes in boat motion. We reproduced all the modes of motion by varying the air-water interfacial tension using Sodium Dodecyl Sulfate (SDS).

A thermodynamical model for the surface tension of silicate melts in contact with H2O gas

USGS Publications Warehouse

Colucci, Simone; Battaglia, Maurizio; Trigila, Raffaello

2016-01-01

Surface tension plays an important role in the nucleation of H2O gas bubbles in magmatic melts and in the time-dependent rheology of bubble-bearing magmas. Despite several experimental studies, a physics based model of the surface tension of magmatic melts in contact with H2O is lacking. This paper employs gradient theory to develop a thermodynamical model of equilibrium surface tension of silicate melts in contact with H2O gas at low to moderate pressures. In the last decades, this approach has been successfully applied in studies of industrial mixtures but never to magmatic systems. We calibrate and verify the model against literature experimental data, obtained by the pendant drop method, and by inverting bubble nucleation experiments using the Classical Nucleation Theory (CNT). Our model reproduces the systematic decrease in surface tension with increased H2O pressure observed in the experiments. On the other hand, the effect of temperature is confirmed by the experiments only at high pressure. At atmospheric pressure, the model shows a decrease of surface tension with temperature. This is in contrast with a number of experimental observations and could be related to microstructural effects that cannot be reproduced by our model. Finally, our analysis indicates that the surface tension measured inverting the CNT may be lower than the value measured by the pendant drop method, most likely because of changes in surface tension controlled by the supersaturation.

Dependence of surface tension on curvature obtained from a diffuse-interface approach

NASA Astrophysics Data System (ADS)

Badillo, Arnoldo; Lafferty, Nathan; Matar, Omar K.

2017-11-01

From a sharp-interface viewpoint, the surface tension force is f = σκδ (x -xi) n , where σ is the surface tension, κ the local interface curvature, δ the delta function, and n the unit normal vector. The numerical implementation of this force on discrete domains poses challenges that arise from the calculation of the curvature. The continuous surface tension force model, proposed by Brackbill et al. (1992), is an alternative, used commonly in two-phase computational models. In this model, δ is replaced by the gradient of a phase indicator field, whose integral across a diffuse-interface equals unity. An alternative to the Brackbill model are Phase-Field models, which do not require an explicit calculation of the curvature. However, and just as in Brackbill's approach, there are numerical errors that depend on the thickness of the diffuse interface, the grid spacing, and the curvature. We use differential geometry to calculate the leading errors in this force when obtained from a diffuse-interface approach, and outline possible routes to eliminate them. Our results also provide a simple geometrical explanation to the dependence of surface tension on curvature, and to the problem of line tension.

Nonequilibrium Interfacial Tension in Simple and Complex Fluids

NASA Astrophysics Data System (ADS)

Truzzolillo, Domenico; Mora, Serge; Dupas, Christelle; Cipelletti, Luca

2016-10-01

Interfacial tension between immiscible phases is a well-known phenomenon, which manifests itself in everyday life, from the shape of droplets and foam bubbles to the capillary rise of sap in plants or the locomotion of insects on a water surface. More than a century ago, Korteweg generalized this notion by arguing that stresses at the interface between two miscible fluids act transiently as an effective, nonequilibrium interfacial tension, before homogenization is eventually reached. In spite of its relevance in fields as diverse as geosciences, polymer physics, multiphase flows, and fluid removal, experiments and theoretical works on the interfacial tension of miscible systems are still scarce, and mostly restricted to molecular fluids. This leaves crucial questions unanswered, concerning the very existence of the effective interfacial tension, its stabilizing or destabilizing character, and its dependence on the fluid's composition and concentration gradients. We present an extensive set of measurements on miscible complex fluids that demonstrate the existence and the stabilizing character of the effective interfacial tension, unveil new regimes beyond Korteweg's predictions, and quantify its dependence on the nature of the fluids and the composition gradient at the interface. We introduce a simple yet general model that rationalizes nonequilibrium interfacial stresses to arbitrary mixtures, beyond Korteweg's small gradient regime, and show that the model captures remarkably well both our new measurements and literature data on molecular and polymer fluids. Finally, we briefly discuss the relevance of our model to a variety of interface-driven problems, from phase separation to fracture, which are not adequately captured by current approaches based on the assumption of small gradients.

Marangoni flow in an evaporating water droplet

NASA Astrophysics Data System (ADS)

Xu, Xuefeng; Luo, Jianbin

2007-09-01

Marangoni effect has been observed in many liquids, but its existence in pure water is still a debated problem. In the present work, the Marangoni flow in evaporating water droplets has been observed by using fluorescent nanoparticles. Flow patterns indicate that a stagnation point where the surface flow, the surface tension gradient, and the surface temperature gradient change their directions exists at the droplet surface. The deduced nonmonotonic variation of the droplet surface temperature, which is different from that in some previous works, is explained by a heat transfer model considering the adsorbed thin film of the evaporating liquid droplet.

A preview of a modular surface light scattering instrument with autotracking optics

NASA Technical Reports Server (NTRS)

Meyer, William V.; Tin, Padetha; Mann, J. Adin, Jr.; Cheung, H. Michael; Rogers, Richard B.; Lading, Lars

1994-01-01

NASA's Advanced Technology Development (ATD) program is sponsoring the development of a new generation of surface light scattering hardware. This instrument is designed to non-invasively measure the surface response function of liquids over a wide range of operating conditions while automatically compensating for a sloshing surface. The surface response function can be used to compute surface tension, properties of monolayers present, viscosity, surface tension gradient and surface temperature. The instrument uses optical and electronic building blocks developed for the laser light scattering program at NASA Lewis along with several unique surface light scattering components. The emphasis of this paper is the compensation for bulk surface motion (slosh). Some data processing background information is also included.

Understanding the Impact of Model Surfactants on Cloud Condensation Nuclei Activity of Sea Spray Aerosols

NASA Astrophysics Data System (ADS)

Forestieri, S.; Cappa, C. D.; Ruehl, C. R.; Bertram, T. H.; Staudt, S.; Kuborn, T.

2017-12-01

Aerosol impacts on cloud properties, also known as indirect effects, remain a major source of uncertainty in modeling global radiative forcing. Reducing this uncertainty necessitates better understanding of how aerosol chemical composition impacts the cloud-forming ability of aerosols. The presence of surfactants in aerosols can decrease the surface tension of activating droplets relative to water and lead to more efficient activation. The importance of this effect has been debated, but recent surface tension measurements of microscopic droplets indicate that surface tension is substantially depressed relative to water for lab-generated particles consisting of salt and a single organic species and for complex mixtures of organic matter. However, little work has been done on understanding how chemical complexity (i.e. interaction between different surfactant species) impacts surface tension for particles containing mixtures of surfactants. In this work, we quantified the surface tension of lab-generated aerosols containing surfactants that are commonly found in nascent sea spray aerosol (SSA) at humidities close to activation using a continuous flow stream-wise thermal gradient chamber (CFSTGC). Surface tension was quantified for particles containing single surfactant species and mixtures of these surfactants to investigate the role of chemical complexity on surface tension and molecular packing at the air-water interface. For all surfactants tested in this study, substantial surface tension depression (20-40 mN/m) relative to water was observed for particles containing large fractions of organic matter at humidities just below activation. However, the presence of these surfactants only weakly depressed surface tension at activation. Kinetic limitations were observed for particles coated with just palmitic acid, since palmitic acid molecules inhibit water uptake through their ability to pack tightly at the surface. However, these kinetic limitations disappeared when palmitic acid was mixed with oleic acid, indicating a disruption in packing. The impact of oxidation on droplet surface tension will also be discussed.

The physics of water droplets on surfaces: exploring the effects of roughness and surface chemistry

NASA Astrophysics Data System (ADS)

Eid, K. F.; Panth, M.; Sommers, A. D.

2018-03-01

This paper explores the fluid property commonly called surface tension, its effect on droplet shape and contact angle, and the major influences of contact angle behaviour (i.e. surface roughness and surface chemistry). Images of water droplets placed on treated copper surfaces are used to measure the contact angles between the droplets and the surface. The surface wettability is manipulated either by growing a self-assembled monolayer on the surface to make it hydrophobic or by changing the surface roughness. The main activities in this experiment, then, are (1) preparing and studying surfaces with different surface wettability and roughness; (2) determining the shape and contact angles of water droplets on these surfaces; and (3) demonstrating the spontaneous motion of water droplets using surface tension gradients.

Study of homogeneous bubble nucleation in liquid carbon dioxide by a hybrid approach combining molecular dynamics simulation and density gradient theory

NASA Astrophysics Data System (ADS)

Langenbach, K.; Heilig, M.; Horsch, M.; Hasse, H.

2018-03-01

A new method for predicting homogeneous bubble nucleation rates of pure compounds from vapor-liquid equilibrium (VLE) data is presented. It combines molecular dynamics simulation on the one side with density gradient theory using an equation of state (EOS) on the other. The new method is applied here to predict bubble nucleation rates in metastable liquid carbon dioxide (CO2). The molecular model of CO2 is taken from previous work of our group. PC-SAFT is used as an EOS. The consistency between the molecular model and the EOS is achieved by adjusting the PC-SAFT parameters to VLE data obtained from the molecular model. The influence parameter of density gradient theory is fitted to the surface tension of the molecular model. Massively parallel molecular dynamics simulations are performed close to the spinodal to compute bubble nucleation rates. From these simulations, the kinetic prefactor of the hybrid nucleation theory is estimated, whereas the nucleation barrier is calculated from density gradient theory. This enables the extrapolation of molecular simulation data to the whole metastable range including technically relevant densities. The results are tested against available experimental data and found to be in good agreement. The new method does not suffer from typical deficiencies of classical nucleation theory concerning the thermodynamic barrier at the spinodal and the bubble size dependence of surface tension, which is typically neglected in classical nucleation theory. In addition, the density in the center of critical bubbles and their surface tension is determined as a function of their radius. The usual linear Tolman correction to the capillarity approximation is found to be invalid.

Study of homogeneous bubble nucleation in liquid carbon dioxide by a hybrid approach combining molecular dynamics simulation and density gradient theory.

PubMed

Langenbach, K; Heilig, M; Horsch, M; Hasse, H

2018-03-28

A new method for predicting homogeneous bubble nucleation rates of pure compounds from vapor-liquid equilibrium (VLE) data is presented. It combines molecular dynamics simulation on the one side with density gradient theory using an equation of state (EOS) on the other. The new method is applied here to predict bubble nucleation rates in metastable liquid carbon dioxide (CO 2 ). The molecular model of CO 2 is taken from previous work of our group. PC-SAFT is used as an EOS. The consistency between the molecular model and the EOS is achieved by adjusting the PC-SAFT parameters to VLE data obtained from the molecular model. The influence parameter of density gradient theory is fitted to the surface tension of the molecular model. Massively parallel molecular dynamics simulations are performed close to the spinodal to compute bubble nucleation rates. From these simulations, the kinetic prefactor of the hybrid nucleation theory is estimated, whereas the nucleation barrier is calculated from density gradient theory. This enables the extrapolation of molecular simulation data to the whole metastable range including technically relevant densities. The results are tested against available experimental data and found to be in good agreement. The new method does not suffer from typical deficiencies of classical nucleation theory concerning the thermodynamic barrier at the spinodal and the bubble size dependence of surface tension, which is typically neglected in classical nucleation theory. In addition, the density in the center of critical bubbles and their surface tension is determined as a function of their radius. The usual linear Tolman correction to the capillarity approximation is found to be invalid.

Surface Tension Mediated Conversion of Light to Work

PubMed Central

Okawa, David; Pastine, Stefan J.; Zettl, Alex; Fréchet, Jean M. J.

2009-01-01

As energy demands increase, new, more direct, energy collection and utilization processes must be explored. We present a system that intrinsically combines the absorption of sunlight with the production of useful work in the form of locomotion of objects on liquids. Focused sunlight is locally absorbed by a nanostructured composite, creating a thermal surface tension gradient and, subsequently, motion. Controlled linear motion and rotational motion are demonstrated. The system is scale independent, with remotely powered and controlled motion shown for objects in the milligram to tens of grams range. PMID:20560635

Influence of aspect and slope gradient on hydraulic conductivity measured by tension infiltrometer

NASA Astrophysics Data System (ADS)

Casanova, Manuel; Messing, Ingmar; Joel, Abraham

2000-01-01

A tension infiltrometer technique was used to characterize differences in hydraulic conductivity (K) in two rain-fed hillsides (north-facing and south-facing) in central Chile. For the north-facing locations, smaller values of K (at a range of supply water pressure heads ) compared with south-facing locations were found, with accentuated differences close to saturation (zero pressure head). The differences were attributed to differences in texture and organic matter contents observed for the two sites. Furthermore, K() had a tendency to increase with increasing slope gradient. This tendency was to an extent explained by the deviation from requirements of measurements on level ground. The differences found in K() between different slope gradients were explained by the differences in the vertical and lateral hydraulic conductivity and by the occurrence of surface sealing in low slope plots.

Changes in air flow patterns using surfactants and thickeners during air sparging: bench-scale experiments.

PubMed

Kim, Juyoung; Kim, Heonki; Annable, Michael D

2015-01-01

Air injected into an aquifer during air sparging normally flows upward according to the pressure gradients and buoyancy, and the direction of air flow depends on the natural hydrogeologic setting. In this study, a new method for controlling air flow paths in the saturated zone during air sparging processes is presented. Two hydrodynamic parameters, viscosity and surface tension of the aqueous phase in the aquifer, were altered using appropriate water-soluble reagents distributed before initiating air sparging. Increased viscosity retarded the travel velocity of the air front during air sparging by modifying the viscosity ratio. Using a one-dimensional column packed with water-saturated sand, the velocity of air intrusion into the saturated region under a constant pressure gradient was inversely proportional to the viscosity of the aqueous solution. The air flow direction, and thus the air flux distribution was measured using gaseous flux meters placed at the sand surface during air sparging experiments using both two-, and three-dimensional physical models. Air flow was found to be influenced by the presence of an aqueous patch of high viscosity or suppressed surface tension in the aquifer. Air flow was selective through the low-surface tension (46.5 dyn/cm) region, whereas an aqueous patch of high viscosity (2.77 cP) was as an effective air flow barrier. Formation of a low-surface tension region in the target contaminated zone in the aquifer, before the air sparging process is inaugurated, may induce air flow through the target zone maximizing the contaminant removal efficiency of the injected air. In contrast, a region with high viscosity in the air sparging influence zone may minimize air flow through the region prohibiting the region from de-saturating. Copyright © 2014 Elsevier B.V. All rights reserved.

Micro-channel filling flow considering surface tension effect

NASA Astrophysics Data System (ADS)

Kim, Dong Sung; Lee, Kwang-Cheol; Kwon, Tai Hun; Lee, Seung S.

2002-05-01

Understanding filling flow into micro-channels is important in designing micro-injection molding, micro-fluidic devices and an MIMIC (micromolding in capillaries) process. In this paper, we investigated, both experimentally and numerically, 'transient filling' flow into micro-channels, which differs from steady-state completely 'filled' flow in micro-channels. An experimental flow visualization system was devised to facilitate observation of flow characteristics in filling into micro-channels. Three sets of micro-channels of various widths of different thicknesses (20, 30, and 40 μm) were fabricated using SU-8 on the silicon substrate to find a geometric effect with regard to pressure gradient, viscous force and, in particular, surface tension. A numerical analysis system has also been developed taking into account the surface tension effect with a contact angle concept. Experimental observations indicate that surface tension significantly affects the filling flow to such an extent that even a flow blockage phenomenon was observed at channels of small width and thickness. A numerical analysis system also confirms that the flow blockage phenomenon could take place due to the flow hindrance effect of surface tension, which is consistent with experimental observation. For proper numerical simulations, two correction factors have also been proposed to correct the conventional hydraulic radius for the filling flow in rectangular cross-sectioned channels.

Biomimicry and the culinary arts.

PubMed

Burton, Lisa J; Cheng, Nadia; Vega, César; Andrés, José; Bush, John W M

2013-12-01

We present the results of a recent collaboration between scientists, engineers and chefs. Two particular devices are developed, both inspired by natural phenomena reliant on surface tension. The cocktail boat is a drink accessory, a self-propelled edible boat powered by alcohol-induced surface tension gradients, whose propulsion mechanism is analogous to that employed by a class of water-walking insects. The floral pipette is a novel means of serving small volumes of fluid in an elegant fashion, an example of capillary origami modeled after a class of floating flowers. The biological inspiration and mechanics of these two devices are detailed, along with the process that led to their development and deployment.

Molecular assembly, interfacial rheology and foaming properties of oligofructose fatty acid esters.

PubMed

van Kempen, Silvia E H J; Schols, Henk A; van der Linden, Erik; Sagis, Leonard M C

2014-01-01

Two major types of food-grade surfactants used to stabilize foams are proteins and low molecular weight (LMW) surfactants. Proteins lower the surface tension of interfaces and tend to unfold and stabilize the interface by the formation of a visco-elastic network, which leads to high surface moduli. In contrast, LMW surfactants lower the surface tension more than proteins, but do not form interfaces with a high modulus. Instead, they stabilize the interface through the Gibbs-Marangoni mechanism that relies on rapid diffusion of surfactants, when surface tension gradients develop as a result of deformations of the interface. A molecule than can lower the surface tension considerably, like a LMW surfactant, but also provide the interface with a high modulus, like a protein, would be an excellent foam stabilizer. In this article we will discuss molecules with those properties: oligofructose fatty acid esters, both in pure and mixed systems. First, we will address the synthesis and structural characterization of the esters. Next, we will address self-assembly and rheological properties of air/water interfaces stabilized by the esters. Subsequently, this paper will deal with mixed systems of mono-esters with either di-esters and lauric acid, or proteins. Then, the foaming functionality of the esters is discussed.

Microgravity

NASA Image and Video Library

1998-12-01

The Magnetically Damped Furnace (MDF) breadboard is being developed in response to NASA's mission and goals to advance the scientific knowledge of microgravity research, materials science, and related technologies. The objective of the MDF is to dampen the fluid flows due to density gradients and surface tension gradients in conductive melts by introducing a magnetic field during the sample processing. The MDF breadboard will serve as a proof of concept that the MDF performance requirements can be attained within the International Space Station resource constraints.

Surface tension and density of liquid In-Sn-Zn alloys

NASA Astrophysics Data System (ADS)

Pstruś, Janusz

2013-01-01

Using the dilatometric method, measurements of the density of liquid alloys of the ternary system In-Sn-Zn in four sections with a constant ratio Sn:In = 24:1, 3:1, 1:1, 1:3, for various Zn additions (5, 10, 14, 20, 3 5, 50 and 75 at.% Zn) were performed at the temperature ranges of 500-1150 K. Density decreases linearly for all compositions. The molar volume calculated from density data exhibits close to ideal dependence on composition. Measurements of the surface tension of liquid alloys have been conducted using the method of maximum pressure in the gas bubbles. There were observed linear dependences on temperature with a negative gradients dσ/dT. Generally, with two exceptions, there was observed the increase of surface tension with increasing content of zinc. Using the Butler's model, the surface tension isotherms were calculated for temperatures T = 673 and 1073 K. Calculations show that only for high temperatures and for low content of zinc (up to about 35 at.%), the modeling is in very good agreement with experiment. Using the mentioned model, the composition of the surface phase was defined at two temperatures T = 673 and 973 K. Regardless of the temperature and of the defined section, the composition of the bulk is very different in comparison with the composition of the surface.

Method and apparatus for monitoring and measuring the surface tension of a fluid using fiber optics

DOEpatents

Abraham, Bernard M.; Ketterson, John B.; Bohanon, Thomas M.; Mikrut, John M.

1994-01-01

A non-contact method and apparatus for measuring and monitoring the surface of a fluid using fiber optics and interferometric detection to permit measurement mechanical characteristics' fluid surfaces. The apparatus employs an alternating electric field gradient for generating a capillary wave on the surface of the fluid. A fiber optic coupler and optical fiber directs a portion of a laser beam onto the surface of the fluid, another portion of the laser beam onto the photo sensor, and directs light reflected from the surface of the fluid onto the photo sensor. The output of the photo sensor is processed and coupled to a phase sensitive detector to permit measurement of phase shift between the drive signal creating the capillary wave and the detected signal. This phase shift information is then used to determine mechanical properties of the fluid surface such as surface tension, surface elasticity, and surface inhomogeneity. The resulting test structure is easily made compact, portable, and easy to align and use.

Thermally induced delay and reversal of liquid film dewetting on chemically patterned surfaces.

PubMed

Kalpathy, Sreeram K; Francis, Lorraine F; Kumar, Satish

2013-10-15

A thin liquid film resting on a solid substrate that is heated or cooled from below experiences surface tension gradients, which lead to Marangoni flows. We explore the behavior of such a film on a chemically patterned substrate which drives film dewetting in order to determine how surface patterning and applied temperature gradients can be designed to influence the behavior of thin-film coatings. A nonlinear partial differential equation for the film height based on lubrication theory is solved numerically for a broad range of problem parameters. Uniform cooling of the substrate is found to significantly delay dewetting that is driven by wettability gradients. Uniform heating speeds up dewetting but can destroy the near-perfect templating imposed by the surface patterning. However, localized heating and cooling together can accelerate dewetting while maintaining templating quality. Localized heating and cooling can also be used to drive liquid onto areas that it would dewet from in the absence of heating. Overall, these results indicate that applied temperature gradients can significantly influence dewetting driven by surface patterning, and suggest strategies for the creation of spatially patterned thin-film coatings and flow control in microfluidic devices. Copyright © 2013 Elsevier Inc. All rights reserved.

Tears of Wine

ERIC Educational Resources Information Center

Gugliotti, Marcos

2004-01-01

The unique occurrence of the upward motion of a thin film of wine, and its formation into drops inside the wall of a wine glass is explained. Evaporation of alcohol generates a surface tension gradient, moving the film of wine upwards on the internal sides of a wine glass, where it collects and forms into drops or tears.

Thin film instabilities: Rayleigh-Taylor with thermocapillarity and Kolmogorov flow in a soap film

NASA Astrophysics Data System (ADS)

Burgess, John Matthew

The Rayleigh-Taylor instability occurs when a more dense fluid layer is suspended above a less dense fluid layer in a gravitational field. The horizontal interface between the two fluids is unstable to infinitesimal deformations and the dense fluid falls. To counteract the destabilizing effects of gravity on the interface between two thin fluid layers, we apply a vertical temperature gradient, heating from below. The dependence of surface tension on temperature (``thermocapillarity'') can cause spatially-varying interfacial forces between two immiscible fluid layers if a variation in temperature along the interface is introduced. With an applied vertical temperature gradient, the deforming interface spontaneously develops temperature variations which locally adjust the surface tension to restore a flat interface. We find that these surface tension gradients can stabilize a more dense thin fluid layer (silicone oil, 0.015 cm thick) above a less dense thin fluid layer (air, 0.025 cm thick) in a gravitational field, in qualitative agreement with linear stability analysis. This is the first experimental observation of the stabilization of Rayleigh-Taylor instability by thermocapillary forces. We also examine the instability of a soap film flow driven by a time-independent force that is spatially periodic in the direction perpendicular to the forcing (Kolmogorov flow). The film is in the x- y plane, where the forcing approximates a shape sin (y)x̂. Linear stability analysis of an idealized model of this flow predicts a critical Reynolds number Rc~2 . In our soap film experiment, we find a critical value Rc~70 . This discrepancy can be ascribed to frictional effects from viscous coupling of gas to the film, which is neglected in the idealized model. The kinematic viscosity of the surrounding gas and the thickness of gas layers on each side of the soap film are varied in the experiments to better understand these frictional effects. We conclude that flows in soap films cannot be decoupled from flows in the surrounding gas.

Cyclic Fatigue Durability of Uncoated and EBC Coated 3D SiC/SiC Composites Under Thermal Gradient Conditions at 2700F in Air

NASA Technical Reports Server (NTRS)

Smith, Craig; Harder, Bryan; Zhu, Dongming; Bhatt, Ramakrishna; Kalluri, Sreeramesh

2017-01-01

Ceramic matrix composites (CMCs) such as SiC/SiC are currently being designed and implemented in high temperature sections of aerospace turbine engines. Such components will be subject to through-thickness thermal gradients, which may affect the durability. In this study, SiC/SiC CMCs with a hybrid chemical vapor infiltrated (CVI) and polymer infiltration and pyrolysis (PIP) matrix were loaded in tension while one surface was heated with a laser and the opposite surface was cooled. Issues associated with laser testing will be discussed, along with initial results for coated and uncoated samples.

Similar solutions of double-diffusive dissipative layers along free surfaces

NASA Astrophysics Data System (ADS)

Napolitano, L. G.; Viviani, A.; Savino, R.

1990-10-01

Free convection due to buoyant forces (natural convection) and surface tension gradients (Marangoni convection) generated by temperature and concentration gradients is discussed together with the formation of double-diffusive boundary layers along liquid-gas interfaces. Similarity solutions for each class of free convection are derived and the resulting nonlinear two-point problems are solved numerically using the quasi-linearization method. Velocity, temperature, concentration profiles, interfacial velocity, heat and mass transfer bulk coefficients for various Prandtl and Schmidt numbers, and different values of the similarity parameters are determined. The convective flows are of particular interest because they are considered to influence the processes of crystal growth, both on earth and in a microgravity environment.

Guiding automated left ventricular chamber segmentation in cardiac imaging using the concept of conserved myocardial volume.

PubMed

Garson, Christopher D; Li, Bing; Acton, Scott T; Hossack, John A

2008-06-01

The active surface technique using gradient vector flow allows semi-automated segmentation of ventricular borders. The accuracy of the algorithm depends on the optimal selection of several key parameters. We investigated the use of conservation of myocardial volume for quantitative assessment of each of these parameters using synthetic and in vivo data. We predicted that for a given set of model parameters, strong conservation of volume would correlate with accurate segmentation. The metric was most useful when applied to the gradient vector field weighting and temporal step-size parameters, but less effective in guiding an optimal choice of the active surface tension and rigidity parameters.

Thermodiffusion as a means to manipulate liquid film dynamics on chemically patterned surfaces

PubMed Central

Kalpathy, Sreeram K.; Shreyes, Amrita Ravi

2017-01-01

The model problem examined here is the stability of a thin liquid film consisting of two miscible components, resting on a chemically patterned solid substrate and heated from below. In addition to surface tension gradients, the temperature variations also induce gradients in the concentration of the film by virtue of thermodiffusion/Soret effects. We study the stability and dewetting behaviour due to the coupled interplay between thermal gradients, Soret effects, long-range van der Waals forces, and wettability gradient-driven flows. Linear stability analysis is first employed to predict growth rates and the critical Marangoni number for chemically homogeneous surfaces. Then, nonlinear simulations are performed to unravel the interfacial dynamics and possible locations of the film rupture on chemically patterned substrates. Results suggest that appropriate tuning of the Soret parameter and its direction, in conjunction with either heating or cooling, can help manipulate the location and time scales of the film rupture. The Soret effect can either potentially aid or oppose film instability depending on whether the thermal and solutal contributions to flow are cooperative or opposed to each other. PMID:28595391

Counter-current thermocapillary migration of bubbles in self-rewetting liquids

NASA Astrophysics Data System (ADS)

Nazareth, R.; Saenz, P.; Sefiane, K.; Kim, J.; Valluri, P.

2016-11-01

In this work, we study the counter-current thermocapillary propulsion of a suspended bubble in the fluid flowing inside a channel subject to an axial temperature gradient when the surface tension dependence on temperature is non-monotonic. We use direct numerical simulations to address the two-phase conservation of mass, momentum and energy with a volume-of-fluid method to resolve the deformable interface. Two distinct regimes of counter-current bubble migration are characterized: i) "exponential decay" where the bubble decelerates rapidly until it comes to a halt at the spatial position corresponding to the minimum surface tension and ii) "sustained oscillations" where the bubble oscillates about the point of minimum surface tension. We illustrate how these sustained oscillations arise at low capillary number O(10-5) and moderate Reynolds number O(10) and, they are dampened by viscosity at lower Reynolds number. These results are in agreement with the experiments by Shanahan and Sefiane (Sci. Rep. 4, 2014). The work was supported by the Science without Borders program from CAPES agency of Brazilian Ministry of Education and the European Commission's Thermapower Project (294905).

Surface Tension Induced Instabilities in Reduced Gravity: the Benard Problem

NASA Technical Reports Server (NTRS)

Koschmieder, E.; Chai, A. T.

1985-01-01

A Benard convection experiment has been set up, and the onset of convection in shallow layers of silicone oil two millimeters or less deep has been studied. The onset has been observed visually or has been determined by the break in the heat transfer curve which accompanies the onset of convection. The outcome of these experiments has been very surprising, from the point of view of theoretical expectations. The onset of convection at temperature differences far below the critical value for fluid depths smaller than 2mm was observed. The discrepancy between experiments and theory increases with decreasing fluid depth. According to theoretical considerations, the effects of surface tension become more important as the fluid depth is decreased. Actually, one observes that the onset of convection tales place in two stages. There is first an apparently surface tension driven instability, occuring at subcritical temperature differences according to conventional theory. If then the temperature difference is increased, a second instability occurs which transform the first pattern into conventional strong hexagonal Benard cells. The second instability is in agreement with the critical temperature gradients predicted by Nield.

Marangoni Effects of a Drop in an Extensional Flow: The Role of Surfactant Physical Chemistry

NASA Technical Reports Server (NTRS)

Stebe, Kathleen J.; Balasubramaniam, R. (Technical Monitor)

2002-01-01

While the changes in stresses caused by surfactant adsorption on non-deforming interfaces have been fairly well established, prior to this work, there were few studies addressing how surfactants alter stresses on strongly deforming interfaces. We chose the model problem of a drop in a uniaxial extensional flow to study these stress conditions To model surfactant effects at fluid interfaces, a proper description of the dependence of the surface tension on surface concentration, the surface equation of state, is required. We have adopted a surface equation of state that accounts for the maximum coverage limit; that is, because surfactants have a finite cross sectional area, there is an upper bound to the amount of surfactant that can adsorb in a monolayer. The surface tension reduces strongly only when this maximum coverage is approached. Since the Marangoni stresses go as the derivative of the surface equation of state times the surface concentration gradient, the non-linear equation of state determines both the effect of surfactants in the normal stress jump, (which is balanced by the product of the mean curvature of the interface times the surface tension), and the tangential stress jump, which is balanced by Marangoni stresses. First, the effects of surface coverage and intermolecular interactions among surfactants which drive aggregation of surfactants in the interface were studied. (see Pawar and Stebe, Physics of Fluids).

A Theoretical Study of Remobilizing Surfactant Retarded Fluid Particle Interfaces

NASA Technical Reports Server (NTRS)

Wang, Yanping; Papageorgiou, Dimitri; Maldarelli, Charles

1996-01-01

Microgravity processes must rely on mechanisms other than bouyancy to move bubbles or droplets from one region to another in a continuous liquid phase. One suggested method is thermocapillary migration in which a temperature gradient is applied to the continuous phase. When a fluid particle contacts this gradient, one pole of the particle becomes warmer than the opposing pole. The interfacial tension between the drop or bubble phase and the continuous phase usually decreases with temperature. Thus the cooler pole is of higher interfacial tension than the warmer pole, and the interface is tugged in the direction of the cooler end. This thermocapillary or thermally induced Marangoni surface stress causes a fluid streaming in the continuous phase from which develops a viscous shear traction and pressure gradient which together propel the particle in the direction of the warmer fluid. In this paper, we provide a theoretical basis for remobilizing surfactant retarded fluid particle interfaces in an effort to make viable the use of thermocapillary migrations for the management of bubbles and drops in microgravity,

Method and apparatus for monitoring and measuring the surface tension of a fluid using fiber optics

DOEpatents

Abraham, B.M.; Ketterson, J.B.; Bohanon, T.M.; Mikrut, J.M.

1994-04-12

A non-contact method and apparatus are described for measuring and monitoring the surface of a fluid using fiber optics and interferometric detection to permit measurement of mechanical characteristics of fluid surfaces. The apparatus employs an alternating electric field gradient for generating a capillary wave on the surface of the fluid. A fiber optic coupler and optical fiber directs a portion of a laser beam onto the surface of the fluid, another portion of the laser beam onto the photo sensor, and directs light reflected from the surface of the fluid onto the photo sensor. The output of the photo sensor is processed and coupled to a phase sensitive detector to permit measurement of phase shift between the drive signal creating the capillary wave and the detected signal. This phase shift information is then used to determine mechanical properties of the fluid surface such as surface tension, surface elasticity, and surface inhomogeneity. The resulting test structure is easily made compact, portable, and easy to align and use. 4 figures.

Initial Investigation of a Novel Thermal Storage Concept as Part of a Renewable Energy System

DTIC Science & Technology

2013-06-01

stress (pascal) z-component of shear stress (pascal) Fslip constant Esl ip constant surface tension gradient (n/m-k) specularity coefficient...Axis x-component of ¥-Component of z- component of x -component of v-component of z-component of Fs l ip constant Esl i p constant Rotation

Binary breath figures for straightforward and controllable self-assembly of microspherical caps.

PubMed

Gong, Jianliang; Xu, Bingang; Tao, Xiaoming; Li, Lei

2016-05-11

The intense interest surrounding asymmetrical microparticles originates from their unique anisotropic properties and promising applications. In this work, direct self-assembly of polymeric microspherical caps without the assistance of any additives has been achieved by using low-surface-tension methanol (MeOH) and high-surface-tension water as binary breath figures (BFs). With the evaporation of polystyrene (PS) solution containing low-boiling-point solvent in the binary vapors, the formed MeOH BFs could quickly diffuse into solution, while water BFs tended to remain at the solution surface. This led to the formation of a gradient nonsolvent layer at the vapor/solution interface, which induced the formation of nuclei and guided further asymmetrical growth of polymer particles. After the spontaneous removal of MeOH, water and residual solvent by evaporation, polymeric microspherical caps were left on the substrate. Through controlling the proportion of water introduced by adjusting the ratios of MeOH and water, polymeric microspherical caps with a range of controllable shapes (divided at different positions of a sphere) were successfully obtained. The formation mechanism was explained based on the difference of vapor pressure, surface tension and miscibility between the employed solvents and nonsolvents. A solvent possessing a high vapor pressure, low surface tension and good miscibility with MeOH contributed to the formation of microspherical caps. This flexible, green and straightforward technique is a nondestructive strategy, and avoids complicated work on design, preparation and removal of hard templates and additives.

Mathematical modelling of convective processes in a weld pool under electric arc surfacing

NASA Astrophysics Data System (ADS)

Sarychev, V. D.; Granovskii, A. Yu; Nevskii, S. A.; Konovalov, S. V.

2017-01-01

The authors develop the mathematical model of convective processes in a molten pool under electric arc surfacing with flux-cored wire. The model is based on the ideas of how convective flows appear due to temperature gradient and action of electromagnetic forces. Influence of alloying elements in the molten metal was modeled as a non-linear dependence of surface tension upon temperature. Surface tension and its temperature coefficient were calculated according to the electron density functional method with consideration to asymmetric electron distribution at the interface “molten metal / shielding gas”. Simultaneous solution of Navier-Stokes and Maxwell equations according to finite elements method with consideration to the moving heat source at the interface showed that there is a multi-vortex structure in the molten metal. This structure gives rise to a downward heat flux which, at the stage of heating, moves from the centre of the pool and stirs it full width. At the cooling stage this flux moves towards the centre of the pool and a single vortex is formed near the symmetry centre. This flux penetration is ∼ 10 mm. Formation of the downward heat flux is determined by sign reversal of the temperature coefficient of surface tension due to the presence of alloying elements.

Propelling a water drop with the vapor-mediated Marangoni effect

NASA Astrophysics Data System (ADS)

Kim, Seungho; Kim, Ho-Young

2013-11-01

We show that a water drop on solid surfaces can be propelled just by placing a volatile alcohol drop nearby. It is found to be because the water-air interface near the alcohol drop mixes with alcohol vapor, thereby locally lowering the surface tension. The surface-tension-gradient induces the motion of the water drop, enabling the trajectory control of water drops through the motion of remote alcohol drops. This vapor-mediated Marangoni effect also gives rise to other interesting interfacial flow phenomena, such as nucleation of holes on a water film and ballooning of a water drop hanging from a syringe needle with the approach of an alcohol drop. We visualize such interfacial dynamics with a high-speed camera and rationalize their salient features by scaling analysis. This work was supported by the National Research Foundation of Korea (grant no. 2012-008023).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu Yong; Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996; Liu Fengxiao

Cemented carbides with a functionally graded structure have significantly improved mechanical properties and lifetimes in cutting, drilling and molding. In this work, WC-6 wt.% Co cemented carbides with three-layer graded structure (surface layer rich in WC, mid layer rich in Co and the inner part of the average composition) were prepared by carburizing pre-sintered {eta}-phase-containing cemented carbides. The three-point bending fatigue tests based on the total-life approach were conducted on both WC-6wt%Co functionally graded cemented carbides (FGCC) and conventional WC-6wt%Co cemented carbides. The functionally graded cemented carbide shows a slightly higher fatigue limit ({approx}100 MPa) than the conventional ones undermore » the present testing conditions. However, the fatigue crack nucleation behavior of FGCC is different from that of the conventional ones. The crack nucleates preferentially along the Co-gradient and perpendicular to the tension surface in FGCC, while parallel to the tension surface in conventional cemented carbides.« less

System noise analysis of the dumbbell tethered satellite for gravity-gradient measurements

NASA Technical Reports Server (NTRS)

Colombo, G.

1979-01-01

An analysis of the dumbbell gravity gradiometer concept for measuring short wavelength variations in the earth's gravity gradient is presented. Variations in the gradient are recorded by measuring tension variations in a vertically stabilized satellite consisting of heavy masses connected by a long wire or rod. Tension noise arises from the excitation of various mechanical oscillations of the system. The principal noise sources that were identified are fluctuations in atmospheric drag heating and drag force resulting from density variations and winds. Approximate analytical expressions are presented for the tension noise as a function of the system design parameters for various possible configurations. Computer simulations using numerical integration were performed to study the tension noise for several sample cases. Three designs consistent with Shuttle launch capabilities are discussed.

Cyclic Fatigue Durability of Uncoated and EBC Coated 3D SiC/SiC Composites Under Thermal Gradient Conditions at 2700F in Air

NASA Technical Reports Server (NTRS)

Smith, Craig; Harder, Bryan; Zhu, Dongming; Bhatt, Ramakrishna; Kalluri, Sreeramesh

2017-01-01

Ceramic matrix composites (CMCs) such as SiCSiC are currently being designed and implemented in high temperature sections of aerospace turbine engines. Such components will be subject to through-thickness thermal gradients, which may affect the durability. In this study, SiCSiC CMCs with a hybrid chemical vapor infiltrated (CVI) and polymer infiltration and pyrolysis (PIP) matrix were loaded in tension while one surface was heated with a laser and the opposite surface was cooled. The samples were each coated with an environmental barrier coating (EBC), which was produced by electron beam physical deposition (EBPVD). Results for CMCs tested with and without the EBC be discussed.

Droplet Deformation in an Extensional Flow: The Role of Surfactant Physical Chemistry

NASA Technical Reports Server (NTRS)

Stebe, Kathleen J.

1996-01-01

Surfactant-induced Marangoni effects strongly alter the stresses exerted along fluid particle interfaces. In low gravity processes, these stresses can dictate the system behavior. The dependence of Marangoni effects on surfactant physical chemistry is not understood, severely impacting our ability to predict and control fluid particle flows. A droplet in an extensional flow allows the controlled study of stretching and deforming interfaces. The deformations of the drop allow both Marangoni stresses, which resist tangential shear, and Marangoni elasticities, which resist surface dilatation, to develop. This flow presents an ideal model system for studying these effects. Prior surfactant-related work in this flow considered a linear dependence of the surface tension on the surface concentration, valid only at dilute surface concentrations, or a non-linear framework at concentrations sufficiently dilute that the linear approximation was valid. The linear framework becomes inadequate for several reasons. The finite dimensions of surfactant molecules must be taken into account with a model that includes surfaces saturation. Nonideal interactions between adsorbed surfactant molecules alter the partitioning of surfactant between the bulk and the interface, the dynamics of surfactant adsorptive/desorptive exchange, and the sensitivity of the surface tension to adsorbed surfactant. For example, cohesion between hydrocarbon chains favors strong adsorption. Cohesion also slows the rate of desorption from interfaces, and decreases the sensitivity of the surface tension to adsorbed surfactant. Strong cohesive interactions result in first order surface phase changes with a plateau in the surface tension vs surface concentration. Within this surface concentration range, the surface tension is decoupled from surface concentration gradients. We are engaged in the study of the role of surfactant physical chemistry in determining the Marangoni stresses on a drop in an extensional flow in a numerical and experimental program. Using surfactants whose dynamics and equilibrium behavior have been characterized in our laboratory, drop deformation will be studied in ground-based experiment. In an accompanying numerical study, predictive drop deformations will be determined based on the isotherm and equation of state determined in our laboratory. This work will improve our abilities to predict and control all fluid particle flows.

Tears of Wine

NASA Astrophysics Data System (ADS)

Rathore, Prerana; Sharma, Vivek

`Tears of wine' refer to the rows of wine-drops that spontaneously emerge within a glass of strong wine. Evaporation-driven Marangoni flows near the meniscus of water-alcohol mixtures drive liquid upward forming a thin liquid film, and a rim or ridge forms near the moving contact line. Eventually the rim undergoes an instability forming drops, that roll back into bulk reservoir forming so called tears or legs of wine. Most studies in literature argue the evaporation of more volatile, lower surface tension component (alcohol) results in a concentration-dependent surface tension gradient that drives the climbing flow within the thin film. Though it is well-known that evaporative cooling can create temperature gradients that could provide additional contribution to the climbing flows, the role of thermocapillary flows is less well-understood. Furthermore, the patterns, flows and instabilities that occur near the rim, and determine the size and periodicity of tears, are not well-studied. Using experiments and theory, we visualize and analyze the formation and growth of tears of wine. The sliding drops, released from the rim towards the bulk reservoir, show oscillations and a cascade of fascinating flows that are analyzed for the first time.

Stability analysis of rimming flow inside a horizontally rotating cylinder in the presence of an insoluble surfactant

NASA Astrophysics Data System (ADS)

Kumawat, Tara Chand; Tiwari, Naveen

2017-12-01

Two-dimensional base state solutions for rimming flows and their stability analysis to small axial perturbations are analyzed numerically. A thin liquid film which is uniformly covered with an insoluble surfactant flows inside a counterclockwise rotating horizontal cylinder. In the present work, a mathematical model is obtained which consists of coupled thin film thickness and surfactant concentration evolution equations. The governing equations are obtained by simplifying the momentum and species transport equations using the thin-film approximation. The model equations include the effect of gravity, viscosity, capillarity, inertia, and Marangoni stress. The concentration gradients generated due to flow result in the surface tension gradient that generates the Marangoni stress near the interface region. The oscillations in the flow due to inertia are damped out by the Marangoni stress. It is observed that the Marangoni stress has stabilizing effect, whereas inertia and surface tension enhance the instability growth rate. In the presence of low diffusion of the surfactant or large value of the Péclet number, the Marangoni stress becomes more effective. The analytically obtained eigenvalues match well with the numerically computed eigenvalues in the absence of gravity.

Transpiration-induced axial and radial tension gradients in trunks of Douglas-fir trees.

Treesearch

J.C. Domec; F. C. Meinzer; B. L. Gartner; D. Woodruff

2006-01-01

We determined the axial and radial xylem tension gradients in trunks of young Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees. Axial specific conductivity (ks-a) and sap flux density (Js) were measured at four consecutive depths within the sapwood at a...

Capillary wave theory of adsorbed liquid films and the structure of the liquid-vapor interface

NASA Astrophysics Data System (ADS)

MacDowell, Luis G.

2017-08-01

In this paper we try to work out in detail the implications of a microscopic theory for capillary waves under the assumption that the density is given along lines normal to the interface. Within this approximation, which may be justified in terms of symmetry arguments, the Fisk-Widom scaling of the density profile holds for frozen realizations of the interface profile. Upon thermal averaging of capillary wave fluctuations, the resulting density profile yields results consistent with renormalization group calculations in the one-loop approximation. The thermal average over capillary waves may be expressed in terms of a modified convolution approximation where normals to the interface are Gaussian distributed. In the absence of an external field we show that the phenomenological density profile applied to the square-gradient free energy functional recovers the capillary wave Hamiltonian exactly. We extend the theory to the case of liquid films adsorbed on a substrate. For systems with short-range forces, we recover an effective interface Hamiltonian with a film height dependent surface tension that stems from the distortion of the liquid-vapor interface by the substrate, in agreement with the Fisher-Jin theory of short-range wetting. In the presence of long-range interactions, the surface tension picks up an explicit dependence on the external field and recovers the wave vector dependent logarithmic contribution observed by Napiorkowski and Dietrich. Using an error function for the intrinsic density profile, we obtain closed expressions for the surface tension and the interface width. We show the external field contribution to the surface tension may be given in terms of the film's disjoining pressure. From literature values of the Hamaker constant, it is found that the fluid-substrate forces may be able to double the surface tension for films in the nanometer range. The film height dependence of the surface tension described here is in full agreement with results of the capillary wave spectrum obtained recently in computer simulations, and the predicted translation mode of surface fluctuations reproduces to linear order in field strength an exact solution of the density correlation function for the Landau-Ginzburg-Wilson Hamiltonian in an external field.

Unraveling Deformation Mechanisms in Gradient Structured Metals

NASA Astrophysics Data System (ADS)

Moering, Jordan Alexander

Gradient structures have demonstrated high strength and high ductility, introducing new mechanisms to challenge conventional mechanics. This work develops a method for characterizing the shear strain in gradient structured steel and presents evidence of a texture gradient that develops in Surface Mechanical Attrition Treatment (SMAT). Mechanics underlying some theories of the strengthening mechanisms in gradient structured metals are introduced, followed by the fabrication and testing of gradient structured aluminum rod. The round geometry is intrinsically different from its flat counterparts, which leads to a multiaxial stress state evolving in tension. The aluminum exhibits strengthening beyond rule of mixtures, and texture evolution in the post-mortem sample indicates that out of plane stresses operate within the gradient. Finally, another gradient structured aluminum rod is shown to exhibit higher strength and higher elongation to failure in a variety of sample diameters and processing conditions. The GND density and microstructural evolution showed no significant changes during mechanical testing, and high resolution strain mapping was successfully completed within the core of the material. These discoveries and contributions to the field should help continue unraveling the deformation mechanisms of gradient structured metals.

Vapour-mediated sensing and motility in two-component droplets

NASA Astrophysics Data System (ADS)

Cira, N. J.; Benusiglio, A.; Prakash, M.

2015-03-01

Controlling the wetting behaviour of liquids on surfaces is important for a variety of industrial applications such as water-repellent coatings and lubrication. Liquid behaviour on a surface can range from complete spreading, as in the `tears of wine' effect, to minimal wetting as observed on a superhydrophobic lotus leaf. Controlling droplet movement is important in microfluidic liquid handling, on self-cleaning surfaces and in heat transfer. Droplet motion can be achieved by gradients of surface energy. However, existing techniques require either a large gradient or a carefully prepared surface to overcome the effects of contact line pinning, which usually limit droplet motion. Here we show that two-component droplets of well-chosen miscible liquids such as propylene glycol and water deposited on clean glass are not subject to pinning and cause the motion of neighbouring droplets over a distance. Unlike the canonical predictions for these liquids on a high-energy surface, these droplets do not spread completely but exhibit an apparent contact angle. We demonstrate experimentally and analytically that these droplets are stabilized by evaporation-induced surface tension gradients and that they move in response to the vapour emitted by neighbouring droplets. Our fundamental understanding of this robust system enabled us to construct a wide variety of autonomous fluidic machines out of everyday materials.

Self-spinning nanoparticle laden microdroplets for sensing and energy harvesting

NASA Astrophysics Data System (ADS)

Bhattacharjee, Mitradip; Pasumarthi, Viswanath; Chaudhuri, Joydip; Singh, Amit Kumar; Nemade, Harshal; Bandyopadhyay, Dipankar

2016-03-01

Exposure of a volatile organic vapour could set in powerful rotational motion a microdroplet composed of an aqueous salt solution loaded with metal nanoparticles. The solutal Marangoni motion on the surface originating from the sharp difference in the surface tension of water and organic vapour stimulated the strong vortices inside the droplet. The vapour sources of methanol, ethanol, diethyl ether, toluene, and chloroform stimulated motions of different magnitudes could easily be correlated to the surface tension gradient on the drop surface. Interestingly, when the nanoparticle laden droplet of aqueous salt solution was connected to an external electric circuit through a pair of electrodes, an ~85-95% reduction in the electrical resistance was observed across the spinning droplet. The extent of reduction in the resistance was found to have a correlation with the difference in the surface tension of the vapour source and the water droplet, which could be employed to distinguish the vapour sources. Remarkably, the power density of the same prototype was estimated to be around 7 μW cm-2, which indicated the potential of the phenomenon in converting surface energy into electrical in a non-destructive manner and under ambient conditions. Theoretical analysis uncovered that the difference in the ζ-potential near the electrodes was the major reason for the voltage generation. The prototype could also detect the repeated exposure and withdrawal of vapour sources, which helped in the development of a proof-of-concept detector to sense alcohol issuing out of the human breathing system.Exposure of a volatile organic vapour could set in powerful rotational motion a microdroplet composed of an aqueous salt solution loaded with metal nanoparticles. The solutal Marangoni motion on the surface originating from the sharp difference in the surface tension of water and organic vapour stimulated the strong vortices inside the droplet. The vapour sources of methanol, ethanol, diethyl ether, toluene, and chloroform stimulated motions of different magnitudes could easily be correlated to the surface tension gradient on the drop surface. Interestingly, when the nanoparticle laden droplet of aqueous salt solution was connected to an external electric circuit through a pair of electrodes, an ~85-95% reduction in the electrical resistance was observed across the spinning droplet. The extent of reduction in the resistance was found to have a correlation with the difference in the surface tension of the vapour source and the water droplet, which could be employed to distinguish the vapour sources. Remarkably, the power density of the same prototype was estimated to be around 7 μW cm-2, which indicated the potential of the phenomenon in converting surface energy into electrical in a non-destructive manner and under ambient conditions. Theoretical analysis uncovered that the difference in the ζ-potential near the electrodes was the major reason for the voltage generation. The prototype could also detect the repeated exposure and withdrawal of vapour sources, which helped in the development of a proof-of-concept detector to sense alcohol issuing out of the human breathing system. Electronic supplementary information (ESI) available: Discussion of simulation with results, characterization and movies of particle motion inside droplets along with detailed explanation. See DOI: 10.1039/c6nr00217j

Effects of non-uniform temperature gradients on surface tension driven two component magneto convection in a porous- fluid system

NASA Astrophysics Data System (ADS)

Manjunatha, N.; Sumithra, R.

2018-04-01

The problem of surface tension driven two component magnetoconvection is investigated in a Porous-Fluid system, consisting of anincompressible two component electrically conducting fluid saturatedporous layer above which lies a layer of the same fluid in the presence of a uniform vertical magnetic field. The lower boundary of the porous layeris rigid and the upper boundary of the fluid layer is free with surfacetension effects depending on both temperature and concentration, boththese boundaries are insulating to heat and mass. At the interface thevelocity, shear and normal stress, heat and heat flux, mass and mass fluxare assumed to be continuous suitable for Darcy-Brinkman model. Theeigenvalue problem is solved in linear, parabolic and inverted parabolictemperature profiles and the corresponding Thermal Marangoni Numberis obtained for different important physical parameters.

Physics, mathematics and numerics of particle adsorption on fluid interfaces

NASA Astrophysics Data System (ADS)

Schmuck, Markus; Pavliotis, Grigorios A.; Kalliadasis, Serafim

2012-11-01

We study two arbitrary immiscible fuids where one phase contains small particles of the size of the interface and smaller. We primarily focus on charge-free particles with wetting characteristics described by the contact angle formed at the interface between the two phases and the particles. Based on the experimental observation that particles are adsorbed on the interface to reduce the interfacial energy and hence the surface tension as well, we formulate a free-energy functional that accounts for these physical effects. Using elements from calculus of variations and formal gradient flow theory, we derive partial differential equations describing the location of the interface and the density of the particles in the fluid phases. Via numerical experiments we analyse the time evolution of the surface tension, the particle concentration, and the free energy over time and reflect basic experimentally observed phenomena.

Biomimetic Water-Collecting Fabric with Light-Induced Superhydrophilic Bumps.

PubMed

Wang, Yuanfeng; Wang, Xiaowen; Lai, Chuilin; Hu, Huawen; Kong, Yeeyee; Fei, Bin; Xin, John H

2016-02-10

To develop an efficient water-collecting surface that integrates both fast water-capturing and easy drainage properties is of high current interest for addressing global water issues. In this work, a superhydrophobic surface was fabricated on cotton fabric via manipulation of both the surface roughness and surface energy. This was followed by a subsequent spray coating of TiO2 nanosol that created light-induced superhydrophilic bumps with a unique raised structure as a result of the interfacial tension of the TiO2 nanosol sprayed on the superhydrophobic fiber surface. These raised TiO2 bumps induce both a wettability gradient and a shape gradient, synergistically accelerating water coalescence and water collection. The in-depth study revealed that the quantity and the distribution of the TiO2 had a significant impact on the final water collection efficiency. This inexpensive and facilely fabricated fabric biomimicks the desert beetle's back and spider silk, which are capable of fog harvesting without additional energy consumption.

Peptide assembly-driven metal-organic framework (MOF) motors for micro electric generators

DOE PAGES

Ikezoe, Yasuhiro; Fang, Justin; Wasik, Tomasz L.; ...

2014-11-22

Peptide–metal–organic framework (Pep-MOF) motors, whose motions are driven by anisotropic surface tension gradients created via peptide self-assembly around frameworks, can rotate microscopic rotors and magnets fast enough to generate an electric power of 0.1 μW. Finally, a new rigid Pep-MOF motor can be recycled by refilling the peptide fuel into the nanopores of the MOF.

Depolymerization-powered autonomous motors using biocompatible fuel.

PubMed

Zhang, Hua; Duan, Wentao; Liu, Lei; Sen, Ayusman

2013-10-23

We report the design of autonomous motors powered by the rapid depolymerization reaction of poly(2-ethyl cyanoacrylate) (PECA), an FDA-approved polymer. Motors were fabricated in two different length scales, 3 cm and 300 μm. The motion of the motors is induced by self-generated surface tension gradients along their bodies. The motors are capable of moving in various media, including salt solutions and artificial serum.

Fast and Universal Approach to Encapsulating Transition Bimetal Oxide Nanoparticles in Amorphous Carbon Nanotubes under an Atmospheric Environment Based on the Marangoni Effect.

PubMed

Li, Shuoyu; Liu, Yuyi; Guo, Peisheng; Wang, Chengxin

2017-09-13

Transition metal oxide nanoparticles capsuled in amorphous carbon nanotubes (ACNTs) are attractive anode materials of lithium-ion batteries (LIBs). Here, we first designed a fast and universal method with a hydromechanics conception which is called Marangoni flow to fabricate transition bimetal oxides (TBOs) in the ACNT composite with a better electrochemistry performance. Marangoni flows can produce a liquid column with several centimeters of height in a tube with one side immersed in the liquid. The key point to induce a Marangoni flow is to make a gradient of the surface tension between the surface and the inside of the solution. With our research, we control the gradient of the surface tension by controlling the viscosity of a solution. To show how our method could be generally used, we synthesize two anode materials such as (a) CoFe 2 O 4 @ACNTs, and (b) NiFe 2 O 4 @ACNTs. All of these have a similar morphology which is ∼20 μm length with a diameter of 80-100 nm for the ACNTs, and the particles (inside the ACNTs) are smaller than 5 nm. In particular, there are amorphous carbons between the nanoparticles. All of the composite materials showed an outstanding electrochemistry performance which includes a high capacity and cycling stability so that after 600 cycles the capacity changed by less than 3%.

Are Organic Aerosols Good Cloud Condensation Nuclei?

NASA Astrophysics Data System (ADS)

Abbatt, J. P.; Broekhuizen, K.; Kumar, P. P.

2002-12-01

The ability of a set of organic-containing aerosols to act as cloud condensation nuclei has been measured in the laboratory using a thermal-gradient diffusion chamber operated at a fixed supersaturation. We observe that particles composed of soluble organics, such as malonic acid and adipic acid, activate at dry particle diameters in agreement with Kohler theory predications assuming the solutes are fully soluble and the droplet has the surface tension of water. Surprisingly, we also observe that sparingly soluble azelaic acid and cis-pinonic acid particles also activate, perhaps because they are being formed in a supersaturated, amorphous state or that their activation is aided by surface uptake of water. Mixed organic/ammonium sulfate particles have also been studied, and a range of behavior is observed. Soluble species such as malonic acid enhance activation through the vapour-pressure lowering effect whereas a thick coating of stearic acid on ammonium sulfate makes the particles totally inactive. Lastly, we have observed that pure oleic acid particles, which show no indication of activation when pure, can be activated after exposure to gas-phase ozone. The atmospheric implications of our results will be discussed. An interesting issue is the degree to which we can quantitatively model our results by assuming the surface tension of the growing droplet is that of water, i.e. without the need to invoke the surface-tension-lowering effect due to surface-active organics.

Tolman lengths and rigidity constants of multicomponent fluids: Fundamental theory and numerical examples

NASA Astrophysics Data System (ADS)

Aasen, Ailo; Blokhuis, Edgar M.; Wilhelmsen, Øivind

2018-05-01

The curvature dependence of the surface tension can be described by the Tolman length (first-order correction) and the rigidity constants (second-order corrections) through the Helfrich expansion. We present and explain the general theory for this dependence for multicomponent fluids and calculate the Tolman length and rigidity constants for a hexane-heptane mixture by use of square gradient theory. We show that the Tolman length of multicomponent fluids is independent of the choice of dividing surface and present simple formulae that capture the change in the rigidity constants for different choices of dividing surface. For multicomponent fluids, the Tolman length, the rigidity constants, and the accuracy of the Helfrich expansion depend on the choice of path in composition and pressure space along which droplets and bubbles are considered. For the hexane-heptane mixture, we find that the most accurate choice of path is the direction of constant liquid-phase composition. For this path, the Tolman length and rigidity constants are nearly linear in the mole fraction of the liquid phase, and the Helfrich expansion represents the surface tension of hexane-heptane droplets and bubbles within 0.1% down to radii of 3 nm. The presented framework is applicable to a wide range of fluid mixtures and can be used to accurately represent the surface tension of nanoscopic bubbles and droplets.

Droplet flow along the wall of rectangular channel with gradient of wettability

NASA Astrophysics Data System (ADS)

Kupershtokh, A. L.

2018-03-01

The lattice Boltzmann equations (LBE) method (LBM) is applicable for simulating the multiphysics problems of fluid flows with free boundaries, taking into account the viscosity, surface tension, evaporation and wetting degree of a solid surface. Modeling of the nonstationary motion of a drop of liquid along a solid surface with a variable level of wettability is carried out. For the computer simulation of such a problem, the three-dimensional lattice Boltzmann equations method D3Q19 is used. The LBE method allows us to parallelize the calculations on multiprocessor graphics accelerators using the CUDA programming technology.

Front-to-rear membrane tension gradient in rapidly moving cells.

PubMed

Lieber, Arnon D; Schweitzer, Yonatan; Kozlov, Michael M; Keren, Kinneret

2015-04-07

Membrane tension is becoming recognized as an important mechanical regulator of motile cell behavior. Although membrane-tension measurements have been performed in various cell types, the tension distribution along the plasma membrane of motile cells has been largely unexplored. Here, we present an experimental study of the distribution of tension in the plasma membrane of rapidly moving fish epithelial keratocytes. We find that during steady movement the apparent membrane tension is ∼30% higher at the leading edge than at the trailing edge. Similar tension differences between the front and the rear of the cell are found in keratocyte fragments that lack a cell body. This front-to-rear tension variation likely reflects a tension gradient developed in the plasma membrane along the direction of movement due to viscous friction between the membrane and the cytoskeleton-attached protein anchors embedded in the membrane matrix. Theoretical modeling allows us to estimate the area density of these membrane anchors. Overall, our results indicate that even though membrane tension equilibrates rapidly and mechanically couples local boundary dynamics over cellular scales, steady-state variations in tension can exist in the plasma membranes of moving cells. Copyright © 2015 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Respiration in heterotrophic unicellular eukaryotic organisms.

PubMed

Fenchel, Tom

2014-08-01

Surface:volume quotient, mitochondrial volume fraction, and their distribution within cells were investigated and oxygen gradients within and outside cells were modelled. Cell surface increases allometrically with cell size. Mitochondrial volume fraction is invariant with cell size and constitutes about 10% and mitochondria are predominantly found close to the outer membrane. The results predict that for small and medium sized protozoa maximum respiration rates should be proportional to cell volume (scaling exponent ≈1) and access to intracellular O2 is not limiting except at very low ambient O2-tensions. Available data do not contradict this and some evidence supports this interpretation. Cell size is ultimately limited because an increasing fraction of the mitochondria becomes exposed to near anoxic conditions with increasing cell size. The fact that mitochondria cluster close to the cell surface and the allometric change in cell shape with increasing cell size alleviates the limitation of aerobic life at low ambient O2-tension and for large cell size. Copyright © 2014 Elsevier GmbH. All rights reserved.

Estimating zero-g flow rates in open channels having capillary pumping vanes

NASA Astrophysics Data System (ADS)

Srinivasan, Radhakrishnan

2003-02-01

In vane-type surface tension propellant management devices (PMD) commonly used in satellite fuel tanks, the propellant is transported along guiding vanes from a reservoir at the inlet of the device to a sump at the outlet from where it is pumped to the satellite engine. The pressure gradient driving this free-surface flow under zero-gravity (zero-g) conditions is generated by surface tension and is related to the differential curvatures of the propellant-gas interface at the inlet and outlet of the PMD. A new semi-analytical procedure is prescribed for accurately calculating the extremely small fuel flow rates under reasonably idealized conditions. Convergence of the algorithm is demonstrated by detailed numerical calculations. Owing to the substantial cost and the technical hurdles involved in accurately estimating these minuscule flow rates by either direct numerical simulation or by experimental methods which simulate zero-g conditions in the lab, it is expected that the proposed method will be an indispensable tool in the design and operation of satellite fuel tanks.

Self-spinning nanoparticle laden microdroplets for sensing and energy harvesting.

PubMed

Bhattacharjee, Mitradip; Pasumarthi, Viswanath; Chaudhuri, Joydip; Singh, Amit Kumar; Nemade, Harshal; Bandyopadhyay, Dipankar

2016-03-21

Exposure of a volatile organic vapour could set in powerful rotational motion a microdroplet composed of an aqueous salt solution loaded with metal nanoparticles. The solutal Marangoni motion on the surface originating from the sharp difference in the surface tension of water and organic vapour stimulated the strong vortices inside the droplet. The vapour sources of methanol, ethanol, diethyl ether, toluene, and chloroform stimulated motions of different magnitudes could easily be correlated to the surface tension gradient on the drop surface. Interestingly, when the nanoparticle laden droplet of aqueous salt solution was connected to an external electric circuit through a pair of electrodes, an ∼85-95% reduction in the electrical resistance was observed across the spinning droplet. The extent of reduction in the resistance was found to have a correlation with the difference in the surface tension of the vapour source and the water droplet, which could be employed to distinguish the vapour sources. Remarkably, the power density of the same prototype was estimated to be around 7 μW cm(-2), which indicated the potential of the phenomenon in converting surface energy into electrical in a non-destructive manner and under ambient conditions. Theoretical analysis uncovered that the difference in the ζ-potential near the electrodes was the major reason for the voltage generation. The prototype could also detect the repeated exposure and withdrawal of vapour sources, which helped in the development of a proof-of-concept detector to sense alcohol issuing out of the human breathing system.

The influence of a surface tension minimum on the convective motion of a fluid in microgravity (D1 mission results)

NASA Astrophysics Data System (ADS)

Limbourg, M. C.; Legros, J. C.; Petre, G.

The experiment STEM (Surface Tension Minimum) was performed in an experimental cell integrated in the FMP (Fluid Physics Module) during the D1 mission of Spacelab. The observation volume (1×2×3) cm3 was constituted by a stainless steel frame and by two optical Pyrex windows. It was fixed on the front disk of the FPM. The cell was filled under microgravity conditions by an aqueous solution of n-heptanol 6,04 10-3 molal. At equilibrium this system presents a minimum of surface tension as a function of temperature around 40°C. The fluid was heated from the front disk side of the cell. A temperature difference of 35°C was maintained between two opposite sides of the cell, by using the large heat capacity of a water reservoir in thermal contact with the cold side of the cell. The thermal gradient was parallel to the liquid/gas interface. The motions of the fluid were recorded on video-tapes and the velocities were determined by following latex particles used as tracers. The convective pattern is analysed and compared with ground experiments. In this case the tracer trajectories allow to determine the convective patterns and the velocities are determined by laser doppler anemometry.

Study of bubble behavior in weightlessness (effects of thermal gradient and acoustic stationary wave) (M-16)

NASA Technical Reports Server (NTRS)

Azuma, H.

1993-01-01

The aim of this experiment is to understand how bubbles behave in a thermal gradient and acoustic stationary wave under microgravity. In microgravity, bubble or bubbles in a liquid will not rise upward as they do on Earth but will rest where they are formed because there exists no gravity-induced buoyancy. We are interested in how bubbles move and in the mechanisms which support the movement. We will try two ways to make bubbles migrate. The first experiment concerns behavior of bubbles in a thermal gradient. It is well known than an effect of surface tension which is masked by gravity on the ground becomes dominant in microgravity. The surface tension on the side of the bubble at a lower temperature is stronger than at a higher temperature. The bubble migrates toward the higher temperature side due to the surface tension difference. The migration speed depends on the so-called Marangoni number, which is a function of the temperature difference, the bubble diameter, liquid viscosity, and thermal diffusivity. At present, some experimental data about migration speeds in liquids with very small Marangoni numbers were obtained in space experiments, but cases of large Marangoni number are rarely obtained. In our experiment a couple of bubbles are to be injected into a cell filled with silicon oil, and the temperature gradient is to be made gradually in the cell by a heater and a cooler. We will be able to determine migration speeds in a very wide range of Marangoni numbers, as well as study interactions between the bubbles. We will observe bubble movements affected by hydrodynamical and thermal interactions, the two kinds of interactions which occur simultaneously. These observation data will be useful for analyzing the interactions as well as understanding the behavior of particles or drops in materials processing. The second experiment concerns bubble movement in an acoustic stationary wave. It is known that a bubble in a stationary wave moves toward the node or the loop according to whether its diameter is larger or smaller than that of the main resonant radius. In our experiment fine bubbles will be observed to move according to an acoustic field formed in a cylindrical cell. The existence of bubbles varies the acoustic speed, and the interactive force between bubbles will make the bubble behavior collective and complicated. This experiment will be very useful to development of bubble removable technology as well as to the understanding of bubble behavior.

Infrared surface temperature measurements for the surface tension driven convection experiment. M.S. Thesis - Case Western Reserve Univ., Aug. 1988

NASA Technical Reports Server (NTRS)

Pline, Alexander D.

1989-01-01

In support of the Surface Tension Driven Convection Experiment (STDCE), a planned space transportation system (STS) flight experiment, a commercially available infrared thermal imaging system is used to quantify the imposed thermal signature along the free surface. The system was tested and calibrated for the STDCE with ground-based equivalents of the STDCE hardware. Before using the system, consideration was given to the radiation characteristics of the target (silicone oil). Absorption coefficients were calculated to understand the surface depth as seen by the imager and the penetration depth of the surface heater (CO2 laser). The performance and operational specifications for the imager and image processing system are described in detail to provide an understanding of the equipment. Measurements made with the system were compared to thermocouple measurements and a calculated surface temperature distribution. This comparison showed that in certain regions the IR imager measurements were within 5 percent of the overall temperature difference across the free surface. In other regions the measurements were within + or - 10 percent of the overall temperature gradient across the free surface. The effective emissivity of silicone oil for these experimental conditions was also determined. Measurement errors and their possible solutions are discussed.

Aligned carbon nanotube, graphene and graphite oxide thin films via substrate-directed rapid interfacial deposition

NASA Astrophysics Data System (ADS)

D'Arcy, Julio M.; Tran, Henry D.; Stieg, Adam Z.; Gimzewski, James K.; Kaner, Richard B.

2012-05-01

A procedure for depositing thin films of carbon nanostructures is described that overcomes the limitations typically associated with solution based methods. Transparent and conductively continuous carbon coatings can be grown on virtually any type of substrate within seconds. Interfacial surface tension gradients result in directional fluid flow and film spreading at the water/oil interface. Transparent films of carbon nanostructures are produced including aligned ropes of single-walled carbon nanotubes and assemblies of single sheets of chemically converted graphene and graphite oxide. Process scale-up, layer-by-layer deposition, and a simple method for coating non-activated hydrophobic surfaces are demonstrated.A procedure for depositing thin films of carbon nanostructures is described that overcomes the limitations typically associated with solution based methods. Transparent and conductively continuous carbon coatings can be grown on virtually any type of substrate within seconds. Interfacial surface tension gradients result in directional fluid flow and film spreading at the water/oil interface. Transparent films of carbon nanostructures are produced including aligned ropes of single-walled carbon nanotubes and assemblies of single sheets of chemically converted graphene and graphite oxide. Process scale-up, layer-by-layer deposition, and a simple method for coating non-activated hydrophobic surfaces are demonstrated. Electronic supplementary information (ESI) available: Droplet coalescence, catenoid formation, mechanism of film growth, scanning electron micrographs showing carbon nanotube alignment, flexible transparent films of SWCNTs, AFM images of a chemically converted graphene film, and SEM images of SWCNT free-standing thin films. See DOI: 10.1039/c2nr00010e

3D finite element simulation of TIG weld pool

NASA Astrophysics Data System (ADS)

Kong, X.; Asserin, O.; Gounand, S.; Gilles, P.; Bergheau, J. M.; Medale, M.

2012-07-01

The aim of this paper is to propose a three-dimensional weld pool model for the moving gas tungsten arc welding (GTAW) process, in order to understand the main factors that limit the weld quality and improve the productivity, especially with respect to the welding speed. Simulation is a very powerful tool to help in understanding the physical phenomena in the weld process. A 3D finite element model of heat and fluid flow in weld pool considering free surface of the pool and traveling speed has been developed for the GTAW process. Cast3M software is used to compute all the governing equations. The free surface of the weld pool is calculated by minimizing the total surface energy. The combined effects of surface tension gradient, buoyancy force, arc pressure, arc drag force to drive the fluid flow is included in our model. The deformation of the weld pool surface and the welding speed affect fluid flow, heat flow and thus temperature gradients and molten pool dimensions. Welding trials study is presented to compare our numerical results with macrograph of the molten pool.

The effect of surface movements on nitrogen mass transfer in liquid iron

NASA Astrophysics Data System (ADS)

Hirashima, N.; Choo, R. T. C.; Toguri, J. M.; Mukai, K.

1995-10-01

Marangoni convection due to surface tension gradients set up in a nitrogen-liquid iron system at 1873 K has been mathematically simulated and experimentally confirmed by measuring the rate of nitrogen absorption into liquid iron and by observing the free surface motion of liquid iron via zirconium oxide particles using X-ray radiography. This surface flow was created by blowing nitrogen gas through a small lance over the free surface of the liquid iron contained in an alumina boat under resistance heating. Absorption measurements indicated that the mass-transfer coefficient of nitrogen in liquid iron due to Marangoni convection ( k {m/1}>=1.5×10-4 m/s) is slightly less than that due to induction stirring ( k {m/1}=2.1×10-4 to 1.5×10-4 m/s). The free surface velocity induced by the surface tension gradient, with an initial composition difference of 425 to 10 ppm, was found to be of the order of 0.05 to 0.11 m/s. Mathematical modeling was also carried out to determine the velocity and nitrogen concentration profiles in the alumina boat. It was found that Marangoni convection creates mildly turbulent flows in liquid iron. Good agreements between the experimentally obtained data (nitrogen concentration and surface velocity) and the computed results were attained when a constant eddy viscosity which was five times the molecular value was assumed. This prescription allows both the predicted apparent mass-transfer coefficient and the predicted surface velocity to match the experimental results simultaneously. Note that the transport coefficients in the momentum and the convective-diffusive equations are correlated by the turbulent Schmidt number. The dimensionless mass-transfer correlation obtained for the present N-Fe system at 1873 K under resistance heating was found to be Sh=0.104 Re0.7·Sc0.7 with Sc=79.5 (3500

Simulation of Two-Fluid Flows by the Least-Squares Finite Element Method Using a Continuum Surface Tension Model

NASA Technical Reports Server (NTRS)

Wu, Jie; Yu, Sheng-Tao; Jiang, Bo-nan

1996-01-01

In this paper a numerical procedure for simulating two-fluid flows is presented. This procedure is based on the Volume of Fluid (VOF) method proposed by Hirt and Nichols and the continuum surface force (CSF) model developed by Brackbill, et al. In the VOF method fluids of different properties are identified through the use of a continuous field variable (color function). The color function assigns a unique constant (color) to each fluid. The interfaces between different fluids are distinct due to sharp gradients of the color function. The evolution of the interfaces is captured by solving the convective equation of the color function. The CSF model is used as a means to treat surface tension effect at the interfaces. Here a modified version of the CSF model, proposed by Jacqmin, is used to calculate the tension force. In the modified version, the force term is obtained by calculating the divergence of a stress tensor defined by the gradient of the color function. In its analytical form, this stress formulation is equivalent to the original CSF model. Numerically, however, the use of the stress formulation has some advantages over the original CSF model, as it bypasses the difficulty in approximating the curvatures of the interfaces. The least-squares finite element method (LSFEM) is used to discretize the governing equation systems. The LSFEM has proven to be effective in solving incompressible Navier-Stokes equations and pure convection equations, making it an ideal candidate for the present applications. The LSFEM handles all the equations in a unified manner without any additional special treatment such as upwinding or artificial dissipation. Various bench mark tests have been carried out for both two dimensional planar and axisymmetric flows, including a dam breaking, oscillating and stationary bubbles and a conical liquid sheet in a pressure swirl atomizer.

Studies of Two-Phase Flow Dynamics and Heat Transfer at Reduced Gravity Conditions

NASA Technical Reports Server (NTRS)

Witte, Larry C.; Bousman, W. Scott; Fore, Larry B.

1996-01-01

The ability to predict gas-liquid flow patterns is crucial to the design and operation of two-phase flow systems in the microgravity environment. Flow pattern maps have been developed in this study which show the occurrence of flow patterns as a function of gas and liquid superficial velocities as well as tube diameter, liquid viscosity and surface tension. The results have demonstrated that the location of the bubble-slug transition is affected by the tube diameter for air-water systems and by surface tension, suggesting that turbulence-induced bubble fluctuations and coalescence mechanisms play a role in this transition. The location of the slug-annular transition on the flow pattern maps is largely unaffected by tube diameter, liquid viscosity or surface tension in the ranges tested. Void fraction-based transition criteria were developed which separate the flow patterns on the flow pattern maps with reasonable accuracy. Weber number transition criteria also show promise but further work is needed to improve these models. For annular gas-liquid flows of air-water and air- 50 percent glycerine under reduced gravity conditions, the pressure gradient agrees fairly well with a version of the Lockhart-Martinelli correlation but the measured film thickness deviates from published correlations at lower Reynolds numbers. Nusselt numbers, based on a film thickness obtained from standard normal-gravity correlations, follow the relation, Nu = A Re(sup n) Pr(exp l/3), but more experimental data in a reduced gravity environment are needed to increase the confidence in the estimated constants, A and n. In the slug flow regime, experimental pressure gradient does not correlate well with either the Lockhart-Martinelli or a homogeneous formulation, but does correlate nicely with a formulation based on a two-phase Reynolds number. Comparison with ground-based correlations implies that the heat transfer coefficients are lower at reduced gravity than at normal gravity under the same flow conditions. Nusselt numbers can be correlated in a fashion similar to Chu and Jones.

On the instability of a liquid sheet moving in vacuum

NASA Astrophysics Data System (ADS)

Sisoev, G. M.; Osiptsov, A. N.; Koroteev, A. A.

2018-03-01

A linear stability analysis of a non-isothermal liquid sheet moving in vacuum is studied taking into account the temperature dependencies of the liquid viscosity, thermal conductivity, and surface tension coefficients. It is found that there are two mechanisms of instability. The short-wave instability is caused by viscosity stratification across the sheet due to nonuniform temperature profiles developed downstream in the cooling sheet. The long-wave thermocapillary instability is caused by the temperature gradient along the sheet surfaces. Computed examples of steady flows and their instabilities demonstrated that the unstable short waves have much larger amplification factors.

Salt-Finger Convection in a Stratified Fluid Layer Induced by Thermal and Solutal Capillary Motion

NASA Technical Reports Server (NTRS)

Chen, Chuan F.; Chan, Cho Lik

1996-01-01

Salt-finger convection in a double-diffusive system is a motion driven by the release of gravitational potential due to different diffusion rates. Normally, when the gravitational field is reduced, salt-finger convection together with other convective motions driven by buoyancy forces will be rapidly suppressed. However, because the destabilizing effect of the concentration gradient is amplified by the Lewis number, with values varying from 10(exp 2) for aqueous salt solutions to 10 (exp 4) for liquid metals, salt-finger convection may be generated at much reduced gravity levels. In the microgravity environment, the surface tension gradient assumes a dominant role in causing fluid motion. In this paper, we report on some experimental results showing the generation of salt-finger convection due to capillary motio on the surface of a stratified fluid layer. A numerical simulation is presented to show the cause of salt-finger convection.

Sloshing dynamics modulated fluid angular momentum and moment fluctuations driven by orbital gravity gradient and jitter accelerations in microgravity

NASA Technical Reports Server (NTRS)

Hung, R. J.; Pan, H. L.

1995-01-01

The dynamical behavior of spacecraft propellant affected by the asymmetric combined gravity gradient and jitter accelerations, in particular the effect of surface tension on partially-filled rotating fluids applicable to a full-scale Gravity Probe-B Spacecraft dewar tank has been investigated. Three different cases of orbital accelerations: (1) gravity gradient-dominated, (2) equally weighted between gravity gradient and jitter, and (3) gravity jitter-dominated accelerations are studied. The results of slosh wave excitation along the liquid-vapor interface induced by gravity gradient-dominated accelerations provide a torsional moment with tidal motion of bubble oscillations in the rotating dewar. The results are clearly seen from the twisting shape of the bubble oscillations driven by gravity gradient-dominated acceleration. The results of slosh wave excitation along the liquid-vapor interface induced by gravity jitter-dominated acceleration indicate the results of bubble motion in a manner of down-and-up and leftward-and-rightward movement of oscillation when the bubble is rotating with respect to rotating dewar axis. Fluctuations of angular momentum, fluid moment and bubble mass center caused by slosh wave excitations driven by gravity gradient acceleration or gravity jitter acceleration are also investigated.

Peptide assembly-driven metal-organic framework (MOF) motors for micro electric generators.

PubMed

Ikezoe, Yasuhiro; Fang, Justin; Wasik, Tomasz L; Uemura, Takashi; Zheng, Yongtai; Kitagawa, Susumu; Matsui, Hiroshi

2015-01-14

Peptide-metal-organic framework (Pep-MOF) motors, whose motions are driven by anisotropic surface tension gradients created via peptide self-assembly around frameworks, can rotate microscopic rotors and magnets fast enough to generate an electric power of 0.1 μW. A new rigid Pep-MOF motor can be recycled by refilling the peptide fuel into the nanopores of the MOF. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Influence of Marangoni flows on the dynamics of isothermal A + B → C reaction fronts.

PubMed

Tiani, R; Rongy, L

2016-09-28

The nonlinear dynamics of A + B → C fronts is analyzed both numerically and theoretically in the presence of Marangoni flows, i.e., convective motions driven by surface tension gradients. We consider horizontal aqueous solutions where the three species A, B, and C can affect the surface tension of the solution, thereby driving Marangoni flows. The resulting dynamics is studied by numerically integrating the incompressible Navier-Stokes equations coupled to reaction-diffusion-convection (RDC) equations for the three chemical species. We show that the dynamics of the front cannot be predicted solely on the basis of the one-dimensional reaction-diffusion profiles as is the case for buoyancy-driven convection around such fronts. We relate this observation to the structure of Marangoni flows which lead to more complex and exotic dynamics. We find in particular the surprising possibility of a reversal of the front propagation direction in time for some sets of Marangoni numbers, quantifying the influence of each chemical species concentration on the solution surface tension. We explain this reversal analytically and propose a new classification of the convective effects on A + B → C reaction fronts as a function of the Marangoni numbers. The influence of the layer thickness on the RDC dynamics is also presented. Those results emphasize the importance of flow symmetry properties when studying convective front dynamics in a given geometry.

Surface contouring by controlled application of processing fluid using Marangoni effect

DOEpatents

Rushford, Michael C.; Britten, Jerald A.

2003-04-29

An apparatus and method for modifying the surface of an object by contacting said surface with a liquid processing solution using the liquid applicator geometry and Marangoni effect (surface tension gradient-driven flow) to define and confine the dimensions of the wetted zone on said object surface. In particular, the method and apparatus involve contouring or figuring the surface of an object using an etchant solution as the wetting fluid and using realtime metrology (e.g. interferometry) to control the placement and dwell time of this wetted zone locally on the surface of said object, thereby removing material from the surface of the object in a controlled manner. One demonstrated manifestation is in the deterministic optical figuring of thin glasses by wet chemical etching using a buffered hydrofluoric acid solution and Marangoni effect.

Apparatus For Etching Or Depositing A Desired Profile Onto A Surface

DOEpatents

Rushford, Michael C.; Britten, Jerald A.

2004-05-25

An apparatus and method for modifying the surface of an object by contacting said surface with a liquid processing solution using the liquid applicator geometry and Marangoni effect (surface tension gradient-driven flow) to define and confine the dimensions of the wetted zone on said object surface. In particular, the method and apparatus involve contouring or figuring the surface of an object using an etchant solution as the wetting fluid and using real-time metrology (e.g. interferometry) to control the placement and dwell time of this wetted zone locally on the surface of said object, thereby removing material from the surface of the object in a controlled manner. One demonstrated manifestation is in the deterministic optical figuring of thin glasses by wet chemical etching using a buffered hydrofluoric acid solution and Marangoni effect.

The dynamic surface tension of atmospheric aerosol surfactants reveals new aspects of cloud activation.

PubMed

Nozière, Barbara; Baduel, Christine; Jaffrezo, Jean-Luc

2014-02-25

The activation of aerosol particles into cloud droplets in the Earth's atmosphere is both a key process for the climate budget and a main source of uncertainty. Its investigation is facing major experimental challenges, as no technique can measure the main driving parameters, the Raoult's term and surface tension, σ, for sub-micron atmospheric particles. In addition, the surfactant fraction of atmospheric aerosols could not be isolated until recently. Here we present the first dynamic investigation of the total surfactant fraction of atmospheric aerosols, evidencing adsorption barriers that limit their gradient (partitioning) in particles and should enhance their cloud-forming efficiency compared with current models. The results also show that the equilibration time of surfactants in sub-micron atmospheric particles should be beyond the detection of most on-line instruments. Such instrumental and theoretical shortcomings would be consistent with atmospheric and laboratory observations and could have limited the understanding of cloud activation until now.

Separation processes during binary monotectic alloy production

NASA Technical Reports Server (NTRS)

Frazier, D. O.; Facemire, B. R.; Kaukler, W. F.; Witherow, W. K.; Fanning, U.

1984-01-01

Observation of microgravity solidification processes indicates that outside of sedimentation, at least two other important effects can separate the phases: critical-point wetting and spreading; and thermal migration of second-phase droplets due to interfacial tension gradients. It is difficult to study these surface tension effects while in a unit gravity field. In order to investigate the processes occurring over a temperature range, i.e., between a consolute point and the monotectic temperature, it is necessary to use a low-gravity environment. The MSFC drop tube (and tower), the ballistic trajectory KC-135 airplane, and the Space Shuttle are ideal facilities to aid formation and testing of hypotheses. Much of the early work in this area focuses on transparent materials so that process dynamics may be studied by optical techniques such as photography for viewing macro-processes; holography for studying diffusional growth; spinodal decomposition and coalescence; ellipsometry for surface wetting and spreading effects; and interferometry and spectroscopy for small-scale spatial resolution of concentration profiles.

Effect of minor chemistry elements on GTA weld fusion zone characteristics of a commercial grade titanium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marya, S.K.

1996-06-01

Gas Tungsten Arc Welding (GTAW) is the most common technique employed in the fabrication of rolled thin tubes. One of the major manufacturing problems concerns the stability of weld fusion zone on materials from different casts, notwithstanding stringent monitoring of the process parameters -- current, voltage and travel speed. These parameters determine the theoretical weld heat and are expected to control the instantaneous mass of melt. According to the data compiled by Sahoo et al., oxygen is known to reduce the surface tension of most of the metals. However, investigations on the role of minor changes in concentrations of elementsmore » like sulphur, oxygen, selenium, bismuth, aluminium, and titanium in steels have very often attributed the cast to cast variations to different temperature gradients of surface tension over the weldpool. To the author`s knowledge, no reported work so far has revealed changing weld profiles in autogeneous mechanized GTA welds on titanium due to minor composition changes.« less

Direct Determination of the Dependence of the Surface Shear and Dilatational Viscosities on the Thermodynamic State of the Interface: Theoretical Foundations.

PubMed

Lopez; Hirsa

1998-10-01

Recent developments in nonlinear optical techniques for noninvasive probing of a surfactant influenced gas/liquid interface allow for the measurement of the surfactant surface concentration, c, and thus provide new opportunities for the direct determination of its intrinsic viscosities. Here, we present the theoretical foundations, based on the Boussinesq-Scriven surface model without the usual simplification of constant viscosities, for an experimental technique to directly measure the surface shear (µs) and dilatational (kappas) viscosities of a Newtonian interface as functions of the surfactant surface concentration. This ability to directly measure the surfactant concentration permits the use of a simple surface flow for the measurement of the surface viscosities. The requirements are that the interface must be nearly flat, and the flow steady, axisymmetric, and swirling; these flow conditions can be achieved in the deep-channel viscometer driven at relatively fast rates. The tangential stress balance on such an interface leads to two equations; the balance in the azimuthal direction involves only µs and its gradients, and the balance in the radial direction involves both µs and kappas and their gradients. By further exploiting recent developments in laser-based flow measuring techniques, the surface velocities and their gradients which appear in the two equations can be measured directly. The surface tension gradient, which appears in the radial balance equation, is incorporated from the equation of state for the surfactant system and direct measurements of the surfactant surface concentration distribution. The stress balance equations are then ordinary differential equations in the surface viscosities as functions of radial position, which can be readily integrated. Since c is measured as a function of radial position, we then have a direct measurement of µs and kappas as functions of c. Numerical computations of the Navier-Stokes equations are performed to determine the appropriate conditions to achieve the requisite secondary flow. Copyright 1998 Academic Press.

Effect of demulsifiers on interfacial properties governing crude oil demulsification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mukherjee, S.; Kushnick, A.P.

1987-01-01

The purpose of this paper is to illustrate how various parameters such as interfacial tension, interfacial shear viscosity, dynamic interfacial tension gradient, dilational elasticity and demulsifier clustering affect the demulsification effectiveness. The authors believe such an understanding is needed for developing more effective demulsifiers. At small thicknesses, an interfacial oil film can rupture if a continuous hydrophilic pathway exists between the droplets. Such a pathway can be provided by a demulsifier by forming water swollen reverse micelle-like clusters. They believe the differences in the effectiveness between P1 and P2 at low concentrations may be related to this phenomenon. The authorsmore » found that with both P1 and P2, the crude oil-brine interfacial shear viscosity is less than 0.1 surface poise. The interfacial dilational measurements also do not reveal any significant differences in their dynamic tension properties. But the interfacial tension vs. concentration curves show significant differences. The leveling of interfacial tension implies formation of clusters. The data indicate that the demulsifier P1 will form such clusters in the crude oil at a lower concentration than P2. Thus, other parameters being equal, the demulsifier P1 will be more efficient at a lower concentration than P2 for this crude oil emulsion.« less

Surface tension and contact angles: Molecular origins and associated microstructure

NASA Technical Reports Server (NTRS)

Davis, H. T.

1982-01-01

Gradient theory converts the molecular theory of inhomogeneous fluid into nonlinear boundary value problems for density and stress distributions in fluid interfaces, contact line regions, nuclei and microdroplets, and other fluid microstructures. The relationship between the basic patterns of fluid phase behavior and the occurrence and stability of fluid microstructures was clearly established by the theory. All the inputs of the theory have molecular expressions which are computable from simple models. On another level, the theory becomes a phenomenological framework in which the equation of state of homogeneous fluid and sets of influence parameters of inhomogeneous fluids are the inputs and the structures, stress tensions and contact angles of menisci are the outputs. These outputs, which find applications in the science and technology of drops and bubbles, are discussed.

A gradient enhanced plasticity-damage microplane model for concrete

NASA Astrophysics Data System (ADS)

Zreid, Imadeddin; Kaliske, Michael

2018-03-01

Computational modeling of concrete poses two main types of challenges. The first is the mathematical description of local response for such a heterogeneous material under all stress states, and the second is the stability and efficiency of the numerical implementation in finite element codes. The paper at hand presents a comprehensive approach addressing both issues. Adopting the microplane theory, a combined plasticity-damage model is formulated and regularized by an implicit gradient enhancement. The plasticity part introduces a new microplane smooth 3-surface cap yield function, which provides a stable numerical solution within an implicit finite element algorithm. The damage part utilizes a split, which can describe the transition of loading between tension and compression. Regularization of the model by the implicit gradient approach eliminates the mesh sensitivity and numerical instabilities. Identification methods for model parameters are proposed and several numerical examples of plain and reinforced concrete are carried out for illustration.

Crack Initiation and Growth in Rigid Polymeric Closed-Cell Foam Cryogenic Applications

NASA Technical Reports Server (NTRS)

Sayyah, Tarek; Steeve, Brian; Wells, Doug

2006-01-01

Cryogenic vessels, such as the Space Shuttle External Tank, are often insulated with closed-cell foam because of its low thermal conductivity. The coefficient of thermal expansion mismatch between the foam and metallic substrate places the foam under a biaxial tension gradient through the foam thickness. The total foam thickness affects the slope of the stress gradient and is considered a significant contributor to the initiation of subsurface cracks. Rigid polymeric foams are brittle in nature and any subsurface cracks tend to propagate a finite distance toward the surface. This presentation investigates the relationship between foam thickness and crack initiation and subsequent crack growth, using linear elastic fracture mechanics, in a rigid polymeric closed-cell foam through analysis and comparison with experimental results.

Dancing droplets: Contact angle, drag, and confinement

NASA Astrophysics Data System (ADS)

Benusiglio, Adrien; Cira, Nate; Prakash, Manu

2015-11-01

When deposited on a clean glass slide, a mixture of water and propylene glycol forms a droplet of given contact angle, when both pure liquids spread. (Cira, Benusiglio, Prakash: Nature, 2015). The droplet is stabilized by a gradient of surface tension due to evaporation that induces a Marangoni flow from the border to the apex of the droplets. The apparent contact angle of the droplets depends on both their composition and the external humidity as captured by simple models. These droplets present remarkable properties such as lack of a large pinning force. We discuss the drag on these droplets as a function of various parameters. We show theoretical and experimental results of how various confinement geometries change the vapor gradient and the dynamics of droplet attraction.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rofouie, P.; Rey, A. D., E-mail: alejandro.rey@mail.mcgill.ca; Pasini, D.

Periodic surface nano-wrinkling is found throughout biological liquid crystalline materials, such as collagen films, spider silk gland ducts, exoskeleton of beetles, and flower petals. These surface ultrastructures are responsible for structural colors observed in some beetles and plants that can dynamically respond to external conditions, such as humidity and temperature. In this paper, the formation of the surface undulations is investigated through the interaction of anisotropic interfacial tension, swelling through hydration, and capillarity at free surfaces. Focusing on the cellulosic cholesteric liquid crystal (CCLC) material model, the generalized shape equation for anisotropic interfaces using the Cahn-Hoffman capillarity vector and themore » Rapini-Papoular anchoring energy are applied to analyze periodic nano-wrinkling in plant-based plywood free surfaces with water-induced cholesteric pitch gradients. Scaling is used to derive the explicit relations between the undulations’ amplitude expressed as a function of the anchoring strength and the spatially varying pitch. The optical responses of the periodic nano-structured surfaces are studied through finite difference time domain simulations indicating that CCLC surfaces with spatially varying pitch reflect light in a wavelength higher than that of a CCLC’s surface with constant pitch. This structural color change is controlled by the pitch gradient through hydration. All these findings provide a foundation to understand structural color phenomena in nature and for the design of optical sensor devices.« less

Numerical studies of surface tensions

NASA Technical Reports Server (NTRS)

Hung, R. J.

1995-01-01

Liquid-vapor (bubble) interface disturbances caused by various types of accelerations, including centrifugal, lateral and axial impulses, gravity gradient and g-jitter accelerations associated with spinning and slew motion in microgravity, are reviewed. Understanding of bubble deformations and fluctuations is important in the development of spacecraft orbital and attitude control techniques to secure its normal operation. This review discusses bubble deformations and oscillations driven by various forces in the microgravity environment. The corresponding bubble mass center fluctuations and slosh reaction forces and torques due to bubble deformations are also reviewed.

Melt layer erosion of metallic armour targets during off-normal events in tokamaks

NASA Astrophysics Data System (ADS)

Bazylev, B.; Wuerz, H.

2002-12-01

Melt layer erosion by melt motion is the dominating erosion mechanism for metallic armours under high heat loads. A 1-D fluid dynamics simulation model for calculation of melt motion was developed and validated against experimental results for tungsten from the e-beam facility JEBIS and beryllium from the e-beam facility JUDITH. The driving force in each case is the gradient of the surface tension. Due to the high velocity which develops in the Be melt considerable droplet splashing occurs.

Pore-scale modeling of moving contact line problems in immiscible two-phase flow.

NASA Astrophysics Data System (ADS)

Kucala, A.; Noble, D.; Martinez, M. J.

2016-12-01

Two immiscible fluids in static equilibrium form a common interface along a solid surface, characterized as the static contact (wetting) angle and is a function of surface geometry, intermolecular forces, and interfacial surface energies manifested as interfacial tension. This static configuration may become perturbed due to external force imbalances (mass injection, pressure gradients, buoyancy, etc.) and the contact line location and interface curvature becomes dynamic. Accurate modeling of moving contact line (MCL) problems is imperative in predicting capillary pressure vs. saturation curves, permeability, and preferential flow paths for a variety of applications, including geological carbon storage (GCS) and enhanced oil recovery (EOR). Here, we present a model for the moving contact line using pore-scale computational fluid dynamics (CFD) which solves the full, time-dependent Navier-Stokes equations using the Galerkin finite-element method. The MCL is modeled as a surface traction force proportional to the surface tension, dependent on the static properties of the immiscible fluid/solid system. The moving two-phase interface is tracked using the level set method and discretized with the conformal decomposition finite element method (CDFEM), allowing for surface tension effects to be computed at the exact interface location. We present a variety of verification test cases for simple two- and three-dimensional geometries to validate the current model, including threshold pressure predictions in flows through pore-throats for a variety of wetting angles. Simulations involving more complex geometries are also presented to be used in future simulations for GCS and EOR problems. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000

What are the driving forces for water lifting in the xylem conduit?

PubMed

Zimmermann, Ulrich; Schneider, Heike; Wegner, Lars H; Wagner, Hans-Jürgen; Szimtenings, Michael; Haase, Axel; Bentrup, Friedrich-Wilhelm

2002-03-01

After Renner had shown convincingly in 1925 that the transpirational water loss generates tensions larger than 0.1 MPa (i.e. negative pressures) in the xylem of cut leafy twigs the Cohesion Theory proposed by Böhm, Askenasy, Dixon and Joly at the end of the 19th century was immediately accepted by plant physiologists. Introduction of the pressure chamber technique by Scholander et al. in 1965 enforced the general belief that tension is the only driving force for water lifting although substantial criticism regarding the technique and/or the Cohesion Theory was published by several authors. As typical for scientific disciplines, the advent of minimal- and non-invasive techniques in the last decade as well as the development of a new, reliable method for xylem sap sampling have challenged this view. Today, xylem pressure gradients, potentials, ion concentrations and volume flows as well as cell turgor pressure gradients can be monitored online in intact transpiring higher plants, and within a given physiological context by using the pressure probe technique and high-resolution NMR imaging techniques, respectively. Application of the pressure probe technique to transpiring plants has shown that negative absolute pressures (down to - 0.6 MPa) and pressure gradients can exist temporarily in the xylem conduit, but that the magnitude and (occasionally) direction of gradients contrasts frequently the belief that tension is the only driving force. This seems to be particularly the case for plants faced with problems of height, drought, freezing and salinity as well as with cavitation of the tensile water. Reviewing the current data base shows that other forces come into operation when exclusively tension fails to lift water against gravity due to environmental conditions. Possible candidates are longitudinal cellular and xylem osmotic pressure gradients, axial potential gradients in the vessels as well as gel- and gas bubble-supported interfacial gradients. The multiforce theory overcomes the problem of the Cohesion Theory that life on earth depends on water being in a highly metastable state.

Janus droplet as a catalytic micromotor

NASA Astrophysics Data System (ADS)

Shklyaev, Sergey

2015-06-01

Self-propulsion of a Janus droplet in a solution of surfactant, which reacts on a half of a drop surface, is studied theoretically. The droplet acts as a catalytic motor creating a concentration gradient, which generates its surface-tension-driven motion; the self-propulsion speed is rather high, 60 μ \\text{m/s} and more. This catalytic motor has several advantages over other micromotors: simple manufacturing, easily attained neutral buoyancy. In contrast to a single-fluid droplet, which demonstrates a self-propulsion as a result of symmetry breaking instability, for the Janus one no stability threshold exists; hence, the droplet radius can be scaled down to micrometers.

The cocktail boat.

PubMed

Burton, Lisa J; Cheng, Nadia; Bush, John W M

2014-12-01

We describe the inspiration, development, and deployment of a novel cocktail device modeled after a class of water-walking insects. Semi-aquatic insects like Microvelia and Velia evade predators by releasing a surfactant that quickly propels them across the water. We exploit an analogous propulsion mechanism in the design of an edible cocktail boat. We discuss how gradients in surface tension lead to motion across the water's surface, and detail the design considerations associated with the insect-inspired cocktail boat. © The Author 2014. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. All rights reserved. For permissions please email: journals.permissions@oup.com.

Review of literature surface tension data for molten silicon

NASA Technical Reports Server (NTRS)

Hardy, S.

1981-01-01

Measurements of the surface tension of molten silicon are reported. For marangoni flow, the important parameter is the variation of surface tension with temperature, not the absolute value of the surface tension. It is not possible to calculate temperature coefficients using surface tension measurements from different experiments because the systematic errors are usually larger than the changes in surface tension because of temperature variations. The lack of good surface tension data for liquid silicon is probably due to its extreme chemical reactivity. A material which resists attack by molten silicon is not found. It is suggested that all of the sessile drip surface tension measurements are probably for silicon which is contaminated by the substrate materials.

Marangoni-driven chemotaxis, chemotactic collapse, and the Keller-Segel equation

NASA Astrophysics Data System (ADS)

Shelley, Michael; Masoud, Hassan

2013-11-01

Almost by definition, chemotaxis involves the biased motion of motile particles along gradients of a chemical concentration field. Perhaps the most famous model for collective chemotaxis in mathematical biology is the Keller-Segel model, conceived to describe collective aggregation of slime mold colonies in response to an intrinsically produced, and diffusing, chemo-attractant. Heavily studied, particularly in 2D where the system is ``super-critical'', it has been proved that the KS model can develop finite-time singularities - so-called chemotactic collapse - of delta-function type. Here, we study the collective dynamics of immotile particles bound to a 2D interface above a 3D fluid. These particles are chemically active and produce a diffusing field that creates surface-tension gradients along the surface. The resultant Marangoni stresses create flows that carry the particles, possibly concentrating them. Remarkably, we show that this system involving 3D diffusion and fluid dynamics, exactly yields the 2D Keller-Segel model for the surface-flow of active particles. We discuss the consequences of collapse on the 3D fluid dynamics, and generalizations of the fluid-dynamical model.

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 the computations. Agreement was demonstrated between the measurements and computations, but the flow is critically dependent on the nonlinear equation of state.

Remote Detection of Explosive Molecules by a Microfluidic SERS Device

NASA Astrophysics Data System (ADS)

Piorek, Brian; Lee, Seung Joon; Moskovits, Martin; Banerjee, Sanjoy; Meinhart, Carl

2007-11-01

Free-surface microfluidics (FSF) is combined with surface-enhanced Raman spectroscopy (SERS) to detect trace explosives vapors at room temperature and pressure. A free surface, with a large surface to volume ratio, is created using an open microchannel. Since surface tension is a dominant force at the microscale, it can be used to confine the fluid in the microchannel and create a pressure gradient to drive the flow with velocities ranging from ˜ 1um/s - 1mm/s. The curvature of the free surface is measured by confocal microscopy in order to determine the local Laplace pressure in the free-surface microchannel flow. The system has been used for the molecular-specific detection of vapor emanated from explosives such as DNT, TNT and picric acid. The system does not show signs of performance degradation from common interferents such as saturated gasoline vapor and perfume.

Gradient-type modeling of the effects of plastic recovery and surface passivation in thin films

NASA Astrophysics Data System (ADS)

Liu, Jinxing; Kah Soh, Ai

2016-08-01

The elasto-plastic responses of thin films subjected to cyclic tension-compression loading and bending are studied, with a focus on Bauschinger and size effects. For this purpose, a model is established by incorporating plastic recovery into the strain gradient plasticity theory we proposed recently. Elastic and plastic parts of strain and strain gradient, which are determined by the elasto-plastic decomposition according to the associative rule, are assumed to have a degree of material-dependent reversibility. Based on the above assumption, a dislocation reversibility-dependent rule is built to describe evolutions of different deformation components under cyclic loadings. Furthermore, a simple strategy is provided to implement the passivated boundary effects by introducing a gradual change to relevant material parameters in the yield function. Based on this theory, both bulge and bending tests under cyclic loading conditions are investigated. By comparing the present predictions with the existing experimental data, it is found that the yield function is able to exhibit the size effect, the Bauschinger effect, the influence of surface passivation and the hysteresis-loop phenomenon. Thus, the proposed model is deemed helpful in studying plastic deformations of micron-scale films.

Tunable nano-wrinkling of chiral surfaces: Structure and diffraction optics

NASA Astrophysics Data System (ADS)

Rofouie, P.; Pasini, D.; Rey, A. D.

2015-09-01

Periodic surface nano-wrinkling is found throughout biological liquid crystalline materials, such as collagen films, spider silk gland ducts, exoskeleton of beetles, and flower petals. These surface ultrastructures are responsible for structural colors observed in some beetles and plants that can dynamically respond to external conditions, such as humidity and temperature. In this paper, the formation of the surface undulations is investigated through the interaction of anisotropic interfacial tension, swelling through hydration, and capillarity at free surfaces. Focusing on the cellulosic cholesteric liquid crystal (CCLC) material model, the generalized shape equation for anisotropic interfaces using the Cahn-Hoffman capillarity vector and the Rapini-Papoular anchoring energy are applied to analyze periodic nano-wrinkling in plant-based plywood free surfaces with water-induced cholesteric pitch gradients. Scaling is used to derive the explicit relations between the undulations' amplitude expressed as a function of the anchoring strength and the spatially varying pitch. The optical responses of the periodic nano-structured surfaces are studied through finite difference time domain simulations indicating that CCLC surfaces with spatially varying pitch reflect light in a wavelength higher than that of a CCLC's surface with constant pitch. This structural color change is controlled by the pitch gradient through hydration. All these findings provide a foundation to understand structural color phenomena in nature and for the design of optical sensor devices.

Extended analysis of Skylab experiment M558 data

NASA Technical Reports Server (NTRS)

Ukanwa, A. O.

1976-01-01

A careful review of the data from Skylab M558 was made in an effort to explain the apparent anomaly of the existence of radial concentration gradients whereas none should bave been observed. The very close modelling of the experimental axial concentration profiles by the unsteady-state one-dimensional solution of Fick's Law of self-diffusion in liquid zinc, and the condition of initial uniform concentration in the radioactive pellet portion of the experimental specimens would have precluded the appearance of such radial concentration gradients. Statistical analyses were used to test the significance of the observed deviation from radial-concentration homogeneity. A student t-distribution test of significance showed that, at 90% or even at 80% level of significance, there were no significant deviations from uniformity in radial concentrations. It was also concluded that the two likely causes of any deviation that existed were the zinc to zinc-65 bonding procedure and surface phenomena such as surface tension and capillary action.

Investigation of pH response and photo-control of wettability on spiropyran-derivatized surfaces

NASA Astrophysics Data System (ADS)

Park, Choong-Do

2009-12-01

One promising method to control a liquid drop on a surface for microfluidic devices is to use the surface tension gradient on a photo-responsive surface by light irradiation. A photo-switchable spiropyran monolayer was prepared on smooth glass or silicon wafers via 3-aminopropylmethyldiethoxysilane linkages. The pH response of the surface-bound spiropyran was investigated by measuring contact angle as a function of pH, since the pH value of the liquids applied to a microfluidic system can vary widely. Based on the contact angle titration and UV-Vis spectroscopic data, a protonation and deprotonation mechanism of the surface-bound spiropyran was proposed. The advancing contact angles under UV and under visible light irradiation at high pH values were about 100 smaller than those at low pH values. The decrease in contact angle under UV light with decreasing pH value was assigned to the protonation of open merocyanine (MC) to MC-OH+. Meanwhile, the decrease in contact angle under visible light was attributed to the protonation of the closed spiropryan (SP), generating a mixed state of MC-OH+ in equilibrium with N-protonated SP-NH+. In order to examine the possibility of light-induced liquid drop motion on the spiropyran-derivatized smooth surfaces, the light-induced surface tension change between SP and MC was estimated using the contact angle hysteresis (CAH) and the Lifshitz---van der Waals/Acid-Base (LWAB) approaches based on the contact angle data. The average light-induced surface energy change between the two isomers under UV and visible light exposure was 1.4 mJ/m 2, implying that the small change in surface tension is not sufficient to move a liquid droplet on the surface. Liquid drop motion requires that the light-induced switching angle be greater than the contact angle hysteresis. However, the light-induced switching angle of the spiropyran-derivatized surface was significantly smaller than the hysteresis. Thus, in order to achieve liquid drop motion on the spiropyran-derivatized surface, a new surface design which employs a combination of chemical modification of a hydrophobic organosilane and micropatterned rough surface morphology was suggested.

A straightforward method for measuring the range of apparent density of microplastics.

PubMed

Li, Lingyun; Li, Mengmeng; Deng, Hua; Cai, Li; Cai, Huiwen; Yan, Beizhan; Hu, Jun; Shi, Huahong

2018-10-15

Density of microplastics has been regarded as the primary property that affect the distribution and bioavailability of microplastics in the water column. For measuring the density of microplastis, we developed a simple and rapid method based on density gradient solutions. In this study, we tested four solvents to make the density gradient solutions, i.e., ethanol (0.8 g/cm 3 ), ultrapure water (1.0 g/cm 3 ), saturated NaI (1.8 g/cm 3 ) and ZnCl 2 (1.8 g/cm 3 ). Density of microplastics was measured via observing the float or sink status in the density gradient solutions. We found that density gradient solutions made from ZnCl 2 had a larger uncertainty in measuring density than that from NaI, most likely due to a higher surface tension of ZnCl 2 solution. Solutions made from ethanol, ultrapure water, and NaI showed consistent density results with listed densities of commercial products, indicating that these density gradient solutions were suitable for measuring microplastics with a density range of 0.8-1.8 g/cm 3 . Copyright © 2018 Elsevier B.V. All rights reserved.

Collective Surfing of Chemically Active Particles

NASA Astrophysics Data System (ADS)

Masoud, Hassan; Shelley, Michael J.

2014-03-01

We study theoretically the collective dynamics of immotile particles bound to a 2D surface atop a 3D fluid layer. These particles are chemically active and produce a chemical concentration field that creates surface-tension gradients along the surface. The resultant Marangoni stresses create flows that carry the particles, possibly concentrating them. For a 3D diffusion-dominated concentration field and Stokesian fluid we show that the surface dynamics of active particle density can be determined using nonlocal 2D surface operators. Remarkably, we also show that for both deep or shallow fluid layers this surface dynamics reduces to the 2D Keller-Segel model for the collective chemotactic aggregation of slime mold colonies. Mathematical analysis has established that the Keller-Segel model can yield finite-time, finite-mass concentration singularities. We show that such singular behavior occurs in our finite-depth system, and study the associated 3D flow structures.

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 DPPC as the insoluble surfacant monolayer and measured for it a surface dilatational viscosity in the LE phase that is 20 surface poise.

An experimental test of the fluctuation relation in an active camphor boat system

NASA Astrophysics Data System (ADS)

Paroor, H. M.; Nambiar, N.; Bandi, M. M.

The Gallavotti-Cohen fluctuation relation (FR) posits a specific symmetry between positive and negative fluctuations in entropy production, or a related quantity (e.g power) for systems in non-equilibrium stationary state. Successful tests in a variety of systems suggest the FR may be more generally applicable than the conditions under which it was originally derived. Systems where the FR fails are therefore valuable for the insight they provide into the FR's general success. It has recently been suggested that ``active matter'' should not satisfy the fluctuation-dissipation theorem or FR. We experimentally test this possibility in a system of active camphor boats, self-propelled by surface tension gradients at air-water interfaces. The boats interact via short-range capillary attraction which competes with long-range surface tension mediated repulsion. Tuning interaction strength with number density, we test the FR through the statistics of power as one goes from a free non-interacting camphor boat, through a few weakly interacting boats to several, strongly interacting boats. We present preliminary results of our experiments and data analysis.

Geometric effects on bilayer convection in cylindrical containers

NASA Astrophysics Data System (ADS)

Johnson, Duane Thomas

The study of convection in two immiscible fluid layers is of interest for reasons both theoretical as well as applied. Recently, bilayer convection has been used as a model of convection in the earth's mantle. It is also an interesting system to use in the study of pattern formation. Bilayer convection also occurs in a process known as liquid encapsulated crystal growth, which is used to grow compound semiconductors. It is the last application which motivates this study. To analyze bilayer convection, theoretical models, numerical calculations and experiments were used. One theoretical model involves the derivation of the Navier- Stokes and energy equation for two immiscible fluid layers, using the Boussinesq approximation. A weakly nonlinear analysis was also performed to study the behavior of the system slightly beyond the onset of convection. Numerical calculations were necessary to solve both models. The experiments involved a single liquid layer of silicone oil, superposed by a layer of air. The radius and height of each fluid layer were changed to observe different flow patterns at the onset of convection. From the experiments and theory, two major discoveries were made as well as several interesting observations. The first discovery is the existence of codimension-two points-particular aspect ratios where two flow patterns coexist-in cylindrical containers. At these points, dynamic switching between different flow patterns was observed. The second discovery was the effect of air convection on the flow pattern in silicone oil. Historically, air has been considered a passive medium that has no effect on the lower fluid. However, experiments were done to show that for large air heights, convection in the air can cause radial temperature gradients at the liquid interface. These temperature gradients then cause surface tension gradient-driven flows. It was also shown that changing the radius of the container can change the driving force of convection from a surface tension gradient-driven to buoyancy-driven and back again. Finally, the weakly nonlinear analysis was able to give a qualitative description of codimension-two points as well as the change in flow patterns due to the convecting air layer.

Vertical two-phase flow regimes and pressure gradients under the influence of SDS surfactant

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duangprasert, Tanabordee; Sirivat, Anuvat; Siemanond, Kitipat

2008-01-15

Two-phase gas/liquid flows in vertical pipes have been systematically investigated. Water and SDS surfactant solutions at various concentrations were used as the working fluids. In particular, we focus our work on the influence of surfactant addition on the flow regimes, the corresponding pressure gradients, and the bubble sizes and velocity. Adding the surfactant lowers the air critical Reynolds numbers for the bubble-slug flow and the slug flow transitions. The pressure gradients of SDS solutions are lower than those of pure water especially in the slug flow and the slug-churn flow regimes, implying turbulent drag reduction. At low Re{sub air}, themore » bubble sizes of the surfactant solution are lower than those of pure water due to the increase in viscosity. With increasing and at high Re{sub air}, the bubble sizes of the SDS solution become greater than those of pure water which is attributed to the effect of surface tension. (author)« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Britten, J

WET-ETCH FIGURING (WEF) is an automated method of precisely figuring optical materials by the controlled application of aqueous etchant solution. This technology uses surface-tension-gradient-driven flow to confine and stabilize a wetted zone of an etchant solution or other aqueous processing fluid on the surface of an object. This wetted zone can be translated on the surface in a computer-controlled fashion for precise spatial control of the surface reactions occurring (e.g. chemical etching). WEF is particularly suitable for figuring very thin optical materials because it applies no thermal or mechanical stress to the material. Also, because the process is stress-free themore » workpiece can be monitored during figuring using interferometric metrology, and the measurements obtained can be used to control the figuring process in real-time--something that cannot be done with traditional figuring methods.« less

Influence of oxygen partial pressure on surface tension and its temperature coefficient of molten iron

NASA Astrophysics Data System (ADS)

Ozawa, S.; Suzuki, S.; Hibiya, T.; Fukuyama, H.

2011-01-01

Influences of oxygen partial pressure, PO2, of ambient atmosphere and temperature on surface tension and its temperature coefficient for molten iron were experimentally investigated by an oscillating droplet method using an electromagnetic levitation furnace. We successfully measured the surface tension of molten iron over a very wide temperature range of 780 K including undercooling condition in a well controlled PO2 atmosphere. When PO2 is fixed at 10-2 Pa at the inlet of the chamber, a "boomerang shape" temperature dependence of surface tension was experimentally observed; surface tension increased and then decreased with increasing temperature. The pure surface tension of molten iron was deduced from the negative temperature coefficient in the boomerang shape temperature dependence. When the surface tension was measured under the H2-containing gas atmosphere, surface tension did not show a linear relationship against temperature. The temperature dependence of the surface tension shows anomalous kink at around 1850 K due to competition between the temperature dependence of PO2 and that of the equilibrium constant of oxygen adsorption.

Measuring Surface Tension of a Flowing Soap Film

NASA Astrophysics Data System (ADS)

Sane, Aakash; Kim, Ildoo; Mandre, Shreyas

2016-11-01

It is well known that surface tension is sensitive to the presence of surfactants and many conventional methods exist to measure it. These techniques measure surface tension either by intruding into the system or by changing its geometry. Use of conventional methods in the case of a flowing soap film is not feasible because intruding the soap film changes surface tension due to Marangoni effect. We present a technique in which we measure the surface tension in situ of a flowing soap film without intruding into the film. A flowing soap film is created by letting soap solution drip between two wires. The interaction of the soap film with the wires causes the wires to deflect which can be measured. Surface tension is calculated using a relation between curvature of the wires and the surface tension. Our measurements indicate that the surface tension of the flowing soap film for our setup is around 0.05 N/m. The nature of this technique makes it favorable for measuring surface tension of flowing soap films whose properties change on intrusion.

Effects of carbohydrate/protein ratio on the microstructure and the barrier and sorption properties of wheat starch-whey protein blend edible films.

PubMed

Basiak, Ewelina; Lenart, Andrzej; Debeaufort, Frédéric

2017-02-01

Starch and whey protein isolate and their mixtures were used for making edible films. Moisture sorption isotherms, water vapour permeability, sorption of aroma compounds, microstructure, water contact angle and surface properties were investigated. With increasing protein content, the microstructure changes became more homogeneous. The water vapour permeability increases with both the humidity gradient and the starch content. For all films, the hygroscopicity increases with starch content. Surface properties change according to the starch/whey protein ratio and are mainly related to the polar component of the surface tension. Films composed of 80% starch and 20% whey proteins have more hydrophobic surfaces than the other films due to specific interactions. The effect of carbohydrate/protein ratio significantly influences the microstructure, the surface wettability and the barrier properties of wheat starch-whey protein blend films. © 2016 Society of Chemical Industry. © 2016 Society of Chemical Industry.

Effects of surface tension and viscosity on gold and silver sputtered onto liquid substrates

NASA Astrophysics Data System (ADS)

De Luna, Mark M.; Gupta, Malancha

2018-05-01

In this paper, we study DC magnetron sputtering of gold and silver onto liquid substrates of varying viscosities and surface tensions. We were able to separate the effects of viscosity from surface tension by depositing the metals onto silicone oils with a range of viscosities. The effects of surface tension were studied by depositing the metals onto squalene, poly(ethylene glycol), and glycerol. It was found that dispersed nanoparticles were formed on liquids with low surface tension and low viscosity whereas dense films were formed on liquids with low surface tension and high viscosity. Nanoparticles were formed on both the liquid surface and within the bulk liquid for high surface tension liquids. Our results can be used to tailor the metal and liquid interaction to fabricate particles and films for various applications in optics, electronics, and catalysis.

Spontaneous cavitation in a Lennard-Jones liquid: Molecular dynamics simulation and the van der Waals-Cahn-Hilliard gradient theory

NASA Astrophysics Data System (ADS)

Baidakov, Vladimir G.

2016-02-01

The process of bubble nucleation in a Lennard-Jones (LJ) liquid is studied by molecular dynamics (MD) simulation. The bubble nucleation rate J is determined by the mean life-time method at temperatures above that of the triple point in the region of negative pressures. The results of simulation are compared with classical nucleation theory (CNT) and modified classical nucleation theory (MCNT), in which the work of formation of a critical bubble is determined in the framework of the van der Waals-Cahn-Hilliard gradient theory (GT). It has been found that the values of J obtained in MD simulation systematically exceed the data of CNT, and this excess in the nucleation rate reaches 8-10 orders of magnitude close to the triple point temperature. The results of MCNT are in satisfactory agreement with the data of MD simulation. To describe the properties of vapor-phase nuclei in the framework of GT, an equation of state has been built up which describes stable, metastable and labile regions of LJ fluids. The surface tension of critical bubbles γ has been found from CNT and data of MD simulation as a function of the radius of curvature of the surface of tension R*. The dependence γ(R*) has also been calculated from GT. The Tolman length has been determined, which is negative and in modulus equal to ≈(0.1 - 0.2) σ. The paper discusses the applicability of the Tolman formula to the description of the properties of critical nuclei in nucleation.

Thermomechanically coupled conduction mode laser welding simulations using smoothed particle hydrodynamics

NASA Astrophysics Data System (ADS)

Hu, Haoyue; Eberhard, Peter

2017-10-01

Process simulations of conduction mode laser welding are performed using the meshless Lagrangian smoothed particle hydrodynamics (SPH) method. The solid phase is modeled based on the governing equations in thermoelasticity. For the liquid phase, surface tension effects are taken into account to simulate the melt flow in the weld pool, including the Marangoni force caused by a temperature-dependent surface tension gradient. A non-isothermal solid-liquid phase transition with the release or absorption of additional energy known as the latent heat of fusion is considered. The major heat transfer through conduction is modeled, whereas heat convection and radiation are neglected. The energy input from the laser beam is modeled as a Gaussian heat source acting on the initial material surface. The developed model is implemented in Pasimodo. Numerical results obtained with the model are presented for laser spot welding and seam welding of aluminum and iron. The change of process parameters like welding speed and laser power, and their effects on weld dimensions are investigated. Furthermore, simulations may be useful to obtain the threshold for deep penetration welding and to assess the overall welding quality. A scalability and performance analysis of the implemented SPH algorithm in Pasimodo is run in a shared memory environment. The analysis reveals the potential of large welding simulations on multi-core machines.

A hybrid interface tracking - level set technique for multiphase flow with soluble surfactant

NASA Astrophysics Data System (ADS)

Shin, Seungwon; Chergui, Jalel; Juric, Damir; Kahouadji, Lyes; Matar, Omar K.; Craster, Richard V.

2018-04-01

A formulation for soluble surfactant transport in multiphase flows recently presented by Muradoglu and Tryggvason (JCP 274 (2014) 737-757) [17] is adapted to the context of the Level Contour Reconstruction Method, LCRM, (Shin et al. IJNMF 60 (2009) 753-778, [8]) which is a hybrid method that combines the advantages of the Front-tracking and Level Set methods. Particularly close attention is paid to the formulation and numerical implementation of the surface gradients of surfactant concentration and surface tension. Various benchmark tests are performed to demonstrate the accuracy of different elements of the algorithm. To verify surfactant mass conservation, values for surfactant diffusion along the interface are compared with the exact solution for the problem of uniform expansion of a sphere. The numerical implementation of the discontinuous boundary condition for the source term in the bulk concentration is compared with the approximate solution. Surface tension forces are tested for Marangoni drop translation. Our numerical results for drop deformation in simple shear are compared with experiments and results from previous simulations. All benchmarking tests compare well with existing data thus providing confidence that the adapted LCRM formulation for surfactant advection and diffusion is accurate and effective in three-dimensional multiphase flows with a structured mesh. We also demonstrate that this approach applies easily to massively parallel simulations.

Simulation on the Effects of Surfactants and Observed Thermocapillary Motion for Laser Melting Physics

NASA Astrophysics Data System (ADS)

Nourgaliev, Robert; Barney, Rebecca; Weston, Brian; Delplanque, Jean-Pierre; McCallen, Rose

2017-11-01

A newly developed, robust, high-order in space and time, Newton-Krylov based reconstructed discontinuous Galerkin (rDG) method is used to model and analyze thermocapillary convection in melt pools. The application of interest is selective laser melting (SLM) which is an Additive Manufacturing (AM, 3D metal laser printing) process. These surface tension driven flows are influenced by temperature gradients and surfactants (impurities), and are known as the Marangoni flow. They have been experimentally observed in melt pools for welding applications, and are thought to influence the microstructure of the re-solidified material. We study the effects of the laser source configuration (power, beam size and scanning speed), as well as surfactant concentrations. Results indicate that the surfactant concentration influences the critical temperature, which governs the direction of the surface thermocapillary traction. When the surface tension traction changes sign, very complex flow patterns emerge, inducing hydrodynamic instability under certain conditions. These in turn would affect the melt pool size (depth) and shape, influencing the resulting microstructure, properties, and performance of a finished product part produced using 3D metal laser printing technologies. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Information management release number LLNL-ABS-735908.

Mechano-Electrochemical Interaction Gives Rise to Strain Relaxation in Sn Electrodes

DOE PAGES

Barai, Pallab; Huang, Bo; Dillon, Shen J.; ...

2016-01-01

Tin (Sn) anode active particles were electrochemically lithiated during simultaneous imaging in a scanning electron microscope. Relationships among the reaction mechanism, active particle local strain rate, particle size, and microcrack formation are elucidated to demonstrate the importance of strain relaxation due to mechano-electrochemical interaction in Sn-based electrodes under electrochemical cycling. At low rates of operation, due to significant creep relaxation, large Sn active particles, of size 1 μm, exhibit no significant surface crack formation. Microcrack formation within Sn active particles occurs due to two different mechanisms: (i)large concentration gradient induced stress at the two-phase interface, and (ii) high volume expansionmore » induced stress at the surface of the active particles. From the present study, it can be concluded that majority of the microcracks evolve at or near the particle surface due to high volume expansion induced tension. Concentration gradient induced damage prevails near the center of the active particle, though significantly smaller in magnitude. Comparison with experimental results indicates that at operating conditions of C/2, even 500 nm sized Sn active particles remain free from surface crack formation, which emphasizes the importance of creep relaxation. A phase map has been developed to demonstrate the preferred mechano-electrochemical window of operation of Sn-based electrodes.« less

Magnetic field dependent measurement techniques of surface tension of magnetic fluid at an air interface

NASA Astrophysics Data System (ADS)

Nair, Nishant; Virpura, Hiral; Patel, Rajesh

2015-06-01

We describe here two measurement techniques to determine surface tension of magnetic fluid. (i) magneti c field dependent capillary rise method and (ii) Taylor wavelength method in which the distance between the consecutive stable spikes was measured and then surface tension was calculated. The surface tension measurements from both the methods are compared. It is observed that surface tension of magnetic fluid increases with increase in magnetic field due to field dependent structure formation in magnetic fluid at an air interface. We have also measured magnetic susceptibility and surface tension for different volume fractions. The measurement of magnetic susceptibility is carried out using Quincke's experimental techniques.

Surface tension of Nanofluid-type fuels containing suspended nanomaterials

PubMed Central

2012-01-01

The surface tension of ethanol and n-decane based nanofluid fuels containing suspended aluminum (Al), aluminum oxide (Al2O3), and boron (B) nanoparticles as well as dispersible multi-wall carbon nanotubes (MWCNTs) were measured using the pendant drop method by solving the Young-Laplace equation. The effects of nanoparticle concentration, size and the presence of a dispersing agent (surfactant) on surface tension were determined. The results show that surface tension increases both with particle concentration (above a critical concentration) and particle size for all cases. This is because the Van der Waals force between particles at the liquid/gas interface increases surface free energy and thus increases surface tension. At low particle concentrations, however, addition of particles has little influence on surface tension because of the large distance between particles. An exception is when a surfactant was used or when (MWCNTs) was involved. For such cases, the surface tension decreases compared to the pure base fluid. The hypothesis is the polymer groups attached to (MWCNTs) and the surfactant layer between a particle and the surround fluid increases the electrostatic force between particles and thus reduce surface energy and surface tension. PMID:22513039

Surface tension and long range corrections of cylindrical interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bourasseau, E.; Malfreyt, P.; Ghoufi, A., E-mail: aziz.ghoufi@univ-rennes1.fr

2015-12-21

The calculation of the surface tension of curved interfaces has been deeply investigated from molecular simulation during this last past decade. Recently, the thermodynamic Test-Area (TA) approach has been extended to the calculation of surface tension of curved interfaces. In the case of the cylindrical vapour-liquid interfaces of water and Lennard-Jones fluids, it was shown that the surface tension was independent of the curvature of the interface. In addition, the surface tension of the cylindrical interface is higher than that of the planar interface. Molecular simulations of cylindrical interfaces have been so far performed (i) by using a shifted potential,more » (ii) by means of large cutoff without periodic boundary conditions, or (iii) by ignoring the long range corrections to the surface tension due to the difficulty to estimate them. Indeed, unlike the planar interfaces there are no available operational expressions to consider the tail corrections to the surface tension of cylindrical interfaces. We propose here to develop the long range corrections of the surface tension for cylindrical interfaces by using the non-exponential TA (TA2) method. We also extend the formulation of the Mecke-Winkelmann corrections initially developed for planar surfaces to cylindrical interfaces. We complete this study by the calculation of the surface tension of cylindrical surfaces of liquid tin and copper using the embedded atom model potentials.« less

Surface viscosity effects on the motion of self-propelling boat in a channel

NASA Astrophysics Data System (ADS)

Aliperio, M. G.; Nolan Confesor, Mark

2015-06-01

Self-propelled droplets have been conceived as simple chemical toy models to mimic motile biological samples such as bacteria. The motion of these droplets is believe to be due to the surface tension gradient in the boundary of the droplet. We performed experiments to look at the effect of varying the medium viscosity to the speed of a circular boat that was soaked in Pentanol. We found that the boats undergo oscillatory type of motion inside a channel. Moreover we found the maximum speed of the boat is independent on the viscosity of the medium. On the other a time scale describing the width of the velocity profile of the boat was found to increase with increasing viscosity.

A method for the direct measurement of surface tension of collected atmospherically relevant aerosol particles using atomic force microscopy

NASA Astrophysics Data System (ADS)

Hritz, Andrew D.; Raymond, Timothy M.; Dutcher, Dabrina D.

2016-08-01

Accurate estimates of particle surface tension are required for models concerning atmospheric aerosol nucleation and activation. However, it is difficult to collect the volumes of atmospheric aerosol required by typical instruments that measure surface tension, such as goniometers or Wilhelmy plates. In this work, a method that measures, ex situ, the surface tension of collected liquid nanoparticles using atomic force microscopy is presented. A film of particles is collected via impaction and is probed using nanoneedle tips with the atomic force microscope. This micro-Wilhelmy method allows for direct measurements of the surface tension of small amounts of sample. This method was verified using liquids, whose surface tensions were known. Particles of ozone oxidized α-pinene, a well-characterized system, were then produced, collected, and analyzed using this method to demonstrate its applicability for liquid aerosol samples. It was determined that oxidized α-pinene particles formed in dry conditions have a surface tension similar to that of pure α-pinene, and oxidized α-pinene particles formed in more humid conditions have a surface tension that is significantly higher.

Form-Finding Using Nonlinear Analysis Method in Tensioned Fabric Structure in The Form of Handkerchief Surface

NASA Astrophysics Data System (ADS)

Ibrahim, MH Wan; Hadi, MN Abdul; Hooi Min, Yee

2018-04-01

Tensioned fabric structure with different surface form could be realized. Their variations as possible choice form of minimal surface for tensioned fabric structure have been studied. The form of used in TFS is Handkerchief Surface. Handkerchief Surface used in TFS because Handkerchief Surface is the form of minimal surface and Handkerchief Surface has not been studied by other researcher. Besides, no other work on Handkerchief Surface as idea in tensioned fabric structure has been found. The aim of the study is to propose converged shape of Handkerchief Surface with variable u=v=0.4 and u=v=1.0. The method used for Form-Finding is nonlinear analysis method. From the result, the surface of Handkerchief TFS model, u=v=0.4 and u=v=1.0 show the total warp and fill stress deviation is less than 0.01. The initial equilibrium shape of Handkerchief tensioned fabric structure model, u=v=0.4 and u=v=1.0 is corresponding to equal tension surface. Tensioned fabric structure in the form of Handikerchief Surface is a structurally viable surface form to be considered by engineer.

Surface tension in human pathophysiology and its application as a medical diagnostic tool

PubMed Central

Fathi-Azarbayjani, Anahita; Jouyban, Abolghasem

2015-01-01

Introduction: Pathological features of disease appear to be quite different. Despite this diversity, the common feature of various disorders underlies physicochemical and biochemical factors such as surface tension. Human biological fluids comprise various proteins and phospholipids which are capable of adsorption at fluid interfaces and play a vital role in the physiological function of human organs. Surface tension of body fluids correlates directly to the development of pathological states. Methods: In this review, the variety of human diseases mediated by the surface tension changes of biological phenomena and the failure of biological fluids to remain in their native state are discussed. Results: Dynamic surface tension measurements of human biological fluids depend on various parameters such as sex, age and changes during pregnancy or certain disease. It is expected that studies of surface tension behavior of human biological fluids will provide additional information and might become useful in medical practice. Theoretical background on surface tension measurement and surface tension values of reference fluids obtained from healthy and sick patients are depicted. Conclusion: It is well accepted that no single biomarker will be effective in clinical diagnosis. The surface tension measurement combined with routine lab tests may be a novel non-invasive method which can not only facilitate the discovery of diagnostic models for various diseases and its severity, but also be a useful tool for monitoring treatment efficacy. We therefore expect that studies of surface tension behavior of human biological fluids will provide additional useful information in medical practice. PMID:25901295

Thermally induced secondary atomization of droplet in an acoustic field

NASA Astrophysics Data System (ADS)

Basu, Saptarshi; Saha, Abhishek; Kumar, Ranganathan

2012-01-01

We study the thermal effects that lead to instability and break up in acoustically levitated vaporizing fuel droplets. For selective liquids, atomization occurs at the droplet equator under external heating. Short wavelength [Kelvin-Helmholtz (KH)] instability for diesel and bio-diesel droplets triggers this secondary atomization. Vapor pressure, latent heat, and specific heat govern the vaporization rate and temperature history, which affect the surface tension gradient and gas phase density, ultimately dictating the onset of KH instability. We develop a criterion based on Weber number to define a condition for the inception of secondary atomization.

Marshburn works with Marangoni Experiment Hardware in Kibo

NASA Image and Video Library

2013-03-19

ISS035e006147 (19 March 2013) --- NASA astronaut Tom Marshburn, Expedition 35 flight engineer, works on the Marangoni Inside core cleaning in the Kibo Japanese Experiment Module onboard the Earth-orbiting International Space Station. Marangoni convection is the flow driven by the presence of a surface tension gradient which can be produced by temperature difference at a liquid/gas interface. The convection in liquid bridge of silicone oil is generated by heating the one disc higher than the other. Scientists are observing flow patterns of how fluids move to learn more about how heat is transferred in microgravity.

Thermal behavior in single track during selective laser melting of AlSi10Mg powder

NASA Astrophysics Data System (ADS)

Wei, Pei; Wei, Zhengying; Chen, Zhen; He, Yuyang; Du, Jun

2017-09-01

A three-dimensional model was developed to simulate the radiation heat transfer in the AlSi10Mg packed bed. The volume of fluid method (VOF) was used to capture the free surface during selective laser melting (SLM). A randomly packed powder bed was obtained using discrete element method (DEM) in Particle Flow Code (PFC). The proposed model has demonstrated a high potential to simulate the selective laser melting process (SLM) with high accuracy. In this paper, the effect of the laser scanning speed and laser power on the thermodynamic behavior of the molten pool was investigated numerically. The results show that the temperature gradient and the resultant surface tension gradient between the center and the edge of the molten pool increase with decreasing the scanning speed or increasing the laser power, thereby intensifying the Marangoni flow and attendant turbulence within the molten pool. However, at a relatively high scanning speed, a significant instability may be generated in the molten pool. The perturbation and instability in the molten pool during SLM may result in an irregular shaped track.

Oxygen environment and islet size are the primary limiting factors of isolated pancreatic islet survival

PubMed Central

Komatsu, Hirotake; Cook, Colin; Wang, Chia-Hao; Medrano, Leonard; Lin, Henry; Kandeel, Fouad; Tai, Yu-Chong; Mullen, Yoko

2017-01-01

Background Type 1 diabetes is an autoimmune disease that destroys insulin-producing beta cells in the pancreas. Pancreatic islet transplantation could be an effective treatment option for type 1 diabetes once several issues are resolved, including donor shortage, prevention of islet necrosis and loss in pre- and post-transplantation, and optimization of immunosuppression. This study seeks to determine the cause of necrotic loss of isolated islets to improve transplant efficiency. Methodology The oxygen tension inside isolated human islets of different sizes was simulated under varying oxygen environments using a computational in silico model. In vitro human islet viability was also assessed after culturing in different oxygen conditions. Correlation between simulation data and experimentally measured islet viability was examined. Using these in vitro viability data of human islets, the effect of islet diameter and oxygen tension of the culture environment on islet viability was also analyzed using a logistic regression model. Principal findings Computational simulation clearly revealed the oxygen gradient inside the islet structure. We found that oxygen tension in the islet core was greatly lower (hypoxic) than that on the islet surface due to the oxygen consumption by the cells. The hypoxic core was expanded in the larger islets or in lower oxygen cultures. These findings were consistent with results from in vitro islet viability assays that measured central necrosis in the islet core, indicating that hypoxia is one of the major causes of central necrosis. The logistic regression analysis revealed a negative effect of large islet and low oxygen culture on islet survival. Conclusions/Significance Hypoxic core conditions, induced by the oxygen gradient inside islets, contribute to the development of central necrosis of human isolated islets. Supplying sufficient oxygen during culture could be an effective and reasonable method to maintain isolated islets viable. PMID:28832685

Oxytropism: a new twist in pollen tube orientation

NASA Technical Reports Server (NTRS)

Blasiak, J.; Mulcahy, D. L.; Musgrave, M.

2001-01-01

Chemical gradients and structural features within the pistil have been previously proposed as factors determining the directionality of pollen tube growth. In this study, we examine the behavior of pollen of eight species germinated in a dynamic oxygen gradient. While the germination rates of some species decreased directly with decreasing oxygen tension, other species showed no decrease in germination at oxygen tensions as low as 2 kPa. In one species, germination was consistently greater at decreased oxygen tensions than at ambient atmospheric levels. In three of the eight species tested, the developing pollen tube showed clear directional growth away from the more-oxygenated regions of the growth medium, while in one species growth was towards the more-oxygenated region. The remaining four species showed random tube growth. The pattern of oxytropic responses among the taxa suggests that this tropic behavior is both widespread and phylogenetically unpredictable.

Surface tension, surface energy, and chemical potential due to their difference.

PubMed

Hui, C-Y; Jagota, A

2013-09-10

It is well-known that surface tension and surface energy are distinct quantities for solids. Each can be regarded as a thermodynamic property related first by Shuttleworth. Mullins and others have suggested that the difference between surface tension and surface energy cannot be sustained and that the two will approach each other over time. In this work we show that in a single-component system where changes in elastic energy can be neglected, the chemical potential difference between the surface and bulk is proportional to the difference between surface tension and surface energy. By further assuming that mass transfer is driven by this chemical potential difference, we establish a model for the kinetics by which mass transfer removes the difference between surface tension and surface energy.

Viscous free-surface flows on rotating elliptical cylinders

NASA Astrophysics Data System (ADS)

Li, Weihua; Carvalho, Marcio S.; Kumar, Satish

2017-09-01

The flow of liquid films on rotating discrete objects having complicated cross sections is encountered in coating processes for a broad variety of products. To advance fundamental understanding of this problem, we study viscous free-surface flows on rotating elliptical cylinders by solving the governing equations in a rotating reference frame using the Galerkin finite-element method. Results of our simulations agree well with Hunt's maximum-load condition [Hunt, Numer. Methods Partial Differ. Eqs. 24, 1094 (2008), 10.1002/num.20307], which was obtained in the absence of surface tension and inertia. The simulations are also used to track the transient behavior of the free surface. For O (1 ) cylinder aspect ratios, cylinder rotation results in a droplike liquid bulge hanging on the upward-moving side of the cylinder. This bulge shrinks in size due to surface tension provided that the liquid load is smaller than a critical value, leaving a relatively smooth coating on the cylinder. A decrease in cylinder aspect ratio leads to larger gradients in film thickness, but enhances the rate of bulge shrinkage and thus shortens the time required to obtain a smooth coating. Moreover, with a suitably chosen time-dependent rotation rate, more liquid can be supported by the cylinder relative to the constant-rotation-rate case. For cylinders with even smaller aspect ratios, film rupture and liquid shedding may occur over the cylinder tips, so simultaneous drying and rotation along with the introduction of Marangoni stresses will likely be especially important for obtaining a smooth coating.

Estimating intercellular surface tension by laser-induced cell fusion.

PubMed

Fujita, Masashi; Onami, Shuichi

2011-12-01

Intercellular surface tension is a key variable in understanding cellular mechanics. However, conventional methods are not well suited for measuring the absolute magnitude of intercellular surface tension because these methods require determination of the effective viscosity of the whole cell, a quantity that is difficult to measure. In this study, we present a novel method for estimating the intercellular surface tension at single-cell resolution. This method exploits the cytoplasmic flow that accompanies laser-induced cell fusion when the pressure difference between cells is large. Because the cytoplasmic viscosity can be measured using well-established technology, this method can be used to estimate the absolute magnitudes of tension. We applied this method to two-cell-stage embryos of the nematode Caenorhabditis elegans and estimated the intercellular surface tension to be in the 30-90 µN m(-1) range. Our estimate was in close agreement with cell-medium surface tensions measured at single-cell resolution.

Molecular Dynamics Simulation of Surface Tension of NaCl Aqueous Solution at 298.15K: from Diluted to Highly Supersaturated Concentrations

NASA Astrophysics Data System (ADS)

Wang, Xiaoxiang; Chen, Chuchu; Poeschl, Ulirch; Su, Hang; Cheng, Yafang

2017-04-01

Sodium chloride (NaCl) is one of the key components of atmospheric aerosol particles. Concentration-depend surface tension of aqueous NaCl solution is essential to determine the equilibrium between droplet NaCl solution and water vapor, which is important in regards to aerosol-cloud interaction and aerosol climate effects. Although supersaturated NaCl droplets can be widely found under atmospheric conditions, the experimental determined concentration dependency of surface tension is limited up to the saturated concentration range due to technical difficulties, i.e., heterogeneous nucleation since nearly all surface tension measurement techniques requires contact of the sensor and solution surface. In this study, the surface tension of NaCl aqueous solution with solute mass fraction from 0 to 1 was calculated using molecular dynamics (MD) simulation. The surface tension increases monotonically and near linearly when mass fraction of NaCl (xNaCl) is lower than 0.265 (saturation point), which follows theoretical predictions (e.g., E-AIM, SP parameterization, and PK parameterization). Once entering into the supersaturated concentration range, the calculated surface tension starts to deviate from the near-linear extrapolation and adopts a slightly higher increasing rate until xNaCl of 0.35. We found that these two increasing phases (xNaCl 0.35) is mainly driven by the increase of excessive surface enthalpy when the solution becomes concentrated. After that, the surface tension remains almost unchanged until xNaCl of 0.52. This phenomenon is supported by the results from experiment based Differential Koehler Analyses. The stable surface tension in this concentration range is attributed to a simultaneous change of surface excess enthalpy and entropy at similar degree. When the NaCl solution is getting more concentrated than xNaCl of 0.52, the simulated surface tension regains an even faster growing momentum and shows the tendency of ultimately approaching the surface tension of molten NaCl at 298.15 K ( 148.4 mN/m by MD simulation). Energetic analyses imply that this fast increase is primarily still an excessive surface enthalpy-driven process, although concurrent fluctuation of excessive surface entropy is also expected but in a much smaller scale. Our results unfold the global landscape of concentration dependence of aqueous NaCl solution and its driven forces: a water surface tension dominated regime (xNaCl from 0 to 0.35), a transition regime (xNaCl from 0.35 to 0.52) and a molten NaCl surface tension dominated regime (xNaCl beyond 0.52).

Weld pool development during GTA and laser beam welding of Type 304 stainless steel; Part II-experimental correlation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zacharia, T.; David, S.A.; Vitek, J.M.

1989-12-01

In part I of the paper, the results of the heat flow and the fluid flow analysis were presented. Here, in Part II of the paper, predictions of the computational model are verified by comparing the numerically predicted and experimentally observed fusion zone size and shape. Stationary gas tungsten arc and laser beam welds were made on Type 304 stainless steel for different times to provide a variety of solidification conditions such as cooling rate and temperature gradient. Calculated temperatures and cooling rates are correlated with the experimentally observed fusion zone structure. In addition, the effect of sulfur on GTAmore » weld penetration was quantitatively evaluated by considering two heats of 304 stainless steel containing 90 and 240 ppm sulfur. Sulfur, as expected, increased the depth/width ratio by altering the surface tension gradient driven flow in the weld pool.« less

Modeling of UV laser-induced patterning of ultrathin Co films on bulk SiO2: verification of short- and long-range ordering mechanisms

NASA Astrophysics Data System (ADS)

Trice, Justin; Favazza, Christopher; Kalyanaraman, Ramki; Sureshkumar, R.

2006-03-01

Irradiating ultrathin Co films (1 to 10 nm) by a short-pulsed UV laser leads to pattern formation with both short- and long-range order (SRO, LRO). Single beam irradiation produces SRO, while two-beam interference irradiation produces a quasi-2D arrangement of nanoparticles with LRO and SRO. The pattern formation primarily occurs in the molten phase. An estimate of the thermal behavior of the film/substrate composite following a laser pulse is presented. The thermal behavior includes the lifetime of the liquid phase and the thermal gradient during interference heating. Based on this evidence, the SRO is attributed to spinodal dewetting of the film while surface tension gradients induced by the laser interference pattern appear to influence LRO [1]. [1] C.Favazza, J.Trice, H.Krishna, R.Sureshkumar, and R.Kalyanaraman, unpublished.

Nanoscale relaxation oscillator

DOEpatents

Zettl, Alexander K.; Regan, Brian C.; Aloni, Shaul

2009-04-07

A nanoscale oscillation device is disclosed, wherein two nanoscale droplets are altered in size by mass transport, then contact each other and merge through surface tension. The device may also comprise a channel having an actuator responsive to mechanical oscillation caused by expansion and contraction of the droplets. It further has a structure for delivering atoms between droplets, wherein the droplets are nanoparticles. Provided are a first particle and a second particle on the channel member, both being made of a chargeable material, the second particle contacting the actuator portion; and electrodes connected to the channel member for delivering a potential gradient across the channel and traversing the first and second particles. The particles are spaced apart a specified distance so that atoms from one particle are delivered to the other particle by mass transport in response to the potential (e.g. voltage potential) and the first and second particles are liquid and touch at a predetermined point of growth, thereby causing merging of the second particle into the first particle by surface tension forces and reverse movement of the actuator. In a preferred embodiment, the channel comprises a carbon nanotube and the droplets comprise metal nanoparticles, e.g. indium, which is readily made liquid.

Precise, contactless measurements of the surface tension of picolitre aerosol droplets† †Electronic supplementary information (ESI) available: Parametrizations used to infer concentration, density, viscosity, and surface tension from refractive index for sodium chloride and glutaric acid; description of the semi-analytical T-matrix calculations; Fig. S1 and S2. See DOI: 10.1039/c5sc03184b Click here for additional data file.

PubMed Central

Bzdek, Bryan R.; Power, Rory M.; Simpson, Stephen H.; Royall, C. Patrick

2016-01-01

The surface composition and surface tension of aqueous droplets can influence key aerosol characteristics and processes including the critical supersaturation required for activation to form cloud droplets in the atmosphere. Despite its fundamental importance, surface tension measurements on droplets represent a considerable challenge owing to their small volumes. In this work, we utilize holographic optical tweezers to study the damped surface oscillations of a suspended droplet (<10 μm radius) following the controlled coalescence of a pair of droplets and report the first contactless measurements of the surface tension and viscosity of droplets containing only 1–4 pL of material. An advantage of performing the measurement in aerosol is that supersaturated solute states (common in atmospheric aerosol) may be accessed. For pairs of droplets starting at their equilibrium surface composition, surface tensions and viscosities are consistent with bulk equilibrium values, indicating that droplet surfaces respond to changes in surface area on microsecond timescales and suggesting that equilibrium values can be assumed for growing atmospheric droplets. Furthermore, droplet surfaces are shown to be rapidly modified by trace species thereby altering their surface tension. This equilibration of droplet surface tension to the local environmental conditions is illustrated for unknown contaminants in laboratory air and also for droplets exposed to gas passing through a water–ethanol solution. This approach enables precise measurements of surface tension and viscosity over long time periods, properties that currently are poorly constrained. PMID:28758004

Computing Incompressible Flows With Free Surfaces

NASA Technical Reports Server (NTRS)

Kothe, D.

1994-01-01

RIPPLE computer program models transient, two-dimensional flows of incompressible fluids with surface tension on free surfaces of general shape. Surface tension modeled as volume force derived from continuum-surface-force model, giving RIPPLE both robustness and accuracy in modeling surface-tension effects at free surface. Also models wall adhesion effects. Written in FORTRAN 77.

Dynamic surface tension measurements of ionic surfactants using maximum bubble pressure tensiometry

NASA Astrophysics Data System (ADS)

Ortiz, Camilla U.; Moreno, Norman; Sharma, Vivek

Dynamic surface tension refers to the time dependent variation in surface tension, and is intimately linked with the rate of mass transfer of a surfactant from liquid sub-phase to the interface. The diffusion- or adsorption-limited kinetics of mass transfer to interfaces is said to impact the so-called foamability and the Gibbs-Marangoni elasticity of surfaces. Dynamic surface tension measurements carried out with conventional methods like pendant drop analysis, Wilhelmy plate, etc. are limited in their temporal resolution (>50 ms). In this study, we describe design and application of maximum bubble pressure tensiometry for the measurement of dynamic surface tension effects at extremely short (1-50 ms) timescales. Using experiments and theory, we discuss the overall adsorption kinetics of charged surfactants, paying special attention to the influence of added salt on dynamic surface tension.

Concentration Dependences of the Surface Tension and Density of Solutions of Acetone-Ethanol-Water Systems at 293 K

NASA Astrophysics Data System (ADS)

Dadashev, R. Kh.; Dzhambulatov, R. S.; Mezhidov, V. Kh.; Elimkhanov, D. Z.

2018-05-01

Concentration dependences of the surface tension and density of solutions of three-component acetone-ethanol-water systems and the bounding binary systems at 273 K are studied. The molar volume, adsorption, and composition of surface layers are calculated. Experimental data and calculations show that three-component solutions are close to ideal ones. The surface tensions of these solutions are calculated using semi-empirical and theoretical equations. Theoretical equations qualitatively convey the concentration dependence of surface tension. A semi-empirical method based on the Köhler equation allows us to predict the concentration dependence of surface tension within the experimental error.

A New Approach for On-Demand Generation of Various Oxygen Tensions for In Vitro Hypoxia Models

PubMed Central

Li, Chunyan; Chaung, Wayne; Mozayan, Cameron; Chabra, Ranjeev; Wang, Ping; Narayan, Raj K.

2016-01-01

The development of in vitro disease models closely mimicking the functions of human disease has captured increasing attention in recent years. Oxygen tensions and gradients play essential roles in modulating biological systems in both physiologic and pathologic events. Thus, controlling oxygen tension is critical for mimicking physiologically relevant in vivo environments for cell, tissue and organ research. We present a new approach for on-demand generation of various oxygen tensions for in vitro hypoxia models. Proof-of-concept prototypes have been developed for conventional cell culture microplate by immobilizing a novel oxygen-consuming biomaterial on the 3D-printed insert. For the first time, rapid (~3.8 minutes to reach 0.5% O2 from 20.9% O2) and precisely controlled oxygen tensions/gradients (2.68 mmHg per 50 μm distance) were generated by exposing the biocompatible biomaterial to the different depth of cell culture media. In addition, changing the position of 3D-printed inserts with immobilized biomaterials relative to the cultured cells resulted in controllable and rapid changes in oxygen tensions (<130 seconds). Compared to the current technologies, our approach allows enhanced spatiotemporal resolution and accuracy of the oxygen tensions. Additionally, it does not interfere with the testing environment while maintaining ease of use. The elegance of oxygen tension manipulation introduced by our new approach will drastically improve control and lower the technological barrier of entry for hypoxia studies. Since the biomaterials can be immobilized in any devices, including microfluidic devices and 3D-printed tissues or organs, it will serve as the basis for a new generation of experimental models previously impossible or very difficult to implement. PMID:27219067

A New Approach for On-Demand Generation of Various Oxygen Tensions for In Vitro Hypoxia Models.

PubMed

Li, Chunyan; Chaung, Wayne; Mozayan, Cameron; Chabra, Ranjeev; Wang, Ping; Narayan, Raj K

2016-01-01

The development of in vitro disease models closely mimicking the functions of human disease has captured increasing attention in recent years. Oxygen tensions and gradients play essential roles in modulating biological systems in both physiologic and pathologic events. Thus, controlling oxygen tension is critical for mimicking physiologically relevant in vivo environments for cell, tissue and organ research. We present a new approach for on-demand generation of various oxygen tensions for in vitro hypoxia models. Proof-of-concept prototypes have been developed for conventional cell culture microplate by immobilizing a novel oxygen-consuming biomaterial on the 3D-printed insert. For the first time, rapid (~3.8 minutes to reach 0.5% O2 from 20.9% O2) and precisely controlled oxygen tensions/gradients (2.68 mmHg per 50 μm distance) were generated by exposing the biocompatible biomaterial to the different depth of cell culture media. In addition, changing the position of 3D-printed inserts with immobilized biomaterials relative to the cultured cells resulted in controllable and rapid changes in oxygen tensions (<130 seconds). Compared to the current technologies, our approach allows enhanced spatiotemporal resolution and accuracy of the oxygen tensions. Additionally, it does not interfere with the testing environment while maintaining ease of use. The elegance of oxygen tension manipulation introduced by our new approach will drastically improve control and lower the technological barrier of entry for hypoxia studies. Since the biomaterials can be immobilized in any devices, including microfluidic devices and 3D-printed tissues or organs, it will serve as the basis for a new generation of experimental models previously impossible or very difficult to implement.

Predictions of homogeneous nucleation rates for n-alkanes accounting for the diffuse phase interface and capillary waves.

PubMed

Planková, Barbora; Vinš, Václav; Hrubý, Jan

2017-10-28

Homogeneous droplet nucleation has been studied for almost a century but has not yet been fully understood. In this work, we used the density gradient theory (DGT) and considered the influence of capillary waves (CWs) on the predicted size-dependent surface tensions and nucleation rates for selected n-alkanes. The DGT model was completed by an equation of state (EoS) based on the perturbed-chain statistical associating fluid theory and compared to the classical nucleation theory and the Peng-Robinson EoS. It was found that the critical clusters are practically free of CWs because they are so small that even the smallest wavelengths of CWs do not fit into their finite dimensions. The CWs contribute to the entropy of the system and thus decrease the surface tension. A correction for the effect of CWs on the surface tension is presented. The effect of the different EoSs is relatively small because by a fortuitous coincidence their predictions are similar in the relevant range of critical cluster sizes. The difference of the DGT predictions to the classical nucleation theory computations is important but not decisive. Of the effects investigated, the most pronounced is the suppression of CWs which causes a sizable decrease of the predicted nucleation rates. The major difference between experimental nucleation rate data and theoretical predictions remains in the temperature dependence. For normal alkanes, this discrepancy is much stronger than observed, e.g., for water. Theoretical corrections developed here have a minor influence on the temperature dependency. We provide empirical equations correcting the predicted nucleation rates to values comparable with experiments.

Predictions of homogeneous nucleation rates for n-alkanes accounting for the diffuse phase interface and capillary waves

NASA Astrophysics Data System (ADS)

Planková, Barbora; Vinš, Václav; Hrubý, Jan

2017-10-01

Homogeneous droplet nucleation has been studied for almost a century but has not yet been fully understood. In this work, we used the density gradient theory (DGT) and considered the influence of capillary waves (CWs) on the predicted size-dependent surface tensions and nucleation rates for selected n-alkanes. The DGT model was completed by an equation of state (EoS) based on the perturbed-chain statistical associating fluid theory and compared to the classical nucleation theory and the Peng-Robinson EoS. It was found that the critical clusters are practically free of CWs because they are so small that even the smallest wavelengths of CWs do not fit into their finite dimensions. The CWs contribute to the entropy of the system and thus decrease the surface tension. A correction for the effect of CWs on the surface tension is presented. The effect of the different EoSs is relatively small because by a fortuitous coincidence their predictions are similar in the relevant range of critical cluster sizes. The difference of the DGT predictions to the classical nucleation theory computations is important but not decisive. Of the effects investigated, the most pronounced is the suppression of CWs which causes a sizable decrease of the predicted nucleation rates. The major difference between experimental nucleation rate data and theoretical predictions remains in the temperature dependence. For normal alkanes, this discrepancy is much stronger than observed, e.g., for water. Theoretical corrections developed here have a minor influence on the temperature dependency. We provide empirical equations correcting the predicted nucleation rates to values comparable with experiments.

Coaction of intercellular adhesion and cortical tension specifies tissue surface tension

PubMed Central

Manning, M. Lisa; Foty, Ramsey A.; Steinberg, Malcolm S.; Schoetz, Eva-Maria

2010-01-01

In the course of animal morphogenesis, large-scale cell movements occur, which involve the rearrangement, mutual spreading, and compartmentalization of cell populations in specific configurations. Morphogenetic cell rearrangements such as cell sorting and mutual tissue spreading have been compared with the behaviors of immiscible liquids, which they closely resemble. Based on this similarity, it has been proposed that tissues behave as liquids and possess a characteristic surface tension, which arises as a collective, macroscopic property of groups of mobile, cohering cells. But how are tissue surface tensions generated? Different theories have been proposed to explain how mesoscopic cell properties such as cell–cell adhesion and contractility of cell interfaces may underlie tissue surface tensions. Although recent work suggests that both may be contributors, an explicit model for the dependence of tissue surface tension on these mesoscopic parameters has been missing. Here we show explicitly that the ratio of adhesion to cortical tension determines tissue surface tension. Our minimal model successfully explains the available experimental data and makes predictions, based on the feedback between mechanical energy and geometry, about the shapes of aggregate surface cells, which we verify experimentally. This model indicates that there is a crossover from adhesion dominated to cortical-tension dominated behavior as a function of the ratio between these two quantities. PMID:20616053

Surfactant-induced flow compromises determination of air-water interfacial areas by surfactant miscible-displacement.

PubMed

Costanza-Robinson, Molly S; Henry, Eric J

2017-03-01

Surfactant miscible-displacement (SMD) column experiments are used to measure air-water interfacial area (A I ) in unsaturated porous media, a property that influences solute transport and phase-partitioning. The conventional SMD experiment results in surface tension gradients that can cause water redistribution and/or net drainage of water from the system ("surfactant-induced flow"), violating theoretical foundations of the method. Nevertheless, the SMD technique is still used, and some suggest that experimental observations of surfactant-induced flow represent an artifact of improper control of boundary conditions. In this work, we used numerical modeling, for which boundary conditions can be perfectly controlled, to evaluate this suggestion. We also examined the magnitude of surfactant-induced flow and its impact on A I measurement during multiple SMD flow scenarios. Simulations of the conventional SMD experiment showed substantial surfactant-induced flow and consequent drainage of water from the column (e.g., from 75% to 55% S W ) and increases in actual A I of up to 43%. Neither horizontal column orientation nor alternative boundary conditions resolved surfactant-induced flow issues. Even for simulated flow scenarios that avoided surfactant-induced drainage of the column, substantial surfactant-induced internal water redistribution occurred and was sufficient to alter surfactant transport, resulting in up to 23% overestimation of A I . Depending on the specific simulated flow scenario and data analysis assumptions used, estimated A I varied by nearly 40% and deviated up to 36% from the system's initial A I . We recommend methods for A I determination that avoid generation of surface-tension gradients and urge caution when relying on absolute A I values measured via SMD. Copyright © 2016 Elsevier Ltd. All rights reserved.

On the interfacial thermodynamics of nanoscale droplets and bubbles

NASA Astrophysics Data System (ADS)

Corti, David S.; Kerr, Karl J.; Torabi, Korosh

2011-07-01

We present a new self-consistent thermodynamic formalism for the interfacial properties of nanoscale embryos whose interiors do not exhibit bulklike behavior and are in complete equilibrium with the surrounding mother phase. In contrast to the standard Gibbsian analysis, whereby a bulk reference pressure based on the same temperature and chemical potentials of the mother phase is introduced, our approach naturally incorporates the normal pressure at the center of the embryo as an appropriate reference pressure. While the interfacial properties of small embryos that follow from the use of these two reference pressures are different, both methods yield by construction the same reversible work of embryo formation as well as consistency between their respective thermodynamic and mechanical routes to the surface tension. Hence, there is no a priori reason to select one method over another. Nevertheless, we argue, and demonstrate via a density-functional theory (with the local density approximation) analysis of embryo formation in the pure component Lennard-Jones fluid, that our new method generates more physically appealing trends. For example, within the new approach the surface tension at all locations of the dividing surface vanishes at the spinodal where the density profile spanning the embryo and mother phase becomes completely uniform (only the surface tension at the Gibbs surface of tension vanishes in the Gibbsian method at this same limit). Also, for bubbles, the location of the surface of tension now diverges at the spinodal, similar to the divergent behavior exhibited by the equimolar dividing surface (in the Gibbsian method, the location of the surface of tension vanishes instead). For droplets, the new method allows for the appearance of negative surface tensions (the Gibbsian method always yields positive tensions) when the normal pressures within the interior of the embryo become less than the bulk pressure of the surrounding vapor phase. Such a prediction, which is allowed by thermodynamics, is consistent with the interpretation that the mother phase's attempted compression of the droplet is counterbalanced by the negative surface tension, or free energy cost to decrease the interfacial area. Furthermore, for these same droplets, the surface of tension can no longer be meaningfully defined (the surface of tension always remains well defined in the Gibbsian method). Within the new method, the dividing surface at which the surface tension equals zero emerges as a new lengthscale, which has various thermodynamic analogs to and similar behavior as the surface of tension.

Surface tension anomalies in room temperature ionic liquids-acetone solutions

NASA Astrophysics Data System (ADS)

Abe, Hiroshi; Murata, Keisuke; Kiyokawa, Shota; Yoshimura, Yukihiro

2018-05-01

Surface tension anomalies were observed in room temperature ionic liquid (RTIL)-acetone solutions. The RTILs are 1-alkyl-3-methylimidazorium iodide with [Cnmim][I] in a [Cnmim][I]-x mol% acetone. The maximum value of the surface tension appeared at 40 mol% acetone, although density decreased monotonically with an increase in acetone concentration. A small alkyl chain length effect of the Cnmim+ cations was observed in the surface tension. By the Gibbs adsorption isotherm, it was found that I- anion-mediated surface structure became dominant above 40 mol%. In the different [Cnmim][TFSI]-acetone mixtures, normal decay of the surface tension was observed on the acetone concentration scale, where TFSI- is bis(trifluoromethanesulfonyl)imide.

Kinematically irreversible particle motion in 2D suspensions due to surface-pressure-dependent surface rheology

NASA Astrophysics Data System (ADS)

Manikantan, Harishankar; Squires, Todd

2017-11-01

The surface viscosity of many insoluble surfactants depends strongly on the surface pressure (or surface tension) of that surfactant. Surface pressure gradients naturally arise in interfacial flows, and surface-pressure-dependent surface rheology alters 2D suspension dynamics in significant ways. We use the Lorentz reciprocal theorem to asymptotically quantify the irreversible dynamics that break Newtonian symmetries. We first show that a particle embedded in a surfactant-laden interface and translating parallel to or rotating near an interfacial boundary experiences a force in the direction perpendicular to the boundary. Building on this, we extend the theory to compute the first effects of pressure-dependent surface viscosity on 2D particle pairs in suspension. The fore-aft symmetry of pair trajectories in a Newtonian interface is lost, leading to well-separated (when pressure-thickening) or aggregated (when pressure-thinning) particles. Notably, the relative motion is kinematically irreversible, and pairs steadily evolve toward a particular displacement. Based on these irreversible pair interactions, we hypothesize that pressure-thickening (or -thinning) leads to shear-thinning (or -thickening) in 2D suspensions.

Degradation of surfactant-associated protein B (SP-B) during in vitro conversion of large to small surfactant aggregates.

PubMed Central

Veldhuizen, R A; Inchley, K; Hearn, S A; Lewis, J F; Possmayer, F

1993-01-01

Pulmonary surfactant obtained from lung lavages can be separated by differential centrifugation into two distinct subfractions known as large surfactant aggregates and small surfactant aggregates. The large-aggregate fraction is the precursor of the small-aggregate fraction. The ratio of the small non-surface-active to large surface-active surfactant aggregates increases after birth and in several types of lung injury. We have utilized an in vitro system, surface area cycling, to study the conversion of large into small aggregates. Small aggregates generated by surface area cycling were separated from large aggregates by centrifugation at 40,000 g for 15 min rather than by the normal sucrose gradient centrifugation. This new separation method was validated by morphological studies. Surface-tension-reducing activity of total surfactant extracts, as measured with a pulsating-bubble surfactometer, was impaired after surface area cycling. This impairment was related to the generation of small aggregates. Immunoblot analysis of large and small aggregates separated by sucrose gradient centrifugation revealed the presence of detectable amounts of surfactant-associated protein B (SP-B) in large aggregates but not in small aggregates. SP-A was detectable in both large and small aggregates. PAGE of cycled and non-cycled surfactant showed a reduction in SP-B after surface area cycling. We conclude that SP-B is degraded during the formation of small aggregates in vitro and that a change in surface area appears to be necessary for exposing SP-B to protease activity. Images Figure 2 Figure 5 Figure 6 Figure 7 PMID:8216208

Experimental Values of the Surface Tension of Supercooled Water

NASA Technical Reports Server (NTRS)

Hacker, P. T.

1951-01-01

The results of surface-tension measurements for supercooled water are presented. A total of 702 individual measurements of surface tension of triple-distilled water were made in the temperature range, 27 to -22.2 C, with 404 of these measurements at temperatures below 0 C. The increase in magnitude of surface tension with decreasing temperature, as indicated by measurements above 0 C, continues to -22.2 C. The inflection point in the surface-tension - temperature relation in the vicinity of 0 C, as indicated by the International Critical Table values for temperatures down to -8 C, is substantiated by the measurements in the temperature range, 0 to -22.2 C. The surface tension increases at approximately a linear rate from a value of 76.96+/-0.06 dynes per centimeter at -8 C to 79.67+/-0.06 dynes per centimeter at -22.2 C.

Surface Tension of Liquid Alkali, Alkaline, and Main Group Metals: Theoretical Treatment and Relationship Investigations

NASA Astrophysics Data System (ADS)

Aqra, Fathi; Ayyad, Ahmed

2011-09-01

An improved theoretical method for calculating the surface tension of liquid metals is proposed. A recently derived equation that allows an accurate estimate of surface tension to be made for the large number of elements, based on statistical thermodynamics, is used for a means of calculating reliable values for the surface tension of pure liquid alkali, alkaline earth, and main group metals at the melting point, In order to increase the validity of the model, the surface tension of liquid lithium was calculated in the temperature range 454 K to 1300 K (181 °C to 1027 °C), where the calculated surface tension values follow a straight line behavior given by γ = 441 - 0.15 (T-Tm) (mJ m-2). The calculated surface excess entropy of liquid Li (- dγ/ dT) was found to be 0.15 mJ m-2 K-1, which agrees well with the reported experimental value (0.147 mJ/m2 K). Moreover, the relations of the calculated surface tension of alkali metals to atomic radius, heat of fusion, and specific heat capacity are described. The results are in excellent agreement with the existing experimental data.

Evaluation on Dorsey Method in Surface Tension Measurement of Solder Liquids Containing Surfactants

NASA Astrophysics Data System (ADS)

Zhao, Xingke; Xie, Feiming; Fan, Jinsheng; Liu, Dayong; Huang, Jihua; Chen, Shuhai

2018-06-01

With the purpose of developing a feasible approach for measuring the surface tension of solders containing surfactants, the surface tension of Sn-3Ag-0.5Cu-xP solder alloys, with various drop sizes as well as different phosphorus (P) content, was evaluated using the Dorsey method based on the sessile drop test. The results show that the accuracy of the surface tension calculations depends on both of sessile drop size and the liquid metal composition. With a proper drop size, in the range of 4.5 mm to 5.3 mm in equivalent spherical diameters, the deviation of the surface tension calculation can be limited to 1.43 mN·m-1 and 6.30 mN·m-1 for SnAgCu and SnAgCu-P, respectively. The surface tension of SnAgCu-xP solder alloys decreases quickly to a minimum value when the P content reaches 0.5 wt% and subsequently increases slowly with the P content further increasing. The formation of a P-enriched surface layer and Sn4P3 intermetallic phases is regarded to be responsible for the decreasing and subsequent increasing of surface tension, respectively.

Measurement of surface tension by sessile drop tensiometer with superoleophobic surface

NASA Astrophysics Data System (ADS)

Kwak, Wonshik; Park, Jun Kwon; Yoon, Jinsung; Lee, Sanghyun; Hwang, Woonbong

2018-03-01

A sessile drop tensiometer provides a simple and efficient method of determining the surface tension of various liquids. The technique involves obtaining the shape of an axisymmetric liquid droplet and iterative fitting of the Young-Laplace equation, which balances the gravitational deformation of the drop. Since the advent of high quality digital cameras and desktop computers, this process has been automated with precision. However, despite its appealing simplicity, there are complications and limitations in a sessile drop tensiometer, i.e., it must dispense spherical droplets with low surface tension. We propose a method of measuring surface tension using a sessile drop tensiometer with a superoleophobic surface fabricated by acidic etching and anodization for liquids with low surface tension and investigate the accuracy of the measurement by changing the wettability of the measuring plate surface.

Cloud condensation nucleus activity of internally mixed ammonium sulfate/organic acid aerosol particles

NASA Astrophysics Data System (ADS)

Abbatt, J. P. D.; Broekhuizen, K.; Pradeep Kumar, P.

The ability of mixed ammonium sulfate/organic acid particles to act as cloud condensation nuclei (CCN) has been studied in the laboratory using a continuous flow, thermal-gradient diffusion chamber operated at supersaturations between 0.3% and 0.6%. The organic acids studied were malonic acid, azelaic acid, hexanoic acid, cis-pinonic acid, oleic acid and stearic acid, and the particles were largely prepared by condensation of the organic vapor onto a dry ammonium sulfate core. For malonic acid and hexanoic acid, the mixed particles activated as predicted by a simple Köhler theory model where both species are assumed to be fully soluble and the droplet has the surface tension of water. Three low-solubility species, cis-pinonic acid, azelaic acid and oleic acid, are well modeled where the acid was assumed to be either partially or fully insoluble. Interestingly, although thin coats of stearic acid behaved in a manner similar to that displayed by oleic and cis-pinonic acid, we observed that thick coats led to a complete deactivation of the ammonium sulfate, presumably because the water vapor could not diffuse through the solid stearic acid. We observed no CCN behavior that could be clearly attributed to a lowering of the surface tension of the growing droplet by the presence of the organic constituents, some of which are highly surface active.

Asymptotic stability of shear-flow solutions to incompressible viscous free boundary problems with and without surface tension

NASA Astrophysics Data System (ADS)

Tice, Ian

2018-04-01

This paper concerns the dynamics of a layer of incompressible viscous fluid lying above a rigid plane and with an upper boundary given by a free surface. The fluid is subject to a constant external force with a horizontal component, which arises in modeling the motion of such a fluid down an inclined plane, after a coordinate change. We consider the problem both with and without surface tension for horizontally periodic flows. This problem gives rise to shear-flow equilibrium solutions, and the main thrust of this paper is to study the asymptotic stability of the equilibria in certain parameter regimes. We prove that there exists a parameter regime in which sufficiently small perturbations of the equilibrium at time t=0 give rise to global-in-time solutions that return to equilibrium exponentially in the case with surface tension and almost exponentially in the case without surface tension. We also establish a vanishing surface tension limit, which connects the solutions with and without surface tension.

Holographic interferometry of ultrasmall-pressure-induced curvature changes of bilayer lipid membranes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Picard, G.; Schneider-Henriquez, J.E.; Fendler, J.H.

Two-exposure interferometric holograms have been shown to sensitively report ultrasmall-pressure (10 natm)-induced curvature changes in glyceryl monooleate (GMO) bilayer lipid membranes (BLMs). The number of concentric fringes observed, and hence the lateral distance between the plane of the Teflon and the BLM, increased linearly with increasing transmembrane pressure and led to a value of 1.1 {plus minus} 0.05 dyn/cm for the surface tension of the BLM. BLMs with appreciable Plateau-Gibbs borders have been shown to undergo nonuniform deformation; the bilayer portion is distorted less than the surrounding Plateau-Gibbs border upon the application of a transmembrane pressure gradient.

Soft Listeria: actin-based propulsion of liquid drops.

PubMed

Boukellal, Hakim; Campás, Otger; Joanny, Jean-François; Prost, Jacques; Sykes, Cécile

2004-06-01

We study the motion of oil drops propelled by actin polymerization in cell extracts. Drops deform and acquire a pearlike shape under the action of the elastic stresses exerted by the actin comet, a tail of cross-linked actin filaments. We solve this free boundary problem and calculate the drop shape taking into account the elasticity of the actin gel and the variation of the polymerization velocity with normal stress. The pressure balance on the liquid drop imposes a zero propulsive force if gradients in surface tension or internal pressure are not taken into account. Quantitative parameters of actin polymerization are obtained by fitting theory to experiment.

Autonomous movement of silica and glass micro-objects based on a catalytic molecular propulsion system.

PubMed

Stock, Christoph; Heureux, Nicolas; Browne, Wesley R; Feringa, Ben L

2008-01-01

A general approach for the easy functionalization of bare silica and glass surfaces with a synthetic manganese catalyst is reported. Decomposition of H(2)O(2) by this dinuclear metallic center into H(2)O and O(2) induced autonomous movement of silica microparticles and glass micro-sized fibers. Although several mechanisms have been proposed to rationalise movement of particles driven by H(2)O(2) decomposition to O(2) and water (recoil from O(2) bubbles, ([36,45]) interfacial tension gradient([37-42]), it is apparent in the present system that ballistic movement is due to the growth of O(2) bubbles.

Natural convection in low-g environments

NASA Technical Reports Server (NTRS)

Grodzka, P. G.; Bannister, T. C.

1974-01-01

The present state of knowledge in the area of low-g natural convection is reviewed, taking into account a number of experiments conducted during the Apollo 14, 16, and 17 space flights. Convections due to steady low-g accelerations are considered. Steady g-levels result from spacecraft rotation, gravity gradients, solar wind, and solar pressure. Varying g-levels are produced by engine burns, attitude control maneuvers, and onboard vibrations from machinery or astronaut movement. Thermoacoustic convection in a low-g environment is discussed together with g-jitter convection, surface tension-driven convection, electrohydrodynamics under low-g conditions, phase change convection, and approaches for the control and the utilization of convection in space.

Marangoni flow on an inkjet nozzle plate

NASA Astrophysics Data System (ADS)

de Jong, Jos; Reinten, Hans; Wijshoff, Herman; van den Berg, Marc; Delescen, Koos; van Dongen, Rini; Mugele, Frieder; Versluis, Michel; Lohse, Detlef

2007-11-01

In piezo inkjet printing, nozzle failures are often caused by an ink layer on the nozzle plate. It is experimentally shown that the ink layer at the nozzle is formed through streamers of ink, emanating from a central ink band on the nozzle plate. The streamers propagate over a wetting nanofilm of 13nm thickness, directed toward the actuated nozzles. The motion of the front end of the streamers follows a power law in time with an exponent 1/2 . The observations are consistent with a surface tension gradient driven flow. The origin of the Marangoni flow is an effective lower surfactant concentration of the ink around the nozzle.

Surfactant-Enhanced Benard Convection on an Evaporating Drop

NASA Astrophysics Data System (ADS)

Nguyen, Van X.; Stebe, Kathleen J.

2001-11-01

Surfactant effects on an evaporating drop are studied experimentally. Using a fluorescent probe, the distribution and surface phase of the surfactant is directly imaged throughout the evaporation process. From these experiments, we identify conditions in which surfactants promote surface tension-driven Benard instabilities in aqueous systems. The drops under study contain finely divided particles, which act as tracers in the flow, and form well-defined patterns after the drop evaporates. Two flow fields have been reported in this system. The first occurs because the contact line becomes pinned by solid particles at the contact line region. In order for the contact line to remain fixed, an outward flow toward the ring results, driving further accumulation at the contact ring. A ‘coffee ring’ of particles is left as residue after the drop evaporates[1]. The second flow is Benard convection, driven by surface tension gradients on the drop[2,3]. In our experiments, an insoluble monolayer of pentadecanoic acid is spread at the interface of a pendant drop. The surface tension is recorded, and the drop is deposited on a well-defined solid substrate. Fluorescent images of the surface phase of the surfactant are recorded as the drop evaporates. The surfactant monolayer assumes a variety of surface states as a function of the area per molecule at the interface: surface gaseous, surface liquid expanded, and surface liquid condensed phases[4]. Depending upon the surface state of the surfactant as the drop evaporates, transitions of residue patterns left by the particles occur, from the coffee ring pattern to Benard cells to irregular patterns, suggesting a strong resistance to outward flow are observed. The occurrence of Benard cells on a surfactant-rich interface occurs when the interface is in LE-LC coexistence. Prior research concerning surfactant effects on this instability predict that surfactants are strongly stabilizing[5]. The mechanisms for this change in behavior are discussed. References: [1]R. D. Deegan,, PRE 61,475 (2000). [2]M. Maillard et al., J. Phys. Chem. B 104, 11871 (2000). [3]H. Wang et al. Langmuir 15, 957 (2001). [4]B. G. Moore et al., J. Phys. Chem. 94, 4588 (1990). [5]J. C. Berg & A. Acrivos, Chem. Eng. Sci. 20,737 (1965).

Surface tension isotherms of the dioxane-acetone-water and glycerol-ethanol-water ternary systems

NASA Astrophysics Data System (ADS)

Dzhambulatov, R. S.; Dadashev, R. Kh.; Elimkhanov, D. Z.; Dadashev, I. N.

2016-10-01

The results of the experimental and theoretical studies of the concentration dependence of surface tension of aqueous solutions of the 1,4-dioxane-acetone-water and glycerol-ethanol-water ternary systems were given. The studies were performed by the hanging-drop method on a DSA100 tensiometer. The maximum error of surface tension was 1%. The theoretical models for calculating the surface tension of the ternary systems of organic solutions were analyzed.

The effects of surface tension on flooding in counter-current two-phase flow in an inclined tube

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deendarlianto; Forschungszentrum Dresden-Rossendorf e.V., Institute of Safety Research, P.O. Box 510 119, D-01314 Dresden; Ousaka, Akiharu

2010-10-15

The purpose of the present study is to investigate the effects of surface tension on flooding phenomena in counter-current two-phase flow in an inclined tube. Previous studies by other researchers have shown that surface tension has a stabilizing effect on the falling liquid film under certain conditions and a destabilizing or unclear trend under other conditions. Experimental results are reported herein for air-water systems in which a surfactant has been added to vary the liquid surface tension without altering other liquid properties. The flooding section is a tube of 16 mm in inner diameter and 1.1 m length, inclined atmore » 30-60 from horizontal. The flooding mechanisms were observed by using two high-speed video cameras and by measuring the time variation of liquid hold-up along the test tube. The results show that effects of surface tension are significant. The gas velocity needed to induce flooding is lower for a lower surface tension. There was no upward motion of the air-water interfacial waves upon flooding occurrence, even for lower a surface tension. Observations on the liquid film behavior after flooding occurred suggest that the entrainment of liquid droplets plays an important role in the upward transport of liquid. Finally, an empirical correlation for flooding velocities is proposed that includes functional dependencies on surface tension and tube inclination. (author)« less

Autonomous Control of Fluids in a Wide Surface Tension Range in Microfluidics.

PubMed

Ge, Peng; Wang, Shuli; Liu, Yongshun; Liu, Wendong; Yu, Nianzuo; Zhang, Jianglei; Shen, Huaizhong; Zhang, Junhu; Yang, Bai

2017-07-25

In this paper, we report the preparation of anisotropic wetting surfaces that could control various wetting behaviors of liquids in a wide surface tension range (from water to oil), which could be employed as a platform for controlling the flow of liquids in microfluidics (MFs). The anisotropic wetting surfaces are chemistry-asymmetric "Janus" silicon cylinder arrays, which are fabricated via selecting and regulating the functional groups on the surface of each cylinder unit. Liquids (in a wide surface tension range) wet in a unidirectional manner along the direction that was modified by the group with large surface energy. Through introducing the Janus structure into a T-shaped pattern and integrating it with an identical T-shaped poly(dimethylsiloxane) microchannel, the as-prepared chips can be utilized to perform as a surface tension admeasuring apparatus or a one-way valve for liquids in a wide surface tension range, even oil. Furthermore, because of the excellent ability in controlling the flowing behavior of liquids in a wide surface tension range in an open system or a microchannel, the anisotropic wetting surfaces are potential candidates to be applied both in open MFs and conventional MFs, which would broaden the application fields of MFs.

Thermal effects on the enhanced ductility in non-monotonic uniaxial tension of DP780 steel sheet

NASA Astrophysics Data System (ADS)

Majidi, Omid; Barlat, Frederic; Korkolis, Yannis P.; Fu, Jiawei; Lee, Myoung-Gyu

2016-11-01

To understand the material behavior during non-monotonic loading, uniaxial tension tests were conducted in three modes, namely, the monotonic loading, loading with periodic relaxation and periodic loading-unloadingreloading, at different strain rates (0.001/s to 0.01/s). In this study, the temperature gradient developing during each test and its contribution to increasing the apparent ductility of DP780 steel sheets were considered. In order to assess the influence of temperature, isothermal uniaxial tension tests were also performed at three temperatures (298 K, 313 K and 328 K (25 °C, 40 °C and 55 °C)). A digital image correlation system coupled with an infrared thermography was used in the experiments. The results show that the non-monotonic loading modes increased the apparent ductility of the specimens. It was observed that compared with the monotonic loading, the temperature gradient became more uniform when a non-monotonic loading was applied.

Solitary wave solutions and their interactions for fully nonlinear water waves with surface tension in the generalized Serre equations

NASA Astrophysics Data System (ADS)

Dutykh, Denys; Hoefer, Mark; Mitsotakis, Dimitrios

2018-04-01

Some effects of surface tension on fully nonlinear, long, surface water waves are studied by numerical means. The differences between various solitary waves and their interactions in subcritical and supercritical surface tension regimes are presented. Analytical expressions for new peaked traveling wave solutions are presented in the dispersionless case of critical surface tension. Numerical experiments are performed using a high-accurate finite element method based on smooth cubic splines and the four-stage, classical, explicit Runge-Kutta method of order 4.

Capillary wave Hamiltonian for the Landau-Ginzburg-Wilson density functional

NASA Astrophysics Data System (ADS)

Chacón, Enrique; Tarazona, Pedro

2016-06-01

We study the link between the density functional (DF) formalism and the capillary wave theory (CWT) for liquid surfaces, focused on the Landau-Ginzburg-Wilson (LGW) model, or square gradient DF expansion, with a symmetric double parabola free energy, which has been extensively used in theoretical studies of this problem. We show the equivalence between the non-local DF results of Parry and coworkers and the direct evaluation of the mean square fluctuations of the intrinsic surface, as is done in the intrinsic sampling method for computer simulations. The definition of effective wave-vector dependent surface tensions is reviewed and we obtain new proposals for the LGW model. The surface weight proposed by Blokhuis and the surface mode analysis proposed by Stecki provide consistent and optimal effective definitions for the extended CWT Hamiltonian associated to the DF model. A non-local, or coarse-grained, definition of the intrinsic surface provides the missing element to get the mesoscopic surface Hamiltonian from the molecular DF description, as had been proposed a long time ago by Dietrich and coworkers.

Capillary wave Hamiltonian for the Landau-Ginzburg-Wilson density functional.

PubMed

Chacón, Enrique; Tarazona, Pedro

2016-06-22

We study the link between the density functional (DF) formalism and the capillary wave theory (CWT) for liquid surfaces, focused on the Landau-Ginzburg-Wilson (LGW) model, or square gradient DF expansion, with a symmetric double parabola free energy, which has been extensively used in theoretical studies of this problem. We show the equivalence between the non-local DF results of Parry and coworkers and the direct evaluation of the mean square fluctuations of the intrinsic surface, as is done in the intrinsic sampling method for computer simulations. The definition of effective wave-vector dependent surface tensions is reviewed and we obtain new proposals for the LGW model. The surface weight proposed by Blokhuis and the surface mode analysis proposed by Stecki provide consistent and optimal effective definitions for the extended CWT Hamiltonian associated to the DF model. A non-local, or coarse-grained, definition of the intrinsic surface provides the missing element to get the mesoscopic surface Hamiltonian from the molecular DF description, as had been proposed a long time ago by Dietrich and coworkers.

Surface tensions of solutions containing dicarboxylic acid mixtures

NASA Astrophysics Data System (ADS)

Lee, Jae Young; Hildemann, Lynn M.

2014-06-01

Organic solutes tend to lower the surface tension of cloud condensation nuclei, allowing them to more readily activate. The surface tension of various dicarboxylic acid aerosol mixtures was measured at 20 °C using the Wilhelmy plate method. At lower concentrations, the surface tension of a solution with equi-molar mixtures of dicarboxylic acids closely followed that of a solution with the most surface-active organic component alone. Measurements of surface tension for these mixtures were lower than predictions using Henning's model and the modified Szyszkowski equation, by ˜1-2%. The calculated maximum surface excess (Γmax) and inverse Langmuir adsorption coefficient (β) from the modified Szyszkowski equation were both larger than measured values for 6 of the 7 mixtures tested. Accounting for the reduction in surface tension in the Köhler equation reduced the critical saturation ratio for these multi-component mixtures - changes were negligible for dry diameters of 0.1 and 0.5 μm, but a reduction from 1.0068 to 1.0063 was seen for the 4-dicarboxylic acid mixture with a dry diameter of 0.05 μm.

The algorithms for rational spline interpolation of surfaces

NASA Technical Reports Server (NTRS)

Schiess, J. R.

1986-01-01

Two algorithms for interpolating surfaces with spline functions containing tension parameters are discussed. Both algorithms are based on the tensor products of univariate rational spline functions. The simpler algorithm uses a single tension parameter for the entire surface. This algorithm is generalized to use separate tension parameters for each rectangular subregion. The new algorithm allows for local control of tension on the interpolating surface. Both algorithms are illustrated and the results are compared with the results of bicubic spline and bilinear interpolation of terrain elevation data.

Study on the surface tensions of MDEA-methanol aqueous solutions

NASA Astrophysics Data System (ADS)

Wang, S. Q.; Wang, L. M.; Wang, F.; Fu, D.

2017-03-01

The surface tensions (γ) of N-methyldiethanolamine (MDEA)-methanol (MeOH) aqueous solutions were measured by using an automatic surface tension-meter (BZY-1). The temperature ranged from 303.2K to 323.2K. The mass fractions of MeOH and MDEA respectively ranged from 0.05 to 0.15 and 0.2 to 0.4. On the basis of the experimental measurement, the effects of temperature and mass fraction of MDEA and MeOH on surface tensions were analyzed.

Origin of change in molecular-weight dependence for polymer surface tension.

PubMed

Thompson, R B; Macdonald, J R; Chen, P

2008-09-01

Self-consistent-field theory is used to reproduce the behavior of polymer surface tension with molecular-weight for both lower and higher molecular-weight polymers. The change in behavior of the surface tension between these two regimes is shown to be due to the almost total exclusion of polymer from the nonpolymer bulk phase. The predicted two regime surface tension behavior with molecular-weight and the exclusion explanation are shown to be valid for a range of different polymer compressibilities.

Surface tension profiles in vertical soap films

NASA Astrophysics Data System (ADS)

Adami, N.; Caps, H.

2015-01-01

Surface tension profiles in vertical soap films are experimentally investigated. Measurements are performed by introducing deformable elastic objets in the films. The shape adopted by those objects once set in the film is related to the surface tension value at a given vertical position by numerically solving the adapted elasticity equations. We show that the observed dependency of the surface tension versus the vertical position is predicted by simple modeling that takes into account the mechanical equilibrium of the films coupled to previous thickness measurements.

Modal analysis of a nonuniform string with end mass and variable tension

NASA Technical Reports Server (NTRS)

Rheinfurth, M. H.; Galaboff, Z. J.

1983-01-01

Modal synthesis techniques for dynamic systems containing strings describe the lateral displacements of these strings by properly chosen shape functions. An iterative algorithm is provided to calculate the natural modes of a nonuniform string and variable tension for some typical boundary conditions including one end mass. Numerical examples are given for a string in a constant and a gravity gradient force field.

Monte Carlo studies on the interfacial properties and interfacial structures of ternary symmetric blends with gradient copolymers.

PubMed

Sun, Dachuan; Guo, Hongxia

2012-08-09

Using Monte Carlo simulation methods, the effects of the comonomer sequence distribution on the interfacial properties (including interfacial tension, interfacial thickness, saturated interfacial area per copolymer, and bending modulus) and interfacial structures (including chain conformations and comonomer distributions of the simulated copolymers at the interfaces) of a ternary symmetric blend containing two immiscible homopolymers and one gradient copolymer are investigated. We find that copolymers with a larger composition gradient width have a broader comonomer distribution along the interface normal, and hence more pronouncedly enlarge the interfacial thickness and reduce the interfacial tension. Furthermore, the counteraction effect, which arises from the tendency of heterogeneous segments in gradient copolymers to phase separate and enter their miscible phases to reduce the local enthalpy, decreases the stretching of copolymers along the interface normal direction. As a result, copolymers with a larger width of gradient composition can occupy a larger interfacial area and form softer monolayers at saturation and are more efficient in facilitating the formation of bicontinuous microemulsions. Additionally, chain length ratio, segregation strength, and interactions between homopolymers and copolymers can alter the interfacial character of gradient copolymers. There exists a strong coupling between the comonomer sequence distribution, chain conformation, and interfacial properties. Especially, bending modulus is mainly determined by the complicated interplay of interfacial copolymer density and interfacial chain conformation.

Determination of the critical surface tension of wetting of minerals treated with surfactants by shear flocculation approach.

PubMed

Ozkan, A

2004-09-15

This paper contributes the shear flocculation method as a new approach to determine the critical surface tension of wetting of minerals treated with surfactants. This newly developed approach is based on the decrease of the shear flocculation of the mineral suspension, with decreasing of the surface tension of the liquids used. The solution surface tension value at which shear flocculation does not occur can be defined as the critical surface tension of wetting (gamma c) of the mineral. By using the shear flocculation method, the critical surface tensions of wetting (gamma c) for calcite and barite minerals, treated with surfactants, were obtained as 30.9 and 35.0 mN/m, respectively. These values are in good agreement with data reported previously on the same minerals obtained by the contact angle measurement and flotation methods. The chemical agents used for the treatment of calcite and barite particles were sodium oleate and sodium dodecyl sulfate, respectively.

A compressible multiphase framework for simulating supersonic atomization

NASA Astrophysics Data System (ADS)

Regele, Jonathan D.; Garrick, Daniel P.; Hosseinzadeh-Nik, Zahra; Aslani, Mohamad; Owkes, Mark

2016-11-01

The study of atomization in supersonic combustors is critical in designing efficient and high performance scramjets. Numerical methods incorporating surface tension effects have largely focused on the incompressible regime as most atomization applications occur at low Mach numbers. Simulating surface tension effects in high speed compressible flow requires robust numerical methods that can handle discontinuities caused by both material interfaces and shocks. A shock capturing/diffused interface method is developed to simulate high-speed compressible gas-liquid flows with surface tension effects using the five-equation model. This includes developments that account for the interfacial pressure jump that occurs in the presence of surface tension. A simple and efficient method for computing local interface curvature is developed and an acoustic non-dimensional scaling for the surface tension force is proposed. The method successfully captures a variety of droplet breakup modes over a range of Weber numbers and demonstrates the impact of surface tension in countering droplet deformation in both subsonic and supersonic cross flows.

Sensory transduction and the mammalian epidermis.

PubMed

Hoath, S B; Donnelly, M M; Boissy, R E

1990-01-01

This paper constitutes, in its main intent, an introduction to the mammalian epidermis as a surface for biosensor applications. In particular, the structure and function of the epidermis of the newborn rat are examined as a model for studies of the human state. Data are presented illustrating an anisotropic organization of the dorsal surface of the neonatal rodent with regard to line of tension and thermal gradients. The dependence of the mechanical properties of the epidermis upon calcium is examined by means of an in-vitro assay of epidermal retraction. The potential role of keratin tonofilaments as piezoelectric and pyroelectric elements in the epidermis is introduced and the spatial alignment of these macromolecular arrays is demonstrated to be a function of physiological tensions. These findings are discussed in the context of noninvasive epidermal sensors utilized to understand mechanisms of sensory development and physiological regulation. Optoelectronic (infrared) imaging of the dorsal temperature field and the alteration in this field by treatment with epidermal growth factor are presented as examples of this methodologic approach. It is concluded that a detailed examination of the material and physical properties of mammalian epidermis is a reasonable goal of biosensor development and research. Hypothetically, such studies may reveal important molecular and cellular mechanisms by which sensory data are transmitted or transduced at the organism-environmental interface.

The Drainage of Thin, Vertical, Model Polyurethane Liquid Films

NASA Astrophysics Data System (ADS)

Snow, Steven; Pernisz, Udo; Braun, Richard; Naire, Shailesh

1999-11-01

We have successfully measured the drainage rate of thin, vertically-aligned, liquid films prepared from model polyurethane foam formulations. The pattern of interference fringes in these films was consistent with a wedge-shaped film profile. The time evolution of this wedge shape (the ``collapsing wedge") obeyed a power law relationship between fringe density s and time t of s = k t^m. Experimentally, m ranged from -0.47 to -0.92. The lower bound for m represented a case where the surface viscosity of the film was very high (a ``rigid" surface). Theoretical modeling of this case yielded m = -0.5, in excellent agreement with experiment. Instantaneous film drainage rate (dV/dt) could be extracted from the ``Collapsing Wedge" model. As expected, dV/dt scaled inversely with bulk viscosity. As surfactant concentration was varied at constant bulk viscosity, dV/dt passed through a maximum value, consistent with a model where the rigidity of the surface was a function of both the intensity of surface tension gradients and the surface viscosity of the film. The influence of surface viscosity on dV/dt was also modeled theoretically.

Pinch-off dynamics, extensional viscosity and relaxation time of dilute and ultradilute aqueous polymer solutions

NASA Astrophysics Data System (ADS)

Biagioli, Madeleine; Dinic, Jelena; Jimenez, Leidy Nallely; Sharma, Vivek

Free surface flows and drop formation processes present in printing, jetting, spraying, and coating involve the development of columnar necks that undergo spontaneous surface-tension driven instability, thinning, and pinch-off. Stream-wise velocity gradients that arise within the thinning neck create and extensional flow field, which induces micro-structural changes within complex fluids that contribute elastic stresses, changing the thinning and pinch-off dynamics. In this contribution, we use dripping-onto-substrate (DoS) extensional rheometry technique for visualization and analysis of the pinch-off dynamics of dilute and ultra-dilute aqueous polyethylene oxide (PEO) solutions. Using a range of molecular weights, we study the effect of both elasticity and finite extensibility. Both effective relaxation time and the transient extensional viscosity are found to be strongly concentration-dependent even for highly dilute solutions.

Quantification of surface tension and internal pressure generated by single mitotic cells

NASA Astrophysics Data System (ADS)

Fischer-Friedrich, Elisabeth; Hyman, Anthony A.; Jülicher, Frank; Müller, Daniel J.; Helenius, Jonne

2014-08-01

During mitosis, adherent cells round up, by increasing the tension of the contractile actomyosin cortex while increasing the internal hydrostatic pressure. In the simple scenario of a liquid cell interior, the surface tension is related to the local curvature and the hydrostatic pressure difference by Laplace's law. However, verification of this scenario for cells requires accurate measurements of cell shape. Here, we use wedged micro-cantilevers to uniaxially confine single cells and determine confinement forces while concurrently determining cell shape using confocal microscopy. We fit experimentally measured confined cell shapes to shapes obeying Laplace's law with uniform surface tension and find quantitative agreement. Geometrical parameters derived from fitting the cell shape, and the measured force were used to calculate hydrostatic pressure excess and surface tension of cells. We find that HeLa cells increase their internal hydrostatic pressure excess and surface tension from ~ 40 Pa and 0.2 mNm-1 during interphase to ~ 400 Pa and 1.6 mNm-1 during metaphase. The method introduced provides a means to determine internal pressure excess and surface tension of rounded cells accurately and with minimal cellular perturbation, and should be applicable to characterize the mechanical properties of various cellular systems.

Surface tension of flowing soap films

NASA Astrophysics Data System (ADS)

Sane, Aakash; Mandre, Shreyas; Kim, Ildoo

2018-04-01

The surface tension of flowing soap films is measured with respect to the film thickness and the concentration of soap solution. We perform this measurement by measuring the curvature of the nylon wires that bound the soap film channel and use the measured curvature to parametrize the relation between the surface tension and the tension of the wire. We find the surface tension of our soap films increases when the film is relatively thin or made of soap solution of low concentration, otherwise it approaches an asymptotic value 30 mN/m. A simple adsorption model with only two parameters describes our observations reasonably well. With our measurements, we are also able to measure Gibbs elasticity for our soap film.

Synthesis of ZnO nanoparticles for oil-water interfacial tension reduction in enhanced oil recovery

NASA Astrophysics Data System (ADS)

Soleimani, Hassan; Baig, Mirza Khurram; Yahya, Noorhana; Khodapanah, Leila; Sabet, Maziyar; Demiral, Birol M. R.; Burda, Marek

2018-02-01

Nanoparticles show potential use in applications associated with upstream oil and gas engineering to increase the performance of numerous methods such as wettability alteration, interfacial tension reduction, thermal conductivity and enhanced oil recovery operations. Surface tension optimization is an important parameter in enhanced oil recovery. Current work focuses on the new economical method of surface tension optimization of ZnO nanofluids for oil-water interfacial tension reduction in enhanced oil recovery. In this paper, zinc oxide (ZnO) nanocrystallites were prepared using the chemical route and explored for enhanced oil recovery (EOR). Adsorption of ZnO nanoparticles (NPs) on calcite (111) surface was investigated using the adsorption locator module of Materials Studio software. It was found that ZnO nanoparticles show maximum adsorption energy of - 253 kcal/mol. The adsorption of ZnO on the rock surface changes the wettability which results in capillary force reduction and consequently increasing EOR. The nanofluids have been prepared by varying the concentration of ZnO nanoparticles to find the optimum value for surface tension. The surface tension (ST) was calculated with different concentration of ZnO nanoparticles using the pendant drop method. The results show a maximum value of ST 35.57 mN/m at 0.3 wt% of ZnO NPs. It was found that the nanofluid with highest surface tension (0.3 wt%) resulted in higher recovery efficiency. The highest recovery factor of 11.82% at 0.3 wt% is due to the oil/water interfacial tension reduction and wettability alteration.

The surface tension of liquid gallium

NASA Technical Reports Server (NTRS)

Hardy, S. C.

1985-01-01

The surface tension of liquid gallium has been measured using the sessile drop technique in an Auger spectrometer. The experimental method is described. The surface tension in mJ/sq m is found to decrease linearly with increasing temperature and may be represented as 708-0.66(T-29.8), where T is the temperature in centigrade. This result is of interest because gallium has been suggested as a model fluid for Marangoni flow experiments. In addition, the surface tension is of technological significance in the processing of compound semiconductors involving gallium.

Fundamental Degradation Mechanisms of Multi-Functional Nanoengineered Surfaces

DTIC Science & Technology

2018-04-08

surface tension fluids with widely used lubricants for designing LIS. We considered a wide range of low surface tension fluids (12 to 48 mN/m) and...selection in designing stable LIS for the low surface tension fluids. Lastly, using steady state condensation experiments, we show that polymeric...polymeric coating to the high surface energy substrate and mechanical delamination of the coating. This finding will be key to future design

Surface tension of dilute alcohol-aqueous binary fluids: n-Butanol/water, n-Pentanol/water, and n-Hexanol/water solutions

NASA Astrophysics Data System (ADS)

Cheng, Kuok Kong; Park, Chanwoo

2017-07-01

Surface tension of pure fluids, inherently decreasing with regard to temperature, creates a thermo-capillary-driven (Marangoni) flow moving away from a hot surface. It has been known that few high-carbon alcohol-aqueous solutions exhibit an opposite behavior of the surface tension increasing with regard to temperature, such that the Marangoni flow moves towards the hot surface (self-rewetting effect). We report the surface tensions of three dilute aqueous solutions of n-Butanol, n-Pentanol and n-Hexanol as self-rewetting fluids measured for ranges of alcohol concentration (within solubility limits) and fluid temperatures (25-85 °C). A maximum bubble pressure method using a leak-tight setup was used to measure the surface tension without evaporation losses of volatile components. It was found from this study that the aqueous solutions with higher-carbon alcohols exhibit a weak self-rewetting behavior, such that the surface tensions remain constant or slightly increases above about 60 °C. These results greatly differ from the previously reported results showing a strong self-rewetting behavior, which is attributed to the measurement errors associated with the evaporation losses of test fluids during open-system experiments.

Surface activity of lipid extract surfactant in relation to film area compression and collapse.

PubMed

Schürch, S; Schürch, D; Curstedt, T; Robertson, B

1994-08-01

The physical properties of modified porcine surfactant (Curosurf), isolated from minced lungs by extraction with chloroform-methanol and further purified by liquid-gel chromatography, were investigated with the captive bubble technique. Bubble size, and thus the surface tension of an insoluble film at the bubble surface, is altered by changing the pressure within the closed bubble chamber. The film surface tension and area are determined from the shape (height and diameter) of the bubble. Adsorption of fresh Curosurf is characterized by stepwise decreases in surface tension, which can easily be observed by sudden quick movements of the bubble apex. These "adsorption clicks" imply a cooperative movement of large collective units of molecules, approximately 10(14) (corresponding to approximately 120 ng of phospholipid) or approximately 10(18) molecules/m2, into the interface during adsorption. Films formed in this manner are already highly enriched in dipalmitoyl phosphatidylcholine, as seen by the extremely low compressibility, close to that of dipalmitoyl phosphatidylcholine. Near-zero minimum tensions are obtained, even at phospholipid concentrations as low as 50 micrograms/ml. During dynamic cycling (20-50 cycles/min), low minimum surface tensions, good film stability, low compressibility, and maximum surface tensions between 30 and 40 mN/m are possible only if the films are not overcompressed near zero surface tension; i.e., the overall film area compression should not substantially exceed 30%.

The Dynamic Surface Tension of Water

PubMed Central

2017-01-01

The surface tension of water is an important parameter for many biological or industrial processes, and roughly a factor of 3 higher than that of nonpolar liquids such as oils, which is usually attributed to hydrogen bonding and dipolar interactions. Here we show by studying the formation of water drops that the surface tension of a freshly created water surface is even higher (∼90 mN m–1) than under equilibrium conditions (∼72 mN m–1) with a relaxation process occurring on a long time scale (∼1 ms). Dynamic adsorption effects of protons or hydroxides may be at the origin of this dynamic surface tension. However, changing the pH does not significantly change the dynamic surface tension. It also seems unlikely that hydrogen bonding or dipole orientation effects play any role at the relatively long time scale probed in the experiments. PMID:28301160

The Dynamic Surface Tension of Water.

PubMed

Hauner, Ines M; Deblais, Antoine; Beattie, James K; Kellay, Hamid; Bonn, Daniel

2017-04-06

The surface tension of water is an important parameter for many biological or industrial processes, and roughly a factor of 3 higher than that of nonpolar liquids such as oils, which is usually attributed to hydrogen bonding and dipolar interactions. Here we show by studying the formation of water drops that the surface tension of a freshly created water surface is even higher (∼90 mN m -1 ) than under equilibrium conditions (∼72 mN m -1 ) with a relaxation process occurring on a long time scale (∼1 ms). Dynamic adsorption effects of protons or hydroxides may be at the origin of this dynamic surface tension. However, changing the pH does not significantly change the dynamic surface tension. It also seems unlikely that hydrogen bonding or dipole orientation effects play any role at the relatively long time scale probed in the experiments.

The Temperature and Structure Dependence of Surface Tension of CaO-SiO2-Na2O-CaF2 Mold Fluxes

NASA Astrophysics Data System (ADS)

Gao, Qiang; Min, Yi; Jiang, Maofa

2018-06-01

The surface tension of mold flux is one of the most important properties and varies with the temperature from the top to the bottom of the mold, which influences the adhesion and lubrication between the liquid mold flux and the solidified shell, further influencing the quality of the continuous billet. In the present paper, the effect of temperature on the surface tension of CaO-SiO2-Na2O-CaF2 mold-flux melts with different CaO/SiO2 mass ratios was investigated using the maximum-pull method. Furthermore, the microstructure of mold fluxes was analyzed using FT-IR and Raman spectra to discuss the change mechanism of surface tension. The results indicated that the temperature dependence of surface tension was different with different CaO/SiO2 mass ratios, and agreed with the modification of melt structure. When the CaO/SiO2 mass ratio was 0.67 and 0.85, the change of surface tension with temperature was relatively stable, and the influence of temperature on the structure was small. When the CaO/SiO2 mass ratio was 1.03 and 1.16, with an increase of temperature, the surface tension decreased linearly and the changing amplitude was large; the degree of polymerization of melts and average radii of silicon-oxygen anions also decreased, which intensified the molecular thermal motion and weakened the intermolecular interaction, resulting in a decrease of surface tension of melts.

The Temperature and Structure Dependence of Surface Tension of CaO-SiO2-Na2O-CaF2 Mold Fluxes

NASA Astrophysics Data System (ADS)

Gao, Qiang; Min, Yi; Jiang, Maofa

2018-02-01

The surface tension of mold flux is one of the most important properties and varies with the temperature from the top to the bottom of the mold, which influences the adhesion and lubrication between the liquid mold flux and the solidified shell, further influencing the quality of the continuous billet. In the present paper, the effect of temperature on the surface tension of CaO-SiO2-Na2O-CaF2 mold-flux melts with different CaO/SiO2 mass ratios was investigated using the maximum-pull method. Furthermore, the microstructure of mold fluxes was analyzed using FT-IR and Raman spectra to discuss the change mechanism of surface tension. The results indicated that the temperature dependence of surface tension was different with different CaO/SiO2 mass ratios, and agreed with the modification of melt structure. When the CaO/SiO2 mass ratio was 0.67 and 0.85, the change of surface tension with temperature was relatively stable, and the influence of temperature on the structure was small. When the CaO/SiO2 mass ratio was 1.03 and 1.16, with an increase of temperature, the surface tension decreased linearly and the changing amplitude was large; the degree of polymerization of melts and average radii of silicon-oxygen anions also decreased, which intensified the molecular thermal motion and weakened the intermolecular interaction, resulting in a decrease of surface tension of melts.

Surface tension modelling of liquid Cd-Sn-Zn alloys

NASA Astrophysics Data System (ADS)

Fima, Przemyslaw; Novakovic, Rada

2018-06-01

The thermodynamic model in conjunction with Butler equation and the geometric models were used for the surface tension calculation of Cd-Sn-Zn liquid alloys. Good agreement was found between the experimental data for limiting binaries and model calculations performed with Butler model. In the case of ternary alloys, the surface tension variation with Cd content is better reproduced in the case of alloys lying on vertical sections defined by high Sn to Zn molar fraction ratio. The calculated surface tension is in relatively good agreement with the available experimental data. In addition, the surface segregation of liquid ternary Cd-Sn-Zn and constituent binaries has also been calculated.

Analytics of crystal growth in space

NASA Technical Reports Server (NTRS)

Chang, C. E.; Lefever, R. A.; Wilcox, W. R.

1975-01-01

The variation of radial impurity distribution induced by surface tension driven flow increases as the zone length decreases in silicon crystals grown by floating zone melting. In combined buoyancy driven and surface tension driven convection at the gravity of earth, the buoyancy contribution becomes relatively smaller as the zone diameter decreases and eventually convection is dominated by the surface tension driven flow (in the case of silicon, for zones of less than about 0.8 cm in diameter). Preliminary calculations for sapphire suggest the presence of an oscillatory surface tension driven convection as a result of an unstable melt surface temperature that results when the zone is heated by a radiation heater.

Dropwise Condensation of Low Surface Tension Fluids on Omniphobic Surfaces

PubMed Central

Rykaczewski, Konrad; Paxson, Adam T.; Staymates, Matthew; Walker, Marlon L.; Sun, Xiaoda; Anand, Sushant; Srinivasan, Siddarth; McKinley, Gareth H.; Chinn, Jeff; Scott, John Henry J.; Varanasi, Kripa K.

2014-01-01

Compared to the significant body of work devoted to surface engineering for promoting dropwise condensation heat transfer of steam, much less attention has been dedicated to fluids with lower interfacial tension. A vast array of low-surface tension fluids such as hydrocarbons, cryogens, and fluorinated refrigerants are used in a number of industrial applications, and the development of passive means for increasing their condensation heat transfer coefficients has potential for significant efficiency enhancements. Here we investigate condensation behavior of a variety of liquids with surface tensions in the range of 12 to 28 mN/m on three types of omniphobic surfaces: smooth oleophobic, re-entrant superomniphobic, and lubricant-impregnated surfaces. We demonstrate that although smooth oleophobic and lubricant-impregnated surfaces can promote dropwise condensation of the majority of these fluids, re-entrant omniphobic surfaces became flooded and reverted to filmwise condensation. We also demonstrate that on the lubricant-impregnated surfaces, the choice of lubricant and underlying surface texture play a crucial role in stabilizing the lubricant and reducing pinning of the condensate. With properly engineered surfaces to promote dropwise condensation of low-surface tension fluids, we demonstrate a four to eight-fold improvement in the heat transfer coefficient. PMID:24595171

Dropwise condensation of low surface tension fluids on omniphobic surfaces.

PubMed

Rykaczewski, Konrad; Paxson, Adam T; Staymates, Matthew; Walker, Marlon L; Sun, Xiaoda; Anand, Sushant; Srinivasan, Siddarth; McKinley, Gareth H; Chinn, Jeff; Scott, John Henry J; Varanasi, Kripa K

2014-03-05

Compared to the significant body of work devoted to surface engineering for promoting dropwise condensation heat transfer of steam, much less attention has been dedicated to fluids with lower interfacial tension. A vast array of low-surface tension fluids such as hydrocarbons, cryogens, and fluorinated refrigerants are used in a number of industrial applications, and the development of passive means for increasing their condensation heat transfer coefficients has potential for significant efficiency enhancements. Here we investigate condensation behavior of a variety of liquids with surface tensions in the range of 12 to 28 mN/m on three types of omniphobic surfaces: smooth oleophobic, re-entrant superomniphobic, and lubricant-impregnated surfaces. We demonstrate that although smooth oleophobic and lubricant-impregnated surfaces can promote dropwise condensation of the majority of these fluids, re-entrant omniphobic surfaces became flooded and reverted to filmwise condensation. We also demonstrate that on the lubricant-impregnated surfaces, the choice of lubricant and underlying surface texture play a crucial role in stabilizing the lubricant and reducing pinning of the condensate. With properly engineered surfaces to promote dropwise condensation of low-surface tension fluids, we demonstrate a four to eight-fold improvement in the heat transfer coefficient.

Does turgor limit growth in tall trees?

Treesearch

D.R. Woodruff; B.J. Bond; F.C. Meinzer

2004-01-01

The gravitational component of water potential contributes a standing 0.01 MPa m1 to the xylem tension gradient in plants. In tall trees, this contribution can significantly reduce the water potential near the tree tops. The turgor of cells in buds and leaves is expected to decrease in direct proportion with leaf water potential along a height gradient unless osmotic...

Internal Flow in a Free Drop (IFFD) Bubble Surface Tension Experiment

NASA Technical Reports Server (NTRS)

1999-01-01

This digital QuickTime movie is of the Internal Flow in a Free Drop (IFFD) Bubble Surface Tension Experiment taking place in the Microgravity laboratory at NASA's Marshall Space Flight Center (MSFC) in Huntsville, Alabama. The Bubble provides scientists with information about fluid surface tensions in a low-gravity environment.

Pendant-Drop Surface-Tension Measurement On Molten Metal

NASA Technical Reports Server (NTRS)

Man, Kin Fung; Thiessen, David

1996-01-01

Method of measuring surface tension of molten metal based on pendant-drop method implemented in quasi-containerless manner and augmented with digital processing of image data. Electrons bombard lower end of sample rod in vacuum, generating hanging drop of molten metal. Surface tension of drop computed from its shape. Technique minimizes effects of contamination.

On the universality of Marangoni-driven spreading

NASA Astrophysics Data System (ADS)

Visser, Claas; van Capelleveen, Bram; Koldeweij, Robin; Lohse, Detlef

2017-11-01

When two liquids of different surface tensions come into contact, the liquid with lower surface tension spreads over the other. Here we measure the dynamics of this Marangoni-driven spreading in the drop-drop geometry, revealing universal behavior with respect to the control parameters as well as other geometries (such as spreading over a flat interface). The distance L over which the low-surface-tension liquid has covered the high-surface-tension droplet is measured as a function of time t, surface tension difference between the liquids Δσ , and viscosity η, revealing power-law behavior L(t) tα . The exponent α is discussed for the early and late spreading regimes. Spreading inhibition is observed at high viscosity, for which the threshold is discussed. Finally, we show that our results collapse onto a single curve of dimensionless L(t) as a function of dimensionless time, which also captures previous results for different geometries, surface tension modifiers, and miscibility. As this curve spans 7 orders of magnitude, Marangoni-induced spreading can be considered a universal phenomenon for many practically encountered liquid-liquid systems.

Surface tension measurement of undercooled liquid Ni-based multicomponent alloys

NASA Astrophysics Data System (ADS)

Chang, J.; Wang, H. P.; Zhou, K.; Wei, B.

2012-09-01

The surface tensions of liquid ternary Ni-5%Cu-5%Fe, quaternary Ni-5%Cu-5%Fe-5%Sn and quinary Ni-5%Cu-5%Fe-5%Sn-5%Ge alloys were determined as a function of temperature by the electromagnetic levitation oscillating drop method. The maximum undercoolings obtained in the experiments are 272 (0.15T L), 349 (0.21T L) and 363 K (0.22T L), respectively. For all the three alloys, the surface tension decreases linearly with the rise of temperature. The surface tension values are 1.799, 1.546 and 1.357 N/m at their liquidus temperatures of 1719, 1644 and 1641 K. Their temperature coefficients are -4.972 × 10-4, -5.057 × 10-4 and -5.385 × 10-4 N/m/K. It is revealed that Sn and Ge are much more efficient than Cu and Fe in reducing the surface tension of Ni-based alloys. The addition of Sn can significantly enlarge the maximum undercooling at the same experimental condition. The viscosity of the three undercooled liquid alloys was also derived from the surface tension data.

Color-gradient lattice Boltzmann model for simulating droplet motion with contact-angle hysteresis.

PubMed

Ba, Yan; Liu, Haihu; Sun, Jinju; Zheng, Rongye

2013-10-01

Lattice Boltzmann method (LBM) is an effective tool for simulating the contact-line motion due to the nature of its microscopic dynamics. In contact-line motion, contact-angle hysteresis is an inherent phenomenon, but it is neglected in most existing color-gradient based LBMs. In this paper, a color-gradient based multiphase LBM is developed to simulate the contact-line motion, particularly with the hysteresis of contact angle involved. In this model, the perturbation operator based on the continuum surface force concept is introduced to model the interfacial tension, and the recoloring operator proposed by Latva-Kokko and Rothman is used to produce phase segregation and resolve the lattice pinning problem. At the solid surface, the color-conserving wetting boundary condition [Hollis et al., IMA J. Appl. Math. 76, 726 (2011)] is applied to improve the accuracy of simulations and suppress spurious currents at the contact line. In particular, we present a numerical algorithm to allow for the effect of the contact-angle hysteresis, in which an iterative procedure is used to determine the dynamic contact angle. Numerical simulations are conducted to verify the developed model, including the droplet partial wetting process and droplet dynamical behavior in a simple shear flow. The obtained results are compared with theoretical solutions and experimental data, indicating that the model is able to predict the equilibrium droplet shape as well as the dynamic process of partial wetting and thus permits accurate prediction of contact-line motion with the consideration of contact-angle hysteresis.

Pair correlation functions and the wavevector-dependent surface tension in a simple density functional treatment of the liquid-vapour interface.

PubMed

Parry, A O; Rascón, C; Willis, G; Evans, R

2014-09-03

We study the density-density correlation function G(r, r') in the interfacial region of a fluid (or Ising-like magnet) with short-ranged interactions using square gradient density functional theory. Adopting a simple double parabola approximation for the bulk free-energy density, we first show that the parallel Fourier transform G(z, z'; q) and local structure factor S(z; q) separate into bulk and excess contributions. We attempt to account for both contributions by deriving an interfacial Hamiltonian, characterised by a wavevector dependent surface tension σ(q), and then reconstructing density correlations from correlations in the interface position. We show that the standard crossing criterion identification of the interface, as a surface of fixed density (or magnetization), does not explain the separation of G(z, z'; q) and the form of the excess contribution. We propose an alternative definition of the interface position based on the properties of correlations between points that 'float' with the surface and show that this describes the full q and z dependence of the excess contributions to both G and S. However, neither the 'crossing-criterion' nor the new 'floating interface' definition of σ(q) are quantities directly measurable from the total structure factor S(tot)(q) which contains additional q dependence arising from the non-local relation between fluctuations in the interfacial position and local density. Since it is the total structure factor that is measured experimentally or in simulations, our results have repercussions for earlier attempts to extract and interpret σ(q).

Surface tensions of inorganic multicomponent aqueous electrolyte solutions and melts.

PubMed

Dutcher, Cari S; Wexler, Anthony S; Clegg, Simon L

2010-11-25

A semiempirical model is presented that predicts surface tensions (σ) of aqueous electrolyte solutions and their mixtures, for concentrations ranging from infinitely dilute solution to molten salt. The model requires, at most, only two temperature-dependent terms to represent surface tensions of either pure aqueous solutions, or aqueous or molten mixtures, over the entire composition range. A relationship was found for the coefficients of the equation σ = c(1) + c(2)T (where T (K) is temperature) for molten salts in terms of ion valency and radius, melting temperature, and salt molar volume. Hypothetical liquid surface tensions can thus be estimated for electrolytes for which there are no data, or which do not exist in molten form. Surface tensions of molten (single) salts, when extrapolated to normal temperatures, were found to be consistent with data for aqueous solutions. This allowed surface tensions of very concentrated, supersaturated, aqueous solutions to be estimated. The model has been applied to the following single electrolytes over the entire concentration range, using data for aqueous solutions over the temperature range 233-523 K, and extrapolated surface tensions of molten salts and pure liquid electrolytes: HCl, HNO(3), H(2)SO(4), NaCl, NaNO(3), Na(2)SO(4), NaHSO(4), Na(2)CO(3), NaHCO(3), NaOH, NH(4)Cl, NH(4)NO(3), (NH(4))(2)SO(4), NH(4)HCO(3), NH(4)OH, KCl, KNO(3), K(2)SO(4), K(2)CO(3), KHCO(3), KOH, CaCl(2), Ca(NO(3))(2), MgCl(2), Mg(NO(3))(2), and MgSO(4). The average absolute percentage error between calculated and experimental surface tensions is 0.80% (for 2389 data points). The model extrapolates smoothly to temperatures as low as 150 K. Also, the model successfully predicts surface tensions of ternary aqueous mixtures; the effect of salt-salt interactions in these calculations was explored.

Thermophysical Properties Measurement of High-Temperature Liquids Under Microgravity Conditions in Controlled Atmospheric Conditions

NASA Technical Reports Server (NTRS)

Watanabe, Masahito; Ozawa, Shumpei; Mizuno, Akotoshi; Hibiya, Taketoshi; Kawauchi, Hiroya; Murai, Kentaro; Takahashi, Suguru

2012-01-01

Microgravity conditions have advantages of measurement of surface tension and viscosity of metallic liquids by the oscillating drop method with an electromagnetic levitation (EML) device. Thus, we are preparing the experiments of thermophysical properties measurements using the Materials-Science Laboratories ElectroMagnetic-Levitator (MSL-EML) facilities in the international Space station (ISS). Recently, it has been identified that dependence of surface tension on oxygen partial pressure (Po2) must be considered for industrial application of surface tension values. Effect of Po2 on surface tension would apparently change viscosity from the damping oscillation model. Therefore, surface tension and viscosity must be measured simultaneously in the same atmospheric conditions. Moreover, effect of the electromagnetic force (EMF) on the surface oscillations must be clarified to obtain the ideal surface oscillation because the EMF works as the external force on the oscillating liquid droplets, so extensive EMF makes apparently the viscosity values large. In our group, using the parabolic flight levitation experimental facilities (PFLEX) the effect of Po2 and external EMF on surface oscillation of levitated liquid droplets was systematically investigated for the precise measurements of surface tension and viscosity of high temperature liquids for future ISS experiments. We performed the observation of surface oscillations of levitated liquid alloys using PFLEX on board flight experiments by Gulfstream II (G-II) airplane operated by DAS. These observations were performed under the controlled Po2 and also under the suitable EMF conditions. In these experiments, we obtained the density, the viscosity and the surface tension values of liquid Cu. From these results, we discuss about as same as reported data, and also obtained the difference of surface oscillations with the change of the EMF conditions.

Ultrasonic spray coating polymer and small molecular organic film for organic light-emitting devices.

PubMed

Liu, Shihao; Zhang, Xiang; Zhang, Letian; Xie, Wenfa

2016-11-22

Ultrasonic spray coating process (USCP) with high material -utilization, low manufacture costs and compatibility to streamline production has been attractive in researches on photoelectric devices. However, surface tension exists in the solvent is still a huge obstacle to realize smooth organic film for organic light emitting devices (OLEDs) by USCP. Here, high quality polymer anode buffer layer and small molecular emitting layer are successfully realized through USCP by introducing extra-low surface tension diluent and surface tension control method. The introduction of low surface tension methyl alcohol is beneficial to the formation of poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) films and brings obvious phase separation and improved conductivity to PEDOT:PSS film. Besides, a surface tension control method, in which new stable tension equilibrium is built at the border of wetting layer, is proposed to eliminate the effect of surface tension during the solvent evaporation stage of ultrasonic spray coating the film consists of 9,9-Spirobifluoren-2-yl-diphenyl-phosphine oxide doped with 10 wt% tris [2-(p -tolyl) pyridine] iridium (III). A smooth and homogenous small molecular emitting layer without wrinkles is successfully realized. The effectiveness of the ultrasonic spray coating polymer anode buffer layer and small molecular emitting layer are also proved by introducing them in OLEDs.

Ultrasonic spray coating polymer and small molecular organic film for organic light-emitting devices

NASA Astrophysics Data System (ADS)

Liu, Shihao; Zhang, Xiang; Zhang, Letian; Xie, Wenfa

2016-11-01

Ultrasonic spray coating process (USCP) with high material -utilization, low manufacture costs and compatibility to streamline production has been attractive in researches on photoelectric devices. However, surface tension exists in the solvent is still a huge obstacle to realize smooth organic film for organic light emitting devices (OLEDs) by USCP. Here, high quality polymer anode buffer layer and small molecular emitting layer are successfully realized through USCP by introducing extra-low surface tension diluent and surface tension control method. The introduction of low surface tension methyl alcohol is beneficial to the formation of poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) films and brings obvious phase separation and improved conductivity to PEDOT:PSS film. Besides, a surface tension control method, in which new stable tension equilibrium is built at the border of wetting layer, is proposed to eliminate the effect of surface tension during the solvent evaporation stage of ultrasonic spray coating the film consists of 9,9-Spirobifluoren-2-yl-diphenyl-phosphine oxide doped with 10 wt% tris [2-(p -tolyl) pyridine] iridium (III). A smooth and homogenous small molecular emitting layer without wrinkles is successfully realized. The effectiveness of the ultrasonic spray coating polymer anode buffer layer and small molecular emitting layer are also proved by introducing them in OLEDs.

Ultrasonic spray coating polymer and small molecular organic film for organic light-emitting devices

PubMed Central

Liu, Shihao; Zhang, Xiang; Zhang, Letian; Xie, Wenfa

2016-01-01

Ultrasonic spray coating process (USCP) with high material -utilization, low manufacture costs and compatibility to streamline production has been attractive in researches on photoelectric devices. However, surface tension exists in the solvent is still a huge obstacle to realize smooth organic film for organic light emitting devices (OLEDs) by USCP. Here, high quality polymer anode buffer layer and small molecular emitting layer are successfully realized through USCP by introducing extra-low surface tension diluent and surface tension control method. The introduction of low surface tension methyl alcohol is beneficial to the formation of poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) films and brings obvious phase separation and improved conductivity to PEDOT:PSS film. Besides, a surface tension control method, in which new stable tension equilibrium is built at the border of wetting layer, is proposed to eliminate the effect of surface tension during the solvent evaporation stage of ultrasonic spray coating the film consists of 9,9-Spirobifluoren-2-yl-diphenyl-phosphine oxide doped with 10 wt% tris [2-(p -tolyl) pyridine] iridium (III). A smooth and homogenous small molecular emitting layer without wrinkles is successfully realized. The effectiveness of the ultrasonic spray coating polymer anode buffer layer and small molecular emitting layer are also proved by introducing them in OLEDs. PMID:27874030

Surface tension effects on the behavior of a cavity growing, collapsing, and rebounding near a rigid wall.

PubMed

Zhang, Zhen-yu; Zhang, Hui-sheng

2004-11-01

Surface tension effects on the behavior of a pure vapor cavity or a cavity containing some noncondensible contents, which is growing, collapsing, and rebounding axisymmetrically near a rigid wall, are investigated numerically by the boundary integral method for different values of dimensionless stand-off parameter gamma, buoyancy parameter delta, and surface tension parameter beta. It is found that at the late stage of the collapse, if the resultant action of the Bjerknes force and the buoyancy force is not small, surface tension will not have significant effects on bubble behavior except that the bubble collapse time is shortened and the liquid jet becomes wider. If the resultant action of the two force is small enough, surface tension will have significant and in some cases substantial effects on bubble behavior, such as changing the direction of the liquid jet, making a new liquid jet appear, in some cases preventing the bubble from rebound before jet impact, and in other cases causing the bubble to rebound or even recollapse before jet impact. The mechanism of surface tension effects on the collapsing behavior of a cavity has been analyzed. The mechanisms of some complicated phenomena induced by surface tension effects are illustrated by analysis of the computed velocity fields and pressure contours of the liquid flow outside the bubble at different stages of the bubble evolution.

New solutions for steady bubbles in a Hele-Shaw cell

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tanveer, S.

1987-03-01

Exact solutions are presented for steadily moving bubbles in a Hele--Shaw cell when the effect of surface tension is neglected. These solutions form a three-parameter family. For specified area, both the speed of the bubble and the distance of its centroid from the channel centerline remain arbitrary when surface tension is ignored. However, numerical evidence suggests that this twofold arbitrariness is removed by the effect of surface tension, i.e., for given bubble area and surface tension, solutions exist only when the bubble velocity and the centroid distance from the channel centerline attain one or more isolated values. From a limitedmore » numerical search, no nonsymmetric solutions could be found; however, a branch of symmetric bubble solutions that was not found in earlier work was found. This branch corresponds to one of the Romero-Vanden-Broeck branch of finger solutions when the bubble size is large. A new procedure for numerical calculations of bubble solutions in the presence of surface tension is presented and is found to work very well for reasonably large bubbles, unlike the previous method of Tanveer (Phys. Fluids 29, 3537 (1986)). The precise power law dependence of bubble velocity on surface tension for small surface tension is explored for bubbles of different area. Agreement is noted with recent analytical results for a finger.« less

Combined influence of inertia, gravity, and surface tension on the linear stability of Newtonian fiber spinning

NASA Astrophysics Data System (ADS)

Bechert, M.; Scheid, B.

2017-11-01

The draw resonance effect appears in fiber spinning processes if the ratio of take-up to inlet velocity, the so-called draw ratio, exceeds a critical value and manifests itself in steady oscillations of flow velocity and fiber diameter. We study the effect of surface tension on the draw resonance behavior of Newtonian fiber spinning in the presence of inertia and gravity. Utilizing an alternative scaling makes it possible to visualize the results in stability maps of highly practical relevance. The interplay of the destabilizing effect of surface tension and the stabilizing effects of inertia and gravity lead to nonmonotonic stability behavior and local stability maxima with respect to the dimensionless fluidity and the dimensionless inlet velocity. A region of unconditional instability caused by the influence of surface tension is found in addition to the region of unconditional stability caused by inertia, which was described in previous works [M. Bechert, D. W. Schubert, and B. Scheid, Eur. J. Mech B 52, 68 (2015), 10.1016/j.euromechflu.2015.02.005; Phys. Fluids 28, 024109 (2016), 10.1063/1.4941762]. Due to its importance for a particular group of fiber spinning applications, a viscous-gravity-surface-tension regime, i.e., negligible effect of inertia, is analyzed separately. The mechanism underlying the destabilizing effect of surface tension is discussed and established stability criteria are tested for validity in the presence of surface tension.

Vertical Gradients in Regional Alveolar Oxygen Tension in Supine Human Lung Imaged by Hyperpolarized 3He MRI

PubMed Central

Hamedani, Hooman; Shaghaghi, Hoora; Kadlecek, Stephen J.; Xin, Yi; Han, Biao; Siddiqui, Sarmad; Rajaei, Jennia; Ishii, Masaru; Rossman, Milton; Rizi, Rahim R.

2015-01-01

Purpose To evaluate whether regional alveolar oxygen tension (PAO2) vertical gradients imaged with hyperpolarized 3He can identify smoking-induced pulmonary alterations. To compare these gradients with common clinical measurements including pulmonary function tests, the six minute walk test, and the St. George’s Respiratory Questionnaire. Materials and Methods 8 healthy nonsmokers, 12 asymptomatic smokers, and 7 symptomatic subjects with chronic obstructive pulmonary disease (COPD) underwent two sets of back-to-back PAO2 imaging acquisitions in supine position with two opposite directions (top to bottom and bottom to top), followed by clinically standard pulmonary tests. The whole-lung mean, standard deviation (DPAO2) and vertical gradients of PAO2 along the slices were extracted, and the results were compared with clinically derived metrics. Statistical tests were performed to analyze the differences between cohorts. Results The anterior-posterior vertical gradients and DPAO2 effectively differentiated all three cohorts (p<0.05). The average vertical gradient PAO2 in healthy subjects was −1.03 ± 0.51 Torr/cm toward lower values in the posterior/dependent regions. The directional gradient was absent in smokers (0.36 ± 1.22 Torr/cm) and was in the opposite direction in COPD subjects (2.18 ± 1.54 Torr/cm). The vertical gradients correlated with Smoking History (p=0.004); BMI (p=0.037), PFT metrics (FEV1, p=0.025; and %RV/TLC, p=0.033) and with distance walked in six minutes (p=0.009). Discussion Regional PAO2 data indicate that cigarette smoke induces physiological alterations that are not being detected by the most widely used physiologic tests. PMID:25395184

Surface tension measurements with a smartphone

NASA Astrophysics Data System (ADS)

Goy, Nicolas-Alexandre; Denis, Zakari; Lavaud, Maxime; Grolleau, Adrian; Dufour, Nicolas; Deblais, Antoine; Delabre, Ulysse

2017-11-01

Smartphones are increasingly used in higher education and at university in mechanics, acoustics, and even thermodynamics as they offer a unique way to do simple science experiments. In this article, we show how smartphones can be used in fluid mechanics to measure surface tension of various liquids, which could help students understand the concept of surface tension through simple experiments.

The levels and kinetics of oxygen tension detectable at the surface of human dermal fibroblast cultures.

PubMed

Tokuda, Y; Crane, S; Yamaguchi, Y; Zhou, L; Falanga, V

2000-03-01

Low oxygen tension has recently been shown to stimulate cell growth and clonal expansion, as well as synthesis and transcription of certain growth factors and extracellular matrix components. These results have been obtained by exposing cell cultures to a hypoxic environment. Using an oxygen probe, we have now studied how experimental conditions affect the oxygen tension detectable at the cell surface. Dissolved oxygen tension was directly related to the height of the medium above the cell surface (r = 0.8793, P = 0.021), but was constant when no cells were present in the flask (r = -0. 9732, P = 0.001). In both human dermal fibroblasts and NIH/3T3 cultures, oxygen tension decreased linearly as cell density increased (r = -0.835, P < 0.0001; r = -0.916, P < 0.0001, respectively). When human dermal fibroblasts were exposed to 2% O(2), maximum hypoxic levels (0 mmHg) were achieved within approximately 15 min, and the recovery time was within a similar time frame. The addition of rotenone, an inhibitor of cellular respiration, blocked this decrease in oxygen tension at the cell surface, suggesting that cellular consumption of oxygen is responsible for the decline. Finally, we examined the cell-surface oxygen tension in control and acutely wounded human skin equivalents (HSE), consisting of a keratinocyte layer over a type I collagen matrix containing fibroblasts. We found that oxygen tension dropped significantly (P < 0.0001) in acutely wounded areas of HSE as compared to unwounded areas of HSE and that this drop was prevented by the addition of mitomycin C. These results indicate that cell-surface oxygen tension is indirectly related to cell density, and that the amount of detectable oxygen at the cell surface is a function of cell density, the oxygen tension in the incubator, and increased cellular activity, as occurs after injury. Copyright 2000 Wiley-Liss, Inc.

The surface tension of aqueous solutions of some atmospheric water-soluble organic compounds

NASA Astrophysics Data System (ADS)

Tuckermann, Rudolf; Cammenga, Heiko K.

The surface tensions of aqueous solutions of levoglucosan, 3-hydroxybutanoic acid, 3-hydroxybenzoic acid, azelaic acid, pinonic acid, and humic acid have been measured. These compounds are suggested as model substances for the water-soluble organic compounds (WSOC) in atmospheric aerosols and droplets which may play an important role in the aerosol cycle because of their surface-active potentials. The reductions in surface tension induced by single and mixed WSOC in aqueous solution of pure water is remarkable. However, the results of this investigation cannot explain the strong reduction in surface tension in real cloud and fog water samples at concentrations of WSOC below 1 mg/mL.

Calculations of the surface tensions of liquid metals

NASA Technical Reports Server (NTRS)

Stroud, D. G.

1981-01-01

The understanding of the surface tension of liquid metals and alloys from as close to first principles as possible is discussed. The two ingredients which are combined in these calculations are: the electron theory of metals, and the classical theory of liquids, as worked out within the framework of statistical mechanics. The results are a new theory of surface tensions and surface density profiles from knowledge purely of the bulk properties of the coexisting liquid and vapor phases. It is found that the method works well for the pure liquid metals on which it was tested; work is extended to mixtures of liquid metals, interfaces between immiscible liquid metals, and to the temperature derivative of the surface tension.

Surface tension of droplets and Tolman lengths of real substances and mixtures from density functional theory

NASA Astrophysics Data System (ADS)

Rehner, Philipp; Gross, Joachim

2018-04-01

The curvature dependence of interfacial properties has been discussed extensively over the last decades. After Tolman published his work on the effect of droplet size on surface tension, where he introduced the interfacial property now known as Tolman length, several studies were performed with varying results. In recent years, however, some consensus has been reached about the sign and magnitude of the Tolman length of simple model fluids. In this work, we re-examine Tolman's equation and how it relates the Tolman length to the surface tension and we apply non-local classical density functional theory (DFT) based on the perturbed chain statistical associating fluid theory (PC-SAFT) to characterize the curvature dependence of the surface tension of real fluids as well as mixtures. In order to obtain a simple expression for the surface tension, we use a first-order expansion of the Tolman length as a function of droplet radius Rs, as δ(Rs) = δ0 + δ1/Rs, and subsequently expand Tolman's integral equation for the surface tension, whereby a second-order expansion is found to give excellent agreement with the DFT result. The radius-dependence of the surface tension of increasingly non-spherical substances is studied for n-alkanes, up to icosane. The infinite diameter Tolman length is approximately δ0 = -0.38 Å at low temperatures. For more strongly non-spherical substances and for temperatures approaching the critical point, however, the infinite diameter Tolman lengths δ0 turn positive. For mixtures, even if they contain similar molecules, the extrapolated Tolman length behaves strongly non-ideal, implying a qualitative change of the curvature behavior of the surface tension of the mixture.

Surface tension of droplets and Tolman lengths of real substances and mixtures from density functional theory.

PubMed

Rehner, Philipp; Gross, Joachim

2018-04-28

The curvature dependence of interfacial properties has been discussed extensively over the last decades. After Tolman published his work on the effect of droplet size on surface tension, where he introduced the interfacial property now known as Tolman length, several studies were performed with varying results. In recent years, however, some consensus has been reached about the sign and magnitude of the Tolman length of simple model fluids. In this work, we re-examine Tolman's equation and how it relates the Tolman length to the surface tension and we apply non-local classical density functional theory (DFT) based on the perturbed chain statistical associating fluid theory (PC-SAFT) to characterize the curvature dependence of the surface tension of real fluids as well as mixtures. In order to obtain a simple expression for the surface tension, we use a first-order expansion of the Tolman length as a function of droplet radius R s , as δ(R s ) = δ 0 + δ 1 /R s , and subsequently expand Tolman's integral equation for the surface tension, whereby a second-order expansion is found to give excellent agreement with the DFT result. The radius-dependence of the surface tension of increasingly non-spherical substances is studied for n-alkanes, up to icosane. The infinite diameter Tolman length is approximately δ 0 = -0.38 Å at low temperatures. For more strongly non-spherical substances and for temperatures approaching the critical point, however, the infinite diameter Tolman lengths δ 0 turn positive. For mixtures, even if they contain similar molecules, the extrapolated Tolman length behaves strongly non-ideal, implying a qualitative change of the curvature behavior of the surface tension of the mixture.

New generalized corresponding states correlation for surface tension of normal saturated liquids

NASA Astrophysics Data System (ADS)

Yi, Huili; Tian, Jianxiang

2015-08-01

A new simple correlation based on the principle of corresponding state is proposed to estimate the temperature-dependent surface tension of normal saturated liquids. The new correlation contains three coefficients obtained by fitting 17,051 surface tension data of 38 saturated normal liquids. These 38 liquids contain refrigerants, hydrocarbons and some other inorganic liquids. The new correlation requires only the triple point temperature, triple point surface tension and critical point temperature as input and is able to well represent the experimental surface tension data for each of the 38 saturated normal liquids from the triple temperature up to the point near the critical point. The new correlation gives absolute average deviations (AAD) values below 3% for all of these 38 liquids with the only exception being octane with AAD=4.30%. Thus, the new correlation gives better overall results in comparison with other correlations for these 38 normal saturated liquids.

Molecular dynamics simulations of the surface tension of oxygen-supersaturated water

NASA Astrophysics Data System (ADS)

Jain, S.; Qiao, L.

2017-04-01

In this work, non-reactive molecular dynamic simulations were conducted to determine the surface tension of water as a function of the concentration of the dissolved gaseous molecules (O2), which would in turn help to predict the pressure inside the nanobubbles under supersaturation conditions. Knowing the bubble pressure is a prerequisite for understanding the mechanisms behind the spontaneous combustion of the H2/O2 gases inside the nanobubbles. First, the surface tension of pure water was determined using the planar interface method and the Irving and Kirkwood formula. Next, the surface tension of water containing four different supersaturation concentrations (S) of O2 gas molecules was computed considering the curved interface of a nanobubble. The surface tension of water was found to decrease with an increase in the supersaturation ratio or the concentration of the dissolved O2 gas molecules.

Calculation of a solid/liquid surface tension: A methodological study

NASA Astrophysics Data System (ADS)

Dreher, T.; Lemarchand, C.; Soulard, L.; Bourasseau, E.; Malfreyt, P.; Pineau, N.

2018-01-01

The surface tension of a model solid/liquid interface constituted of a graphene sheet surrounded by liquid methane has been computed using molecular dynamics in the Kirkwood-Buff formalism. We show that contrary to the fluid/fluid case, the solid/liquid case can lead to different structurations of the first fluid layer, leading to significantly different values of surface tension. Therefore we present a statistical approach that consists in running a series of molecular simulations of similar systems with different initial conditions, leading to a distribution of surface tensions from which an average value and uncertainty can be extracted. Our results suggest that these distributions converge as the system size increases. Besides we show that surface tension is not particularly sensitive to the choice of the potential energy cutoff and that long-range corrections can be neglected contrary to what we observed in the liquid/vapour interfaces. We have not observed the previously reported commensurability effect.

Measurement of Surface Tension of Solid Cu by Improved Multiphase Equilibrium

NASA Astrophysics Data System (ADS)

Nakamoto, Masashi; Liukkonen, Matti; Friman, Michael; Heikinheimo, Erkki; Hämäläinen, Marko; Holappa, Lauri

2008-08-01

The surface tension of solid Cu was measured with the multiphase equilibrium (MPE) method in a Pb-Cu system at 700 °C, 800 °C, and 900 °C. A special focus was on the measurement of angles involved in MPE. First, the effect of reading error in each angle measurement on the final result of surface tension of solid was simulated. It was found that the two groove measurements under atmosphere conditions are the primary sources of error in the surface tension of solid in the present system. Atomic force microscopy (AFM) was applied to these angle measurements as a new method with high accuracy. The obtained surface-tension values of solid Cu in the present work were 1587, 1610, and 1521 mN/m at 700 °C, 800 °C, and 900 °C, respectively, representing reasonable temperature dependence.

Genetic and chemical analyzes of transformations in compost compounds during biodegradation of oiled bleaching earth with waste sludge.

PubMed

Piotrowska-Cyplik, Agnieszka; Cyplik, Paweł; Marecik, Roman; Czarny, Jakub; Szymański, Andrzej; Wyrwas, Bogdan; Framski, Grzegorz; Chrzanowski, Lukasz; Materna, Katarzyna

2012-06-01

Composting of oiled bleaching earth with waste sludge and corn straw was carried out to investigate the ability of microorganisms to synthesize biosurfactants that might decrease the surface tension of composts. Analytical results and changes in the surface tension suggest that biodegradation of fatty by-products was the consequence of emulsifying properties of higher fatty acids. The surface tension for isolates from all composting phases was between 37 and 43 mN m(-1). No substances synthesized by microorganisms that might be able to decrease the surface tension were detected in composts. Tensammetric, TLC and HPLC-MS results and changes in surface tension suggest that biodegradation of fatty by-products results from the emulsifying properties of higher fatty acids. A decrease in fatty content from 144 to 6 mg g(-1) dry matter was obtained. Copyright © 2012 Elsevier Ltd. All rights reserved.

Surface tension of undercooled liquid cobalt

NASA Astrophysics Data System (ADS)

Yao, W. J.; Han, X. J.; Chen, M.; Wei, B.; Guo, Z. Y.

2002-08-01

This paper provides the results on experimentally measured and numerically predicted surface tensions of undercooled liquid cobalt. The experiments were performed by using the oscillation drop technique combined with electromagnetic levitation. The simulations are carried out with the Monte Carlo (MC) method, where the surface tension is predicted through calculations of the work of cohesion, and the interatomic interaction is described with an embedded-atom method. The maximum undercooling of the liquid cobalt is reached at 231 K (0.13Tm) in the experiment and 268 K (0.17Tm) in the simulation. The surface tension and its relationship with temperature obtained in the experiment and simulation are σexp = 1.93 - 0.000 33 (T - T m) N m-1 and σcal = 2.26 - 0.000 32 (T - T m) N m-1 respectively. The temperature dependence of the surface tension calculated from the MC simulation is in reasonable agreement with that measured in the experiment.

Surface tension of substantially undercooled liquid Ti-Al alloy

NASA Astrophysics Data System (ADS)

Zhou, K.; Wang, H. P.; Chang, J.; Wei, B.

2010-06-01

It is usually difficult to undercool Ti-Al alloys on account of their high reactivity in the liquid state. This results in a serious scarcity of information on their thermophysical properties in the metastable state. Here, we report on the surface tension of a liquid Ti-Al alloy under high undercooling condition. By using the electromagnetic levitation technique, a maximum undercooling of 324 K (0.19 T L) was achieved for liquid Ti-51 at.% Al alloy. The surface tension of this alloy, which was determined over a broad temperature range 1429-2040 K, increases linearly with the enhancement of undercooling. The experimental value of the surface tension at the liquidus temperature of 1753 K is 1.094 N m-1 and its temperature coefficient is -1.422 × 10-4 N m-1 K-1. The viscosity, solute diffusion coefficient and Marangoni number of this liquid Ti-Al alloy are also derived from the measured surface tension.

Surface tension of evaporating nanofluid droplets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Ruey-Hung; Phuoc, Tran X.; Martello, Donald

2011-05-01

Measurements of nanofluid surface tension were made using the pendant droplet method. Three different types of nanoparticles were used - laponite, silver and Fe 2O 3 - with de-ionized water (DW) as the base fluid. The reported results focus on the following categories; (1) because some nanoparticles require surfactants to form stable colloids, the individual effects of the surfactant and the particles were investigated; (2) due to evaporation of the pendant droplet, the particle concentration increases, affecting the apparent surface tension; (3) because of the evaporation process, a hysteresis was found where the evaporating droplet can only achieve lower valuesmore » of surface tension than that of nanofluids at the same prepared concentrations: and (4) the Stefan equation relating the apparent surface tension and heat of evaporation was found to be inapplicable for nanofluids investigated. Comparisons with findings for sessile droplets are also discussed, pointing to additional effects of nanoparticles other than the non-equilibrium evaporation process.« less

The effect of a uniform magnetic field on the onset of steady Benard-Marangoni convection in a layer of conducting fluid

NASA Astrophysics Data System (ADS)

Wilson, S. K.

1993-05-01

Analytical and numerical techniques are used to analyze the effect of a uniform vertical magnetic field on the onset of steady Benard-Marangoni convection in a horizontal layer of quiescent, electrically conducting fluid subject to a uniform vertical temperature gradient. Marangoni numbers for the onset of steady convection are found to be critically dependent on the nondimensional Crispation and Bond numbers. Two different asymptotic limits of strong surface tension and strong magnetic field are analyzed. Data obtained indicate that the presence of the magnetic field always has a stabilizing effect on the layer. Assuming that the Marangoni number is a critical parameter, it is shown that, if the free surface is nondeformable, then any particular disturbance can be stabilized with a sufficiently strong magnetic field. If the free surface is deformable and gravity waves are excluded, then the layer is always unstable to infinitely long wavelength disturbances with or without a magnetic field.

Spontaneous Formation of Nanopillar Arrays in Ultrathin Viscous Films: Critical Role of Thermocapillary Stresses

NASA Astrophysics Data System (ADS)

Troian, Sandra; Dietzel, Mathias

2010-03-01

Nanoscale structures manifest exceedingly large surface to volume ratios and are therefore highly susceptible to control by surface stresses. Actuation techniques which can exploit this feature provide a key strategy for construction and self-organization of large area arrays. During the past decade, several groups have reported that molten polymer nanofilms subject to an ultra-large transverse thermal gradient undergo spontaneous formation of nanopillar arrays. The prevailing explanation is that coherent interfacial reflection of acoustic phonons causes periodic modulation of the radiation pressure leading to instability and pillar growth. We demonstrate instead that thermocapillary forces play a crucial if not dominant role in the formation process due to the strong modulation of surface tension with temperature. Any nanoscale viscous film is prone to such formations, not just polymeric films. Analysis of the governing interface equation reveals the mechanism controlling the growth, spacing and symmetry of these self-assembling arrays. We discuss how these findings are being used in our laboratory to construct nanoscale components for optical and photonic applications.

Combined Molecular Dynamics Simulation-Molecular-Thermodynamic Theory Framework for Predicting Surface Tensions.

PubMed

Sresht, Vishnu; Lewandowski, Eric P; Blankschtein, Daniel; Jusufi, Arben

2017-08-22

A molecular modeling approach is presented with a focus on quantitative predictions of the surface tension of aqueous surfactant solutions. The approach combines classical Molecular Dynamics (MD) simulations with a molecular-thermodynamic theory (MTT) [ Y. J. Nikas, S. Puvvada, D. Blankschtein, Langmuir 1992 , 8 , 2680 ]. The MD component is used to calculate thermodynamic and molecular parameters that are needed in the MTT model to determine the surface tension isotherm. The MD/MTT approach provides the important link between the surfactant bulk concentration, the experimental control parameter, and the surfactant surface concentration, the MD control parameter. We demonstrate the capability of the MD/MTT modeling approach on nonionic alkyl polyethylene glycol surfactants at the air-water interface and observe reasonable agreement of the predicted surface tensions and the experimental surface tension data over a wide range of surfactant concentrations below the critical micelle concentration. Our modeling approach can be extended to ionic surfactants and their mixtures with both ionic and nonionic surfactants at liquid-liquid interfaces.

Effect of Gravity on Surface Tension

NASA Technical Reports Server (NTRS)

Weislogel, M. M.; Azzam, M. O. J.; Mann, J. A.

1998-01-01

Spectroscopic measurements of liquid-vapor interfaces are made in +/- 1-g environments to note the effect of gravity on surface tension. A slight increase is detected at -1-g0, but is arguably within the uncertainty of the measurement technique. An increased dependence of surface tension on the orientation and magnitude of the gravitational vector is anticipated as the critical point is approached.

The Cartesian Diver, Surface Tension and the Cheerios Effect

ERIC Educational Resources Information Center

Chen, Chi-Tung; Lee, Wen-Tang; Kao, Sung-Kai

2014-01-01

A Cartesian diver can be used to measure the surface tension of a liquid to a certain extent. The surface tension measurement is related to the two critical pressures at which the diver is about to sink and about to emerge. After sinking because of increasing pressure, the diver is repulsed to the centre of the vessel. After the pressure is…

Corresponding states correlation for temperature dependent surface tension of normal saturated liquids

NASA Astrophysics Data System (ADS)

Yi, Huili; Tian, Jianxiang

2014-07-01

A new simple correlation based on the principle of corresponding state is proposed to estimate the temperature-dependent surface tension of normal saturated liquids. The correlation is a linear one and strongly stands for 41 saturated normal liquids. The new correlation requires only the triple point temperature, triple point surface tension and critical point temperature as input and is able to represent the experimental surface tension data for these 41 saturated normal liquids with a mean absolute average percent deviation of 1.26% in the temperature regions considered. For most substances, the temperature covers the range from the triple temperature to the one beyond the boiling temperature.

Space storable propellant acquisition system

NASA Technical Reports Server (NTRS)

Tegart, J. R.; Uney, P. E.; Anderson, J. E.; Fester, D. A.

1972-01-01

Surface tension propellant acquisition concepts for an advanced spacecraft propulsion system having a 10-year mission capability were investigated. Surface tension systems were specified because they were shown to be the best propellant acquisition technique for various interplanetery spacecraft in a prior study. A variety of surface tension concepts for accomplishing propellant acquisition were formulated for the baseline space storable propulsion module and Jupiter Orbiter mission. Analyses and evaluations were then conducted on each candidate concept to assess fabricability, performance capability, and spacecraft compatibility. A comparative evaluation of the results showed the Fruhof-class of low-g surface tension systems to be preferred for these interplanetary applications.

Calculating the surface tension of binary solutions of simple fluids of comparable size

NASA Astrophysics Data System (ADS)

Zaitseva, E. S.; Tovbin, Yu. K.

2017-11-01

A molecular theory based on the lattice gas model (LGM) is used to calculate the surface tension of one- and two-component planar vapor-liquid interfaces of simple fluids. Interaction between nearest neighbors is considered in the calculations. LGM is applied as a tool of interpolation: the parameters of the model are corrected using experimental surface tension data. It is found that the average accuracy of describing the surface tension of pure substances (Ar, N2, O2, CH4) and their mixtures (Ar-O2, Ar-N2, Ar-CH4, N2-CH4) does not exceed 2%.

Measurement of Surface Interfacial Tension as a Function of Temperature Using Pendant Drop Images

NASA Astrophysics Data System (ADS)

Yakhshi-Tafti, Ehsan; Kumar, Ranganathan; Cho, Hyoung J.

2011-10-01

Accurate and reliable measurements of surface tension at the interface of immiscible phases are crucial to understanding various physico-chemical reactions taking place between those. Based on the pendant drop method, an optical (graphical)-numerical procedure was developed to determine surface tension and its dependency on the surrounding temperature. For modeling and experimental verification, chemically inert and thermally stable perfluorocarbon (PFC) oil and water was used. Starting with geometrical force balance, governing equations were derived to provide non-dimensional parameters which were later used to extract values for surface tension. Comparative study verified the accuracy and reliability of the proposed method.

Axisymmetric drop shape analysis for estimating the surface tension of cell aggregates by centrifugation.

PubMed

Kalantarian, Ali; Ninomiya, Hiromasa; Saad, Sameh M I; David, Robert; Winklbauer, Rudolf; Neumann, A Wilhelm

2009-02-18

Biological tissues behave in certain respects like liquids. Consequently, the surface tension concept can be used to explain aspects of the in vitro and in vivo behavior of multicellular aggregates. Unfortunately, conventional methods of surface tension measurement cannot be readily applied to small cell aggregates. This difficulty can be overcome by an experimentally straightforward method consisting of centrifugation followed by axisymmetric drop shape analysis (ADSA). Since the aggregates typically show roughness, standard ADSA cannot be applied and we introduce a novel numerical method called ADSA-IP (ADSA for imperfect profile) for this purpose. To examine the new methodology, embryonic tissues from the gastrula of the frog, Xenopus laevis, deformed in the centrifuge are used. It is confirmed that surface tension measurements are independent of centrifugal force and aggregate size. Surface tension is measured for ectodermal cells in four sample batches, and varies between 1.1 and 7.7 mJ/m2. Surface tension is also measured for aggregates of cells expressing cytoplasmically truncated EP/C-cadherin, and is approximately half as large. In parallel, such aggregates show a reduction in convergent extension-driven elongation after activin treatment, reflecting diminished intercellular cohesion.

Surface tension estimation of high temperature melts of the binary alloys Ag-Au

NASA Astrophysics Data System (ADS)

Dogan, Ali; Arslan, Hüseyin

2017-11-01

Surface tension calculation of the binary alloys Ag-Au at the temperature of 1381 K, where Ag and Au have similar electronic structures and their atomic radii are comparable, are carried out in this study using several equations over entire composition range of Au. Apparently, the deviations from ideality of the bulk solutions, such as activities of Ag and Au are small and the maximum excess Gibbs free energy of mixing of the liquid phase is for instance -4500 J/mol at XAu = 0.5. Besides, the results obtained in Ag-Au alloys that at a constant temperature the surface tension increases with increasing composition while the surface tension decreases as the temperature increases for entire composition range of Au. Although data about surface tension of the Ag-Au alloy are limited, it was possible to make a comparison for the calculated results for the surface tension in this study with the available experimental data. Taken together, the average standard error analysis that especially the improved Guggenheim model in the other models gives the best agreement along with the experimental results at temperature 1383 K although almost all models are mutually in agreement with the other one.

Surface-tension phenomena in organismal biology: an introduction to the symposium.

PubMed

Bourouiba, Lydia; Hu, David L; Levy, Rachel

2014-12-01

Flows driven by surface tension are both ubiquitous and diverse, involving the drinking of birds and bees, the flow of xylem in plants, the impact of raindrops on animals, respiration in humans, and the transmission of diseases in plants and animals, including humans. The fundamental physical principles underlying such flows provide a unifying framework to interpret the adaptations of the microorganisms, animals, and plants that rely upon them. The symposium on "Surface-Tension Phenomena in Organismal Biology" assembled an interdisciplinary group of researchers to address a large spectrum of topics, all articulated around the role of surface tension in shaping biology, health, and ecology. The contributions to the symposium and the papers in this issue are meant to be a starting point for novices to familiarize themselves with the fundamentals of flows driven by surface tension; to understand how they can play a governing role in many settings in organismal biology; and how such understanding of nature's use of surface tension can, in turn, inspire humans to innovate. © The Author 2014. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. All rights reserved. For permissions please email: journals.permissions@oup.com.

Design of an experimental apparatus for measurement of the surface tension of metastable fluids

NASA Astrophysics Data System (ADS)

Vinš, V.; Hrubý, J.; Hykl, J.; Blaha, J.; Šmíd, B.

2013-04-01

A unique experimental apparatus for measurement of the surface tension of aqueous mixtures has been designed, manufactured, and tested in our laboratory. The novelty of the setup is that it allows measurement of surface tension by two different methods: a modified capillary elevation method in a long vertical capillary tube and a method inspired by the approach of Hacker (National Advisory Committee for Aeronautics, Technical Note 2510, 1-20, 1951), i.e. in a short horizontal capillary tube. Functionality of all main components of the apparatus, e.g., glass chamber with the capillary tube, temperature control unit consisting of two thermostatic baths with special valves for rapid temperature jumps, helium distribution setup allowing pressure variation above the liquid meniscus inside the capillary tube, has been successfully tested. Preliminary results for the surface tension of the stable and metastable supercooled water measured by the capillary elevation method at atmospheric pressure are provided. The surface tension of water measured at temperatures between +26 °C and -11 °C is in good agreement with the extrapolated IAPWS correlation (IAPWS Release on Surface Tension of Ordinary Water Substance, September 1994); however it disagrees with data by Hacker.

Heat pipe systems using new working fluids

NASA Technical Reports Server (NTRS)

Chao, David F. (Inventor); Zhang, Nengli (Inventor)

2004-01-01

The performance of a heat pipe system is greatly improved by the use of a dilute aqueous solution of about 0.0005 and about 0.005 moles per liter of a long chain alcohol as the working fluid. The surface tension-temperature gradient of the long-chain alcohol solutions turns positive as the temperature exceeds a certain value, for example about 40.degree. C. for n-heptanol solutions. Consequently, the Marangoni effect does not impede, but rather aids in bubble departure from the heating surface. Thus, the bubble size at departure is substantially reduced at higher frequencies and, therefore, increases the boiling limit of heat pipes. This feature is useful in microgravity conditions. In addition to microgravity applications, the heat pipe system may be used for commercial, residential and vehicular air conditioning systems, micro heat pipes for electronic devices, refrigeration and heat exchangers, and chemistry and cryogenics.

Quantification of the Mass Transfer at Fluid Interfaces in Microfluidic Channels

NASA Astrophysics Data System (ADS)

Wismeth, Carina; Manhart, Michael; Niessner, Reinhard; Baumann, Thomas

2017-04-01

Mass transfer rates at interfaces in a complex porous media are relevant in many environmental applications and control the functions of natural filter systems in subsurface environments. The mass transfer at fluid interfaces is associated with interface convection caused by local inhomogeneities in interface tension and hydrodynamic instabilities at the interface. If there is a surface tension gradient along the surface a shear stress jump is generated that results in fluid motion along the surface that is called Marangoni effect. These spontaneous convection currents can lead to an increased mass transfer of the transition component at the phase boundary and to an increased mixing of the phases. Therefore compensatory currents at the interface can have a significant influence on the subsurface transport of contaminants in the groundwater area, especially in the vadose zone. Using microfluidic channels and advanced experimental techniques it is possible to measure the fluid flow and mass transfer rates directly and to quantify the effect of the Marangoni convection on the mass transfer at interfaces between a non-aqueous liquid and water with high temporal and spatial resolution. The use of fluorescent particles as well as the recording and analysis of their trajectories is intended to visualize interfacial processes and to quantify the mass transfer at fluid phase boundaries. Concentration gradients at the interface are analysed by spectroscopic methods and allow an assessment of the enrichment and depletion at the phase boundaries. Extensive test series provide the experimental basis for quantifying and analysing the impact of the Marangoni effect on the mass transfer rates at interfaces in porous media in subsurface aquatic environments. Within this research project we concentrate on the effect of Marangoni convection on the mass transfer near an 1-octanol-water interface, which serves as a well defined proxy for non-aqueous phase liquids in porous media. Experiments and a numerical simulation are closely coupled to provide a generic data set with high reproducibility and used to obtain highly resolved three-dimensional data of mass transfer in two- and three-phase systems to foster the understanding of subsurface transport, especially in the vadose zone.

The influence of surfactant on the propagation of a semi-infinite bubble through a liquid-filled compliant channel

PubMed Central

Halpern, David; Gaver, Donald P.

2012-01-01

We investigate the influence of a soluble surfactant on the steady-state motion of a finger of air through a compliant channel. This study provides a basic model from which to understand the fluid–structure interactions and physicochemical hydrodynamics of pulmonary airway reopening. Airway closure occurs in lung diseases such as respiratory distress syndrome and acute respiratory distress syndrome as a result of fluid accumulation and surfactant insufficiency. This results in ‘compliant collapse’ with the airway walls buckled and held in apposition by a liquid occlusion that blocks the passage of air. Airway reopening is essential to the recovery of adequate ventilation, but has been associated with ventilator-induced lung injury because of the exposure of airway epithelial cells to large interfacial flow-induced pressure gradients. Surfactant replacement is helpful in modulating this deleterious mechanical stimulus, but is limited in its effectiveness owing to slow surfactant adsorption. We investigate the effect of surfactant on micro-scale models of reopening by computationally modelling the steady two-dimensional motion of a semi-infinite bubble propagating through a liquid-filled compliant channel doped with soluble surfactant. Many dimensionless parameters affect reopening, but we primarily investigate how the reopening pressure pb depends upon the capillary number Ca (the ratio of viscous to surface tension forces), the adsorption depth parameter λ (a bulk concentration parameter) and the bulk Péclet number Peb (the ratio of bulk convection to diffusion). These studies demonstrate a dependence of pb on λ, and suggest that a critical bulk concentration must be exceeded to operate as a low-surface-tension system. Normal and tangential stress gradients remain largely unaffected by physicochemical interactions – for this reason, further biological studies are suggested that will clarify the role of wall flexibility and surfactant on the protection of the lung from atelectrauma. PMID:22997476

Fatigue life of additively manufactured Ti6Al4V scaffolds under tension-tension, tension-compression and compression-compression fatigue load.

PubMed

Lietaert, Karel; Cutolo, Antonio; Boey, Dries; Van Hooreweder, Brecht

2018-03-21

Mechanical performance of additively manufactured (AM) Ti6Al4V scaffolds has mostly been studied in uniaxial compression. However, in real-life applications, more complex load conditions occur. To address this, a novel sample geometry was designed, tested and analyzed in this work. The new scaffold geometry, with porosity gradient between the solid ends and scaffold middle, was successfully used for quasi-static tension, tension-tension (R = 0.1), tension-compression (R = -1) and compression-compression (R = 10) fatigue tests. Results show that global loading in tension-tension leads to a decreased fatigue performance compared to global loading in compression-compression. This difference in fatigue life can be understood fairly well by approximating the local tensile stress amplitudes in the struts near the nodes. Local stress based Haigh diagrams were constructed to provide more insight in the fatigue behavior. When fatigue life is interpreted in terms of local stresses, the behavior of single struts is shown to be qualitatively the same as bulk Ti6Al4V. Compression-compression and tension-tension fatigue regimes lead to a shorter fatigue life than fully reversed loading due to the presence of a mean local tensile stress. Fractographic analysis showed that most fracture sites were located close to the nodes, where the highest tensile stresses are located.

van der Waals model for the surface tension of liquid 4He near the λ point

NASA Astrophysics Data System (ADS)

Tavan, Paul; Widom, B.

1983-01-01

We develop a phenomenological model of the 4He liquid-vapor interface. With it we calculate the surface tension of liquid helium near the λ point and compare with the experimental measurements by Magerlein and Sanders. The model is a form of the van der Waals surface-tension theory, extended to apply to a phase equilibrium in which the simultaneous variation of two order parameters-here the superfluid order parameter and the total density-is essential. The properties of the model are derived analytically above the λ point and numerically below it. Just below the λ point the superfluid order parameter is found to approach its bulk-superfluid-phase value very slowly with distance on the liquid side of the interface (the characteristic distance being the superfluid coherence length), and to vanish rapidly with distance on the vapor side, while the total density approaches its bulk-phase values rapidly and nearly symmetrically on the two sides. Below the λ point the surface tension has a |ɛ|32 singularity (ɛ~T-Tλ) arising from the temperature dependence of the spatially varying superfluid order parameter. This is the mean-field form of the more general |ɛ|μ singularity predicted by Sobyanin and by Hohenberg, in which μ (which is in reality close to 1.35 at the λ point of helium) is the exponent with which the interfacial tension between two critical phases vanishes. Above the λ point the surface tension in this model is analytic in ɛ. A singular term |ɛ|μ may in reality be present in the surface tension above as well as below the λ point, although there should still be a pronounced asymmetry. The variation with temperature of the model surface tension is overall much like that in experiment.

Nonzero Ideal Gas Contribution to the Surface Tension of Water.

PubMed

Sega, Marcello; Fábián, Balázs; Jedlovszky, Pál

2017-06-15

Surface tension, the tendency of fluid interfaces to behave elastically and minimize their surface, is routinely calculated as the difference between the lateral and normal components of the pressure or, invoking isotropy in momentum space, of the virial tensor. Here we show that the anisotropy of the kinetic energy tensor close to a liquid-vapor interface can be responsible for a large part of its surface tension (about 15% for water, independent from temperature).

Graphene doped ZnO films for photoelectrowetting on microchannels

NASA Astrophysics Data System (ADS)

Al-Aribe, Khaled; Knopf, George K.

2017-02-01

Photoelectrowetting on dielectric surfaces can be used to drive droplets of liquid along reconfigurable paths on a microfluidic chip using controlled optical signals. These electrostatically activated surfaces along the desired path eliminate the need for precision molded channels and discrete functional components such as microvalves and micropumps. The photoelectrowetting effect exploits the surface tension of the droplet to maintain its volume during the transportation pathway and the photoelectric properties of the substrate surface are used to induce reversible fluidic flow. The active light-driven substrate is structured from graphene doped zinc-oxide (ZnO-G) films deposited on ITO coated glass. This substrate is coated from the ZnO-G side with Ruthenium-based dye (N719) to maximize its absorbability. The light triggers two forces that enable the droplet to be transported along the substrate. The first arises from the induced hydrophobicity gradient formed across the droplet contact area with the substrate surface. Exposing the ZnO-G film to a broad spectrum white light source alters the surface's electric potential which induces a change in the droplet's contact angle and the associated hydrophobicity. Once the hydrophobicity gradient is generated the droplet will start to move in the direction of the wetting zone. The second force is also created by the optical input when the absorbed light generates a photoelectric potential that produces a piezo-electrical effect on the ZnO-G film. The light triggered piezo-electrical behavior of the ZnO-G film can be used to generate the erasable microchannels that can guide droplet movement through a microfluidic chip. Preliminary experiments are performed to investigate the photoelectric potential of light activated ZnO-G films.

Effect of hemoglobin polymerization on oxygen transport in hemoglobin solutions.

PubMed

Budhiraja, Vikas; Hellums, J David

2002-09-01

The effect of hemoglobin (Hb) polymerization on facilitated transport of oxygen in a bovine hemoglobin-based oxygen carrier was studied using a diffusion cell. In high oxygen tension gradient experiments (HOTG) at 37 degrees C the diffusion of dissolved oxygen in polymerized Hb samples was similar to that in unpolymerized Hb solutions during oxygen uptake. However, in the oxygen release experiments, the transport by diffusion of dissolved oxygen was augmented by diffusion of oxyhemoglobin over a range of oxygen saturations. The augmentation was up to 30% in the case of polymerized Hb and up to 100% in the case of unpolymerized Hb solution. In experiments performed at constant, low oxygen tension gradients in the range of physiological significance, the augmentation effect was less than that in the HOTG experiments. Oxygen transport in polymerized Hb samples was approximately the same as that in unpolymerized samples over a wide range of oxygen tensions. However, at oxygen tensions lower than 30 mm Hg, there were more significant augmentation effects in unpolymerized bovine Hb samples than in polymerized Hb. The results presented here are the first accurate, quantitative measurements of effective diffusion coefficients for oxygen transport in hemoglobin-based oxygen carriers of the type being evaluated to replace red cells in transfusions. In all cases the oxygen carrier was found to have higher effective oxygen diffusion coefficients than blood.

Mapping surface tension induced menisci with application to tensiometry and refractometry.

PubMed

Mishra, Avanish; Kulkarni, Varun; Khor, Jian-Wei; Wereley, Steve

2015-07-28

In this work, we discuss an optical method for measuring surface tension induced menisci. The principle of measurement is based upon the change in the background pattern produced by the curvature of the meniscus acting as a lens. We measure the meniscus profile over an inclined glass plate and utilize the measured meniscus for estimation of surface tension and refractive index.

Role of Marangoni stress during breakup of surfactant-covered liquid threads: Reduced rates of thinning and microthread cascades

NASA Astrophysics Data System (ADS)

Kamat, Pritish M.; Wagoner, Brayden W.; Thete, Sumeet S.; Basaran, Osman A.

2018-04-01

Adsorption onto and lowering of surface tension σ of fluid interfaces by surfactants is exploited in drop formation (e.g., inkjet printing) where a thinning liquid thread (radius h ) connects an about-to-form drop to the liquid that remains hanging from the nozzle when the former falls from it. Surfactants can affect thread pinch-off in two ways: first, by lowering σ , they lower capillary pressure (σ /h ), and second, as surfactant concentration along the interface can be nonuniform, they cause the interface to be subjected to a surface tension gradient or Marangoni stress. Recent studies show that the location where the thread breaks is devoid of surfactant, and others assert that the influence of Marangoni stress on pinch-off is negligible. We demonstrate by simulations and experiments that surfactants play a major role in drop formation and that Marangoni stresses acting near but not at the pinch point give rise to reduced rates of thread thinning and formation of multiple microthreads that distinguish pinch-off of surfactant-covered threads from surfactant-free ones. Thinning at finite Reynolds and Peclet numbers, Re and Pe, is shown to exhibit intermediate scaling regimes that have heretofore only been observed during pinch-off of threads undergoing creeping flow (Re=0 ) while convection of surfactant is weak compared to its diffusion (Pe<1 ).

Variational Methods For Sloshing Problems With Surface Tension

NASA Astrophysics Data System (ADS)

Tan, Chee Han; Carlson, Max; Hohenegger, Christel; Osting, Braxton

2016-11-01

We consider the sloshing problem for an incompressible, inviscid, irrotational fluid in a container, including effects due to surface tension on the free surface. We restrict ourselves to a constant contact angle and we seek time-harmonic solutions of the linearized problem, which describes the time-evolution of the fluid due to a small initial disturbance of the surface at rest. As opposed to the zero surface tension case, where the problem reduces to a partial differential equation for the velocity potential, we obtain a coupled system for the velocity potential and the free surface displacement. We derive a new variational formulation of the coupled problem and establish the existence of solutions using the direct method from the Calculus of Variations. In the limit of zero surface tension, we recover the variational formulation of the classical Steklov eigenvalue problem, as derived by B. A. Troesch. For the particular case of an axially symmetric container, we propose a finite element numerical method for computing the sloshing modes of the coupled system. The scheme is implemented in FEniCS and we obtain a qualitative description of the effect of surface tension on the sloshing modes.

Effect of Composition of Alloys of Tin-Sodium Systems on Surface Tension

NASA Astrophysics Data System (ADS)

Alchagirov, B. B.; Kyasova, O. Kh.

2018-07-01

The results are presented from investigating the surface tensions of tin-sodium systems, along with original experimental data on the concentration dependences of the surface tensions of 19 tin-based sodium alloys obtained for samples of enhanced purity in a range of compositions with contents of 0.06 to 5.00 at % Na at T = 573 K. It is established that adding small amounts of sodium to tin greatly reduces the surface tensions of the studied melts. Calculations of sodium adsorption in alloys with tin show there is a maximum on the adsorption curve that corresponds to alloys with contents of around 1.5 at % Na in Sn.

Modeling of surface tension effects in venturi scrubbing

NASA Astrophysics Data System (ADS)

Ott, Robert M.; Wu, Tatsu K. L.; Crowder, Jerry W.

A modified model of venturi scrubber performance has been developed that addresses two effects of liquid surface tension: its effect on droplet size and its effect on particle penetration into the droplet. The predictions of the model indicate that, in general, collection efficiency increases with a decrease in liquid surface tension, but the range over which this increase is significant depends on the particle size and on the scrubber operating parameters. The predictions further indicate that the increases in collection efficiency are almost totally due to the effect of liquid surface tension on the mean droplet size, and that the collection efficiency is not significantly affected by the ability of the particle to penetrate the droplet.

Calculation of the surface tension of liquid Ga-based alloys

NASA Astrophysics Data System (ADS)

Dogan, Ali; Arslan, Hüseyin

2018-05-01

As known, Eyring and his collaborators have applied the structure theory to the properties of binary liquid mixtures. In this work, the Eyring model has been extended to calculate the surface tension of liquid Ga-Bi, Ga-Sn and Ga-In binary alloys. It was found that the addition of Sn, In and Bi into Ga leads to significant decrease in the surface tension of the three Ga-based alloy systems, especially for that of Ga-Bi alloys. The calculated surface tension values of these alloys exhibit negative deviation from the corresponding ideal mixing isotherms. Moreover, a comparison between the calculated results and corresponding literature data indicates a good agreement.

Surface Tension: Mechanics, Thermodynamics, and Relaxation Times

NASA Astrophysics Data System (ADS)

Tovbin, Yu. K.

2018-06-01

A microscopic analysis is presented of the existing definitions of equilibrium surface tension, which can be divided into two types: mechanical and thermodynamic. Each type of definition can be studied from the presentation below according to thermodynamic hypotheses or molecular calculations. An analysis of the planar interface is given and its generalization for curved (spherical) interfaces is considered. The distinction between approaches describing the surface tension of metastable and equilibrium droplets is discussed. Based on nonequilibrium thermodynamics, it is shown that the introduction of metastable droplets is due to a violation of the relationship between the times of impulse and chemical potential relaxation in condensed phases. Problems of calculating the surface tension in nonequilibrium situations are created.

Surface segregation and surface tension of polydisperse polymer melts.

PubMed

Minnikanti, Venkatachala S; Qian, Zhenyu; Archer, Lynden A

2007-04-14

The effect of polydispersity on surface segregation of a lower molecular weight polymer component in a higher molecular weight linear polymer melt host is investigated theoretically. We show that the integrated surface excess zM of a polymer component of molecular weight M satisfies a simple relation zM=2Ue(M/Mw-1)phiM, where Mw is the weight averaged molecular weight, phiM is the polymer volume fraction, and Ue is the attraction of polymer chain ends to the surface. Ue is principally of entropic origin, but also reflects any energetic preference of chain ends to the surface. We further show that the surface tension gammaM of a polydisperse melt of high molar mass components depends on the number average degree of polymerization Mn as, gammaM=gammainfinity+2UerhobRT/Mn. The parameter gammainfinity is the asymptotic surface tension of an infinitely long polymer of the same chemistry, rhob is the bulk density of the polymer, R is the universal gas constant, and T is the temperature. The predicted gammaM compare favorably with surface tension values obtained from self-consistent field theory simulations that include equation of state effects, which account for changes in polymer density with molecular weight. We also compare the predicted surface tension with available experimental data.

Prediction of surface tension of HFD-like fluids using the Fowler’s approximation

NASA Astrophysics Data System (ADS)

Goharshadi, Elaheh K.; Abbaspour, Mohsen

2006-09-01

The Fowler's expression for calculation of the reduced surface tension has been used for simple fluids using the Hartree-Fock Dispersion (HFD)-like potential (HFD-like fluids) obtained from the inversion of the viscosity collision integrals at zero pressure. In order to obtain the RDFs values needed for calculation of the surface tension, we have performed the MD simulation at different temperatures and densities and then fitted with an expression and compared the resulting RDFs with the experiment. Our results are in excellent accordance with experimental values when the vapor density has been considered, especially at high temperatures. We have also calculated the surface tension using a RDF's expression based on the Lennard-Jones (LJ) potential which was in good agreement with the molecular dynamics simulations. In this work, we have shown that our results based on HFD-like potential can describe the temperature dependence of the surface tension superior than that of LJ potential.

Smoothed dissipative particle dynamics model for mesoscopic multiphase flows in the presence of thermal fluctuations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lei, Huan; Baker, Nathan A.; Wu, Lei

2016-08-05

Thermal fluctuations cause perturbations of fluid-fluid interfaces and highly nonlinear hydrodynamics in multiphase flows. In this work, we develop a novel multiphase smoothed dissipative particle dynamics model. This model accounts for both bulk hydrodynamics and interfacial fluctuations. Interfacial surface tension is modeled by imposing a pairwise force between SDPD particles. We show that the relationship between the model parameters and surface tension, previously derived under the assumption of zero thermal fluctuation, is accurate for fluid systems at low temperature but overestimates the surface tension for intermediate and large thermal fluctuations. To analyze the effect of thermal fluctuations on surface tension,more » we construct a coarse-grained Euler lattice model based on the mean field theory and derive a semi-analytical formula to directly relate the surface tension to model parameters for a wide range of temperatures and model resolutions. We demonstrate that the present method correctly models the dynamic processes, such as bubble coalescence and capillary spectra across the interface.« less

Engineering Surface Energy and Nanostructure of Microporous Films for Expanded Membrane Distillation Applications.

PubMed

Boo, Chanhee; Lee, Jongho; Elimelech, Menachem

2016-08-02

We investigated the factors that determine surface omniphobicity of microporous membranes and evaluated the potential application of these membranes in desalination of low surface tension wastewaters by membrane distillation (MD). Specifically, the effects of surface morphology and surface energy on membrane surface omniphobicity were systematically investigated by evaluating wetting resistance to low surface tension liquids. Single and multilevel re-entrant structures were achieved by using cylindrical glass fibers as a membrane substrate and grafting silica nanoparticles (SiNPs) on the fibers. Surface energy of the membrane was tuned by functionalizing the fiber substrate with fluoroalkylsilane (FAS) having two different lengths of fluoroalkyl chains. Results show that surface omniphobicity of the modified fibrous membrane increased with higher level of re-entrant structure and with lower surface energy. The secondary re-entrant structure achieved by SiNP coating on the cylindrical fibers was found to play a critical role in enhancing the surface omniphobicity. Membranes coated with SiNPs and chemically modified by the FAS with a longer fluoroalkyl chain (or lower surface energy) exhibited excellent surface omniphobicity and showed wetting resistance to low surface tension liquids such as ethanol (22.1 mN m(-1)). We further evaluated performance of the membranes in desalination of saline feed solutions with varying surface tensions by membrane distillation (MD). The engineered membranes exhibited stable MD performance with low surface tension feed waters, demonstrating the potential application omniphobic membranes in desalinating complex, high salinity industrial wastewaters.

Modeling the surface tension of complex, reactive organic-inorganic mixtures

NASA Astrophysics Data System (ADS)

Schwier, A. N.; Viglione, G. A.; Li, Z.; McNeill, V. F.

2013-01-01

Atmospheric aerosols can contain thousands of organic compounds which impact aerosol surface tension, affecting aerosol properties such as cloud condensation nuclei (CCN) ability. We present new experimental data for the surface tension of complex, reactive organic-inorganic aqueous mixtures mimicking tropospheric aerosols. Each solution contained 2-6 organic compounds, including methylglyoxal, glyoxal, formaldehyde, acetaldehyde, oxalic acid, succinic acid, leucine, alanine, glycine, and serine, with and without ammonium sulfate. We test two surface tension models and find that most reactive, complex, aqueous organic mixtures which do not contain salt are well-described by a weighted Szyszkowski-Langmuir (S-L) model which was first presented by Henning et al. (2005). Two approaches for modeling the effects of salt were tested: (1) the Tuckermann approach (an extension of the Henning model with an additional explicit salt term), and (2) a new implicit method proposed here which employs experimental surface tension data obtained for each organic species in the presence of salt used with the Henning model. We recommend the use of method (2) for surface tension modeling because the Henning model (using data obtained from organic-inorganic systems) and Tuckermann approach provide similar modeling fits and goodness of fit (χ2) values, yet the Henning model is a simpler and more physical approach to modeling the effects of salt, requiring less empirically determined parameters.

Numerical Study on the Effects of Gravity and Surface Tension on Condensation Process in Square Minichannel

NASA Astrophysics Data System (ADS)

Li, Panpan; Chen, Zhenqian; Shi, Juan

2018-02-01

A volume of fluid (VOF) method is adopted to simulate the condensation of R134a in a horizontal single square minichannel with 1 mm side length. The effect of gravity, surface tension and gas-liquid interfacial shear stress are taken into account. The result denotes that condensation is first appeared at the corner of channel, and then the condensation is stretched at the effect of surface tension until the whole channel boundary covered. The effect of gravity on the distribution of the liquid film depends on the channel length. In short channel, the gravity shows no significant effect, the distribution shape of steam in the cross section of the channel is approximately circular. In long channel, due to the influence of gravity, the liquid converges at the bottom under the effect of gravity, and the thickness of the liquid film at the bottom is obviously higher than that of the upper part of the channel. The effect of surface tension on condensation is also analysed. The surface tension can enhance the condensation heat transfer significantly when the inlet mass flux is low. Whilst, at high mass flux, the enhancement of surface tension on heat transfer is unobvious and can be neglected.

Test-area surface tension calculation of the graphene-methane interface: Fluctuations and commensurability

NASA Astrophysics Data System (ADS)

d'Oliveira, H. D.; Davoy, X.; Arche, E.; Malfreyt, P.; Ghoufi, A.

2017-06-01

The surface tension (γ) of methane on a graphene monolayer is calculated by using the test-area approach. By using a united atom model to describe methane molecules, strong fluctuations of surface tension as a function of the surface area of the graphene are evidenced. In contrast with the liquid-vapor interfaces, the use of a larger cutoff does not fully erase the fluctuations in the surface tension. Counterintuitively, the description of methane and graphene from the Optimized Potentials for Liquid Simulations all-atom model and a flexible model, respectively, led to a lessening in the surface tension fluctuations. This result suggests that the origin of fluctuations in γ is due to a model-effect rather than size-effects. We show that the molecular origin of these fluctuations is the result of a commensurable organization between both graphene and methane. This commensurable structure can be avoided by describing methane and graphene from a flexible force field. Although differences in γ with respect to the model have been often reported, it is the first time that the model drastically affects the physics of a system.

Surface properties of liquid In-Zn alloys

NASA Astrophysics Data System (ADS)

Pstruś, J.; Moser, Z.; Gąsior, W.

2011-02-01

The measurements of surface tension and density of zinc, indium and liquid In-Zn alloys containing 0.9, 0.85, 0.75, 0.70, 0.60, 0.40, 0.25 and 0.10 mole fraction of In were carried out using the method of maximum pressure in gaseous bubbles (MBP) as well as dilatometric technique. The technique of sessile drop was additionally applied in the measurements of surface tension for pure indium and zinc. The measurements were performed at temperature range 474-1151 K. The isotherms of surface tension calculated based on Butler's equation at 700 and 1100 K corresponded well with the experimental values for zinc content lower than 0.6 mole fraction. The surface tension calculated for alloys of higher zinc concentrations (0.6 < XZn < 0.95) had a positive value of the surface tension temperature coefficient (dσ/dT), which did not coincide with the experimental results. The density as well as molar volume of liquid In-Zn alloys showed almost identical behaviour like the ideal solutions. The observed little deviations were contained within assessed experimental errors.

Effects of Oxygen Partial Pressure on the Surface Tension of Liquid Nickel

NASA Technical Reports Server (NTRS)

SanSoucie, Michael P.; Rogers, Jan R.; Gowda, Vijaya Kumar Malahalli Shankare; Rodriguez, Justin; Matson, Douglas M.

2015-01-01

The NASA Marshall Space Flight Center's electrostatic levitation (ESL) laboratory has been recently upgraded with an oxygen partial pressure controller. This system allows the oxygen partial pressure within the vacuum chamber to be measured and controlled, theoretically in the range from 10-36 to 100 bar. The oxygen control system installed in the ESL laboratory's main chamber consists of an oxygen sensor, oxygen pump, and a control unit. The sensor is a potentiometric device that determines the difference in oxygen activity in two gas compartments (inside the chamber and the air outside of the chamber) separated by an electrolyte, which is yttria-stabilized zirconia. The pump utilizes coulometric titration to either add or remove oxygen. The system is controlled by a desktop control unit, which can also be accessed via a computer. The controller performs temperature control for the sensor and pump, PID-based current loop, and a control algorithm. Oxygen partial pressure has been shown to play a significant role in the surface tension of liquid metals. Oxide films or dissolved oxygen may lead to significant changes in surface tension. The effects of oxygen partial pressure on the surface tension of undercooled liquid nickel will be analyzed, and the results will be presented. The surface tension will be measured at several different oxygen partial pressures while the sample is undercooled. Surface tension will be measured using the oscillating drop method. While undercooled, each sample will be oscillated several times consecutively to investigate how the surface tension behaves with time while at a particular oxygen partial pressure.

Membrane tension controls the assembly of curvature-generating proteins

PubMed Central

Simunovic, Mijo; Voth, Gregory A.

2015-01-01

Proteins containing a Bin/Amphiphysin/Rvs (BAR) domain regulate membrane curvature in the cell. Recent simulations have revealed that BAR proteins assemble into linear aggregates, strongly affecting membrane curvature and its in-plane stress profile. Here, we explore the opposite question: do mechanical properties of the membrane impact protein association? By using coarse-grained molecular dynamics simulations, we show that increased surface tension significantly impacts the dynamics of protein assembly. While tensionless membranes promote a rapid formation of long-living linear aggregates of N-BAR proteins, increase in tension alters the geometry of protein association. At high tension, protein interactions are strongly inhibited. Increasing surface density of proteins leads to a wider range of protein association geometries, promoting the formation of meshes, which can be broken apart with membrane tension. Our work indicates that surface tension may play a key role in recruiting proteins to membrane-remodelling sites in the cell. PMID:26008710

Effect of Baffle on Gravity-Gradient-Excited Slosh Waves and Spacecraft Moment and Angular-Momentum Fluctuations in Microgravity

NASA Technical Reports Server (NTRS)

Hung, R. J.; Lee, C. C.

1995-01-01

The dynamical behavior of fluids affected by the asymmetric gravity gradient acceleration has been investigated. In particular, the effects of surface tension on partially filled rotating fluids applicable to a full-scale Gravity Probe-B Spacecraft dewar tank with and without baffles are studied. Results of slosh wave excitation along the liquid-vapor interface induced by gravity gradient acceleration indicate that the gravity gradient acceleration is equivalent to the combined effect of a twisting force and a torsional moment acting on the spacecraft. The results are clearly seen from one-up one-down and one-down one-up oscillations in the cross-section profiles of two bubbles in the vertical (r, z)-plane of the rotating dewar, and from the eccentric contour of the bubble rotating around the axis of the dewar in a horizontal (r, theta)-plane. As the viscous force, between liquid and solid interface, greatly contributes to the damping of slosh wave excitation, a rotating dewar with baffles provides more areas of liquid-solid interface than that of a rotating dewar without baffles. Results show that the damping effect provided by the baffles reduces the amplitude of slosh wave excitation and lowers the degree of asymmetry in liquid-vapor distribution. Fluctuations of angular momentum and fluid moment caused by the slosh wave excited by gravity gradient acceleration with and without baffle boards are also investigated. It is also shown that the damping effect provided by the baffles greatly reduces the amplitudes of angular momentum and fluid moment fluctuations.

The dynamical simulation of transient three-dimensional cryogenic liquid sloshing oscillations under low-gravity and microgravity

NASA Astrophysics Data System (ADS)

Chi, Yong Mann

A numerical simulation model has been developed for the dynamical behavior of spacecraft propellant, both during the draining and the closing of the tank outlet at the onset of suction dip affected by the asymmetric combined gravity gradient and gravity jitter accelerations. In particular the effect of the surface tension of the fluids in the partially filled dewar (applicable to the Gravity Probe-B spacecraft dewar tank and fuel tanks for a liquid rocket) with rotation has been simulated and investigated. Two different cases of accelerations, one with gravity jitter dominated and the other equally weighted between gravity gradient and gravity jitter accelerations, are studied. In the development of this numerical simulation model, the NASA-VOF3D has been used as a supplement to the numerical program of this dissertation. The NASA-VOF3D code has been used for performing the three-dimensional incompressible flows with free surface. This is also used for controlling liquid sloshing inside the tank when the spacecraft is orbiting. To keep track of the location of the liquid, the fractional volume of fluid (VOF) technique was used. The VOF is based on the indicator function of the region occupied by the liquid with an Eulerian approach to solve the free surface phenomena between liquid and gas phases. For the calculation of surface tension force, the VOF model is also used. The newly developed simulation model is used to investigate the characteristics of liquid hydrogen draining in terms of the residual amount of trapped liquid at the onset of the suction dip and residual liquid volume at the time the dip of the liquid-vapor interface formed. This investigation simulates the characteristics of liquid oscillations due to liquid container outlet shut-off at the onset of suction dip. These phenomena checked how these mechanisms affected the excitation of slosh waves during the course of liquid draining and after shut-off tank outlet. In the present study, the dynamical evolution of sloshing dynamics excited by fluid stress forces, fluid stress moments, and the arm of fluid moment exerted on the dewar container, is considered. This excitation was driven by the combined gravity gradient and gravity jitter acceleration inside the tank during the draining process and closing the tank outlet. The time evolution of the liquid-vapor interface profiles and the bubble mass center fluctuation, as well as liquid mass center and fluctuations of angular momentum caused by slosh wave excitations with 0.1 rpm in a reduced gravity, are also investigated and simulated. Force, angular momentum, and torque vector time histories and Power Spectral Density (PSD) are also plotted and discussed. The results of this investigation may be applied to determine the magnitude and nature of control forces and torques needed to minimize influence of slosh on the dynamics of liquid fueled vehicles in near earth orbit. Results show that induced fluid forces (or angular momentum) exerted on the container wall along x and y-axes, which are non-existent at the beginning, are introduced by the slosh waves excited by asymmetric gravity gradient and the gravity jitter acceleration.

Effects of surface tension and intraluminal fluid on mechanics of small airways.

PubMed

Hill, M J; Wilson, T A; Lambert, R K

1997-01-01

Airway constriction is accompanied by folding of the mucosa to form ridges that run axially along the inner surface of the airways. The mucosa has been modeled (R. K. Lambert. J. Appl. Physiol. 71:666-673, 1991) as a thin elastic layer with a finite bending stiffness, and the contribution of its bending stiffness to airway elastance has been computed. In this study, we extend that work by including surface tension and intraluminal fluid in the model. With surface tension, the pressure on the inner surface of the elastic mucosa is modified by the pressure difference across the air-liquid interface. As folds form in the mucosa, intraluminal fluid collects in pools in the depressions formed by the folds, and the curvature of the air-liquid interface becomes nonuniform. If the amount of intraluminal fluid is small, < 2% of luminal volume, the pools of intraluminal fluid are small, the air-liquid interface nearly coincides with the surface of the mucosa, and the area of the air-liquid interface remains constant as airway cross-sectional area decreases. In that case, surface energy is independent of airway area, and surface tension has no effect on airway mechanics. If the amount of intraluminal fluid is > 2%, the area of the air-liquid interface decreases as airway cross-sectional area decreases. and surface tension contributes to airway compression. The model predicts that surface tension plus intraluminal fluid can cause an instability in the area-pressure curve of small airways. This instability provides a mechanism for abrupt airway closure and abrupt reopening at a higher opening pressure.

Numerical simulation and stability analysis of solutocapillary effect in ultrathin films

NASA Astrophysics Data System (ADS)

Gordeeva, V. Yu.; Lyushnin, A. V.

2017-04-01

Polar fluids, like water or polydimethylsiloxane, are widely used in technical and medical applications. Capillary effects arising from surface tension gradients can be significant in thin liquid films. The present paper is dedicated to investigation of capillary flow due to a surfactant added to a polar liquid under conditions when intermolecular forces and disjoining pressure play an important role. Evolution equations are formulated for a film profile and the surfactant concentration. Stability analysis shows that the Marangoni effect destabilizes the film, and oscillatory modes appear at slow evaporation rates. We find that the film has four stability modes of at slow evaporation: monotonic stable, monotonic unstable, oscillatory stable, and oscillatory unstable, depending on the wave number of disturbances.

Growth and shrinkage of pluronic micelles by uptake and release of flurbiprofen: variation of pH.

PubMed

Alexander, Shirin; de Vos, Wiebe M; Castle, Thomas C; Cosgrove, Terence; Prescott, Stuart W

2012-04-24

The micellization of Pluronic triblock copolymers (P103, P123, and L43) in the presence of flurbiprofen at different pH was studied by small-angle neutron scattering (SANS), pulsed-field gradient stimulated-echo nuclear magnetic resonance (PFGSE-NMR), and surface tension measurements. Addition of flurbiprofen to the Pluronic at low pH leads to an increase in the fraction of micellization, aggregation number, and the core radius of the micelles. However, changing the pH to above the pKa of flurbiprofen in an ethanol/water mixture (∼6.5) reduces the fraction of micellization and results in a weaker interaction between the drug and micelles due to the increased drug solubility in aqueous solution.

Vapor mediated droplet interactions - models and mechanisms (Part 2)

NASA Astrophysics Data System (ADS)

Benusiglio, Adrien; Cira, Nate; Prakash, Manu

2014-11-01

When deposited on clean glass a two-component binary mixture of propylene glycol and water is energetically inclined to spread, as both pure liquids do. Instead the mixture forms droplets stabilized by evaporation induced surface tension gradients, giving them unique properties such as negligible hysteresis. When two of these special droplets are deposited several radii apart they attract each other. The vapor from one droplet destabilizes the other, resulting in an attraction force which brings both droplets together. We present a flux-based model for droplet stabilization and a model which connects the vapor profile to net force. These simple models capture the static and dynamic experimental trends, and our fundamental understanding of these droplets and their interactions allowed us to build autonomous fluidic machines.

Tethered orbital propellant depot

NASA Technical Reports Server (NTRS)

Fester, D. A.; Rudolph, L. K.; Kiefel, E. R.

1985-01-01

A planned function of the Space Station is to refurbish and refuel an advanced space-based LO2/LH2 orbit transfer vehicle. An alternative to propellant storage at the station is to use a remote facility tied to the station with a log tether. Preliminary design of such a facility is described with emphasis on fluid transfer and storage requirements. Using tether lengths of at least 300 ft, gravity gradient forces will dominate surface tension in such a system. Although gravity given transfer is difficult because of line pressure drops, fluid settling over the tank outlet greatly alleviates acquisition concerns and will facilitate vented tank fills. The major concern with a tethered orbital refueling facility is its considerable operational complexity including transport of the OTV to and from the facility.

Low-gravity fluid flows

NASA Technical Reports Server (NTRS)

Ostrach, S.

1982-01-01

The behavior of fluids in micro-gravity conditions is examined, with particular regard to applications in the growth of single crystals. The effects of gravity on fluid behavior are reviewed, and the advent of Shuttle flights are noted to offer extended time for experimentation and processing in a null-gravity environment, with accelerations resulting solely from maneuvering rockets. Buoyancy driven flows are considered for the cases stable-, unstable-, and mixed-mode convection. Further discussion is presented on g-jitter, surface-tension gradient, thermoacoustic, and phase-change convection. All the flows are present in both gravity and null gravity conditions, although the effects of buoyancy and g-jitter convection usually overshadow the other effects while in a gravity field. Further work is recommended on critical-state and sedimentation processes in microgravity conditions.

Adsorption of surfactant ions and binding of their counterions at an air/water interface.

PubMed

Tagashira, Hiroaki; Takata, Youichi; Hyono, Atsushi; Ohshima, Hiroyuki

2009-01-01

An expression for the surface tension of an aqueous mixed solution of surfactants and electrolyte ions in the presence of the common ions was derived from the Helmholtz free energy of an air/water surface. By applying the equation to experimental data for the surface tension, the adsorption constant of surfactant ions onto the air/water interface, the binding constant of counterions on the surfactants, and the surface potential and surface charge density of the interface were estimated. The adsorption constant and binding constant were dependent on the species of surfactant ion and counterion, respectively. Taking account of the dependence of surface potential and surface charge density on the concentration of electrolyte, it was suggested that the addition of electrolyte to the aqueous surfactant solution brings about the decrease in the surface potential, the increase in the surface density of surfactant ions, and consequently, the decrease in the surface tension. Furthermore, it was found that the configurational entropy plays a predominant role for the surface tension, compared to the electrical work.

A Method to Manipulate Surface Tension of a Liquid Metal via Surface Oxidation and Reduction

PubMed Central

Dickey, Michael D.

2016-01-01

Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where interfacial tension is a dominant force. A variety of methods exist for controlling the interfacial tension of aqueous and organic liquids on this scale; however, these techniques have limited utility for liquid metals due to their large interfacial tension. Liquid metals can form soft, stretchable, and shape-reconfigurable components in electronic and electromagnetic devices. Although it is possible to manipulate these fluids via mechanical methods (e.g., pumping), electrical methods are easier to miniaturize, control, and implement. However, most electrical techniques have their own constraints: electrowetting-on-dielectric requires large (kV) potentials for modest actuation, electrocapillarity can affect relatively small changes in the interfacial tension, and continuous electrowetting is limited to plugs of the liquid metal in capillaries. Here, we present a method for actuating gallium and gallium-based liquid metal alloys via an electrochemical surface reaction. Controlling the electrochemical potential on the surface of the liquid metal in electrolyte rapidly and reversibly changes the interfacial tension by over two orders of magnitude (~500 mN/m to near zero). Furthermore, this method requires only a very modest potential (< 1 V) applied relative to a counter electrode. The resulting change in tension is due primarily to the electrochemical deposition of a surface oxide layer, which acts as a surfactant; removal of the oxide increases the interfacial tension, and vice versa. This technique can be applied in a wide variety of electrolytes and is independent of the substrate on which it rests. PMID:26863045

Effect of Temperature on the Physico-Chemical Properties of a Room Temperature Ionic Liquid (1-Methyl-3-pentylimidazolium Hexafluorophosphate) with Polyethylene Glycol Oligomer

PubMed Central

Wu, Tzi-Yi; Chen, Bor-Kuan; Hao, Lin; Peng, Yu-Chun; Sun, I-Wen

2011-01-01

A systematic study of the effect of composition on the thermo-physical properties of the binary mixtures of 1-methyl-3-pentyl imidazolium hexafluorophosphate [MPI][PF6] with poly(ethylene glycol) (PEG) [Mw = 400] is presented. The excess molar volume, refractive index deviation, viscosity deviation, and surface tension deviation values were calculated from these experimental density, ρ, refractive index, n, viscosity, η, and surface tension, γ, over the whole concentration range, respectively. The excess molar volumes are negative and continue to become increasingly negative with increasing temperature; whereas the viscosity and surface tension deviation are negative and become less negative with increasing temperature. The surface thermodynamic functions, such as surface entropy, enthalpy, as well as standard molar entropy, Parachor, and molar enthalpy of vaporization for pure ionic liquid, have been derived from the temperature dependence of the surface tension values. PMID:21731460

Surface tension and density of Si-Ge melts

NASA Astrophysics Data System (ADS)

Ricci, Enrica; Amore, Stefano; Giuranno, Donatella; Novakovic, Rada; Tuissi, Ausonio; Sobczak, Natalia; Nowak, Rafal; Korpala, Bartłomiej; Bruzda, Grzegorz

2014-06-01

In this work, the surface tension and density of Si-Ge liquid alloys were determined by the pendant drop method. Over the range of measurements, both properties show a linear temperature dependence and a nonlinear concentration dependence. Indeed, the density decreases with increasing silicon content exhibiting positive deviation from ideality, while the surface tension increases and deviates negatively with respect to the ideal solution model. Taking into account the Si-Ge phase diagram, a simple lens type, the surface tension behavior of the Si-Ge liquid alloys was analyzed in the framework of the Quasi-Chemical Approximation for the Regular Solutions model. The new experimental results were compared with a few data available in the literature, obtained by the containerless method.

The Earth: Kinda like a Mai Tai?

NASA Astrophysics Data System (ADS)

Jellinek, M.

2005-12-01

Many problems in the Earth sciences involve fluid flow. Examples include the formation and differentiation of planets, mantle convection, plate tectonics, the generation of planetary magnetic fields, the generation, rise, and chemical differentiation of magmas, crystal nucleation and growth, sedimentation and mechanical erosion at riverbeds, and circulation in the atmosphere and oceans. In each of these situations fluid motions arise as a result of balances among body forces (e.g. effects of gravitational and magnetic fields) and (or) surface forces (e.g. effects of surface tension, shear and pressure gradients). Processes in which such force balance arise naturally are examples of ``Natural convection''. Familiar examples of natural convection include thermally-driven motions above a radiator in a cold room or inside a pot of pasta sauce warmed on a stove. Analog fluid mechanics experiments are a useful and fun way to isolate and learn about the mechanics of such processes. Experiments need not be done in a fluid dynamics laboratory. Indeed some of the most interesting occur in your favorite cocktails. In this demonstration I first use household materials from the kitchen and from the liquor cabinet to isolate and build understanding of individual examples of convection driven by thermal, compositional and surface tension effects over a range of conditions. Next, using more complicated experiments with actual and analog bar drinks I will present and analyze a number of coupled convective processes and also address the role of the rheology of the working fluids. In particular, the structure, transport and mixing properties of the motions are investigated.

Reactive-brittle dynamics in peridotite alteration

NASA Astrophysics Data System (ADS)

Evans, O.; Spiegelman, M. W.; Kelemen, P. B.

2017-12-01

The interactions between reactive fluids and brittle solids are critical in Earth dynamics. Implications of such processes are wide-ranging: from earthquake physics to geologic carbon sequestration and the cycling of fluids and volatiles through subduction zones. Peridotite alteration is a common feature in many of these processes, which - despite its obvious importance - is relatively poorly understood from a geodynamical perspective. In particular, alteration reactions are thought to be self-limiting in nature, contradicting observations of rocks that have undergone 100% hydration/carbonation. One potential explanation of this observation is the mechanism of "reaction-driven cracking": that volume changes associated with these reactions are large enough to fracture the surrounding rock, leading to a positive feedback where new reactive surfaces are exposed and fluid pathways are created. The purpose of this study is to investigate the relative roles of reaction, elastic stresses and surface tension in alteration reactions. In this regard we derive a system of equations describing reactive fluid flow in an elastically deformable porous media, and explore them via a combination of analytic and numerical solutions. Using this model we show that the final stress state of a dry peridotite that has undergone reaction depends strongly on the rates of reaction versus fluid transport: significant fluid flow driven by pressure and/or surface tension gradients implies higher fractions of serpentinization, leaving behind a highly stressed residuum of partially reacted material. Using a model set-up that mimics a cylindrical triaxial apparatus we predict that the resulting stresses would lead to tensile failure and the generation of radially oriented cracks.

Influence of alkane and perfluorocarbon vapors on adsorbed surface layers and spread insoluble monolayers of surfactants, proteins and lipids.

PubMed

Fainerman, V B; Aksenenko, E V; Miller, R

2017-06-01

The influence of hexane vapor in the air atmosphere on the surface tension of water and solutions of C 10 EO 8 , C n TAB and proteins are presented. For dry air, a fast and strong decrease of surface tension of water was observed. In humid air, the process is slower and the surface tension higher. There are differences between the results obtained by the maximum bubble pressure, pendant drop and emerging bubble methods, which are discussed in terms of depletion and initial surface load. The surface tension of aqueous solutions of β-сasein (BCS), β-lactoglobulin (BLG) and human serum albumin (HSA) at the interfaces with air and air-saturated hexane vapor were measured. The results indicate that the equilibrium surface tension in the hexane vapor atmosphere is considerably lower (at 13-20mN/m) as compared to the values at the interface with pure air. A reorientation model is proposed assuming several states of adsorbed molecules with different molar area values. The newly developed theoretical model is used to describe the effect of alkane vapor in the gas phase on the surface tension. This model assumes that the first layer is composed of surfactant (or protein) molecules mixed with alkane, and the second layer is formed by alkane molecules only. The processing of the experimental data for the equilibrium surface tension for the C 10 EO 8 and BCS solutions results in a perfect agreement between the observed and calculated values. The co-adsorption mechanism of dipalmitoyl phosphatidyl choline (DPPC) and the fluorocarbon molecules leads to remarkable differences in the surface pressure term of cohesion Π coh . This in turn leads to a very efficient fluidization of the monolayer. It was found that the adsorption equilibrium constant for dioctanoyl phosphatidyl choline is increased in the presence of perfluorohexane, and the intermolecular interaction of the components is strong. Copyright © 2015 Elsevier B.V. All rights reserved.

Effect of atmosphere on the surface tension and viscosity of molten LiNbO 3 measured using the surface laser-light scattering method

NASA Astrophysics Data System (ADS)

Nagasaka, Yuji; Kobayashi, Yusuke

2007-09-01

The surface tension and the viscosity of molten LiNbO 3 (LN) having the congruent composition have been measured simultaneously in a temperature range from 1537 to 1756 K under argon gas and dry-air atmospheres. The present measurement technique involves surface laser-light scattering (SLLS) that detects nanometer-order-amplitude surface waves usually regarded as ripplons excited by thermal fluctuations. This technique's non-invasive nature allows it to avoid the experimental difficulties of conventional techniques resulting from the insertion of an actuator in the melt. The results of surface tension measurement obtained under a dry-air atmosphere are about 5% smaller than those obtained under an argon atmosphere near the melting temperature, and the temperature dependence of the surface tension under a dry-air atmosphere is twice that under an argon atmosphere. The uncertainty of surface tension measurement is estimated to be ±2.6% under argon and ±1.9% under dry air. The temperature dependence of viscosity can be well correlated with the results of Arrhenius-type equations without any anomalous behavior near the melting point. The viscosities obtained under a dry-air atmosphere were slightly smaller than those obtained under an argon atmosphere. The uncertainty of viscosity measurement is estimated to be ±11.1% for argon and ±14.3% for dry air. Moreover, we observed the real-time dynamic behavior of the surface tension and the viscosity of molten LN in response to argon and dry-air atmospheres.

The effect of oxygen tension on human articular chondrocyte matrix synthesis: Integration of experimental and computational approaches

PubMed Central

Li, S; Oreffo, ROC; Sengers, BG; Tare, RS

2014-01-01

Significant oxygen gradients occur within tissue engineered cartilaginous constructs. Although oxygen tension is an important limiting parameter in the development of new cartilage matrix, its precise role in matrix formation by chondrocytes remains controversial, primarily due to discrepancies in the experimental setup applied in different studies. In this study, the specific effects of oxygen tension on the synthesis of cartilaginous matrix by human articular chondrocytes were studied using a combined experimental-computational approach in a “scaffold-free” 3D pellet culture model. Key parameters including cellular oxygen uptake rate were determined experimentally and used in conjunction with a mathematical model to estimate oxygen tension profiles in 21-day cartilaginous pellets. A threshold oxygen tension (pO2 ≈ 8% atmospheric pressure) for human articular chondrocytes was estimated from these inferred oxygen profiles and histological analysis of pellet sections. Human articular chondrocytes that experienced oxygen tension below this threshold demonstrated enhanced proteoglycan deposition. Conversely, oxygen tension higher than the threshold favored collagen synthesis. This study has demonstrated a close relationship between oxygen tension and matrix synthesis by human articular chondrocytes in a “scaffold-free” 3D pellet culture model, providing valuable insight into the understanding and optimization of cartilage bioengineering approaches. Biotechnol. Bioeng. 2014;111: 1876–1885. PMID:24668194

Intravital phosphorescence lifetime imaging of the renal cortex accurately measures renal hypoxia.

PubMed

Hirakawa, Yosuke; Mizukami, Kiichi; Yoshihara, Toshitada; Takahashi, Ippei; Khulan, Purevsuren; Honda, Tomoko; Mimura, Imari; Tanaka, Tetsuhiro; Tobita, Seiji; Nangaku, Masaomi

2018-06-01

Renal tubulointerstitial hypoxia is recognized as a final common pathway of chronic kidney disease and is considered a promising drug target. However, hypoxia in the tubules is not well examined because of limited detection methods. Here, we devised a method to visualize renal tubular oxygen tension with spatial resolution at a cellular level using the cell-penetrating phosphorescent probe, BTPDM1 (an iridium-based cationic lipophilic dye), and confocal phosphorescence lifetime imaging microscopy to precisely assess renal hypoxia. Imaging with BTPDM1 revealed an oxygen gradient between S1 and S2 segments in mouse kidney. We also demonstrated that our microscopy system can detect subtle changes of hypoxemia and reoxygenation, and the acquired phosphorescence lifetime can be converted to partial pressure of oxygen. This new method allows, for the first time, visualization of intravital oxygen gradients at the renal surface with high spatial resolution. Thus, the confocal phosphorescence lifetime imaging microscopy platform, combined with BTPDM1, will promote an accurate understanding of tissue hypoxia, including renal hypoxia. Copyright © 2018 International Society of Nephrology. Published by Elsevier Inc. All rights reserved.

Surface tension driven flow in glass melts and model fluids

NASA Technical Reports Server (NTRS)

Mcneil, T. J.; Cole, R.; Subramanian, R. S.

1982-01-01

Surface tension driven flow has been investigated analytically and experimentally using an apparatus where a free column of molten glass or model fluids was supported at its top and bottom faces by solid surfaces. The glass used in the experiments was sodium diborate, and the model fluids were silicone oils. In both the model fluid and glass melt experiments, conclusive evidence was obtained to prove that the observed flow was driven primarily by surface tension forces. The experimental observations are in qualitative agreement with predictions from the theoretical model.

Working Fluids for Increasing Capacities of Heat Pipes

NASA Technical Reports Server (NTRS)

Chao, David F.; Zhang, Nengli

2004-01-01

A theoretical and experimental investigation has shown that the capacities of heat pipes can be increased through suitable reformulation of their working fluids. The surface tensions of all of the working fluids heretofore used in heat pipes decrease with temperature. As explained in more detail below, the limits on the performance of a heat pipe are associated with the decrease in the surface tension of the working fluid with temperature, and so one can enhance performance by reformulating the working fluid so that its surface tension increases with temperature. This improvement is applicable to almost any kind of heat pipe in almost any environment. The heat-transfer capacity of a heat pipe in its normal operating-temperature range is subject to a capillary limit and a boiling limit. Both of these limits are associated with the temperature dependence of surface tension of the working fluid. In the case of a traditional working fluid, the decrease in surface tension with temperature causes a body of the liquid phase of the working fluid to move toward a region of lower temperature, thus preventing the desired spreading of the liquid in the heated portion of the heat pipe. As a result, the available capillary-pressure pumping head decreases as the temperature of the evaporator end of the heat pipe increases, and operation becomes unstable. Water has widely been used as a working fluid in heat pipes. Because the surface tension of water decreases with increasing temperature, the heat loads and other aspects of performance of heat pipes that contain water are limited. Dilute aqueous solutions of long-chain alcohols have shown promise as substitutes for water that can offer improved performance, because these solutions exhibit unusual surface-tension characteristics: Experiments have shown that in the cases of an aqueous solution of an alcohol, the molecules of which contain chains of more than four carbon atoms, the surface tension increases with temperature when the temperature exceeds a certain value. There are also other liquids that have surface tensions that increase with temperature and could be used as working fluids in heat pipes. For example, as a substitute for ammonia, which is the working fluid in some heat pipes, one could use a solution of ammonia and an ionic surfactant.

Force-activatable coating enables high-resolution cellular force imaging directly on regular cell culture surfaces.

PubMed

Sarkar, Anwesha; Zhao, Yuanchang; Wang, Yongliang; Wang, Xuefeng

2018-06-25

Integrin-transmitted cellular forces are crucial mechanical signals regulating a vast range of cell functions. Although various methods have been developed to visualize and quantify cellular forces at the cell-matrix interface, a method with high performance and low technical barrier is still in demand. Here we developed a force-activatable coating (FAC), which can be simply coated on regular cell culture apparatus' surfaces by physical adsorption, and turn these surfaces to force reporting platforms that enable cellular force mapping directly by fluorescence imaging. The FAC molecule consists of an adhesive domain for surface coating and a force-reporting domain which can be activated to fluoresce by integrin molecular tension. The tension threshold required for FAC activation is tunable in 10-60 piconewton (pN), allowing the selective imaging of cellular force contributed by integrin tension at different force levels. We tested the performance of two FACs with tension thresholds of 12 and 54 pN (nominal values), respectively, on both glass and polystyrene surfaces. Cellular forces were successfully mapped by fluorescence imaging on all the surfaces. FAC-coated surfaces also enable co-imaging of cellular forces and cell structures in both live cells and immunostained cells, therefore opening a new avenue for the study of the interplay of force and structure. We demonstrated the co-imaging of integrin tension and talin clustering in live cells, and concluded that talin clustering always occurs before the generation of integrin tension above 54 pN, reinforcing the notion that talin is an important adaptor protein for integrin tension transmission. Overall, FAC provides a highly convenient approach that is accessible to general biological laboratories for the study of cellular forces with high sensitivity and resolution, thus holding the potential to greatly boost the research of cell mechanobiology.

Practical significance and calculation of surface tension of glass, enamels and glazes

NASA Technical Reports Server (NTRS)

Dietzel, A.

1987-01-01

Surface tension is important in the formation of streaks in the whole procedure of enameling and glazing., in the action of TiO2 as opacifier, in the addition of borax to enamels, or metals to glasses, and in the corrosion of refractories by molten charges. By the use of known methods for measuring surface tension additive constants are found which give correct results within 1% with no discrepancy due to B2O3.

Prediction of Phase Separation of Immiscible Ga-Tl Alloys

NASA Astrophysics Data System (ADS)

Kim, Yunkyum; Kim, Han Gyeol; Kang, Youn-Bae; Kaptay, George; Lee, Joonho

2017-06-01

Phase separation temperature of Ga-Tl liquid alloys was investigated using the constrained drop method. With this method, density and surface tension were investigated together. Despite strong repulsive interactions, molar volume showed ideal mixing behavior, whereas surface tension of the alloy was close to that of pure Tl due to preferential adsorption of Tl. Phase separation temperatures and surface tension values obtained with this method were close to the theoretically calculated values using three different thermodynamic models.

Modeling the surface tension of complex, reactive organic-inorganic mixtures

NASA Astrophysics Data System (ADS)

Schwier, A. N.; Viglione, G. A.; Li, Z.; McNeill, V. Faye

2013-11-01

Atmospheric aerosols can contain thousands of organic compounds which impact aerosol surface tension, affecting aerosol properties such as heterogeneous reactivity, ice nucleation, and cloud droplet formation. We present new experimental data for the surface tension of complex, reactive organic-inorganic aqueous mixtures mimicking tropospheric aerosols. Each solution contained 2-6 organic compounds, including methylglyoxal, glyoxal, formaldehyde, acetaldehyde, oxalic acid, succinic acid, leucine, alanine, glycine, and serine, with and without ammonium sulfate. We test two semi-empirical surface tension models and find that most reactive, complex, aqueous organic mixtures which do not contain salt are well described by a weighted Szyszkowski-Langmuir (S-L) model which was first presented by Henning et al. (2005). Two approaches for modeling the effects of salt were tested: (1) the Tuckermann approach (an extension of the Henning model with an additional explicit salt term), and (2) a new implicit method proposed here which employs experimental surface tension data obtained for each organic species in the presence of salt used with the Henning model. We recommend the use of method (2) for surface tension modeling of aerosol systems because the Henning model (using data obtained from organic-inorganic systems) and Tuckermann approach provide similar modeling results and goodness-of-fit (χ2) values, yet the Henning model is a simpler and more physical approach to modeling the effects of salt, requiring less empirically determined parameters.

Dynamic surface tension measurement for the screening of biosurfactants produced by Lactobacillus plantarum subsp. plantarum PTCC 1896.

PubMed

Bakhshi, Nafiseh; Soleimanian-Zad, Sabihe; Sheikh-Zeinoddin, Mahmoud

2017-06-01

Currently, screening of microbial biosurfactants (BSs) is based on their equilibrium surface tension values obtained using static surface tension measurement. However, a good surfactant should not only have a low equilibrium surface tension, but its dynamic surface tension (DST) should also decrease rapidly with time. In this study, screening of BSs produced by Lactobacillus plantarum subsp. plantarum PTCC 1896 (probiotic) was performed based on their DST values measured by Wilhelmy plate tensiometry. The relationship between DST and structural and functional properties (anti-adhesive activity) of the BSs was investigated. The results showed that the changes in the yield, productivity and structure of the BSs were growth medium and incubation time dependent (p<0.05). Structurally different BSs produced exhibited identical equilibrium surface tension values. However, differences among the structure/yield of the BSs were observed through the measurement of their DST. The considerable dependence of DST on the concentration and composition of the BS proteins was observed (p<0.05). Moreover, the anti-adhesive activity of the BS was found to be positively correlated with its DST. The results suggest that the DST measurement could serve as an efficient method for the clever screening of BSs producer/production condition, and consequently, for the investigation of probiotic features of bacteria, since the anti-adhesive activity is an important criterion of probiotics. Copyright © 2017 Elsevier Inc. All rights reserved.

The dynamics of nucleation and growth of a particle in the ternary alloy melt with anisotropic surface tension.

PubMed

Chen, Ming-Wen; Li, Lin-Yan; Guo, Hui-Min

2017-08-28

The dynamics of nucleation and growth of a particle affected by anisotropic surface tension in the ternary alloy melt is studied. The uniformly valid asymptotic solution for temperature field, concentration field, and interface evolution of nucleation and particle growth is obtained by means of the multiple variable expansion method. The asymptotic solution reveals the critical radius of nucleation in the ternary alloy melt and an inward melting mechanism of the particle induced by the anisotropic effect of surface tension. The critical radius of nucleation is dependent on isotropic surface tension, temperature undercooling, and constitutional undercooling in the ternary alloy melt, and the solute diffusion melt decreases the critical radius of nucleation. Immediately after a nucleus forms in the initial stage of solidification, the anisotropic effect of surface tension makes some parts of its interface grow inward while some parts grow outward. Until the inward melting attains a certain distance (which is defined as "the melting depth"), these parts of interface start to grow outward with other parts. The interface of the particle evolves into an ear-like deformation, whose inner diameter may be less than two times the critical radius of nucleation within a short time in the initial stage of solidification. The solute diffusion in the ternary alloy melt decreases the effect of anisotropic surface tension on the interface deformation.

In situ measurement of contact angles and surface tensions of interfacial nanobubbles in ethanol aqueous solutions.

PubMed

Zhao, Binyu; Wang, Xingya; Wang, Shuo; Tai, Renzhong; Zhang, Lijuan; Hu, Jun

2016-04-14

The astonishing long lifetime and large contact angles of interfacial nanobubbles are still in hot debate despite numerous experimental and theoretical studies. One hypothesis to reconcile the two abnormalities of interfacial nanobubbles is that they have low surface tensions. However, few studies have been reported to measure the surface tensions of nanobubbles due to the lack of effective measurements. Herein, we investigate the in situ contact angles and surface tensions of individual interfacial nanobubbles immersed in different ethanol aqueous solutions using quantitative nanomechanical atomic force microscopy (AFM). The results showed that the contact angles of nanobubbles in the studied ethanol solutions were also much larger than the corresponding macroscopic counterparts on the same substrate, and they decreased with increasing ethanol concentrations. More significantly, the surface tensions calculated were much lower than those of the gas-liquid interfaces of the solutions at the macroscopic scale but have similar tendencies with increasing ethanol concentrations. Those results are expected to be helpful in further understanding the stability of interfacial nanobubbles in complex solutions.

Temperature dependence of surface tension of molten iron under reducing gas atmosphere

NASA Astrophysics Data System (ADS)

Ozawa, S.; Takahashi, S.; Fukuyama, H.; Watanabe, M.

2011-12-01

Surface tension of molten iron was measured under Ar-He-5vol.%H2 gas by oscillating droplet method using electromagnetic levitation furnace in consideration of the temperature dependence of oxygen partial pressure, Po2, of the gas. For comparison, the measurement was carried under Ar-He atmosphere to fix the Po2 of the inlet gas at 10-2Pa. The surface tension was successfully measured over a wide temperature range of about 780K including undercooling condition. When Po2 is fixed at 10-2 Pa, the surface tension increased and then decreased with increasing temperature like a boomerang shape. When the measurement was carried out under the H2-containing gas atmosphere, the temperature dependence of the surface tension shows unique kink at around 1810K instead of liner relationship due to competition between the temperature dependence of the Po2 and that of the equilibrium constant of oxygen adsorption reaction. The relationship between the calculated lnKad with respect to inverse temperature using Szyszkowski model was different between the atmospheric gases.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Allen, C.A.W.; Watts, K.C.

Engine results using biofuels have varied considerably in the reported literature. This article addresses two potential sources of this variation, atomization differences and impurities due to lack of quality control during production. Atomization is the first process encountered during the combustion of fuels in a compression ignition engine and is largely determined by the fuel's viscosity and surface tension. Previous work using five experimentally produced methyl ester biodiesel fuels showed that the viscosity and surface tension could be predicted from their fatty acid ester composition, and the atomization characteristics in turn could be predicted from their viscosity and surface tension.more » This article utilizes the results of that work to give a quantitative comparison of the atomization characteristics of fifteen biodiesel fuel types using the fuel's viscosity and surface tension, predicted directly from the fatty acid composition of the fuels. Except for coconut and rapeseed biodiesel fuels, all of the rest of the 15 biodiesel fuels had similar atomization characteristics. Since the most likely contaminant in the fuel from the processing was residual glycerides, their effect on viscosity and surface tension was studied experimentally and their effect on the atomization characteristics was computed.« less

Reducing surface tension in endodontic chelator solutions has no effect on their ability to remove calcium from instrumented root canals.

PubMed

Zehnder, Matthias; Schicht, Olivier; Sener, Beatrice; Schmidlin, Patrick

2005-08-01

The aim of this study was to evaluate the effect of reducing surface tension in endodontic chelator solutions on their ability to remove calcium from instrumented root canals. Aqueous solutions containing 15.5% EDTA, 10% citric acid, or 18% 1- hydroxyethylidene-1, 1-bisphosphonate (HEBP) were prepared with and without 1% (wt/wt) polysorbate (Tween) 80 and 9% propylene glycol. Surface tension in these solutions was measured using the Wilhelmy method. Sixty-four extracted, single-rooted human teeth of similar length were instrumented and irrigated with a 1% sodium hypochlorite solution and then randomly assigned (n = 8 per group) to receive a final one-minute rinse with 5 ml of test solutions, water, or the pure aqueous Tween/propylene glycol solution. Calcium concentration in eluates was measured using atomic absorption spectrometry. Incorporation of wetting agents resulted in a reduction of surface tension values by approximately 50% in all tested solutions. However, none of the solutions with reduced surface tension chelated more calcium from canals than their pure counterparts (p > 0.05).

Interfacial Tension and Surface Pressure of High Density Lipoprotein, Low Density Lipoprotein, and Related Lipid Droplets

PubMed Central

Ollila, O. H. Samuli; Lamberg, Antti; Lehtivaara, Maria; Koivuniemi, Artturi; Vattulainen, Ilpo

2012-01-01

Lipid droplets play a central role in energy storage and metabolism on a cellular scale. Their core is comprised of hydrophobic lipids covered by a surface region consisting of amphiphilic lipids and proteins. For example, high and low density lipoproteins (HDL and LDL, respectively) are essentially lipid droplets surrounded by specific proteins, their main function being to transport cholesterol. Interfacial tension and surface pressure of these particles are of great interest because they are related to the shape and the stability of the droplets and to protein adsorption at the interface. Here we use coarse-grained molecular-dynamics simulations to consider a number of related issues by calculating the interfacial tension in protein-free lipid droplets, and in HDL and LDL particles mimicking physiological conditions. First, our results suggest that the curvature dependence of interfacial tension becomes significant for particles with a radius of ∼5 nm, when the area per molecule in the surface region is <1.4 nm2. Further, interfacial tensions in the used HDL and LDL models are essentially unaffected by single apo-proteins at the surface. Finally, interfacial tensions of lipoproteins are higher than in thermodynamically stable droplets, suggesting that HDL and LDL are kinetically trapped into a metastable state. PMID:22995496

Modeling of multiple equilibria in the self-aggregation of di-n-decyldimethylammonium chloride/octaethylene glycol monododecyl ether/cyclodextrin ternary systems.

PubMed

Leclercq, Loïc; Lubart, Quentin; Aubry, Jean-Marie; Nardello-Rataj, Véronique

2013-05-28

The surface tension equations of binary surfactant mixtures (di-n-decyldimethylammonium chloride and octaethylene glycol monododecyl ether) are established by combining the Szyszkowski equation of surfactant solutions, the ideal or nonideal mixing theory, and the phase separation model. For surfactant mixtures, the surface tension at the air-water interface is calculated using nonideal theory due to synergism between the two adsorbed surfactant types. The incorporation of cyclodextrin complexation model to the surface tension equations gives a robust model for the description of the surface tension isotherms of binary, ternary, and more complex systems involving numerous inclusion complexes. The surface tension data obtained experimentally shows excellent agreement with the theoretical model below and above the formation of micelles. The strong synergistic effect observed between the two surfactants is disrupted by the presence of CDs, leading to ideal behavior of ternary systems. Indeed, depending on the nature of the cyclodextrin (i.e., α, β, or γ), which allows a tuning of the cavity size, the binding constants with the surfactants are modified as well as the surface properties due to strong modification of equilibria involved in the ternary mixture.

Liquid gallium-lead mixture phase diagram, surface tension near the critical mixing point, and prewetting transition.

PubMed

Osman, S M; Grosdidier, B; Ali, I; Abdellah, A Ben

2013-06-01

Quite recently, we reported a semianalytical equation of state (EOS) for the Ga-Pb alloy [Phys. Rev. B 78, 024205 (2008)], which was based on the first-order perturbation theory of fluid mixtures, within the simplified random phase approximation, in conjunction with the Grosdidier et al. model pair potentials for Ga-Ga and Pb-Pb with a suitable nonadditive pair potential between Ga-Pb unlike pairs. In the present work, we employ the present EOS to calculate the Ga-Pb phase diagram along the immiscibility gap region. The accuracy of the EOS is tested by consulting the empirical binodal curve. A statistical-mechanical-based theory for the surface tension is employed to obtain an analytical expression for the alloy surface tension. We calculated the surface tension along the bimodal curve and at extreme conditions of temperatures and pressures. The surface tension exhibits reasonably well the prewetting transition of Pb atoms at the surface of the Ga-rich liquid alloy and could qualitatively explain the prewetting phenomena occurring in the Ga-rich side of the phase diagram. The predicted prewetting line and wetting temperature qualitatively agree with the empirical measurements.

Effects of the kinematic viscosity and surface tension on the bubble take-off period in a catalase-hydrogen peroxide system.

PubMed

Sasaki, Satoshi; Iida, Yoshinori

2009-06-01

The effect of kinematic viscosity and surface tension of the solution was investigated by adding catalase, glucose oxidase, or glucose on the bubble movement in a catalase-hydrogen peroxide system. The kinematic viscosity was measured using a Cannon-Fenske kinematic viscometer. The surface tension of the solution was measured by the Wilhelmy method using a self-made apparatus. The effects of the hole diameter/cell wall thickness, catalase concentration, glucose concentration, and glucose oxidase concentration on the kinematic viscosity, surface tension, and bubble take-off period were investigated. With our system, the effects of the changes in the solution materiality on the bubble take-off period were proven to be very small in comparison to the change in the oxygen-producing rate.

Unifying models of dialect spread and extinction using surface tension dynamics

PubMed Central

2018-01-01

We provide a unified mathematical explanation of two classical forms of spatial linguistic spread. The wave model describes the radiation of linguistic change outwards from a central focus. Changes can also jump between population centres in a process known as hierarchical diffusion. It has recently been proposed that the spatial evolution of dialects can be understood using surface tension at linguistic boundaries. Here we show that the inclusion of long-range interactions in the surface tension model generates both wave-like spread, and hierarchical diffusion, and that it is surface tension that is the dominant effect in deciding the stable distribution of dialect patterns. We generalize the model to allow population mixing which can induce shrinkage of linguistic domains, or destroy dialect regions from within. PMID:29410847

Surface tension models for a multi-material ALE code with AMR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Wangyi; Koniges, Alice; Gott, Kevin

A number of surface tension models have been implemented in a 3D multi-physics multi-material code, ALE–AMR, which combines Arbitrary Lagrangian Eulerian (ALE) hydrodynamics with Adaptive Mesh Refinement (AMR). ALE–AMR is unique in its ability to model hot radiating plasmas, cold fragmenting solids, and most recently, the deformation of molten material. The surface tension models implemented include a diffuse interface approach with special numerical techniques to remove parasitic flow and a height function approach in conjunction with a volume-fraction interface reconstruction package. These surface tension models are benchmarked with a variety of test problems. In conclusion, based on the results, themore » height function approach using volume fractions was chosen to simulate droplet dynamics associated with extreme ultraviolet (EUV) lithography.« less

Surface tension models for a multi-material ALE code with AMR

DOE PAGES

Liu, Wangyi; Koniges, Alice; Gott, Kevin; ...

2017-06-01

A number of surface tension models have been implemented in a 3D multi-physics multi-material code, ALE–AMR, which combines Arbitrary Lagrangian Eulerian (ALE) hydrodynamics with Adaptive Mesh Refinement (AMR). ALE–AMR is unique in its ability to model hot radiating plasmas, cold fragmenting solids, and most recently, the deformation of molten material. The surface tension models implemented include a diffuse interface approach with special numerical techniques to remove parasitic flow and a height function approach in conjunction with a volume-fraction interface reconstruction package. These surface tension models are benchmarked with a variety of test problems. In conclusion, based on the results, themore » height function approach using volume fractions was chosen to simulate droplet dynamics associated with extreme ultraviolet (EUV) lithography.« less

The effect of surface tension on steadily translating bubbles in an unbounded Hele-Shaw cell

PubMed Central

2017-01-01

New numerical solutions to the so-called selection problem for one and two steadily translating bubbles in an unbounded Hele-Shaw cell are presented. Our approach relies on conformal mapping which, for the two-bubble problem, involves the Schottky-Klein prime function associated with an annulus. We show that a countably infinite number of solutions exist for each fixed value of dimensionless surface tension, with the bubble shapes becoming more exotic as the solution branch number increases. Our numerical results suggest that a single solution is selected in the limit that surface tension vanishes, with the scaling between the bubble velocity and surface tension being different to the well-studied problems for a bubble or a finger propagating in a channel geometry. PMID:28588410

Thermocapillary migration of liquid droplets in a temperature gradient in a density matched system

NASA Technical Reports Server (NTRS)

Rashidnia, N.; Balasubramaniam, R.

1991-01-01

An experimental investigation of thermocapillary flow in droplets of a vegetable oil (partially hydrogenated soybean oil) immersed in silicone oil was conducted in a test cell with a heated top wall and a cooled bottom wall. The liquids are nearly immiscible and have equal densities at a temperature below the room temperature, thus providing a simulation of low-gravity conditions by reducing the buoyancy forces. The interfacial tension between the two oils was measured in the temperature range 20 to 50 C using a capillary tube and (d sigma)/(d T) was determined to be negative. Droplets ranging in sizes from 3 mm to 1 cm diameter were injected into the silicone oil. The vertical temperature profile in the bulk liquid (silicone oil) produces temperature variations along the interface which induce variations in the interfacial tension. The flow inside the droplet driven by the resulting interfacial shear stresses was observed using a laser light-sheet flow visualization technique. The flow direction is consistent with the sign of (d sigma)/(d T). The observed maximum surface velocities are compared to the theoretical predictions of Young et al. (1959).

Thermocapillary migration of liquid droplets in a temperature gradient in a density matched system

NASA Technical Reports Server (NTRS)

Rashidnia, N.; Balasubramaniam, R.

1989-01-01

An experimental investigation of thermocapillary flow in droplets of a vegetable oil (partially hydrogenated soybean oil) immersed in silicone oil was conducted in a test cell with a heated top wall and a cooled bottom wall. The liquids are nearly immiscible and have equal densities at a temperature below the room temperature, thus providing a simulation of low-gravity conditions by reducing the buoyancy forces. The interfacial tension between the two oils was measured in the temperature range 20 to 50 C using a capillary tube and (d sigma)/(d T) was determined to be negative. Droplets ranging in sizes from 3 mm to 1 cm diameter were injected into the silicone oil. The vertical temperature profile in the bulk liquid (silicone oil) produces temperature variations along the interface which induce variations in the interfacial tension. The flow inside the droplet driven by the resulting interfacial shear stresses was observed using a laser light-sheet flow visualization technique. The flow direction is consistent with the sign of (d sigma)/(d T). The observed maximum surface velocities are compared to the theoretical predictions of Young et al. (1959).

Computer modelling of the surface tension of the gas-liquid and liquid-liquid interface.

PubMed

Ghoufi, Aziz; Malfreyt, Patrice; Tildesley, Dominic J

2016-03-07

This review presents the state of the art in molecular simulations of interfacial systems and of the calculation of the surface tension from the underlying intermolecular potential. We provide a short account of different methodological factors (size-effects, truncation procedures, long-range corrections and potential models) that can affect the results of the simulations. Accurate calculations are presented for the calculation of the surface tension as a function of the temperature, pressure and composition by considering the planar gas-liquid interface of a range of molecular fluids. In particular, we consider the challenging problems of reproducing the interfacial tension of salt solutions as a function of the salt molality; the simulations of spherical interfaces including the calculation of the sign and size of the Tolman length for a spherical droplet; the use of coarse-grained models in the calculation of the interfacial tension of liquid-liquid surfaces and the mesoscopic simulations of oil-water-surfactant interfacial systems.

Surface tension propellant control for Viking 75 Orbiter

NASA Technical Reports Server (NTRS)

Dowdy, M. W.; Hise, R. E.; Peterson, R. G.; Debrock, S. C.

1976-01-01

The paper describes the selection, development and qualification of the surface tension system and includes results of low-g drop tower tests of scale models, 1-g simulation tests of low-g large ullage settling and liquid withdrawal, structural qualification tests, and propellant surface tension/contact angle studies. Subscale testing and analyses were used to evaluate the ability of the system to maintain or recover the desired propellant orientation following possible disturbances during the Viking mission. This effort included drop tower tests to demonstrate that valid wick paths exist for moving any displaced propellant back over the tank outlet. Variations in surface tension resulting from aging, temperature, and lubricant contamination were studied and the effects of surface finish, referee fluid exposure, aging, and lubricant contamination on contact angle were assessed. Results of movies of typical subscale drop tower tests and full scale slosh tests are discussed.

The Thin Oil Film Equation

NASA Technical Reports Server (NTRS)

Brown, James L.; Naughton, Jonathan W.

1999-01-01

A thin film of oil on a surface responds primarily to the wall shear stress generated on that surface by a three-dimensional flow. The oil film is also subject to wall pressure gradients, surface tension effects and gravity. The partial differential equation governing the oil film flow is shown to be related to Burgers' equation. Analytical and numerical methods for solving the thin oil film equation are presented. A direct numerical solver is developed where the wall shear stress variation on the surface is known and which solves for the oil film thickness spatial and time variation on the surface. An inverse numerical solver is also developed where the oil film thickness spatial variation over the surface at two discrete times is known and which solves for the wall shear stress variation over the test surface. A One-Time-Level inverse solver is also demonstrated. The inverse numerical solver provides a mathematically rigorous basis for an improved form of a wall shear stress instrument suitable for application to complex three-dimensional flows. To demonstrate the complexity of flows for which these oil film methods are now suitable, extensive examination is accomplished for these analytical and numerical methods as applied to a thin oil film in the vicinity of a three-dimensional saddle of separation.

Drainage and impregnation capillary pressure curves calculated by the X-ray CT model of Berea sandstone using Lattice Boltzmann's method

NASA Astrophysics Data System (ADS)

Zakirov, T.; Galeev, A.; Khramchenkov, M.

2018-05-01

The study deals with the features of the technique for simulating the capillary pressure curves of porous media on their X-ray microtomographic images. The results of a computational experiment on the immiscible displacement of an incompressible fluid by another in the pore space represented by a digital image of the Berea sandstone are presented. For the mathematical description of two-phase fluid flow we use Lattice Boltzmann Equation (LBM), and phenomena at the fluids interface are described by the color-gradient model. Compared with laboratory studies, the evaluation of capillary pressure based on the results of a computational filtration experiment is a non-destructive method and has a number of advantages: the absence of labor for preparation of fluids and core; the possibility of modeling on the scale of very small core fragments (several mm), which is difficult to realize under experimental conditions; three-dimensional visualization of the dynamics of filling the pore space with a displacing fluid during drainage and impregnation; the possibility of carrying out multivariate calculations for specified parameters of multiphase flow (density and viscosity of fluids, surface tension, wetting contact angle). A satisfactory agreement of the capillary pressure curves during drainage with experimental results was obtained. It is revealed that with the increase in the volume of the digital image, the relative deviation of the calculated and laboratory data decreases and for cubic digital cores larger than 1 mm it does not exceed 5%. The behavior of the non-wetting fluid flow during drainage is illustrated. It is shown that flow regimes under which computational and laboratory experiments are performed the distribution of the injected phase in directions different from the gradient of the hydrodynamic drop, including the opposite ones, is characteristic. Experimentally confirmed regularities are obtained when carrying out calculations for drainage and imbibition at different values of interfacial tension. There is a close coincidence in the average diameters of permeable channels, estimated by capillary curves for different interfacial tension and pore network model. The differences do not exceed 15%.

Surface finishing. [for aircraft wings

NASA Technical Reports Server (NTRS)

Kinzler, J. A.; Heffernan, J. T.; Fehrenkamp, L. G.; Lee, W. S. (Inventor)

1977-01-01

A surface of an article adapted for relative motion with a fluid environment is finished by coating the surface with a fluid adhesive. The adhesive is covered with a sheet of flexible film material under tension, and the adhesive is set while maintaining tension on the film material.

The influence of surface-active agents in gas mixture on the intensity of jet condensation

NASA Astrophysics Data System (ADS)

Yezhov, YV; Okhotin, VS

2017-11-01

The report presents: the methodology of calculation of contact condensation of steam from the steam-gas mixture into the stream of water, taking into account: the mass flow of steam through the boundary phase, particularly the change in turbulent transport properties near the interface and their connection to the interface perturbations due to the surface tension of the mixture; the method of calculation of the surface tension at the interface water - a mixture of fluorocarbon vapor and water, based on the previously established analytical methods we calculate the surface tension for simple one - component liquid-vapor systems. The obtained analytical relation to calculate the surface tension of the mixture is a function of temperature and volume concentration of the fluorocarbon gas in the mixture and is true for all sizes of gas molecules. On the newly created experimental stand is made verification of experimental studies to determine the surface tension of pure substances: water, steam, C3F8 pair C3F8, produced the first experimental data on surface tension at the water - a mixture of water vapor and fluorocarbon C3F8. The obtained experimental data allow us to refine the values of the two constants used in the calculated model of the surface tension of the mixture. Experimental study of jet condensation was carried out with the flow in the zone of condensation of different gases. The condensation process was monitored by measurement of consumption of water flowing from the nozzle, and the formed condensate. When submitting C3F8, there was a noticeable, intensification condensation process compared with the condensation of pure water vapor. The calculation results are in satisfactory agreement with the experimental data on surface tension of the mixture and steam condensation from steam-gas mixture. Analysis of calculation results shows that the presence of surfactants in the condensation zone affects the partial vapor pressure on the interfacial surface, and the thermal conductivity of the liquid jet. The first circumstance leads to deterioration of the condensation process, the second to the intensification of this process. There is obviously an optimum value of concentration of the additive surfactants to the vapour when the condensation process is maximum. According to the developed design methodology contact condensation can evaluate these optimum conditions, their practical effect in the field study.

Alkyl chain interaction at the surface of room temperature ionic liquids: systematic variation of alkyl chain length (R = C(1)-C(4), C(8)) in both cation and anion of [RMIM][R-OSO(3)] by sum frequency generation and surface tension.

PubMed

Santos, Cherry S; Baldelli, Steven

2009-01-29

The gas-liquid interface of halide-free 1,3-dialkylimidazolium alkyl sulfates [RMIM][R-OSO(3)] with R chain length from C(1)-C(4) and C(8) has been studied systematically using the surface-specific sum frequency generation (SFG) vibrational spectroscopy and surface tension measurements. From the SFG spectra, vibrational modes from the methyl group of both cation and anion are observed for all ionic liquid samples considered in the present study. These results suggest the presence of both ions at the gas-liquid interface, which is further supported by surface tension measurements. Surface tension data show a decreasing trend as the alkyl chain in the imidazolium cation is varied from methyl to butyl chain, with a specific anion. A similar trend is observed when the alkyl chain of the anion is modified and the cation is fixed.

Influence of Nanosegregation on the Surface Tension of Fluorinated Ionic Liquids

PubMed Central

Luís, Andreia; Shimizu, Karina; Araújo, João M. M.; Carvalho, Pedro J.; Lopes-da-Silva, José A.; Canongia Lopes, José N.; Rebelo, Luís Paulo N.; Coutinho, João A. P.; Freire, Mara G.; Pereiro, Ana B.

2017-01-01

We have investigated, both theoretically and experimentally, the balance between the presence of alkyl and perfluoroalkyl side chains on the surface organization and surface tension of fluorinated ionic liquids (FILs). A series of ILs composed of 1-alkyl-3-methylimidazolium cations ([CnC1im] with n = 2, 4, 6, 8, 10 or 12) combined with the perfluorobutanesulfonate anion was used. The surface tensions of the investigated liquid salts are considerably lower than those reported for non-fluorinated ionic liquids. The most surprising and striking feature was the identification, for the first time, of a minimum at n = 8 in the surface tension versus the length of the IL cation alkyl side chain. Supported by molecular dynamic simulations it was found that this trend is a result of the competition between the two nonpolar domains (perfluorinated and aliphatic) on pointing towards the gas-liquid interface, a phenomenon which occurs in ionic liquids with perfluorinated anions. Furthermore, these ionic liquids present the lowest surface entropy reported to date. PMID:27218210

Assessing Impact Direction in 3-point Bending of Human Femora: Incomplete Butterfly Fractures and Fracture Surfaces,.

PubMed

Isa, Mariyam I; Fenton, Todd W; Deland, Trevor; Haut, Roger C

2018-01-01

Current literature associates bending failure with butterfly fracture, in which fracture initiates transversely at the tensile surface of a bent bone and branches as it propagates toward the impact surface. The orientation of the resulting wedge fragment is often considered diagnostic of impact direction. However, experimental studies indicate bending does not always produce complete butterfly fractures or produces wedge fragments variably in tension or compression, precluding their use in interpreting directionality. This study reports results of experimental 3-point bending tests on thirteen unembalmed human femora. Complete fracture patterns varied following bending failure, but incomplete fractures and fracture surface characteristics were observed in all impacted specimens. A flat, billowy fracture surface was observed in tension, while jagged, angular peaks were observed in compression. Impact direction was accurately reconstructed using incomplete tension wedge butterfly fractures and tension and compression fracture surface criteria in all thirteen specimens. © 2017 American Academy of Forensic Sciences.

The relationship between surface tension and the industrial performance of water-soluble polymers prepared from acid hydrolysis lignin, a saccharification by-product from woody materials.

PubMed

Matsushita, Yasuyuki; Imai, Masanori; Iwatsuki, Ayuko; Fukushima, Kazuhiko

2008-05-01

In this study, water-soluble anionic and cationic polymers were prepared from sulfuric acid lignin (SAL), an acid hydrolysis lignin, and the relationship between the surface tension of these polymers and industrial performance was examined. The SAL was phenolized (P-SAL) to enhance its solubility and reactivity. Sulfonation and the Mannich reaction with aminocarboxylic acids produced water-soluble anionic polymers and high-dispersibility gypsum paste. The dispersing efficiency increased as the surface tension decreased, suggesting that the fluidity of the gypsum paste increased with the polymer adsorption on the gypsum particle surface. Water-soluble cationic polymers were prepared using the Mannich reaction with dimethylamine. The cationic polymers showed high sizing efficiency under neutral papermaking conditions; the sizing efficiency increased with the surface tension. This suggests that the polymer with high hydrophilicity spread in the water and readily adhered to the pulp surface and the rosin, showing good retention.

Density, Molar Volume, and Surface Tension of Liquid Al-Ti

NASA Astrophysics Data System (ADS)

Wessing, Johanna Jeanette; Brillo, Jürgen

2017-02-01

Al-Ti-based alloys are of enormous technical relevance due to their specific properties. For studies in atomic dynamics, surface physics and industrial processing the precise knowledge of the thermophysical properties of the liquid phase is crucial. In the present work, we systematically measure mass density, ρ (g cm-3), and the surface tension, γ (N m-1), as functions of temperature, T, and compositions of binary Al-Ti melts. Electromagnetic levitation in combination with the optical dilatometry method is used for density measurements and the oscillating drop method for surface tension measurements. It is found that, for all compositions, density and surface tension increase linearly upon decreasing temperature in the liquid phase. Within the Al-Ti system, we find the largest values for pure titanium and the smallest for pure aluminum, which amount to ρ(L,Ti) = 4.12 ± 0.04 g cm-3 and γ(L,Ti) = 1.56 ± 0.02 N m-1; and ρ(L,Al) = 2.09 ± 0.01 g cm-3 and γ(L,Al) = 0.87 ± 0.06 N m-1, respectively. The data are analyzed concerning the temperature coefficients, ρ T and γ T, excess molar volume, V E, excess surface tension, γ E, and surface segregation of the surface active component, Al. The results are compared with thermodynamic models. Generally, it is found that Al-Ti is a highly nonideal system.

Computational Study of Surface Tension and Wall Adhesion Effects on an Oil Film Flow Underneath an Air Boundary Layer

NASA Technical Reports Server (NTRS)

Celic, Alan; Zilliac, Gregory G.

1998-01-01

The fringe-imaging skin friction (FISF) technique, which was originally developed by D. J. Monson and G. G. Mateer at Ames Research Center and recently extended to 3-D flows, is the most accurate skin friction measurement technique currently available. The principle of this technique is that the skin friction at a point on an aerodynamic surface can be determined by measuring the time-rate-of-change of the thickness of an oil drop placed on the surface under the influence of the external air boundary layer. Lubrication theory is used to relate the oil-patch thickness variation to shear stress. The uncertainty of FISF measurements is estimated to be as low as 4 percent, yet little is known about the effects of surface tension and wall adhesion forces on the measured results. A modified version of the free-surface Navier-Stokes solver RIPPLE, developed at Los Alamos National Laboratories, was used to compute the time development of an oil drop on a surface under a simulated air boundary layer. RIPPLE uses the volume of fluid method to track the surface and the continuum surface force approach to model surface tension and wall adhesion effects. The development of an oil drop, over a time period of approximately 4 seconds, was studied. Under the influence of shear imposed by an air boundary layer, the computed profile of the drop rapidly changes from its initial circular-arc shape to a wedge-like shape. Comparison of the time-varying oil-thickness distributions computed using RIPPLE and also computed using a greatly simplified numerical model of an oil drop equation which does not include surface tension and wall adhesion effects) was used to evaluate the effects of surface tension on FISF measurement results. The effects of surface tension were found to be small but not necessarily negligible in some cases.

Contact Angles and Surface Tension of Germanium-Silicon Melts

NASA Technical Reports Server (NTRS)

Croell, A.; Kaiser, N.; Cobb, S.; Szofran, F. R.; Volz, M.; Rose, M. Franklin (Technical Monitor)

2001-01-01

Precise knowledge of material parameters is more and more important for improving crystal growth processes. Two important parameters are the contact (wetting) angle and the surface tension, determining meniscus shapes and surface-tension driven flows in a variety of methods (Czochralski, EFG, floating-zone, detached Bridgman growth). The sessile drop technique allows the measurement of both parameters simultaneously and has been used to measure the contact angles and the surface tension of Ge(1-x)Si(x) (0 less than or equal to x less than or equal to 1.3) alloys on various substrate materials. Fused quartz, Sapphire, glassy carbon, graphite, SiC, carbon-based aerogel, pyrolytic boron nitride (pBN), AIN, Si3N4, and polycrystalline CVD diamond were used as substrate materials. In addition, the effect of different cleaning procedures and surface treatments on the wetting behavior were investigated. Measurements were performed both under dynamic vacuum and gas atmospheres (argon or forming gas), with temperatures up to 1100 C. In some experiments, the sample was processed for longer times, up to a week, to investigate any changes of the contact angle and/or surface tension due to slow reactions with the substrate. For pure Ge, stable contact angles were found for carbon-based substrates and for pBN, for Ge(1-x)Si(x) only for pBN. The highest wetting angles were found for pBN substrates with angles around 170deg. For the surface tension of Ge, the most reliable values resulted in gamma(T) = (591- 0.077 (T-T(sub m)) 10(exp -3)N/m. The temperature dependence of the surface tension showed similar values for Ge(1-x)Si(x), around -0.08 x 10(exp -3)N/m K, and a compositional dependence of 2.2 x 10(exp -3)N/m at%Si.

Solutal Marangoni flow as the cause of ring stains from drying salty colloidal drops

NASA Astrophysics Data System (ADS)

Marin, Alvaro; Karpitschka, Stefan; Rossi, Massimiliano; Kaehler, Christian J.; Noguera-Marin, Diego; Rodriguez-Valverde, Miguel A.

2017-11-01

Salts can be found in different forms in almost any evaporating droplet in nature, our homes and in laboratories. The transport processes in such apparently simple systems differ strongly from `sweet' evaporating droplets since the liquid flows in the inverse direction due to Marangoni stresses at the surface. Such an effect has crucial consequences to salt crystallization processes and to the evaporation itself. In this work we show measurements that not only confirm clearly the details of the inverted flow patterns, but also permit us to calculate the surface tension gradients responsible for the reversal. Such a reversal does not prevent the coffee-stain effect; on the contrary, particles accumulate and get trapped at the liquid-air interface driven by the surface flow. In order to prove this, we show measurements of the full three-dimensional flow inside the evaporating salty droplet, confocal imaging is used to quantify the growth of the particle deposits for different salt concentrations, and we compare the experimental results with numerical simulations that capture the solvent evaporation, the evaporation-induced liquid flow and the quasi-equilibrium liquid-gas interface.

Simultaneous measurement of surface tension and viscosity using freely decaying oscillations of acoustically levitated droplets.

PubMed

Kremer, J; Kilzer, A; Petermann, M

2018-01-01

Oscillations of small liquid drops around a spherical shape have been of great interest to scientists measuring physical properties such as interfacial tension and viscosity, over the last few decades. A powerful tool for contactless positioning is acoustic levitation, which has been used to simultaneously determine the surface tension and viscosity of liquids at ambient pressure. In order to extend this acoustic levitation measurement method to high pressure systems, the method is first evaluated under ambient pressure. To measure surface tension and viscosity using acoustically levitated oscillating drops, an image analysis method has to be developed and factors which may affect measurement, such as sound field or oscillation amplitude, have to be analyzed. In this paper, we describe the simultaneous measurement of surface tension and viscosity using freely decaying shape oscillations of acoustically levitated droplets of different liquids (silicone oils AK 5 and AK 10, squalane, 1-propanol, 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, and 1-octanol) in air. These liquids vary in viscosity from 2 to about 30 mPa s. An acoustic levitation system, including an optimized standing wave acoustic levitator and a high-speed camera, was used for this study. An image analysis was performed with a self-written Matlab® code. The frequency of oscillation and the damping constant, required for the determination of surface tension and viscosity, respectively, were calculated from the evolution of the equatorial and polar radii. The results and observations are compared to data from the literature in order to analyze the accuracy of surface tension and viscosity determination, as well as the effect of non-spherical drop shape or amplitude of oscillation on measurement.

Simultaneous measurement of surface tension and viscosity using freely decaying oscillations of acoustically levitated droplets

NASA Astrophysics Data System (ADS)

Kremer, J.; Kilzer, A.; Petermann, M.

2018-01-01

Oscillations of small liquid drops around a spherical shape have been of great interest to scientists measuring physical properties such as interfacial tension and viscosity, over the last few decades. A powerful tool for contactless positioning is acoustic levitation, which has been used to simultaneously determine the surface tension and viscosity of liquids at ambient pressure. In order to extend this acoustic levitation measurement method to high pressure systems, the method is first evaluated under ambient pressure. To measure surface tension and viscosity using acoustically levitated oscillating drops, an image analysis method has to be developed and factors which may affect measurement, such as sound field or oscillation amplitude, have to be analyzed. In this paper, we describe the simultaneous measurement of surface tension and viscosity using freely decaying shape oscillations of acoustically levitated droplets of different liquids (silicone oils AK 5 and AK 10, squalane, 1-propanol, 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, and 1-octanol) in air. These liquids vary in viscosity from 2 to about 30 mPa s. An acoustic levitation system, including an optimized standing wave acoustic levitator and a high-speed camera, was used for this study. An image analysis was performed with a self-written Matlab® code. The frequency of oscillation and the damping constant, required for the determination of surface tension and viscosity, respectively, were calculated from the evolution of the equatorial and polar radii. The results and observations are compared to data from the literature in order to analyze the accuracy of surface tension and viscosity determination, as well as the effect of non-spherical drop shape or amplitude of oscillation on measurement.

Oscillatory/Chaotic Thermocapillary Flow Induced by Radiant Heating

NASA Technical Reports Server (NTRS)

DeWitt, Kenneth J.

1998-01-01

There is a continuing need to understand the fluid physics occurring under low gravity conditions in processes such as crystal growth, materials processing, and the movement of bubbles or droplets. The fluid flow in such situations is often caused by a gradient in interfacial tension. If a temperature gradient is created due to a heat source, the resulting flow is called thermocapillary flow, a special case of Marangoni Convection. In this study, an experimental investigation was conducted using silicone oil in cylindrical containers with a laser heat source at the free surface. It was desired to determine the conditions under which steady, axisymmetrical thermocapillary flow becomes unstable and oscillatory three-dimensional flow states develop. The critical Marangoni number for each observed oscillatory state was measured as a function of the container aspect ratio and the dynamic Bond number, a measure of buoyant force versus ii thermocapillary force. Various oscillatory modes were observed during three- dimensional convection, and chaotic flow was reached in one test condition. The critical Marangoni numbers are compared with those measured in previous studies, and the power spectra and phase trajectories of the instantaneous surface temperature distributions are used to characterize the routes of transitions to the chaotic flow state. Results show that only superharmonic modes appear in the routes to chaos while infinite number of subharmonic modes occur in flow transitions for pure Rayleigh convection.

Penetration in GTA welding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heiple, C.R.; Burgardt, P.

1990-01-01

The size and shape of the weld bead produced in GTA welding depends on the magnitude and distribution of the energy incident on the workpiece surfaces as well as the dissipation of that energy in the workpiece. The input energy is largely controllable through the welding parameters selected, however the dissipation of that energy in the workpiece is less subject to control. Changes in energy dissipation can produce large changes in weld shape or penetration. Heat transport away from the weld pool is almost entirely by conduction, but heat transport in the weld pool is more complicated. Heat conduction throughmore » the liquid is an important component, but heat transport by convection (mass transport) is often the dominant mechanism. Convective heat transport is directional and changes the weld pool shape from that produced by conduction alone. Surface tension gradients are often the dominant forces driving fluid flow in GTA weld pools. These gradients are sensitive functions of weld pool chemistry and the energy input distribution to the weld. Experimental and theoretical work conducted primarily in the past decade has greatly enhanced our understanding of weld pool fluid flow, the forces which drive it, and its effects on weld pool shape. This work is reviewed here. While less common, changes in energy dissipation through the unmelted portion of the workpiece can also affect fusion zone shape or penetration. These effects are also described. 41 refs., 9 figs.« less

Mathematical model of Rayleigh-Taylor and Richtmyer-Meshkov instabilities for viscoelastic fluids

NASA Astrophysics Data System (ADS)

Rollin, Bertrand; Andrews, Malcolm J.

2011-04-01

We extended the Goncharov model [V. N. Goncharov, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.88.134502 88, 134502 (2002)] for nonlinear Rayleigh-Taylor instability of perfect fluids to the case of Rivlin-Ericksen viscoelastic fluids [R. S. Rivlin and J. L. Ericksen, Rat. Mech. Anal. 4, 323 (1955)], with surface tension. For Rayleigh-Taylor instability, viscosity, surface tension, and viscoelasticity decrease the exponential growth rate predicted by linear stability analysis. In particular, we find that viscosity and surface tension decrease the terminal bubble velocity, whereas viscoelasticity is found to have no effect. All three properties increase the saturation height of the bubble. In Richmyer-Meshkov instability, the decay of the asymptotic velocity depends on the balance between viscosity and surface tension, and viscoelasticity tends to slow the asymptotic velocity decay.

Noncontact surface tension and viscosity measurements of molten oxides with a pressurized hybrid electrostatic-aerodynamic levitator

NASA Astrophysics Data System (ADS)

Ishikawa, Takehiko; Yu, Jianding; Paradis, Paul-François

2006-05-01

In order to measure the surface tension and the viscosity of molten oxides, the oscillation drop technique has been applied on a pressurized hybrid electrostatic-aerodynamic levitator. To suppress the electrical discharge between the top and bottom electrodes, the drop excitation method which has been used with high vacuum electrostatic levitators has been modified. As a demonstration, the surface tension and viscosity of liquid BaTiO3 were measured using this new method. Over the 1500-2000K interval, the surface tension was measured as γ(T )=349-0.03 (T-Tm) (10-3N/m), where Tm=1893K is the melting temperature. Similarly, the viscosity was determined as η(T )=0.53exp[5.35×104/(RT)](10-3Pas) over the same temperature interval.

Effects of Environmental Oxygen Content and Dissolved Oxygen on the Surface Tension and Viscosity of Liquid Nickel

NASA Astrophysics Data System (ADS)

SanSoucie, M. P.; Rogers, J. R.; Kumar, V.; Rodriguez, J.; Xiao, X.; Matson, D. M.

2016-07-01

The NASA Marshall Space Flight Center's electrostatic levitation (ESL) laboratory has recently added an oxygen partial pressure controller. This system allows the oxygen partial pressure within the vacuum chamber to be measured and controlled in the range from approximately 10^{-28} {to} 10^{-9} bar, while in a vacuum atmosphere. The oxygen control system installed in the ESL laboratory's main chamber consists of an oxygen sensor, oxygen pump, and a control unit. The sensor is a potentiometric device that determines the difference in oxygen activity in two gas compartments (inside the chamber and the air outside of the chamber) separated by an electrolyte. The pump utilizes coulometric titration to either add or remove oxygen. The system is controlled by a desktop control unit, which can also be accessed via a computer. The controller performs temperature control for the sensor and pump, has a PID-based current loop and a control algorithm. Oxygen partial pressure has been shown to play a significant role in the surface tension of liquid metals. Oxide films or dissolved oxygen may lead to significant changes in surface tension. The effects on surface tension and viscosity by oxygen partial pressure in the surrounding environment and the melt dissolved oxygen content will be evaluated, and the results will be presented. The surface tension and viscosity will be measured at several different oxygen partial pressures while the sample is undercooled. Surface tension and viscosity will be measured using the oscillating droplet method.

A free energy-based surface tension force model for simulation of multiphase flows by level-set method

NASA Astrophysics Data System (ADS)

Yuan, H. Z.; Chen, Z.; Shu, C.; Wang, Y.; Niu, X. D.; Shu, S.

2017-09-01

In this paper, a free energy-based surface tension force (FESF) model is presented for accurately resolving the surface tension force in numerical simulation of multiphase flows by the level set method. By using the analytical form of order parameter along the normal direction to the interface in the phase-field method and the free energy principle, FESF model offers an explicit and analytical formulation for the surface tension force. The only variable in this formulation is the normal distance to the interface, which can be substituted by the distance function solved by the level set method. On one hand, as compared to conventional continuum surface force (CSF) model in the level set method, FESF model introduces no regularized delta function, due to which it suffers less from numerical diffusions and performs better in mass conservation. On the other hand, as compared to the phase field surface tension force (PFSF) model, the evaluation of surface tension force in FESF model is based on an analytical approach rather than numerical approximations of spatial derivatives. Therefore, better numerical stability and higher accuracy can be expected. Various numerical examples are tested to validate the robustness of the proposed FESF model. It turns out that FESF model performs better than CSF model and PFSF model in terms of accuracy, stability, convergence speed and mass conservation. It is also shown in numerical tests that FESF model can effectively simulate problems with high density/viscosity ratio, high Reynolds number and severe topological interfacial changes.

Promising characteristics of gradient porosity Ti-6Al-4V alloy prepared by SLM process.

PubMed

Fousová, Michaela; Vojtěch, Dalibor; Kubásek, Jiří; Jablonská, Eva; Fojt, Jaroslav

2017-05-01

Porous structures, manufactured of a biocompatible metal, mimicking human bone structure are the future of orthopedic implantology. Fully porous materials, however, suffer from certain drawbacks. To overcome these, gradient in structure can be prepared. With gradient in porosity mechanical properties can be optimized to an appropriate value, implant can be attributed a similar gradient macrostructure as bone, tissue adhesion may be promoted and also various modification with organic or inorganic substances are possible. In this study, additive technology selective laser melting (SLM) was used to produce three types of gradient porosity model specimens of titanium alloy Ti-6Al-4V. As this technology has the potential to prepare complex structures in the near-net form, to control porosity, pore size and shape, it represents a promising option. The first part of the research work was focused on the characterization of the material itself in the as-produced state, only with heat treatment applied. The second part dealt with the influence of porosity on mechanical properties. The study has shown SLM brings significant changes in the surface chemistry. Despite this finding, titanium alloy retained its cytocompatibility, as it was outlined by in vitro tests with U-2 OS cells. With introduced porosity yield strength, ultimate strength and stiffness showed linear decrease, both in tension and compression. With respect to the future use in the form of orthopedic implant, especially reduction in Young's modulus down to the human bone value (30.5±2GPa) is very appreciated as the stress-shielding effect followed by possible implant loosening is limited. Copyright © 2017 Elsevier Ltd. All rights reserved.

Surfactant effects on interfacial flow and thermal transport processes during phase change in film boiling

NASA Astrophysics Data System (ADS)

Premnath, Kannan N.; Hajabdollahi, Farzaneh; Welch, Samuel W. J.

2018-04-01

The presence of surfactants in two-phase flows results in the transport and adsorption of surfactants to the interface, and the resulting local interfacial concentration significantly influences the surface tension between the liquid and vapor phases in a fluid undergoing phase change. This computational study is aimed at understanding and elucidating the mechanisms of enhanced flows and thermal transport processes in film boiling due to the addition of surfactants. A change in surface tension results in a change in the critical Rayleigh-Taylor wavelength leading to different bubble release patterns and a change in the overall heat transfer rates. Due to the presence of surfactants, an additional transport mechanism of the Marangoni convection arises from the resulting tangential gradients in the surfactant concentration along the phase interface. Our computational approach to study such phenomena consists of representing the interfacial motion by means of the coupled level set-volume-of-fluid method, the fluid motion via the classical marker-and-cell approach, as well as representations for the bulk transport of energy and surfactants, in conjunction with a phase change model and an interfacial surfactant model. Using such an approach, we perform numerical simulations of surfactant-laden single mode as well as multiple mode film boiling and study the effect of surfactants on the transport processes in film boiling, including bubble release patterns, vapor generation rates, and heat transfer rates at different surfactant concentrations. The details of the underlying mechanisms will be investigated and interpreted.

A Space Station tethered orbital refueling facility

NASA Technical Reports Server (NTRS)

Fester, D. A.; Rudolph, L. K.; Kiefel, E. R.

1985-01-01

A planned function of the Space Station is to refurbish and refuel an advanced space-based LO2/LH2 orbit transfer vehicle. An alternative to propellant storage at the station is to use a remote facility tied to the station with a long tether. Preliminary design of such a facility is described with emphasis on fluid transfer and storage requirements. Using tether lengths of at least 300 ft, gravity gradient forces will dominate surface tension in such a system. Although gravity driven transfer is difficult because of line pressure drops, fluid settling over the tank outlet greatly alleviates acquisition concerns and will facilitate vented tank fills. The major concern with a tethered orbital refueling facility is its considerable operational complexity including transport of the OTV to and from the facility.

Surface Tension Mediated Under-Water Adhesion of Rigid Spheres on Soft, Charged Surfaces

NASA Astrophysics Data System (ADS)

Sinha, Shayandev; Das, Siddhartha

2015-11-01

Understanding the phenomenon of surface-tension-mediated under-water adhesion is necessary for studying a plethora of physiological and technical phenomena, such as the uptake of bacteria or nanoparticle by cells, attachment of virus on bacterial surfaces, biofouling on large ocean vessels and marine devices, etc. This adhesion phenomenon becomes highly non-trivial in case the soft surface where the adhesion occurs is also charged. Here we propose a theory for analyzing such an under-water adhesion of a rigid sphere on a soft, charged surface, represented by a grafted polyelectrolyte layer (PEL). We develop a model based on the minimization of free energy that, in addition to considering the elastic and the surface-tension-mediated adhesion energies, also accounts for the PEL electric double layer (EDL) induced electrostatic energies. We show that in the presence of surface charges, adhesion gets enhanced. This can be explained by the fact that the increase in the elastic energy is better balanced by the lowering of the EDL energy associated with the adhesion process. The entire behaviour is further dictated by the surface tension components that govern the adhesion energy.

Effect of adsorption on the surface tensions of solid-fluid interfaces.

PubMed

Ward, C A; Wu, Jiyu

2007-04-12

A method is proposed for determining the surface tensions of a solid in contact with either a liquid or a vapor. Only an equilibrium adsorption isotherm at the solid-vapor interface needs to be added to Gibbsian thermodynamics to obtain the expressions for the solid-vapor and the solid-liquid surface tensions, gamma[1](SV) and gamma[1](SL), respectively. An equilibrium adsorption isotherm relation is formulated that has the essential property of not predicting an infinite amount adsorbed when the pressure is equal to the saturation-vapor pressure. Five different solid-vapor systems from the literature are examined, and found to be well described by the new isotherm relation. The surface-tension expressions obtained from the isotherm relation are examined by determining the surface tension of the solid in the absence of adsorption, gamma[1](S0), a material property of a solid surface. The value of gamma[1](S0) can be determined by adsorbing different vapors on the same solid, determining the isotherm parameters in each case, and then from the expression for gamma[1](SV) taking the limit of the pressure vanishing to determine gamma[1](S0). From previously reported measurements of benzene and of n-hexane adsorbing on graphitized carbon, the same value of gamma[1](S0) is obtained.

Multiphase mean curvature flows with high mobility contrasts: A phase-field approach, with applications to nanowires

NASA Astrophysics Data System (ADS)

Bretin, Elie; Danescu, Alexandre; Penuelas, José; Masnou, Simon

2018-07-01

The structure of many multiphase systems is governed by an energy that penalizes the area of interfaces between phases weighted by surface tension coefficients. However, interface evolution laws depend also on interface mobility coefficients. Having in mind some applications where highly contrasted or even degenerate mobilities are involved, for which classical phase field models are inapplicable, we propose a new effective phase field approach to approximate multiphase mean curvature flows with mobilities. The key aspect of our model is to incorporate the mobilities not in the phase field energy (which is conventionally the case) but in the metric which determines the gradient flow. We show the consistency of such an approach by a formal analysis of the sharp interface limit. We also propose an efficient numerical scheme which allows us to illustrate the advantages of the model on various examples, as the wetting of droplets on solid surfaces or the simulation of nanowires growth generated by the so-called vapor-liquid-solid method.

Patterning of ultrathin polymethylmethacrylate films by in-situ photodirecting of the Marangoni flow

NASA Astrophysics Data System (ADS)

Elashnikov, Roman; Fitl, Premysl; Svorcik, Vaclav; Lyutakov, Oleksiy

2017-02-01

Laser heating and Marangoni flow result in the formation of surface structures with different geometries and shape on thin polymer films. By laser beam irradiation combined with a sample movement the solid polymethylmethacrylate (PMMA) films are heated and undergo phase transition which leads to a material flow. Since the laser beam has a non-linear distribution of energy, the PMMA film is heated inhomogeneously and a surface tension gradient in a lateral direction is introduced. During this procedure additional phenomena such as "reversible" or cyclic polymer flow also take place. The careful choice of experimental conditions enables the preparation of patterns with sophisticated geometries and with hierarchical pattern organization. Depending on initial PMMA film thickness and speed of the sample movement line arrays are created, which can subsequently be transformed into the crimped lines or system of circular holes. In addition, the introduction of a constant acceleration in the sample movement or a laser beam distortion enables the preparation of regularly crimped lines, ordered hexagonal holes or overlapped plates.

Mass transfer in fuel cells. [electron microscopy of components, thermal decomposition of Teflon, water transport, and surface tension of KOH solutions

NASA Technical Reports Server (NTRS)

Walker, R. D., Jr.

1973-01-01

Results of experiments on electron microscopy of fuel cell components, thermal decomposition of Teflon by thermogravimetry, surface area and pore size distribution measurements, water transport in fuel cells, and surface tension of KOH solutions are described.

Enhancements of Nucleate Boiling Under Microgravity Conditions

NASA Technical Reports Server (NTRS)

Zhang, Nengli; Chao, David F.; Yang, W. J.

2000-01-01

This paper presents two means for enhancing nucleate boiling and critical heat flux under microgravity conditions: using micro-configured metal-graphite composites as the boiling surface and dilute aqueous solutions of long-chain alcohols as the working fluid. In the former, thermocapillary force induced by temperature difference between the graphite-fiber tips and the metal matrix plays an important role in bubble detachment. Thus boiling-heat transfer performance does not deteriorate in a reduced-gravity environment. In the latter cases, the surface tension-temperature gradient of the long-chain alcohol solutions turns positive as the temperature exceeds a certain value. Consequently, the Marangoni effect does not impede, but rather aids in bubble departure from the heating surface. This feature is most favorable in microgravity. As a result, the bubble size of departure is substantially reduced at higher frequencies. Based on the existing experimental data, and a two-tier theoretical model, correlation formulas are derived for nucleate boiling on the copper-graphite and aluminum-graphite composite surfaces, in both the isolated and coalesced bubble regimes. In addition, performance equations for nucleate boiling and critical heat flux in dilute aqueous solutions of long-chain alcohols are obtained.

Numerical Study of Nonlinear Structures of Locally Excited Marangoni Convection in the Long-Wave Approximation

NASA Astrophysics Data System (ADS)

Wertgeim, Igor I.

2018-02-01

We investigate stationary and non-stationary solutions of nonlinear equations of the long-wave approximation for the Marangoni convection caused by a localized source of heat or a surface active impurity (surfactant) in a thin horizontal layer of a viscous incompressible fluid with a free surface. The distribution of heat or concentration flux is determined by the uniform vertical gradient of temperature or impurity concentration, distorted by the imposition of a slightly inhomogeneous heating or of surfactant, localized in the horizontal plane. The lower boundary of the layer is considered thermally insulated or impermeable, whereas the upper boundary is free and deformable. The equations obtained in the long-wave approximation are formulated in terms of the amplitudes of the temperature distribution or impurity concentration, deformation of the surface, and vorticity. For a simplification of the problem, a sequence of nonlinear equations is obtained, which in the simplest form leads to a nonlinear Schrödinger equation with a localized potential. The basic state of the system, its dependence on the parameters and stability are investigated. For stationary solutions localized in the region of the surface tension inhomogeneity, domains of parameters corresponding to different spatial patterns are delineated.

Formation mechanisms of nano and microcones by laser radiation on surfaces of Si, Ge, and SiGe crystals

PubMed Central

2013-01-01

In this work we study the mechanisms of laser radiation interaction with elementary semiconductors such as Si and Ge and their solid solution SiGe. As a result of this investigation, the mechanisms of nanocones and microcones formation on a surface of semiconductor were proposed. We have shown the possibility to control the size and the shape of cones both by the laser. The main reason for the formation of nanocones is the mechanical compressive stresses due to the atoms’ redistribution caused by the gradient of temperature induced by strongly absorbed laser radiation. According to our investigation, the nanocone formation mechanism in semiconductors is characterized by two stages. The first stage is characterized by formation of a p-n junction for elementary semiconductors or of a Ge/Si heterojunction for SiGe solid solution. The generation and redistribution of intrinsic point defects in elementary semiconductors and Ge atoms concentration on the irradiated surface of SiGe solid solution in temperature gradient field take place at this stage due to the thermogradient effect which is caused by strongly absorbed laser radiation. The second stage is characterized by formation of nanocones due to mechanical plastic deformation of the compressed Ge layer on Si. Moreover, a new 1D-graded band gap structure in elementary semiconductors due to quantum confinement effect was formed. For the formation of microcones Ni/Si structure was used. The mechanism of the formation of microcones is characterized by two stages as well. The first stage is the melting of Ni film after irradiation by laser beam and formation of Ni islands due to surface tension force. The second step is the melting of Ni and subsequent manifestations of Marangoni effect with the growth of microcones. PMID:23735193

The wavelength of supercritical surface tension driven Benard convection

NASA Technical Reports Server (NTRS)

Koschmieder, E. L.

1991-01-01

The size or the wavelength of moderately supercritical surface tension driven Benard convection has been investigated experimentally in a thin fluid layer of large aspect ratio. It has been found that the number of the hexagonal convection cells increases with increased temperature differences, up to 1.3 times the critical temperature difference. That means that the wavelength of surface tension driven convection decreases after onset of the instability for moderately nonlinear conditions. This result is in striking contrast to the well-known increase of the wavelength of buoyancy driven Rayleigh-Benard convection.

The length-force behavior and operating length range of squid muscle vary as a function of position in the mantle wall.

PubMed

Thompson, Joseph T; Shelton, Ryan M; Kier, William M

2014-06-15

Hollow cylindrical muscular organs are widespread in animals and are effective in providing support for locomotion and movement, yet are subject to significant non-uniformities in circumferential muscle strain. During contraction of the mantle of squid, the circular muscle fibers along the inner (lumen) surface of the mantle experience circumferential strains 1.3 to 1.6 times greater than fibers along the outer surface of the mantle. This transmural gradient of strain may require the circular muscle fibers near the inner and outer surfaces of the mantle to operate in different regions of the length-tension curve during a given mantle contraction cycle. We tested the hypothesis that circular muscle contractile properties vary transmurally in the mantle of the Atlantic longfin squid, Doryteuthis pealeii. We found that both the length-twitch force and length-tetanic force relationships of the obliquely striated, central mitochondria-poor (CMP) circular muscle fibers varied with radial position in the mantle wall. CMP circular fibers near the inner surface of the mantle produced higher force relative to maximum isometric tetanic force, P0, at all points along the ascending limb of the length-tension curve than CMP circular fibers near the outer surface of the mantle. The mean ± s.d. maximum isometric tetanic stresses at L₀ (the preparation length that produced the maximum isometric tetanic force) of 212 ± 105 and 290 ± 166 kN m(-2) for the fibers from the outer and inner surfaces of the mantle, respectively, did not differ significantly (P=0.29). The mean twitch:tetanus ratios for the outer and inner preparations, 0.60 ± 0.085 and 0.58 ± 0.10, respectively, did not differ significantly (P=0.67). The circular fibers did not exhibit length-dependent changes in contraction kinetics when given a twitch stimulus. As the stimulation frequency increased, L₀ was approximately 1.06 times longer than LTW, the mean preparation length that yielded maximum isometric twitch force. Sonomicrometry experiments revealed that the CMP circular muscle fibers operated in vivo primarily along the ascending limb of the length-tension curve. The CMP fibers functioned routinely over muscle lengths at which force output ranged from only 85% to 40% of P₀, and during escape jets from 100% to 30% of P₀. Our work shows that the functional diversity of obliquely striated muscles is much greater than previously recognized. © 2014. Published by The Company of Biologists Ltd.

Synthesis and properties evaluation of sulfobetaine surfactant with double hydroxyl

NASA Astrophysics Data System (ADS)

Zhou, Ming; Luo, Gang; Zhang, Ze; Li, Sisi; Wang, Chengwen

2017-09-01

A series of sulfobetaine surfactants {N-[(3-alkoxy-2-hydroxyl)propoxy] ethyl-N,N-dimethyl-N-(2-hydroxyl)propyl sulfonate} ammonium chloride were synthesized with raw materials containing linear saturated alcohol, N,N-dimethylethanolamine, sodium 3-chloro-2-hydroxyl propane sulfonic acid and epichlorohydrin. The molecule structures of sulfobetaine surfactants were characterized by FTIR, 1HNMR and elemental analysis. Surface tension measurements can provide us information about the surface tension at the CMC (γCMC), pC20, Γmax and Amin. The pC20 values of sulfobetaine surfactants increase with the hydrophobic chain length increasing. Amin values of the surfactants decrease with increasing hydrophobic chain length from 10 to 14. The critical micelle concentration (CMC) and surface tension (γCMC) values of the sulfobetaine surfactants decrease with increasing hydrophobic chain length from 10 to 16. The lipophilicity of surfactant was enhanced with the increase of the carbon chain, however, the ability of anti-hard water was weakened. The minimum oil/water interfacial tension of four kinds of sulfobetaine surfactants is 10-2-10-3 mN/m magnitude, which indicates that the synthesized bis-hydroxy sulfobetaine surfactants have a great ability to reduce interfacial tension in the surfactant flooding system. The surface tension (γCMC) values of synthesized surfactants were lower compared with conventional anionic surfactant sodium dodecyl sulfonate.

Carbon speciation and surface tension of fog

USGS Publications Warehouse

Capel, P.D.; Gunde, R.; Zurcher, F.; Giger, W.

1990-01-01

The speciation of carbon (dissolved/particulate, organic/inorganic) and surface tension of a number of radiation fogs from the urban area of Zurich, Switzerland, were measured. The carbon species were dominated by "dissolved" organic carbon (DOC; i.e., the fraction that passes through a filter), which was typically present at levels of 40-200 mg/L. Less than 10% of the DOC was identified as specific individual organic compounds. Particulate organic carbon (POC) accounted for 26-41% of the mass of the particles, but usually less than 10% of the total organic carbon mass. Inorganic carbon species were relatively minor. The surface tensions of all the measured samples were less than pure water and were correlated with their DOC concentrations. The combination of high DOC and POC and low surface tension suggests a mechanism for the concentration of hydrophobic organic contaminants in the fog droplet, which have been observed by numerous investigators. ?? 1990 American Chemical Society.

Effect of surface tension on the behavior of adhesive contact based on Lennard-Jones potential law

NASA Astrophysics Data System (ADS)

Zhu, Xinyao; Xu, Wei

2018-02-01

The present study explores the effect of surface tension on adhesive contact behavior where the adhesion is interpreted by long-range intermolecular forces. The adhesive contact is analyzed using the equivalent system of a rigid sphere and an elastic half space covered by a membrane with surface tension. The long-range intermolecular forces are modeled with the Lennard‒Jones (L‒J) potential law. The current adhesive contact issue can be represented by a nonlinear integral equation, which can be solved by Newton‒Raphson method. In contrast to previous studies which consider intermolecular forces as short-range, the present study reveals more details of the features of adhesive contact with surface tension, in terms of jump instabilities, pull-off forces, pressure distribution within the contact area, etc. The transition of the pull-off force is not only consistent with previous studies, but also presents some new interesting characteristics in the current situation.

Molecular dynamics simulations of the surface tension and structure of salt solutions and clusters.

PubMed

Sun, Lu; Li, Xin; Hede, Thomas; Tu, Yaoquan; Leck, Caroline; Ågren, Hans

2012-03-15

Sodium halides, which are abundant in sea salt aerosols, affect the optical properties of aerosols and are active in heterogeneous reactions that cause ozone depletion and acid rain problems. Interfacial properties, including surface tension and halide anion distributions, are crucial issues in the study of the aerosols. We present results from molecular dynamics simulations of water solutions and clusters containing sodium halides with the interatomic interactions described by a conventional force field. The simulations reproduce experimental observations that sodium halides increase the surface tension with respect to pure water and that iodide anions reach the outermost layer of water clusters or solutions. It is found that the van der Waals interactions have an impact on the distribution of the halide anions and that a conventional force field with optimized parameters can model the surface tension of the salt solutions with reasonable accuracy. © 2012 American Chemical Society

Surface Tension and Viscosity Measurements in Microgravity: Some Results and Fluid Flow Observations during MSL-1

NASA Technical Reports Server (NTRS)

Hyer, Robert W.; Trapaga, G.; Flemings, M. C.

1999-01-01

The viscosity of a liquid metal was successfully measured for the first time by a containerless method, the oscillating drop technique. This method also provides a means to obtain a precise, non-contact measurement of the surface tension of the droplet. This technique involves exciting the surface of the molten sample and then measuring the resulting oscillations; the natural frequency of the oscillating sample is determined by its surface tension, and the damping of the oscillations by the viscosity. These measurements were performed in TEMPUS, a microgravity electromagnetic levitator (EML), on the Space Shuttle as a part of the First Microgravity Science Laboratory (MSL-1), which flew in April and July 1997 (STS-83 and STS-94). Some results of the surface tension and viscosity measurements are presented for Pd82Si18. Some observations of the fluid dynamic characteristics (dominant flow patterns, turbulent transition, cavitation, etc.) of levitated droplets are presented and discussed together with magnetohydrodynamic calculations, which were performed to justify these findings.

Effect of surface roughness on droplet splashing

NASA Astrophysics Data System (ADS)

Hao, Jiguang

2017-12-01

It is well known that rough surfaces trigger prompt splashing and suppress corona splashing on droplet impact. Upon water droplet impact, we experimentally found that a slightly rough substrate triggers corona splashing which is suppressed to prompt splashing by both further increase and further decrease of surface roughness. The nonmonotonic effect of surface roughness on corona splashing weakens with decreasing droplet surface tension. The threshold velocities for prompt splashing and corona splashing are quantified under different conditions including surface roughness, droplet diameter, and droplet surface tension. It is determined that slight roughness significantly enhances both prompt splashing and corona splashing of a water droplet, whereas it weakly affects low-surface-tension droplet splashing. Consistent with previous studies, high roughness triggers prompt splashing and suppresses corona splashing. Further experiments on droplet spreading propose that the mechanism of slight roughness enhancing water droplet splashing is due to the decrease of the wetted area with increasing surface roughness.

Influence of Surface Tension and Surface Shear on Final Coat Thickness in Jet-Stripped Continuous Coating of Sheet Materials.

DTIC Science & Technology

1983-11-01

galvanising industry, this pressure distribution is created by blowing a thin high-speed air jet onto the coated steel sheet, just after it emerges from the...if that free surface possesses curvature and non-zero surface tension, the internal pressure will differ from that in the jet. In the galvanising

Chemical demulsification of petroleum emulsions using oil-soluable demulsifiers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krawczyk, M.A.; Wasan, D.T.; Shetty, C.S.

1991-02-01

This paper investigates the factors affecting the coalescence and interfacial behavior of water- in-crude-oil emulsions in the presence of oil-soluble demulsifiers. The emulsion-breaking characteristics and interfacial properties of East Texas Crude and a model system were compared. The variation of interfacial tension with demulsifier concentration for the model system was ascertained by measuring the interfacial tensions between the oil and water phase. Interfacial activity, adsorption kinetics, and partitioning were shown to be the most important parameters governing demulsifier performance. A conceptual model of drop-drop coalescence process in demulsification was presented which indicates that the interfacial activity of the demulsifier mustmore » be high enough to suppress the interfacial tension gradient. This accelerates the rate of film drainage, thus promoting coalescence.« less

Survismeter, 2-IN-1 for Viscosity and Surface Tension Measurement, AN Excellent Invention for Industrial Proliferation of Surface Forces in Liquids

NASA Astrophysics Data System (ADS)

Singh, Man

Viscosities (η, N s m-2) and surface tensions (γ, N m-1) of methanol, ethanol, glycerol, ethyl acetate, n-hexane, diethyl ether, chloroform, benzene, carbon tetrachloride (CCl4), tetrahydrofuran (THF), dimethylformamide (DMF), dimethylsulfoxide (DMSO), acetonitrile, and formic acid have been measured with survismeter and compared with the data obtained by Ubbehold viscometer and stalagmometer, respectively. The ±1.1 × 10-5 N s m-2 and ±1.3 × 10-6 N m-1 deviations are noted in the data, in fact literature data of surface tension and viscosity are available to 2nd and 3rd place of decimals, respectively, while the survismeter measures them to 3rd and 4th place of decimals, respectively. The survismeter is 2-in-1 for viscosity and surface tension measurements together with high accuracies several times better than those of the separately measured data. Viscosities and surface tensions of aqueous DMSO, THF, DMF, and acetonitrile from 0.01 to 0.20 mol kg-1 and mannitol from 0.005 to 0.02 mol kg-1 have been measured with survismeter with ±1.2 × 10-5 N s m-2 and ±1.3 × 10-6 N m-1 deviations, respectively. The data are used for friccohesity and dipole moment determination, the lower viscosities, surface tension, and friccohesity values are noted for mannitol as compared to DMSO, THF, DMF, and acetonitrile solutions. The weaker molecular interactions are noted for mannitol. As compared to viscometer and stalagmometer individually, it is inexpensive and minimizes 2/3rd of consumables, human efforts, and infrastructure with 10 times better accuracies.

Effect of surface tension on global modes of confined wake flows

NASA Astrophysics Data System (ADS)

Tammisola, Outi; Lundell, Fredrik; Söderberg, L. Daniel

2011-01-01

Many wake flows are susceptible to self-sustained oscillations, such as the well-known von Kármán vortex street behind a cylinder that makes a rope beat against a flagpole at a distinct frequency on a windy day. One appropriate method to study these global instabilities numerically is to look at the growth rates of the linear temporal global modes. If all growth rates for all modes are negative for a certain flow field then a self-sustained oscillation should not occur. On the other hand, if one growth rate for one mode is slightly positive, the oscillation will approximately obtain the frequency and shape of this global mode. In our study, we first introduce surface tension between two fluids to the wake-flow problem. Then we investigate its effects on the global linear instability of a spatially developing wake with two co-flowing immiscible fluids. The inlet profile consists of two uniform layers, which makes the problem easily parametrizable. The fluids are assumed to have the same density and viscosity, with the result that the interface position becomes dynamically important solely through the action of surface tension. Two wakes with different parameter values and surface tension are studied in detail. The results show that surface tension has a strong influence on the oscillation frequency, growth rate, and shape of the global mode(s). Finally, we make an attempt to confirm and explain the surface-tension effect based on a local stability analysis of the same flow field in the streamwise position of maximum reverse flow.

The Effect of Surface Tension on the Gravity-driven Thin Film Flow of Newtonian and Power-law Fluids.

PubMed

Hu, Bin; Kieweg, Sarah L

2012-07-15

Gravity-driven thin film flow is of importance in many fields, as well as for the design of polymeric drug delivery vehicles, such as anti-HIV topical microbicides. There have been many prior works on gravity-driven thin films. However, the incorporation of surface tension effect has not been well studied for non-Newtonian fluids. After surface tension effect was incorporated into our 2D (i.e. 1D spreading) power-law model, we found that surface tension effect not only impacted the spreading speed of the microbicide gel, but also had an influence on the shape of the 2D spreading profile. We observed a capillary ridge at the front of the fluid bolus. Previous literature shows that the emergence of a capillary ridge is strongly related to the contact line fingering instability. Fingering instabilities during epithelial coating may change the microbicide gel distribution and therefore impact how well it can protect the epithelium. In this study, we focused on the capillary ridge in 2D flow and performed a series of simulations and showed how the capillary ridge height varies with other parameters, such as surface tension coefficient, inclination angle, initial thickness, and power-law parameters. As shown in our results, we found that capillary ridge height increased with higher surface tension, steeper inclination angle, bigger initial thickness, and more Newtonian fluids. This study provides the initial insights of how to optimize the flow and prevent the appearance of a capillary ridge and fingering instability.

Investigation of Dynamic Oxygen Adsorption in Molten Solder Jetting Technology

NASA Technical Reports Server (NTRS)

Megaridis, Constantine M.; Bellizia, Giulio; McNallan, Michael; Wallace, David B.

2003-01-01

Surface tension forces play a critical role in fluid dynamic phenomena that are important in materials processing. The surface tension of liquid metals has been shown to be very susceptible to small amounts of adsorbed oxygen. Consequently, the kinetics of oxygen adsorption can influence the capillary breakup of liquid-metal jets targeted for use in electronics assembly applications, where low-melting-point metals (such as tin-containing solders) are utilized as an attachment material for mounting of electronic components to substrates. By interpreting values of surface tension measured at various surface ages, adsorption and diffusion rates of oxygen on the surface of the melt can be estimated. This research program investigates the adsorption kinetics of oxygen on the surface of an atomizing molten-metal jet. A novel oscillating capillary jet method has been developed for the measurement of dynamic surface tension of liquids, and in particular, metal melts which are susceptible to rapid surface degradation caused by oxygen adsorption. The experimental technique captures the evolution of jet swells and necks continuously along the jet propagation axis and is used in conjunction with an existing linear, axisymmetric, constant-property model to determine the variation of the instability growth rate, and, in turn, surface tension of the liquid as a function of surface age measured from the exit orifice. The conditions investigated so far focus on a time window of 2-4ms from the jet orifice. The surface properties of the eutectic 63%Sn-37%Pb solder alloy have been investigated in terms of their variation due to O2 adsorption from a N2 atmosphere containing controlled amounts of oxygen (from 8 ppm to 1000 ppm). The method performed well for situations where the oxygen adsorption was low in that time window. The value of surface tension for the 63Sn-37Pb solder in pure nitrogen was found to be 0.49 N/m, in good agreement with previously published work. A characteristic time of O(1ms) or less was determined for the molten-metal surface to be saturated by oxygen at 1000 ppm concentration in N2.

A Method to Calculate the Surface Tension of a Cylindrical Droplet

ERIC Educational Resources Information Center

Wang, Xiaosong; Zhu, Ruzeng

2010-01-01

The history of Laplace's equations for spherical and cylindrical droplets and the concept of dividing surface in Gibbs' thermodynamic theory of capillary phenomena are briefly reviewed. The existing theories of surface tensions of cylindrical droplets are briefly reviewed too. For cylindrical droplets, a new method to calculate the radius and the…

Effect of a surface tension imbalance on a partly submerged cylinder

NASA Astrophysics Data System (ADS)

Janssens, Stoffel; Chaurasia, Vikash; Fried, Eliot

We perform a force analysis of a circular cylinder which lays between a liquid-gas interface and acts as a barrier between a surfactant-free surface and a surfactant-loaded surface. The respective surfaces have uniform surface tensions γa and γb which generate a surface tension imbalance Δγ =γa -γb , also referred to as surface pressure. In addition to the general force analysis, we determine the effect of Δγ on the load-bearing capacity of a floating cylinder upon sinking for a specific set of parameters. Moreover, we demonstrate that Δγ induces a horizontal force component which in magnitude is equal to Δγ , when measured per unit length cylinder, and use an energetic argument to prove that this relation applies to prismatic bodies in general.

Subcritical and supercritical fuel injection and mixing in single and binary species systems

NASA Astrophysics Data System (ADS)

Roy, Arnab

Subcritical and supercritical fluid injection using a single round injector into a quiescent atmosphere comprising single and binary species was investigated using optical diagnostics. Different disintegration and mixing modes are expected for the two cases. In the binary species case, the atmosphere comprised an inert gas of a different composition than that of the injected fluid. In single species case, the atmosphere consisted of the same species as that of the injected fluid. Density values were quantified and density gradient profiles were inferred from the experimental data. A novel method was applied for the detection of detailed structures throughout the entire jet center plane. Various combinations of injectant and chamber conditions were tested and a wide range of density ratios were covered. The subcritical cases demonstrated the importance of surface tension and inertial forces, while the supercritical cases showed no signs of surface tension and, in most situations, resembled the mixing characteristics of a gaseous jet injected into a gaseous environment. A comparison between the single and binary species systems has also been provided. A detailed laser calibration procedure was undertaken to account for the laser absorption through the gas and liquid phases and for fluorescence in the non-linear excitation regime for high laser pulse energy. Core lengths were measured for binary species cases and correlated with visualization results. An eigenvalue approach was taken to determine the location of maximum gradients for determining the core length. Jet divergence angles were also calculated and were found to increase with chamber-to-injectant density ratio for both systems. A model was proposed for the spreading angle dependence on density ratio for both single and binary species systems and was compared to existing theoretical studies and experimental work. Finally, a linear stability analysis was performed for the jet injected into both subcritical and supercritical atmospheres. The subcritical cases showed good correlation with previous and current experimental results. The supercritical solutions, which have not yet been solved earlier by researchers, are found here through an asymptotic solution of the dispersion equation for exceedingly high Weber numbers.

Radial-based tail methods for Monte Carlo simulations of cylindrical interfaces

NASA Astrophysics Data System (ADS)

Goujon, Florent; Bêche, Bruno; Malfreyt, Patrice; Ghoufi, Aziz

2018-03-01

In this work, we implement for the first time the radial-based tail methods for Monte Carlo simulations of cylindrical interfaces. The efficiency of this method is then evaluated through the calculation of surface tension and coexisting properties. We show that the inclusion of tail corrections during the course of the Monte Carlo simulation impacts the coexisting and the interfacial properties. We establish that the long range corrections to the surface tension are the same order of magnitude as those obtained from planar interface. We show that the slab-based tail method does not amend the localization of the Gibbs equimolar dividing surface. Additionally, a non-monotonic behavior of surface tension is exhibited as a function of the radius of the equimolar dividing surface.

Surface Tension and Viscosity of SCN and SCN-acetone Alloys at Melting Points and Higher Temperatures Using Surface Light Scattering Spectrometer

NASA Technical Reports Server (NTRS)

Tin, Padetha; deGroh, Henry C., III.

2003-01-01

Succinonitrile has been and is being used extensively in NASA's Microgravity Materials Science and Fluid Physics programs and as well as in several ground-based and microgravity studies including the Isothermal Dendritic Growth Experiment (IDGE). Succinonitrile (SCN) is useful as a model for the study of metal solidification, although it is an organic material, it has a BCC crystal structure and solidifies dendriticly like a metal. It is also transparent and has a low melting point (58.08 C). Previous measurements of succinonitrile (SCN) and alloys of succinonitrile and acetone surface tensions are extremely limited. Using the Surface Light Scattering technique we have determined non invasively, the surface tension and viscosity of SCN and SCN-Acetone Alloys at different temperatures. This relatively new and unique technique has several advantages over the classical methods such as, it is non invasive, has good accuracy and measures the surface tension and viscosity simultaneously. The accuracy of interfacial energy values obtained from this technique is better than 2% and viscosity about 10 %. Succinonitrile and succinonitrile-acetone alloys are well-established model materials with several essential physical properties accurately known - except the liquid/vapor surface tension at different elevated temperatures. We will be presenting the experimentally determined liquid/vapor surface energy and liquid viscosity of succinonitrile and succinonitrile-acetone alloys in the temperature range from their melting point to around 100 C using this non-invasive technique. We will also discuss about the measurement technique and new developments of the Surface Light Scattering Spectrometer.

Controlling the Mobility of the Fluid Interface of Moving Gas Bubbles or Liquid Drops by Using Micellar Solutions of Surfactants

NASA Technical Reports Server (NTRS)

Maldarelli, Charles; Papageorgiou, Demetrios

1998-01-01

Microgravity processes must rely on mechanisms other than buoyancy to move bubbles or droplets from one region to another in a continuous liquid phase. One suggested method is thermocapillary migration in which a temperature gradient is applied to the continuous phase. A significant and as yet unresolved impediment to the use of thermocapillary migration to direct bubble or drop motion is that these migrations can be significantly retarded by the adsorption onto the fluid particle surface of surface active impurities unavoidably present in the continuous or (if the particle is a liquid) droplet phases. The focus of our research was to develop a theory for remobilizing fluid particle interfaces retarded by a surfactant impurity in an effort to make more viable the use of thermocapillary migrations for the management of bubbles and drops in microgravity. We postulated that a surfactant at high bulk concentration which kinetically exchanges rapidly with the surface can restore interface mobility. The scaling arguments along with a discussion of the previous literature is reviewed in the context of the scaling framework. The specific objectives of the research were twofold. The first was to prove the remobilization theory by studying a model problem. As the mechanism for remobilization is independent of the force which drives the particle, the fluid particle shape and the presence of fluid inertia, we chose the simplest model consisting of a spherical bubble rising steadily by buoyancy in creeping flow. We solved the hydrodynamic and surfactant transport equations for rapid kinetic exchange to demonstrate that as the concentration increases, the Marangoni retardation at first increases (the low k behavior) and then decreases (the high k behavior). The second objective was to develop a method to determine the kinetic rate constants of a surfactant molecule, since this information is necessary to select surfactants which will exchange rapidly enough relative to the convective rate in the thermocapillary process of interest. To measure the kinetic rate, we measure the dynamic tension change accompanying adsorption onto an initially clean interface, or the re-equilibration in tension when an equilibrium interface is compressed. The dynamic tension measurements are made by a pendant bubble method, in which surfactant adsorbs onto a pendant bubble, and the tension is measured by analyzing the shape change in the bubble. We conclude this report by detailing the publications, presentations and doctoral thesis completed under the auspices of this grant.

Where and why do large shallow intraslab earthquakes occur?

NASA Astrophysics Data System (ADS)

Seno, Tetsuzo; Yoshida, Masaki

2004-03-01

We try to find how often, and in what regions large earthquakes ( M≥7.0) occur within the shallow portion (20-60 km depth) of a subducting slab. Searching for events in published individual studies and the Harvard University centroid moment tensor catalogue, we find twenty such events in E. Hokkaido, Kyushu-SW, Japan, S. Mariana, Manila, Sumatra, Vanuatu, N. Chile, C. Peru, El Salvador, Mexico, N. Cascadia and Alaska. Slab stresses revealed from the mechanism solutions of these large intraslab events and nearby smaller events are almost always down-dip tensional. Except for E. Hokkaido, Manila, and Sumatra, the upper plate shows horizontal stress gradient in the arc-perpendicular direction. We infer that shear tractions are operating at the base of the upper plate in this direction to produce the observed gradient and compression in the outer fore-arc, balancing the down-dip tensional stress of the slab. This tectonic situation in the subduction zone might be realized as part of the convection system with some conditions, as shown by previous numerical simulations.

Testing Machine for Biaxial Loading

NASA Technical Reports Server (NTRS)

Demonet, R. J.; Reeves, R. D.

1985-01-01

Standard tensile-testing machine applies bending and tension simultaneously. Biaxial-loading test machine created by adding two test fixtures to commercial tensile-testing machine. Bending moment applied by substrate-deformation fixture comprising yoke and anvil block. Pneumatic tension-load fixture pulls up on bracket attached to top surface of specimen. Tension and deflection measured with transducers. Modified test apparatus originally developed to load-test Space Shuttle surface-insulation tiles and particuarly important for composite structures.

Analytic theory for the determination of velocity and stability of bubbles in a Hele-Shaw cell. I - Velocity selection. II - Stability

NASA Technical Reports Server (NTRS)

Tanveer, S.

1989-01-01

An asymptotic theory is presented for the determination of velocity and linear stability of a steady symmetric bubble in a Hele-Shaw cell for small surface tension. First the bubble velocity relative to the fluid velocity at infinity is determined for small surface tension by means of a transcendentally small correction to the asymptotic series solution. In addition, a linear stability analysis shows that only the solution branch corresponding to the largest possible bubble velocity for given surface tension is stable, while all the others are unstable.

Surface tension effects on fully developed liquid layer flow over a convex corner

NASA Astrophysics Data System (ADS)

Bhatti, Ifrah; Farid, Saadia; Ullah, Saif; Riaz, Samia; Faryad, Maimoona

2018-04-01

This investigation deals with the study of fully developed liquid layer flow along with surface tension effects, confronting a convex corner in the direction of fluid flow. At the point of interaction, the related equations are formulated using double deck structure and match asymptotic techniques. Linearized solutions for small angle are obtained analytically. The solutions corresponding to similar flow neglecting surface tension effects are also recovered as special case of our general solutions. Finally, the influence of pertinent parameters on the flow, as well as a comparison between models, are shown by graphical illustration.

Flow analysis in a vane-type surface tension propellant tank

NASA Astrophysics Data System (ADS)

Yu, A.; Ji, B.; Zhuang, B. T.; Hu, Q.; Luo, X. W.; Y Xu, H.

2013-12-01

Vane-type surface tension tanks are widely used as the propellant management devices in spacecrafts. This paper treats the two-phase flow inside a vane-type surface tension tank. The study indicates that the present numerical methods such as time-dependent Navier-Stokes equations, VOF model can reasonably predict the flow inside a propellant tank. It is clear that the vane geometry has important effects on transmission performance of the liquid. for a vane type propellant tank, the vane having larger width, folding angle, height of folded side and clearance is preferable if possible.

Surface tension measurements of aqueous ammonium chloride (NH4Cl) in air

NASA Technical Reports Server (NTRS)

Lowry, S. A.; Mccay, M. H.; Mccay, T. D.; Gray, P. A.

1989-01-01

Aqueous NH4Cl's solidification is often used to model metal alloy solidification processes. The present determinations of the magnitude of the variation of aqueous NH4Cl's surface tension as a function of both temperature and solutal concentration were conducted at 3, 24, and 40 C over the 72-100 wt pct water solutal range. In general, the surface tension increases 0.31 dyn/cm per percent decrease in wt pct of water, and decreases 0.13 dyn/cm for each increase in deg C. Attention is given to the experimental apparatus employed.

Evolution of melt-vapor surface tension in silicic volcanic systems: Experiments with hydrous melts

USGS Publications Warehouse

Mangan, M.; Sisson, T.

2005-01-01

We evaluate the melt-vapor surface tension (??) of natural, water-saturated dacite melt at 200 MPa, 950-1055??C, and 4.8-5.7 wt % H2O. We experimentally determine the critical supersaturation pressure for bubble nucleation as a function of dissolved water and then solve for ?? at those conditions using classical nucleation theory. The solutions obtained give dacite melt-vapor surface tensions that vary inversely with dissolved water from 0.042 (??0.003) J m-2 at 5.7 wt% H2O to 0.060 (??0.007) J m-2 at 5.2 wt% H2O to 0.073 (??0.003) J m-2 at 4.8 wt% H2O. Combining our dacite results with data from published hydrous haplogranite and high-silica rhyolite experiments reveals that melt-vapor surface tension also varies inversely with the concentration of mafic melt components (e.g., CaO, FeOtotal, MgO). We develop a thermodynamic context for these observations in which melt-vapor surface tension is represented by a balance of work terms controlled by melt structure. Overall, our results suggest that cooling, crystallization, and vapor exsolution cause systematic changes in ?? that should be considered in dynamic modeling of magmatic processes.

What selects the velocity of fingers and bubbles in a Hele-Shaw cell?

NASA Astrophysics Data System (ADS)

Vasconcelos, Giovani; Mineev-Weinstein, Mark; Brum, Arthur

2017-11-01

It has been widely accepted that surface tension is responsible for the selection of a single pattern out of a continuum of steady solutions for the interface dynamics. Recently, however, it was demonstrated by using time-dependent solutions that surface tension is not required for velocity selection in a Hele-Shaw cell: the velocity is selected entirely within the zero surface tension dynamics, as the selected pattern is the only attractor of the dynamics. These works changed the paradigm regarding the necessity of surface tension for selection, but were limited to a single interface. Here we show that the same selection mechanism holds for any number of interfaces. We present a new class of exact solutions for multiple time-evolving bubbles in a Hele-Shaw cell. The solution is given by a conformal mapping from a multiply connected domain and is written in closed form in terms of certain special functions (the secondary Schottky-Klein prime functions). We demonstrate that the bubbles reach an asymptotic steady velocity, U, which is twice greater than the velocity, V, of the uniform background flow, i.e., U = 2 V . The result does not depend on the number of bubbles. This confirms the prediction that contrary to common belief velocity selection does not require surface tension

Fluoride glass: Crystallization, surface tension

NASA Technical Reports Server (NTRS)

Doremus, R. H.

1988-01-01

Fluoride glass was levitated acoustically in the ACES apparatus on STS-11, and the recovered sample had a different microstructure from samples cooled in a container. Further experiments on levitated samples of fluoride glass are proposed. These include nucleation, crystallization, melting observations, measurement of surface tension of molten glass, and observation of bubbles in the glass. Ground experiments are required on sample preparation, outgassing, and surface reactions. The results should help in the development and evaluation of containerless processing, especially of glass, in the development of a contaminent-free method of measuring surface tensions of melts, in extending knowledge of gas and bubble behavior in fluoride glasses, and in increasing insight into the processing and properties of fluoride glasses.

Determination of surface tension from the measurement of internal pressure of mini soap bubbles

NASA Astrophysics Data System (ADS)

Behroozi, F.; Behroozi, P. S.

2011-11-01

We review the elementary theory that gives the internal pressure of a soap bubble in terms of its radius and surface tension. The theory is generalized to relate the pressure difference across any element of a soap film to its local curvature. This result is used to introduce the concept of the mean curvature of a surface element and is applied to a double soap bubble to obtain the relation between the three radii that characterize its geometry. We also describe a simple setup, suitable for the undergraduate laboratory, to produce mini bubbles and to obtain the surface tension of the soap solution by measuring the radius and internal pressure of the bubbles.

Biosurface engineering through ink jet printing.

PubMed

Khan, Mohidus Samad; Fon, Deniece; Li, Xu; Tian, Junfei; Forsythe, John; Garnier, Gil; Shen, Wei

2010-02-01

The feasibility of thermal ink jet printing as a robust process for biosurface engineering was demonstrated. The strategy investigated was to reconstruct a commercial printer and take advantage of its colour management interface. High printing resolution was achieved by formulating bio-inks of viscosity and surface tension similar to those of commercial inks. Protein and enzyme denaturation during thermal ink jet printing was shown to be insignificant. This is because the time spent by the biomolecules in the heating zone of the printer is negligible; in addition, the air and substrate of high heat capacity absorb any residual heat from the droplet. Gradients of trophic/tropic factors can serve as driving force for cell growth or migration for tissue regeneration. Concentration gradients of proteins were printed on scaffolds to show the capability of ink jet printing. The printed proteins did not desorb upon prolonged immersion in aqueous solutions, thus allowing printed scaffold to be used under in vitro and in vivo conditions. Our group portrait was ink jet printed with a protein on paper, illustrating that complex biopatterns can be printed on large area. Finally, patterns of enzymes were ink jet printed within the detection and reaction zones of a paper diagnostic.

Elasticity-based determination of isovolumetric phases in the human heart

PubMed Central

2010-01-01

Background/Motivation To directly determine isovolumetric cardiac time intervals by magnetic resonance elastography (MRE) using the magnitude of the complex signal for deducing morphological information combined with the phase of the complex signal for tension-relaxation measurements. Methods Thirty-five healthy volunteers and 11 patients with relaxation abnormalities were subjected to transthoracic wave stimulation using vibrations of approximately 25 Hz. A k-space-segmented, ECG-gated gradient-recalled echo steady-state sequence with a 500-Hz bipolar motion-encoding gradient was used for acquiring a series of 360 complex images of a short-axis view of the heart at a frame rate of less than 5.2 ms. Magnitude images were employed for measuring the cross-sectional area of the left ventricle, while phase images were used for analyzing the amplitudes of the externally induced waves. The delay between the decrease in amplitude and onset of ventricular contraction was determined in all subjects and assigned to the time of isovolumetric tension. Conversely, the delay between the increase in wave amplitude and ventricular dilatation was used for measuring the time of isovolumetric elasticity relaxation. Results Wave amplitudes decreased during systole and increased during diastole. The variation in wave amplitude occurred ahead of morphological changes. In healthy volunteers the time of isovolumetric elasticity relaxation was 75 ± 31 ms, which is significantly shorter than the time of isovolumetric tension of 136 ± 36 ms (P < 0.01). In patients with relaxation abnormalities (mild diastolic dysfunction, n = 11) isovolumetric elasticity relaxation was significantly prolonged, with 133 ± 57 ms (P < 0.01), whereas isovolumetric tension time was in the range of healthy controls (161 ± 45 ms; P = 0.053). Conclusion The complex MRE signal conveys complementary information on cardiac morphology and elasticity, which can be combined for directly measuring isovolumetric tension and elasticity relaxation in the human heart. PMID:20979648

Elasticity-based determination of isovolumetric phases in the human heart.

PubMed

Elgeti, Thomas; Beling, Mark; Hamm, Bernd; Braun, Jürgen; Sack, Ingolf

2010-10-27

BACKGROUND/MOTIVATION: To directly determine isovolumetric cardiac time intervals by magnetic resonance elastography (MRE) using the magnitude of the complex signal for deducing morphological information combined with the phase of the complex signal for tension-relaxation measurements. Thirty-five healthy volunteers and 11 patients with relaxation abnormalities were subjected to transthoracic wave stimulation using vibrations of approximately 25 Hz. A k-space-segmented, ECG-gated gradient-recalled echo steady-state sequence with a 500-Hz bipolar motion-encoding gradient was used for acquiring a series of 360 complex images of a short-axis view of the heart at a frame rate of less than 5.2 ms. Magnitude images were employed for measuring the cross-sectional area of the left ventricle, while phase images were used for analyzing the amplitudes of the externally induced waves. The delay between the decrease in amplitude and onset of ventricular contraction was determined in all subjects and assigned to the time of isovolumetric tension. Conversely, the delay between the increase in wave amplitude and ventricular dilatation was used for measuring the time of isovolumetric elasticity relaxation. Wave amplitudes decreased during systole and increased during diastole. The variation in wave amplitude occurred ahead of morphological changes. In healthy volunteers the time of isovolumetric elasticity relaxation was 75 ± 31 ms, which is significantly shorter than the time of isovolumetric tension of 136 ± 36 ms (P < 0.01). In patients with relaxation abnormalities (mild diastolic dysfunction, n = 11) isovolumetric elasticity relaxation was significantly prolonged, with 133 ± 57 ms (P < 0.01), whereas isovolumetric tension time was in the range of healthy controls (161 ± 45 ms; P = 0.053). The complex MRE signal conveys complementary information on cardiac morphology and elasticity, which can be combined for directly measuring isovolumetric tension and elasticity relaxation in the human heart.

Transmembrane Na+ and Ca2+ electrochemical gradients in cardiac muscle and their relationship to force development

PubMed Central

1982-01-01

Na+- and CA2+-sensitive microelectrodes were used to measure intracellular Na+ and Ca2+ activities (alpha iCa) of sheep ventricular muscle and Purkinje strands to study the interrelationship between Na+ and Ca2+ electrochemical gradients (delta muNa and delta muCa) under various conditions. In ventricular muscle, alpha iNa was 6.4 +/- 1.2 mM and alpha iCa was 87 +/- 20 nM ([Ca/+] = 272 nM). A graded decrease of external Na+ activity (alpha oNa) resulted in decrease of alpha iNa, and increase of alpha iCa. There was increase of twitch tension in low- alpha oNa solutions, and occasional increase of resting tension in 40% alpha oNa. Increase of external Ca2+ (alpha oCa) resulted in increase of alpha iCa and decrease of alpha iNa. Decrease of alpha oCa resulted in decrease of alpha iCa and increase of alpha iNa. The apparent resting Na-Ca energy ratio (delta muCa/delta muNa) was between 2.43 and 2.63. When the membrane potential (Vm) was depolarized by 50 mM K+ in ventricular muscle, Vm depolarized by 50 mV, alpha iNa decreased, and alpha iCa increased, with the development of a contracture. The apparent energy coupling ratio did not change with depolarization. 5 x 10(-6) M ouabain induced a large increase in alpha iNa ad alpha iCa, accompanied by an increase in twitch and resting tension. Under the conditions we have studied, delta muNa and delta muCa appeared to be coupled and n was nearly constant at 2.5, as would be expected if the Na-Ca exchange system was able to set the steady level of alpha iCa. Tension threshold was about 230 nM alpha iCa. The magnitude of twitch tension was directly related to alpha iCa. PMID:6292328

A methodology for modeling surface effects on stiff and soft solids

NASA Astrophysics Data System (ADS)

He, Jin; Park, Harold S.

2017-09-01

We present a computational method that can be applied to capture surface stress and surface tension-driven effects in both stiff, crystalline nanostructures, like size-dependent mechanical properties, and soft solids, like elastocapillary effects. We show that the method is equivalent to the classical Young-Laplace model. The method is based on converting surface tension and surface elasticity on a zero-thickness surface to an initial stress and corresponding elastic properties on a finite thickness shell, where the consideration of geometric nonlinearity enables capturing the out-of-plane component of the surface tension that results for curved surfaces through evaluation of the surface stress in the deformed configuration. In doing so, we are able to use commercially available finite element technology, and thus do not require consideration and implementation of the classical Young-Laplace equation. Several examples are presented to demonstrate the capability of the methodology for modeling surface stress in both soft solids and crystalline nanostructures.

A methodology for modeling surface effects on stiff and soft solids

NASA Astrophysics Data System (ADS)

He, Jin; Park, Harold S.

2018-06-01

We present a computational method that can be applied to capture surface stress and surface tension-driven effects in both stiff, crystalline nanostructures, like size-dependent mechanical properties, and soft solids, like elastocapillary effects. We show that the method is equivalent to the classical Young-Laplace model. The method is based on converting surface tension and surface elasticity on a zero-thickness surface to an initial stress and corresponding elastic properties on a finite thickness shell, where the consideration of geometric nonlinearity enables capturing the out-of-plane component of the surface tension that results for curved surfaces through evaluation of the surface stress in the deformed configuration. In doing so, we are able to use commercially available finite element technology, and thus do not require consideration and implementation of the classical Young-Laplace equation. Several examples are presented to demonstrate the capability of the methodology for modeling surface stress in both soft solids and crystalline nanostructures.

Heterogeneous structure and surface tension effects on mechanical response in pulmonary acinus: A finite element analysis.

PubMed

Koshiyama, Kenichiro; Nishimoto, Keisuke; Ii, Satoshi; Sera, Toshihiro; Wada, Shigeo

2018-01-20

The pulmonary acinus is a dead-end microstructure that consists of ducts and alveoli. High-resolution micro-CT imaging has recently provided detailed anatomical information of a complete in vivo acinus, but relating its mechanical response with its detailed acinar structure remains challenging. This study aimed to investigate the mechanical response of acinar tissue in a whole acinus for static inflation using computational approaches. We performed finite element analysis of a whole acinus for static inflation. The acinar structure model was generated based on micro-CT images of an intact acinus. A continuum mechanics model of the lung parenchyma was used for acinar tissue material model, and surface tension effects were explicitly included. An anisotropic mechanical field analysis based on a stretch tensor was combined with a curvature-based local structure analysis. The airspace of the acinus exhibited nonspherical deformation as a result of the anisotropic deformation of acinar tissue. A strain hotspot occurred at the ridge-shaped region caused by a rod-like deformation of acinar tissue on the ridge. The local structure becomes bowl-shaped for inflation and, without surface tension effects, the surface of the bowl-shaped region primarily experiences isotropic deformation. Surface tension effects suppressed the increase in airspace volume and inner surface area, while facilitating anisotropic deformation on the alveolar surface. In the lungs, the heterogeneous acinar structure and surface tension induce anisotropic deformation at the acinar and alveolar scales. Further research is needed on structural variation of acini, inter-acini connectivity, or dynamic behavior to understand multiscale lung mechanics. Copyright © 2018 Elsevier Ltd. All rights reserved.

Fine Tuning of Tissues' Viscosity and Surface Tension through Contractility Suggests a New Role for α-Catenin

PubMed Central

Stirbat, Tomita Vasilica; Mgharbel, Abbas; Bodennec, Selena; Ferri, Karine; Mertani, Hichem C.; Rieu, Jean-Paul; Delanoë-Ayari, Hélène

2013-01-01

What governs tissue organization and movement? If molecular and genetic approaches are able to give some answers on these issues, more and more works are now giving a real importance to mechanics as a key component eventually triggering further signaling events. We chose embryonic cell aggregates as model systems for tissue organization and movement in order to investigate the origin of some mechanical constraints arising from cells organization. Steinberg et al. proposed a long time ago an analogy between liquids and tissues and showed that indeed tissues possess a measurable tissue surface tension and viscosity. We question here the molecular origin of these parameters and give a quantitative measurement of adhesion versus contractility in the framework of the differential interfacial tension hypothesis. Accompanying surface tension measurements by angle measurements (at vertexes of cell-cell contacts) at the cell/medium interface, we are able to extract the full parameters of this model: cortical tensions and adhesion energy. We show that a tunable surface tension and viscosity can be achieved easily through the control of cell-cell contractility compared to cell-medium one. Moreover we show that -catenin is crucial for this regulation to occur: these molecules appear as a catalyser for the remodeling of the actin cytoskeleton underneath cell-cell contact, enabling a differential contractility between the cell-medium and cell-cell interface to take place. PMID:23390488

Effect of temperature and concentration on the surface tension of chia seed mucilage

NASA Astrophysics Data System (ADS)

Fu, Yuting; Arye, Gilboa

2017-04-01

The production of mucilage by the seed coat during hydration is a common adaptation of many different plant species. The mucilage may play many ecological roles in adaptation and seed germination in diverse environments, especially in extreme desert conditions. The major compound of the seed mucilage is polysaccharides (e.g. pectins and hemicelluloses), which makes it highly hydrophilic. Consequently, it can hydrate quickly in the presence of water; forming a gel like coating surrounding the seed. However, the seed mucilage also reported to contain small amounts of protein and lipid which may exhibit surface activity at the water-air interface. As a result, decay in the surface tension of water can be occur and consequently a reduction in soil capillary pressure. This in turn may affect the water retention and transport during seed germination. The physical properties of the seeds mucilage have been studied mainly in conjunction with its rheological properties. To the best of our knowledge, its surface activity at the water-air interface has been reported mainly in the realms of food engineering, using a robust method of extraction. The main objective of this study was to quantify the effect of temperature and concentration on the surface tension of seed mucilage. The mucilage in this study was extracted from chia (Salvia hispanica L.) seeds, using distilled water (1:20 w/w) by shaking for 12 h at 4°C. The extracts were freeze dried after centrifuge (5000rpm for 20min). Fresh samples of different concentrations, ranging from 0.5 to 6 mg/ml, were prepared before each surface tension measurements. The equilibrium surface tension was measured by the Wilhelmy plate method using a tensiometer (DCAT 11, Data Physics) with temperature control unit. For a given mucilage concentration, surface tension measurements carried out at 5, 15, 25, 35, 45 °C. The quantitative and thermodynamic analysis of the results will be presented and discussed.

Transition of Blast Furnace Slag from Silicate Based to Aluminate Based: Density and Surface Tension

NASA Astrophysics Data System (ADS)

Yan, Zhiming; Lv, Xuewei; Pang, Zhengde; Lv, Xueming; Bai, Chenguang

2018-03-01

The effects of the Al2O3 concentration and Al2O3/SiO2 ratio on the density and surface tension of molten aluminosilicate CaO-SiO2-Al2O3-9 mass pct MgO-1 mass pct TiO2 slag were investigated at temperatures from 1723 K to 1823 K (1450 °C to 1550 °C) using the Archimedean method and the maximum bubble pressure (MBP) technique, respectively. The mechanism of the changes in density and surface tension with composition was analyzed from the viewpoint of the degree of polymerization in the structure and the types of oxygen species in the melts. At a fixed CaO/SiO2 ratio of 1.20, the density decreased with increasing Al2O3 content up to 25 mass pct, subsequently increasing. Increasing the Al2O3/SiO2 ratio from 0.47 to 0.92 caused an increase in the density at a fixed CaO content, and the density decreased slightly when the Al2O3/SiO2 ratio was greater than 0.92. Based on the structural information, the density decreased when the Al2O3 content enhanced the network structure and increased when the (Q 2 + Q 3)/(Q 0 + Q 1) ratio and structural complexity decreased. The surface tension increased with increasing Al2O3 content and Al2O3/SiO2 ratio. On the one hand, the surface-active component of SiO2 decreased; on the other hand, the concentration of [AlO4]5- tetrahedra and metal cations that act as charge compensators increased at the melt surface. A model based on the anionic and cationic radii and the Butler equation was employed to predict the surface tension, and an iso-surface tension diagram was obtained at 1773 K (1500 °C).

Transition of Blast Furnace Slag from Silicate Based to Aluminate Based: Density and Surface Tension

NASA Astrophysics Data System (ADS)

Yan, Zhiming; Lv, Xuewei; Pang, Zhengde; Lv, Xueming; Bai, Chenguang

2018-06-01

The effects of the Al2O3 concentration and Al2O3/SiO2 ratio on the density and surface tension of molten aluminosilicate CaO-SiO2-Al2O3-9 mass pct MgO-1 mass pct TiO2 slag were investigated at temperatures from 1723 K to 1823 K (1450 °C to 1550 °C) using the Archimedean method and the maximum bubble pressure (MBP) technique, respectively. The mechanism of the changes in density and surface tension with composition was analyzed from the viewpoint of the degree of polymerization in the structure and the types of oxygen species in the melts. At a fixed CaO/SiO2 ratio of 1.20, the density decreased with increasing Al2O3 content up to 25 mass pct, subsequently increasing. Increasing the Al2O3/SiO2 ratio from 0.47 to 0.92 caused an increase in the density at a fixed CaO content, and the density decreased slightly when the Al2O3/SiO2 ratio was greater than 0.92. Based on the structural information, the density decreased when the Al2O3 content enhanced the network structure and increased when the ( Q 2 + Q 3)/( Q 0 + Q 1) ratio and structural complexity decreased. The surface tension increased with increasing Al2O3 content and Al2O3/SiO2 ratio. On the one hand, the surface-active component of SiO2 decreased; on the other hand, the concentration of [AlO4]5- tetrahedra and metal cations that act as charge compensators increased at the melt surface. A model based on the anionic and cationic radii and the Butler equation was employed to predict the surface tension, and an iso-surface tension diagram was obtained at 1773 K (1500 °C).

In situ droplet surface tension and viscosity measurements in gas metal arc welding

NASA Astrophysics Data System (ADS)

Bachmann, B.; Siewert, E.; Schein, J.

2012-05-01

In this paper, we present an adaptation of a drop oscillation technique that enables in situ measurements of thermophysical properties of an industrial pulsed gas metal arc welding (GMAW) process. Surface tension, viscosity, density and temperature were derived expanding the portfolio of existing methods and previously published measurements of surface tension in pulsed GMAW. Natural oscillations of pure liquid iron droplets are recorded during the material transfer with a high-speed camera. Frame rates up to 30 000 fps were utilized to visualize iron droplet oscillations which were in the low kHz range. Image processing algorithms were employed for edge contour extraction of the droplets and to derive parameters such as oscillation frequencies and damping rates along different dimensions of the droplet. Accurate surface tension measurements were achieved incorporating the effect of temperature on density. These are compared with a second method that has been developed to accurately determine the mass of droplets produced during the GMAW process which enables precise surface tension measurements with accuracies up to 1% and permits the study of thermophysical properties also for metals whose density highly depends on temperature. Thermophysical properties of pure liquid iron droplets formed by a wire with 1.2 mm diameter were investigated in a pulsed GMAW process with a base current of 100 A and a pulse current of 600 A. Surface tension and viscosity of a sample droplet were 1.83 ± 0.02 N m-1 and 2.9 ± 0.3 mPa s, respectively. The corresponding droplet temperature and density are 2040 ± 50 K and 6830 ± 50 kg m-3, respectively.

Water liquid-vapor interface subjected to various electric fields: A molecular dynamics study.

PubMed

Nikzad, Mohammadreza; Azimian, Ahmad Reza; Rezaei, Majid; Nikzad, Safoora

2017-11-28

Investigation of the effects of E-fields on the liquid-vapor interface is essential for the study of floating water bridge and wetting phenomena. The present study employs the molecular dynamics method to investigate the effects of parallel and perpendicular E-fields on the water liquid-vapor interface. For this purpose, density distribution, number of hydrogen bonds, molecular orientation, and surface tension are examined to gain a better understanding of the interface structure. Results indicate enhancements in parallel E-field decrease the interface width and number of hydrogen bonds, while the opposite holds true in the case of perpendicular E-fields. Moreover, perpendicular fields disturb the water structure at the interface. Given that water molecules tend to be parallel to the interface plane, it is observed that perpendicular E-fields fail to realign water molecules in the field direction while the parallel ones easily do so. It is also shown that surface tension rises with increasing strength of parallel E-fields, while it reduces in the case of perpendicular E-fields. Enhancement of surface tension in the parallel field direction demonstrates how the floating water bridge forms between the beakers. Finally, it is found that application of external E-fields to the liquid-vapor interface does not lead to uniform changes in surface tension and that the liquid-vapor interfacial tension term in Young's equation should be calculated near the triple-line of the droplet. This is attributed to the multi-directional nature of the droplet surface, indicating that no constant value can be assigned to a droplet's surface tension in the presence of large electric fields.

Immersed Boundary Simulations of Active Fluid Droplets

PubMed Central

Hawkins, Rhoda J.

2016-01-01

We present numerical simulations of active fluid droplets immersed in an external fluid in 2-dimensions using an Immersed Boundary method to simulate the fluid droplet interface as a Lagrangian mesh. We present results from two example systems, firstly an active isotropic fluid boundary consisting of particles that can bind and unbind from the interface and generate surface tension gradients through active contractility. Secondly, a droplet filled with an active polar fluid with homeotropic anchoring at the droplet interface. These two systems demonstrate spontaneous symmetry breaking and steady state dynamics resembling cell motility and division and show complex feedback mechanisms with minimal degrees of freedom. The simulations outlined here will be useful for quantifying the wide range of dynamics observable in these active systems and modelling the effects of confinement in a consistent and adaptable way. PMID:27606609

Analytical description of concentration dependence of surface tension in multicomponent systems

NASA Astrophysics Data System (ADS)

R, Dadashev; R, Kutuev; D, Elimkhanov

2008-02-01

From the basic fundamental thermodynamic expressions the equation of isotherms of the surface tension of a ternary system is received. Various assumptions concerning the concentration dependence of molar areas are usually made when the equation is derived. The dependence of the molar areas is calculated as an additive function of the structure of a volumetric phase or the structure of a surface layer. To define the concentration dependence of the molar areas we used a stricter thermodynamic expression offered by Butler. In the received equation the dependence of molar areas on the structure of the solution is taken into account. Therefore, the equation can be applied for the calculation of surface tension over a wide concentration range of the components. Unlike the known expressions, the equation includes the surface tension properties of lateral binary systems, which makes the accuracy of the calculated values considerably higher. Thus, among the advantages of the offered equation we can point out the mathematical simplicity of the received equation and the fact that the equation includes physical parameters the experimental definition of which does not present any special difficulties.

The effect of surface tension reduction on the clinical performance of sodium hypochlorite in endodontics.

PubMed

Rossi-Fedele, G; Prichard, J W; Steier, L; de Figueiredo, J A P

2013-06-01

Sodium hypochlorite (NaOCl) is recommended as an endodontic irrigant in view of its broad antimicrobial and tissue dissolution capacities. To enhance its penetration into inaccessible areas of root canals and to improve its overall effect, the addition of surface-active agents has been suggested. The aim of this investigation was to review the effect of the reduction of the surface tension on the performance of NaOCl in endodontics. A search was performed in the Medline electronic database (articles published up to 28 July 2012, in English) with the search terms and combinations as follows: 'sodium hypochlorite AND surface tension or interfacial force or interfacial tension or surface-active agent or amphiphilic agent or surface active agent or surfactant or tenside or detergent'. The purpose of this search was to identify publications that compared NaOCl alone and NaOCl modified with the addition of a surface-active agent in endodontics. A hand search of articles published online ('in-press' and 'early view'), and appearing in the reference list of the articles included, was further performed, using the same search criteria as the electronic search. The search identified 302 publications, of which 11 fulfilled the inclusion/exclusion criteria of the review. The evidence available suggests that surface-active agents improve the penetration of NaOCl in the main canal and have no effect on its pulp tissue dissolution ability. There are, however, insufficient data to enable a sound conclusion to be drawn regarding the effect of modifying NaOCl's surface tension on lubrication, antimicrobial and smear layer or debris removal abilities. © 2012 International Endodontic Journal.

Facile method for preparing superoleophobic surfaces with hierarchical microcubic/nanowire structures

NASA Astrophysics Data System (ADS)

Kwak, Wonshik; Hwang, Woonbong

2016-02-01

To facilitate the fabrication of superoleophobic surfaces having hierarchical microcubic/nanowire structures (HMNS), even for low surface tension liquids including octane (surface tension = 21.1 mN m-1), and to understand the influences of surface structures on the oleophobicity, we developed a convenient method to achieve superoleophobic surfaces on aluminum substrates using chemical acid etching, anodization and fluorination treatment. The liquid repellency of the structured surface was validated through observable experimental results the contact and sliding angle measurements. The etching condition required to ensure high surface roughness was established, and an optimal anodizing condition was determined, as a critical parameter in building the superoleophobicity. The microcubic structures formed by acid etching are essential for achieving the formation of the hierarchical structure, and therefore, the nanowire structures formed by anodization lead to an enhancement of the superoleophobicity for low surface tension liquids. Under optimized morphology by microcubic/nanowire structures with fluorination treatment, the contact angle over 150° and the sliding angle less than 10° are achieved even for octane.

Drops, Sieves, and Paintbrushes: Teaching About Surface Tension

ERIC Educational Resources Information Center

Barnes, George B.

1978-01-01

Surface tension, a characteristic of liquids, is discussed in this article. Several activities appropriate to the elementary grades are described and explained. Each activity uses common materials to explore this tendancy of water to act as if it were surrounded by a membrane. (MA)

A Modified Jaeger's Method for Measuring Surface Tension.

ERIC Educational Resources Information Center

Ntibi, J. Effiom-Edem

1991-01-01

A static method of measuring the surface tension of a liquid is presented. Jaeger's method is modified by replacing the pressure source with a variable pressure head. By using this method, stationary air bubbles are obtained thus resulting in controllable external parameters. (Author/KR)

Analysis of surface cracks in finite plates under tension or bending loads

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.; Raju, I. S.

1979-01-01

Stress-intensity factors calculated with a three-dimensional, finite-element analysis for shallow and deep semielliptical surface cracks in finite elastic isotropic plates subjected to tension or bending loads are presented. A wide range of configuration parameters was investigated. The ratio of crack depth to plate thickness ranged from 0.2 to 0.8 and the ratio of crack depth to crack length ranged from 0.2 to 2.0. The effects of plate width on stress-intensity variations along the crack front was also investigated. A wide-range equation for stress-intensity factors along the crack front as a function of crack depth, crack length, plate thickness, and plate width was developed for tension and bending loads. The equation was used to predict patterns of surface-crack growth under tension or bending fatigue loads. A modified form of the equation was also used to correlate surface-crack fracture data for a brittle epoxy material within + or - 10 percent for a wide range of crack shapes and crack sizes.

Adhesive contact of a rigid circular cylinder to a soft elastic substrate--the role of surface tension.

PubMed

Liu, Tianshu; Jagota, Anand; Hui, Chung-Yuen

2015-05-21

This article studies the effects of surface tension on the adhesive contact mechanics of a long rigid cylinder on an infinite half space comprising an incompressible elastic material. We present an exact solution based on small strain theory. The relationship between the indentation force and contact width was found to depend on a single dimensionless parameter ω = σ/[4(μR)(2/3)(W(ad)/2π)(1/3'), where R is the cylinder radius, Wad is the interfacial work of adhesion, and σ and μ are the surface tension and shear modulus of the half space, respectively. For small ω the solution reduces to the classical Johnson-Kendall-Roberts (JKR) theory, whereas for large ω the solution reduces to the small slope version of the Young-Dupre equation. The pull-off phenomenon was carefully examined and it was found that the contact width at pull-off reduces to zero when surface tension is larger than a critical value.

A micro surface tension pump (MISPU) in a glass microchip.

PubMed

Peng, Xing Yue Larry

2011-01-07

A non-membrane micro surface tension pump (MISPU) was fabricated on a glass microchip by one-step glass etching. It needs no material other than glass and is driven by digital gas pressure. The MISPU can be seen working like a piston pump inside the glass microchip under a microscope. The design of the valves (MISVA) and pistons (MISTON) was based on the surface tension theory of the micro surface tension alveolus (MISTA). The digital gas pressure controls the moving gas-liquid interface to open or close the input and output MISVAs to refill or drive the MISTON for pumping a liquid. Without any moving parts, a MISPU is a kind of long-lasting micro pump for micro chips that does not lose its water pumping efficiency over a 20-day period. The volumetric pump output varied from 0 to 10 nl s(-1) when the pump cycle time decreased from 5 min to 15 s. The pump head pressure was 1 kPa.

SS/RCS surface tension propellant acquisition/expulsion tankage technology program

NASA Technical Reports Server (NTRS)

1974-01-01

An evaluation of published propellant physical property data together with bubble point tests of fine-mesh screen in propellants, was conducted. The effort consisted of: (1) the collection and evaluation of pertinent physical property data for hydrazine (N2H4), monomethylhydrazine (MMH), and nitrogen tetroxide (N2O4); (2) testing to determine the effect of dissolved pressurant gas, temperature, purity, and system cleanliness or contamination on system bubble point, and (3) the compilation and publishing of both the literature and test results. The space shuttle reaction control system (SS/RCS) is a bipropellant system using N2O4 and MMH, while the auxiliary power system (SS/APU) employs monopropellant N2H4. Since both the RCS and the APU use a surface tension device for propellant acquisition, the propellant properties of interest are those which impact the design and operation of surface tension systems. Information on propellant density, viscosity, surface tension, and contact angle was collected, compiled, and evaluated.

Water ball collision

NASA Technical Reports Server (NTRS)

Fujimoto, K.

1986-01-01

What happens if a stainless steel ball hits a water ball in the weightless space ot the Universe? In other words, it was the objective of our experiments in the Space to observe the surface tension of liquid by means of making a solid collide with a liquid. Place a small volume of water between 2 glass sheets to make a thin water membrane: the 2 glass sheets cannot be separated unless an enormous force is applied. It is obvious from this phenomenom that the surface tension of water is far greater than presumed. On Earth, however, it is impossible in most cases to observe only the surface tension of liquid, because gravity always acts on the surface tension. Water and stainless steel balls were chosen the liquid and solids for the experiments. Because water is the liquid most familiar to us, its properties are well known. And it is also of great interest to compare its properties on the Earth with those in the weightless space.

Shock wave-free interface interaction

NASA Astrophysics Data System (ADS)

Frolov, Roman; Minev, Peter; Krechetnikov, Rouslan

2016-11-01

The problem of shock wave-free interface interaction has been widely studied in the context of compressible two-fluid flows using analytical, experimental, and numerical techniques. While various physical effects and possible interaction patterns for various geometries have been identified in the literature, the effects of viscosity and surface tension are usually neglected in such models. In our study, we apply a novel numerical algorithm for simulation of viscous compressible two-fluid flows with surface tension to investigate the influence of these effects on the shock-interface interaction. The method combines together the ideas from Finite Volume adaptation of invariant domains preserving algorithm for systems of hyperbolic conservation laws by Guermond and Popov and ADI parallel solver for viscous incompressible NSEs by Guermond and Minev. This combination has been further extended to a two-fluid flow case, including surface tension effects. Here we report on a quantitative study of how surface tension and viscosity affect the structure of the shock wave-free interface interaction region.

Fuzzy Clustering-Based Modeling of Surface Interactions and Emulsions of Selected Whey Protein Concentrate Combined to i-Carrageenan and Gum Arabic Solutions

USDA-ARS?s Scientific Manuscript database

Gums and proteins are valuable ingredients with a wide spectrum of applications. Surface properties (surface tension, interfacial tension, emulsion activity index “EAI” and emulsion stability index “ESI”) of 4% whey protein concentrate (WPC) in a combination with '- carrageenan (0.05%, 0.1%, and 0.5...

Epitaxially influenced boundary layer model for size effect in thin metallic films

NASA Astrophysics Data System (ADS)

Bažant, Zdeněk P.; Guo, Zaoyang; Espinosa, Horacio D.; Zhu, Yong; Peng, Bei

2005-04-01

It is shown that the size effect recently observed by Espinosa et al., [J. Mech. Phys. Solids51, 47 (2003)] in pure tension tests on free thin metallic films can be explained by the existence of a boundary layer of fixed thickness, located at the surface of the film that was attached onto the substrate during deposition. The boundary layer is influenced by the epitaxial effects of crystal growth on the dislocation density and texture (manifested by prevalent crystal plane orientations). This influence is assumed to cause significantly elevated yield strength. Furthermore, the observed gradual postpeak softening, along with its size independence, which is observed in short film strips subjected to pure tension, is explained by slip localization, originating at notch-like defects, and by damage, which can propagate in a stable manner when the film strip under pure tension is sufficiently thin and short. For general applications, the present epitaxially influenced boundary layer model may be combined with the classical strain-gradient plasticity proposed by Gao et al., [J. Mech. Phys. Solids 47, 1239 (1999)], and it is shown that this combination is necessary to fit the test data on both pure tension and bending of thin films by one and the same theory. To deal with films having different crystal grain sizes, the Hall-Petch relation for the yield strength dependence on the grain size needs to be incorporated into the combined theory. For very thin films, in which a flattened grain fills the whole film thickness, the Hall-Petch relation needs a cutoff, and the asymptotic increase of yield strength with diminishing film thickness is then described by the extension of Nix's model of misfit dislocations by Zhang and Zhou [J. Adv. Mater. 38, 51 (2002)]. The final result is a proposal of a general theory for strength, size effect, hardening, and softening of thin metallic films.

Development of Omniphobic Desalination Membranes Using a Charged Electrospun Nanofiber Scaffold.

PubMed

Lee, Jongho; Boo, Chanhee; Ryu, Won-Hee; Taylor, André D; Elimelech, Menachem

2016-05-04

In this study, we present a facile and scalable approach to fabricate omniphobic nanofiber membranes by constructing multilevel re-entrant structures with low surface energy. We first prepared positively charged nanofiber mats by electrospinning a blend polymer-surfactant solution of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and cationic surfactant (benzyltriethylammonium). Negatively charged silica nanoparticles (SiNPs) were grafted on the positively charged electrospun nanofibers via dip-coating to achieve multilevel re-entrant structures. Grafted SiNPs were then coated with fluoroalkylsilane to lower the surface energy of the membrane. The fabricated membrane showed excellent omniphobicity, as demonstrated by its wetting resistance to various low surface tension liquids, including ethanol with a surface tension of 22.1 mN/m. As a promising application, the prepared omniphobic membrane was tested in direct contact membrane distillation to extract water from highly saline feed solutions containing low surface tension substances, mimicking emerging industrial wastewaters (e.g., from shale gas production). While a control hydrophobic PVDF-HFP nanofiber membrane failed in the desalination/separation process due to low wetting resistance, our fabricated omniphobic membrane exhibited a stable desalination performance for 8 h of operation, successfully demonstrating clean water production from the low surface tension feedwater.

Contact angle and surface tension measurements of a five-ring polyphenyl ether

NASA Technical Reports Server (NTRS)

Jones, W. R., Jr.

1986-01-01

Contact angle measurements were performed for a five-ring polyphenyl ether isomeric mixture on M-50 steel in a dry nitrogen atmosphere. Two different techniques were used: (1) a tilting plate apparatus, and (2) a sessile drop apparatus. Measurements were made for the temperature range 25 to 190 C. Surface tension was measured by a differential maximum bubble pressure technique over the range 23 to 220 C in room air. The critical surface energy of spreading (gamma /sub c/) was determined for the polyphenyl ether by plotting the cosine of the contact angle (theta) versus the surface tension (gamma /sub LV/). The straight line intercept at cosine theta = 1 is defined as gamma (sub c). Gamma (sub c) was found to be 30.1 dyn/cm for the tilting plate technique and 31.3 dyn/cm for the sessile drop technique. These results indicate that the polyphenyl ether is inherently autophobic (i.e., it will not spread on its own surface film until its surface tension is less than gamma /sub c/). This phenomenon is discussed in light of the wettability and wear problems encountered with this fluid.

Contact angle and surface tension measurements of a five-ring polyphenyl ether

NASA Technical Reports Server (NTRS)

Jones, W. R., Jr.

1985-01-01

Contact angle measurements were performed for a five-ring polyphenyl ether isomeric mixture on M-50 steel in a dry nitrogen atmosphere. Two different techniques were used: (1) a tilting plate apparatus, and (2) a sessile drop apparatus. Measurements were made for the temperature range 25 to 190 C. Surface tension was measured by a differential maximum bubble pressure technique over the range 23 to 220C in room air. The critical surface energy of spreading (gamma (sub c)) was determined for the polyphenyl ether by plotting the cosine of the contact angle (theta) versus the surface tension (gamma (sub LV)). The straight line intercept at cosine theta = 1 is defined as gamma (sub c). Gamma (sub c) was found to be 30.1 dyn/cm for the tilting plate technique and 31.3 dyn/cm for the sessile drop technique. These results indicate that the polyphenyl ether is inherently autophobic (i.e., it will not spread on its own surface film until its surface tension is less than gamma (sub c). This phenomenon is discussed in light of the wettability and wear problems encountered with this fluid.

Surface tension mediated conversion of light to work

DOEpatents

Okawa, David; Pastine, Stefan J; Zettl, Alexander K; Frechet, Jean M. J

2014-12-02

Disclosed are a method and apparatus for converting light energy to mechanical energy by modification of surface tension on a supporting fluid. The apparatus comprises an object which may be formed as a composite object comprising a support matrix and a highly light absorptive material. The support matrix may comprise a silicon polymer. The highly light absorptive material may comprise vertically aligned carbon nanotubes (VANTs) embedded in the support matrix. The composite object is supported on a fluid. By exposing the highly light absorptive material to light, heat is generated, which changes the surface tension of the composite object, causing it to move physically within the fluid.

Empirical equation for predicting the surface tension of some liquid metals at their melting point

NASA Astrophysics Data System (ADS)

Ceotto, D.

2014-07-01

A new empirical equation is proposed for predicting the surface tension of some pure metals at their melting point. The investigation has been conducted adopting a statistical approach using some of the most accredited data available in literature. It is found that for Ag, Al, Au, Co, Cu, Fe, Ni, and Pb the surface tension can be conveniently expressed in function of the latent heat of fusion and of the geometrical parameters of an ideal liquid spherical drop. The equation proposed has been compared also with the model proposed by Lu and Jiang giving satisfactory agreement for the metals considered.

Dynamic Bubble Surface Tension Measurements in Northwest Atlantic Seawater

NASA Astrophysics Data System (ADS)

Kieber, D. J.; Long, M. S.; Keene, W. C.; Kinsey, J. D.; Frossard, A. A.; Beaupre, S. R.; Duplessis, P.; Maben, J. R.; Lu, X.; Chang, R.; Zhu, Y.; Bisgrove, J.

2017-12-01

Numerous reports suggest that most organic matter (OM) associated with newly formed primary marine aerosol (PMA) originates from the sea-surface microlayer. However, surface-active OM rapidly adsorbs onto bubble surfaces in the water column and is ejected into the atmosphere when bubbles burst at the air-water interface. Here we present dynamic surface tension measurements of bubbles produced in near surface seawater from biologically productive and oligotrophic sites and in deep seawater collected from 2500 m in the northwest Atlantic. In all cases, the surface tension of bubble surfaces decreased within seconds after the bubbles were exposed to seawater. These observations demonstrate that bubble surfaces are rapidly saturated by surfactant material scavenged from seawater. Spatial and diel variability in bubble surface evolution indicate corresponding variability in surfactant concentrations and/or composition. Our results reveal that surface-active OM is found throughout the water column, and that at least some surfactants are not of recent biological origin. Our results also support the hypothesis that the surface microlayer is a minor to negligible source of OM associated with freshly produced PMA.

Controlled droplet transport to target on a high adhesion surface with multi-gradients

PubMed Central

Deng, Siyan; Shang, Weifeng; Feng, Shile; Zhu, Shiping; Xing, Yan; Li, Dan; Hou, Yongping; Zheng, Yongmei

2017-01-01

We introduce multi-gradients including Laplace pressure gradient, wettable gradient and wettable different gradient on a high adhesion surface via special wedge-pattern and improved anodic oxidation method. As a result of the cooperative effect mentioned above, controlled directional motion of a droplet on a high adhesion surface is realized, even when the surface is turned upside down. The droplet motion can be predicted and the movement distances can be controlled by simply adjusting the wedge angle and droplet volume. More interestingly, when Laplace pressure gradient is introduced on a V-shaped wettable gradient surface, two droplets can move toward one another as designed. PMID:28368020

Indentation of a rigid sphere into an elastic substrate with surface tension and adhesion

PubMed Central

Hui, Chung-Yuen; Liu, Tianshu; Salez, Thomas; Raphael, Elie; Jagota, Anand

2015-01-01

The surface tension of compliant materials such as gels provides resistance to deformation in addition to and sometimes surpassing that owing to elasticity. This paper studies how surface tension changes the contact mechanics of a small hard sphere indenting a soft elastic substrate. Previous studies have examined the special case where the external load is zero, so contact is driven by adhesion alone. Here, we tackle the much more complicated problem where, in addition to adhesion, deformation is driven by an indentation force. We present an exact solution based on small strain theory. The relation between indentation force (displacement) and contact radius is found to depend on a single dimensionless parameter: ω=σ(μR)−2/3((9π/4)Wad)−1/3, where σ and μ are the surface tension and shear modulus of the substrate, R is the sphere radius and Wad is the interfacial work of adhesion. Our theory reduces to the Johnson–Kendall–Roberts (JKR) theory and Young–Dupre equation in the limits of small and large ω, respectively, and compares well with existing experimental data. Our results show that, although surface tension can significantly affect the indentation force, the magnitude of the pull-off load in the partial wetting liquid-like limit is reduced only by one-third compared with the JKR limit and the pull-off behaviour is completely determined by ω. PMID:25792953

Probing microscopic material properties inside simulated membranes through spatially resolved three-dimensional local pressure fields and surface tensions

PubMed Central

Kasson, Peter M.; Hess, Berk; Lindahl, Erik

2013-01-01

Cellular lipid membranes are spatially inhomogeneous soft materials. Materials properties such as pressure and surface tension thus show important microscopic-scale variation that is critical to many biological functions. We present a means to calculate pressure and surface tension in a 3D-resolved manner within molecular-dynamics simulations and show how such measurements can yield important insight. We also present the first corrections to local virial and pressure fields to account for the constraints typically used in lipid simulations that otherwise cause problems in highly oriented systems such as bilayers. Based on simulations of an asymmetric bacterial ion channel in a POPC bilayer, we demonstrate how 3D-resolved pressure can probe for both short-range and long-range effects from the protein on the membrane environment. We also show how surface tension is a sensitive metric for inter-leaflet equilibrium and can be used to detect even subtle imbalances between bilayer leaflets in a membrane-protein simulation. Since surface tension is known to modulate the function of many proteins, this effect is an important consideration for predictions of ion channel function. We outline a strategy by which our local pressure measurements, which we make available within a version of the GROMACS simulation package, may be used to design optimally equilibrated membrane-protein simulations. PMID:23318532

First-order curvature corrections to the surface tension of multicomponent systems.

PubMed

Boltachev, Grey Sh; Baidakov, Vladimir G; Schmelzer, Jürn W P

2003-08-01

The dependence of surface tension on curvature is investigated for the case of an equilibrium phase coexistence in multicomponent systems. Employing Gibbs's method of description of heterogeneous systems, an equation is derived to determine the dependence of surface tension on curvature for widely arbitrary paths of variation of the independent thermodynamic parameters. It is supposed hereby merely that the temperature is kept constant and that the variations of the different molar fractions are such that the radius of the dividing surface varies monotonically in dependence on the change of the state parameters of the ambient phase along any of the chosen paths. In the analysis, an approach developed by Blokhuis and Bedeaux for one-component systems is utilized. It relies on the expansion of the surface free energy on curvature of the dividing surface. An equation is derived that connects the first-order correction term in the expansion with the interaction potential of the particles in the multicomponent solution and with the two-particle distribution functions in the planar interfacial layer between the two phases coexisting in equilibrium at planar interfaces. The connection of the first-order curvature correction to the surface tension and the first moment of the pressure tensor at a planar interface is analyzed as well.

Mixing in Sessile Drops Merging on a Surface

NASA Astrophysics Data System (ADS)

Anna, Shelley; Zhang, Ying; Oberdick, Samuel; Garoff, Stephen

2011-11-01

We investigate the mixing of two sessile drops that merge on a surface. The drops consist of low viscosity glycerol-water mixtures deposited on a silicone elastomer surface with contact angle near 90°. We observe the shape of the drops and the location of their intersection by placing a fluorescent dye in one drop and using a laser light sheet to image a plane perpendicular to the surface. The initial healing of the meniscus bridge between the merging drops, and the damping of capillary waves appearing on their surfaces occur on timescales comparable to the inertio-capillary relaxation time. However, the interface between the two fluids remains sharp, broadening diffusively over several minutes. The shape of the merged drops and the boundary between them also continues to evolve on a timescale of minutes. This later motion is controlled by gravity, capillary pressure, and viscous stresses. Images of the 3D drop shape indicate that small contact line motions are correlated to the slow relaxation. Although the two drops contain identical liquids except for the presence of the dye, the shape of the interface consistently evolves asymmetrically, assuming a characteristic crescent shape. We note that very tiny surface tension gradients can produce an asymmetric flow like the one observed here. We characterize the long timescale flow as a function of the drop sizes, and we use numerical simulations to aid in elucidating the essential physics.

Monitoring massive fracture growth at 2-km depths using surface tiltmeter arrays

USGS Publications Warehouse

Wood, M.D.

1979-01-01

Tilt due to massive hydraulic fractures induced in sedimentary rocks at depths of up to 2.2 km have been recorded by surface tiltmeters. Injection of fluid volumes up to 4 ?? 105 liters and masses of propping agent up to 5 ?? 105 kg is designed to produce fractures approximately 1 km long, 50-100 m high and about 1 cm wide. The surface tilt data adequately fit a dislocation model of a tensional fault in a half-space. Theoretical and observational results indicate that maximum tilt occurs at a distance off the strike of the fracture equivalent to 0.4 of the depth to the fracture. Azimuth and extent of the fracture deduced from the geometry of the tilt field agree with other kinds of geophysical measurements. Detailed correlation of the tilt signatures with pumping parameters (pressure, rate, volume, mass) have provided details on asymmetry in geometry and growth rate. Whereas amplitude variations in tilt vary inversely with the square of the depth, changes in flow rate or pressure gradient can produce a cubic change in width. These studies offer a large-scale experimental approach to the study of problems involving fracturing, mass transport, and dilatancy processes. ?? 1979.

The role of size in synchronous air breathing of Hoplosternum littorale.

PubMed

Sloman, Katherine A; Sloman, Richard D; De Boeck, Gudrun; Scott, Graham R; Iftikar, Fathima I; Wood, Chris M; Almeida-Val, Vera M F; Val, Adalberto L

2009-01-01

Synchronized air breathing may have evolved as a way of minimizing the predation risk known to be associated with air breathing in fish. Little is known about how the size of individuals affects synchronized air breathing and whether some individuals are required to surface earlier than necessary in support of conspecifics, while others delay air intake. Here, the air-breathing behavior of Hoplosternum littorale held in groups or in isolation was investigated in relation to body mass, oxygen tensions, and a variety of other physiological parameters (plasma lactate, hepatic glycogen, hematocrit, hemoglobin, and size of heart, branchial basket, liver, and air-breathing organ [ABO]). A mass-specific relationship with oxygen tension of first surfacing was seen when fish were held in isolation; smaller individuals surfaced at higher oxygen tensions. However, this relationship was lost when the same individuals were held in social groups of four, where synchronous air breathing was observed. In isolation, 62% of fish first surfaced at an oxygen tension lower than the calculated P(crit) (8.13 kPa), but in the group environment this was reduced to 38% of individuals. Higher oxygen tensions at first surfacing in the group environment were related to higher levels of activity rather than any of the physiological parameters measured. In fish held in isolation but denied access to the water surface for 12 h before behavioral testing, there was no mass-specific relationship with oxygen tension at first surfacing. Larger individuals with a greater capacity to store air in their ABOs may, therefore, remain in hypoxic waters for longer periods than smaller individuals when held in isolation unless prior access to the air is prevented. This study highlights how social interaction can affect air-breathing behaviors and the importance of considering both behavioral and physiological responses of fish to hypoxia to understand the survival mechanisms they employ.

Non-equilibrium surface tension of the vapour-liquid interface of active Lennard-Jones particles

NASA Astrophysics Data System (ADS)

Paliwal, Siddharth; Prymidis, Vasileios; Filion, Laura; Dijkstra, Marjolein

2017-08-01

We study a three-dimensional system of self-propelled Brownian particles interacting via the Lennard-Jones potential. Using Brownian dynamics simulations in an elongated simulation box, we investigate the steady states of vapour-liquid phase coexistence of active Lennard-Jones particles with planar interfaces. We measure the normal and tangential components of the pressure tensor along the direction perpendicular to the interface and verify mechanical equilibrium of the two coexisting phases. In addition, we determine the non-equilibrium interfacial tension by integrating the difference of the normal and tangential components of the pressure tensor and show that the surface tension as a function of strength of particle attractions is well fitted by simple power laws. Finally, we measure the interfacial stiffness using capillary wave theory and the equipartition theorem and find a simple linear relation between surface tension and interfacial stiffness with a proportionality constant characterized by an effective temperature.

Fluoroalkylated Silicon-Containing Surfaces - Estimation of Solid Surface Energy

DTIC Science & Technology

2010-10-20

surface tension liquids such as octane (γlv = 21.6 mN/m) and methanol (γlv = 22.7 mN/m), requires an appropriately chosen surface micro/nano-texture in...addition to a low solid surface energy (γsv). 1H,1H,2H,2H- Heptadecafluorodecyl polyhedral oligomeric silsesquioxane (fluorodecyl POSS) offers one of...27.5 mN/m), while Girifalco-Good analysis was performed using a set of polar and non-polar liquids with a wider range of liquid surface tension (15.5

On the temperature derivative of the surface tension at a critical end point

NASA Astrophysics Data System (ADS)

Robert, M.; Tavan, P.

1983-03-01

It is shown that, according to the van der Waals theory of fluid interfaces, the surface tension of the interface between a This result holds for any number of phases and independently varying densities and is not restricted to classical values of the critical exponents.

Singular perturbation of smoothly evolving Hele-Shaw solutions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Siegel, M.; Tanveer, S.

1996-01-01

We present analytical scaling results, confirmed by accurate numerics, to show that there exists a class of smoothly evolving zero surface tension solutions to the Hele-Shaw problem that are significantly perturbed by an arbitrarily small amount of surface tension in order one time. {copyright} {ital 1996 The American Physical Society.}

Creating gradient wetting surfaces via electroless displacement of zinc-coated carbon steel by nickel ions

NASA Astrophysics Data System (ADS)

Xu, Chang; Liu, Huicong; Liang, Weitao; Zhu, Liqun; Li, Weiping; Chen, Haining

2018-03-01

Gradient wetting surfaces are getting increasing attention due to their wide application in multiple fields such as droplet movement and biosorption. However, the fabrication processes of full gradient wetting surfaces are still complex and costly. In present work, a facile and low-cost chemical immersion method was used to create a full gradient wetting surface. By controlling the displacement time in Ni2+ solution, the prepared surfaces perform hydrophilic to superhydrophilic. After being modified by stearic acid, the gradient hydrophilic surfaces convert into hydrophobic. The surface morphology, composition, and wetting behaviors of the as-prepared surfaces were systematically studied and discussed. The gradient wetting property could be attributed to the change in microroughness and surface energy. In addition, these surfaces also exhibited excellent self-cleaning and wax prevention properties. Furthermore, high stability and corrosion resistance were also found for these surfaces, which further highlight their promising practical applications in many fields.

Correlation between Surface Tension and Water Activity in New Particle Formation

NASA Astrophysics Data System (ADS)

Daskalakis, E.; Salameh, A.

2016-12-01

The impact of aerosol properties on cloud dynamics and the radiative balance of the atmosphere relies on the parametrizations of cloud droplet formation. Such parametrization is based on equilibrium thermodynamics proposed by Köhler in 1936. There is considerable debate in the literature on the importance of factors like the surface tension depression or the water activity decrease for the correct parametrization. To gain fundamental insight into New Particle Formation (NPF), or Cloud Condensation Nuclei (CCN) activation one has to study microscopic properties of aqueous droplets, involving surface and bulk dynamics. The surface tension of droplets can be associated with the effects from Organic Matter (OM), whereas the static dielectric constant of water reflects the structure and dynamics of ions within solutions and can present a measure of water activity. In this study we employ Molecular Dynamics Simulations on aquatic droplets that contain surface active OM (acetaldehyde, methylglyoxal) and salts. We give insight into the dynamics of aquatic droplets with radials of 3.6nm at a level of detail that is not accessible experimentally (J. Phys. Chem. C 2016, 120:11508). We propose that as the surface tension of an aquatic droplet is decreased in the presence of surface-active OM, the water activity is affected as well. This is due to the fact that the water dipoles are oriented based on the salt morphology within the droplet. We suggest that the surface tension depression can be accompanied by the water activity change. This can be associated with the possible effects of surface-active species in terms of salt morphology transitions within an aerosol at the NPF and early particle growth time scales. Based on this study, surface-active OM seems important in controlling (a) the salt morphology transitions within a nucleus during NPF and particle growth and (b) a correlation between surface activity and water activity of ionic aquatic droplets. The latter correlation could be a fundamental property to consider when assessing NPF and the Köhler theory.

Oxygen Modulates Human Decidual Natural Killer Cell Surface Receptor Expression and Interactions with Trophoblasts1

PubMed Central

Wallace, Alison E.; Goulwara, Sonu S.; Whitley, Guy S.; Cartwright, Judith E.

2014-01-01

Decidual natural killer (dNK) cells have been shown to both promote and inhibit trophoblast behavior important for decidual remodeling in pregnancy and have a distinct phenotype compared to peripheral blood NK cells. We investigated whether different levels of oxygen tension, mimicking the physiological conditions of the decidua in early pregnancy, altered cell surface receptor expression and activity of dNK cells and their interactions with trophoblast. dNK cells were isolated from terminated first-trimester pregnancies and cultured in oxygen tensions of 3%, 10%, and 21% for 24 h. Cell surface receptor expression was examined by flow cytometry, and the effects of secreted factors in conditioned medium (CM) on the trophoblast cell line SGHPL-4 were assessed in vitro. SGHPL-4 cells treated with dNK cell CM incubated in oxygen tensions of 10% were significantly more invasive (P < 0.05) and formed endothelial-like networks to a greater extent (P < 0.05) than SGHPL-4 cells treated with dNK cell CM incubated in oxygen tensions of 3% or 21%. After 24 h, a lower percentage of dNK cells expressed CD56 at 21% oxygen (P < 0.05), and an increased percentage of dNK cells expressed NKG2D at 10% oxygen (P < 0.05) compared to other oxygen tensions, with large patient variation. This study demonstrates dNK cell phenotype and secreted factors are modulated by oxygen tension, which induces changes in trophoblast invasion and endovascular-like differentiation. Alterations in dNK cell surface receptor expression and secreted factors at different oxygen tensions may represent regulation of function within the decidua during the first trimester of pregnancy. PMID:25232021

Continuum-kinetic-microscopic model of lung clearance due to core-annular fluid entrainment

PubMed Central

Mitran, Sorin

2013-01-01

The human lung is protected against aspirated infectious and toxic agents by a thin liquid layer lining the interior of the airways. This airway surface liquid is a bilayer composed of a viscoelastic mucus layer supported by a fluid film known as the periciliary liquid. The viscoelastic behavior of the mucus layer is principally due to long-chain polymers known as mucins. The airway surface liquid is cleared from the lung by ciliary transport, surface tension gradients, and airflow shear forces. This work presents a multiscale model of the effect of airflow shear forces, as exerted by tidal breathing and cough, upon clearance. The composition of the mucus layer is complex and variable in time. To avoid the restrictions imposed by adopting a viscoelastic flow model of limited validity, a multiscale computational model is introduced in which the continuum-level properties of the airway surface liquid are determined by microscopic simulation of long-chain polymers. A bridge between microscopic and continuum levels is constructed through a kinetic-level probability density function describing polymer chain configurations. The overall multiscale framework is especially suited to biological problems due to the flexibility afforded in specifying microscopic constituents, and examining the effects of various constituents upon overall mucus transport at the continuum scale. PMID:23729842

Polymer Stress-Gradient Induced Migration in Thin Film Flow Over Topography

NASA Astrophysics Data System (ADS)

Tsouka, Sophia; Dimakopoulos, Yiannis; Tsamopoulos, John

2014-11-01

We consider the 2D, steady film flow of a dilute polymer solution over a periodic topography. We examine how the distribution of polymer in the planarization of topographical features is affected by flow intensity and physical properties. The thermodynamically acceptable, Mavrantzas-Beris two-fluid Hamiltonian model is used for polymer migration. The resulting system of differential equations is solved via the mixed FE method combined with an elliptic grid generation scheme. We present numerical results for polymer concentration, stress, velocity and flux of components as a function of the non-dimensional parameters of the problem (Deborah, Peclet, Reynolds and Capillary numbers, ratio of solvent viscosity to total liquid viscosity and geometric features of the topography). Polymer migration to the free surface is enhanced when the cavity gets steeper and deeper. This increases the spatial extent of the polymer depletion layer and induces strong banding in the stresses away from the substrate wall, especially in low polymer concentration. Macromolecules with longer relaxation times are predicted to migrate towards the free surface more easily, while high surface tension combined with a certain range of Reynolds numbers affects the free surface deformations. Work supported by the General Secretariat of Research & Technology of Greece through the program ``Excellence'' (Grant No. 1918) in the framework ``Education and Lifelong Learning'' co-funded by the ESF.

Continuum-kinetic-microscopic model of lung clearance due to core-annular fluid entrainment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mitran, Sorin, E-mail: mitran@unc.edu

2013-07-01

The human lung is protected against aspirated infectious and toxic agents by a thin liquid layer lining the interior of the airways. This airway surface liquid is a bilayer composed of a viscoelastic mucus layer supported by a fluid film known as the periciliary liquid. The viscoelastic behavior of the mucus layer is principally due to long-chain polymers known as mucins. The airway surface liquid is cleared from the lung by ciliary transport, surface tension gradients, and airflow shear forces. This work presents a multiscale model of the effect of airflow shear forces, as exerted by tidal breathing and cough,more » upon clearance. The composition of the mucus layer is complex and variable in time. To avoid the restrictions imposed by adopting a viscoelastic flow model of limited validity, a multiscale computational model is introduced in which the continuum-level properties of the airway surface liquid are determined by microscopic simulation of long-chain polymers. A bridge between microscopic and continuum levels is constructed through a kinetic-level probability density function describing polymer chain configurations. The overall multiscale framework is especially suited to biological problems due to the flexibility afforded in specifying microscopic constituents, and examining the effects of various constituents upon overall mucus transport at the continuum scale.« less

Continuum-kinetic-microscopic model of lung clearance due to core-annular fluid entrainment

NASA Astrophysics Data System (ADS)

Mitran, Sorin

2013-07-01

The human lung is protected against aspirated infectious and toxic agents by a thin liquid layer lining the interior of the airways. This airway surface liquid is a bilayer composed of a viscoelastic mucus layer supported by a fluid film known as the periciliary liquid. The viscoelastic behavior of the mucus layer is principally due to long-chain polymers known as mucins. The airway surface liquid is cleared from the lung by ciliary transport, surface tension gradients, and airflow shear forces. This work presents a multiscale model of the effect of airflow shear forces, as exerted by tidal breathing and cough, upon clearance. The composition of the mucus layer is complex and variable in time. To avoid the restrictions imposed by adopting a viscoelastic flow model of limited validity, a multiscale computational model is introduced in which the continuum-level properties of the airway surface liquid are determined by microscopic simulation of long-chain polymers. A bridge between microscopic and continuum levels is constructed through a kinetic-level probability density function describing polymer chain configurations. The overall multiscale framework is especially suited to biological problems due to the flexibility afforded in specifying microscopic constituents, and examining the effects of various constituents upon overall mucus transport at the continuum scale.

Estimation of changes in alveolar-arterial oxygen gradient induced by hypoxia.

PubMed

Hoffstein, V; Duguid, N; Zamel, N; Rebuck, A S

1984-11-01

The alveolar-arterial oxygen tension difference provides a useful clinical indication of ventilation-blood flow mismatching in the lungs. In some clinical situations involving alveolar hypoxia (e.g., patients with chronic obstructive lung disease flying in commercial aircraft or normal humans at high altitudes) it would be useful to know this tension difference to predict the likely arterial PO2 under such potentially stressful conditions. Such estimates would require multiple arterial punctures performed under a variety of trying circumstances, conditions usually far distant from a suitable analytic facility. Consequently, we induced controlled hypoxia in 23 healthy humans and calculated changes in the alveolar-arterial oxygen tension difference during the hypoxic challenge test. We plotted this difference as a function of the alveolar oxygen tension over a range from 35 to 110 mm Hg. In addition to a series of control studies in which multiple arterial blood samples were obtained, we calculated arterial PO2 by converting the arterial oxyhemoglobin saturation (measured with an ear oximeter) into partial pressure of oxygen. During hypoxic procedures in which levels of oxygenation fell on the steep section of the oxyhemoglobin dissociation curve, fixing PCO2 at constant predetermined levels allowed accurate predictions of arterial PO2. We were able to demonstrate that the alveolar-arterial oxygen tension difference narrowed with decreasing alveolar oxygen tension, and that measurement with an ear oximeter provided data that allowed a reasonable estimate of the tension difference during hypoxic conditions.

RIPPLE - A new model for incompressible flows with free surfaces

NASA Technical Reports Server (NTRS)

Kothe, D. B.; Mjolsness, R. C.

1991-01-01

A new free surface flow model, RIPPLE, is summarized. RIPPLE obtains finite difference solutions for incompressible flow problems having strong surface tension forces at free surfaces of arbitrarily complex topology. The key innovation is the continuum surface force model which represents surface tension as a (strongly) localized volume force. Other features include a higher-order momentum advection model, a volume-of-fluid free surface treatment, and an efficient two-step projection solution method. RIPPLE's unique capabilities are illustrated with two example problems: low-gravity jet-induced tank flow, and the collision and coalescence of two cylindrical rods.

Vapour-liquid interfacial properties of square-well chains from density functional theory and Monte Carlo simulation.

PubMed

Martínez-Ruiz, Francisco José; Blas, Felipe J; Moreno-Ventas Bravo, A Ignacio; Míguez, José Manuel; MacDowell, Luis G

2017-05-17

The statistical associating fluid theory for attractive potentials of variable range (SAFT-VR) density functional theory (DFT) developed by [Gloor et al., J. Chem. Phys., 2004, 121, 12740-12759] is used to predict the interfacial behaviour of molecules modelled as fully-flexible square-well chains formed from tangentially-bonded monomers of diameter σ and potential range λ = 1.5σ. Four different model systems, comprising 4, 8, 12, and 16 monomers per molecule, are considered. In addition to that, we also compute a number of interfacial properties of molecular chains from direct simulation of the vapour-liquid interface. The simulations are performed in the canonical ensemble, and the vapour-liquid interfacial tension is evaluated using the wandering interface (WIM) method, a technique based on the thermodynamic definition of surface tension. Apart from surface tension, we also obtain density profiles, coexistence densities, vapour pressures, and critical temperature and density, paying particular attention to the effect of the chain length on these properties. According to our results, the main effect of increasing the chain length (at fixed temperature) is to sharpen the vapour-liquid interface and to increase the width of the biphasic coexistence region. As a result, the interfacial thickness decreases and the surface tension increases as the molecular chains get longer. The interfacial thickness and surface tension appear to exhibit an asymptotic limiting behaviour for long chains. A similar behaviour is also observed for the coexistence densities and critical properties. Agreement between theory and simulation results indicates that SAFT-VR DFT is only able to predict qualitatively the interfacial properties of the model. Our results are also compared with simulation data taken from the literature, including the vapour-liquid coexistence densities, vapour pressures, and surface tension.

Superhydrophobic-superhydrophilic binary micropatterns by localized thermal treatment of polyhedral oligomeric silsesquioxane (POSS)-silica films

NASA Astrophysics Data System (ADS)

Schutzius, Thomas M.; Bayer, Ilker S.; Jursich, Gregory M.; Das, Arindam; Megaridis, Constantine M.

2012-08-01

Surfaces patterned with alternating (binary) superhydrophobic-superhydrophilic regions can be found naturally, offering a bio-inspired template for efficient fluid collection and management technologies. We describe a simple wet-processing, thermal treatment method to produce such patterns, starting with inherently superhydrophobic polysilsesquioxane-silica composite coatings prepared by spray casting nanoparticle dispersions. Such coatings become superhydrophilic after localized thermal treatment by means of laser irradiation or open-air flame exposure. When laser processed, the films are patternable down to ~100 μm scales. The dispersions consist of hydrophobic fumed silica (HFS) and methylsilsesquioxane resin, which are dispersed in isopropanol and deposited onto various substrates (glass, quartz, aluminum, copper, and stainless steel). The coatings are characterized by advancing, receding, and sessile contact angle measurements before and after thermal treatment to delineate the effects of HFS filler concentration and thermal treatment on coating wettability. SEM, XPS and TGA measurements reveal the effects of thermal treatment on surface chemistry and texture. The thermally induced wettability shift from superhydrophobic to superhydrophilic is interpreted with the Cassie-Baxter wetting theory. Several micropatterned wettability surfaces demonstrate potential in pool boiling heat transfer enhancement, capillarity-driven liquid transport in open surface-tension-confined channels (e.g., lab-on-a-chip), and select surface coating applications relying on wettability gradients. Advantages of the present approach include the inherent stability and inertness of the organosilane-based coatings, which can be applied on many types of surfaces (glass, metals, etc.) with ease. The present method is also scalable to large areas, thus being attractive for industrial coating applications.Surfaces patterned with alternating (binary) superhydrophobic-superhydrophilic regions can be found naturally, offering a bio-inspired template for efficient fluid collection and management technologies. We describe a simple wet-processing, thermal treatment method to produce such patterns, starting with inherently superhydrophobic polysilsesquioxane-silica composite coatings prepared by spray casting nanoparticle dispersions. Such coatings become superhydrophilic after localized thermal treatment by means of laser irradiation or open-air flame exposure. When laser processed, the films are patternable down to ~100 μm scales. The dispersions consist of hydrophobic fumed silica (HFS) and methylsilsesquioxane resin, which are dispersed in isopropanol and deposited onto various substrates (glass, quartz, aluminum, copper, and stainless steel). The coatings are characterized by advancing, receding, and sessile contact angle measurements before and after thermal treatment to delineate the effects of HFS filler concentration and thermal treatment on coating wettability. SEM, XPS and TGA measurements reveal the effects of thermal treatment on surface chemistry and texture. The thermally induced wettability shift from superhydrophobic to superhydrophilic is interpreted with the Cassie-Baxter wetting theory. Several micropatterned wettability surfaces demonstrate potential in pool boiling heat transfer enhancement, capillarity-driven liquid transport in open surface-tension-confined channels (e.g., lab-on-a-chip), and select surface coating applications relying on wettability gradients. Advantages of the present approach include the inherent stability and inertness of the organosilane-based coatings, which can be applied on many types of surfaces (glass, metals, etc.) with ease. The present method is also scalable to large areas, thus being attractive for industrial coating applications. Electronic supplementary information (ESI) available. See DOI: 10.1039/c2nr30979c

Fabrication of high wettability gradient on copper substrate

NASA Astrophysics Data System (ADS)

Huang, Ding-Jun; Leu, Tzong-Shyng

2013-09-01

Copper is one of the most widely used materials in condensation heat transfer. Recently there has been great interest in improving the condensation heat transfer efficiency through copper surface modification. In this study, we describe the fabrication processes of how copper surfaces were modified to be superhydrophilic (CA ≤ 10°) and superhydrophobic (CA > 150°) by means of H2O2 immersion and fluorination with Teflon. The wettability gradient of copper surfaces with contact angles (CA) changing from superhydrophilic to superhydrophobic are also demonstrated. Unlike previous studies on gradient surfaces in which the wettability gradient is controlled either non-precisely or entirely uncontrolled, in this study, the contact angles along wettability gradient copper surfaces vary with a precisely designed gradient. It is demonstrated that a high wettability gradient copper surface can be successfully fabricated using photolithography to define the area ratios between superhydrophilic and superhydrophobic patterns within a short distance. The fabricated wettability gradient of copper surfaces is expected to be able to enhance the condensation heat transfer efficiency.

Thermophysical Property Measurements of Silicon-Transition Metal Alloys

NASA Technical Reports Server (NTRS)

Banish, R. Michael; Erwin, William R.; Sansoucie, Michael P.; Lee, Jonghyun; Gave, Matthew A.

2014-01-01

Metals and metallic alloys often have high melting temperatures and highly reactive liquids. Processing reactive liquids in containers can result in significant contamination and limited undercooling. This is particularly true for molten silicon and it alloys. Silicon is commonly termed "the universal solvent". The viscosity, surface tension, and density of several silicon-transition metal alloys were determined using the Electrostatic Levitator system at the Marshall Space Flight Center. The temperature dependence of the viscosity followed an Arrhenius dependence, and the surface tension followed a linear temperature dependence. The density of the melts, including the undercooled region, showed a linear behavior as well. Viscosity and surface tension values were obtain for several of the alloys in the undercooled region.

Light Meets Water in Nonlocal Media: Surface Tension Analogue in Optics

NASA Astrophysics Data System (ADS)

Horikis, Theodoros P.; Frantzeskakis, Dimitrios J.

2017-06-01

Shallow water wave phenomena find their analogue in optics through a nonlocal nonlinear Schrödinger (NLS) model in 2 +1 dimensions. We identify an analogue of surface tension in optics, namely, a single parameter depending on the degree of nonlocality, which changes the sign of dispersion, much like surface tension does in the shallow water wave problem. Using multiscale expansions, we reduce the NLS model to a Kadomtsev-Petviashvili (KP) equation, which is of the KPII (KPI) type, for strong (weak) nonlocality. We demonstrate the emergence of robust optical antidark solitons forming Y -, X -, and H -shaped wave patterns, which are approximated by colliding KPII line solitons, similar to those observed in shallow waters.

Light Meets Water in Nonlocal Media: Surface Tension Analogue in Optics.

PubMed

Horikis, Theodoros P; Frantzeskakis, Dimitrios J

2017-06-16

Shallow water wave phenomena find their analogue in optics through a nonlocal nonlinear Schrödinger (NLS) model in 2+1 dimensions. We identify an analogue of surface tension in optics, namely, a single parameter depending on the degree of nonlocality, which changes the sign of dispersion, much like surface tension does in the shallow water wave problem. Using multiscale expansions, we reduce the NLS model to a Kadomtsev-Petviashvili (KP) equation, which is of the KPII (KPI) type, for strong (weak) nonlocality. We demonstrate the emergence of robust optical antidark solitons forming Y-, X-, and H-shaped wave patterns, which are approximated by colliding KPII line solitons, similar to those observed in shallow waters.

Thermophysical properties of a highly superheated and undercooled Ni-Si alloy melt

NASA Astrophysics Data System (ADS)

Wang, H. P.; Cao, C. D.; Wei, B.

2004-05-01

The surface tension of superheated and undercooled liquid Ni-5 wt % Si alloy was measured by an electromagnetic oscillating drop method over a wide temperature range from 1417 to 1994 K. The maximum undercooling of 206 K (0.13TL) was achieved. The surface tension of liquid Ni-5 wt % Si alloy is 1.697 N m-1 at the liquidus temperature 1623 K, and its temperature coefficient is -3.97×10-4 N m-1 K-1. On the basis of the experimental data of surface tension, the other thermophysical properties such as the viscosity, the solute diffusion coefficient, and the density of liquid Ni-5 wt % Si alloy were also derived.

Surface Tension and Viscosity Measurements of Liquid and Undercooled Alumina by Containerless Techniques

NASA Astrophysics Data System (ADS)

Paradis, Paul-François; Ishikawa, Takehiko

2005-07-01

Electrostatic levitation and multi-beam radiative heating overcame contamination and sample position instability problems associated with handling of liquid alumina. This allowed the measurements of the surface tension and viscosity in the superheated and undercooled states using the oscillation drop method. Over the 2190-2500 K interval, the surface tension of alumina was measured as σ(T)=0.64--8.2× 10-5 (T-Tm) (N/m), where Tm, the melting temperature, is 2327 K. Similarly, on the same temperature range, the viscosity was determined as η(T)=3.2\\exp[43.2× 103/(RT)] (mPa\\cdots). Both sets of data agree well with the literature values.

Rotational Motion of Axisymmetric Marangoni Swimmers

NASA Astrophysics Data System (ADS)

Rothstein, Jonathan; Uvanovic, Nick

2017-11-01

A series of experiments will be presented investigating the motion of millimeter-sized particles on the surface of water. The particles were partially coated with ethanol and carefully placed on a water interface in a series of Petri dishes with different diameters. High speed particle motion was driven by strong surface tension gradients as the ethanol slowly diffuses from the particles into the water resulting in a Marangoni flow. The velocity and acceleration of the particles where measured. In addition to straight line motion, the presence of the bounding walls of the circular Petri dish was found to induce an asymmetric, rotational motion of the axisymmetric Marangoni swimmers. The rotation rate and radius of curvature was found to be a function of the size of the Petri dish and the curvature of the air-water interface near the edge of the dish. For large Petri dishes or small particles, rotation motion was observed far from the bounding walls. In these cases, the symmetry break appears to be the result of the onset of votex shedding. Finally, multiple spherical particles were observed to undergo assembly driven by capillary forces followed by explosive disassembly.

Moving zone Marangoni drying of wet objects using naturally evaporated solvent vapor

DOEpatents

Britten, Jerald A.

1997-01-01

A surface tension gradient driven flow (a Marangoni flow) is used to remove the thin film of water remaining on the surface of an object following rinsing. The process passively introduces by natural evaporation and diffusion of minute amounts of alcohol (or other suitable material) vapor in the immediate vicinity of a continuously refreshed meniscus of deionized water or another aqueous-based, nonsurfactant rinsing agent. Used in conjunction with cleaning, developing or wet etching application, rinsing coupled with Marangoni drying provides a single-step process for 1) cleaning, developing or etching, 2) rinsing, and 3) drying objects such as flat substrates or coatings on flat substrates without necessarily using heat, forced air flow, contact wiping, centrifugation or large amounts of flammable solvents. This process is useful in one-step cleaning and drying of large flat optical substrates, one-step developing/rinsing and drying or etching/rinsing/drying of large flat patterned substrates and flat panel displays during lithographic processing, and room-temperature rinsing/drying of other large parts, sheets or continuous rolls of material.

Moving zone Marangoni drying of wet objects using naturally evaporated solvent vapor

DOEpatents

Britten, J.A.

1997-08-26

A surface tension gradient driven flow (a Marangoni flow) is used to remove the thin film of water remaining on the surface of an object following rinsing. The process passively introduces by natural evaporation and diffusion of minute amounts of alcohol (or other suitable material) vapor in the immediate vicinity of a continuously refreshed meniscus of deionized water or another aqueous-based, nonsurfactant rinsing agent. Used in conjunction with cleaning, developing or wet etching application, rinsing coupled with Marangoni drying provides a single-step process for (1) cleaning, developing or etching, (2) rinsing, and (3) drying objects such as flat substrates or coatings on flat substrates without necessarily using heat, forced air flow, contact wiping, centrifugation or large amounts of flammable solvents. This process is useful in one-step cleaning and drying of large flat optical substrates, one-step developing/rinsing and drying or etching/rinsing/drying of large flat patterned substrates and flat panel displays during lithographic processing, and room-temperature rinsing/drying of other large parts, sheets or continuous rolls of material. 5 figs.

Numerical study of coupled turbulent flow and solidification for steel slab casters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aboutalebi, M.R.; Hasan, M.; Guthrie, R.I.L.

1995-09-01

A two-dimensional numerical modeling study was undertaken to account for coupled turbulent flow and heat transfer with solidification in the mold and submold regions of a steel slab coaster. Liquid steel is introduced into a water-cooled mold through a bifurcated submerged entry nozzle. Turbulence phenomena in the melt pool of the caster were accounted for, using a modified version of the low-Reynolds-number {kappa}-{epsilon} turbulence model of Launder and Sharma. The mushy region solidification, in the presence of turbulence, was taken into account by modifying the standard enthalpy-porosity technique, which is presently popular for modeling solidification problems. Thermocapillary and buoyancy effectsmore » have been considered in this model to evaluate the influences of the liquid surface tension gradient at the meniscus surface, and natural convection on flow patterns in the liquid pool. Parametric studies were carried out to evaluate the effects of typical variables, such as inlet superheat and casting speed, on the fluid flow and heat transfer results. The numerical predictions were compared with available experimental data.« less

A technique to functionalize and self-assemble macroscopic nanoparticle-ligand monolayer films onto template-free substrates.

PubMed

Fontana, Jake; Spillmann, Christopher; Naciri, Jawad; Ratna, Banahalli R

2014-05-09

This protocol describes a self-assembly technique to create macroscopic monolayer films composed of ligand-coated nanoparticles. The simple, robust and scalable technique efficiently functionalizes metallic nanoparticles with thiol-ligands in a miscible water/organic solvent mixture allowing for rapid grafting of thiol groups onto the gold nanoparticle surface. The hydrophobic ligands on the nanoparticles then quickly phase separate the nanoparticles from the aqueous based suspension and confine them to the air-fluid interface. This drives the ligand-capped nanoparticles to form monolayer domains at the air-fluid interface. The use of water-miscible organic solvents is important as it enables the transport of the nanoparticles from the interface onto template-free substrates. The flow is mediated by a surface tension gradient and creates macroscopic, high-density, monolayer nanoparticle-ligand films. This self-assembly technique may be generalized to include the use of particles of different compositions, size, and shape and may lead to an efficient assembly method to produce low-cost, macroscopic, high-density, monolayer nanoparticle films for wide-spread applications.

Natural convection with evaporation in a vertical cylindrical cavity under the effect of temperature-dependent surface tension

NASA Astrophysics Data System (ADS)

Kozhevnikov, Danil A.; Sheremet, Mikhail A.

2018-01-01

The effect of surface tension on laminar natural convection in a vertical cylindrical cavity filled with a weak evaporating liquid has been analyzed numerically. The cylindrical enclosure is insulated at the bottom, heated by a constant heat flux from the side, and cooled by a non-uniform evaporative heat flux from the top free surface having temperature-dependent surface tension. Governing equations with corresponding boundary conditions formulated in dimensionless stream function, vorticity, and temperature have been solved by finite difference method of the second-order accuracy. The influence of Rayleigh number, Marangoni number, and aspect ratio on the liquid flow and heat transfer has been studied. Obtained results have revealed that the heat transfer rate at free surface decreases with Marangoni number and increases with Rayleigh number, while the average temperature inside the cavity has an opposite behavior; namely, it growths with Marangoni number and reduces with Rayleigh number.

Reduced Capillary Length Scale in the Application of Ostwald Ripening Theory to the Coarsening of Charged Colloidal Crystals in Electrolyte Solutions

NASA Astrophysics Data System (ADS)

Rowe, Jeffrey D.; Baird, James K.

2007-06-01

A colloidal crystal suspended in an electrolyte solution will ordinarily exchange ions with the surrounding solution and develop a net surface charge density and a corresponding double layer. The interfacial tension of the charged surface has contributions arising from: (a) background interfacial tension of the uncharged surface, (b) the entropy associated with the adsorption of ions on the surface, and (c) the polarizing effect of the electrostatic field within the double layer. The adsorption and polarization effects make negative contributions to the surface free energy and serve to reduce the interfacial tension below the value to be expected for the uncharged surface. The diminished interfacial tension leads to a reduced capillary length scale. According to the Ostwald ripening theory of particle coarsening, the reduced capillary length will cause the solute supersaturation to decay more rapidly and the colloidal particles to be smaller in size and greater in number than in the absence of the double layer. Although the length scale for coarsening should be little affected in the case of inorganic colloids, such as AgI, it should be greatly reduced in the case of suspensions of protein crystals, such as apoferritin, catalase, and thaumatin.

A miniature surface tension-driven robot using spatially elliptical moving legs to mimic a water strider's locomotion.

PubMed

Yan, J H; Zhang, X B; Zhao, J; Liu, G F; Cai, H G; Pan, Q M

2015-08-04

The highly agile and efficient water-surface locomotion of the water strider has stimulated substantial interest in biomimetic research. In this paper, we propose a new miniature surface tension-driven robot inspired by the water strider. A key feature of this robot is that its actuating leg possesses an ellipse-like spatial trajectory similar to that of a water strider by using a cam-link mechanism. Simplified models are presented to discuss the leg-water interactions as well as critical conditions for a leg penetrating the water surface, and simulations are performed on the robot's dynamic properties. The final fabricated robot weighs about 3.9 g, and can freely and stably walk on water at different gaits. The maximum forward and turning speeds of the robot are measured as 16 cm s(-1) and 23°/s, respectively. Furthermore, a similarity analysis with Bond number and Weber number demonstrates that the locomotion of this robot is quite analogous to that of a real water strider: the surface tension force dominates the lifting force and plays a major role in the propulsion force. This miniature surface tension-driven robot might have potential applications in many areas such as water quality monitoring and aquatic search and rescue.

Surface Tension Measurements with a Smartphone

ERIC Educational Resources Information Center

Goy, Nicolas-Alexandre; Denis, Zakari; Lavaud, Maxime; Grolleau, Adrian; Dufour, Nicolas; Deblais, Antoine; Delabre, Ulysse

2017-01-01

Smartphones are increasingly used in higher education and at university in mechanics, acoustics, and even thermodynamics as they offer a unique way to do simple science experiments. In this article, we show how smartphones can be used in fluid mechanics to measure surface tension of various liquids, which could help students understand the concept…

Measuring the surface tension of soap bubbles

NASA Technical Reports Server (NTRS)

Sorensen, Carl D.

1992-01-01

The objectives are for students to gain an understanding of surface tension, to see that pressure inside a small bubble is larger than that inside a large bubble. These concepts can be used to explain the behavior of liquid foams as well as precipitate coarsening and grain growth. Equipment, supplies, and procedures are explained.

Measuring the surface tension of soap bubbles

NASA Astrophysics Data System (ADS)

Sorensen, Carl D.

1992-06-01

The objectives are for students to gain an understanding of surface tension, to see that pressure inside a small bubble is larger than that inside a large bubble. These concepts can be used to explain the behavior of liquid foams as well as precipitate coarsening and grain growth. Equipment, supplies, and procedures are explained.

On the balance of stresses in the plasma sheet.

NASA Technical Reports Server (NTRS)

Rich, F. J.; Wolf, R. A.; Vasyliunas, V. M.

1972-01-01

The stress resulting from magnetic tension on the neutral sheet must, in a steady state, be balanced by any one or a combination of (1) a pressure gradient in the direction along the axis of the tail, (2) a similar gradient of plasma flow kinetic energy, and (3) the tension resulting from a pressure anisotropy within the plasma sheet. Stress balance in the first two cases requires that the ratios h/LX and BZ/BX be of the same order of magnitude, where h is the half-thickness of the neutral sheet, LX is the length scale for variations along the axis of the tail, and BZ and BX are the magnetic field components in the plasma sheet just outside the neutral sheet. The second case requires, in addition, that the plasma flow speed within the neutral sheet be of the order of or larger than the Alfven speed outside the neutral sheet. Stress balance in the third case requires that just outside the neutral sheet the plasma pressure obey the marginal firehose stability condition.

Effect of liquid surface tension on circular and linear hydraulic jumps; theory and experiments

NASA Astrophysics Data System (ADS)

Bhagat, Rajesh Kumar; Jha, Narsing Kumar; Linden, Paul F.; Wilson, David Ian

2017-11-01

The hydraulic jump has attracted considerable attention since Rayleigh published his account in 1914. Watson (1964) proposed the first satisfactory explanation of the circular hydraulic jump by balancing the momentum and hydrostatic pressure across the jump, but this solution did not explain what actually causes the jump to form. Bohr et al. (1992) showed that the hydraulic jump happens close to the point where the local Froude number equals to one, suggesting a balance between inertial and hydrostatic contributions. Bush & Aristoff (2003) subsequently incorporated the effect of surface tension and showed that this is important when the jump radius is small. In this study, we propose a new account to explain the formation and evolution of hydraulic jumps under conditions where the jump radius is strongly influenced by the liquid surface tension. The theory is compared with experiments employing liquids of different surface tension and different viscosity, in circular and linear configurations. The model predictions and the experimental results show excellent agreement. Commonwealth Scholarship Commission, St. John's college, University of Cambridge.

Stability Analysis of an Encapsulated Microbubble against Gas Diffusion

PubMed Central

Katiyar, Amit; Sarkar, Kausik

2009-01-01

Linear stability analysis is performed for a mathematical model of diffusion of gases from an encapsulated microbubble. It is an Epstein-Plesset model modified to account for encapsulation elasticity and finite gas permeability. Although, bubbles, containing gases other than air is considered, the final stable bubble, if any, contains only air, and stability is achieved only when the surrounding medium is saturated or oversaturated with air. In absence of encapsulation elasticity, only a neutral stability is achieved for zero surface tension, the other solution being unstable. For an elastic encapsulation, different equilibrium solutions are obtained depending on the saturation level and whether the surface tension is smaller or higher than the elasticity. For an elastic encapsulation, elasticity can stabilize the bubble. However, imposing a non-negativity condition on the effective surface tension (consisting of reference surface tension and the elastic stress) leads to an equilibrium radius which is only neutrally stable. If the encapsulation can support net compressive stress, it achieves actual stability. The linear stability results are consistent with our recent numerical findings. Physical mechanisms for the stability or instability of various equilibriums are provided. PMID:20005522

Marangoni-flow-induced partial coalescence of a droplet on a liquid/air interface

NASA Astrophysics Data System (ADS)

Sun, Kai; Zhang, Peng; Che, Zhizhao; Wang, Tianyou

2018-02-01

The coalescence of a droplet and a liquid/air interface of lower surface tension was numerically studied by using the lattice Boltzmann phase-field method. The experimental phenomenon of droplet ejection observed by Blanchette et al. [Phys. Fluids 21, 072107 (2009), 10.1063/1.3177339] at sufficiently large surface tension differences was successfully reproduced for the first time. Furthermore, the emergence, disappearance, and re-emergence of "partial coalescence" with increasing surface tension difference was observed and explained. The re-emergence of partial coalescence under large surface tension differences is caused by the remarkable lifting motion of the Marangoni flow, which significantly retards the vertical collapse. Two different modes of partial coalescence were identified by the simulation, namely peak injection occurs at lower Ohnesorge numbers and bottom pinch-off at higher Ohnesorge numbers. By comparing the characteristic timescales of the upward Marangoni flow with that of the downward flow driven by capillary pressure, a criterion for the transition from partial to total coalescence was derived based on scaling analysis and numerically validated.

Surface tension and phase coexistence properties of the lattice fluid from a virtual site removal Monte Carlo strategy

NASA Astrophysics Data System (ADS)

Provata, Astero; Prassas, Vassilis D.; Theodorou, Doros N.

1997-10-01

A thin liquid film of lattice fluid in equilibrium with its vapor is studied in 2 and 3 dimensions with canonical Monte Carlo simulation (MC) and Self-Consistent Field Theory (SCF) in the temperature range 0.45Tc to Tc, where Tc the liquid-gas critical temperature. Extending the approach of Oates et al. [Philos. Mag. B 61, 337 (1990)] to anisotropic systems, we develop a method for the MC computation of the transverse and normal pressure profiles, hence of the surface tension, based on virtual removals of individual sites or blocks of sites from the system. Results from implementation of this new method, obtained at very modest computational cost, are in reasonable agreement with exact values and other MC estimates of the surface tension of the 2-d and 3-d model systems, respectively. SCF estimates of the interfacial density profiles, the surface tension, the vapor pressure curve and the binodal curve compare well with MC results away from Tc, but show the expected deviations at high temperatures.

Effects of Frothers and Oil at Saltwater–Air Interfaces for Oil Separation: Molecular Dynamics Simulations and Experimental Measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chong, Leebyn; Lai, Yungchieh; Gray, McMahan

Separating oil from saltwater is a process relevant to some industries and may be aided by bubble and froth generation. Simulating saltwater–air interfaces adsorbed with surfactants and oil molecules can assist in understanding froth stability to improve separation. Here, combining with surface tension experimental measurements, in this work we employ molecular dynamics with a united-atom force field to linear alkane oil and three surfactant frothers, methyl isobutyl carbinol (MIBC), terpineol, and ethyl glycol butyl ether (EGBE), to investigate their synergistic behaviors for oil separation. The interfacial phenomena were measured for a range of frother surface coverages on saltwater. Density profilesmore » of the hydrophilic and hydrophobic portions of the frothers show an expected orientation of alcohol groups adsorbing to the polar water. A decrease in surface tension with increasing surface coverage of MIBC and terpineol was observed and reflected in experiments where the frother concentration increased. Relations between surface coverage and bulk concentration were observed by comparing the surface tension decreases. Additionally, a range of oil surface coverages was explored when the interface has a thin layer of adsorbed frother molecules. Finally, the obtained results indicate that an increase in surface coverage of oil molecules led to an increase in surface tension for all frother types and the pair correlation functions depicted MIBC and terpineol as having higher distributions with water at closer distances than with oil.« less

Effects of Frothers and Oil at Saltwater–Air Interfaces for Oil Separation: Molecular Dynamics Simulations and Experimental Measurements

DOE PAGES

Chong, Leebyn; Lai, Yungchieh; Gray, McMahan; ...

2017-06-16

Separating oil from saltwater is a process relevant to some industries and may be aided by bubble and froth generation. Simulating saltwater–air interfaces adsorbed with surfactants and oil molecules can assist in understanding froth stability to improve separation. Here, combining with surface tension experimental measurements, in this work we employ molecular dynamics with a united-atom force field to linear alkane oil and three surfactant frothers, methyl isobutyl carbinol (MIBC), terpineol, and ethyl glycol butyl ether (EGBE), to investigate their synergistic behaviors for oil separation. The interfacial phenomena were measured for a range of frother surface coverages on saltwater. Density profilesmore » of the hydrophilic and hydrophobic portions of the frothers show an expected orientation of alcohol groups adsorbing to the polar water. A decrease in surface tension with increasing surface coverage of MIBC and terpineol was observed and reflected in experiments where the frother concentration increased. Relations between surface coverage and bulk concentration were observed by comparing the surface tension decreases. Additionally, a range of oil surface coverages was explored when the interface has a thin layer of adsorbed frother molecules. Finally, the obtained results indicate that an increase in surface coverage of oil molecules led to an increase in surface tension for all frother types and the pair correlation functions depicted MIBC and terpineol as having higher distributions with water at closer distances than with oil.« less

[Study of Interaction between Fluorinated Coating Glass and the Medicines].

PubMed

Kawano, Yayoi; Otsu, Saki; Bamba, Takao; Hanawa, Takehisa

2017-11-01

 The adsorption of active pharmaceutical ingredients on the surface of medical devices such as polyvinl chloride, ethylene-vinyl acetate copolymer and glass often prevent the acuurate dose of drug. At dispensing of pharmaceuticals, mètre glass (MG) has been widely used for dispensing syrup. When measuring the viscous syrup, it often takes long time to dispense the accurate volume due to their adhesiveness on the glass surface. In this study, we investigate the adhesion of various syrups to MG made with uncoated glass or glass with a strongly hydrophobic silicone or fluorinated coating in terms of the following formulation parameters: viscosity, surface tension, contact angle, and surface free energy. The contact angles for syrups on the coated glass surfaces were significantly higher than those on the uncoated glass surface. In addition, the relationship between surface tension and contact angle was examined. We found that the contact angle was independent of surface tension for the uncoated glass, while it increased with increasing surface tension for the coated glasses. These results can be explained as follows: the silicone or fluorinated coatings inhibit the hydrogen bonding that usually takes place between water and silanol and siloxane groups at glass surfaces. The coatings reduced the surface free energy and increased the hydrophobicity of the glass, reduced its wettability by the syrups, and thus reduced the adhesion loss for the syrups. It was considered that as for the hydrophobic action, properties of matter of sample influence the coated device by coating in order that it is reinforced.

Characterization of the surface tension and solubility parameter of epoxy resin by using inverse gas chromatography.

PubMed

Shi, Fenghui; Dai, Zhishuang; Zhang, Baoyan

2010-07-01

Inverse gas chromatography (IGC) was used to measure the surface tension and solubility parameter of E51 epoxy resin in this work. By using the Schultz method, decane, nonane, octane and heptane were chosen as the neutral probes to calculate the dispersive surface tensions (gamma(D)). Based on the Good-van Oss equation, the specific surface tension (gamma(SP)) of E51 epoxy resin was calculated with the acidic probe of dichloromethane and the basic probe of toluene. The results showed that the gamma(D) and gamma(SP) of the E51 resin decreased linearly with the increase of temperature. According to the Flory-Huggins parameters (chi) between the resin and a series of probes, the solubility parameters (delta) of E51 resin at different temperatures were estimated using the method developed by DiPaola-Baranyi and Guillet. It was found that the values of delta of the E51 resin were 11.78, 11.57, 11.48 and 11.14 MPa1/2 at 30, 40, 50 and 60 degrees C, respectively. The dispersive component (delta(D)) and the specific component (delta(SP)) of solubility parameter at different temperatures of the E51 resin were investigated according to the relationships between surface tension, cohesion energy and solubility parameter. The results showed that the values of delta(D) were higher than those of delta(SP) for the epoxy resin, and both of them decreased with the increase of temperature.

Solidification phenomena of binary organic mixtures

NASA Technical Reports Server (NTRS)

Chang, K.

1982-01-01

The coalescence rates and motion of liquid bubbles in binary organic mixtures were studied. Several factors such as temperature gradient, composition gradient, interfacial tension, and densities of the two phases play important roles in separation of phases of immiscible liquids. An attempt was made to study the effect of initial compositions on separation rates of well-dispersed organic mixtures at different temperatures and, ultimately, on the homogeneity of solidification of the immiscible binary organic liquids. These organic mixtures serve as models for metallic pseudo binary systems under study. Two specific systems were investigated: ethyl salicylate - diethyl glycol and succinonitrile - water.

The influence of oxygen additions on argon-shielded gas metal arc welding processes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joensson, P.G.; Murphy, A.B.; Szekely, J.

1995-02-01

It has been observed experimentally that small additions of oxygen to the argon shielding gas affect the general operation of GMAW processes. By theoretically modeling the arc column, it is shown that the addition of 2 to 5% oxygen to argon has an insignificant effect on the arc characteristics. This corresponds to the minor changes in the thermophysical transport and thermodynamic properties caused by the oxygen addition. Therefore, it is concluded that the addition of oxygen to the argon shielding gas mainly affects the anode and the cathode regions. From the literature, it was found that the formation of oxidesmore » initiates arcing at the cathode and decreases the movement of the cathode spots. These oxides can also improve the wetting conditions at the workpiece and the electrode. Finally, oxygen is found to affect the surface tension gradient and thereby the convective flow of liquid metal in the weld pool.« less

Low-gravity fluid physics: A program overview

NASA Technical Reports Server (NTRS)

1990-01-01

An overview is presented of the microgravity fluid physics program at Lewis Research Center. One of the main reasons for conducting low gravity research in fluid physics is to study phenomena such as surface tension, interfacial contact angles, and diffusion independent of such gravitationally induced effects as buoyant convection. Fluid physics is at the heart of many space-based technologies including power systems, thermal control systems, and life support systems. Fundamental understanding of fluid physics is a key ingredient to successful space systems design. In addition to describing ground-based and space-based low-gravity facilities, selected experiments are presented which highlight Lewis work in fluid physics. These experiments can be categorized into five theme areas which summarize the work being conducted at Lewis for OSSA: (1) isothermal/iso-solutal capillary phenomena; (2) capillary phenomena with thermal/solutal gradients; (3) thermal-solutal convection; (4) first- and second-order phase transitions in a static fluid; and (5) multiphase flow.

Inclusions in freely suspended smectic films

NASA Astrophysics Data System (ADS)

Stannarius, Ralf; Harth, Kirsten

Smectic liquid crystal phases have a unique property: Like soap solutions, they can form stable freely suspended films. Their aspect ratios can be larger than one million to one. Such films can serve as models for two-dimensional (2D) uids, with or without in-plane anisotropy. Solid or liquid inclusions trapped in these films by capillary forces can move in the film plane and interact with other inclusions, with film thickness gradients or the film boundaries, and even with the local orientation field. We describe preparation techniques to incorporate particles or droplets in thin smectic films, and optical observation methods. Several aspects make inclusions in freely suspended films interesting research objects: They provide rich information on capillary forces as well as surface and interfacial tensions, they can serve as platforms for hydrodynamic studies in 2D, and they may help to understand coalescence dynamics at the transition from 2D to 3D...

Mechanism study and numerical simulation of Uranium nitriding induced by high energy laser

NASA Astrophysics Data System (ADS)

Zhu, Yuan; Xu, Jingjing; Qi, Yanwen; Li, Shengpeng; Zhao, Hui

2018-06-01

The gradients of interfacial tension induced by local heating led to Marangoni convection, which had a significant effect on surface formation and the process of mass transport in the laser nitriding of uranium. An experimental observation of the underlying processes was very difficult. In present study, the Marangoni convection was considered and the computational fluid dynamic (CFD) analysis technique of FLUENT program was performed to determine the physical processes such as heat transfer and mass transport. The progress of gas-liquid falling film desorption was presented by combining phase-change model with fluid volume function (VOF) model. The time-dependent distribution of the temperature had been derived. Moreover, the concentration and distribution of nitrogen across the laser spot are calculated. The simulation results matched with the experimental data. The numerical resolution method provided a better approach to know the physical processes and dependencies of the coating formation.

The impact of dissolved fluorine on bubble nucleation in hydrous rhyolite melts

NASA Astrophysics Data System (ADS)

Gardner, James E.; Hajimirza, Sahand; Webster, James D.; Gonnermann, Helge M.

2018-04-01

Surface tension of hydrous rhyolitic melt is high enough that large degrees of supersaturation are needed to homogeneously nucleate H2O bubbles during eruptive magma ascent. This study examines whether dissolved fluorine lowers surface tension of hydrous rhyolite, and thus lowers the supersaturation required for bubble nucleation. Fluorine was targeted because it, like H2O, changes melt properties and is highly soluble, unlike all other common magmatic volatiles. Rhyolite melts were saturated at Ps = 245 MPa with H2O fluid that contained F, generating rhyolite with 6.7 ± 0.4 wt.% H2O and 1.1-1.3 wt.% F. When these melts were decompressed rapidly to Pf = 149-202 MPa and quenched after 60 s, bubbles nucleated at supersaturations of ΔP = Ps - Pf ≥52 MPa, and reached bubble number densities of NB = 1012-13 m-3 at ΔP = 78-101 MPa. In comparison, rhyolite saturated with 6.34 ± 0.09 wt.% H2O, but only 0.25 wt.% F, did not nucleate bubbles until ΔP ≥ 100-116 MPa, and even then, at significantly lower NB (<1010 m-3). Numerical modeling of bubble nucleation and growth was used to estimate the values of surface tension required to generate the observed values of NB. Slight differences in melt compositions (i.e., alkalinity and H2O content), H2O diffusivity, or melt viscosity cannot explain the observed differences in NB. Instead, surface tension of F-rich rhyolite must be lower by approximately 4% than that of F-poor rhyolite. This difference in surface tension is significant and, for example, exceeds that found between hydrous basaltic andesite and hydrous rhyolite. These results suggest that is likely that surface tension for F-rich magmas, such as topaz rhyolite, is significantly lower than for F-poor magmas.

Development of Maximum Bubble Pressure Method for Surface Tension Measurement of High Viscosity Molten Silicate

NASA Astrophysics Data System (ADS)

Takeda, Osamu; Iwamoto, Hirone; Sakashita, Ryota; Iseki, Chiaki; Zhu, Hongmin

2017-07-01

A surface tension measurement method based on the maximum bubble pressure (MBP) method was developed in order to precisely determine the surface tension of molten silicates in this study. Specifically, the influence of viscosity on surface tension measurements was quantified, and the criteria for accurate measurement were investigated. It was found that the MBP apparently increased with an increase in viscosity. This was because extra pressure was required for the flowing liquid inside the capillary due to viscous resistance. It was also expected that the extra pressure would decrease by decreasing the fluid velocity. For silicone oil with a viscosity of 1000 \\hbox {mPa}{\\cdot }\\hbox {s}, the error on the MBP could be decreased to +1.7 % by increasing the bubble detachment time to 300 \\hbox {s}. However, the error was still over 1 % even when the bubble detachment time was increased to 600 \\hbox {s}. Therefore, a true value of the MBP was determined by using a curve-fitting technique with a simple relaxation function, and that was succeeded for silicone oil at 1000 \\hbox {mPa}{\\cdot } \\hbox {s} of viscosity. Furthermore, for silicone oil with a viscosity as high as 10 000 \\hbox {mPa}{\\cdot }\\hbox {s}, the apparent MBP approached a true value by interrupting the gas introduction during the pressure rising period and by re-introducing the gas at a slow flow rate. Based on the fundamental investigation at room temperature, the surface tension of the \\hbox {SiO}2-40 \\hbox {mol}%\\hbox {Na}2\\hbox {O} and \\hbox {SiO}2-50 \\hbox {mol}%\\hbox {Na}2\\hbox {O} melts was determined at a high temperature. The obtained value was slightly lower than the literature values, which might be due to the influence of viscosity on surface tension measurements being removed in this study.

Tension amplification in tethered layers of bottle-brush polymers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Leuty, Gary M.; Tsige, Mesfin; Grest, Gary S.

2016-02-26

In this paper, molecular dynamics simulations of a coarse-grained bead–spring model have been used to study the effects of molecular crowding on the accumulation of tension in the backbone of bottle-brush polymers tethered to a flat substrate. The number of bottle-brushes per unit surface area, Σ, as well as the lengths of the bottle-brush backbones N bb (50 ≤ N bb ≤ 200) and side chains N sc (50 ≤ N sc ≤ 200) were varied to determine how the dimensions and degree of crowding of bottle-brushes give rise to bond tension amplification along the backbone, especially near the substrate.more » From these simulations, we have identified three separate regimes of tension. For low Σ, the tension is due solely to intramolecular interactions and is dominated by the side chain repulsion that governs the lateral brush dimensions. With increasing Σ, the interactions between bottle-brush polymers induce compression of the side chains, transmitting increasing tension to the backbone. For large Σ, intermolecular side chain repulsion increases, forcing side chain extension and reorientation in the direction normal to the surface and transmitting considerable tension to the backbone.« less

Cable tensioned membrane solar collector module with variable tension control

DOEpatents

Murphy, Lawrence M.

1985-01-01

Disclosed is a solar collector comprising a membrane for concentrating sunlight, a plurality of elongated structural members for suspending the membrane member thereon, and a plurality of control members for adjustably tensioning the membrane member, as well as for controlling a focus produced by the membrane members. Each control member is disposed at a different corresponding one of the plurality of structural members. The collector also comprises an elongated flexible tensioning member, which serves to stretch the membrane member and to thereafter hold it in tension, and a plurality of sleeve members, which serve to provide the membrane member with a desired surface contour during tensioning of the membrane member. The tensioning member is coupled to the structural members such that the tensioning member is adjustably tensioned through the structural members. The tensioning member is also coupled to the membrane member through the sleeve members such that the sleeve members uniformly and symmetrically stretch the membrane member upon applying tension to the tensioning member with the control members.

Cable tensioned membrane solar collector module with variable tension control

DOEpatents

Murphy, L.M.

1984-01-09

Disclosed is a solar collector comprising a membrane member for concentrating sunlight, a plurality of elongated structural members for suspending the membrane member thereon, and a plurality of control members for adjustably tensioning the membrane member, as well as for controlling a focus produced by the membrane members. Each control member is disposed at a different corresponding one of the plurality of structural members. The collector also comprises an elongated flexible tensioning member, which serves to stretch the membrane member and to thereafter hold it in tension, and a plurality of sleeve members which serve to provide the membrane member with a desired surface contour during tensioning of the membrane member. The tensioning member is coupled to the structural members such that the tensioning member is adjustably tensioned through the structural members. The tensioning member is also coupled to the membrane member through the sleeve members such that the sleeve members uniformly and symmetrically stretch the membrane member upon applying tension to the tensioning member with the control members.

Liquid metal actuator driven by electrochemical manipulation of surface tension

NASA Astrophysics Data System (ADS)

Russell, Loren; Wissman, James; Majidi, Carmel

2017-12-01

We examine the electrocapillary properties of a fluidic actuator composed of a liquid metal droplet that is submerged in electrolytic solution and attached to an elastic beam. The beam deflection is controlled by electrochemically driven changes in the surface energy of the droplet. The metal is a eutectic gallium-indium alloy that is liquid at room temperature and forms an nm-thin Ga2O3 skin when oxidized. The effective surface tension of the droplet changes dramatically with oxidation and reduction, which are reversibly controlled by applying low voltage to the electrolytic bath. Wetting the droplet to two copper pads allows for a controllable tensile force to be developed between the opposing surfaces. We demonstrate the ability to reliably control force by changing the applied oxidizing voltage. Actuator forces and droplet geometries are also examined by performing a computational fluid mechanics simulation using Surface Evolver. The theoretical predictions are in qualitative agreement with the experimental measurements and provide additional confirmation that actuation is driven by surface tension.

Giant and switchable surface activity of liquid metal via surface oxidation

PubMed Central

Khan, Mohammad Rashed; Eaker, Collin B.; Bowden, Edmond F.; Dickey, Michael D.

2014-01-01

We present a method to control the interfacial tension of a liquid alloy of gallium via electrochemical deposition (or removal) of the oxide layer on its surface. In sharp contrast with conventional surfactants, this method provides unprecedented lowering of surface tension (∼500 mJ/m2 to near zero) using very low voltage, and the change is completely reversible. This dramatic change in the interfacial tension enables a variety of electrohydrodynamic phenomena. The ability to manipulate the interfacial properties of the metal promises rich opportunities in shape-reconfigurable metallic components in electronic, electromagnetic, and microfluidic devices without the use of toxic mercury. This work suggests that the wetting properties of surface oxides—which are ubiquitous on most metals and semiconductors—are intrinsic “surfactants.” The inherent asymmetric nature of the surface coupled with the ability to actively manipulate its energetics is expected to have important applications in electrohydrodynamics, composites, and melt processing of oxide-forming materials. PMID:25228767

Managing oils pumplessly on open surfaces

NASA Astrophysics Data System (ADS)

Ghosh, Aritra; Morrissette, Jared; Mates, Joseph; Megaridis, Constantine

2017-11-01

Passive management of low-surface-tension liquids (e.g. oils) can be achieved by tuning curvature of liquid volumes (Laplace pressure) on juxtaposed oleophobic/oleophilic domains. Recent advancements in material chemistry in repelling low-surface-tension liquids has enabled researchers to fabricate surfaces and transport oils without the aid of gravity or using a pump. Liquid transport on such surfaces harnesses the force arising from the spatial contrast of surface energy on the substrate, providing rapid fluid actuation. In this work, we demonstrate and study the liquid transport dynamics (velocity, acceleration) in open air for several oils of interest (Jet A, hexadecane, mineral oil) with varying surface tension and viscosity. High-speed image analysis of the motion of the bulk liquid is performed using a droplet-shape tracking algorithm; dominant forces are identified and model predictions are compared with experimental data. Experimental and analytical tools offer new insight on a problem that is relevant to open-surface passive oil transport devices like propellant management devices, oil tankers and many more. Office of Naval Research, Air Force Research Laboratory.

Surface tension propulsion of fungal spores by use of microdroplets

NASA Astrophysics Data System (ADS)

Noblin, Xavier; Yang, Sylvia; Dumais, Jacques

2010-11-01

Most basidiomycete fungi (such as edible mushrooms) actively eject their spores. The process begins with the condensation of a water droplet at the base of the spore. The fusion of the droplet onto the spore creates a momentum that propels the spore forward. The use of surface tension for spore ejection offers a new paradigm to perform work at small length scales. However, this mechanism of force generation remains poorly understood. To elucidate how fungal spores make effective use of surface tension, we performed high-speed video imaging of spore ejection in Auricularia auricula and Sporobolomyces yeast, along with a detailed mechanical analysis of the spore ejection. We developed an explicit relation for the conversion of surface energy into kinetic energy during the coalescence process. The relation was validated with a simple artificial system.

A Technique for Estimating the Surface Conductivity of Single Molecules

NASA Astrophysics Data System (ADS)

Bau, Haim; Arsenault, Mark; Zhao, Hui; Purohit, Prashant; Goldman, Yale

2007-11-01

When an AC electric field at 2MHz was applied across a small gap between two metal electrodes elevated above a surface, rhodamine-phalloidin-labeled actin filaments were attracted to the gap and became suspended between the two electrodes. The variance of each filament's horizontal, lateral displacement was measured as a function of electric field intensity and position along the filament. The variance significantly decreased as the electric field intensity increased. Hypothesizing that the electric field induces electroosmotic flow around the filament that, in turn, induces drag on the filament, which appears as effective tension, we estimated the tension using a linear, Brownian dynamic model. Based on the tension, we estimated the filament's surface conductivity. Our experimental method provides a novel means for trapping and manipulating biological filaments and for probing the surface conductance and mechanical properties of single polymers.

From density to interface fluctuations: The origin of wavelength dependence in surface tension

NASA Astrophysics Data System (ADS)

Hiester, Thorsten

2008-12-01

The height-height correlation function for a fluctuating interface between two coexisting bulk phases is derived by means of general equilibrium properties of the corresponding density-density correlation function. A wavelength-dependent surface tension γ(q) can be defined and expressed in terms of the direct correlation function c(r,r') , the equilibrium density profile ρ0(r) , and an operator which relates density to surface configurations. Neither the concept of an effective interface Hamiltonian nor the difference in pressure is needed to determine the general structure of the height-height correlations or γ(q) , respectively. This result generalizes the Mecke-Dietrich surface tension γMD(q) [Phys. Rev. E 59, 6766 (1999)] and modifies recently published criticism concerning γMD(q) [Tarazona, Checa, and Chacón, Phys. Rev. Lett. 99, 196101 (2007)].

Stress Related Surface Tension Effects in Hard Elastic Polymers.

DTIC Science & Technology

1982-08-19

tension 4, and viscosity and the ,_;.rain imposed csn the materials. Results indicate that these microfi-r! Slated polymers contain a substantia- surface...modulus, 2) large recoverability (up to 98%), 3) ’energetic’ elasticity, and 4) high porosity. This field was thoroughly reviewed by Cannon, McKenna, and...influenced ’N load bearing microfibrils, open to the environment. The stress sensitivity of hard elastic polymers to changes in environmental surface

Measurement of oxygen tension within mesenchymal stem cell spheroids.

PubMed

Murphy, Kaitlin C; Hung, Ben P; Browne-Bourne, Stephen; Zhou, Dejie; Yeung, Jessica; Genetos, Damian C; Leach, J Kent

2017-02-01

Spheroids formed of mesenchymal stem cells (MSCs) exhibit increased cell survival and trophic factor secretion compared with dissociated MSCs, making them therapeutically advantageous for cell therapy. Presently, there is no consensus for the mechanism of action. Many hypothesize that spheroid formation potentiates cell function by generating a hypoxic core within spheroids of sufficiently large diameters. The purpose of this study was to experimentally determine whether a hypoxic core is generated in MSC spheroids by measuring oxygen tension in aggregates of increasing diameter and correlating oxygen tension values with cell function. MSC spheroids were formed with 15 000, 30 000 or 60 000 cells per spheroid, resulting in radii of 176 ± 8 µm, 251 ± 12 µm and 353 ± 18 µm, respectively. Oxygen tension values coupled with mathematical modelling revealed a gradient that varied less than 10% from the outer diameter within the largest spheroids. Despite the modest radial variance in oxygen tension, cellular metabolism from spheroids significantly decreased as the number of cells and resultant spheroid size increased. This may be due to adaptive reductions in matrix deposition and packing density with increases in spheroid diameter, enabling spheroids to avoid the formation of a hypoxic core. Overall, these data provide evidence that the enhanced function of MSC spheroids is not oxygen mediated. © 2017 The Author(s).

On the Onset of Thermocapillary Convection in a Liquid bridge

NASA Astrophysics Data System (ADS)

Shukla, Kedar

Thermo capillary convection refers to motion driven by the application of a temperature gradient along the interface. The temperature gradient may be large enough to cause oscillations in the basic state of the fluid. The vast majority of the liquid bridge investigations performed aboard on the sounding rockets or the space shuttles [1, 2] focused on the float zone processes because the process has been regarded as a candidate for the space based manufacturing of semiconductor materials. Although the buoyancy effect is avoided in the floating zone techniques during space operation, it experiences surface tension driven convection initiated by the temperature gradient along the free surface of the zone [3]. The appearance of the oscillatory thermo capillary convection couples with the solidification processes leads to the striations and results into the degradation of the crystals [4, 5]. The half zone consists of the liquid bridge held between two solid, planar end walls across which a temperature gradient is applied. Thus the basic state of thermo capillary convection consists of a single toroidal roll with the surface motion directed downwards from the hot upper disc to the cold lower one. Bennacer et al [6] studied how different axial profiles of the heat flux affect the flow patterns and transition from ax symmetric steady to ax symmetric oscillatory flow. The three dimensional instability of liquid bridges located between isothermal differentially heated disks were studied by several authors [7-14]. The interface deformation caused by the gravity jitters depends on the volume of the liquid bridge and cause changes in the physical properties of the liquid, which ultimately influence the basic state of the fluid [15-16]. The paper discusses Marangoni convection in a liquid bridge subject to g-jitters in a micro gravity environment. The parametric excitement of the liquid bridge with surface tension variation along with the free surface is considered. We will follow the method of Shukla [17] for Boussinesq flow to model the convective instability in an axisymmetric flow in the liquid bridge. The surface deformation caused by g-jitters and its effects on the onset of oscillatory flow will be examined. References: [1] Grodzka, P.G. and Bannister, T.C., Heat flow and convection demonstration experiments abord Appolo 14, Science (Washington, D.C.), Vol.176, May 1972, pp. 506-508. [2] Bannister, T C., etal, NASA, TMX-64772, 1973. [3] Shukla, K.N. Hydrodynamics of Diffusive Processes, Applied Mechanics Review, Vol.54, No.5, 2001, pp. 391-404. [4] Chen, G., Lizee, A., Roux, B.,, Bifurcation analysis of the thermo capillary convection in cylindrical liquid bridge, J Crystal growth, Vol. 180, 1997, pp.638-647. [5] Imaishi, N., Yasuhiro, S., Akiyama, Y and Yoda, S., Numerical simulation of oscillatory Marangoni flow in half zone liquid bridge of low Prandtl number fluid, J., Crystal Growth, Vol. 230, 2001, pp. 164-171. [6] Bennacer, R., Mohamad, A.A., Leonardi, E., The effect o heat flux distribution on thermo capillary convection in a sideheated liquid bridge, Numer. Heat transfer, Part A, vol. 41, 2002, pp. 657-671. [7] Kuhlmann, H C., Rath, H J., Hydrodynamic instabilities in Cylindrical thermocapillary liquid bridges, J Fluid Mech., Vol. 247,1993, pp. 247-274. [8] Wanshura, M., Shevtsova, V M, Kuhlmann, H C and Rath, H J., Convective instability in thermocapillary liquid bridges, Phys. Fluids, Vol. 7, 1995, pp. 912-925. [9] Kasperski, G., Batoul, A., Labrosse, G., Up to the unsteadiness of axisymmetric thermocapillary low in a laterally heated liquid bridge, Phys. Fluids, Vol. 12, 2000, pp. 103-119. [10] Lappa, M., Savino, R., Monti, R., Three dimensional numerical simulation of Marangoni instabilities in non cylindrical liquid bridges in microgravity, Int. J Heat Mass Transfer, Vol. 44, 2001, pp. 1983-2003 [11] Zeng, Z, Mizuseki, H., Simamura, K., Fukud, T. Higashino, K, Kawaazoe, Y., Three dimensional oscillatory thermocapillary convection in liquid bridgeunder microgravity, Int. J heat Mass Transf., Vol. 44, 2001, pp. 3765-3774. [12] Kamotani, Y., Wang, L, Hatta, S., Wang, A., Yoda, S., Free surface heat loss effect on Oscillatory thermocapillary flow in a liquid bridges of high Prandtl number fluids, Int. J heat Mass Transfer, Vol. 46, 2003, pp. 3211-3220.

Impact of carbon nanotubes based nanofluid on oil recovery efficiency using core flooding

NASA Astrophysics Data System (ADS)

Soleimani, Hassan; Baig, Mirza Khurram; Yahya, Noorhana; Khodapanah, Leila; Sabet, Maziyar; Demiral, Birol M. R.; Burda, Marek

2018-06-01

This study aims to investigate the influence of carbon nanotubes based nanofluid on interfacial tension and oil recovery efficiency. Practically multi-walled carbon nanotubes were successfully synthesized using chemical vapour deposition technique and characterized using X-ray diffraction and Field Emission Scanning Electron microscope in order to understand its structure, shape, and morphology. Nanofluids are one of the interesting new agents for enhanced oil recovery (EOR) that can change the reservoir rock-fluid properties in terms of interfacial tension and wettability. In this work, different concentration of carbon nanotubes based fluids were prepared and the effect of each concentration on surface tension was determined using pendant drop method. After specifying the optimum concentration of carbon nanotubes based nanofluid, core flooding experiment was conducted by two pore volume of brine and two pore volume of nanofluid and then oil recovery factor was calculated. The results show that carbon nanotubes can bring in additional recovery factor of 18.57% in the glass bead sample. It has been observed that nanofluid with high surface tension value gives higher recovery. It was found that the optimum value of concentration is 0.3 wt% at which maximum surface tension of 33.46 mN/m and oil recovery factor of 18.57% was observed. This improvement in recovery factor can be recognized due to interfacial tension reduction and wettability alteration.

Structures associated with strike-slip faults that bound landslide elements

USGS Publications Warehouse

Fleming, R.W.; Johnson, A.M.

1989-01-01

Large landslides are bounded on their flanks and on elements within the landslides by structures analogous to strike-slip faults. We observed the formation of thwse strike-slip faults and associated structures at two large landslides in central Utah during 1983-1985. The strike-slip faults in landslides are nearly vertical but locally may dip a few degrees toward or away from the moving ground. Fault surfaces are slickensided, and striations are subparallel to the ground surface. Displacement along strike-slip faults commonly produces scarps; scarps occur where local relief of the failure surface or ground surface is displaced and becomes adjacent to higher or lower ground, or where the landslide is thickening or thinning as a result of internal deformation. Several types of structures are formed at the ground surface as a strike-slip fault, which is fully developed at some depth below the ground surface, propagates upward in response to displacement. The simplest structure is a tension crack oriented at 45?? clockwise or counterclockwise from the trend of an underlying right- or left-lateral strike-slip fault, respectively. The tension cracks are typically arranged en echelon with the row of cracks parallel to the trace of the underlying strike-slip fault. Another common structure that forms above a developing strike-slip fault is a fault segment. Fault segments are discontinuous strike-slip faults that contain the same sense of slip but are turned clockwise or counterclockwise from a few to perhaps 20?? from the underlying strike-slip fault. The fault segments are slickensided and striated a few centimeters below the ground surface; continued displacement of the landslide causes the fault segments to open and a short tension crack propagates out of one or both ends of the fault segments. These structures, open fault segments containing a short tension crack, are termed compound cracks; and the short tension crack that propagates from the tip of the fault segment is typically oriented 45?? to the trend of the underlying fault. Fault segments are also typically arranged en echelon above the upward-propagating strike-slip fault. Continued displacement of the landslide causes the ground to buckle between the tension crack portions of the compound cracks. Still more displacement produces a thrust fault on one or both limbs of the buckle fold. These compressional structures form at right angles to the short tension cracks at the tips of the fault segments. Thus, the compressional structures are bounded on their ends by one face of a tension crack and detached from underlying material by thrusting or buckling. The tension cracks, fault segments, compound cracks, folds, and thrusts are ephemeral; they are created and destroyed with continuing displacement of the landslide. Ultimately, the structures are replaced by a throughgoing strike-slip fault. At one landslide, we observed the creation and destruction of the ephemeral structures as the landslide enlarged. Displacement of a few centimeters to about a decimeter was sufficient to produce scattered tension cracks and fault segments. Sets of compound cracks with associated folds and thrusts were produced by displacements of up to 1 m, and 1 to 2 m of displacement was required to produce a throughgoing strike-slip fault. The type of first-formed structure above an upward-propagating strike-slip fault is apparently controlled by the rheology of the material. Brittle material such as dry topsoil or the compact surface of a gravel road produces echelon tension cracks and sets of tension cracks and compressional structures, wherein the cracks and compressional structures are normal to each other and 45?? to the strike-slip fault at depth. First-formed structures in more ductile material such as moist cohesive soil are fault segments. In very ductile material such as soft clay and very wet soil in swampy areas, the first-formed structure is a throughgoing strike-slip fault. There are othe

Interfacial properties of acidified skim milk.

PubMed

Cases, E; Rampini, C; Cayot, Ph

2005-02-01

The purpose of this study is to investigate the tension properties and dilatational viscoelastic modulus of various skim milk proteins (whole milk, EDTA-treated milk, beta-casein, and beta-lactoglobulin) at an oil/water interface at 20 degrees C. Measurements are performed using a dynamic drop tensiometer for 15,000 s. The aqueous bulk phase is a skim milk simulated ultrafiltrate containing 11 x 10(-3) g L(-1) milk protein. At pH 6.7, beta-casein appears as the best to decrease the interfacial tension, whereas beta-lactoglobulin leads to the highest interfacial viscoelastic modulus value. Whole milk was almost as surface-active as individual beta-casein in terms of the final (steady-state) lowering of the interfacial tension, but the rate of tension lowering was smaller. EDTA treatment improved the rate of tension lowering of whole milk. The acidification of milk, from previous measurements, would lead to the enhancement of surface activity. At t=15,000 s, the order of effectiveness is pH 4.3 > pH 5.3 = pH 5.6 > pH 6.7 whole milk, suggesting that pH 4.3 whole milk is the best surface active. As compared to pH 6.7 whole milk, the use of pH 5.3 and pH 5.6 milk as surface active would result in the use of milk containing more free beta-casein born of pH-dissociated casein micelles.

Biocompatible patterning of proteins on wettability gradient surface by thermo-transfer printing.

PubMed

Kim, Sungho; Ryu, Yong-Sang; Suh, Jeng-Hun; Keum, Chang-Min; Sohn, Youngjoo; Lee, Sin-Doo

2014-08-01

We develop a simple and biocompatible method of patterning proteins on a wettability gradient surface by thermo-transfer printing. The wettability gradient is produced on a poly(dimethylsiloxane) (PDMS)-modified glass substrate through the temperature gradient during thermo-transfer printing. The water contact angle on the PDMS-modified surface is found to gradually increase along the direction of the temperature gradient from a low to a high temperature region. Based on the wettability gradient, the gradual change in the adsorption and immobilization of proteins (cholera toxin B subunit) is achieved in a microfluidic cell with the PDMS-modified surface.

Surface tension phenomena in the xylem sap of three diffuse porous temperate tree species

Treesearch

K. K. Christensen-Dalsgaard; M. T. Tyree; P. G. Mussone

2011-01-01

In plant physiology models involving bubble nucleation, expansion or elimination, it is typically assumed that the surface tension of xylem sap is equal to that of pure water, though this has never been tested. In this study we collected xylem sap from branches of the tree species Populus tremuloides, Betula papyrifera and Sorbus...

Infinite stream of Hele--Shaw bubbles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burgess, D.; Tanveer, S.

1991-03-01

Exact solutions are presented for a steady stream of bubbles in a Hele--Shaw cell when the effect of surface tension is neglected. These solutions form a three-parameter family. For specified area and distance between bubbles, the speed of the bubble remains arbitrary when surface tension is neglected. However, numerical and analytical evidence indicates that this arbitrariness is removed by the effect of surface tension. The branch of solutions that corresponds to the McLean--Saffman finger solution were primarily studied. A dramatic increase was observed in bubble speeds when the distance between bubbles is on the order of a bubble diameter, whichmore » may have relevance to experiments done by Maxworthy (J. Fluid Mech. {bold 173}, 95 (1986)).« less

Clathrin-Independent Endocytosis Suppresses Cancer Cell Blebbing and Invasion.

PubMed

Holst, Mikkel Roland; Vidal-Quadras, Maite; Larsson, Elin; Song, Jie; Hubert, Madlen; Blomberg, Jeanette; Lundborg, Magnus; Landström, Maréne; Lundmark, Richard

2017-08-22

Cellular blebbing, caused by local alterations in cell-surface tension, has been shown to increase the invasiveness of cancer cells. However, the regulatory mechanisms balancing cell-surface dynamics and bleb formation remain elusive. Here, we show that an acute reduction in cell volume activates clathrin-independent endocytosis. Hence, a decrease in surface tension is buffered by the internalization of the plasma membrane (PM) lipid bilayer. Membrane invagination and endocytosis are driven by the tension-mediated recruitment of the membrane sculpting and GTPase-activating protein GRAF1 (GTPase regulator associated with focal adhesion kinase-1) to the PM. Disruption of this regulation by depleting cells of GRAF1 or mutating key phosphatidylinositol-interacting amino acids in the protein results in increased cellular blebbing and promotes the 3D motility of cancer cells. Our data support a role for clathrin-independent endocytic machinery in balancing membrane tension, which clarifies the previously reported role of GRAF1 as a tumor suppressor. Copyright © 2017 The Author(s). Published by Elsevier Inc. All rights reserved.

Oxygen consumption rate of cells in 3D culture: the use of experiment and simulation to measure kinetic parameters and optimise culture conditions.

PubMed

Streeter, Ian; Cheema, Umber

2011-10-07

Understanding the basal O(2) and nutrient requirements of cells is paramount when culturing cells in 3D tissue models. Any scaffold design will need to take such parameters into consideration, especially as the addition of cells introduces gradients of consumption of such molecules from the surface to the core of scaffolds. We have cultured two cell types in 3D native collagen type I scaffolds, and measured the O(2) tension at specific locations within the scaffold. By changing the density of cells, we have established O(2) consumption gradients within these scaffolds and using mathematical modeling have derived rates of consumption for O(2). For human dermal fibroblasts the average rate constant was 1.19 × 10(-17) mol cell(-1) s(-1), and for human bone marrow derived stromal cells the average rate constant was 7.91 × 10(-18) mol cell(-1) s(-1). These values are lower than previously published rates for similar cells cultured in 2D, but the values established in this current study are more representative of rates of consumption measured in vivo. These values will dictate 3D culture parameters, including maximum cell-seeding density and maximum size of the constructs, for long-term viability of tissue models.

Low Piconewton Towing of CNS Axons against Diffusing and Surface-Bound Repellents Requires the Inhibition of Motor Protein-Associated Pathways

NASA Astrophysics Data System (ADS)

Kilinc, Devrim; Blasiak, Agata; O'Mahony, James J.; Lee, Gil U.

2014-11-01

Growth cones, dynamic structures at axon tips, integrate chemical and physical stimuli and translate them into coordinated axon behaviour, e.g., elongation or turning. External force application to growth cones directs and enhances axon elongation in vitro; however, direct mechanical stimulation is rarely combined with chemotactic stimulation. We describe a microfluidic device that exposes isolated cortical axons to gradients of diffusing and substrate-bound molecules, and permits the simultaneous application of piconewton (pN) forces to multiple individual growth cones via magnetic tweezers. Axons treated with Y-27632, a RhoA kinase inhibitor, were successfully towed against Semaphorin 3A gradients, which repel untreated axons, with less than 12 pN acting on a small number of neural cell adhesion molecules. Treatment with Y-27632 or monastrol, a kinesin-5 inhibitor, promoted axon towing on substrates coated with chondroitin sulfate proteoglycans, potent axon repellents. Thus, modulating key molecular pathways that regulate contractile stress generation in axons counteracts the effects of repellent molecules and promotes tension-induced growth. The demonstration of parallel towing of axons towards inhibitory environments with minute forces suggests that mechanochemical stimulation may be a promising therapeutic approach for the repair of the damaged central nervous system, where regenerating axons face repellent factors over-expressed in the glial scar.

Tension-dependent structural deformation alters single-molecule transition kinetics.

PubMed

Sudhanshu, B; Mihardja, S; Koslover, E F; Mehraeen, S; Bustamante, C; Spakowitz, A J

2011-02-01

We analyze the response of a single nucleosome to tension, which serves as a prototypical biophysical measurement where tension-dependent deformation alters transition kinetics. We develop a statistical-mechanics model of a nucleosome as a wormlike chain bound to a spool, incorporating fluctuations in the number of bases bound, the spool orientation, and the conformations of the unbound polymer segments. With the resulting free-energy surface, we perform dynamic simulations that permit a direct comparison with experiments. This simple approach demonstrates that the experimentally observed structural states at nonzero tension are a consequence of the tension and that these tension-induced states cease to exist at zero tension. The transitions between states exhibit substantial deformation of the unbound polymer segments. The associated deformation energy increases with tension; thus, the application of tension alters the kinetics due to tension-induced deformation of the transition states. This mechanism would arise in any system where the tether molecule is deformed in the transition state under the influence of tension.

Tension-dependent structural deformation alters single-molecule transition kinetics

PubMed Central

Sudhanshu, B.; Mihardja, S.; Koslover, E. F.; Mehraeen, S.; Bustamante, C.; Spakowitz, A. J.

2011-01-01

We analyze the response of a single nucleosome to tension, which serves as a prototypical biophysical measurement where tension-dependent deformation alters transition kinetics. We develop a statistical-mechanics model of a nucleosome as a wormlike chain bound to a spool, incorporating fluctuations in the number of bases bound, the spool orientation, and the conformations of the unbound polymer segments. With the resulting free-energy surface, we perform dynamic simulations that permit a direct comparison with experiments. This simple approach demonstrates that the experimentally observed structural states at nonzero tension are a consequence of the tension and that these tension-induced states cease to exist at zero tension. The transitions between states exhibit substantial deformation of the unbound polymer segments. The associated deformation energy increases with tension; thus, the application of tension alters the kinetics due to tension-induced deformation of the transition states. This mechanism would arise in any system where the tether molecule is deformed in the transition state under the influence of tension. PMID:21245354

Surface tension prevails over solute effect in organic-influenced cloud droplet activation.

PubMed

Ovadnevaite, Jurgita; Zuend, Andreas; Laaksonen, Ari; Sanchez, Kevin J; Roberts, Greg; Ceburnis, Darius; Decesari, Stefano; Rinaldi, Matteo; Hodas, Natasha; Facchini, Maria Cristina; Seinfeld, John H; O' Dowd, Colin

2017-06-29

The spontaneous growth of cloud condensation nuclei (CCN) into cloud droplets under supersaturated water vapour conditions is described by classic Köhler theory. This spontaneous activation of CCN depends on the interplay between the Raoult effect, whereby activation potential increases with decreasing water activity or increasing solute concentration, and the Kelvin effect, whereby activation potential decreases with decreasing droplet size or increases with decreasing surface tension, which is sensitive to surfactants. Surface tension lowering caused by organic surfactants, which diminishes the Kelvin effect, is expected to be negated by a concomitant reduction in the Raoult effect, driven by the displacement of surfactant molecules from the droplet bulk to the droplet-vapour interface. Here we present observational and theoretical evidence illustrating that, in ambient air, surface tension lowering can prevail over the reduction in the Raoult effect, leading to substantial increases in cloud droplet concentrations. We suggest that consideration of liquid-liquid phase separation, leading to complete or partial engulfing of a hygroscopic particle core by a hydrophobic organic-rich phase, can explain the lack of concomitant reduction of the Raoult effect, while maintaining substantial lowering of surface tension, even for partial surface coverage. Apart from the importance of particle size and composition in droplet activation, we show by observation and modelling that incorporation of phase-separation effects into activation thermodynamics can lead to a CCN number concentration that is up to ten times what is predicted by climate models, changing the properties of clouds. An adequate representation of the CCN activation process is essential to the prediction of clouds in climate models, and given the effect of clouds on the Earth's energy balance, improved prediction of aerosol-cloud-climate interactions is likely to result in improved assessments of future climate change.

A finite-volume HLLC-based scheme for compressible interfacial flows with surface tension

NASA Astrophysics Data System (ADS)

Garrick, Daniel P.; Owkes, Mark; Regele, Jonathan D.

2017-06-01

Shock waves are often used in experiments to create a shear flow across liquid droplets to study secondary atomization. Similar behavior occurs inside of supersonic combustors (scramjets) under startup conditions, but it is challenging to study these conditions experimentally. In order to investigate this phenomenon further, a numerical approach is developed to simulate compressible multiphase flows under the effects of surface tension forces. The flow field is solved via the compressible multicomponent Euler equations (i.e., the five equation model) discretized with the finite volume method on a uniform Cartesian grid. The solver utilizes a total variation diminishing (TVD) third-order Runge-Kutta method for time-marching and second order TVD spatial reconstruction. Surface tension is incorporated using the Continuum Surface Force (CSF) model. Fluxes are upwinded with a modified Harten-Lax-van Leer Contact (HLLC) approximate Riemann solver. An interface compression scheme is employed to counter numerical diffusion of the interface. The present work includes modifications to both the HLLC solver and the interface compression scheme to account for capillary force terms and the associated pressure jump across the gas-liquid interface. A simple method for numerically computing the interface curvature is developed and an acoustic scaling of the surface tension coefficient is proposed for the non-dimensionalization of the model. The model captures the surface tension induced pressure jump exactly if the exact curvature is known and is further verified with an oscillating elliptical droplet and Mach 1.47 and 3 shock-droplet interaction problems. The general characteristics of secondary atomization at a range of Weber numbers are also captured in a series of simulations.

A finite-volume HLLC-based scheme for compressible interfacial flows with surface tension

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garrick, Daniel P.; Owkes, Mark; Regele, Jonathan D., E-mail: jregele@iastate.edu

Shock waves are often used in experiments to create a shear flow across liquid droplets to study secondary atomization. Similar behavior occurs inside of supersonic combustors (scramjets) under startup conditions, but it is challenging to study these conditions experimentally. In order to investigate this phenomenon further, a numerical approach is developed to simulate compressible multiphase flows under the effects of surface tension forces. The flow field is solved via the compressible multicomponent Euler equations (i.e., the five equation model) discretized with the finite volume method on a uniform Cartesian grid. The solver utilizes a total variation diminishing (TVD) third-order Runge–Kuttamore » method for time-marching and second order TVD spatial reconstruction. Surface tension is incorporated using the Continuum Surface Force (CSF) model. Fluxes are upwinded with a modified Harten–Lax–van Leer Contact (HLLC) approximate Riemann solver. An interface compression scheme is employed to counter numerical diffusion of the interface. The present work includes modifications to both the HLLC solver and the interface compression scheme to account for capillary force terms and the associated pressure jump across the gas–liquid interface. A simple method for numerically computing the interface curvature is developed and an acoustic scaling of the surface tension coefficient is proposed for the non-dimensionalization of the model. The model captures the surface tension induced pressure jump exactly if the exact curvature is known and is further verified with an oscillating elliptical droplet and Mach 1.47 and 3 shock-droplet interaction problems. The general characteristics of secondary atomization at a range of Weber numbers are also captured in a series of simulations.« less

In situ strain profiling of elastoplastic bending in Ti-6Al-4V alloy by synchrotron energy dispersive x-ray diffraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Croft, M.; National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York 11973; Shukla, V.

Elastic and plastic strain evolution under four-point bending has been studied by synchrotron energy dispersive x-ray diffraction. Measured strain profiles across the specimen thickness showed an increasing linear elastic strain gradient under increasing four-point bending load up to approx2 kN. The bulk elastic modulus of Ti-6Al-4V was determined as 118 GPa. The onset of plastic deformation was found to set in at a total in-plane strain of approx0.008, both under tension and compression. Plastic deformation under bending is initiated in the vicinity of the surface and at a stress of 1100 MPa, and propagates inward, while a finite core regionmore » remains elastically deformed up to 3.67 kN loading. The onset of the plastic regime and the plastic regime itself has been verified by monitoring the line broadening of the (100) peak of alpha-Ti. The effective compression/tension stress-strain curve has been obtained from the scaling collapse of strain profile data taken at seven external load levels. A similar multiple load scaling collapse of the plastic strain variation has also been obtained. The level of precision in strain measurement reported herein was evaluated and found to be 1.5x10{sup -5} or better.« less