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Sample records for charged solvent droplets

  1. Reactions of Microsolvated Organic Compounds at Ambient Surfaces: Droplet Velocity, Charge State, and Solvent Effects

    NASA Astrophysics Data System (ADS)

    Badu-Tawiah, Abraham K.; Campbell, Dahlia I.; Cooks, R. Graham

    2012-06-01

    The exposure of charged microdroplets containing organic ions to solid-phase reagents at ambient surfaces results in heterogeneous ion/surface reactions. The electrosprayed droplets were driven pneumatically in ambient air and then electrically directed onto a surface coated with reagent. Using this reactive soft landing approach, acid-catalyzed Girard condensation was achieved at an ambient surface by directing droplets containing Girard T ions onto a dry keto-steroid. The charged droplet/surface reaction was much more efficient than the corresponding bulk solution-phase reaction performed on the same scale. The increase in product yield is ascribed to solvent evaporation, which causes moderate pH values in the starting droplet to reach extreme values and increases reagent concentrations. Comparisons are made with an experiment in which the droplets were pneumatically accelerated onto the ambient surface (reactive desorption electrospray ionization, DESI). The same reaction products were observed but differences in spatial distribution were seen associated with the "splash" of the high velocity DESI droplets. In a third type of experiment, the reactions of charged droplets with vapor phase reagents were examined by allowing electrosprayed droplets containing a reagent to intercept the headspace vapor of an analyte. Deposition onto a collector surface and mass analysis showed that samples in the vapor phase were captured by the electrospray droplets, and that instantaneous derivatization of the captured sample is possible in the open air. The systems examined under this condition included the derivatization of cortisone vapor with Girard T and that of 4-phenylpyridine N-oxide and 2-phenylacetophenone vapors with ethanolamine.

  2. Electrostatic charging of jumping droplets

    NASA Astrophysics Data System (ADS)

    Miljkovic, Nenad; Preston, Daniel J.; Enright, Ryan; Wang, Evelyn N.

    2013-09-01

    With the broad interest in and development of superhydrophobic surfaces for self-cleaning, condensation heat transfer enhancement and anti-icing applications, more detailed insights on droplet interactions on these surfaces have emerged. Specifically, when two droplets coalesce, they can spontaneously jump away from a superhydrophobic surface due to the release of excess surface energy. Here we show that jumping droplets gain a net positive charge that causes them to repel each other mid-flight. We used electric fields to quantify the charge on the droplets and identified the mechanism for the charge accumulation, which is associated with the formation of the electric double layer at the droplet-surface interface. The observation of droplet charge accumulation provides insight into jumping droplet physics as well as processes involving charged liquid droplets. Furthermore, this work is a starting point for more advanced approaches for enhancing jumping droplet surface performance by using external electric fields to control droplet jumping.

  3. Electrostatic charging of jumping droplets.

    PubMed

    Miljkovic, Nenad; Preston, Daniel J; Enright, Ryan; Wang, Evelyn N

    2013-01-01

    With the broad interest in and development of superhydrophobic surfaces for self-cleaning, condensation heat transfer enhancement and anti-icing applications, more detailed insights on droplet interactions on these surfaces have emerged. Specifically, when two droplets coalesce, they can spontaneously jump away from a superhydrophobic surface due to the release of excess surface energy. Here we show that jumping droplets gain a net positive charge that causes them to repel each other mid-flight. We used electric fields to quantify the charge on the droplets and identified the mechanism for the charge accumulation, which is associated with the formation of the electric double layer at the droplet-surface interface. The observation of droplet charge accumulation provides insight into jumping droplet physics as well as processes involving charged liquid droplets. Furthermore, this work is a starting point for more advanced approaches for enhancing jumping droplet surface performance by using external electric fields to control droplet jumping.

  4. Charged Slurry Droplet Research

    DTIC Science & Technology

    1989-02-20

    verified that -a’/1’ is a constant for a wide variety of fluids including No. 2 Heating Oil and Jet -A, to name but two. Equally startling are the...for a large droplet against 1-g conditions has only been achieved before in the Jet Propulsion Laboratory at California Institute of Technology 10...Drop Levitation Against Gravity," IEEE - CH2272 ( Jet Propulsion Laboratory, California Institute of Technology), 1986, pp. 1338 - 1341. [11] Rhim, Won

  5. Droplet Charging Effects in the Space Environment

    SciTech Connect

    Joslyn, Thomas B.; Ketsdever, Andrew D.

    2011-05-20

    Several applications exist for transiting liquid droplets through the near-Earth space environment. Numerical results are presented for the charging of liquid droplets of trimethyl pentaphenyl siloxane (DC705) in three different plasma environments: ionosphere, auroral, and geosynchronous Earth orbit (GEO). Nominal and high geomagnetic activity cases are investigated. In general, high levels of droplet charging (>100 V) exist only in GEO during periods of high geomagnetic or solar activity. An experiment was conducted to assess the charging of silicon-oil droplets due to photoemission. The photoemission yield in the 120-200 nm wavelength range was found to be approximately 0.06.

  6. Characterization of "Star" Droplet Morphologies Induced by Charged Macromolecules.

    PubMed

    Sharawy, Mahmoud; Consta, Styliani

    2016-11-10

    "Star" morphologies of charged liquid droplets are distinct droplet conformations that, for a certain charge squared to volume ratio, have lower energy than their spherically shaped analogues. For these shapes to appear, the charge should be carried by a single ionic species. A typical example of a charge carrier that we employ in this study is a fully charged double-stranded oligodeoxynucleotide (dsDNA) in an aqueous and an acetonitrile droplet. We characterize the structure and dynamics of the star-shaped droplets. We find that by increasing the charge squared to volume ratio, the droplet evolves from spherical to "spiky" shapes, by first passing from droplet sizes that undergo enhanced shape fluctuations relative to those of the larger spherical droplets. These fluctuations mark the onset of the instability. We also find that in the spiky droplet, the orientation of the solvent molecules in the first shell about the dsDNA is very close to that in the bulk solution. However, this orientation is substantially different farther away from the dsDNA. With regards to dynamics, the motion of the spikes is reflected in the autocorrelation functions of rotationally invariant order parameters that show a damped oscillator form of decay, indicative of the elastic motion of the spikes. We compare the formation of spikes with that of the ferrofluids and the dielectric materials in an electric field, and we conclude that they represent a different entity that deserves its own characterization. The study provides insight into the manner in which the charge distribution may give rise to well-controlled droplet morphologies and calls for experiments in this direction.

  7. Nucleation of electrically charged droplets

    NASA Technical Reports Server (NTRS)

    De, B. R.

    1979-01-01

    The nucleating droplets or clusters in many nucleation environments (various colloidal plasmas in laboratory and technological applications, astrophysical condensation environments, etc.) are likely to be at a finite electric potential. This may be due either to the presence of electrons and ions in the gas phase or to the thermal ionization or photoionization of the droplets. The paper demonstrates that this potential may introduce a nontrivial modification in the conventional nucleation theory. Some results for the typical case of nucleation of water droplets are presented. The general conclusion is that the electric potential makes nucleation harder to achieve, thereby demonstrating the importance of a finite droplet potential in the theory of nucleation.

  8. Classification of the ejection mechanisms of charged macromolecules from liquid droplets

    NASA Astrophysics Data System (ADS)

    Consta, Styliani; Malevanets, Anatoly

    2013-01-01

    The relation between the charge state of a macromolecule and its ejection mechanism from droplets is one of the important questions in electrospray ionization methods. In this article, effects of solvent-solute interaction on the manifestation of the charge induced instability in a droplet are examined. We studied the instabilities in a prototype system of a droplet comprised of charged poly(ethylene glycol) and methanol, acetonitrile, and water solvents. We observed instances of three, previously only conjectured, [S. Consta, J. Phys. Chem. B 114, 5263 (2010), 10.1021/jp912119v] mechanisms of macroion ejection. The mechanism of ejection of charged macroion in methanol is reminiscent of "pearl" model in polymer physics. In acetonitrile droplets, the instability manifests through formation of solvent spines around the solvated macroion. In water, we find that the macroion is ejected from the droplet through contiguous extrusion of a part of the chain. The difference in the morphology of the instabilities is attributed to the interplay between forces arising from the macroion solvation energy and the surface energy of the droplet interface. For the contiguous extrusion of a charged macromolecule from a droplet, we demonstrate that the proposed mechanism leads to ejection of the macromolecule from droplets with sizes well below the Rayleigh limit. The ejected macromolecule may hold charge significantly higher than that suggested by prevailing theories. The simulations reveal new mechanisms of macroion evaporation that differ from conventional charge residue model and ion evaporation mechanisms.

  9. Electrostatic charging and control of droplets in microfluidic devices.

    PubMed

    Zhou, Hongbo; Yao, Shuhuai

    2013-03-07

    Precharged droplets can facilitate manipulation and control of low-volume liquids in droplet-based microfluidics. In this paper, we demonstrate non-contact electrostatic charging of droplets by polarizing a neutral droplet and splitting it into two oppositely charged daughter droplets in a T-junction microchannel. We performed numerical simulation to analyze the non-contact charging process and proposed a new design with a notch at the T-junction in aid of droplet splitting for more efficient charging. We experimentally characterized the induced charge in droplets in microfabricated devices. The experimental results agreed well with the simulation. Finally, we demonstrated highly effective droplet manipulation in a path selection unit appending to the droplet charging. We expect our work could enable precision manipulation of droplets for more complex liquid handling in microfluidics and promote electric-force based manipulation in 'lab-on-a-chip' systems.

  10. Droplet-model predictions of charge moments

    SciTech Connect

    Myers, W.D.

    1982-04-01

    The Droplet Model expressions for calculating various moments of the nuclear charge distribution are given. There are contributions to the moments from the size and shape of the system, from the internal redistribution induced by the Coulomb repulsion, and from the diffuseness of the surface. A case is made for the use of diffuse charge distributions generated by convolution as an alternative to Fermi-functions.

  11. Coalescence and Breakup of Oppositely Charged Droplets

    PubMed Central

    Wang, Junfeng; Wang, Bin; Qiu, Huihe

    2014-01-01

    The coalescence process of oppositely charged drops for different electrical conductivities of liquids is presented. When the electrical conductivity was relatively low, oppositely charged drops failed to coalesce under sufficiently high electrical fields and capillary ripples were formed on the surfaces of droplets after rebound. For a high electrically conductive liquid, it was found that a crown profile of drop fission always appeared on the top surface of negatively charged drops after the two charged drops contacted and bounced off. Furthermore, we report here, for the first time, the newly found phenomenon and argue that the break up might be caused by Rayleigh instability, a form of Coulomb fission. The different mobility of positive and negative ions is the underlying mechanism that explains why the break up always happened on the negative side of charged drops. PMID:25410022

  12. Retreat behavior of a charged droplet for electrohydrodynamic inkjet printing

    NASA Astrophysics Data System (ADS)

    Yudistira, Hadi Teguh; Nguyen, Vu Dat; Tran, Si Bui Quang; Kang, Tae Sam; Park, Jung Keun; Byun, Doyoung

    2011-02-01

    The charged droplet retreat phenomenon in electrohydrodynamic inkjet printing is experimentally observed and theoretically explained. If the charge concentration of a droplet generated from a nozzle is high enough, Coulomb fission is generated a second time and the main droplet retreats to the meniscus on the nozzle. The retreat phenomenon is due to interactions between the charged droplet, the meniscus, and charges on the substrate. The Rayleigh limit is used to give a theoretical estimate of the amount of charge on the droplet and the meniscus during the retreat.

  13. Retreating behavior of a charged ionic liquid droplet in a dielectric liquid under electric field

    NASA Astrophysics Data System (ADS)

    Ahn, Myung Mo; Im, Do Jin; Kang, In Seok

    2013-11-01

    Ionic liquids show great promise as excellent solvents or catalysts in energy and biological fields due to their unique chemical and physical properties. The ionic liquid droplets in microfluidic systems can also be used as a potential platform for chemical biological reactions. In order to control electrically the ionic liquid droplets in a microfluidic device, the charging characteristics of ionic liquid droplets need to be understood. In this work, the charging characteristics of various ionic liquids are investigated by using the parallel plate electrodes system. Under normal situation, a charged droplet shows bouncing motion between electrodes continuously. However, for some special ionic liquids, interesting retreating behavior of charged ionic liquid droplet has been observed. This retreating behavior of ionic liquid droplet has been analyzed experimentally by the image analysis and the electrometer signal analysis. Based on the hypothesis of charge leakage of the retreating ionic liquid droplets, FT-IR spectroscopy analysis has also been performed. The retreating behavior of ionic liquid droplet is discussed from the intermolecular point of view according to the species of ionic liquids. This research was supported by grant No. 2013R1A1A2011956 funded by the Ministry of Science, ICT and Future Planning (MSIP) and by grant No. 2013R1A1A2010483 funded by the Ministry of Education, Science and Technology (MEST) through the NRF.

  14. Spontaneous electrical charging of droplets by conventional pipetting

    PubMed Central

    Choi, Dongwhi; Lee, Horim; Im, Do Jin; Kang, In Seok; Lim, Geunbae; Kim, Dong Sung; Kang, Kwan Hyoung

    2013-01-01

    We report that a droplet dispensed from a micropipette almost always has a considerable electrical charge of a magnitude dependent on the constituents of the droplet, on atmospheric humidity and on the coating material of pipette tip. We show that this natural electrification of a droplet originates from the charge separation between a droplet and pipette tip surface by contact with water due to the ionization of surface chemical groups. Charge on a droplet can make it difficult to detach the droplet from the pipette tip, can decrease its surface tension, can affect the chemical characteristics of solutions due to interactions with charged molecules, and can influence the combination and localization of charged bio-molecules; in all cases, the charge may affect results of experiments in which any of these factors is important. Thus, these findings reveal experimental parameters that should be controlled in experiments that use micropipettes. PMID:23784001

  15. Electrically Charged Droplets in Microgravity - Impact and Trajectories

    NASA Astrophysics Data System (ADS)

    Brandenbourger, Martin; Caps, Hervé; Vitry, Youen; Dorbolo, Stéphane

    2017-03-01

    In this work, the interaction between electrically charged droplets in microgravity is considered. During the 22 s of microgravity brought by a parabolic flight, water droplets with a radius r ∈ [0.41 - 0.97] mm were released one in front of the other. A high-speed camera allowed studying their interaction in the focal plane. The trajectories of the droplets are well adjusted by a punctual charge model. In some experiments, a physical contact between the charged droplets was observed. These collisions are studied via a phase diagram comparing the droplet Weber number, We, and the collision parameter, χ. By comparing these collisions to experiments involving neutral droplets, we deduce how the collision diagram is affected by electric charges. In particular, we show that the criterion for an impact between two droplets is no more χ < 1.

  16. Charged Water Droplets can Melt Metallic Electrodes

    NASA Astrophysics Data System (ADS)

    Elton, Eric; Rosenberg, Ethan; Ristenpart, William

    2016-11-01

    A water drop, when immersed in an insulating fluid, acquires charge when it contacts an energized electrode. Provided the electric field is strong enough, the drop will move away to the opposite electrode, acquire the opposite charge, and repeat the process, effectively 'bouncing' back and forth between the electrodes. A key implicit assumption, dating back to Maxwell, has been that the electrode remains unaltered by the charging process. Here we demonstrate that the electrode is physically deformed during each charge transfer event with an individual water droplet or other conducting object. We used optical, electron, and atomic force microscopy to characterize a variety of different metallic electrodes before and after drops were electrically bounced on them. Although the electrodes appear unchanged to the naked eye, the microscopy reveals that each charge transfer event yielded a crater approximately 1 micron wide and 50 nm deep, with the exact dimensions proportional to the applied field strength. We present evidence that the craters are formed by localized melting of the electrodes via Joule heating in the metal and concurrent dielectric breakdown of the surrounding fluid, suggesting that the electrode locally achieves temperatures exceeding 3400°C. Present address: Dept. Materials Sci. Engineering, MIT.

  17. Discrete electrostatic charge transfer by the electrophoresis of a charged droplet in a dielectric liquid.

    PubMed

    Im, Do Jin; Ahn, Myung Mo; Yoo, Byeong Sun; Moon, Dustin; Lee, Dong Woog; Kang, In Seok

    2012-08-14

    We have experimentally investigated the electrostatic charging of a water droplet on an electrified electrode surface to explain the detailed inductive charging processes and use them for the detection of droplet position in a lab-on-a-chip system. The periodic bouncing motion of a droplet between two planar electrodes has been examined by using a high-resolution electrometer and an image analysis method. We have found that this charging process consists of three steps. The first step is inductive charge accumulation on the opposite electrode by the charge of a droplet. This induction process occurs while the droplet approaches the electrode, and it produces an induction current signal at the electrometer. The second step is the discharging of the droplet by the accumulated induced charge at the moment of contact. For this second step, there is no charge-transfer detection at the electrometer. The third step is the charging of the neutralized droplet to a certain charged state while the droplet is in contact with the electrode. The charge transfer of the third step is detected as the pulse-type signal of an electrometer. The second and third steps occur simultaneously and rapidly. We have found that the induction current by the movement of a charged droplet can be accurately used to measure the charge of the droplet and can also be used to monitor the position of a droplet under actuation. The implications of the current findings for understanding and measuring the charging process are discussed.

  18. Flight behavior of charged droplets in electrohydrodynamic inkjet printing

    NASA Astrophysics Data System (ADS)

    Yudistira, Hadi Teguh; Nguyen, Vu Dat; Dutta, Prashanta; Byun, Doyoung

    2010-01-01

    Flight behaviors of charged droplets are presented for electrohydrodynamic (EHD) inkjet printing. Three different kinds of EHD spraying techniques, pulsed dc, ac, and single potential (SP) ac, have been investigated and both conductive and dielectric target surfaces were considered. Experimental results show that the flight paths of charged droplets may deviate from their regular straight route, i.e., directly from the nozzle to the substrate. Depending on the droplet charge and applied electric field, droplets may deflect, reflect, or retreat to the meniscus. We can solve these drawbacks by SP EHD printing.

  19. Evidence of molecular fragmentation inside the charged droplets produced by electrospray process.

    PubMed

    Banerjee, Shibdas; Prakash, Halan; Mazumdar, Shyamalava

    2011-10-01

    The behavior of the analyte molecules inside the neutral core of the charged droplet produced by the electrospray (ES) process is not unambiguously known to date. We have identified interesting molecular transformations of two suitably chosen analytes inside the ES droplets. The highly stable Ni(II) complex of 1,8-dimethyl-1,3,6,8,10,13-hexaazacyclotetradecane (1) that consists of a positive charge at the metal center, and the allyl pendant armed tertiary amine containing macrocycle 3,4,5:12,13,14-dipyridine-2,6,11,15-tetramethyl-1,7,10,16-tetraallyl-1,4,7,10,13,16-hexaazacyclooctadeca-3,13-diene (M(4p)) have been studied by ESI mass spectrometry as the model analytes. We have shown that these two molecules are not representatively transferred from solution to gas phase by ESI; rather, they undergo fragmentation inside the charged droplets. The results indicated that a charged analyte such as 1 was possibly unstable inside the neutral core of the ES droplet and undergoes fragmentation due to the Coulombic repulsion imparted by the surface protons. Brownian motion of the neutral analyte such as M(4p) inside the droplet, on the other hand, may lead to proton attachment on interaction with the charged surface causing destabilization that leads to fragmentation of M(4p) and release of resonance stabilized allyl cations from the core of the droplet. Detailed solvent dependence and collision-induced dissociation (CID) studies provided compelling evidences that the fragmentation of the analytes indeed occurs inside the charged ES droplets. A viable model of molecular transformations inside the ES droplet was proposed based on these results to rationalize the behavior of the analyte molecules inside the charged ES droplets.

  20. The Orbit of Water Droplets around Charged Rod

    ERIC Educational Resources Information Center

    Ferstl, Andrew; Burns, Andrew

    2013-01-01

    The motion of charges around a centrally charged object is often compared to gravitational orbits (such as satellites around planets). Recently, a video taken by astronaut Don Pettit onboard the International Space Station shows water droplets orbiting a charged knitting needle. Here we attempt to model this motion and estimate the charges on the…

  1. Surface area generation and droplet size control in solvent extraction systems utilizing high intensity electric fields

    DOEpatents

    Scott, Timothy C.; Wham, Robert M.

    1988-01-01

    A method and system for solvent extraction where droplets are shattered by a high intensity electric field. These shattered droplets form a plurality of smaller droplets which have a greater combined surface area than the original droplet. Dispersion, coalescence and phase separation are accomplished in one vessel through the use of the single pulsing high intensity electric field. Electric field conditions are chosen so that simultaneous dispersion and coalescence are taking place in the emulsion formed in the electric field. The electric field creates a large amount of interfacial surface area for solvent extraction when the droplet is disintegrated and is capable of controlling droplet size and thus droplet stability. These operations take place in the presence of a counter current flow of the continuous phase.

  2. Electrostatic Model Applied to ISS Charged Water Droplet Experiment

    NASA Technical Reports Server (NTRS)

    Stevenson, Daan; Schaub, Hanspeter; Pettit, Donald R.

    2015-01-01

    The electrostatic force can be used to create novel relative motion between charged bodies if it can be isolated from the stronger gravitational and dissipative forces. Recently, Coulomb orbital motion was demonstrated on the International Space Station by releasing charged water droplets in the vicinity of a charged knitting needle. In this investigation, the Multi-Sphere Method, an electrostatic model developed to study active spacecraft position control by Coulomb charging, is used to simulate the complex orbital motion of the droplets. When atmospheric drag is introduced, the simulated motion closely mimics that seen in the video footage of the experiment. The electrostatic force's inverse dependency on separation distance near the center of the needle lends itself to analytic predictions of the radial motion.

  3. Droplet formation and lateral migration via solvent shifting in a microfluidic setup

    NASA Astrophysics Data System (ADS)

    Hajian, Ramin; Hardt, Steffen

    2014-11-01

    When a non-solvent is added to a solvent/solute mixture and if the solvent and the non-solvent are miscible, a part of the solute transforms to tiny (i.e. micron-/submicron-sized) droplets when the solvent concentration reduces. This phenomenon, resulting from supersaturation, is termed solvent shifting or Ouzo effect. Here we investigate this process in a co-flow microfluidic device. Thanks to the laminar nature of the flow, the mass transfer is mainly diffusive and can be analyzed employing (semi)analytical models. Using the resulting concentration profiles along with the ternary phase diagram (TPD) we analyze droplet formation and their lateral migration in the channel. The ternary system consists of a binary mixture (0.5wt% divinyle benzene (DVB) + 95.5wt% ethanol) and deionized water (non-solvent). Plotting concentration trajectories in the TPD we show that they hit the binodal curve in a region in which droplets of DVB form via nucleation, as opposed to spinodal decomposition. The lateral migration of droplets is partially attributed to the Marangoni effect induced by concentration gradients. However, the main effect governing droplet migration appears to be the phase-separation front (separating the one-phase and two-phase regions) moving toward the center of the channel.

  4. Electrohydrodynamic migration of charged droplets in an insulating fluid

    NASA Technical Reports Server (NTRS)

    Balasubramaniam, R.; Wilkinson, R. A.

    1988-01-01

    The motion of charged, conducting droplets present in an insulating fluid medium is analyzed under the action of an electric field, in microgravity. Previous analyses of this problem have considered the Maxwell stresses as the only driving force. In the present study, arguments from macroscopic thermodynamics and the molecular theory of surface tension are used to show that the surface tension gradients can be induced due to the variation of the electric potential on the interface. In the limit of Reynolds numbers small compared to unity, the terminal velocity of migration of the droplet is calculated under the combined action of the Maxwell stresses and the surface tension gradients. The results show that there are no surface tension gradients (i.e., no electric potential variation at the interface) in a case that is due to the convection of the surface charges, surface tension gradients do exist and tend to reduce the terminal velocity of the droplet. The shape of the droplet altered by the motion was also calculated, when the deformations from the spherical shape are small.

  5. Isolating Protein Charge State Reduction in Electrospray Droplets Using Femtosecond Laser Vaporization

    NASA Astrophysics Data System (ADS)

    Karki, Santosh; Sistani, Habiballah; Archer, Jieutonne J.; Shi, Fengjian; Levis, Robert J.

    2017-01-01

    Charge state distributions are measured using mass spectrometry for both native and denatured cytochrome c and myoglobin after laser vaporization from the solution state into an electrospray (ES) plume consisting of a series of solution additives differing in gas-phase basicity. The charge distribution depends on both the pH of the protein solution prior to laser vaporization and the gas-phase basicity of the solution additive employed in the ES solvent. Cytochrome c (myoglobin) prepared in solutions with pH of 7.0, 2.6, and 2.3 resulted in the average charge state distribution (Zavg) of 7.0 ± 0.1 (8.2 ± 0.1), 9.7 ± 0.2 (14.5 ± 0.3), and 11.6 ± 0.3 (16.4 ± 0.1), respectively, in ammonium formate ES solvent. The charge distribution shifted from higher charge states to lower charge states when the ES solvent contained amines additives with higher gas-phase basicity. In the case of triethyl ammonium formate, Zavg of cytochrome c (myoglobin) prepared in solutions with pH of 7.0, 2.6, and 2.3 decreased to 4.9 (5.7), 7.4 ± 0.2 (9.6 ± 0.3), and 7.9 ± 0.3 (9.8 ± 0.2), respectively. The detection of a charge state distribution corresponding to folded protein after laser vaporized, acid-denatured protein interacts with the ES solvent containing ammonium formate, ammonium acetate, triethyl ammonium formate, and triethyl ammonium acetate suggests that at least a part of protein population folds within the electrospray droplet on a millisecond timescale.

  6. Isolating Protein Charge State Reduction in Electrospray Droplets Using Femtosecond Laser Vaporization

    NASA Astrophysics Data System (ADS)

    Karki, Santosh; Sistani, Habiballah; Archer, Jieutonne J.; Shi, Fengjian; Levis, Robert J.

    2017-03-01

    Charge state distributions are measured using mass spectrometry for both native and denatured cytochrome c and myoglobin after laser vaporization from the solution state into an electrospray (ES) plume consisting of a series of solution additives differing in gas-phase basicity. The charge distribution depends on both the pH of the protein solution prior to laser vaporization and the gas-phase basicity of the solution additive employed in the ES solvent. Cytochrome c (myoglobin) prepared in solutions with pH of 7.0, 2.6, and 2.3 resulted in the average charge state distribution (Zavg) of 7.0 ± 0.1 (8.2 ± 0.1), 9.7 ± 0.2 (14.5 ± 0.3), and 11.6 ± 0.3 (16.4 ± 0.1), respectively, in ammonium formate ES solvent. The charge distribution shifted from higher charge states to lower charge states when the ES solvent contained amines additives with higher gas-phase basicity. In the case of triethyl ammonium formate, Zavg of cytochrome c (myoglobin) prepared in solutions with pH of 7.0, 2.6, and 2.3 decreased to 4.9 (5.7), 7.4 ± 0.2 (9.6 ± 0.3), and 7.9 ± 0.3 (9.8 ± 0.2), respectively. The detection of a charge state distribution corresponding to folded protein after laser vaporized, acid-denatured protein interacts with the ES solvent containing ammonium formate, ammonium acetate, triethyl ammonium formate, and triethyl ammonium acetate suggests that at least a part of protein population folds within the electrospray droplet on a millisecond timescale.

  7. Orientation of charged clay nanotubes in evaporating droplet meniscus.

    PubMed

    Zhao, Yafei; Cavallaro, Giuseppe; Lvov, Yuri

    2015-02-15

    During drying, an aqueous suspension of strongly charged halloysite clay nanotubes concentrates at the edge of the droplet ("coffee-ring" effect) which provides alignment of the tubes along the liquid-substrate contact line. First, the surface charge of the nanotubes was enhanced by polyanion adsorption inside of the lumen to compensate for the internal positive charges. This increased the magnitude of the ξ-potential of the tubes from -36 to -81 mV and stabilized the colloids. Then, colloidal halloysite was dropped onto the substrate, dried at 65 °C and after a concentration of ∼0.05 mg mL(-1) was reached, the alignment of nanotubes occurred starting from the droplet edges. The process was described with Onsager's theory, in which longer nanorods, which have higher surface charge, give better ordering after a critical concentration is reached. This study indicates a new application of halloysite clay nanotubes in polymeric composites with anisotropic properties, microchannel orientation, and production of coatings with aligned nanotubes.

  8. Hidden topological constellations and polyvalent charges in chiral nematic droplets

    PubMed Central

    Posnjak, Gregor; Čopar, Simon; Muševič, Igor

    2017-01-01

    Topology has an increasingly important role in the physics of condensed matter, quantum systems, material science, photonics and biology, with spectacular realizations of topological concepts in liquid crystals. Here we report on long-lived hidden topological states in thermally quenched, chiral nematic droplets, formed from string-like, triangular and polyhedral constellations of monovalent and polyvalent singular point defects. These topological defects are regularly packed into a spherical liquid volume and stabilized by the elastic energy barrier due to the helical structure and confinement of the liquid crystal in the micro-sphere. We observe, for the first time, topological three-dimensional point defects of the quantized hedgehog charge q=−2, −3. These higher-charge defects act as ideal polyvalent artificial atoms, binding the defects into polyhedral constellations representing topological molecules. PMID:28220770

  9. Hidden topological constellations and polyvalent charges in chiral nematic droplets

    NASA Astrophysics Data System (ADS)

    Posnjak, Gregor; Čopar, Simon; Muševič, Igor

    2017-02-01

    Topology has an increasingly important role in the physics of condensed matter, quantum systems, material science, photonics and biology, with spectacular realizations of topological concepts in liquid crystals. Here we report on long-lived hidden topological states in thermally quenched, chiral nematic droplets, formed from string-like, triangular and polyhedral constellations of monovalent and polyvalent singular point defects. These topological defects are regularly packed into a spherical liquid volume and stabilized by the elastic energy barrier due to the helical structure and confinement of the liquid crystal in the micro-sphere. We observe, for the first time, topological three-dimensional point defects of the quantized hedgehog charge q=-2, -3. These higher-charge defects act as ideal polyvalent artificial atoms, binding the defects into polyhedral constellations representing topological molecules.

  10. Droplet charging regimes for ultrasonic atomization of a liquid electrolyte in an external electric field

    NASA Astrophysics Data System (ADS)

    Forbes, Thomas P.; Degertekin, F. Levent; Fedorov, Andrei G.

    2011-01-01

    Distinct regimes of droplet charging, determined by the dominant charge transport process, are identified for an ultrasonic droplet ejector using electrohydrodynamic computational simulations, a fundamental scale analysis, and experimental measurements. The regimes of droplet charging are determined by the relative magnitudes of the dimensionless Strouhal and electric Reynolds numbers, which are a function of the process (pressure forcing), advection, and charge relaxation time scales for charge transport. Optimal (net maximum) droplet charging has been identified to exist for conditions in which the electric Reynolds number is of the order of the inverse Strouhal number, i.e., the charge relaxation time is on the order of the pressure forcing (droplet formation) time scale. The conditions necessary for optimal droplet charging have been identified as a function of the dimensionless Debye number (i.e., liquid conductivity), external electric field (magnitude and duration), and atomization drive signal (frequency and amplitude). The specific regime of droplet charging also determines the functional relationship between droplet charge and charging electric field strength. The commonly expected linear relationship between droplet charge and external electric field strength is only found when either the inverse of the Strouhal number is less than the electric Reynolds number, i.e., the charge relaxation is slower than both the advection and external pressure forcing, or in the electrostatic limit, i.e., when charge relaxation is much faster than all other processes. The analysis provides a basic understanding of the dominant physics of droplet charging with implications to many important applications, such as electrospray mass spectrometry, ink jet printing, and drop-on-demand manufacturing.

  11. Droplet charging regimes for ultrasonic atomization of a liquid electrolyte in an external electric field

    PubMed Central

    Forbes, Thomas P.; Degertekin, F. Levent; Fedorov, Andrei G.

    2011-01-01

    Distinct regimes of droplet charging, determined by the dominant charge transport process, are identified for an ultrasonic droplet ejector using electrohydrodynamic computational simulations, a fundamental scale analysis, and experimental measurements. The regimes of droplet charging are determined by the relative magnitudes of the dimensionless Strouhal and electric Reynolds numbers, which are a function of the process (pressure forcing), advection, and charge relaxation time scales for charge transport. Optimal (net maximum) droplet charging has been identified to exist for conditions in which the electric Reynolds number is of the order of the inverse Strouhal number, i.e., the charge relaxation time is on the order of the pressure forcing (droplet formation) time scale. The conditions necessary for optimal droplet charging have been identified as a function of the dimensionless Debye number (i.e., liquid conductivity), external electric field (magnitude and duration), and atomization drive signal (frequency and amplitude). The specific regime of droplet charging also determines the functional relationship between droplet charge and charging electric field strength. The commonly expected linear relationship between droplet charge and external electric field strength is only found when either the inverse of the Strouhal number is less than the electric Reynolds number, i.e., the charge relaxation is slower than both the advection and external pressure forcing, or in the electrostatic limit, i.e., when charge relaxation is much faster than all other processes. The analysis provides a basic understanding of the dominant physics of droplet charging with implications to many important applications, such as electrospray mass spectrometry, ink jet printing, and drop-on-demand manufacturing. PMID:21301636

  12. Droplet charging regimes for ultrasonic atomization of a liquid electrolyte in an external electric field.

    PubMed

    Forbes, Thomas P; Degertekin, F Levent; Fedorov, Andrei G

    2011-01-01

    Distinct regimes of droplet charging, determined by the dominant charge transport process, are identified for an ultrasonic droplet ejector using electrohydrodynamic computational simulations, a fundamental scale analysis, and experimental measurements. The regimes of droplet charging are determined by the relative magnitudes of the dimensionless Strouhal and electric Reynolds numbers, which are a function of the process (pressure forcing), advection, and charge relaxation time scales for charge transport. Optimal (net maximum) droplet charging has been identified to exist for conditions in which the electric Reynolds number is of the order of the inverse Strouhal number, i.e., the charge relaxation time is on the order of the pressure forcing (droplet formation) time scale. The conditions necessary for optimal droplet charging have been identified as a function of the dimensionless Debye number (i.e., liquid conductivity), external electric field (magnitude and duration), and atomization drive signal (frequency and amplitude). The specific regime of droplet charging also determines the functional relationship between droplet charge and charging electric field strength. The commonly expected linear relationship between droplet charge and external electric field strength is only found when either the inverse of the Strouhal number is less than the electric Reynolds number, i.e., the charge relaxation is slower than both the advection and external pressure forcing, or in the electrostatic limit, i.e., when charge relaxation is much faster than all other processes. The analysis provides a basic understanding of the dominant physics of droplet charging with implications to many important applications, such as electrospray mass spectrometry, ink jet printing, and drop-on-demand manufacturing.

  13. On the theory of the noncoalescence effect for oppositely charged droplets

    SciTech Connect

    Saranin, V. A.

    2011-05-15

    A theory is proposed and numerical simulation is conducted for oppositely charged mutually approaching droplets of an aqueous electrolytic solution in silicon oil. It is shown that at small distances between droplets, a conductive bridge leveling out the potentials of the droplets may form between them due to electrohydrodynamic instability of the equilibrium surface of one of the droplets. As a result, the droplets start to repel each other and may drift apart without coagulation. The proposed theory is confirmed by the effect of nonconfluent droplets observed in experiments [W.D. Ristenpart, J.C. Bird, A. Belmonte, et al., Nature 461, 377 (2009)].

  14. Influence of relative humidity and ambient temperature on hydrothermal waves (HTWs) of organic solvent volatile droplets

    NASA Astrophysics Data System (ADS)

    Orejon, Daniel; Kita, Yutaku; Okauchi, Yuya; Fukatani, Yuki; Kohno, Masamichi; Takata, Yasuyuki; Sefiane, Khellil; Kim, Jungho

    2016-11-01

    Droplets of organic solvents undergoing evaporation have been found to display distinctive hydrothermal patterns or HTWs at the liquid-vapor interface. Since the evaporation of mentioned organic solvents in ambient conditions is ubiquitous, in this work we investigate the effect of ambient temperature and relative humidity on the self-generated HTWs by means of infrared thermography. The intensity of the HTWs was found to decrease when lowering the ambient temperature due to a reduction in droplet evaporative cooling. On other hand, the enhancement or suppression of the HTWs was also possible by controlling the relative humidity of the system. Absorption and/or condensation of water vapor onto the evaporating droplet was found to be the main cause for the differences observed on the HTWs retrieved at the liquid-vapor interface. To account for the water adsorbed or condensed we perform in-situ gas chromatography analysis at different droplet lifetimes. Experimental results showed an increase in the amount of water condensed when increasing the relative humidity of the system as expected. In addition, for the same ambient temperature ethanol evaporation was enhanced by high relative humidity. The authors acknowledge the support of WPI-I2CNER.

  15. Redistribution of mobile surface charges of an oil droplet in water in applied electric field.

    PubMed

    Li, Mengqi; Li, Dongqing

    2016-10-01

    Most researches on oil droplets immersed in aqueous solutions assume that the surface charges of oil droplets are, similar to that of solid particles, immobile and distributed uniformly under external electric field. However, the surface charges at the liquid-liquid interface are mobile and will redistribute under external electric field. This paper studies the redistribution of surface charges on an oil droplet under the influence of the external electrical field. Analytical expressions of the local zeta potential on the surface of an oil droplet after the charge redistribution in a uniform electrical field were derived. The effects of the initial zeta potential, droplet radius and strength of applied electric field on the surface charge redistribution were studied. In analogy to the mobile surface charges, the redistribution of Al2O3-passivated aluminum nanoparticles on the oil droplet surface was observed under applied electrical field. Experimental results showed that these nanoparticles moved and accumulated towards one side of the oil droplet under electric field. The redistribution of the nanoparticles is in qualitative agreement with the redistribution model of the mobile surface charges developed in this work.

  16. Non-coalescence of oppositely charged droplets in pH-sensitive emulsions

    PubMed Central

    Liu, Tingting; Seiffert, Sebastian; Thiele, Julian; Abate, Adam R.; Weitz, David A.; Richtering, Walter

    2012-01-01

    Like charges stabilize emulsions, whereas opposite charges break emulsions. This is the fundamental principle for many industrial and practical processes. Using micrometer-sized pH-sensitive polymeric hydrogel particles as emulsion stabilizers, we prepare emulsions that consist of oppositely charged droplets, which do not coalesce. We observe noncoalescence of oppositely charged droplets in bulk emulsification as well as in microfluidic devices, where oppositely charged droplets are forced to collide within channel junctions. The results demonstrate that electrostatic interactions between droplets do not determine their stability and reveal the unique pH-dependent properties of emulsions stabilized by soft microgel particles. The noncoalescence can be switched to coalescence by neutralizing the microgels, and the emulsion can be broken on demand. This unusual feature of the microgel-stabilized emulsions offers fascinating opportunities for future applications of these systems. PMID:22203968

  17. Crystallization and reentrant melting of charged colloids in nonpolar solvents.

    PubMed

    Kanai, Toshimitsu; Boon, Niels; Lu, Peter J; Sloutskin, Eli; Schofield, Andrew B; Smallenburg, Frank; van Roij, René; Dijkstra, Marjolein; Weitz, David A

    2015-03-01

    We explore the crystallization of charged colloidal particles in a nonpolar solvent mixture. We simultaneously charge the particles and add counterions to the solution with aerosol-OT (AOT) reverse micelles. At low AOT concentrations, the charged particles crystallize into body-centered-cubic (bcc) or face-centered-cubic (fcc) Wigner crystals; at high AOT concentrations, the increased screening drives a thus far unobserved reentrant melting transition. We observe an unexpected scaling of the data with particle size, and account for all behavior with a model that quantitatively predicts both the reentrant melting and the data collapse.

  18. Visualization of the evolution of charged droplet formation and jet transition in electrostatic atomization

    SciTech Connect

    Huo, Yuanping Wang, Junfeng Zuo, Ziwen; Fan, Yajun

    2015-11-15

    A detailed experimental study on the evolution of charged droplet formation and jet transition from a capillary is reported. By means of high-speed microscopy, special attention has been paid to the dynamics of the liquid thread and satellite droplets in the dripping mode, and a method for calculating the surface charge on the satellite droplet is proposed. Jet transition behavior based on the electric Bond number has been visualized, droplet sizes and velocities are measured to obtain the ejection characteristic of the spray plume, and the charge and hydrodynamic relaxation are linked to give explanations for ejection dynamics with different properties. The results show that the relative length is very sensitive to the hydrodynamic relaxation time. The magnitude of the electric field strength dominates the behavior of coalescence and noncoalescence, with the charge relationship between the satellite droplet and the main droplet being clear for every noncoalescence movement. Ejection mode transitions mainly depend on the magnitude of the electric Bond number, and the meniscus dynamics is determined by the ratio of the charge relaxation time to the hydrodynamic relaxation time.

  19. Electrostatic interactions in charged nanoslits within an explicit solvent theory.

    PubMed

    Buyukdagli, Sahin

    2015-11-18

    Within a dipolar Poisson-Boltzmann theory including electrostatic correlations, we consider the effect of explicit solvent structure on solvent and ion partition confined to charged nanopores. We develop a relaxation scheme for the solution of this highly non-linear integro-differential equation for the electrostatic potential. The scheme is an extension of the approach previously introduced for simple planes (Buyukdagli and Blossey 2014 J. Chem. Phys. 140 234903) to nanoslit geometry. We show that the reduced dielectric response of solvent molecules at the membrane walls gives rise to an electric field significantly stronger than the field of the classical Poisson-Boltzmann equation. This peculiarity associated with non-local electrostatic interactions results in turn in an interfacial counterion adsorption layer absent in continuum theories. The observation of this enhanced counterion affinity in the very close vicinity of the interface may have important impacts on nanofluidic transport through charged nanopores. Our results indicate the quantitative inaccuracy of solvent implicit nanofiltration theories in predicting the ionic selectivity of membrane nanopores.

  20. Electrostatic interactions in charged nanoslits within an explicit solvent theory

    NASA Astrophysics Data System (ADS)

    Buyukdagli, Sahin

    2015-11-01

    Within a dipolar Poisson-Boltzmann theory including electrostatic correlations, we consider the effect of explicit solvent structure on solvent and ion partition confined to charged nanopores. We develop a relaxation scheme for the solution of this highly non-linear integro-differential equation for the electrostatic potential. The scheme is an extension of the approach previously introduced for simple planes (Buyukdagli and Blossey 2014 J. Chem. Phys. 140 234903) to nanoslit geometry. We show that the reduced dielectric response of solvent molecules at the membrane walls gives rise to an electric field significantly stronger than the field of the classical Poisson-Boltzmann equation. This peculiarity associated with non-local electrostatic interactions results in turn in an interfacial counterion adsorption layer absent in continuum theories. The observation of this enhanced counterion affinity in the very close vicinity of the interface may have important impacts on nanofluidic transport through charged nanopores. Our results indicate the quantitative inaccuracy of solvent implicit nanofiltration theories in predicting the ionic selectivity of membrane nanopores.

  1. Exact solutions for the static dewetting of two-dimensional charged conducting droplets on a substrate

    NASA Astrophysics Data System (ADS)

    Crowdy, Darren

    2015-06-01

    A one parameter family of analytical solutions for the equilibrium shapes of two-dimensional charged conducting droplets on a substrate with 90° contact angle is presented. The solutions exhibit the tendency to dewet at the droplet centre as the electrostatic stress increases. Such electrostatic deformations are believed to underlie the recently observed stick-slip dynamics of nanodroplets on substrates. Our theoretical results complement a number of other recent analytical and numerical studies of this phenomenon.

  2. Numerical Investigation of Two-Phase Flows With Charged Droplets in Electrostatic Field

    NASA Technical Reports Server (NTRS)

    Kim, Sang-Wook

    1996-01-01

    A numerical method to solve two-phase turbulent flows with charged droplets in an electrostatic field is presented. The ensemble-averaged Navier-Stokes equations and the electrostatic potential equation are solved using a finite volume method. The transitional turbulence field is described using multiple-time-scale turbulence equations. The equations of motion of droplets are solved using a Lagrangian particle tracking scheme, and the inter-phase momentum exchange is described by the Particle-In-Cell scheme. The electrostatic force caused by an applied electrical potential is calculated using the electrostatic field obtained by solving a Laplacian equation and the force exerted by charged droplets is calculated using the Coulombic force equation. The method is applied to solve electro-hydrodynamic sprays. The calculated droplet velocity distributions for droplet dispersions occurring in a stagnant surrounding are in good agreement with the measured data. For droplet dispersions occurring in a two-phase flow, the droplet trajectories are influenced by aerodynamic forces, the Coulombic force, and the applied electrostatic potential field.

  3. Apparatus for Suspension of Charged Particles and Droplets

    ERIC Educational Resources Information Center

    Berg, T. G. Owe

    1969-01-01

    Describes an apparatus designed to study the properties of charged particles suspended in an electric field. The apparatus consists of a suspension chamber, an optical system and power supplies and controls. Experiments conducted include determination of particle size, charge-to-mass ratio and particle collisions and exchange. (LC)

  4. Dynamic corona characteristics of water droplets on charged conductor surface

    NASA Astrophysics Data System (ADS)

    Xu, Pengfei; Zhang, Bo; Wang, Zezhong; Chen, Shuiming; He, Jinliang

    2017-03-01

    The formation of the Taylor cone of a water droplet on the surface of the conductor in a line-ground electrode system is captured using a high-speed camera, while the corona current is synchronously measured using a current measurement system. Repeated Taylor cone deformation is observed, yielding regular groupings of corona current pulses. The underlying mechanism of this deformation is studied and the correlation between corona discharge characteristics and cone deformation is investigated. Depending on the applied voltage and rate of water supply, the Taylor cone may be stable or unstable and has a significant influence on the characteristics of the corona currents. If the rate of water supply is large enough, the Taylor cone tends to be unstable and generates corona-current pulses of numerous induced current pulses with low amplitudes. In consequence, this difference suggests that large rainfall results in simultaneously lower radio interference and higher corona loss.

  5. Estimation of droplet charge forming out of an electrified ligament in the presence of a uniform electric field

    NASA Astrophysics Data System (ADS)

    Osman, H.; Castle, G. S. P.; Adamiak, K.; Fan, H. T.; Simmer, J.

    2015-10-01

    The charge on a liquid droplet is a critical parameter that needs to be determined to accurately predict the behaviour of the droplet in many electrostatic applications, for example, electrostatic painting and ink-jet printing. The charge depends on many factors, such as the liquid conductivity, droplet and ligament radii, ligament length, droplet shape, electric field intensity, space charge, the presence of adjacent ligaments and previously formed droplets. In this paper, a 2D axisymmetric model is presented which can be used to predict the electric charge on a conductive spherical droplet ejected from a single ligament directly supplied with high voltage. It was found that the droplet charging levels for the case of isolated electrified ligaments are as much as 60 times higher than that in the case of ligaments connected to a planar high voltage electrode. It is suggested that practical atomization systems lie somewhere between these two extremes and that a better model was achieved by developing a 3D approximation of a linear array of ligaments connected to an electrode having variable width. The effect on droplet charge and its radius was estimated for several cases of different boundary conditions.

  6. Electrohydrodynamics of Charge Separation in Droplet-Based Ion Sources with Time-Varying Electrical and Mechanical Actuation

    PubMed Central

    Forbes, Thomas P.; Degertekin, F. Levent; Fedorov, Andrei G.

    2010-01-01

    Charge transport and separation in mechanically-driven, droplet-based ion sources are investigated using computational analysis and supporting experiments. A first-principles model of electrohydrodynamics (EHD) and charge migration is formulated and implemented using FLUENT CFD software for jet/droplet formation. For validation, classical experiments of electrospraying from a thin capillary are simulated, specifically, the transient EHD cone-jet formation of a fluid with finite electrical conductivity, and the Taylor cone formation in a perfectly electrically-conducting fluid. The model is also used to investigate the microscopic physics of droplet charging in mechanically-driven droplet-based ion sources, such as AMUSE (Array of Micromachined UltraSonic Electrospray). Here, AMUSE is subject to DC and AC electric fields of varying amplitude and phase, with respect to a time-varying mechanical force driving the droplet formation. For the DC-charging case, a linear relationship is demonstrated between the charge carried by each droplet and an applied electric field magnitude, in agreement with previously reported experiments. For the AC-charging case, a judiciously-chosen phase-shift in the time-varying mechanical (driving ejection) and electrical (driving charge transport) signals allows for a significantly increased amount of charge, of desired polarity, to be pumped into a droplet upon ejection. Complementary experimental measurements of electrospray electrical current and charge-per-droplet, produced by the AMUSE ion source, are performed and support theoretical predictions for both DC and AC-charging cases. The theoretical model and simulation tools provide a versatile and general analytical framework for fundamental investigations of coupled electrohydrodynamics and charge transport. The model also allows for the exploration of different configurations and operating modes to optimize charge separation in atmospheric pressure electrohydrodynamic ion sources

  7. Producing highly charged ions without solvent using laserspray ionization: a total solvent-free analysis approach at atmospheric pressure.

    PubMed

    Wang, Beixi; Lietz, Christopher B; Inutan, Ellen D; Leach, Samantha M; Trimpin, Sarah

    2011-06-01

    First examples of highly charged ions in mass spectrometry (MS) produced from the solid state without using solvent during either sample preparation or mass measurement are reported. Matrix material, matrix/analyte homogenization time and frequency, atmospheric pressure (AP) to vacuum inlet temperature, and mass analyzer ion trap conditions are factors that influence the abundance of the highly charged ions created by laserspray ionization (LSI). LSI, like matrix-assisted laser desorption/ionization (MALDI), uses laser ablation of a matrix/analyte mixture from a surface to produce ions. Preparing the matrix/analyte sample without the use of solvent provides the ability to perform total solvent-free analysis (TSA) consisting of solvent-free ionization and solvent-free gas-phase separation using ion mobility spectrometry (IMS) MS. Peptides and small proteins such as non-β-amyloid components of Alzheimer's disease and bovine insulin are examples in which LSI and TSA were combined to produce multiply charged ions, similar to electrospray ionization, but without the use of solvent. Advantages using solvent-free LSI and IMS-MS include simplicity, rapid data acquisition, reduction of sample complexity, and the potential for an enhanced effective dynamic range. This is achieved by more inclusive ionization and improved separation of mixture components as a result of multiple charging.

  8. Charge tuning in [111] grown GaAs droplet quantum dots

    SciTech Connect

    Bouet, L.; Vidal, M.; Marie, X.; Amand, T.; Wang, G.; Urbaszek, B.; Mano, T.; Ha, N.; Kuroda, T.; Sakoda, K.; Durnev, M. V.; Glazov, M. M.; Ivchenko, E. L.

    2014-08-25

    We demonstrate charge tuning in strain free GaAs/AlGaAs quantum dots (QDs) grown by droplet epitaxy on a GaAs(111)A substrate. Application of a bias voltage allows the controlled charging of the QDs from −3|e| to +2|e|. The resulting changes in QD emission energy and exciton fine-structure are recorded in micro-photoluminescence experiments at T = 4 K. We uncover the existence of excited valence and conduction states, in addition to the s-shell-like ground state. We record a second series of emission lines about 25 meV above the charged exciton emission coming from excited charged excitons. For these excited interband transitions, a negative diamagnetic shift of large amplitude is uncovered in longitudinal magnetic fields.

  9. Controlled Gelation of Particle Suspensions Using Controlled Solvent Removal in Picoliter Droplets

    NASA Astrophysics Data System (ADS)

    Vuong, Sharon; Walker, Lynn; Anna, Shelley

    2013-11-01

    Droplets in microfluidic devices have proven useful as uniform picoliter reactors for nanoparticle synthesis and as components in tunable emulsions. However, there can be significant transport between the component phases depending on solubility and other factors. In the present talk, we show that water droplets trapped within a microfluidic device for tens of hours slowly dehydrate, concentrating the contents encapsulated within. We use this slow dehydration along with control of the initial droplet composition to monitor gelation of aqueous suspensions of spherical silica particles (Ludox) and disk-shaped clay particles (Laponite). Droplets are generated in a microfluidic device containing small wells that trap the droplets. We monitor the concentration process through size and shape changes of these droplets as a function of time in tens of droplets and use the large number of individual reactors to generate statistics regarding the gelation process. We also examine changes in suspension viscosity through fluorescent particle tracking as a function of dehydration rate, initial suspension concentration and initial droplet volume, and added salt, and compare the results with the Krieger-Dougherty model in which viscosity increases dramatically with particle volume fraction.

  10. Fission of multiply charged alkali clusters in helium droplets - approaching the Rayleigh limit.

    PubMed

    Renzler, Michael; Harnisch, Martina; Daxner, Matthias; Kranabetter, Lorenz; Kuhn, Martin; Scheier, Paul; Echt, Olof

    2016-04-21

    Electron ionization of helium droplets doped with sodium, potassium or cesium results in doubly and, for cesium, triply charged cluster ions. The smallest observable doubly charged clusters are Na9(2+), K11(2+), and Cs9(2+); they are a factor two to three smaller than reported previously. The size of sodium and potassium dications approaches the Rayleigh limit nRay for which the fission barrier is calculated to vanish, i.e. their fissilities are close to 1. Cesium dications are even smaller than nRay, implying that their fissilities have been significantly overestimated. Triply charged cesium clusters as small as Cs19(3+) are observed; they are a factor 2.6 smaller than previously reported. Mechanisms that may be responsible for enhanced formation of clusters with high fissilities are discussed.

  11. Role of hydrophobicity and solvent-mediated charge-charge interactions in stabilizing alpha-helices.

    PubMed Central

    Vila, J A; Ripoll, D R; Villegas, M E; Vorobjev, Y N; Scheraga, H A

    1998-01-01

    A theoretical study to identify the conformational preferences of lysine-based oligopeptides has been carried out. The solvation free energy and free energy of ionization of the oligopeptides have been calculated by using a fast multigrid boundary element method that considers the coupling between the conformation of the molecule and the ionization equilibria explicitly, at a given pH value. It has been found experimentally that isolated alanine and lysine residues have somewhat small intrinsic helix-forming tendencies; however, results from these simulations indicate that conformations containing right-handed alpha-helical turns are energetically favorable at low values of pH for lysine-based oligopeptides. Also, unusual patterns of interactions among lysine side chains with large hydrophobic contacts and close proximity (5-6 A) between charged NH3+ groups are observed. Similar arrangements of charged groups have been seen for lysine and arginine residues in experimentally determined structures of proteins available from the Protein Data Bank. The lowest-free-energy conformation of the sequence Ac-(LYS)6-NMe from these simulations showed large pKalpha shifts for some of the NH3+ groups of the lysine residues. Such large effects are not observed in the lowest-energy conformations of oligopeptide sequences with two, three, or four lysine residues. Calculations on the sequence Ac-LYS-(ALA)4-LYS-NMe also reveal low-energy alpha-helical conformations with interactions of one of the LYS side chains with the helix backbone in an arrangement quite similar to the one described recently by (Proc. Natl. Acad. Sci. U.S.A. 93:4025-4029). The results of this study provide a sound basis with which to discuss the nature of the interactions, such as hydrophobicity, charge-charge interaction, and solvent polarization effects, that stabilize right-handed alpha-helical conformations. PMID:9826588

  12. Levitation dynamics of a collection of charged droplets in an electrodynamic balance

    NASA Astrophysics Data System (ADS)

    Singh, Mohit; Mayya, Y. S.; Gaware, Jitendra; Thaokar, Rochish M.

    2017-02-01

    The study explores the stable levitation and self-organization of charged multi-drop assemblies in a large sized quadrupole trap both experimentally and through numerical simulations. The trap is benchmarked by comparing single drop levitation experiments with numerical simulations. Important observation and findings of the study are: (i) long time stabilization and formation of patterns of droplet collections over a range of operating parameters (ii) Numerical prediction of polygonal patterns for few drop (2 to 8) systems and lattice structures for many drop (>10) systems, (iii) Numerical prediction of Non-dependence of the inter-drop spacing on droplet charge for similarly charged drops, consistent with earlier analytical formulations [Aardahl et al., J. Aerosol Sci. 28, 1491-1505 (1997)], (iv) numerical observation of two drops oscillations with a secular frequency distinctly higher than the single drop Dehmelt frequency (v) Simulations of a systematic transition from disordered to coulombic crystals with mean size increasing with the number of levitated drops (N) as ˜N0.29. The experimental observations on different patterns and lattice spacings are closely reproduced by simulations.

  13. A model for the prediction of droplet size in Pickering emulsions stabilized by oppositely charged particles.

    PubMed

    Nallamilli, Trivikram; Mani, Ethayaraja; Basavaraj, Madivala G

    2014-08-12

    Colloidal particles irreversibly adsorb at fluid-fluid interfaces stabilizing what are commonly called "Pickering" emulsions and foams. A simple geometrical model, the limited coalescence model, was earlier proposed to estimate droplet sizes in emulsions. This model assumes that all of the particles are effective in stabilization. The model predicts that the average emulsion drop size scales inversely with the total number of particles, confirmed qualitatively with experimental data on Pickering emulsions. In recent years, there has been an increasing interest in synthesizing emulsions with oppositely charged particles (OCPs). In our experimental study, we observed that the drop size varies nonmonotonically with the number ratio of oppositely charged colloids, even when a fixed total number concentration of colloids is used, showing a minimum. We develop a mathematical model to predict this dependence of drop size on number ratio in such a mixed particle system. The proposed model is based on the hypothesis that oppositely charged colloids form stable clusters due to the strong electrostatic attraction between them and that these clusters are the effective stabilizing agents. The proposed model is a two-parameter model, parameters being the ratio of effective charge of OCPs (denoted as k) and the size of the aggregate containing X particles formed due to aggregation of OCPs. Because the size of aggregates formed during emulsification is not directly measurable, we use suitable values of parameters k and X to best match the experimental observations. The model predictions are in qualitative agreement with experimentally observed nonmonotonic variation of droplet sizes. Using experiments and theory, we present a physical insight into the formation of OCP stabilized Pickering emulsions. Our model upgrades the existing Wiley's limited coalescence model as applied to emulsions containing a binary mixture of oppositely charged particles.

  14. Searching for solvent cavities via electron photodetachment: The ultrafast charge-transfer-to-solvent dynamics of sodide in a series of ether solvents

    SciTech Connect

    Larsen, Molly C.; Schwartz, Benjamin J.

    2009-10-21

    It was recently predicted by simulations and confirmed by neutron diffraction experiments that the structure of liquid tetrahydrofuran (THF) contains cavities. The cavities can be quite large and have a net positive electrostatic potential, so they can serve as pre-existing traps for excess electrons created via photodetachment from various solutes. In this paper, we use electron photodetachment via charge-transfer-to-solvent (CTTS) excitation of sodide (Na{sup -}) to probe for the presence of pre-existing cavities in a series of ether solvents: THF, diethyl ether, 1,2-dimethoxyethane (DME), and diglyme (DG). We find that electrons photodetached from sodide appear after a time delay with their equilibrium spectrum in all of these solvents, suggesting that the entire series of ethers contains pre-existing solvent cavities. We then use the variation in electron recombination dynamics with CTTS excitation wavelength to probe the nature of the cavities in the different ethers. We find that the cavities that form the deepest electron traps turn on at about the same energy in all four ether solvents investigated, but that the density of cavities is lower in DG and DME than in THF. We also examine the dynamics of the neutral sodium species that remains following CTTS photodetachment of an electron from sodide. We find that the reaction of the initially created gas-phase-like Na atom to form a (Na{sup +},e{sup -}) tight-contact pair occurs at essentially the same rate in all four ether solvents, indicating that only local solvent motions and not bulk solvent rearrangements are what is responsible for driving the partial ejection of the remaining Na valence electron.

  15. Electric discharges produced by clouds of charged water droplets in the presence of moving conducting object

    NASA Astrophysics Data System (ADS)

    Kostinskiy, Alexander Y.; Syssoev, Vladimir S.; Mareev, Eugene A.; Rakov, Vladimir A.; Andreev, Mikhail G.; Bogatov, Nikolai A.; Makal'sky, Leonid M.; Sukharevsky, Dmitry I.; Aleshchenko, Alexander S.; Kuznetsov, Vladimir E.; Shatalina, Maria V.

    2015-12-01

    The possibility of initiation of electric discharges by a crossbow bolt (projectile) moving in the electric field of a cloud of negatively charged water droplets has been demonstrated for the first time. Over one hundred of discharges have been produced. For each event, a high-speed video camera recorded the images of upward positive leaders developing from both the nearby grounded sphere and the projectile, followed by the return-stroke-like process. Corresponding currents were measured and integrated photos of the events were obtained. The results can help to improve our understanding of lightning initiation by airborne vehicles and by a vertical conductor rapidly extended below the thundercloud in order to trigger lightning with the rocket-and-wire technique.

  16. Solvent based hydrogen bonding: impact on poly(3-hexylthiophene) nanoscale morphology and charge transport characteristics.

    PubMed

    Chang, Mincheol; Choi, Dalsu; Fu, Boyi; Reichmanis, Elsa

    2013-06-25

    We demonstrate that supramolecular assembly and subsequent enhancement of charge transport characteristics of conjugated polymers can be facilitated simply by adding small amounts of a more volatile poor solvent, which can hydrogen bond with the majority solvent. Addition of up to 2 vol % acetone to a precursor solution of poly(3-hexylthiophene) (P3HT) in chloroform leads to approximately a 4-fold increase in P3HT field-effect mobility. The improvement is associated with hydrogen bonding interactions between acetone and chloroform which decrease the evaporation rate of the mixed solvent. P3HT is less soluble in the binary solvent than in the more readily vaporized chloroform component, and this characteristic enables the supramolecular assembly of P3HT chains at the nanoscale. Two-dimensional molecular ordering of the polymer film was controlled by varying the quantity of poor solvent added to the precursor solution, and the correlation between field-effect mobility and molecular ordering was investigated. Hansen solubility parameters were used to systematically understand how the solvent mixture enhances the alignment and assembly of polymer chains and influences subsequent thin film properties. The value of the relative energy difference (RED) of the solvent with respect to P3HT increased from less than 1 to more than 1 during film formation, which indicates that the solvent characteristics are initially those of a good solvent but transform into those of a poor dissolution medium. A mechanistic illustration of the molecular ordering process during film formation is postulated.

  17. Incorporating the excluded solvent volume and surface charges for computing solvation free energy.

    PubMed

    Yang, Pei-Kun

    2014-01-05

    Gauss's law or Poisson's equation is conventionally used to calculate solvation free energy. However, the near-solute dielectric polarization from Gauss's law or Poisson's equation differs from that obtained from molecular dynamics (MD) simulations. To mimic the near-solute dielectric polarization from MD simulations, the first-shell water was treated as two layers of surface charges, the densities of which are proportional to the electric field at the solvent molecule that is modeled as a hard sphere. The intermediate water was treated as a bulk solvent. An equation describing the solvation free energy of ions using this solvent scheme was derived using the TIP3P water model.

  18. Energetics of charge transfer reactions in solvents of dipolar and higher order multipolar character. II. Results

    NASA Astrophysics Data System (ADS)

    Perng, Baw-Ching; Newton, Marshall D.; Raineri, Fernando O.; Friedman, Harold L.

    1996-05-01

    We apply the theories developed in the preceding paper (paper I) to calculate various energy quantities of charge transfer (CT) reactions in nine solvents that cover a wide range of polarity, and for which interaction site models (ISM's) may be found in the literature. Besides the two surrogate Hamiltonian theories developed in paper I, the renormalized site-density theory (RST) and the renormalized dielectric theory (RDT), we also investigate a simple harmonic approximation (HXA) for the diabatic free energy profiles, whose characteristic parameters are calculated taking specific advantage of the expression given by the extended reference interaction site method (XRISM) for the free energy of solvation. For each CT process we analyze (a) the solvent reorganization energy λ, (b) the shift of the absorption transition energy due to the solvatochromic effect, and (c) the solvent contribution to the free energy change ΔA. In addition, for a few selected examples, we also report the detailed diabatic free energy profiles. The calculations reported rely on solute-solvent and solvent-solvent pair correlation functions obtained with the XRISM integral equation method applied to nonpolarizable (with fixed mean partial charges) ISM representations of the solute and solvent molecules. To rectify the omission of the solvent electronic degrees of freedom, we correct the dielectric part of the solvent reorganization energy with an additive term designed to compensate for the use of fixed charge ISM models. Contact with theories in which the solvent is represented as a dielectric continuum medium (with or without spatial dispersion) and the solute as a set of charges inside spherical cavities carved out of the dielectric is made straightforwardly within the RDT theory by considering a particularly simple form of the solute-solvent RISM site-site direct correlation functions. Using simple ISM models for several solute species, including Reichardt's betaine-30 dye and a

  19. The effect of the charge density of microemulsion droplets on the bending elasticity of their amphiphilic film

    NASA Astrophysics Data System (ADS)

    Farago, B.; Gradzielski, M.

    2001-06-01

    Oil-in-water (O/W) microemulsion droplets have been investigated with respect to the effect of the electric charge density on the bending elasticity of the amphiphilic film. For this an originally uncharged microemulsion system became charged by the substitution of the nonionic by an ionic surfactant (up to 5 mol %). The sum of the bending constants, 2κ+κ¯, has been determined from the polydispersity index p of the droplets and alternatively from the macroscopic interfacial tension γ together with the maximum particle radius Rm. p and Rm were measured by means of small-angle neutron scattering (SANS) experiments in the shell contrast. Neutron spin echo (NSE) has been employed to measure directly the dynamics of the shape fluctuations of the droplets. This method enables a separate determination of κ on its own. It is found that the effect of the increasing charge density leads only to a fairly small increase for the sum of the bending constants 2κ+κ¯. Also the change of the ionic strength for a charged microemulsion system has almost no influence on this sum. NSE measurements show no measurable difference in the dynamics of the charged and uncharged system leading to the conclusion that not only the sum but separately the two bending constants stay within experimental error unchanged. This experimental observation is in contrast to simple electrostatic theories that would predict a much more pronounced influence of the electric charge density on the bending properties of the amphiphilic film.

  20. Influence of droplet charge on the chemical stability of citral in oil-in-water emulsions.

    PubMed

    Choi, Seung Jun; Decker, Eric Andrew; Henson, Lulu; Popplewell, L Michael; McClements, David Julian

    2010-08-01

    The chemical stability of citral, a flavor component widely used in beverage, food, and fragrance products, in oil-in-water emulsions stabilized by surfactants with different charge characteristics was investigated. Emulsions were prepared using cationic (lauryl alginate, LAE), non-ionic (polyoxyethylene (23) lauryl ether, Brij 35), and anionic (sodium dodecyl sulfate, SDS) surfactants at pH 3.5. The citral concentration decreased over time in all the emulsions, but the rate of decrease depended on surfactant type. After 7 d storage, the citral concentrations remaining in the emulsions were around 60% for LAE- or Brij 35-stabilized emulsions and 10% for SDS-stabilized emulsions. An increase in the local proton (H(+)) concentration around negatively charged droplet surfaces may account for the more rapid citral degradation observed in SDS-stabilized emulsions. A strong metal ion chelator (EDTA), which has previously been shown to be effective at increasing the oxidative stability of labile components, had no effect on citral stability in LAE- or Brij 35-stabilized emulsions, but it slightly decreased the initial rate of citral degradation in SDS-stabilized emulsions. These results suggest the surfactant type used to prepare emulsions should be controlled to improve the chemical stability of citral in emulsion systems.

  1. Finite-size effect on the charging free energy of protein in explicit solvent.

    PubMed

    Ekimoto, Toru; Matubayasi, Nobuyuki; Ikeguchi, Mitsunori

    2015-01-13

    The finite-size effect in periodic system is examined for the charging free energy of protein in explicit solvent over a variety of charged states. The key to the finite-size correction is the self-energy, which is defined as the interaction energy of the solute with its own periodic images and the neutralizing background. By employing the thermodynamic-integration method with systematically varied sizes of the unit cell of molecular dynamics (MD) simulations, we show for ubiquitin that the self-energy corrects the finite-size effect on the charging free energy within 1 kcal/mol at total charges of -5e, -1e, neutral, and +1e and within 5 kcal/mol even for a highly charged state with +8e. We then sought the additional correction from the solvation effect using the numerical solution to the Poisson equation of the protein with implicit solvent. This correction reduces the cell-size dependence of the charging free energy at +8e to 3 kcal/mol and is well expressed as the self-energy divided by the dielectric constant of solvent water.

  2. Ions in mixed dielectric solvents: density profiles and osmotic pressure between charged interfaces.

    PubMed

    Ben-Yaakov, Dan; Andelman, David; Harries, Daniel; Podgornik, Rudi

    2009-04-30

    The forces between charged macromolecules, usually given in terms of osmotic pressure, are highly affected by the intervening ionic solution. While in most theoretical studies the solution is treated as a homogeneous structureless dielectric medium, recent experimental studies concluded that, for a bathing solution composed of two solvents (binary mixture), the osmotic pressure between charged macromolecules is affected by the binary solvent composition. By adding local solvent composition terms to the free energy, we obtain a general expression for the osmotic pressure, in planar geometry and within the mean-field framework. The added effect is due to the permeability inhomogeneity and nonelectrostatic short-range interactions between the ions and solvents (preferential solvation). This effect is mostly pronounced at small distances and leads to a reduction in the osmotic pressure for macromolecular separations of the order 1-2 nm. Furthermore, it leads to a depletion of one of the two solvents from the charged macromolecules (modeled as planar interfaces). Lastly, by comparing the theoretical results with experimental ones, an explanation based on preferential solvation is offered for recent experiments on the osmotic pressure of DNA solutions.

  3. Solvent dependence of structure, charge distribution, and absorption spectrum in the photochromic merocyanine-spiropyran pair.

    PubMed

    Murugan, N Arul; Chakrabarti, Swapan; Ågren, Hans

    2011-04-14

    We have studied the structures and absorption spectra of merocyanine, the photoresponsive isomer of the spiropyran (SP)-merocyanine (MC) pair, in chloroform and in water solvents using a combined hybrid QM/MM Car-Parrinello molecular dynamics (CP-QM/MM) and ZINDO approach. We report remarkable differences in the molecular structure and charge distribution of MC between the two solvents; the molecular structure of MC remains in neutral form in chloroform while it becomes charge-separated, zwitterionic, in water. The dipole moment of MC in water is about 50% larger than in chloroform, while the value for SP in water is in between, suggesting that the solvent is more influential than the conformation itself in deciding the dipole moment for the merocyanine-spiropyran pair. The calculations could reproduce the experimentally reported blue shift in the absorption spectra of MC when going from the nonpolar to the polar solvent, though the actual value of the absorption maximum is overestimated in chloroform solvent. We find that the CP-QM/MM approach is appropriate for structure modeling of solvatochromic and thermochromic molecules as this approach is able to capture the solvent and thermal-induced structural changes within the solute important for an accurate assessment of the properties.

  4. Stable nonpolar solvent droplet generation using a poly(dimethylsiloxane) microfluidic channel coated with poly-p-xylylene for a nanoparticle growth.

    PubMed

    Lim, Heejin; Moon, SangJun

    2015-08-01

    Applications of microfluidic devices fabricated in poly(dimethylsiloxane) (PDMS) have been limited to water-based analysis rather than nonpolar solvent based chemistry due to a PDMS swelling problem that occurs by the absorption of the solvents. The absorption and swelling causes PDMS channel deformation in shape, and changes the cross sectional area making it difficult to control the flow rate and concentrations of solution in PDMS microfluidic channels. We propose that poly-p-xylylene polymers (parylenes) are chemical vapors deposited on the surfaces of PDMS channels that alleviate the effect of solvents on the absorption and swelling. The parylene coated surface sustains 3 h with a small volumetric change (less than 22 % of PDMS swelling ratio). By generating an air-nonpolar solvent interface based on droplets in PDMS channel, we confirmed poly-p-xylylene coated PDMS microfluidic channels have the potential to be applicable to nanocrystal growth using nonpolar solvents.

  5. Regimes of electrostatic collapse of a highly charged polyelectrolyte in a poor solvent.

    PubMed

    Tom, Anvy Moly; Vemparala, Satyavani; Rajesh, R; Brilliantov, Nikolai V

    2017-02-08

    We perform extensive molecular dynamics simulations of a highly charged, collapsed, flexible polyelectrolyte chain in a poor solvent for the case when the electrostatic interactions, characterized by the reduced Bjerrum length lB, are strong. We find the existence of several sub-regimes in the dependence of the gyration radius of the chain Rg on lB characterized by Rg ∼ l. In contrast to a good solvent, the exponent γ for a poor solvent crucially depends on the size and valency of the counterions. To explain the different sub-regimes, we generalize the existing counterion fluctuation theory by including a more complete account of all possible volume interactions in the free energy of the polyelectrolyte chain. We also show that the presence of condensed counterions modifies the effective attraction among the chain monomers and modulates the sign of the second virial coefficient under poor solvent conditions.

  6. Solvent-tuned intramolecular charge-recombination rates in a conjugated donor-acceptor molecule

    NASA Technical Reports Server (NTRS)

    Khundkar, Lutfur R.; Stiegman, A. E.; Perry, Joseph W.

    1990-01-01

    The nonradiative charge-recombination rates from the charge-transfer state of a new conjugated donor-acceptor molecule (p-cyano-p-prime-methylthiodiphenylacetylene) can be tuned over almost an order of magnitude by varying the polarity of the solvent. These measurements of intramolecular recombination show a turnover of rates as a function of emission energy, consistent with the 'normal' and 'inverted' behavior of Marcus theory. Steady-state spectra and time-resolved measurements make it possible to quantitatively compare thermal and optical electron-transfer rates as a function of driving force and demonstrate their correspondence.

  7. Plasma charging and electron-based reactions at the plasma-liquid interface of an isolated liquid droplet

    NASA Astrophysics Data System (ADS)

    Maguire, Paul; Mahony, Charles; Kelsey, Colin; Rutherford, David; Mariotti, Davide; Diver, Declan

    2016-09-01

    The study of plasma-liquid interactions opens up exciting new opportunities for applications but numerous investigative challenges remain. The use of isolated and stable spherical liquid microdroplets in a non-thermal equilibrium atmospheric pressure plasma offers a new platform for experimental and theoretical investigations. Since the droplet assumes floating potential, a high flux of electrons with low net energy ( thermal) becomes fixed and solvated within the first monolayers of the liquid leading to highly reactive and rapid chemical reactions. We observe such reactions, e.g. H2 O2 and metal nanoparticle formation, at rates that are much higher than reported elsewhere. Since the isolated droplet radius is greater than Debye lengths and mean free paths, we have an opportunity to directly compare, for the first time, long-standing collisional probe theories in this important regime. We measure a lower bound average charge of >1E5 electrons on a 13um droplet. Simulations of unipolar corona charging for this size predict 1E3 electrons. A Comsol-based drift-diffusion model is currently under development and so far experiment and theory match within 1 order of magnitude but improvements in measurement technique are in progress. Funding from EPSRC acknowledged (Grants EP/K006088/1 and EP/K006142/1).

  8. Rotational Diffusion of Charged and Nondipolar Solutes in Ionic Liquid-Organic Solvent Mixtures: Evidence for Stronger Specific Solute-Solvent Interactions in Presence of Organic Solvent.

    PubMed

    Prabhu, Sugosh R; Dutt, G B

    2015-08-20

    Rotational diffusion of a charged solute, rhodamine 110 (R110), and a nondipolar solute, 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP), has been investigated in ionic liquids, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][Tf2N]) and 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([BMIM][FAP]), with 0.8 mole fraction of dibenzyl ether (DBE). This study has been undertaken to find out how specific interactions between the solute and the ionic liquid are affected upon dilution with a nondipolar solvent. It has been observed that at a given viscosity (η) and temperature (T), the reorientation times of R110 increase by 40-60% in the ionic liquid-organic solvent mixtures compared to ones in the corresponding neat ionic liquids. In the case of DMDPP, the influence of DBE is less pronounced, and its reorientation times increase by 25-50% at a given η/T. The addition of DBE weakens the numerous interactions prevailing between the cations and the anions of the ionic liquids, which results in stronger specific interactions between the solutes and the constituent ions, consequently leading to slower rotation of the solutes.

  9. Indirectly suspended droplet microextraction of water-miscible organic solvents by salting-out effect for the determination of polycyclic aromatic hydrocarbons.

    PubMed

    Daneshfar, Ali; Khezeli, Tahere

    2014-12-01

    A simple and low-cost method that indirectly suspended droplet microextraction of water-miscible organic solvents (ISDME) by salting-out effect before high-performance liquid chromatography and ultraviolet (HPLC-UV) detection was used for the determination of polycyclic aromatic hydrocarbons (PAHs) in different samples. The ISDME is a combination of salting-out extraction of water-miscible organic solvent and directly suspended droplet microextraction (DSDME). Ninety-five microliters water-miscible organic solvent (1-propanol) was added to a 500-µL sample. A homogeneous solution was formed immediately. To produce a steady vortex at the top of the solution, the sample was agitated at 700 rpm using a magnetic stirrer. By the addition of ammonium sulfate (saturated solution) to the homogeneous solution, 1-propanol was separated and collected at the bottom of the steady vortex. Finally, 20 µL 1-propanol was injected into HPLC-UV. The effects of important parameters such as water-miscible organic solvent (type and volume), type of salt, and extraction time were evaluated. Under optimum conditions, the method has a good linear calibration range (0.1 µg/L-300 µg/L), coefficients of determination (R(2) > 0.998), low limits of detection (between 0.02 µg/L and 0.27 µg/L), and acceptable recovery (>85.0%).

  10. Spectrophotometric study of the charge-transfer complexes of iodine with antipyrine in organic solvents

    NASA Astrophysics Data System (ADS)

    Hasani, Masoumeh; Rezaei, Alireza

    2006-12-01

    The charge-transfer complex formation of iodine with antipyrine has been studied spectrophotometrically in chloroform, dichloromethane (DCM) and 1,2-dichloroethane (DCE) solutions at 25 °C. The results indicate the formation of 1:1 charge-transfer complexes. The observed time dependence of the charge-transfer band and subsequent formation of I 3- in solution were related to the slow transformation of the initially formed 1:1 antipyrine:I 2 outer complex to an inner electron donor-acceptor (EDA) complex, followed by fast reaction of the inner complex with iodine to form a triiodide ion. The values of the equilibrium constant, K, are calculated for each complex and the influence of the solvent properties on the formation of EDA complexes and the rates of subsequent reaction is evaluated.

  11. Spectrophotometric study of the charge-transfer complexes of iodine with antipyrine in organic solvents.

    PubMed

    Hasani, Masoumeh; Rezaei, Alireza

    2006-12-01

    The charge-transfer complex formation of iodine with antipyrine has been studied spectrophotometrically in chloroform, dichloromethane (DCM) and 1,2-dichloroethane (DCE) solutions at 25 degrees C. The results indicate the formation of 1:1 charge-transfer complexes. The observed time dependence of the charge-transfer band and subsequent formation of I(3)(-) in solution were related to the slow transformation of the initially formed 1:1 antipyrine:I(2) outer complex to an inner electron donor-acceptor (EDA) complex, followed by fast reaction of the inner complex with iodine to form a triiodide ion. The values of the equilibrium constant, K, are calculated for each complex and the influence of the solvent properties on the formation of EDA complexes and the rates of subsequent reaction is evaluated.

  12. Profiling an electrospray plume by laser-induced fluorescence and Fraunhofer diffraction combined to mass spectrometry: influence of size and composition of droplets on charge-state distributions of electrosprayed proteins.

    PubMed

    Girod, Marion; Dagany, Xavier; Boutou, Véronique; Broyer, Michel; Antoine, Rodolphe; Dugourd, Philippe; Mordehai, Alex; Love, Craig; Werlich, Mark; Fjeldsted, John; Stafford, George

    2012-07-14

    We investigated how physico-chemical properties of charged droplets are affected by the electrospray process, using simultaneous in situ measurements by laser-induced fluorescence (LIF), Fraunhofer diffraction and mass spectrometry. For this purpose, we implemented a laser-induced-fluorescence profiling setup in conjunction with a fast, high-resolution particle sizing scheme on a modified Agilent Jet Stream electrospray source coupled to a single quadrupole mass analyser. The optical setup permits us to profile the solvent fractionation and the size of the droplets as they evaporate in an electrospray plume by measuring both the angular scattering pattern and emission spectra of a solvatochromic fluorescent dye. Mass spectra are recorded simultaneously. These mass spectrometry and optical spectroscopy investigations allow us to study the relation between the observed charge-state distributions of protein anions and physico-chemical properties of evaporating droplets in the spray plume. By mixing water with methanol, a refolding of cytochrome C is observed as the water percentage increases in the plume due to the preponderant evaporation of volatile methanol.

  13. On the hardness evaluation in solvent for neutral and charged systems.

    PubMed

    De Luca, G; Sicilia, E; Russo, N; Mineva, T

    2002-02-20

    The influence of water on the hardness values of a series of neutral and charged molecules has been studied in the framework of density functional theory using the polarizable continuum model to take into account solvent effects. Three working formulas already widely tested in gas-phase have been used and the results compared. Two of the methods employed going from gas phase to solvent phase give values that do not change, while the results of the third method show remarkable changes. To check the reliability of the hardness behavior found, a test based on the hard-soft/acid-base principle and the calculation of the free energy of reaction has been applied using the adopted procedures.

  14. A comparative study of room temperature ionic liquids and their organic solvent mixtures near charged electrodes

    NASA Astrophysics Data System (ADS)

    Vatamanu, Jenel; Vatamanu, Mihaela; Borodin, Oleg; Bedrov, Dmitry

    2016-11-01

    The structural properties of electrolytes consisting of solutions of ionic liquids in a polar solvent at charged electrode surfaces are investigated using classical atomistic simulations. The studied electrolytes consisted of tetraethylammonium tetrafluoroborate (NEt4-BF4), 1-ethyl-3-methylimidazolium tetrafluoroborate (c2mim-BF4) and 1-octyl-3-methylimidazolium tetrafluoroborate (c8mim-BF4) salts dissolved in acetonitrile solvent. We discuss the influence of electrolyte concentration, chemical structure of the ionic salt, temperature, conducting versus semiconducting nature of the electrode, electrode geometry and surface roughness on the electric double layer structure and capacitance and compare these properties with those obtained for pure room temperature ionic liquids. We show that electrolytes consisting of solutions of ions can behave quite differently from pure ionic liquid electrolytes.

  15. Scaling Atomic Partial Charges of Carbonate Solvents for Lithium Ion Solvation and Diffusion

    SciTech Connect

    Chaudhari, Mangesh I.; Nair, Jijeesh R.; Pratt, Lawrence R.; Soto, Fernando A.; Balbuena, Perla B.; Rempe, Susan B.

    2016-10-21

    Lithium-ion solvation and diffusion properties in ethylene carbonate (EC) and propylene carbonate (PC) were studied by molecular simulation, experiments, and electronic structure calculations. Studies carried out in water provide a reference for interpretation. Classical molecular dynamics simulation results are compared to ab initio molecular dynamics to assess nonpolarizable force field parameters for solvation structure of the carbonate solvents. Quasi-chemical theory (QCT) was adapted to take advantage of fourfold occupancy of the near-neighbor solvation structure observed in simulations and used to calculate solvation free energies. The computed free energy for transfer of Li+ to PC from water, based on electronic structure calculations with cluster-QCT, agrees with the experimental value. The simulation-based direct-QCT results with scaled partial charges agree with the electronic structure-based QCT values. The computed Li+/PF6- transference numbers of 0.35/0.65 (EC) and 0.31/0.69 (PC) agree well with NMR experimental values of 0.31/0.69 (EC) and 0.34/0.66 (PC) and similar values obtained here with impedance spectroscopy. These combined results demonstrate that solvent partial charges can be scaled in systems dominated by strong electrostatic interactions to achieve trends in ion solvation and transport properties that are comparable to ab initio and experimental results. Thus, the results support the use of scaled partial charges in simple, nonpolarizable force fields in future studies of these electrolyte solutions.

  16. Scaling Atomic Partial Charges of Carbonate Solvents for Lithium Ion Solvation and Diffusion

    DOE PAGES

    Chaudhari, Mangesh I.; Nair, Jijeesh R.; Pratt, Lawrence R.; ...

    2016-10-21

    Lithium-ion solvation and diffusion properties in ethylene carbonate (EC) and propylene carbonate (PC) were studied by molecular simulation, experiments, and electronic structure calculations. Studies carried out in water provide a reference for interpretation. Classical molecular dynamics simulation results are compared to ab initio molecular dynamics to assess nonpolarizable force field parameters for solvation structure of the carbonate solvents. Quasi-chemical theory (QCT) was adapted to take advantage of fourfold occupancy of the near-neighbor solvation structure observed in simulations and used to calculate solvation free energies. The computed free energy for transfer of Li+ to PC from water, based on electronic structuremore » calculations with cluster-QCT, agrees with the experimental value. The simulation-based direct-QCT results with scaled partial charges agree with the electronic structure-based QCT values. The computed Li+/PF6- transference numbers of 0.35/0.65 (EC) and 0.31/0.69 (PC) agree well with NMR experimental values of 0.31/0.69 (EC) and 0.34/0.66 (PC) and similar values obtained here with impedance spectroscopy. These combined results demonstrate that solvent partial charges can be scaled in systems dominated by strong electrostatic interactions to achieve trends in ion solvation and transport properties that are comparable to ab initio and experimental results. Thus, the results support the use of scaled partial charges in simple, nonpolarizable force fields in future studies of these electrolyte solutions.« less

  17. Predicting solvent-water partitioning of charged organic species using quantum-chemically estimated Abraham pp-LFER solute parameters.

    PubMed

    Davis, Craig Warren; Di Toro, Dominic M

    2016-12-01

    Methods for obtaining accurate predictions of solvent-water partitioning for neutral organic chemicals (e.g., Kow) are well-established. However, methods that provide comparable accuracy are not available for predicting the solvent-water partitioning of ionic species. Previous methods for addressing charge contributions to solvent-water partitioning rely on charged solute descriptors which are obtained from regressions to neutral species descriptors as well as charged descriptors which are specific to unique charge-functionalities and structural moieties. This paper presents a method for obtaining Abraham poly-parameter linear free energy relationship (pp-LFER) descriptors using quantum chemical calculations and molecular structure, only. The method utilizes a large number of solvent-water systems to overcome large errors in individual quantum chemical computations of ionic solvent-water partition coefficients. The result is a single set of quantum-chemically estimated Abraham solute parameters (QCAP) which are solvent-independent, and can be used to predict the solvent-water partitioning of ionic species. Predictions of solvent-water partition coefficients for ionic species using quantum-chemically estimated Abraham parameters (QCAPs) are shown to provide improved accuracy compared over both existing Absolv-estimated Abraham solute parameters (AAP) as well as direct a priori quantum chemical (QC) calculations for partitioning of anionic solutes in 4 organic solvent-water systems (RMS = 0.740, 2.48 and 0.426 for the Absolv, QC and QCAP methods, respectively). For quaternary amine cations in the octanol-water system the RMS errors of the solvent-water partition coefficients were larger and similar between the two Abraham models (RMSE = 0.997 and 1.16, for the AAP and QCAP methods, respectively). Both methods showed significant improvement over direct QC calculations (RMSE = 2.82).

  18. Solvent blends can control cationic reversed micellar interdroplet interactions. The effect of n-heptane:benzene mixture on BHDC reversed micellar interfacial properties: droplet sizes and micropolarity.

    PubMed

    Agazzi, Federico M; Falcone, R Dario; Silber, Juana J; Correa, N Mariano

    2011-10-27

    We have investigated, for the first time, the effect of the composition of the nonpolar organic media on the benzyl-n-hexadecyl-dimethylammonium chloride (BHDC) reversed micelles (RMs) properties at fixed temperature. To achieve this goal we have used the solvatochromic behavior of 1-methyl-8-oxyquinolinium betaine (QB) as absorption probe and dynamic light scattering (DLS), to monitor droplet sizes, interfacial micropolarity, and sequestrated water structure of water/BHDC/n-heptane:benzene RMs. DLS results confirm the formation of the water/BHDC/n-heptane:benzene RMs at every n-heptane mole fraction (X(Hp)) investigated, that is, X(Hp) = 0.00, 0.13, 0.21, 0.30, and 0.38. Also, DLS was used to measure the RMs diffusion coefficient and to calculate the apparent droplet hydrodynamic diameter (d(App)) at different compositions of the nonpolar organic medium. The data suggest that as the n-heptane content increases, the interdroplet attractive interactions also increase with the consequent increment in the droplet size. Moreover, the interdroplet attractive interactions can be "switched on (increased)" or "switched off (decreased)" by formulation of appropriate n-heptane:benzene mixtures. Additionally, QB spectroscopy was used to obtain the "operational" critical micellar concentration (cmc) and to investigate both the RMs interfacial micropolarity and the sequestrated water structure in every RMs studied. The results show that BHDC RMs are formed at lower surfactant concentration when n-heptane or water content increases. When the interdroplet interaction "switches on", the RMs droplet sizes growth expelling benzene molecules from the RMs interface, favoring the water-BHDC interaction at the interface with the consequent increases in the interfacial micropolarity. Therefore, changing the solvent blend is possible to affect dramatically the interfacial micropolarity, the droplet sizes and the structure of the entrapped water.

  19. An implicit solvent model for SCC-DFTB with Charge-Dependent Radii

    PubMed Central

    Hou, Guanhua; Zhu, Xiao; Cui, Qiang

    2010-01-01

    Motivated by the need of rapidly exploring the potential energy surface of chemical reactions that involve highly charged species, we have developed an implicit solvent model for the approximate density functional theory, SCC-DFTB. The solvation free energy is calculated using the popular model that employs Poisson-Boltzmann for electrostatics and a surface-area term for non-polar contributions. To balance the treatment of species with different charge distributions, we make the atomic radii that define the dielectric boundary and solute cavity depend on the solute charge distribution. Specifically, the atomic radii are assumed to be linearly dependent on the Mulliken charges and solved self-consistently together with the solute electronic structure. Benchmark calculations indicate that the model leads to solvation free energies of comparable accuracy to the SM6 model (especially for ions), which requires much more expensive DFT calculations. With analytical first derivatives and favorable computational speed, the SCC-DFTB based solvation model can be effectively used, in conjunction with high-level QM calculations, to explore the mechanism of solution reactions. This is illustrated with a brief analysis of the hydrolysis of mono-methyl mono-phosphate ester (MMP) and tri-methyl mono-phosphate ester (TMP). Possible future improvements are also briefly discussed. PMID:20711513

  20. Solvent Role in the Formation of Electric Double Layers with Surface Charge Regulation: A Bystander or a Key Participant?

    NASA Astrophysics Data System (ADS)

    Fleharty, Mark E.; van Swol, Frank; Petsev, Dimiter N.

    2016-01-01

    The charge formation at interfaces involving electrolyte solutions is due to the chemical equilibrium between the surface reactive groups and the potential determining ions in the solution (i.e., charge regulation). In this Letter we report our findings that this equilibrium is strongly coupled to the precise molecular structure of the solution near the charged interface. The neutral solvent molecules dominate this structure due to their overwhelmingly large number. Treating the solvent as a structureless continuum leads to a fundamentally inadequate physical picture of charged interfaces. We show that a proper account of the solvent effect leads to an unexpected and complex system behavior that is affected by the molecular and ionic excluded volumes and van der Waals interactions.

  1. Substituent and Solvent Effects on Excited State Charge Transfer Behavior of Highly Fluorescent Dyes Containing Thiophenylimidazole-Based Aldehydes

    NASA Technical Reports Server (NTRS)

    Santos, Javier; Bu, Xiu R.; Mintz, Eric A.

    2001-01-01

    The excited state charge transfer for a series of highly fluorescent dyes containing thiophenylimidazole moiety was investigated. These systems follow the Twisted Intramolecular Charge Transfer (TICT) model. Dual fluorescence was observed for each substituted dye. X-ray structures analysis reveals a twisted ground state geometry for the donor substituted aryl on the 4 and 5 position at the imidazole ring. The excited state charge transfer was modeled by a linear solvation energy relationship using Taft's pi and Dimroth's E(sub T)(30) as solvent parameters. There is linear relation between the energy of the fluorescence transition and solvent polarity. The degree of stabilization of the excited state charge transfer was found to be consistent with the intramolecular molecular charge transfer. Excited dipole moment was studied by utilizing the solvatochromic shift method.

  2. Solvent electronic polarization effects on a charge transfer excitation studied by the mean-field QM/MM method

    SciTech Connect

    Nakano, Hiroshi

    2015-12-31

    Electronic polarization effects of a medium can have a significant impact on a chemical reaction in condensed phases. We discuss the effects on the charge transfer excitation of a chromophore, N,N-dimethyl-4-nitroaniline, in various solvents using the mean-field QM/MM method with a polarizable force field. The results show that the explicit consideration of the solvent electronic polarization effects is important especially for a solvent with a low dielectric constant when we study the solvatochromism of the chromophore.

  3. Generating electric current based on the solvent-dependent charging effects of defective boron nitride nanosheets.

    PubMed

    Que, Ronghui; Huang, Yucheng; Li, Qinling; Yao, Hong; Geng, Baoyou; Shao, Mingwang

    2014-11-26

    This work presents a method of generating electric current based on the defects of few-layer boron nitride nanosheets (BNNSs). The density functional theory calculations showed that the atomic charge of the B atom in acetone was more positive than in water. The electrostatic force microscopy measurements illustrated that the local electrical potential was 0.35 mV in acetone, while the potential signal was very difficult to capture when using water as the dispersant. This effect was further demonstrated by the performance of the acoustic energy-harvesting nanogenerator: the BNNSs were assembled into a film after being dispersed in acetone and then integrated into the generator device, generating average output current of ∼0.98 nA, which was much better than 0.2 nA, the average output current of another device with water as the dispersant. These results demonstrated that solvent effects made the as-prepared BNNSs carry net charges, which could be utilized to harvest acoustic energy and generate current.

  4. Insight into nanoparticle charging mechanism in nonpolar solvents to control the formation of Pt nanoparticle monolayers by electrophoretic deposition

    DOE PAGES

    Cernohorsky, Ondrej; Grym, Jan; Yatskiv, Roman; ...

    2016-08-13

    We report on the formation of Pt nanoparticle monolayers by electrophoretic deposition from nonpolar solvents. First, the growth kinetics of Pt nanoparticles prepared by the reverse micelle technique are described in detail. Second, a model of nanoparticle charging in nonpolar media is discussed and methods to control the nanoparticle charging are proposed. Lastly, essential parameters of the electrophoretic deposition process to control the deposition of nanoparticle monolayers are discussed and mechanisms of their formation are analyzed.

  5. Theoretical evidence of charge transfer interaction between SO₂ and deep eutectic solvents formed by choline chloride and glycerol.

    PubMed

    Li, Hongping; Chang, Yonghui; Zhu, Wenshuai; Wang, Changwei; Wang, Chao; Yin, Sheng; Zhang, Ming; Li, Huaming

    2015-11-21

    The nature of the interaction between deep eutectic solvents (DESs), formed by ChCl and glycerol, and SO2 has been systematically investigated using the M06-2X density functional combined with cluster models. Block-localized wave function energy decomposition (BLW-ED) analysis shows that the interaction between SO2 and DESs is dominated by a charge transfer interaction. After this interaction, the SO2 molecule becomes negatively charged, whereas the ChCl-glycerol molecule is positively charged, which is the result of Lewis acid-base interaction. The current result affords a theoretical proof that it is highly useful and efficient to manipulate the Lewis acidity of absorbents for SO2 capture. Moreover, hydrogen bonding as well as electrostatic interactions may also contribute to the stability of the complex. Structure analysis shows that solvent molecules will adjust their geometries to interact with SO2. In addition, the structure of SO2 is barely changed after interaction. The interaction energy between different cluster models and SO2 ranges from -6.8 to -14.4 kcal mol(-1). It is found that the interaction energy is very sensitive to the solvent structure. The moderate interaction between ChCl-glycerol and SO2 is consistent with the concept that highly efficient solvents for SO2 absorption should not only be solvable but also regenerable.

  6. Solvent effects on global reactivity properties for neutral and charged systems using the sequential Monte Carlo quantum mechanics model.

    PubMed

    Jaramillo, Paula; Pérez, Patricia; Fuentealba, Patricio; Canuto, Sylvio; Coutinho, Kaline

    2009-04-02

    The energy of the frontier molecular orbitals and reactivity indices such as chemical potential, hardness, and electrophilicity of neutral and charged molecules have been investigated in aqueous solution using explicit model for the solvent with the sequential Monte Carlo/quantum mechanics methodology. The supermolecular structures of the solute-solvent system were generated by Monte Carlo simulation. Statistically uncorrelated structures have been extracted for quantum mechanical calculations of the solute surrounded by the first solvation shell, using explicit water molecules, and the second and third shells as atomic point charges. The supermolecular calculations treating both the solute and the solvent explicitly were performed within density functional theory. The solvent dependence of the frontier molecular orbital energies was analyzed and used to calculate the reactivity indices in solution. The dependence of the results with respect to the number of explicit solvent molecules is also analyzed. It is seen that for the systems considered here, the energies of the highest occupied molecular orbital and the lowest unoccupied molecular orbital show a strong dependence with the number of solvent molecules. However, the properties derived from these are relatively stable. In particular, the results reported here for the reactivity indices obtained using the first solvation shell are similar to those obtained for the limit bulk value. For comparison, the reactivity indices were also calculated in the gas phase and using the polarizable continuum model (PCM). As frequently reported in the literature, neutral molecules do not show significant changes in the reactivity indices between gas phase and the PCM model. However, with the explicit solvent model some important changes were observed: a larger negative chemical potential, a smaller hardness, and a larger electrophilicity. The stabilization of an anion corresponding to a negative chemical potential is obtained

  7. A counter-charge layer in generalized solvents framework for electrical double layers in neat and hybrid ionic liquid electrolytes

    SciTech Connect

    Huang, Jingsong; Feng, Guang; Sumpter, Bobby G; Qiao, Rui; Meunier, Vincent

    2011-01-01

    Room-temperature ionic liquids (RTILs) have received significant attention as electrolytes due to a number of attractive properties such as their wide electrochemical windows. Since electrical double layers (EDLs) are the cornerstone for the applications of RTILs in electrochemical systems such as supercapacitors, it is important to develop an understanding of the structure capacitance relationships for these systems. Here we present a theoretical framework termed counter-charge layer in generalized solvents (CGS) for describing the structure and capacitance of the EDLs in neat RTILs and in RTILs mixed with different mass fractions of organic solvents. Within this framework, an EDL is made up of a counter-charge layer exactly balancing the electrode charge, and of polarized generalized solvents (in the form of layers of ion pairs, each of which has a zero net charge but has a dipole moment the ion pairs thus can be considered as a generalized solvent) consisting of all RTILs inside the system except the counter-ions in the counter-charge layer, together with solvent molecules if present. Several key features of the EDLs that originate from the strong ion ion correlation in RTILs, e.g., overscreening of electrode charge and alternating layering of counter-ions and co-ions, are explicitly incorporated into this framework. We show that the dielectric screening in EDLs is governed predominately by the polarization of generalized solvents (or ion pairs) in the EDL, and the capacitance of an EDL can be related to its microstructure with few a priori assumptions or simplifications. We use this framework to understand two interesting phenomena observed in molecular dynamics simulations of EDLs in a neat IL of 1-butyl-3- methylimidazolium tetrafluoroborate ([BMIM][BF4]) and in a mixture of [BMIM][BF4] and acetonitrile (ACN): (1) the capacitance of the EDLs in the [BMIM][BF4]/ACN mixture increases only slightly when the mass fraction of ACN in the mixture increases from zero

  8. Lateral resolution of desorption nanoelectrospray: a nanospray tip without nebulizing gas as a source of primary charged droplets.

    PubMed

    Hartmanová, L; Lorencová, I; Volný, M; Fryčák, P; Havlíček, V; Chmelíčková, H; Ingr, T; Lemr, K

    2016-04-07

    Desorption nanoelectrospray (nanoDESI) was described in 2007 and it represents a miniaturized version of desorption electrospray without the assistance of the nebulizing gas. Compared to DESI, a nanoelectrospray tip (2 ± 1 μm I.D.) generates primary charged droplets of smaller sizes and lower spray liquid flow rates. This is the first report on utilization of nanoDESI for mass spectrometry imaging (MSI). Its new coupling with a Q-TOF instrument allowed faster mass spectra acquisition (4 Hz) essential for MSI of fine surface details. To evaluate nanoDESI potential for mass spectrometry imaging, etched glass substrates with Rhodamine B patterns of different dimensions were prepared. The Rhodamine B lines were analysed in 1D scanning mode and their width was determined experimentally by nanoDESI measurement. The experimental data revealed that the lateral resolution of nanoDESI is close to 30 μm along the x-axis (orthogonal to the inlet). 2D scanning mode confirmed good resolution along both axes as dye squares with dimensions about 60 μm × 60 μm were easily distinguished. The low flow rate of the spray liquid reduced undesirable analyte washing effects, which allowed repeated scanning analysis of the surface. The presented results demonstrate the applicability of nanoDESI for high surface resolution mass spectrometry imaging.

  9. Solvation effect on conformations of 1,2:Dimethoxyethane: Charge dependent nonlinear response in implicit solvent models

    PubMed Central

    Jha, Abhishek K; Freed, Karl F

    2009-01-01

    We provide an improvement in the Langevin-Debye model currently being used in some implicit solvent models for computer simulations of solvation free energies of small organic molecules, as well as of biomolecular folding and binding. The analysis is based on the implementation of a charge-dependent Langevin-Debye (qLD) model that is modified by subsequent corrections due to Onsager and Kirkwood. The physical content of the model is elucidated by discussing the general treatment within the LD model of the self-energy of a charge submerged in a dielectric medium for three different limiting conditions and by considering the nonlinear response of the medium. The modified qLD model is used to refine an implicit solvent model (previously applied to protein dynamics). The predictions of the modified implicit solvent model are compared with those from explicit solvent molecular dynamics simulations for the equilibrium conformational populations of 1,2-dimethoxyethane (DME), which is the shortest ether molecule to reproduce the local conformational properties of PEO, a polymer with tremendous technological importance and a wide variety of applications. Because the conformational population preferences of DME change dramatically upon solvation, DME provides a good test case to validate our modified qLD model. PMID:18205504

  10. Synthesis and spectrophotometric studies of charge transfer complexes of p-nitroaniline with benzoic acid in different polar solvents

    NASA Astrophysics Data System (ADS)

    Singh, Neeti; Ahmad, Afaq

    2014-09-01

    The charge transfer complexes of the donor p-nitroaniline (PNA) with the π-acceptor benzoic acid (BEA) have been studied spectrophotometrically in various solvents such as acetone, ethanol, and methanol at room temperature using an absorption spectrophotometer. The outcome suggests that the formation of the CT-complex is comparatively high in less polar solvent. The stoichiometry of the CT-complex was found to be 1:1. The physical parameters of the CT-complex were evaluated by the Benesi-Hildebrand equation. The data are discussed in terms of the formation constant (KCT), molar extinction coefficient (ɛCT), Standard Gibbs free energy (ΔG0), oscillator strength (f), transition dipole moment (μEN), resonance energy (RN) and ionization potential (ID). The formation constant (KCT) of the complex was depends upon the nature of electron acceptor, donor, and polarity of solvents used. It is also observed that a charge transfer molecular complex is stabilized by hydrogen bonding. The formation of the complex has been confirmed by UV-visible, FT-IR, 1H NMR and TGA/DTA. The structure of the CT-complex is [(PNA)+ (BEA)-]. A general mechanism for its formation of the complex has also been proposed.

  11. Accelerated Chemical Reactions and Organic Synthesis in Leidenfrost Droplets.

    PubMed

    Bain, Ryan M; Pulliam, Christopher J; Thery, Fabien; Cooks, R Graham

    2016-08-22

    Leidenfrost levitated droplets can be used to accelerate chemical reactions in processes that appear similar to reaction acceleration in charged microdroplets produced by electrospray ionization. Reaction acceleration in Leidenfrost droplets is demonstrated for a base-catalyzed Claisen-Schmidt condensation, hydrazone formation from precharged and neutral ketones, and for the Katritzky pyrylium into pyridinium conversion under various reaction conditions. Comparisons with bulk reactions gave intermediate acceleration factors (2-50). By keeping the volume of the Leidenfrost droplets constant, it was shown that interfacial effects contribute to acceleration; this was confirmed by decreased reaction rates in the presence of a surfactant. The ability to multiplex Leidenfrost microreactors, to extract product into an immiscible solvent during reaction, and to use Leidenfrost droplets as reaction vessels to synthesize milligram quantities of product is also demonstrated.

  12. Effect of solvent hydrogen bonding on the photophysical properties of intramolecular charge transfer probe trans-ethyl p-(dimethylamino) cinamate and its derivative

    NASA Astrophysics Data System (ADS)

    Singh, T. Sanjoy; Moyon, N. S.; Mitra, Sivaprasad

    2009-08-01

    Intramolecular charge transfer (ICT) behavior of trans-ethyl p-(dimethylamino) cinamate (EDAC) and 4-(dimethylamino) cinnamic acid (DMACA) were studied by steady state absorption and emission, picosecond time-resolved fluorescence experiments in various pure and mixed solvent systems. The large fluorescence spectral shift in more polar solvents indicates an efficient charge transfer from the donor site to the acceptor moiety in the excited state compared to the ground state. The energy for 0,0 transition ( ν0,0) for EDAC shows very good linear correlation with static solvent dielectric property; however, fluorescence emission maximum, stokes shift and fluorescence quantum yield show significant deviation from linearity in polar protic solvents, indicating a large contribution of solvent hydrogen bonding on the excited state relaxation mechanism. A quantitative estimation of contribution from different solvatochromic parameters was made using linear free energy relationship based on Kamlet-Taft equation.

  13. Effect of partial atomic charges on the calculated free energy of solvation of poly(vinyl alcohol) in selected solvents.

    PubMed

    Noorjahan, Abolfazl; Choi, Phillip

    2015-03-01

    It is well-known that properties of poly(vinyl alcohol) (PVA) in the pure and solution states depend largely on the hydrogen bonding networks formed. In the context of molecular simulation, such networks are handled through the Coulombic interactions. Therefore, a good set of partial atom charges (PACs) for simulations involving PVA is highly desirable. In this work, we calculated the PACs for PVA using a few commonly used population analysis schemes with a hope to identify an accurate set of PACs for PVA monomers. To evaluate the quality of the calculated parameters, we have benchmarked their predictions for free energy of solvation (FES) in selected solvents by molecular dynamics simulations against the ab initio calculated values. Selected solvents were water, ethanol and benzene as they covered a range of size and polarity. Also, PVA with different tacticities were used to capture their effect on the calculated FESs. Based on our results, neither PACs nor FESs are affected by the chain tacticity. While PACs predicted by the Merz-Singh-Kollman scheme were close to original values in the OPLS-AA force field in way that no significant difference in properties of pure PVA was observed, free energy of solvation calculated using such PACs showed greater agreement with ab initio calculated values than those calculated by OPLS-AA (and all other schemes used in this work) in all three solvents considered.

  14. Equation of motion for the solvent polarization apparent charges in the polarizable continuum model: Application to time-dependent CI

    NASA Astrophysics Data System (ADS)

    Pipolo, Silvio; Corni, Stefano; Cammi, Roberto

    2017-02-01

    The dynamics of the electrons for a molecule in solution is coupled to the dynamics of its polarizable environment, i.e., the solvent. To theoretically investigate such electronic dynamics, we have recently developed equations of motion (EOM) for the apparent solvent polarization charges that generate the reaction field in the Polarizable Continuum Model (PCM) for solvation and we have coupled them to a real-time time-dependent density functional theory (RT TDDFT) description of the solute [S. Corni et al., J. Phys. Chem. A 119, 5405 (2014)]. Here we present an extension of the EOM-PCM approach to a Time-Dependent Configuration Interaction (TD CI) description of the solute dynamics, which is free from the qualitative artifacts of RT TDDFT in the adiabatic approximation. As tests of the developed approach, we investigate the solvent Debye relaxation after an electronic excitation of the solute obtained either by a π pulse of light or by assuming the idealized sudden promotion to the excited state. Moreover, we present EOM for the Onsager solvation model and we compare the results with PCM. The developed approach provides qualitatively correct real-time evolutions and is promising as a general tool to investigate the electron dynamics elicited by external electromagnetic fields for molecules in solution.

  15. Solvent accessibility, residue charge and residue volume, the three ingredients of a robust amino acid substitution matrix.

    PubMed

    Goodarzi, Hani; Katanforoush, Ali; Torabi, Noorossadat; Najafabadi, Hamed Shateri

    2007-04-21

    Cost measure matrices or different amino acid indices have been widely used for studies in many fields of biology. One major criticism of these studies might be based on the unavailability of an unbiased and yet effective amino acid substitution matrix. Throughout this study we have devised a cost measure matrix based on the solvent accessibility, residue charge, and residue volume indices. Performed analyses on this novel substitution matrix (i.e. solvent accessibility charge volume (SCV) matrix) support the uncontaminated nature of this matrix regarding the genetic code. Although highly similar to a number of previously available cost measure matrices, the SCV matrix results in a more significant optimality in the error-buffering capacity of the genetic code when compared to many other amino acid substitution matrices. Besides, a method to compare an SCV-based scoring matrix with a number of widely used matrices has been devised, the results of which highlights the robustness of this matrix in protein family discrimination.

  16. Photoinduced charge generation rates in soluble P3HT : PCBM nano-aggregates predict the solvent-dependent film morphology

    NASA Astrophysics Data System (ADS)

    Roy, Palas; Jha, Ajay; Dasgupta, Jyotishman

    2016-01-01

    The device efficiency of bulk heterojunction (BHJ) solar cells is critically dependent on the nano-morphology of the solution-processed polymer : fullerene blend. Active control on blend morphology can only emanate from a detailed understanding of solution structures during the film casting process. Here we use photoinduced charge transfer (CT) rates to probe the effective length scale of the pre-formed solution structures and their energy disorder arising from a mixture of poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in three different organic solvents. The observed solvent-dependent ultrafast biphasic rise of the transient polaron state in solution along with changes detected in the C&z.dbd;C stretching frequency of bound PCBM provides direct evidence for film-like P3HT : PCBM interfaces in solution. Using the diffusive component of the charge transfer rate, we deduce ~3-times larger functional nano-domain size in toluene than in chlorobenzene thereby correctly predicting the relative polymer nanofiber widths observed in annealed films. We thus provide first experimental evidence for the postulated polymer : fullerene : solvent ternary phase that seeds the eventual morphology in spin-cast films. Our work motivates the design of new chemical additives to tune the grain size of the evolving polymer : fullerene domains within the solution phase.The device efficiency of bulk heterojunction (BHJ) solar cells is critically dependent on the nano-morphology of the solution-processed polymer : fullerene blend. Active control on blend morphology can only emanate from a detailed understanding of solution structures during the film casting process. Here we use photoinduced charge transfer (CT) rates to probe the effective length scale of the pre-formed solution structures and their energy disorder arising from a mixture of poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in three

  17. Solvent additive to achieve highly ordered nanostructural semicrystalline DPP copolymers: toward a high charge carrier mobility.

    PubMed

    An, Tae Kyu; Kang, Il; Yun, Hui-jun; Cha, Hyojung; Hwang, Jihun; Park, Seonuk; Kim, Jiye; Kim, Yu Jin; Chung, Dae Sung; Kwon, Soon-Ki; Kim, Yun-Hi; Park, Chan Eon

    2013-12-23

    A facile spin-coating method in which a small percentage of the solvent additive, 1-chloronaphthalene (CN), is found to increase the drying time during film deposition, is reported. The field-effect mobility of a PDPPDBTE film cast from a chloroform-CN mixed solution is 0.46 cm(2) V(-1) s(-1). The addition of CN to the chloroform solution facilitates the formation of highly crystalline polymer structures.

  18. Combined application of dispersive liquid-liquid microextraction based on the solidification of floating organic droplets and charged aerosol detection for the simple and sensitive quantification of macrolide antibiotics in human urine.

    PubMed

    Jia, Shaodong; Li, Jing; Park, So-Ra; Ryu, Yeonsuk; Park, Il Ho; Park, Jeong Hill; Hong, Soon-Sun; Kwon, Sung Won; Lee, Jeongmi

    2013-12-01

    A novel analytical method combining dispersive liquid-liquid microextraction based on the solidification of floating organic droplets (DLLME-SFO) and liquid chromatography with charged aerosol detection (LC-CAD) was established. For the first time, CAD was applied for the detection of macrolide antibiotics lacking chromophores. Parameters influencing the microextraction efficiency were systematically investigated, and the optimized microextraction conditions yielded high enrichment factors in the range of 60-106. The combined application of DLLME-SFO and LC-CAD provided the sensitivity of the method, expressed as the limit of detection (LOD), as low as 10 to 40ngmL(-1) and intra-day and inter-day precisions below 8.7% and 12.6%, respectively. The measured absolute recovery values were approximately 100%, indicating that the extraction efficiency was very high. Direct comparisons of the liquid-liquid extraction and organic solvent precipitation methods demonstrated that the proposed method was more sensitive, specific, rapid, and environmentally friendly for the determination of five macrolide antibiotics in human urine. The results suggest that the combined use of DLLME-SFO and LC-CAD may be applicable to the analysis of various compounds with poor to no chromophores in complex matrices.

  19. Dynamics of electron solvation in methanol: Excited state relaxation and generation by charge-transfer-to-solvent

    SciTech Connect

    Elkins, Madeline H.; Williams, Holly L.; Neumark, Daniel M.

    2015-06-21

    The charge-transfer-to-solvent dynamics (CTTS) and excited state relaxation mechanism of the solvated electron in methanol are studied by time-resolved photoelectron spectroscopy on a liquid methanol microjet by means of two-pulse and three-pulse experiments. In the two-pulse experiment, CTTS excitation is followed by a probe photoejection pulse. The resulting time-evolving photoelectron spectrum reveals multiple time scales characteristic of relaxation and geminate recombination of the initially generated electron which are consistent with prior results from transient absorption. In the three-pulse experiment, the relaxation dynamics of the solvated electron following electronic excitation are measured. The internal conversion lifetime of the excited electron is found to be 130 ± 40 fs, in agreement with extrapolated results from clusters and the non-adiabatic relaxation mechanism.

  20. Droplet Combustion Experiment

    NASA Technical Reports Server (NTRS)

    Nayagam, Vedha

    1998-01-01

    Liquid fuel combustion provides a major portion of the world's energy supply. In most practical combustion devices, liquid burns after being separated into a droplet spray. Essential to the design of efficient combustion systems is a knowledge of droplet combustion behavior. The microgravity environment aboard spacecraft provides an opportunity to investigate the complex interactions between the physical and chemical combustion processes involved in droplet combustion without the complications of natural buoyancy. Launched on STS-83 and STS-94 (April 4 and July 1, 1997), the Droplet Combustion Experiment (DCE) investigated the fundamentals of droplet combustion under a range of pressures (0.25 to 1 atm), oxygen mole fractions (<0.5), and droplet sizes (1.5 to 5 mm). Principal DCE flight hardware features were a chamber to supply selected test environments, the use of crew-inserted bottles, and a vent system to remove unwanted gaseous combustion products. The internal apparatus contained the droplet deployment and ignition mechanisms to burn single, freely deployed droplets in microgravity. Diagnostics systems included a 35-mm high-speed motion picture camera (see the following sequence of photos) with a backlight to photograph burning droplets and a camcorder to monitor experiment operations. Additional diagnostics included an ultraviolet-light-sensitive CCD (charge couple discharge) camera to obtain flame radiation from hydroxyl radicals (see the final figure) and a 35-mm SLR (single-lens-reflex) camera to obtain color still photographs of the flames.

  1. Universal fluid droplet ejector

    DOEpatents

    Lee, E.R.; Perl, M.L.

    1999-08-24

    A droplet generator comprises a fluid reservoir having a side wall made of glass or quartz, and an end cap made from a silicon plate. The end cap contains a micromachined aperture through which the fluid is ejected. The side wall is thermally fused to the end cap, and no adhesive is necessary. This means that the fluid only comes into contact with the side wall and the end cap, both of which are chemically inert. Amplitudes of drive pulses received by reservoir determine the horizontal displacements of droplets relative to the ejection aperture. The drive pulses are varied such that the dropper generates a two-dimensional array of vertically-falling droplets. Vertical and horizontal inter-droplet spacings may be varied in real time. Applications include droplet analysis experiments such as Millikan fractional charge searches and aerosol characterization, as well as material deposition applications. 8 figs.

  2. Effect of droplet shape on ring stains from dried liquid

    NASA Astrophysics Data System (ADS)

    Santiago, Melvin; Brown, Katherine; Mathur, Harsh

    A landmark experimental paper on coffee stains by Deegan et al included a simple theoretical analysis of circular droplets. The analysis was based on a model informally called the Maxwell House equations. It describes the evolving height profile of the droplet, the evaporation of the solvent and the outflow of solute to the rim of the droplet. Since typical droplets are not circles, here we extend the analysis to more general shapes. We find that for thin droplets the height profile may be determined by solving Poisson's equation in a domain corresponding to the footprint of the droplet. Evaporation is treated in a simple approximation via an electrostatic analogy and is dominated by the sharp edges of the droplet. Assuming zero vorticity allows us to analyze the solvent flow in droplets of arbitrary shape. We compare circular droplets to other shapes including long linear droplets, ring shaped droplets and droplets with an elliptical footprint

  3. Cyclic variations of fuel-droplet distribution during the early intake stroke of a lean-burn stratified-charge spark-ignition engine

    NASA Astrophysics Data System (ADS)

    Aleiferis, P. G.; Hardalupas, Y.; Taylor, A. M. K. P.; Ishii, K.; Urata, Y.

    2005-11-01

    Lean-burn spark-ignition engines exhibit higher efficiency and lower specific emissions in comparison with stoichiometrically charged engines. However, as the air-to-fuel (A/F) ratio of the mixture is made leaner than stoichiometric, cycle-by-cycle variations in the early stages of in-cylinder combustion, and subsequent indicated mean effective pressure (IMEP), become more pronounced and limit the range of lean-burn operation. Viable lean-burn engines promote charge stratification, the mixture near the spark plug being richer than the cylinder volume averaged value. Recent work has shown that cycle-by-cycle variations in the early stages of combustion in a stratified-charge engine can be associated with variations in both the local value of A/F ratio near the spark plug around ignition timing, as well as in the volume averaged value of the A/F ratio. The objective of the current work was to identify possible sources of such variability in A/F ratio by studying the in-cylinder field of fuel-droplet distribution during the early intake stroke. This field was visualised in an optical single-cylinder 4-valve pentroof-type spark-ignition engine by means of laser-sheet illumination in planes parallel to the cylinder head gasket 6 and 10 mm below the spark plug. The engine was run with port-injected isooctane at 1500 rpm with 30% volumetric efficiency and air-to-fuel ratio corresponding to both stoichiometric firing (A/F=15, Φ =1.0) and mixture strength close to the lean limit of stable operation (A/F=22, Φ =0.68). Images of Mie intensity scattered by the cloud of fuel droplets were acquired on a cycle-by-cycle basis. These were studied in order to establish possible correlations between the cyclic variations in size, location and scattered-light intensity of the cloud of droplets with the respective variations in IMEP. Because of the low level of Mie intensity scattered by the droplets and because of problems related to elastic scattering on the walls of the combustion

  4. Charge separation in a covalently-linked phthalocyanine-oligo(p-phenylenevinylene)-C60 system. Influence of the solvent polarity.

    PubMed

    Cid, Juan-José; Kahnt, Axel; Vázquez, Purificación; Guldi, Dirk M; Torres, Tomás

    2012-03-01

    A photo- and redoxactive system ZnPc-oPPV-C(60)2, in which the photoexcited state electron donor - zinc phthalocyanine - and the ground state electron acceptor - C(60) - are connected by a oligo(p-phenylenevinylene) (oPPV) spacer, has been synthesized in a multi-step synthesis by means of two consecutive Wadsworth-Horner-Emmons and a dipolar 1,3-cycloaddition reactions as key steps. The simpler system ZnPc-C(60)1 has also been prepared as a reference model for photophysical studies. In this regards, the photophysical investigations by means of fluorescence, flash photolysis, and transient-absorption spectroscopy have manifested a clear dependence between charge transfer kinetics and spatial arrangement. In both systems, intramolecular charge separation evolves from the photoexcited ZnPc and yields the ZnPc(·+)/C(60)(·-) radical ion pairs. Interestingly, the ZnPc(·+)/C(60)(·-) radical ion pair lifetimes and quantum yields are strongly impacted by the solvent polarity and the distance. To this end, maximum radical ion pair lifetimes of 2900 and 5530 ps were found in anisol for 1 and 2, respectively.

  5. Coalescence of repelling colloidal droplets: a route to monodisperse populations.

    PubMed

    Roger, Kevin; Botet, Robert; Cabane, Bernard

    2013-05-14

    Populations of droplets or particles dispersed in a liquid may evolve through Brownian collisions, aggregation, and coalescence. We have found a set of conditions under which these populations evolve spontaneously toward a narrow size distribution. The experimental system consists of poly(methyl methacrylate) (PMMA) nanodroplets dispersed in a solvent (acetone) + nonsolvent (water) mixture. These droplets carry electrical charges, located on the ionic end groups of the macromolecules. We used time-resolved small angle X-ray scattering to determine their size distribution. We find that the droplets grow through coalescence events: the average radius (R) increases logarithmically with elapsed time while the relative width σR/(R) of the distribution decreases as the inverse square root of (R). We interpret this evolution as resulting from coalescence events that are hindered by ionic repulsions between droplets. We generalize this evolution through a simulation of the Smoluchowski kinetic equation, with a kernel that takes into account the interactions between droplets. In the case of vanishing or attractive interactions, all droplet encounters lead to coalescence. The corresponding kernel leads to the well-known "self-preserving" particle distribution of the coalescence process, where σR/(R) increases to a plateau value. However, for droplets that interact through long-range ionic repulsions, "large + small" droplet encounters are more successful at coalescence than "large + large" encounters. We show that the corresponding kernel leads to a particular scaling of the droplet-size distribution-known as the "second-scaling law" in the theory of critical phenomena, where σR/(R) decreases as 1/√(R) and becomes independent of the initial distribution. We argue that this scaling explains the narrow size distributions of colloidal dispersions that have been synthesized through aggregation processes.

  6. The effect of solvent polarity on the balance between charge transfer and non-charge transfer pathways in the sensitization of singlet oxygen by pipi triplet states.

    PubMed

    Schmidt, Reinhard

    2006-05-11

    A large set of literature kinetic data on triplet (T(1)) sensitization of singlet oxygen by two series of biphenyl and naphthalene sensitizers in solvents of strongly different polarity has been analyzed. The rate constants and the efficiencies of singlet oxygen formation are quantitatively reproduced by a model that assumes the competition of a non-charge transfer (nCT) and a CT deactivation channel. nCT deactivation occurs from a fully established spin-statistical equilibrium of (1)(T(1)(3)Sigma) and (3)(T(1)(3)Sigma) encounter complexes by internal conversion (IC) to lower excited complexes that dissociate to yield O(2)((1)Sigma(g)(+)), O(2)((1)Delta(g)), and O(2)((3)Sigma(g)(-)). IC of (1,3)(T(1)(3)Sigma) encounter complexes is controlled by an energy gap law that is generally valid for the transfer of electronic energy to and from O(2). (1,3)(T(1)(3)Sigma) nCT complexes form in competition to IC (1)(T(1)(3)Sigma) and (3)(T(1)(3)Sigma) exciplexes if CT interactions between T(1) and O(2) are important. The rate constants of exciplex formation depend via a Marcus type parabolic model on the corresponding free energy change DeltaG(CT), which varies with sensitizer triplet energy, oxidation potential, and solvent polarity. O(2)((1)Sigma(g)(+)), O(2)((1)Delta(g)), and O(2)((3)Sigma(g)(-)) are formed in the product ratio (1/6):(1/12):(3/4) in the CT deactivation channel. The balance between nCT and CT deactivation is described by the relative contribution p(CT) of CT induced deactivation calculated for a sensitizer of known triplet energy from its quenching rate constant. It is shown how the change of p(CT) influences the quenching rate constant and the efficiency of singlet oxygen formation in both series of sensitizers. p(CT) is sensitive to differences of solvent polarity and varies for the biphenyls and the naphthalenes as sigmoidal with DeltaG(CT). This quantitative model represents a realistic and general mechanism for the quenching of pipi triplet states by O

  7. Determination of fungicides in fruit juice by ultrasound-assisted dispersive liquid-liquid microextraction based on solidification of floating organic solvent droplets followed by high performance liquid chromatography.

    PubMed

    Fan, Run-Zhen; Liu, Congyun; Jiang, Wenqing; Wang, Xiaonan; Liu, Fengmao

    2014-01-01

    Ultrasound-assisted dispersive liquid-liquid microextraction (UA-DLLME) based on solidification of the floating organic solvent droplets (SFO) combined with HPLC was used for determination of five fungicides in fruit juice samples. 1-Dodecanol, which has a low density and low toxicity, was used as the extraction solvent in UA-DLLME. The solidification of floating organic droplets facilitates the transfer of analytes from the aqueous phase to the organic phase. This method was easy, quick, inexpensive, precise, and linear over a wide range. Under the optimized conditions, the enrichment factors for a 5 mL fruit juice sample were 25 to 56, and the LODs for the five fungicides ranged from 5 to 50 microg/L. The average recoveries ranged from 71.8 to 118.2% with RSDs of 0.9 to 13.9%. Application of the DLLME-SFO technique allows successful separation and preconcentration of the fungicides at a low concentration level in fruit juice samples.

  8. Intramolecular charge transfer and dielectric solvent relaxation in n-propyl cyanide. N-phenylpyrrole and 4-dimethylamino-4'-cyanostilbene.

    PubMed

    Druzhinin, Sergey I; Galievsky, Victor A; Yoshihara, Toshitada; Zachariasse, Klaas A

    2006-11-30

    Fast intramolecular charge transfer (ICT) accompanied by dual fluorescence from a locally excited (LE) and an ICT state taking place with N-phenylpyrrole (PP) in the solvent n-propyl cyanide (PrCN) is investigated as a function of temperature between 25 and -112 degrees C. The LE and ICT fluorescence decays from -45 to -70 degrees C can be adequately fitted with two exponentials, in accordance with a two state (LE + ICT) reaction mechanism, similar to what has been observed with PP in the more polar and less viscous alkyl cyanides acetonitrile (MeCN) and ethyl cyanide (EtCN). At lower temperatures, triple-exponential fits are required for the LE and ICT decays. The ICT emission band maximum of the time-resolved fluorescence spectra of PP in PrCN at -100 degrees C displays a spectral shift from 29 230 cm-1 at t = 0 to 27 780 cm-1 at infinite time, which equilibration process is attributed to dielectric solvent relaxation. From the time dependence of this shift, in global analysis with that of the band integrals BI(LE) and BI(ICT) of the time-resolved LE and ICT fluorescence bands, the decay times 119 and 456 ps are obtained. Dielectric relaxation times of 20 and 138 ps are determined from the double-exponential spectral solvation response function C(t) of the probe molecule 4-dimethylamino-4'-cyanostilbene in PrCN at -100 degrees C. It is concluded from the similarity of the times 119 ps (PP) and 138 ps (DCS) that the deviation from double-exponential character for the fluorescence decays of PP in PrCN below -70 degrees C is due to the interference of dielectric solvent relaxation with the ICT reaction. This fact complicates the kinetic analysis of the LE and ICT fluorescence decays. The kinetic analysis for PP in PrCN is hence restricted to temperatures between -70 and -45 degrees C. From this analysis, the forward and backward ICT activation energies Ea (12 kJ/mol) and Ed (17 kJ/mol) are obtained, giving an ICT stabilization enthalpy -DeltaH of 5 kJ/mol. A

  9. Molecular Dynamics Simulation Study of Solvent and State of Charge Effects on Solid-Phase Structure and Counterion Binding in a Nitroxide Radical Containing Polymer Energy Storage Material

    DOE PAGES

    Kemper, Travis W.; Gennett, Thomas; Larsen, Ross E.

    2016-10-19

    Here we performed molecular dynamics simulations to understand the effects of solvent swelling and state of charge (SOC) on the redox active, organic radical cathode material poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate) (PTMA). We show that the polar solvent acetonitrile primarily solvates the nitroxide radical without disrupting the packing of the (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) pendant groups of PTMA. We also simulated bulk PTMA in different SOC, 25%, 50%, 75%, and 100%, by converting the appropriate number of TEMPO groups to the cation charge state and adding BF4- counterions to the simulation. At each SOC the packing of PTMA, the solvent, and the counterions were examined.more » The binding of the anion to the nitroxide cation site was examined using the potential of mean force and found to be on the order of tens of meV, with a binding energy that decreased with increasing SOC. Additionally, we found that the cation state is stabilized by the presence of a nearby anion by more than 1 eV, and the implications of this stabilization on charge transport are discussed. Finally, we describe the implications of our results for how the SOC of an organic electrode affects electron and anion charge transport during the charging and discharging processes.« less

  10. Molecular Dynamics Simulation Study of Solvent and State of Charge Effects on Solid-Phase Structure and Counterion Binding in a Nitroxide Radical Containing Polymer Energy Storage Material

    SciTech Connect

    Kemper, Travis W.; Gennett, Thomas; Larsen, Ross E.

    2016-10-19

    Here we performed molecular dynamics simulations to understand the effects of solvent swelling and state of charge (SOC) on the redox active, organic radical cathode material poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate) (PTMA). We show that the polar solvent acetonitrile primarily solvates the nitroxide radical without disrupting the packing of the (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) pendant groups of PTMA. We also simulated bulk PTMA in different SOC, 25%, 50%, 75%, and 100%, by converting the appropriate number of TEMPO groups to the cation charge state and adding BF4- counterions to the simulation. At each SOC the packing of PTMA, the solvent, and the counterions were examined. The binding of the anion to the nitroxide cation site was examined using the potential of mean force and found to be on the order of tens of meV, with a binding energy that decreased with increasing SOC. Additionally, we found that the cation state is stabilized by the presence of a nearby anion by more than 1 eV, and the implications of this stabilization on charge transport are discussed. Finally, we describe the implications of our results for how the SOC of an organic electrode affects electron and anion charge transport during the charging and discharging processes.

  11. Solvent-drop Assisted Mechanochemical Synthesis of the Black and Green Polymorphs of the Tetrathiafulvalene-chloranil Charge Transfer Salt

    SciTech Connect

    S Benjamin; S Pagola; Z Huba; E Carpenter; T Abdel-Fattah

    2011-12-31

    This work describes the synthesis of the green and black polymorphic forms of the tetrathiafulvalene-chloranil (TTF-CA) charge transfer salt as pure phases, by solvent-assisted mechanochemistry. Both materials were characterized using laboratory and high-resolution X-ray powder diffraction (XRPD), elemental analysis and scanning electron microscopy (SEM). The high-resolution XRPD pattern of the TTF-CA black polymorph was indexed with a triclinic lattice a = 10.756(5) {angstrom}, b = 11.057(4) {angstrom}, c = 6.614(2) {angstrom}, {alpha} = 101.36(2){sup o}, {beta} = 93.69(3){sup o}, {gamma} = 89.37(3){sup o}, V = 769.6(5) {angstrom}{sup 3}. The chemical stability of these phases upon heating was investigated using thermogravimetric analysis (TGA), elemental analysis and X-ray powder diffraction (XRPD), indicating that both polymorphs undergo chemical decomposition, and ruling out the transition to an air-stable high temperature polymorph.

  12. Intramolecular charge transfer with crystal violet lactone in acetonitrile as a function of temperature: reaction is not solvent-controlled.

    PubMed

    Druzhinin, Sergey I; Demeter, Attila; Zachariasse, Klaas A

    2013-08-22

    Intramolecular charge transfer (ICT) with crystal violet lactone (CVL) in the excited singlet state takes place in solvents more polar than n-hexane, such as ethyl acetate, tetrahydrofuran, and acetonitrile (MeCN). In these solvents, the fluorescence spectrum of CVL consists of two emission bands, from a locally excited (LE) and an ICT state. The dominant deactivation channel of the lowest excited singlet state is internal conversion, as the quantum yields of fluorescence (0.007) and intersystem crossing (0.015) in MeCN at 25 °C are very small. CVL is a weakly coupled electron donor/acceptor (D/A) molecule, similar to an exciplex (1)(A(-)D(+)). A solvatochromic treatment of the LE and ICT emission maxima results in the dipole moments μe(LE) = 17 D and μe(ICT) = 33 D, much larger than those previously reported. This discrepancy is attributed to different Onsager radii and spectral fluorimeter calibration. The LE and ICT fluorescence decays of CVL in MeCN are double exponential. As determined by global analysis, the LE and ICT decays at 25 °C have the times τ2 = 9.2 ps and τ1 = 1180 ps, with an amplitude ratio of 35.3 for LE. From these parameters, the rate constants ka = 106 × 10(9) s(-1) and kd = 3.0 × 10(9) s(-1) of the forward and backward reaction in the LE ⇄ ICT equilibrium are calculated, resulting in a free enthalpy difference ΔG of -8.9 kJ/mol. The amplitude ratio of the ICT fluorescence decay equals -1.0, which signifies that the ICT state is not prepared by light absorption in the S0 ground state, but originates exclusively from the directly excited LE precursor. From the temperature dependence of the fluorescence decays of CVL in MeCN (-45 to 75 °C), activation energies E(a) = 3.9 kJ/mol (LE → ICT) and E(d) = 23.6 kJ/mol (ICT → LE) are obtained, giving an enthalpy difference ΔH (= E(a) - E(d)) of -19.7 kJ/mol, and an entropy difference ΔS = -35.5 J mol(-1) K(-1). These data show that the ICT reaction of CVL in MeCN is not barrierless

  13. High-Voltage Droplet Dispenser

    NASA Technical Reports Server (NTRS)

    Eichenberg, Dennis J.

    2003-01-01

    An apparatus that is extremely effective in dispensing a wide range of droplets has been developed. This droplet dispenser is unique in that it utilizes a droplet bias voltage, as well as an ionization pulse, to release a droplet. Apparatuses that deploy individual droplets have been used in many applications, including, notably, study of combustion of liquid fuels. Experiments on isolated droplets are useful in that they enable the study of droplet phenomena under well-controlled and simplified conditions. In this apparatus, a syringe dispenses a known value of liquid, which emerges from, and hangs onto, the outer end of a flat-tipped, stainless steel needle. Somewhat below the needle tip and droplet is a ring electrode. A bias high voltage, followed by a high-voltage pulse, is applied so as to attract the droplet sufficiently to pull it off the needle. The voltages are such that the droplet and needle are negatively charged and the ring electrode is positively charged.

  14. A perspective on MALDI alternatives-total solvent-free analysis and electron transfer dissociation of highly charged ions by laserspray ionization.

    PubMed

    Trimpin, Sarah

    2010-05-01

    Progress in research is hindered by analytical limitations, especially in biological areas in which sensitivity and dynamic range are critical to success. Inherent difficulties of characterization associated with complexity arising from heterogeneity of various materials including topologies (isomeric composition) and insolubility also limit progress. For this reason, we are developing methods for total solvent-free analysis by mass spectrometry consisting of solvent-free ionization followed by solvent-free gas-phase separation. We also recently constructed a novel matrix-assisted laser desorption ionization (MALDI) source that provides a simple, practical and sensitive way of producing highly charged ions by laserspray ionization (LSI) or singly charged ions commonly observed with MALDI by choice of matrix or matrix preparation. This is the first ionization source with such freedom-an extremely powerful analytical 'switch'. Multiply charged LSI ions allow molecules exceeding the mass-to-charge range of the instrument to be observed and permit for the first time electron transfer dissociation fragment ion analysis.

  15. Solvent-dependent intramolecular charge transfer dual fluorescence of p-dimethylaminobenzanilide bearing steric ortho,ortho-dimethyl substituents at amido aniline.

    PubMed

    Zhang, Xuan; Jiang, Yun-Bao

    2011-11-01

    Intramolecular charge transfer (ICT) dual fluorescence was observed in various organic solvents with p-dimethylaminobenzanilide (DMBA) derivatives bearing ortho-methyl (DMOMBA) and ortho,ortho-dimethyl (DMDMBA) substituents at amido aniline moiety. Ab initio calculation and absorption spectral data indicated that high steric hindrance was introduced by the ortho,ortho-dimethyl substitutions. It was found that, with DMDMBA, the CT emission initially shifted to the red with increasing solvent polarity from cyclohexane (CHX, 480 nm) to diethyl ether (DEE, 520 nm), similar to those of DMBA derivatives with the ortho-, meta- or para-methyl substitutions at amido aniline moiety. However, there is a characteristic blue-shift of the long wavelength emission between DEE and tetrahydrofuran (THF, 424 nm) then a bathochromic shift again in highly polar solvent acetonitrile (ACN, 484 nm). The unusual solvent-dependent CT emission was ascribed to two competitive CT channels. One is benzanilide (BA)-like CT, whose CT reaction occurs from amido aniline to benzoyl moiety in nonpolar solvent CHX and DEE; the other one is p-dimethylaminobenzamide (DMABA)-like, whose CT reaction occurs from dimethylamino to benzanilide moiety in highly polar solvent THF and ACN. These findings revealed the steric effect plays an important role in the ICT process, which may alter the properties of the electron donor and/or acceptor, but also change the reaction potential.

  16. Universal fluid droplet ejector

    DOEpatents

    Lee, Eric R.; Perl, Martin L.

    1999-08-24

    A droplet generator comprises a fluid reservoir having a side wall made of glass or quartz, and an end cap made from a silicon plate. The end cap contains a micromachined aperture through which the fluid is ejected. The side wall is thermally fused to the end cap, and no adhesive is necessary. This means that the fluid only comes into contact with the side wall and the end cap, both of which are chemically inert. Amplitudes of drive pulses received by reservoir determine the horizontal displacements of droplets relative to the ejection aperture. The drive pulses are varied such that the dropper generates a two-dimensional array of vertically-falling droplets. Vertical and horizontal interdroplet spacings may be varied in real time. Applications include droplet analysis experiments such as Millikan fractional charge searches and aerosol characterization, as well as material deposition applications.

  17. Solvent bandwidth dependence and band asymmetry features of charge-transfer transitions in N-pyridinium phenolates

    SciTech Connect

    Kjaer, A.M.; Ulstrup, J.

    1987-04-01

    They have investigated the shape of the solvatochromic absorption band for Betaine-26 2,4,6-triphenyl-N-(di-tert-butyl-4-hydroxyphenyl)pyridinium ion in a range of polar, apolar, protic, and aprotic solvents. Multiphonon band theory, including both molecular modes and a vibrationally dispersive solvent, indicates that the solvents fall in three categories: (1) The bandshape for polar, aprotic solvents is well reproduced by that for a structureless continuous dielectric and a single high-frequency molecular mode. Solvent broadening correlates with epsilon/sub o//sup -1/ - epsilon/sub s//sup -1/, epsilon/sub o/ being the optical and epsilon/sub s/ the static dielectric constant. The molecular frequency, Omega/sub c/, and displacement, ..delta../sub c/, are not very solvent dependent, emphasizing their molecular character, and the value Omega/sub c/ approx. = 1600 cm/sup -1/ suggests that C-O, C-N, and C-C stretching is involved. (2) Bands for apolar, aprotic solvents correspond to the same model. Omega/sub c/ and ..delta../sub c/ are again not very solvent dependent and coincide with the values for polar aprotic solvents. The solvent broadening is solvent independent, and wider than that for a structureless dielectric. This points to multipolar, dispersive, pressure, or pseudopotential forces as coupling mechanisms. (3) The bandshape for normal alcohols can only be produced by a model resting on two molecular modes and a vibrational high-frequency solvent tail. Broadening, asymmetry, molecular frequencies, and deuterium isotope effects trace the protic solvent spectral entanglement to coupling between betaine-26 and a local mode group with features of both O-H stretching and bending and of librational solvent motion.

  18. Spectrophotometric studies on the charge-transfer interaction between p-nitroaniline with chloranilic acid as π-acceptor in different polar solvents

    NASA Astrophysics Data System (ADS)

    Singh, Neeti; Ahmad, Afaq

    2017-01-01

    The charge transfer interaction between the donor p-nitroaniline with the acceptor chloranilic acid has been studied spectrophotometrically in various solvents such as chloroform, ethanol, and methanol at room temperature. The results indicate that formation of CTC in non-polar solvent is high. The stoichiometry of the complex was found to be 1:1 ratio by straight-line method between donor and acceptor with maximum absorption bands. The data are discussed in terms of formation constant (KCT), molar extinction coefficient (εCT), standard free energy (ΔG), oscillator strength (f), transition dipole moment (μN), resonance energy (RN) and ionization potential (ID). The results indicate that the formation constant (KCT) for the complex was shown to be dependent upon the nature of electron acceptor, donor and polarity of solvents that were used. The formation of the complex has been confirmed by UV-visible, FT-IR, and 1H NMR techniques.

  19. Mechanism of the intramolecular charge transfer state formation in all-trans-β-apo-8'-carotenal: influence of solvent polarity and polarizability.

    PubMed

    Ragnoni, Elena; Di Donato, Mariangela; Iagatti, Alessandro; Lapini, Andrea; Righini, Roberto

    2015-01-15

    In this work we analyzed the infrared and visible transient absorption spectra of all-trans-β-apo-8'-carotenal in several solvents, differing in both polarity and polarizability at different excitation wavelengths. We correlate the solvent dependence of the kinetics and the band shape changes in the infrared with that of the excited state absorption bands in the visible, and we show that the information obtained in the two spectral regions is complementary. All the collected time-resolved data can be interpreted in the frame of a recently proposed relaxation scheme, according to which the major contributor to the intramolecular charge transfer (ICT) state is the bright 1Bu(+) state, which, in polar solvents, is dynamically stabilized through molecular distortions and solvent relaxation. A careful investigation of the solvent effects on the visible and infrared excited state bands demonstrates that both solvent polarity and polarizability have to be considered in order to rationalize the excited state relaxation of trans-8'-apo-β-carotenal and clarify the role and the nature of the ICT state in this molecule. The experimental observations reported in this work can be interpreted by considering that at the Franck-Condon geometry the wave functions of the S1 and S2 excited states have a mixed ionic/covalent character. The degree of mixing depends on solvent polarity, but it can be dynamically modified by the effect of polarizability. Finally, the effect of different excitation wavelengths on the kinetics and spectral dynamics can be interpreted in terms of photoselection of a subpopulation of partially distorted molecules.

  20. Solvent dependence on bond length alternation and charge distribution in phenol blue: a Car-Parrinello molecular dynamics investigation.

    PubMed

    Murugan, N Arul; Rinkevicius, Zilvinas; Agren, Hans

    2009-04-30

    Car-Parrinello mixed quantum mechanics/classical mechanics (CP-QM/MM) calculations are performed for phenol blue (PB) in chloroform and water solvents along with Car-Parrinello molecular dynamics (CPMD) calculations on PB in the gas phase. The solvent effect on molecular geometry, particularly of bond length alternation (BLA), has been studied. As reported for similar donor-acceptor polyenic systems, a remarkable solvent effect is seen on the BLA. The calculated BLA parameter suggests that PB is in the neutral form in the gas phase and in chloroform solvent, while in water, it is cyanine-like, which is a mixture of neutral and zwitterionic resonant forms, something that clarifies the controversial reports on the structure of PB in chloroform. We have also verified that the structures obtained from CPMD and CP-QM/MM calculations are correct by calculating absorption spectra for PB in the gas phase and in chloroform solvent and compared with experimental results. To understand the structure for PB in the gas phase and in water solvent, we have carried out Mayer bond order analysis, supporting that the structure of PB in water is cyanine-like. Moreover, PB in water is found to be much more polarized than that in chloroform solvent. Overall, the present work demonstrates that CP-QM/MM calculations can be used to understand the solvent effects on polyenic and merocyanine-like systems, which are usually difficult to model.

  1. Dancing Droplets

    NASA Astrophysics Data System (ADS)

    Cira, Nate; Prakash, Manu

    2013-11-01

    Inspired by the observation of intricate and beautifully dynamic patterns generated by food coloring on corona treated glass slides, we have investigated the behavior of propylene glycol and water droplets on clean glass surfaces. These droplets exhibit a range of interesting behaviors including long distance attraction or repulsion, and chasing/fleeing upon contact. We present explanations for each of these behaviors, and propose a detailed model for the long distance interactions based on vapor facilitated coupling. Finally we use our understanding to create several novel devices which: passively sort droplets by surface tension, spontaneously align droplets, drive droplets in circles, and cause droplets to bounce on a vertical surface. The simplicity of this system lends it particularly well to application as a toy model for physical systems with force fields and biological systems such as chemotaxis and motility.

  2. A novel extraction method for β-carotene and other carotenoids in fruit juices using air-assisted, low-density solvent-based liquid-liquid microextraction and solidified floating organic droplets.

    PubMed

    Sricharoen, Phitchan; Limchoowong, Nunticha; Techawongstien, Suchila; Chanthai, Saksit

    2016-07-15

    Green extraction using air-assisted, low-density solvent-based liquid-liquid microextraction and solidified floating organic droplets (AA-LDS-LLME-SFOD) prior to spectrophotometry was successfully applied for quantitation of carotenoids in fruit juices. Under optimal conditions, β-carotene could be quantified with a linear response up to a concentration of 60 μg mL(-1). The procedure was performed in a microcentrifuge tube with 40 μL of 1-dodecanol as the extraction solvent and a 1.0 mL juice sample containing 8% NaCl under seven extraction cycles of air pumping by syringe. This method was validated based on linearity (0.2-30 μg mL(-1), R(2) 0.998), limit of detection (0.04 μg mL(-1)) and limit of quantification (0.13 μg mL(-1)). The precision, expressed as the relative standard deviation (RSD) of the calibration curve slope (n=12), for inter-day and intra-day analysis was 4.85% and 7.92%, respectively. Recovery of β-carotene was in the range of 93.6-101.5%. The newly proposed method is simple, rapid and environmentally friendly, particularly as a useful screening test for food analysis.

  3. Photoinduced charge generation rates in soluble P3HT : PCBM nano-aggregates predict the solvent-dependent film morphology.

    PubMed

    Roy, Palas; Jha, Ajay; Dasgupta, Jyotishman

    2016-02-07

    The device efficiency of bulk heterojunction (BHJ) solar cells is critically dependent on the nano-morphology of the solution-processed polymer : fullerene blend. Active control on blend morphology can only emanate from a detailed understanding of solution structures during the film casting process. Here we use photoinduced charge transfer (CT) rates to probe the effective length scale of the pre-formed solution structures and their energy disorder arising from a mixture of poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in three different organic solvents. The observed solvent-dependent ultrafast biphasic rise of the transient polaron state in solution along with changes detected in the C=C stretching frequency of bound PCBM provides direct evidence for film-like P3HT : PCBM interfaces in solution. Using the diffusive component of the charge transfer rate, we deduce ∼3-times larger functional nano-domain size in toluene than in chlorobenzene thereby correctly predicting the relative polymer nanofiber widths observed in annealed films. We thus provide first experimental evidence for the postulated polymer : fullerene : solvent ternary phase that seeds the eventual morphology in spin-cast films. Our work motivates the design of new chemical additives to tune the grain size of the evolving polymer : fullerene domains within the solution phase.

  4. Morphological transition of the host-structure influences solvent-relaxation: A wavelength-selective fluorescence exploration through environment-sensitive intramolecular charge transfer photophysics

    NASA Astrophysics Data System (ADS)

    Paul, Bijan Kumar; Guchhait, Nikhil

    2011-10-01

    Here, we report the modulation of photo-induced intramolecular charge transfer (ICT) photophysics of N,N-dimethylaminonaphthyl-acrylo-nitrile (DMANAN) associated with sphere-to-rod structural transition of SDS micelles induced by increasing ionic strength of the medium. Emphasis is rendered on the exploration of solvent-relaxation associated with this transition on the basis of wavelength-selective fluorescence technique which includes monitoring of red-edge excitation shift (REES) and excitation/emission anisotropy profiles. Based on micropolarity determination and organization of solvent water around the probe microenvironment we argue that the present results advocate for rod-shaped micelles to be a better mimic for membrane bilayers than spherical micelles.

  5. Morphological transition of the host-structure influences solvent-relaxation: a wavelength-selective fluorescence exploration through environment-sensitive intramolecular charge transfer photophysics.

    PubMed

    Paul, Bijan Kumar; Guchhait, Nikhil

    2011-10-15

    Here, we report the modulation of photo-induced intramolecular charge transfer (ICT) photophysics of N,N-dimethylaminonaphthyl-acrylo-nitrile (DMANAN) associated with sphere-to-rod structural transition of SDS micelles induced by increasing ionic strength of the medium. Emphasis is rendered on the exploration of solvent-relaxation associated with this transition on the basis of wavelength-selective fluorescence technique which includes monitoring of red-edge excitation shift (REES) and excitation/emission anisotropy profiles. Based on micropolarity determination and organization of solvent water around the probe microenvironment we argue that the present results advocate for rod-shaped micelles to be a better mimic for membrane bilayers than spherical micelles.

  6. Persisting Water Droplets on Water Surfaces†

    PubMed Central

    Klyuzhin, Ivan S.; Ienna, Federico; Roeder, Brandon; Wexler, Adam; Pollack, Gerald H.

    2011-01-01

    Droplets of various liquids may float on the respective surfaces for extended periods of time prior to coalescence. We explored the features of delayed coalescence in highly purified water. Droplets several millimeters in diameter were released from a nozzle onto a water surface. Results showed that droplets had float times up to hundreds of milliseconds. When the droplets did coalesce, they did so in stepwise fashion, with periods of quiescence interspersed between periods of coalescence. Up to six steps were noted before the droplet finally vanished. Droplets were released in a series, which allowed the detection of unexpected abrupt float-time changes throughout the duration of the series. Factors such as electrostatic charge, droplet size, and sideways motion had considerable effect on droplet lifetime, as did reduction of pressure, which also diminished the number of steps needed for coalescence. On the basis of present observations and recent reports, a possible mechanism for noncoalescence is considered. PMID:20961076

  7. Droplet Handling

    NASA Astrophysics Data System (ADS)

    Torii, Toru

    When quantitative analysis or quantitative chemical synthesis is performed using a micrototal analysis system (microTAS), the technologies for precise metering, transporting, and mixing of droplets are required. In this chapter, several technologies for the handling of droplets are described. For metering, dispensing and transporting of droplets, pneumatic and electrokinetic forces are used. Separation of cells and particles is also performed by electrical operation. Other handling technique, such as ultrasonic or centrifugal force applications, are also reviewed. Robotic synthesis devices or high throughput screening devices are promising applications for these technologies.

  8. Droplet handling.

    PubMed

    Torii, Toru

    2010-01-01

    When quantitative analysis or quantitative chemical synthesis is performed using a micrototal analysis system (microTAS), the technologies for precise metering, transporting, and mixing of droplets are required. In this chapter, several technologies for the handling of droplets are described. For metering, dispensing and transporting of droplets, pneumatic and electrokinetic forces are used. Separation of cells and particles is also performed by electrical operation. Other handling technique, such as ultrasonic or centrifugal force applications, are also reviewed. Robotic synthesis devices or high throughput screening devices are promising applications for these technologies.

  9. Microscopic solvation and femtochemistry of charge-transfer reactions: the problem of benzene(s)-iodine binary complexes and their solvent structures

    NASA Astrophysics Data System (ADS)

    Cheng, P. Y.; Zhong, D.; Zewail, A. H.

    1995-08-01

    Charge-transfer reactions are studied on the femtosecond and picosecond time scales and under controlled composition in a molecular beam. The system of interest is iodine in aromatic and non-aromatic solvents, which goes back to Hildebrand and Mulliken almost 50 years ago. For the first time, the isolated binary complex and its solvated structural dynamics are studied. The product iodine atoms are positively identified and the concept of harpoon mechanism introduced. The dynamics are related to the impact geometry of the transition state and the electronic structure. A global potential energy surface is described with molecular dynamics detailing the motion in the reaction coordinates.

  10. Splashing Droplets

    NASA Technical Reports Server (NTRS)

    VanderWal, Randall L.; Kizito, John Patrick; Berger, Gordon M.; Iwan, J.; Alexander, D.; Tryggvason, Gretar

    2002-01-01

    Current data on droplet breakup is scarce for the sizes and velocities typical of practical applications such as in spray combustion processes and coating processes. While much more representative of practical applications, the small spatial scales and rapid time-scales prevent detailed measurement of the internal fluid dynamics and liquid property gradients produced by impinging upon surfaces. Realized through the extended spatial and temporal scales afforded by a microgravity environment, an improved understanding of drop breakup dynamics is sought to understand and ultimately control the impingement dynamics of droplets upon surfaces in practical situations. The primary objective of this research will be to mark the onset of different 'splashing modes' and to determine their temperature, pressure and angle dependence for impinging droplets representative of practical fluids. In addition, we are modeling the evolution of droplets that do not initially splash but rather undergo a 'fingering' evolution observed on the spreading fluid front and the transformation of these fingers into splashed products. An example of our experimental data is presented below. These images are of Isopar V impacting a mirror-polished surface. They were acquired using a high-speed camera at 1000 frames per second. They show the spreading of a single droplet after impact and ensuing finger instabilities. Normal gravity experimental data such as this will guide low gravity measurements in the 2.2 second drop tower and KC-135 aircraft as available. Presently we are in the process of comparing the experimental data of droplet shape evolution to numerical models, which can also capture the internal fluid dynamics and liquid property gradients such as produced by impingement upon a heated surface. To-date isothermal numerical data has been modeled using direct numerical simulations of representative splashing droplets. The data obtained so far indicates that the present model describes well

  11. Dynamics of charge recombination processes in the singlet electron-transfer state of pyrene-pyromellitic dianhydride systems in various solvents. Picosecond laser photolysis studies

    SciTech Connect

    Mataga, N.; Shioyama, H.; Kanda, Y.

    1987-01-15

    In order to elucidate the underlying mechanisms showing that no dissociated ion radicals are produced even in acetonitrile solution when some complexes of the strong electron donors and acceptors with CT absorption bands in the visible region are photoexcited, the authors have made detailed time-resolved transient absorption spectral measurements and time-resolved fluorescence measurements upon the pyrene-pyromellitic dianhydride (PMDA) system in various solvents with picosecond laser spectroscopy. A weakly fluorescent electron-transfer (ET) state with 400-ps lifetime is formed by photoexcitation in benzene solution, while nonfluorescent geminate ion pairs with much shorter lifetimes due to the charge recombination (CR) deactivation are formed in more polar solvents. In all solutions examined, dissociation into free ions from the geminate pair cannot compete with the CR deactivation which becomes faster in more polar solvents due to the decrease of the energy gap between the ion pair and neutral ground state. Moreover, it has been demonstrated that ion pairs produced by encounter between excited pyrene and unexcited PMDA in acetonitrile have more loose structure and show a smaller CR rate constant than those produced by exciting the ground-state complex.

  12. Liquid droplet radiator development status

    NASA Technical Reports Server (NTRS)

    White, K. Alan, III

    1987-01-01

    Development of the Liquid Droplet Radiator (LDR) is described. Significant published results of previous investigators are presented, and work currently in progress is discussed. Several proposed LDR configurations are described, and the rectangular and triangular configurations currently of most interest are examined. Development of the droplet generator, collector, and auxiliary components are discussed. Radiative performance of a droplet sheet is considered, and experimental results are seen to be in very good agreement with analytical predictions. The collision of droplets in the droplet sheet, the charging of droplets by the space plasma, and the effect of atmospheric drag on the droplet sheet are shown to be of little consequence, or can be minimized by proper design. The LDR is seen to be less susceptible than conventional technology to the effects of micrometeoroids or hostile threats. The identification of working fluids which are stable in the orbital environments of interest is also made. Methods for reducing spacecraft contamination from an LDR to an acceptable level are discussed. Preliminary results of microgravity testing of the droplet generator are presented. Possible future NASA and Air Force missions enhanced or enabled by a LDR are also discussed. System studies indicate that the LDR is potentially less massive than heat pipe radiators. Planned microgravity testing aboard the Shuttle or space station is seen to be a logical next step in LDR development.

  13. High-Voltage Droplet Dispenser Developed

    NASA Technical Reports Server (NTRS)

    Eichenberg, Dennis J.; VanderWal, Randy L.

    2001-01-01

    Various techniques have been applied to deploying individual droplets for many applications, such as the study of the combustion of liquid fuels. Isolated droplet studies are useful in that they allow phenomena to be studied under well-controlled and simplified conditions. A high-voltage droplet dispenser has been developed that is extremely effective in dispensing a wide range of droplets. The dispenser is quite unique in that it utilizes a droplet bias voltage, as well as an ionization pulse, to release the droplet. The droplet is deployed from the end of a needle. A flat-tipped, stainless steel needle attached to a syringe dispenses a known value of liquid that hangs on the needle tip. Somewhat below the droplet is an annular ring electrode. A bias voltage, followed by a voltage pulse, is applied to attract the droplet sufficiently to pull it off the needle. The droplet and needle are oppositely charged relative to the annular electrode. The needle is negatively charged, and the annular ring is positively charged.

  14. Droplet microactuator system

    NASA Technical Reports Server (NTRS)

    Pamula, Vamsee K. (Inventor); Srinivasan, Vijay (Inventor); Pollack, Michael G. (Inventor); Eckhardt, Allen E. (Inventor); Paik, Philip Y. (Inventor)

    2010-01-01

    The present invention relates to a droplet microactuator system. According to one embodiment, the droplet microactuator system includes: (a) a droplet microactuator configured to conduct droplet operations; (b) a magnetic field source arranged to immobilize magnetically responsive beads in a droplet during droplet operations; (c) a sensor configured in a sensing relationship with the droplet microactuator, such that the sensor is capable of sensing a signal from and/or a property of one or more droplets on the droplet microactuator; and (d) one or more processors electronically coupled to the droplet microactuator and programmed to control electrowetting-mediated droplet operations on the droplet actuator and process electronic signals from the sensor.

  15. Charge-transfer-to-solvent reactions from I- to water, methanol, and ethanol studied by time-resolved photoelectron spectroscopy of liquids

    NASA Astrophysics Data System (ADS)

    Okuyama, Haruki; Suzuki, Yoshi-Ichi; Karashima, Shutaro; Suzuki, Toshinori

    2016-08-01

    The charge-transfer-to-solvent (CTTS) reactions from iodide (I-) to H2O, D2O, methanol, and ethanol were studied by time-resolved photoelectron spectroscopy of liquid microjets using a magnetic bottle time-of-flight spectrometer with variable pass energy. Photoexcited iodide dissociates into a weak complex (a contact pair) of a solvated electron and an iodine atom in similar reaction times, 0.3 ps in H2O and D2O and 0.5 ps in methanol and ethanol, which are much shorter than their dielectric relaxation times. The results indicate that solvated electrons are formed with minimal solvent reorganization in the long-range solvent polarization field created for I-. The photoelectron spectra for CTTS in H2O and D2O—measured with higher accuracy than in our previous study [Y. I. Suzuki et al., Chem. Sci. 2, 1094 (2011)]—indicate that internal conversion yields from the photoexcited I-* (CTTS) state are less than 10%, while alcohols provide 2-3 times greater yields of internal conversion from I-*. The overall geminate recombination yields are found to be in the order of H2O > D2O > methanol > ethanol, which is opposite to the order of the mutual diffusion rates of an iodine atom and a solvated electron. This result is consistent with the transition state theory for an adiabatic outer-sphere electron transfer process, which predicts that the recombination reaction rate has a pre-exponential factor inversely proportional to a longitudinal solvent relaxation time.

  16. Charge-transfer-to-solvent reactions from I(-) to water, methanol, and ethanol studied by time-resolved photoelectron spectroscopy of liquids.

    PubMed

    Okuyama, Haruki; Suzuki, Yoshi-Ichi; Karashima, Shutaro; Suzuki, Toshinori

    2016-08-21

    The charge-transfer-to-solvent (CTTS) reactions from iodide (I(-)) to H2O, D2O, methanol, and ethanol were studied by time-resolved photoelectron spectroscopy of liquid microjets using a magnetic bottle time-of-flight spectrometer with variable pass energy. Photoexcited iodide dissociates into a weak complex (a contact pair) of a solvated electron and an iodine atom in similar reaction times, 0.3 ps in H2O and D2O and 0.5 ps in methanol and ethanol, which are much shorter than their dielectric relaxation times. The results indicate that solvated electrons are formed with minimal solvent reorganization in the long-range solvent polarization field created for I(-). The photoelectron spectra for CTTS in H2O and D2O-measured with higher accuracy than in our previous study [Y. I. Suzuki et al., Chem. Sci. 2, 1094 (2011)]-indicate that internal conversion yields from the photoexcited I(-*) (CTTS) state are less than 10%, while alcohols provide 2-3 times greater yields of internal conversion from I(-*). The overall geminate recombination yields are found to be in the order of H2O > D2O > methanol > ethanol, which is opposite to the order of the mutual diffusion rates of an iodine atom and a solvated electron. This result is consistent with the transition state theory for an adiabatic outer-sphere electron transfer process, which predicts that the recombination reaction rate has a pre-exponential factor inversely proportional to a longitudinal solvent relaxation time.

  17. A novel actuation technique for the on-demand injection of charge-free conducting droplets in a viscous dielectric liquid

    NASA Astrophysics Data System (ADS)

    Raisin, Jonathan; Atten, Pierre; Reboud, Jean-Luc

    2013-03-01

    The paper presents recent improvements and results on the on-demand injection of small electrically neutral water drops in oil by high electric field pulses. The technique consists in applying a voltage pulse promoting the deformation of a water meniscus at the end of a capillary tube through the action of electric forces. For pulses of calibrated energy, the transient deformation can lead to the inertia-based ejection of a small uncharged droplet. Application of in-house developed multi-stage electric pulses offers, in contrast to usual single pulses, wider ranges of droplet size, improved reproducibility and stable ejection trajectories. Influence of the main parameters on the extracted droplet diameter is presented: it is shown that, by using capillary tubes of outer tip diameter close to 0.5 mm, it is possible to obtain, in a reproducible way, drops of diameter ranging from less than 15 μm up to more than 250 μm.

  18. Spectroscopy and optical imaging of coalescing droplets

    NASA Astrophysics Data System (ADS)

    Ivanov, Maksym; Viderström, Michel; Chang, Kelken; Ramírez Contreras, Claudia; Mehlig, Bernhard; Hanstorp, Dag

    2016-09-01

    We report on experimental investigations of the dynamics of colliding liquid droplets by combining optical trapping, spectroscopy and high-speed color imaging. Two droplets with diameters between 5 and 50 microns are suspended in quiescent air by optical traps. The traps allows us to control the initial positions, and hence the impact parameter and the relative velocity of the colliding droplets. Movies of the droplet dynamics are recorded using high-speed digital movie cameras at a frame rate of up to 63000 frames per second. A fluorescent dye is added to one of the colliding droplets. We investigate the temporal evolution of the scattered and fluorescence light from the colliding droplets with concurrent spectroscopy and color imaging. This technique can be used to detect the exchange of molecules between a pair of neutral or charged droplets.

  19. Kinetics of complex plasma with liquid droplets

    NASA Astrophysics Data System (ADS)

    Misra, Shikha; Mishra, S. K.; Sodha, M. S.

    2013-12-01

    This paper provides a theoretical basis for the reduction of electron density by spray of water (or other liquids) in hot plasma. This phenomenon has been observed in a hypersonic flight experiment for relief of radio black out, caused by high ionization in the plasma sheath of a hypersonic vehicle, re-entering the atmosphere. The analysis incorporates a rather little known phenomenon for de-charging of the droplets, viz., evaporation of ions from the surface and includes the charge balance on the droplets and number cum energy balance of electrons, ions, and neutral molecules; the energy balance of the evaporating droplets has also been taken into account. The analysis has been applied to a realistic situation and the transient variations of the charge and radius of water droplets, and other plasma parameters have been obtained and discussed. The analysis through made in the context of water droplets is applicable to all liquids.

  20. Modular droplet actuator drive

    NASA Technical Reports Server (NTRS)

    Pollack, Michael G. (Inventor); Paik, Philip (Inventor)

    2011-01-01

    A droplet actuator drive including a detection apparatus for sensing a property of a droplet on a droplet actuator; circuitry for controlling the detection apparatus electronically coupled to the detection apparatus; a droplet actuator cartridge connector arranged so that when a droplet actuator cartridge electronically is coupled thereto: the droplet actuator cartridge is aligned with the detection apparatus; and the detection apparatus can sense the property of the droplet on a droplet actuator; circuitry for controlling a droplet actuator coupled to the droplet actuator connector; and the droplet actuator circuitry may be coupled to a processor.

  1. Detection of heavy-metal ions using liquid crystal droplet patterns modulated by interaction between negatively charged carboxylate and heavy-metal cations.

    PubMed

    Han, Gyeo-Re; Jang, Chang-Hyun

    2014-10-01

    Herein, we demonstrated a simple, sensitive, and rapid label-free detection method for heavy-metal (HM) ions using liquid crystal (LC) droplet patterns on a solid surface. Stearic-acid-doped LC droplet patterns were spontaneously generated on an n-octyltrichlorosilane (OTS)-treated glass substrate by evaporating a solution of the nematic LC, 4-cyano-4'-pentylbiphenyl (5CB), dissolved in heptane. The optical appearance of the droplet patterns was a dark crossed texture when in contact with air, which represents the homeotropic orientation of the LC. This was caused by the steric interaction between the LC molecules and the alkyl chains of the OTS-treated surface. The dark crossed appearance of the acid-doped LC patterns was maintained after the addition of phosphate buffered saline (PBS) solution (pH 8.1 at 25°C). The deprotonated stearic-acid molecules self-assembled through the LC/aqueous interface, thereby supporting the homeotropic anchoring of 5CB. However, the optical image of the acid-doped LC droplet patterns incubated with PBS containing HM ions appeared bright, indicating a planar orientation of 5CB at the aqueous/LC droplet interface. This dark to bright transition of the LC patterns was caused by HM ions attached to the deprotonated carboxylate moiety, followed by the sequential interruption of the self-assembly of the stearic acid at the LC/aqueous interface. The results showed that the acid-doped LC pattern system not only enabled the highly sensitive detection of HM ions at a sub-nanomolar concentration but it also facilitated rapid detection (<10 min) with simple procedures.

  2. Determination of nicotine in tobacco with second-order spectra data of charge-transfer complex in ethanol-water binary solvents processed by parallel factor analysis

    NASA Astrophysics Data System (ADS)

    Gao, Shuqin; Liao, Lifu; Xiao, Xilin; Zhao, Zhiyuan; Du, Nan; Du, Jiangfeng

    2010-05-01

    A new spectrophotometric method for the determination of nicotine in mixtures without pre-separation has been proposed. Nicotine could react with 2,4-dinitrophenol through a charge-transfer reaction to form a colored complex. The second-order data from the visible absorption spectra of the complex in a series of ethanol-water binary solvents with various water volume fractions could be expressed as the combination of two bilinear data matrices. With the bilinear model, the second-order spectra data of mixtures containing nicotine and other interferents could be analysed by using second-order calibration algorithms, and the determination of nicotine in the mixtures could be achieved. The algorithm used here was parallel factor analysis. The method has been successfully used to determine nicotine in tobacco samples with satisfactory results.

  3. Determination of nicotine in tobacco with second-order spectra data of charge-transfer complex in ethanol-water binary solvents processed by parallel factor analysis.

    PubMed

    Gao, Shuqin; Liao, Lifu; Xiao, Xilin; Zhao, Zhiyuan; Du, Nan; Du, Jiangfeng

    2010-05-01

    A new spectrophotometric method for the determination of nicotine in mixtures without pre-separation has been proposed. Nicotine could react with 2,4-dinitrophenol through a charge-transfer reaction to form a colored complex. The second-order data from the visible absorption spectra of the complex in a series of ethanol-water binary solvents with various water volume fractions could be expressed as the combination of two bilinear data matrices. With the bilinear model, the second-order spectra data of mixtures containing nicotine and other interferents could be analysed by using second-order calibration algorithms, and the determination of nicotine in the mixtures could be achieved. The algorithm used here was parallel factor analysis. The method has been successfully used to determine nicotine in tobacco samples with satisfactory results.

  4. Solvent and temperature effects on diastereodifferentiating Paternó-Büchi reaction of chiral alkyl cyanobenzoates with diphenylethene upon direct versus charge-transfer excitation.

    PubMed

    Matsumura, Kazuyuki; Mori, Tadashi; Inoue, Yoshihisa

    2010-08-20

    In the Paternó-Büchi reaction of chiral p-cyanobenzoates (1) with 1,1-diphenylethene (2), we revealed that the excited charge-transfer (CT) complex formed upon selective excitation at the CT band is distinctly different in structure and reactivity from the conventional exciplex generated through the direct excitation of acceptor 1 which subsequently associates with donor 2. Thus, the favored diastereoface upon photocycloaddition, as well as the temperature- and solvent-dependent behavior of the product's diastereoselectivity, were highly contrasting, often opposite, to each other upon direct versus CT excitation. From the activation parameters obtained by the Eyring analyses of the diastereoselectivity, we are able to infer that the conventional exciplex is relatively flexible and susceptible to the environmental variants, whereas the CT complex is better pi-pi stacked and more rigid in the ground state and also in the excited state, leading to the significantly smaller differential activation enthalpies and entropies. More interestingly, the signs of the differential activation parameters determined for direct and CT excitation are consistently opposite to each other and the isokinetic temperatures calculated therefrom differ significantly, unambiguously revealing the distinctly different nature in structure and reactivity of these two excited-state complex species. Thus, the combined use of irradiation wavelength, temperature, and solvent provides us with a convenient, powerful tool not only for elucidating the mechanistic details of photoreaction but also for critically controlling the stereochemical outcomes of photochirogenic reaction.

  5. Nanospiral Formation by Droplet Drying: One Molecule at a Time.

    PubMed

    Wan, Lei; Li, Li; Mao, Guangzhao

    2011-12-01

    We have created nanospirals by self-assembly during droplet evaporation. The nanospirals, 60-70 nm in diameter, formed when solvent mixtures of methanol and m-cresol were used. In contrast, spin coating using only methanol as the solvent produced epitaxial films of stripe nanopatterns and using only m-cresol disordered structure. Due to the disparity in vapor pressure between the two solvents, droplets of m-cresol solution remaining on the substrate serve as templates for the self-assembly of carboxylic acid molecules, which in turn allows the visualization of solution droplet evaporation one molecule at a time.

  6. Foam droplet separation for nanoparticle synthesis

    NASA Astrophysics Data System (ADS)

    Tyree, Corey A.; Allen, Jonathan O.

    2008-03-01

    A novel approach to nanoparticle synthesis was developed whereby foam bubble bursting produced aerosol droplets, an approach patterned after the marine foam aerosol cycle. The droplets were dried to remove solvent, leaving nanometer-sized particles composed of precursor material. Nanoparticles composed of sodium chloride (mean diameter, bar{D}_p≈ 100 nm), phosphotungstic acid (bar{D}_p≈ 55 nm), and bovine insulin ({D}_p≈ 5-30 nm) were synthesized. Foam droplet separation can be carried out at ambient temperature and pressure. The `soft' nature of the process makes it compatible with a wide range of materials.

  7. Photofragment Coincidence Imaging of Small I- (H2O)n Clusters Excited to the Charge-transfer-to-solvent State

    SciTech Connect

    Neumark, D. E. Szpunar, K. E. Kautzman, A. E. Faulhaber, and D. M.; Kautzman, K.E.; Faulhaber, A.E.; Faulhaber, A.E.

    2005-11-09

    The photodissociation dynamics of small I{sup -}(H{sub 2}O){sub n} (n = 2-5) clusters excited to their charge-transfer-to-solvent (CTTS) states have been studied using photofragment coincidence imaging. Upon excitation to the CTTS state, two photodissociation channels were observed. The major channel ({approx}90%) is a 2-body process forming neutral I + (H{sub 2}O){sub n} photofragments, and the minor channel is a 3-body process forming I + (H{sub 2}O){sub n-1} + H{sub 2}O fragments. Both process display translational energy (P(E{sub T})) distributions peaking at E{sub T} = 0 with little available energy partitioned into translation. Clusters excited to the detachment continuum rather than to the CTTS state display the same two channels with similar P(E{sub T}) distributions. The observation of similar P(E{sub T}) distributions from the two sets of experiments suggests that in the CTTS experiments, I atom loss occurs after autodetachment of the excited (I(H{sub 2}O){sub n}{sup -})* cluster, or, less probably, that the presence of the excess electron has little effect on the departing I atom.

  8. Mass Spectrometry of Acoustically Levitated Droplets

    PubMed Central

    Westphall, Michael S.; Jorabchi, Kaveh; Smith, Lloyd M.

    2008-01-01

    Containerless sample handling techniques such as acoustic levitation offer potential advantages for mass spectrometry, by eliminating surfaces where undesired adsorption/desorption processes can occur. In addition, they provide a unique opportunity to study fundamental aspects of the ionization process as well as phenomena occurring at the air–droplet interface. Realizing these advantages is contingent, however, upon being able to effectively interface levitated droplets with a mass spectrometer, a challenging task that is addressed in this report. We have employed a newly developed charge and matrix-assisted laser desorption/ionization (CALDI) technique to obtain mass spectra from a 5-μL acoustically levitated droplet containing peptides and an ionic matrix. A four-ring electrostatic lens is used in conjunction with a corona needle to produce bursts of corona ions and to direct those ions toward the droplet, resulting in droplet charging. Analyte ions are produced from the droplet by a 337-nm laser pulse and detected by an atmospheric sampling mass spectrometer. The ion generation and extraction cycle is repeated at 20 Hz, the maximum operating frequency of the laser employed. It is shown in delayed ion extraction experiments that both positive and negative ions are produced, behavior similar to that observed for atmospheric pressure matrix-assisted laser absorption/ionization. No ion signal is observed in the absence of droplet charging. It is likely, although not yet proven, that the role of the droplet charging is to increase the strength of the electric field at the surface of the droplet, reducing chargere combination after ion desorption. PMID:18582090

  9. Solvent alternatives guide

    SciTech Connect

    Elion, J.M.; Monroe, K.R.; Hill, E.A.

    1996-06-01

    It is no longer legal to manufacture or import chlorofluorocarbon 113 or methyl chloroform solvents, and companies that currently clean their parts with either material are now required to implement environmentally safe substitutes. To help find alternative methods, Research Triangle Institute`s Surface Cleaning Technology Program has designed a Solvent Alternatives Guide (SAGE), an online tool that enables access to practical information and recommendations for acceptable solvents. Developed in partnership with the US Environmental Protection Agency, SAGE is available free of charge on the Internet`s World Wide Web.

  10. A new droplet generator

    NASA Technical Reports Server (NTRS)

    Slack, W. E.

    1982-01-01

    A new droplet generator is described. A loud speaker driven extractor needle was immersed in a pendant drop. Pulsing the speaker extracted the needle forming a fluid ligament which will decay into a droplet. The droplets were sized by stroboscopic photographs. The droplet's size was changed by varying the amplitude of the speaker pulses and the extractor needle diameter. The mechanism of droplet formation is discussed and photographs of ligament decay are presented. The droplet generator worked well on both oil and water based pesticide formulations. Current applications and results are discussed.

  11. Droplet fusion by alternating current (AC) field electrocoalescence in microchannels.

    PubMed

    Chabert, Max; Dorfman, Kevin D; Viovy, Jean-Louis

    2005-10-01

    We present a system for the electrocoalescence of microfluidic droplets immersed in an immiscible solvent, where the undeformed droplet diameters are comparable to the channel diameter. The electrodes are not in direct contact with the carrier liquid or the droplets, thereby minimizing the risk of cross-contamination between different coalescence events. Results are presented for the coalescence of buffered aqueous droplets in both quiescent and flowing fluorocarbon streams, and on-flight coalescence is demonstrated. The capillary-based system presented here is readily amenable to further miniaturization to any lab-on-a-chip application where the conductivity of the droplets is much greater than the conductivity of the stream containing them, and should aid in the further application of droplet microreactors to biological analyses.

  12. Directional electrostatic accretion process employing acoustic droplet formation

    NASA Technical Reports Server (NTRS)

    Oeftering, Richard C. (Inventor)

    1996-01-01

    The present invention is directed to an apparatus for manufacturing a free standing solid metal part. In the present invention metal droplets are produced from a free surface pool of molten metal is when an acoustic wave impacts an acoustic lens that is contiguous with the free standing pool of molten metal. The metal droplets are then charged and deflected toward a target. The build up of the metal droplets combine to form the free standing solid metal part.

  13. UV-Vis spectroscopy and density functional study of solvent effect on the charge transfer band of the n → σ* complexes of 2-Methylpyridine and 2-Chloropyridine with molecular iodine

    NASA Astrophysics Data System (ADS)

    Gogoi, Pallavi; Mohan, Uttam; Borpuzari, Manash Protim; Boruah, Abhijit; Baruah, Surjya Kumar

    2017-03-01

    UV-Vis spectroscopy has established that Pyridine substitutes form n→σ* charge transfer (CT) complexes with molecular Iodine. This study is a combined approach of purely experimental UV-Vis spectroscopy, Multiple linear regression theory and Computational chemistry to analyze the effect of solvent upon the charge transfer band of 2-Methylpyridine-I2 and 2-Chloropyridine-I2 complexes. Regression analysis verifies the dependence of the CT band upon different solvent parameters. Dielectric constant and refractive index are considered among the bulk solvent parameters and Hansen, Kamlet and Catalan parameters are taken into consideration at the molecular level. Density Functional Theory results explain well the blue shift of the CT bands in polar medium as an outcome of stronger donor acceptor interaction. A logarithmic relation between the bond length of the bridging atoms of the donor and the acceptor with the dielectric constant of the medium is established. Tauc plot and TDDFT study indicates a non-vertical electronic transition in the complexes. Buckingham and Lippert Mataga equations are applied to check the Polarizability effect on the CT band.

  14. Electric field mediated spraying of miniaturized droplets inside microchannel.

    PubMed

    Timung, Seim; Chaudhuri, Joydip; Borthakur, Manash Pratim; Mandal, Tapas Kumar; Biswas, Gautam; Bandyopadhyay, Dipankar

    2016-10-17

    We report a facile and noninvasive way to disintegrate a microdroplet into a string of further miniaturized ones under the influence of an external electrohydrodynamic field inside a microchannel. The deformation and breakup of the droplet was engendered by the Maxwell's stress originating from the accumulation of induced and free charges at the oil-water interface. While at smaller field intensities, for example less than 1 MV/m, the droplet deformed into a plug, at relatively higher field intensities, e.g. ∼1.16 MV/m, a pair of droplets having opposite surface charge was formed. The charged droplets showed an interesting periodic bridging and breakup during their translation motion across the channel. For even higher field intensities, for example more than 1.2 MV/m, the entire droplet underwent dielectrophoresis toward one of the electrodes before experiencing a strong attractive force from the other electrode to deform into a shape of a Taylor cone. With progress in time, mimicking the electrospraying phenomenon, the cone tip periodically ejected a string of miniaturized water droplets to form a microemulsion inside the channel. The frequency and size of the droplet ejection could be tuned by varying the applied field intensity. A water droplet of ∼214 μm diameter could continuously eject droplets of size ∼10 μm or even smaller to form a microemulsion inside the channel.

  15. Mechanisms of droplet combustion

    NASA Technical Reports Server (NTRS)

    Law, C. K.

    1982-01-01

    The fundamental physico-chemical mechanisms governing droplet vaporization and combustion are discussed. Specific topics include governing equations and simplifications, the classical d(2)-Law solution and its subsequent modification, finite-rate kinetics and the flame structure, droplet dynamics, near- and super-critical combustion, combustion of multicomponent fuel blends/emulsions/suspensions, and droplet interaction. Potential research topics are suggested.

  16. Single droplet separations and surface partition coefficient measurements using laser ablation mass spectrometry

    PubMed Central

    Jorabchi, Kaveh; Smith, Lloyd M.

    2010-01-01

    Surface activity of analytes plays a significant role in many chemical and physical phenomena. We present here a mass spectrometric method to characterize surface activity and solute partitioning between bulk liquid and the gas-liquid interface in droplets. The approach employs ablation by an IR laser from the surface of a microliter droplet deposited on a stainless steel post. The ablated material is ionized for mass spectrometric analysis by either droplet charging or by post-ionization in an electrospray plume. Three areas of application have been explored using this method; 1) separations in a single droplet: continuous ablation by a series of many successive laser pulses results in faster depletion of more surface active analytes, effectively comprising a surface activity-based separation. 2) Partition coefficient measurements: droplet volume is held constant during ablation by continually replenishing lost solvent. This leads to analyte-specific ion signal decay curves that may be fitted to a model based on Langmuir adsorption isotherms and simple analytical expressions, yielding quantitative values for the analyte surface partition coefficients. 3) Studies of the relationship between surface partitioning and HPLC phase partitioning: comparisons of surface activities measured by laser desorption with retention times in reversed phase HPLC reveal that the relationship between the two partitioning processes is very sensitive to chemical structure. Poor correlation between the retention time and surface activity is also observed within a subcategory of analytes (peptides). This effect is attributed to multi-modal solute-stationary phase interactions. The laser desorption approach presented here provides direct information on analyte surface activities free from the complications encountered in chromatographic methods due to chemical structure variations. PMID:19886638

  17. Ternary water-in-oil microemulsions made of cationic surfactants, water, and aromatic solvents. 3. Self-diffusion studies in relation to exchange of material between droplets and percolation

    SciTech Connect

    Zana, R.; Lang, J. ); Canet, D. )

    1991-04-18

    Ternary water-in-oil microemulsions using alkylbenzyldimethylammonium chloride (alkyl = dodecyl (N12), tetradecyl (N14), and hexadecyl (N16)) surfactants and benzene or chlorobenzene as oils have been investigated by means of electrical conductivity and NMR self-diffusion. The variations of the water self-diffusion coefficient with the (water)/(surfactant) molar concentration ratio {omega} and with the volume fraction of benzene in the oil mixture in water/(benzene + chlorobenzene)/N16 microemulsions are well correlated with the changes of electrical conductivity, as expected from a model of microemulsions where the water cores of the droplets become increasingly connected above the percolation threshold. These connections, however, have a strongly dynamic character. This model permits the authors to explain the widely differing magnitudes of the changes of electrical conductivity, water self-diffusion coefficient, and rate of exchange reactants between droplets upon increasing {omega}. The self-diffusion coefficient of the oil has been found to be about half that of the bulk oil, as in studies reported by others.

  18. Systems and methods for producing metal clusters; functionalized surfaces; and droplets including solvated metal ions

    DOEpatents

    Cooks, Robert Graham; Li, Anyin; Luo, Qingjie

    2017-01-24

    The invention generally relates to systems and methods for producing metal clusters; functionalized surfaces; and droplets including solvated metal ions. In certain aspects, the invention provides methods that involve providing a metal and a solvent. The methods additionally involve applying voltage to the solvated metal to thereby produce solvent droplets including ions of the metal containing compound, and directing the solvent droplets including the metal ions to a target. In certain embodiments, once at the target, the metal ions can react directly or catalyze reactions.

  19. Droplet-Based Production of Liposomes

    NASA Technical Reports Server (NTRS)

    Ackley, Donald E.; Forster, Anita

    2009-01-01

    A process for making monodisperse liposomes having lipid bilayer membranes involves fewer, simpler process steps than do related prior methods. First, a microfluidic, cross junction droplet generator is used to produce vesicles comprising aqueous solution droplets contained in single layer lipid membranes. The vesicles are collected in a lipid-solvent mix that is at most partially soluble in water and is less dense than is water. A layer of water is dispensed on top of the solvent. By virtue of the difference in densities, the water sinks to the bottom and the solvent floats to the top. The vesicles, which have almost the same density as that of water, become exchanged into the water instead of floating to the top. As there are excess lipids in the solvent solution, in order for the vesicles to remain in the water, the addition of a second lipid layer to each vesicle is energetically favored. The resulting lipid bilayers present the hydrophilic ends of the lipid molecules to both the inner and outer membrane surfaces. If lipids of a second kind are dissolved in the solvent in sufficient excess before use, then asymmetric liposomes may be formed.

  20. Electric-field-induced response of a droplet embedded in a polyelectrolyte gel

    NASA Astrophysics Data System (ADS)

    Mohammadi, Aliasghar

    2013-08-01

    The electric-field induced response of a droplet embedded in a quenched polyelectrolyte gel is calculated theoretically. The response comprises the droplet translation and the electric-field induced flow fields within the droplet. The gel is modeled as a soft, and electrically charged porous solid saturated with a salted Newtonian fluid. The droplet is considered an incompressible Newtonian fluid with no free charge. An analytical solution, using the perturbation methodology and linear superposition, is obtained for the leading-order steady response to a DC electric-field. The fluid within the droplet is driven due to hydrodynamic coupling with the electroosmotic flow. The fluid velocity within the droplet is linearly proportional to the electroosmotic flow. Moreover, the microrheological response function of a droplet within a polyelectrolyte gel is also provided, highlighting the importance of boundary conditions at the droplet-gel interface on microrheological measurements.

  1. Calculating the binding free energies of charged species based on explicit-solvent simulations employing lattice-sum methods: An accurate correction scheme for electrostatic finite-size effects

    SciTech Connect

    Rocklin, Gabriel J.; Mobley, David L.; Dill, Ken A.; Hünenberger, Philippe H.

    2013-11-14

    -periodic PB calculations for a given system, its dependence on the box size being analytical. The latter scheme also provides insight into the physical origin of the finite-size effects. These two schemes also encompass a correction for discrete solvent effects that persists even in the limit of infinite box sizes. Application of either scheme essentially eliminates the size dependence of the corrected charging free energies (maximal deviation of 1.5 kJ mol{sup −1}). Because it is simple to apply, the analytical correction scheme offers a general solution to the problem of finite-size effects in free-energy calculations involving charged solutes, as encountered in calculations concerning, e.g., protein-ligand binding, biomolecular association, residue mutation, pK{sub a} and redox potential estimation, substrate transformation, solvation, and solvent-solvent partitioning.

  2. Calculating the binding free energies of charged species based on explicit-solvent simulations employing lattice-sum methods: An accurate correction scheme for electrostatic finite-size effects

    PubMed Central

    Rocklin, Gabriel J.; Mobley, David L.; Dill, Ken A.; Hünenberger, Philippe H.

    2013-01-01

    calculations for a given system, its dependence on the box size being analytical. The latter scheme also provides insight into the physical origin of the finite-size effects. These two schemes also encompass a correction for discrete solvent effects that persists even in the limit of infinite box sizes. Application of either scheme essentially eliminates the size dependence of the corrected charging free energies (maximal deviation of 1.5 kJ mol−1). Because it is simple to apply, the analytical correction scheme offers a general solution to the problem of finite-size effects in free-energy calculations involving charged solutes, as encountered in calculations concerning, e.g., protein-ligand binding, biomolecular association, residue mutation, pKa and redox potential estimation, substrate transformation, solvation, and solvent-solvent partitioning. PMID:24320250

  3. Controlling the Growth Modes of Femtoliter Sessile Droplets Nucleating on Chemically Patterned Surfaces

    NASA Astrophysics Data System (ADS)

    Zhang, Xuehua; Bao, Lei; Werbiuk, Zenon; Lohse, Detlef

    2016-11-01

    Femtoliter droplet arrays on immersed substrates are essential elements in a broad range of advanced droplet-based technologies, such as light manipulation, sensing, and high throughput diagnosis. Solvent exchange is a bottom-up approach for producing those droplets from a pulse of oil oversaturation when a good solvent of the droplet liquid is displaced by a poor solvent. The position and arrangement of the droplets are regulated by chemical micropatterns on the substrate. Here we show experimentally and theoretically that the growth modes of droplets confined in planar micropatterns on the surface can be manipulated through the laminar flow of the solvent exchange. The control parameters are the area size of the micropatterns and the flow rate, and the observables are the contact angle and the final droplet volume. For a given pattern size, the Peclet number of the flow determines whether the growing droplets switch from an initial constant contact angle mode to a subsequent constant contact radius mode. Good agreement is achieved between the experimental results and our theoretical model that describes the dependence of the final droplet size on Pe.

  4. Spontaneous Droplet Jump with Electro-Bouncing

    NASA Astrophysics Data System (ADS)

    Schmidt, Erin; Weislogel, Mark

    2016-11-01

    We investigate the dynamics of water droplet jumps from superhydrophobic surfaces in the presence of an electric field during a step reduction in gravity level. In the brief free-fall environment of a drop tower, when a strong non-homogeneous electric field (with a measured strength between 0 . 39 and 2 . 36 kV/cm) is imposed, body forces acting on the jumped droplets are primarily supplied by polarization stress and Coulombic attraction instead of gravity. The droplet charge, measured to be on the order of 2 . 3 . (10-11) C, originates by electro-osmosis of charged species at the (PTFE coated) hydrophobic surface interface. This electric body force leads to a droplet bouncing behavior similar to well-known phenomena in 1-g, though occurring for larger drops 0.1 mL for a given range of impact Weber numbers, We < 20 . In 1-g, for We > 0 . 4 , impact recoil behavior on a super-hydrophobic surface is normally dominated by damping from contact line hysteresis and by air-layer interactions. However, in the strong electric field, the droplet bounce dynamics additionally include electrohydrodynamic effects on wettability and Cassie-Wenzel transition. This is qualitatively discussed in terms of coefficients of restitution and trends in contact time. This work was supported primarily by NASA Cooperative Agreement NNX12A047A.

  5. Flow invariant droplet formation for stable parallel microreactors

    PubMed Central

    Riche, Carson T.; Roberts, Emily J.; Gupta, Malancha; Brutchey, Richard L.; Malmstadt, Noah

    2016-01-01

    The translation of batch chemistries onto continuous flow platforms requires addressing the issues of consistent fluidic behaviour, channel fouling and high-throughput processing. Droplet microfluidic technologies reduce channel fouling and provide an improved level of control over heat and mass transfer to control reaction kinetics. However, in conventional geometries, the droplet size is sensitive to changes in flow rates. Here we report a three-dimensional droplet generating device that exhibits flow invariant behaviour and is robust to fluctuations in flow rate. In addition, the droplet generator is capable of producing droplet volumes spanning four orders of magnitude. We apply this device in a parallel network to synthesize platinum nanoparticles using an ionic liquid solvent, demonstrate reproducible synthesis after recycling the ionic liquid, and double the reaction yield compared with an analogous batch synthesis. PMID:26902825

  6. Droplets on liquids and their journey into equilibrium.

    PubMed

    Bommer, Stefan; Cartellier, Florian; Jachalski, Sebastian; Peschka, Dirk; Seemann, Ralf; Wagner, Barbara

    2013-08-01

    The morphological path of droplets on a liquid substrate towards equilibrium is investigated experimentally and theoretically. The droplets emerge in the late stage of a dewetting process of short chained polystyrene (PS) dewetting from liquid polymethyl-methacrylate (PMMA). The three-dimensional droplet profiles are obtained experimentally by combining the in situ imaged PS/air interface during equilibration and the ex situ imaged PS/PMMA interface after removal of the PS by a selective solvent. Numerically the transient drop shapes are calculated by solving the thin-film equation in lubrication approximation using the experimentally determined input parameter like viscosity, film thickness and surface tensions. The numerically obtained droplet morphologies and time scales agree very well with the experimental drop shapes. An unexpected observation is that droplets with identical volumes synchronise their motion and become independent of the initial geometry long time before equilibrium is reached.

  7. Flow invariant droplet formation for stable parallel microreactors

    NASA Astrophysics Data System (ADS)

    Riche, Carson T.; Roberts, Emily J.; Gupta, Malancha; Brutchey, Richard L.; Malmstadt, Noah

    2016-02-01

    The translation of batch chemistries onto continuous flow platforms requires addressing the issues of consistent fluidic behaviour, channel fouling and high-throughput processing. Droplet microfluidic technologies reduce channel fouling and provide an improved level of control over heat and mass transfer to control reaction kinetics. However, in conventional geometries, the droplet size is sensitive to changes in flow rates. Here we report a three-dimensional droplet generating device that exhibits flow invariant behaviour and is robust to fluctuations in flow rate. In addition, the droplet generator is capable of producing droplet volumes spanning four orders of magnitude. We apply this device in a parallel network to synthesize platinum nanoparticles using an ionic liquid solvent, demonstrate reproducible synthesis after recycling the ionic liquid, and double the reaction yield compared with an analogous batch synthesis.

  8. Wetting of polymers by their solvents.

    PubMed

    Lequeux, François; Talini, Laurence; Verneuil, Emilie; Delannoy, Guillaume; Valois, Pauline

    2016-02-01

    We review the studies on the wetting of soluble polymeric substrates by their solvents, both in the literature and conducted in our group in the past decade. When a droplet of solvent spreads on a soluble polymer layer, its wetting angle can strongly vary with the contact line velocity even at capillary numbers smaller than unity, in contrast to non-soluble substrates. The solvent content in the polymer is a key parameter for the spreading dynamics; that content is set by the initial conditions, but also by the transfers occurring from the droplet to the polymer layer during spreading. We focus on hydrophilic amorphous polymers that are glassy at room temperature, and we discuss the consequences on wetting of the very large changes in the polymer physical properties induced by solvent sorption. We finally present new results on polymers of varying molar masses, and show how they open new perspectives for a better understanding of powder dissolution.

  9. The roles of electronic exchange and correlation in charge-transfer- to-solvent dynamics: Many-electron nonadiabatic mixed quantum/classical simulations of photoexcited sodium anions in the condensed phase.

    PubMed

    Glover, William J; Larsen, Ross E; Schwartz, Benjamin J

    2008-10-28

    The charge-transfer-to-solvent (CTTS) reactions of solvated atomic anions serve as ideal models for studying the dynamics of electron transfer: The fact that atomic anions have no internal degrees of freedom provides one of the most direct routes to understanding how the motions of solvent molecules influence charge transfer, and the relative simplicity of atomic electronic structure allows for direct contact between theory and experiment. To date, molecular dynamics simulations of the CTTS process have relied on a single-electron description of the atomic anion-only the electron involved in the charge transfer has been treated quantum mechanically, and the electronic structure of the atomic solute has been treated via pseudopotentials. In this paper, we examine the severity of approximating the electronic structure of CTTS anions with a one-electron model and address the role of electronic exchange and correlation in both CTTS electronic structure and dynamics. To do this, we perform many-electron mixed quantum/classical molecular dynamics simulations of the ground- and excited-state properties of the aqueous sodium anion (sodide). We treat both of the sodide valence electrons quantum mechanically and solve the Schrodinger equation using configuration interaction with singles and doubles (CISD), which provides an exact solution for two electrons. We find that our multielectron simulations give excellent general agreement with experimental results on the CTTS spectroscopy and dynamics of sodide in related solvents. We also compare the results of our multielectron simulations to those from one-electron simulations on the same system [C. J. Smallwood et al., J. Chem. Phys. 119, 11263 (2003)] and find substantial differences in the equilibrium CTTS properties and the nonadiabatic relaxation dynamics of one- and two-electron aqueous sodide. For example, the one-electron model substantially underpredicts the size of sodide, which in turn results in a dramatically

  10. Droplet breakup dynamics of weakly viscoelastic fluids

    NASA Astrophysics Data System (ADS)

    Marshall, Kristin; Walker, Travis

    2016-11-01

    The addition of macromolecules to solvent, even in dilute quantities, can alter a fluid's response in an extensional flow. For low-viscosity fluids, the presence of elasticity may not be apparent when measured using a standard rotational rheometer, yet it may still alter the response of a fluid when undergoing an extensional deformation, especially at small length scales where elastic effects are enhanced. Applications such as microfluidics necessitate investigating the dynamics of fluids with elastic properties that are not pronounced at large length scales. In the present work, a microfluidic cross-slot configuration is used to study the effects of elasticity on droplet breakup. Droplet breakup and the subsequent iterated-stretching - where beads form along a filament connecting two primary droplets - were observed for a variety of material and flow conditions. We present a relationship on the modes of bead formation and how and when these modes will form based on key parameters such as the properties of the outer continuous-phase fluid. The results are vital not only for simulating the droplet breakup of weakly viscoelastic fluids but also for understanding how the droplet breakup event can be used for characterizing the extensional properties of weakly-viscoelastic fluids.

  11. Droplet transport system and methods

    NASA Technical Reports Server (NTRS)

    Neitzel, G. Paul (Inventor)

    2010-01-01

    Embodiments of droplet transport systems and methods are disclosed for levitating and transporting single or encapsulated droplets using thermocapillary convection. One method embodiment, among others comprises providing a droplet of a first liquid; and applying thermocapillary convection to the droplet to levitate and move the droplet.

  12. Droplet Combustion Experiment (DCE)

    NASA Technical Reports Server (NTRS)

    Haggard, John B., Jr.; Nayagan, Vedha; Dryer, Frederick L.; Williams, Forman A.

    1998-01-01

    The first space-based experiments were performed on the combustion of free, individual liquid fuel droplets in oxidizing atmospheres. The fuel was heptane, with initial droplet diameters ranging about from 1 mm to 4 mm. The atmospheres were mixtures of helium and oxygen, at pressures of 1.00, 0.50 and 0.25 bar, with oxygen mole fractions between 20% and 40%, as well as normal Spacelab cabin air. The temperatures of the atmospheres and of the initial liquid fuel were nominally 300 K. A total of 44 droplets were burned successfully on the two flights, 8 on the shortened STS-83 mission and 36 on STS-94. The results spanned the full range of heptane droplet combustion behavior, from radiative flame extinction at larger droplet diameters in the more dilute atmospheres to diffusive extinction in the less dilute atmospheres, with the droplet disappearing prior to flame extinction at the highest oxygen concentrations. Quasisteady histories of droplet diameters were observed along with unsteady histories of flame diameters. New and detailed information was obtained on burning rates, flame characteristics and soot behavior. The results have motivated new computational and theoretical investigations of droplet combustion, improving knowledge of the chemical kinetics, fluid mechanics and heat and mass transfer processes involved in burning liquid fuels.

  13. Self-propelled droplets

    NASA Astrophysics Data System (ADS)

    Seemann, Ralf; Fleury, Jean-Baptiste; Maass, Corinna C.

    2016-11-01

    Self-propelled droplets are a special kind of self-propelled matter that are easily fabricated by standard microfluidic tools and locomote for a certain time without external sources of energy. The typical driving mechanism is a Marangoni flow due to gradients in the interfacial energy on the droplet interface. In this article we review the hydrodynamic prerequisites for self-sustained locomotion and present two examples to realize those conditions for emulsion droplets, i.e. droplets stabilized by a surfactant layer in a surrounding immiscible liquid. One possibility to achieve self-propelled motion relies on chemical reactions affecting the surface active properties of the surfactant molecules. The other relies on micellar solubilization of the droplet phase into the surrounding liquid phase. Remarkable cruising ranges can be achieved in both cases and the relative insensitivity to their own `exhausts' allows to additionally study collective phenomena.

  14. Solvent substitution

    SciTech Connect

    Not Available

    1990-01-01

    The DOE Environmental Restoration and Waste Management Office of Technology Development and the Air Force Engineering and Services Center convened the First Annual International Workshop on Solvent Substitution on December 4--7, 1990. The primary objectives of this joint effort were to share information and ideas among attendees in order to enhance the development and implementation of required new technologies for the elimination of pollutants associated with industrial use of hazardous and toxic solvents; and to aid in accelerating collaborative efforts and technology transfer between government and industry for solvent substitution. There were workshop sessions focusing on Alternative Technologies, Alternative Solvents, Recovery/Recycling, Low VOC Materials and Treatment for Environmentally Safe Disposal. The 35 invited papers presented covered a wide range of solvent substitution activities including: hardware and weapons production and maintenance, paint stripping, coating applications, printed circuit boards, metal cleaning, metal finishing, manufacturing, compliance monitoring and process control monitoring. This publication includes the majority of these presentations. In addition, in order to further facilitate information exchange and technology transfer, the US Air Force and DOE solicited additional papers under a general Call for Papers.'' These papers, which underwent review and final selection by a peer review committee, are also included in this combined Proceedings/Compendium. For those involved in handling, using or managing hazardous and toxic solvents, this document should prove to be a valuable resource, providing the most up-to-date information on current technologies and practices in solvent substitution. Individual papers are abstracted separated.

  15. Precision stacking of nanoparticle laden sessile droplets to control solute deposit morphology

    NASA Astrophysics Data System (ADS)

    Kabi, Prasenjit; Basu, Saptarshi; Sanyal, Apratim; Chaudhuri, Swetaprovo

    2015-02-01

    Stacking pure solvent droplets on a solid substrate is apparently impossible in the absence of an external force as the second droplet will invariably spill over the first leading to a large wetted area. However, the unique feature that emerges during the drying of a nanoparticle laden droplet is the progressively enlarging thin solid film along the evaporating sessile droplet liquid periphery. This solid interface: the edge of which we shall refer to as the agglomeration front comprises of a thin layer of nanoparticle assembly and can support a carefully dispensed second droplet thereby allowing droplet stacking. It will be shown that the growth of this agglomeration front can also be effectively controlled by the dispensing time difference and the nanoparticle concentration in the two droplets. So far, we are commonly aware of material stacking in solid phase. This letter demonstrates stacking in the liquid phase and control over the thin solid interface growth.

  16. Ultrafast imaging method to measure surface tension and viscosity of inkjet-printed droplets in flight

    NASA Astrophysics Data System (ADS)

    Staat, Hendrik J. J.; van der Bos, Arjan; van den Berg, Marc; Reinten, Hans; Wijshoff, Herman; Versluis, Michel; Lohse, Detlef

    2017-01-01

    In modern drop-on-demand inkjet printing, the jetted droplets contain a mixture of solvents, pigments and surfactants. In order to accurately control the droplet formation process, its in-flight dynamics, and deposition characteristics upon impact at the underlying substrate, it is key to quantify the instantaneous liquid properties of the droplets during the entire inkjet-printing process. An analysis of shape oscillation dynamics is known to give direct information of the local liquid properties of millimeter-sized droplets and bubbles. Here, we apply this technique to measure the surface tension and viscosity of micrometer-sized inkjet droplets in flight by recording the droplet shape oscillations microseconds after pinch-off from the nozzle. From the damped oscillation amplitude and frequency we deduce the viscosity and surface tension, respectively. With this ultrafast imaging method, we study the role of surfactants in freshly made inkjet droplets in flight and compare to complementary techniques for dynamic surface tension measurements.

  17. Solvent effects on charge transport through solid deposits of [Os(4,4'-diphenyl-2,2'-dipyridyl)2Cl2].

    PubMed

    Forster, Robert J; Iqbal, Javed; Hjelm, Johan; Keyes, Tia E

    2004-12-01

    Mechanically attached, solid-state films of [Os(4,4'-diphenyl-2,2'-dipyridyl)2Cl2] have been formed on gold macro- and microelectrodes and their voltammetric properties investigated. The voltammetric response of these films associated with the Os(2+/3+) redox reaction is reminiscent of that observed for an ideal reversible, solution phase redox couple only when the contacting electrolyte contains of the order of 40% v/v of acetonitrile (ACN). The origin of this effect appears to involve preferential solvation of the redox centres by acetonitrile which facilitates the incorporation of charge compensating counterions. Scanning electron microscopy reveals that voltammetric cycling in 40:60 ACN-H2O containing 1.0 M LiClO4 as the electrolyte induces the formation of microcrystals. Voltammetry conducted under semi-infinite linear diffusion conditions has been used to determine the apparent diffusion coefficient, Dapp, for homogeneous charge transport through the deposit. The dynamics of charge transport decrease with increasing film thickness but appear to increase with increasing electrolyte concentration. These observations suggest that ion transport rather than the rate of electron self-exchange limit the overall rate of charge transport through these solids. When in contact with 40:60 ACN-H2O containing 1.0 M LiClO4 as electrolyte, Dapp values for oxidation and reduction are identical at 1.7 +/- 0.4 x 10(-12) cm2 s(-1). In the same electrolyte, the standard heterogeneous electron transfer rate constant, k(o), determined by fitting the full voltammogram using the Butler-Volmer formalism, is 8.3 +/- 0.5 x 10(-7) cm s(-1). The importance of these results for the rational design of solid state redox active materials for battery, display and sensor applications is considered.

  18. Supercritical microgravity droplet vaporization

    NASA Technical Reports Server (NTRS)

    Hartfield, J.; Curtis, E.; Farrell, P.

    1990-01-01

    Supercritical droplet vaporization is an important issue in many combustion systems, such as liquid fueled rockets and compression-ignition (diesel) engines. In order to study the details of droplet behavior at these conditions, an experiment was designed to provide a gas phase environment which is above the critical pressure and critical temperature of a single liquid droplet. In general, the droplet begins as a cold droplet in the hot, high pressure environment. In order to eliminate disruptions to the droplet by convective motion in the gas, forced and natural convection gas motion are required to be small. Implementation of this requirement for forced convection is straightforward, while reduction of natural convection is achieved by reduction in the g-level for the experiment. The resulting experiment consists of a rig which can stably position a droplet without restraint in a high-pressure, high temperature gas field in microgravity. The microgravity field is currently achieved by dropping the device in the NASA Lewis 2.2 second drop tower. The performance of the experimental device and results to date are presented.

  19. Bioreactor droplets from liposome-stabilized all-aqueous emulsions

    NASA Astrophysics Data System (ADS)

    Dewey, Daniel C.; Strulson, Christopher A.; Cacace, David N.; Bevilacqua, Philip C.; Keating, Christine D.

    2014-08-01

    Artificial bioreactors are desirable for in vitro biochemical studies and as protocells. A key challenge is maintaining a favourable internal environment while allowing substrate entry and product departure. We show that semipermeable, size-controlled bioreactors with aqueous, macromolecularly crowded interiors can be assembled by liposome stabilization of an all-aqueous emulsion. Dextran-rich aqueous droplets are dispersed in a continuous polyethylene glycol (PEG)-rich aqueous phase, with coalescence inhibited by adsorbed ~130-nm diameter liposomes. Fluorescence recovery after photobleaching and dynamic light scattering data indicate that the liposomes, which are PEGylated and negatively charged, remain intact at the interface for extended time. Inter-droplet repulsion provides electrostatic stabilization of the emulsion, with droplet coalescence prevented even for submonolayer interfacial coatings. RNA and DNA can enter and exit aqueous droplets by diffusion, with final concentrations dictated by partitioning. The capacity to serve as microscale bioreactors is established by demonstrating a ribozyme cleavage reaction within the liposome-coated droplets.

  20. Directional Electrostatic Accretion Process Employing Acoustic Droplet Formation

    NASA Technical Reports Server (NTRS)

    Oeftering, Richard (Inventor)

    1998-01-01

    The present invention is directed to an apparatus for manufacturing a free standing solid metal part. In the present invention, metal droplets are ejected in a nozzleless fashion from a free surface pool of molten metal by applying focused acoustic radiation pressure. The acoustic radiation pressure is produced by high intensity acoustic tone bursts emitted from an acoustic source positioned at the bottom of the pool which directs the acoustic energy at the pool surface. The metal droplets are electrostatically charged so their trajectory can be controlled by electric fields that guide the droplets to predetermined points on a target. The droplets impinge upon the target and solidify with the target material. The accretion of the electrostatically directed solidified droplets forms the free standing metal part.

  1. Hydrophobic polymers in nano-sized water droplets

    NASA Astrophysics Data System (ADS)

    Tilakaratne, Buddhi; Masood, Samina; Cheung, Margaret

    2008-03-01

    As simulations of biopolymers take place in confined and tight spaces, such as protein folding in the interior of bacteria chaperones or the exit tunnels of ribosomes, quantitative analyses of the confinement effects on both biopolymers and solvent molecules become the center of attention as the solvent-mediated interactions are too profound to solve analytically. We are in the progress to investigate the solvation of hexane molecules in various nano-sized water droplets. Free energy profiles for a single hexane molecule in droplets show that the droplet surfaces are favored. Averaged configurations of hexane molecules at the interior and the surface are computed using the umbrella sampling methods. The implications of our results for protein stability in confined spaces will be discussed.

  2. Active droplet generation in microfluidics.

    PubMed

    Chong, Zhuang Zhi; Tan, Say Hwa; Gañán-Calvo, Alfonso M; Tor, Shu Beng; Loh, Ngiap Hiang; Nguyen, Nam-Trung

    2016-01-07

    The reliable generation of micron-sized droplets is an important process for various applications in droplet-based microfluidics. The generated droplets work as a self-contained reaction platform in droplet-based lab-on-a-chip systems. With the maturity of this platform technology, sophisticated and delicate control of the droplet generation process is needed to address increasingly complex applications. This review presents the state of the art of active droplet generation concepts, which are categorized according to the nature of the induced energy. At the liquid/liquid interface, an energy imbalance leads to instability and droplet breakup.

  3. Charge-transfer complexes of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone with amino molecules in polar solvents

    NASA Astrophysics Data System (ADS)

    Berto, Silvia; Chiavazza, Enrico; Ribotta, Valentina; Daniele, Pier Giuseppe; Barolo, Claudia; Giacomino, Agnese; Vione, Davide; Malandrino, Mery

    2015-10-01

    The charge-transfer complexes have scientific relevance because this type of molecular interaction is at the basis of the activity of pharmacological compounds and because the absorption bands of the complexes can be used for the quantification of electron donor molecules. This work aims to assess the stability of the charge-transfer complexes between the electron acceptor 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and two drugs, procaine and atenolol, in acetonitrile and ethanol. The stability of DDQ in solution and the time required to obtain the maximum complex formation were evaluated. The stoichiometry and the stability of the complexes were determined, respectively, by Job's plot method and by the elaboration of UV-vis titrations data. The latter task was carried out by using the non-linear global analysis approach to determine the equilibrium constants. This approach to data elaboration allowed us to overcome the disadvantages of the classical linear-regression method, to obtain reliable values of the association constants and to calculate the entire spectra of the complexes. NMR spectra were recorded to identify the portion of the donor molecule that was involved in the interaction. The data support the participation of the aliphatic amino groups in complex formation and exclude the involvement of the aromatic amine present in the procaine molecule.

  4. Material forming apparatus using a directed droplet stream

    DOEpatents

    Holcomb, David E.; Viswanathan, Srinath; Blue, Craig A.; Wilgen, John B.

    2000-01-01

    Systems and methods are described for rapidly forming precision metallic and intermetallic alloy net shape parts directly from liquid metal droplets. A directed droplet deposition apparatus includes a crucible with an orifice for producing a jet of material, a jet destabilizer, a charging structure, a deflector system, and an impact zone. The systems and methods provide advantages in that fully dense, microstructurally controlled parts can be fabricated at moderate cost.

  5. Microscopic Rayleigh Droplet Beams

    NASA Astrophysics Data System (ADS)

    Doak, R. B.

    2005-11-01

    A periodically triggered Rayleigh Droplet Beam (RDB) delivers a perfectly linear and periodic stream of identical, monoenergetic droplets that are phase-locked to the trigger signal. The droplet diameter and spacing are easily adjusted of choice of nozzle diameter and trigger frequency. Any liquid of low viscosity may be emloyed as the beam fluid. Although the field of nanofluidics is expanding rapidly, little effort has yet been devoted to ``external flows'' such as RDB's. At ASU we have generated RDB's of water and methanol down to 2 microns in droplet diameter. Nozzle clogging is the sole impediment to smaller droplets. Microscopic Rayleigh droplet beams offer tremendous potential for fundamental physical measurements, fluid dynamics research, and nanofabrication. This talk will describe the apparatus and techniques used at ASU to generate RDB's (surprisingly simple and inexpensive), discuss the triboelectric phenomena that play a role (surprisingly significant), present some initial experimental fluid dynamics measurements, and briefly survey RDB applications. Our particular interest in RDB's is as microscopic transport systems to deliver hydrated, undenatured proteins into vacuum for structure determination via serial diffraction of x-rays or electrons. This may offer the first general method for structure determination of non-crystallizable proteins.

  6. Droplet based microfluidics.

    PubMed

    Seemann, Ralf; Brinkmann, Martin; Pfohl, Thomas; Herminghaus, Stephan

    2012-01-01

    Droplet based microfluidics is a rapidly growing interdisciplinary field of research combining soft matter physics, biochemistry and microsystems engineering. Its applications range from fast analytical systems or the synthesis of advanced materials to protein crystallization and biological assays for living cells. Precise control of droplet volumes and reliable manipulation of individual droplets such as coalescence, mixing of their contents, and sorting in combination with fast analysis tools allow us to perform chemical reactions inside the droplets under defined conditions. In this paper, we will review available drop generation and manipulation techniques. The main focus of this review is not to be comprehensive and explain all techniques in great detail but to identify and shed light on similarities and underlying physical principles. Since geometry and wetting properties of the microfluidic channels are crucial factors for droplet generation, we also briefly describe typical device fabrication methods in droplet based microfluidics. Examples of applications and reaction schemes which rely on the discussed manipulation techniques are also presented, such as the fabrication of special materials and biophysical experiments.

  7. Fuel Droplet Burning During Droplet Combustion Experiment

    NASA Technical Reports Server (NTRS)

    2003-01-01

    Fuel ignites and burns in the Droplet Combustion Experiment (DCE) on STS-94 on July 4 1997, MET:2/05:40 (approximate). The DCE was designed to investigate the fundamental combustion aspects of single, isolated droplets under different pressures and ambient oxygen concentrations for a range of droplet sizes varying between 2 and 5 mm. DCE used various fuels -- in drops ranging from 1 mm (0.04 inches) to 5 mm (0.2 inches) -- and mixtures of oxidizers and inert gases to learn more about the physics of combustion in the simplest burning configuration, a sphere. The experiment elapsed time is shown at the bottom of the composite image. The DCE principal investigator was Forman Williams, University of California, San Diego. The experiment was part of the space research investigations conducted during the Microgravity Science Laboratory-1R mission (STS-94, July 1-17 1997). Advanced combustion experiments will be a part of investigations plarned for the International Space Station. (1.4MB, 13-second MPEG, screen 320 x 240 pixels; downlinked video, higher quality not available)A still JPG composite of this movie is available at http://mix.msfc.nasa.gov/ABSTRACTS/MSFC-0300168.html.

  8. Numerical simulation of the drying of inkjet-printed droplets.

    PubMed

    Siregar, D P; Kuerten, J G M; van der Geld, C W M

    2013-02-15

    In this paper we study the behavior of an inkjet-printed droplet of a solute dissolved in a solvent on a solid horizontal surface by numerical simulation. An extended model for drying of a droplet and the final distribution of the solute on an impermeable substrate is proposed. The model extends the work by Deegan, Fischer and Kuerten by taking into account convection, diffusion and adsorption of the solute in order to describe more accurately the surface coverage on the substrate. A spherically shaped droplet is considered such that the model can be formulated as an axially symmetric problem. The droplet dynamics is driven by the combined action of surface tension and evaporation. The fluid flow in the droplet is modeled by the Navier-Stokes equation and the continuity equation, where the lubrication approximation is applied. The rate of evaporation is determined by the distribution of vapor pressure in the air surrounding the droplet. Numerical results are compared with experimental results for droplets of various sizes.

  9. Spatially resolved measurements of size and velocity distributions of aerosol droplets from a direct injection nebulizer

    SciTech Connect

    Shum, S.C.K.; Johnson, S.K.; Pang, H.M.; Houk, R.S. )

    1993-05-01

    Aerosol droplet sizes and velocities from a direct injection nebulizer (DIN) are measured with radial and axial spatial resolution by phase Doppler particle analysis (PDPA). The droplets on the central axis of the spray become finer and their size becomes more uniform when [approx]20% methanol is added to the usual aqueous solvent. This could explain why the analyte signal is a maximum at this solvent composition when the DIN is used for inductively coupled plasma-mass spectrometry (ICP-MS). Mean droplet velocities are 12 to 22 m s[sup [minus]1] with standard deviations of [plus minus]4 to [plus minus]7 m s[sup [minus]1]. The outer fringes of the aerosol plume tend to be enriched in large droplets. The Sauter mean diameter (D[sub 3,2]) and velocity of the droplets also vary substantially with axial position in the aerosol plume. 35 refs., 10 figs., 1 tab.

  10. Increasing Protein Charge State When Using Laser Electrospray Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Karki, Santosh; Flanigan, Paul M.; Perez, Johnny J.; Archer, Jieutonne J.; Levis, Robert J.

    2015-05-01

    Femtosecond (fs) laser vaporization is used to transfer cytochrome c, myoglobin, lysozyme, and ubiquitin from the condensed phase into an electrospray (ES) plume consisting of a mixture of a supercharging reagent, m-nitrobenzyl alcohol ( m-NBA), and trifluoroacetic acid (TFA), acetic acid (AA), or formic acid (FA). Interaction of acid-sensitive proteins like cytochrome c and myoglobin with the highly charged ES droplets resulted in a shift to higher charge states in comparison with acid-stable proteins like lysozyme and ubiquitin. Laser electrospray mass spectrometry (LEMS) measurements showed an increase in both the average charge states (Zavg) and the charge state with maximum intensity (Zmode) for acid-sensitive proteins compared with conventional electrospray ionization mass spectrometry (ESI-MS) under equivalent solvent conditions. A marked increase in ion abundance of higher charge states was observed for LEMS in comparison with conventional electrospray for cytochrome c (ranging from 19+ to 21+ versus 13+ to 16+) and myoglobin (ranging from 19+ to 26+ versus 18+ to 21+) using an ES solution containing m-NBA and TFA. LEMS measurements as a function of electrospray flow rate yielded increasing charge states with decreasing flow rates for cytochrome c and myoglobin.

  11. Interfacial phenomena in droplet evaporation and nanoparticle-cell systems

    NASA Astrophysics Data System (ADS)

    Fang, Xiaohua

    2005-11-01

    The factors affecting droplet evaporation are discussed. It is found that the droplet morphology at a specific temperature is controlled by the physical properties of the liquid itself, such as the molecular weight, density, diffusion coefficient in air, and heat of vaporization. Two processes are included in droplet evaporation: (1) diffusion of liquid molecules into the air (diffusion part) and (2) flow of the liquid molecules from inside the droplet to the free outer shell liquid layer within the liquid-vapor interface (energy part). The diffusion part remains steady during drying and was not sensitive to the variation of temperature. The energy part, however, was an active factor and determined the differences in drop evaporation behaviors. A model is developed to measure the solubility parameters of the solvents via droplet evaporation. Droplets were deposited on Octadecyltrichlorosilane (OTS) covered silicon surfaces and the contact angle and overall drop morphology are observed using a KSV contact angle goniometer as a function of time. OTS is considered a non-absorbing surface for the solvents examined and does not affect the accuracy of the measured results. This method allows determination of the attraction forces between solvent molecules in the condensed phases. The solubility parameter values of droplets containing pure water, methanol, ethanol and butanol are measured. The test results are independent of the droplet size. The evaporation kinetics of droplets containing DNA is studied. Simultaneously, the DNA re-distribution and adsorption kinetics are measured by confocal microscopy. The DNA droplets are stained with ethidium bromide solution and deposited on OTS covered silicon surfaces. The results showed that the drying behavior depended on the DNA concentration. During drying, DNA relocation inside of the drop affects the internal forces of the liquid. A ring is formed at the air/solid/liquid interface. The absorbed amount of DNA was obtained by

  12. Nematic droplets on fibers

    NASA Astrophysics Data System (ADS)

    Batista, V. M. O.; Silvestre, N. M.; Telo da Gama, M. M.

    2015-12-01

    The emergence of new techniques for the fabrication of nematic droplets with nontrivial topology provides new routes for the assembly of responsive devices. Here we explore some of the properties of nematic droplets on fibers, which constitute the basic units of a type of device that is able to respond to external stimuli, including the detection of gases. We perform a numerical study of spherical nematic droplets on fibers. We analyze the equilibrium textures for homogeneous and hybrid boundary conditions and find that in some cases the nematic avoids the nucleation of topological defects, which would provide a different optical response. We consider in detail a homeotropic nematic droplet wrapped around a fiber with planar anchoring. We investigate the effect of an electric field on the texture of this droplet. In the presence of a dc field, the system undergoes an orientational transition above a given threshold Ec, for which a ring defect is transformed into a figure-eight defect. We also consider ac fields, at high and low frequencies, and find that the textures are similar to those observed for static fields, in contrast with recently reported experiments.

  13. Microfluidic devices for droplet injection

    NASA Astrophysics Data System (ADS)

    Aubrecht, Donald; Akartuna, Ilke; Weitz, David

    2012-02-01

    As picoliter-scale reaction vessels, microfluidic water-in-oil emulsions have found application for high-throughput, large-sample number analyses. Often, the biological or chemical system under investigation needs to be encapsulated into droplets to prevent cross contamination prior to the introduction of reaction reagents. Previous techniques of picoinjection or droplet synchronization and merging enable the addition of reagents to individual droplets, but present limitations on what can be added to each droplet. We present microfluidic devices that couple the strengths of picoinjection and droplet merging, allowing us to selectively add precise volume to our droplet reactions.

  14. Generation of multicomponent polymer blend microparticles using droplet evaporation technique and modeling evaporation of binary droplet containing nonvolatile solute

    NASA Astrophysics Data System (ADS)

    Rajagopalan, Venkat Narayan

    Recently, considerable attention has been focused on the generation of nano- and micrometer scale multicomponent polymer particles with specifically tailored mechanical, electrical and optical properties. As only a few polymer-polymer pairs are miscible, the set of multicomponent polymer systems achievable by conventional methods, such as melt blending, is severely limited in property ranges. Therefore, researchers have been evaluating synthesis methods that can arbitrarily blend immiscible solvent pairs, thus expanding the range of properties that are practical. The generation of blended microparticles by evaporating a co-solvent from aerosol droplets containing two dissolved immiscible polymers in solution seems likely to exhibit a high degree of phase uniformity. A second important advantage of this technique is the formation of nano- and microscale particulates with very low impurities, which are not attainable through conventional solution techniques. When the timescale of solvent evaporation is lower than that of polymer diffusion and self-organization, phase separation is inhibited within the atto- to femto-liter volume of the droplet, and homogeneous blends of immiscible polymers can be produced. We have studied multicomponent polymer particles generated from highly monodisperse micrordroplets that were produced using a Vibrating Orifice Aerosol Generator (VOAG). The particles are characterized for both external and internal morphology along with homogeneity of the blends. Ultra-thin slices of polymer particles were characterized by a Scanning Electron Microscope (SEM), and the degree of uniformity was examined using an Electron Dispersive X-ray Analysis (EDAX). To further establish the homogeneity of the polymer blend microparticles, differential scanning calorimeter was used to measure the glass transition temperature of the microparticles obtained. These results have its significance in the field of particulate encapsulation. Also, better control of the

  15. Sagging of evaporating droplets of colloidal suspensions on inclined substrates.

    PubMed

    Espín, Leonardo; Kumar, Satish

    2014-10-14

    A droplet of a colloidal suspension placed on an inclined substrate may sag under the action of gravity. Solvent evaporation raises the concentration of the colloidal particles, and the resulting viscosity changes may influence the sag of the droplet. To investigate this phenomenon, we have developed a mathematical model for perfectly wetting droplets based on lubrication theory and the rapid-vertical-diffusion approximation. Precursor films are assumed to be present, the colloidal particles are taken to be hard spheres, and particle and liquid dynamics are coupled through a concentration-dependent viscosity and diffusivity. Evaporation is assumed to be limited by how rapidly solvent molecules can transfer from the liquid to the vapor phase. The resulting one-dimensional system of nonlinear partial differential equations describing the evolution of the droplet height and particle concentration is solved numerically for a range of initial particle concentrations and substrate temperatures. The solutions reveal that the interaction between evaporation and non-Newtonian suspension rheology gives rise to several distinct regimes of droplet shapes and particle concentration distributions. The results provide insight into how evaporation and suspension rheology can be tuned to minimize sagging as well as the well-known coffee-ring effect, an outcome which is important for industrial coating processes.

  16. Insight into the Evaporation Dynamics of a Pair of Sessile Droplets on a Hydrophobic Substrate.

    PubMed

    Shaikeea, Angkur Jyoti Dipanka; Basu, Saptarshi

    2016-02-09

    In this work, we have demonstrated three unique regimes in the evaporation lifecycle of a pair of sessile droplets placed in variable proximity on a hydrophobic substrate. For small separation distance, the droplets undergo asymmetric spatiotemporal evaporation leading to contact angle hysteresis and suppressed vaporization. The reduced evaporation has been attributed quantitatively to the existence of a constrained vapor-rich dome between the two droplets. However, a dynamic decrease in the droplet radius due to solvent removal marks a return to symmetry in terms of evaporation and contact angle. We have described the variation in evaporation flux using a universal correction factor. We have also demonstrated the existence of a critical separation distance beyond which the droplets in the droplet pair do not affect each other. The results are crucial to a plethora of applications ranging from surface patterning to lab-on-a-chip devices.

  17. Droplet Combustion Experiment movie

    NASA Technical Reports Server (NTRS)

    2003-01-01

    The Droplet Combustion Experiment (DCE) was designed to investigate the fundamental combustion aspects of single, isolated droplets under different pressures and ambient oxygen concentrations for a range of droplet sizes varying between 2 and 5 mm. The DCE principal investigator was Forman Williams, University of California, San Diego. The experiment was part of the space research investigations conducted during the Microgravity Science Laboratory-1 mission (STS-83, April 4-8 1997; the shortened mission was reflown as MSL-1R on STS-94). Advanced combustion experiments will be a part of investigations plarned for the International Space Station. (1.1 MB, 12-second MPEG, screen 320 x 240 pixels; downlinked video, higher quality not available)A still JPG composite of this movie is available at http://mix.msfc.nasa.gov/ABSTRACTS/MSFC-0300164.html.

  18. Two-dimensional fluid droplet arrays generated using a single nozzle

    DOEpatents

    Lee, Eric R.; Perl, Martin L.

    1999-11-02

    Amplitudes of drive pulses received by a horizontally-placed dropper determine the horizontal displacements of droplets relative to an ejection aperture of the dropper. The drive pulses are varied such that the dropper generates a two-dimensional array of vertically-falling droplets. Vertical and horizontal interdroplet spacings may be varied in real time. Applications include droplet analysis experiments such as Millikan fractional charge searches and aerosol characterization, as well as material deposition applications.

  19. Chip-based droplet sorting

    SciTech Connect

    Beer, Neil Reginald; Lee, Abraham; Hatch, Andrew

    2014-07-01

    A non-contact system for sorting monodisperse water-in-oil emulsion droplets in a microfluidic device based on the droplet's contents and their interaction with an applied electromagnetic field or by identification and sorting.

  20. Electrofreezing of water droplets under electrowetting fields.

    PubMed

    Carpenter, Katherine; Bahadur, Vaibhav

    2015-02-24

    Electrofreezing is the electrically induced nucleation of ice from supercooled water. This work studies ice nucleation in electrowetted water droplets, wherein there is no electric field inside the droplet resting on a dielectric layer. Instead, there is an interfacial electric field and charge buildup at the solid-liquid interface. This situation is in contrast to most previous electrofreezing studies, which have used bare electrodes, involve current flow, and have a volumetric electric field inside the liquid. Infrared and high-speed visualizations of static water droplets are used to analyze surface electrofreezing. Ultrahigh electric fields of up to 80 V/μm are applied, which is one order of magnitude higher than in previous studies. The results facilitate an in-depth understanding of various mechanisms underlying electrofreezing. First, it is seen that interfacial electric fields alone can significantly elevate freezing temperatures by more than 15 °C, in the absence of current flow. Second, the magnitude of electrofreezing induced temperature elevation saturates at high electric field strengths. Third, the polarity of the interfacial charge does not significantly influence electrofreezing. Overall, it is seen that electrofreezing nucleation kinetics is primarily influenced by the three-phase boundary and not the solid-liquid interface. Through careful electrofreezing measurements on dielectric layers with pinholes to allow current flow, the individual role of electric fields and electric currents on electrofreezing is isolated. It is seen that both the electric field and the electric current influence electrofreezing; however, the physical mechanisms are very different.

  1. Sessile nanofluid droplet drying.

    PubMed

    Zhong, Xin; Crivoi, Alexandru; Duan, Fei

    2015-03-01

    Nanofluid droplet evaporation has gained much audience nowadays due to its wide applications in painting, coating, surface patterning, particle deposition, etc. This paper reviews the drying progress and deposition formation from the evaporative sessile droplets with the suspended insoluble solutes, especially nanoparticles. The main content covers the evaporation fundamental, the particle self-assembly, and deposition patterns in sessile nanofluid droplet. Both experimental and theoretical studies are presented. The effects of the type, concentration and size of nanoparticles on the spreading and evaporative dynamics are elucidated at first, serving the basis for the understanding of particle motion and deposition process which are introduced afterward. Stressing on particle assembly and production of desirable residue patterns, we express abundant experimental interventions, various types of deposits, and the effects on nanoparticle deposition. The review ends with the introduction of theoretical investigations, including the Navier-Stokes equations in terms of solutions, the Diffusion Limited Aggregation approach, the Kinetic Monte Carlo method, and the Dynamical Density Functional Theory. Nanoparticles have shown great influences in spreading, evaporation rate, evaporation regime, fluid flow and pattern formation of sessile droplets. Under different experimental conditions, various deposition patterns can be formed. The existing theoretical approaches are able to predict fluid dynamics, particle motion and deposition patterns in the particular cases. On the basis of further understanding of the effects of fluid dynamics and particle motion, the desirable patterns can be obtained with appropriate experimental regulations.

  2. Enhancing droplet deposition through in-situ precipitation

    PubMed Central

    Damak, Maher; Mahmoudi, Seyed Reza; Hyder, Md Nasim; Varanasi, Kripa K.

    2016-01-01

    Retention of agricultural sprays on plant surfaces is an important challenge. Bouncing of sprayed pesticide droplets from leaves is a major source of soil and groundwater pollution and pesticide overuse. Here we report a method to increase droplet deposition through in-situ formation of hydrophilic surface defects that can arrest droplets during impact. Defects are created by simultaneously spraying oppositely charged polyelectrolytes that induce surface precipitation when two droplets come into contact. Using high-speed imaging, we study the coupled dynamics of drop impact and surface precipitate formation. We develop a physical model to estimate the energy dissipation by the defects and predict the transition from bouncing to sticking. We demonstrate macroscopic enhancements in spray retention and surface coverage for natural and synthetic non-wetting surfaces and provide insights into designing effective agricultural sprays. PMID:27572948

  3. Thermophoresis in nanoliter droplets to quantify aptamer binding.

    PubMed

    Seidel, Susanne A I; Markwardt, Niklas A; Lanzmich, Simon A; Braun, Dieter

    2014-07-21

    Biomolecule interactions are central to pharmacology and diagnostics. These interactions can be quantified by thermophoresis, the directed molecule movement along a temperature gradient. It is sensitive to binding induced changes in size, charge, or conformation. Established capillary measurements require at least 0.5 μL per sample. We cut down sample consumption by a factor of 50, using 10 nL droplets produced with acoustic droplet robotics (Labcyte). Droplets were stabilized in an oil-surfactant mix and locally heated with an IR laser. Temperature increase, Marangoni flow, and concentration distribution were analyzed by fluorescence microscopy and numerical simulation. In 10 nL droplets, we quantified AMP-aptamer affinity, cooperativity, and buffer dependence. Miniaturization and the 1536-well plate format make the method high-throughput and automation friendly. This promotes innovative applications for diagnostic assays in human serum or label-free drug discovery screening.

  4. Enhancing droplet deposition through in-situ precipitation

    NASA Astrophysics Data System (ADS)

    Damak, Maher; Mahmoudi, Seyed Reza; Hyder, Md Nasim; Varanasi, Kripa K.

    2016-08-01

    Retention of agricultural sprays on plant surfaces is an important challenge. Bouncing of sprayed pesticide droplets from leaves is a major source of soil and groundwater pollution and pesticide overuse. Here we report a method to increase droplet deposition through in-situ formation of hydrophilic surface defects that can arrest droplets during impact. Defects are created by simultaneously spraying oppositely charged polyelectrolytes that induce surface precipitation when two droplets come into contact. Using high-speed imaging, we study the coupled dynamics of drop impact and surface precipitate formation. We develop a physical model to estimate the energy dissipation by the defects and predict the transition from bouncing to sticking. We demonstrate macroscopic enhancements in spray retention and surface coverage for natural and synthetic non-wetting surfaces and provide insights into designing effective agricultural sprays.

  5. An interface tracking model for droplet electrocoalescence.

    SciTech Connect

    Erickson, Lindsay Crowl

    2013-09-01

    This report describes an Early Career Laboratory Directed Research and Development (LDRD) project to develop an interface tracking model for droplet electrocoalescence. Many fluid-based technologies rely on electrical fields to control the motion of droplets, e.g. microfluidic devices for high-speed droplet sorting, solution separation for chemical detectors, and purification of biodiesel fuel. Precise control over droplets is crucial to these applications. However, electric fields can induce complex and unpredictable fluid dynamics. Recent experiments (Ristenpart et al. 2009) have demonstrated that oppositely charged droplets bounce rather than coalesce in the presence of strong electric fields. A transient aqueous bridge forms between approaching drops prior to pinch-off. This observation applies to many types of fluids, but neither theory nor experiments have been able to offer a satisfactory explanation. Analytic hydrodynamic approximations for interfaces become invalid near coalescence, and therefore detailed numerical simulations are necessary. This is a computationally challenging problem that involves tracking a moving interface and solving complex multi-physics and multi-scale dynamics, which are beyond the capabilities of most state-of-the-art simulations. An interface-tracking model for electro-coalescence can provide a new perspective to a variety of applications in which interfacial physics are coupled with electrodynamics, including electro-osmosis, fabrication of microelectronics, fuel atomization, oil dehydration, nuclear waste reprocessing and solution separation for chemical detectors. We present a conformal decomposition finite element (CDFEM) interface-tracking method for the electrohydrodynamics of two-phase flow to demonstrate electro-coalescence. CDFEM is a sharp interface method that decomposes elements along fluid-fluid boundaries and uses a level set function to represent the interface.

  6. An Instrument Employing a Coronal Discharge for the Determination of Droplet-Size Distribution in Clouds

    NASA Technical Reports Server (NTRS)

    Brun, Rinaldo J.; Levine, Joseph; Kleinknecht, Kenneth S.

    1951-01-01

    A flight instrument that uses electric means for measuring the droplet-size distribution in above-freezing clouds has been devised and given preliminary evaluation in flight. An electric charge is placed on the droplets and they are separated aerodynamically according to their mass. Because the charge placed on the droplets is a. function of the droplet size, the size spectrum can 'be determined by measurement of the charge deposited on cylinders of several different sizes placed to intercept the charged droplets. An expression for the rate of charge acquisition by a water droplet in a field of coronal discharge is derived. The results obtained in flight with an instrument based on the method described indicate that continuous records of droplet-size spectrum variations in clouds can be obtained. The experimental instrument was used to evaluate the method and was not refined to the extent necessary for obtaining conclusive meteorological data. The desirable features of an instrument based on the method described are (i) The instrument can be used in clouds with temperatures above freezing; (2) the size and the shape of the cylinders do not change during the exposure time; (3) the readings are instantaneous and continuous; (4) the available sensitivity permits the study of variations in cloud structures of less than 200 feet in extent.

  7. Expanding roles for lipid droplets

    PubMed Central

    Welte, Michael A.

    2015-01-01

    Summary Lipid droplets are the intracellular sites for neutral lipid storage. They are critical for lipid metabolism and energy homeostasis, and their dysfunction has been linked to many diseases. Accumulating evidence suggests that the roles lipid droplets play in biology are significantly broader than previously anticipated. Lipid droplets are the source of molecules important in the nucleus: they can sequester transcription factors and chromatin components and generate the lipid ligands for certain nuclear receptors. Lipid droplets have also emerged as important nodes for fatty acid trafficking, both inside the cell and between cells. In immunity, new roles for droplets, not directly linked to lipid metabolism, have been uncovered, as assembly platforms for specific viruses and as reservoirs for proteins that fight intracellular pathogens. Until recently, knowledge about droplets in the nervous system has been minimal, but now there are multiple links between lipid droplets and neurodegeneration: Many candidate genes for Hereditary Spastic Paraplegia also have central roles in lipid-droplet formation and maintenance, and mitochondrial dysfunction in neurons can lead to transient accumulating of lipid droplets in neighboring glial cells, an event that may, in turn, contribute to neuronal damage. As the cell biology and biochemistry of lipid droplets are increasingly well understood, the next few years should yield many new mechanistic insights into these novel functions of lipid droplets. PMID:26035793

  8. Lysozyme pattern formation in evaporating droplets

    NASA Astrophysics Data System (ADS)

    Gorr, Heather Meloy

    Liquid droplets containing suspended particles deposited on a solid, flat surface generally form ring-like structures due to the redistribution of solute during evaporation (the "coffee ring effect"). The forms of the deposited patterns depend on complex interactions between solute(s), solvent, and substrate in a rapidly changing, far from equilibrium system. Solute self-organization during evaporation of colloidal sessile droplets has attracted the attention of researchers over the past few decades due to a variety of technological applications. Recently, pattern formation during evaporation of various biofluids has been studied due to potential applications in medical screening and diagnosis. Due to the complexity of 'real' biological fluids and other multicomponent systems, a comprehensive understanding of pattern formation during droplet evaporation of these fluids is lacking. In this PhD dissertation, the morphology of the patterns remaining after evaporation of droplets of a simplified model biological fluid (aqueous lysozyme solutions + NaCl) are examined by atomic force microscopy (AFM) and optical microscopy. Lysozyme is a globular protein found in high concentration, for example, in human tears and saliva. The drop diameters, D, studied range from the micro- to the macro- scale (1 microm -- 2 mm). In this work, the effect of evaporation conditions, solution chemistry, and heat transfer within the droplet on pattern formation is examined. In micro-scale deposits of aqueous lysozyme solutions (1 microm < D < 50 microm), the protein motion and the resulting dried residue morphology are highly influenced by the decreased evaporation time of the drop. The effect of electrolytes on pattern formation is also investigated by adding varying concentrations NaCl to the lysozyme solutions. Finally, a novel pattern recognition program is described and implemented which classifies deposit images by their solution chemistries. The results presented in this Ph

  9. Surface Modification of Droplet Polymeric Microfluidic Devices for the Stable and Continuous Generation of Aqueous Droplets

    PubMed Central

    Subramanian, Balamurugan; Kim, Namwon; Lee, Wonbae; Spivak, David A.; Nikitopoulos, Dimitris E.; McCarley, Robin L.; Soper, Steven A.

    2012-01-01

    Droplet microfluidics performed in poly(methylmethacrylate), PMMA, microfluidic devices resulted in significant wall wetting by water droplets formed in a liquid-liquid segmented flow when using a hydrophobic carrier fluid, such as perfluorotripropylamine (FC-3283). This wall wetting led to water droplets with non-uniform sizes that were often trapped on the wall surfaces leading to unstable and poorly controlled liquid-liquid segmented flow. To circumvent this problem, we developed a two-step procedure to hydrophobically modify the surfaces of PMMA and other thermoplastic materials commonly used for making microfluidic devices. The surface modification route involved the introduction of hydroxyl groups by oxygen plasma treatment of the polymer surface followed by a solution phase reaction with heptadecafluoro-1,1,2,2–tetrahydrodecyl trichlorosilane dissolved in the fluorocarbon solvent FC-3283. This procedure was found to be useful for the modification of PMMA and other thermoplastic surfaces, including polycyclic olefin copolymer (COC) and polycarbonate (PC). Angle-resolved X-ray photoelectron spectroscopy indicated that the fluorination of these polymers took place with high surface selectivity. This procedure was used to modify the surface of a PMMA droplet microfluidic device (DMFD) and was shown to be useful to reduce the wetting problem during the generation of aqueous droplets in a perfluorotripropylamine (FC-3283) carrier fluid and could generate stable segmented flows for hours of operation. In the case of the PMMA DMFD, oxygen plasma treatment was carried out after the PMMA cover plate was thermally fusion bonded to the PMMA microfluidic chip. Because the appended chemistry to the channel wall created a hydrophobic surface, it will accommodate the use of other carrier fluids that are hydrophobic as well, such as hexadecane or mineral oils. PMID:21608975

  10. Surface modification of droplet polymeric microfluidic devices for the stable and continuous generation of aqueous droplets.

    PubMed

    Subramanian, Balamurugan; Kim, Namwon; Lee, Wonbae; Spivak, David A; Nikitopoulos, Dimitris E; McCarley, Robin L; Soper, Steven A

    2011-06-21

    Droplet microfluidics performed in poly(methyl methacrylate) (PMMA) microfluidic devices resulted in significant wall wetting by water droplets formed in a liquid-liquid segmented flow when using a hydrophobic carrier fluid such as perfluorotripropylamine (FC-3283). This wall wetting led to water droplets with nonuniform sizes that were often trapped on the wall surfaces, leading to unstable and poorly controlled liquid-liquid segmented flow. To circumvent this problem, we developed a two-step procedure to hydrophobically modify the surfaces of PMMA and other thermoplastic materials commonly used to make microfluidic devices. The surface-modification route involved the introduction of hydroxyl groups by oxygen plasma treatment of the polymer surface followed by a solution-phase reaction with heptadecafluoro-1,1,2,2-tetrahydrodecyl trichlorosilane dissolved in fluorocarbon solvent FC-3283. This procedure was found to be useful for the modification of PMMA and other thermoplastic surfaces, including polycyclic olefin copolymer (COC) and polycarbonate (PC). Angle-resolved X-ray photoelectron spectroscopy indicated that the fluorination of these polymers took place with high surface selectivity. This procedure was used to modify the surface of a PMMA droplet microfluidic device (DMFD) and was shown to be useful in reducing the wetting problem during the generation of aqueous droplets in a perfluorotripropylamine (FC-3283) carrier fluid and could generate stable segmented flows for hours of operation. In the case of PMMA DMFD, oxygen plasma treatment was carried out after the PMMA cover plate was thermally fusion bonded to the PMMA microfluidic chip. Because the appended chemistry to the channel wall created a hydrophobic surface, it will accommodate the use of other carrier fluids that are hydrophobic as well, such as hexadecane or mineral oils.

  11. Glass transition accelerates the spreading of polar solvents on a soluble polymer.

    PubMed

    Dupas, Julien; Verneuil, Emilie; Van Landeghem, Maxime; Bresson, Bruno; Forny, Laurent; Ramaioli, Marco; Lequeux, Francois; Talini, Laurence

    2014-05-09

    We study the wetting of polymer layers by polar solvents. As previously observed, when a droplet of solvent spreads, both its contact angle and velocity decrease with time as a result of solvent transfers from the droplet to the substrate. We show that, when the polymer is initially glassy, the angle decreases steeply for a given value of the velocity, Ug. We demonstrate that those variations result from a plasticization, i.e., a glass transition, undergone by the polymer layer during spreading, owing to the increase of its solvent content. By analyzing previous predictions on the wetting of rigid and soft viscoelastic substrates, we relate Ug to the viscosity of the polymer gel close to the glass transition. Finally, we derive an analytical prediction for Ug based on existing predictions for the water transfer from the droplet to the substrate. Using polar solvents of different natures, we show that the experimental data compare well to the predicted expression for Ug.

  12. Diffraction of walking droplets

    NASA Astrophysics Data System (ADS)

    Harris, Daniel M.; Pucci, Giuseppe; Bush, John W. M.

    2014-11-01

    We present results from our revisitation of the experiment of a walking droplet passing through a single slit, originally investigated by Couder & Fort (PRL, 2006). On each passage, the walker's trajectory is deviated as a result of the spatial confinement of its guiding wave. We explore the role of the droplet size and the bath's vibration amplitude on both the dynamics and statistics. We find the behavior to be remarkably sensitive to these control parameters. A complex physical picture emerges. The authors gratefully acknowledge the financial support of the NSF through Grant CMMI-1333242, DMH through the NSF Graduate Research Fellowship Program, and GP through the Programma Operativo Regionale (POR) Calabria - FSE 2007/2013.

  13. Burning Fuel Droplet

    NASA Technical Reports Server (NTRS)

    2003-01-01

    Fuel ignites and burns in the Droplet Combustion Experiment (DCE) on STS-94 on July 4 1997, MET:2/05:40 (approximate). The DCE was designed to investigate the fundamental combustion aspects of single, isolated droplets under different pressures and ambient oxygen concentrations for a range of droplet sizes varying between 2 and 5 mm. DCE used various fuels -- in drops ranging from 1 mm (0.04 inches) to 5 mm (0.2 inches) -- and mixtures of oxidizers and inert gases to learn more about the physics of combustion in the simplest burning configuration, a sphere. The experiment elapsed time is shown at the bottom of the composite image. The DCE principal investigator was Forman Williams, University of California, San Diego. The experiment was part of the space research investigations conducted during the Microgravity Science Laboratory-1R mission (STS-94, July 1-17 1997). Advanced combustion experiments will be a part of investigations plarned for the International Space Station. (121KB JPEG, 654 x 977 pixels; downlinked video, higher quality not available) The MPG from which this composite was made is available at http://mix.msfc.nasa.gov/ABSTRACTS/MSFC-0300169.html.

  14. Acoustic droplet vaporization of vascular droplets in gas embolotherapy

    NASA Astrophysics Data System (ADS)

    Bull, Joseph

    2016-11-01

    This work is primarily motivated by a developmental gas embolotherapy technique for cancer treatment. In this methodology, infarction of tumors is induced by selectively formed vascular gas bubbles that arise from the acoustic vaporization of vascular droplets. Additionally, micro- or nano-droplets may be used as vehicles for localized drug delivery, with or without flow occlusion. In this talk, we examine the dynamics of acoustic droplet vaporization through experiments and theoretical/computational fluid mechanics models, and investigate the bioeffects of acoustic droplet vaporization on endothelial cells and in vivo. Functionalized droplets that are targeted to tumor vasculature are examined. The influence of fluid mechanical and acoustic parameters, as well as droplet functionalization, is explored. This work was supported by NIH Grant R01EB006476.

  15. The safety of a cell in a droplet under high electric field

    NASA Astrophysics Data System (ADS)

    Noh, Jihoon; Im, Do Jin; Kang, In Seok

    2010-11-01

    Electrically charged aqueous droplet can be transported by electrical field in a dielectric fluid without the flow of medium (Jung et al. J. Colloid Interface Sci. 2008). This phenomenon can be used to transport a single nanoliter droplet in a micro channel, which can serve as biochemical micro-reactor. Because an aqueous droplet is much conductive than the dielectric fluid, there is effectively no electric field inside the droplet suspended in dielectric fluid. Therefore bio-materials are protected from electricity even under high electric field. However, when the droplet is charged near an electrode by direct contact to the electrode, there is possibility that electric field can hurt bio-materials like DNA molecules, microorganisms, cells, protein in droplet. Because of this concern, we should confirm that bio-materials in droplet moving by direct charging are safe under strong external electric field especially to organism cells. Therefore we examine the effect of electric field on the cells such as yeast, E.coli., and sperm in droplet experimentally.

  16. Finger-powered electrophoretic transport of discrete droplets for portable digital microfluidics.

    PubMed

    Peng, Cheng; Wang, Yide; Sungtaek Ju, Y

    2016-07-07

    We report a finger-powered digital microfluidic device based on the electrophoretic transport of discrete droplets (EPD). An array of piezoelectric elements is connected in parallel to metal electrodes immersed in dielectric fluids. When deflected in a controlled sequence via human finger power, the piezoelectric elements charge and actuate droplets across each electrode pair through electrophoretic force. Successful droplet transportation requires the piezoelectric elements to provide both sufficient charge and voltage pulse duration. We quantify these requirements using numerical models to predict the electrical charges induced on the droplets and the corresponding electrophoretic forces. The models are experimentally validated by comparing the predicted and measured droplet translational velocities. We successfully demonstrated transport and merging of aqueous droplets over a range of droplet radii (0.6-0.9 mm). We further showed direct manipulation of body fluids, including droplets of saliva and urine, using our finger-powered EPD device. To facilitate practical implementation of multistep assays based on the approach, a hand/finger-rotated drum system with a programmable pattern of protrusions is designed to induce deflections of multiple piezoelectric elements and demonstrate programmable fluidic functions. An electrode-to-piezoelectric element connection scheme to minimize the number of piezoelectric elements necessary for a sequence of microfluidic functions is also explored. The present work establishes an engineering foundation to enable design and implementation of finger-powered portable EPD microfluidic devices.

  17. Thermophoresis of microemulsion droplets: size dependence of the Soret effect.

    PubMed

    Vigolo, Daniele; Brambilla, Giovanni; Piazza, Roberto

    2007-04-01

    Thermophoresis, akin to thermal diffusion in simple fluid mixtures, consists of particle drift induced by a temperature gradient. Notwithstanding its practical interest, the dependence of thermophoretic effects on particle size R is still theoretically and experimentally debated. By performing measurements of water-in-oil microemulsion droplets with tunable size, we show that the thermal diffusion coefficient, at least for a suspension of small particles in a nonpolar solvent, does not appreciably depend on R .

  18. Experimental determination of layer cloud edge charging from cosmic ray ionisation

    NASA Astrophysics Data System (ADS)

    Nicoll, K. A.; Harrison, R. G.

    2010-07-01

    The cloud-air transition zone at stratiform cloud edges is an electrically active region where droplet charging has been predicted. Cloud edge droplet charging is expected from vertical flow of cosmic ray generated atmospheric ions in the global electric circuit. Experimental confirmation of stratiform cloud edge electrification is presented here, through charge and droplet measurements made within an extensive layer of supercooled stratiform cloud, using a specially designed electrostatic sensor. Negative space charge up to 35 pC m-3 was found in a thin (<100 m) layer at the lower cloud boundary associated with the clear air-cloud conductivity gradient, agreeing closely with space charge predicted from the measured droplet concentration using ion-aerosol theory. Such charge levels carried by droplets are sufficient to influence collision processes between cloud droplets.

  19. Chiral partition functions of quantum Hall droplets

    SciTech Connect

    Cappelli, Andrea Viola, Giovanni; Zemba, Guillermo R.

    2010-02-15

    Chiral partition functions of conformal field theory describe the edge excitations of isolated Hall droplets. They are characterized by an index specifying the quasiparticle sector and transform among themselves by a finite-dimensional representation of the modular group. The partition functions are derived and used to describe electron transitions leading to Coulomb blockade conductance peaks. We find the peak patterns for Abelian hierarchical states and non-Abelian Read-Rezayi states, and compare them. Experimental observation of these features can check the qualitative properties of the conformal field theory description, such as the decomposition of the Hilbert space into sectors, involving charged and neutral parts, and the fusion rules.

  20. Laserspray ionization, a new atmospheric pressure MALDI method for producing highly charged gas-phase ions of peptides and proteins directly from solid solutions.

    PubMed

    Trimpin, Sarah; Inutan, Ellen D; Herath, Thushani N; McEwen, Charles N

    2010-02-01

    The first example of a matrix-assisted laser desorption/ionization (MALDI) process producing multiply charged mass spectra nearly identical to those observed with electrospray ionization (ESI) is presented. MALDI is noted for its ability to produce singly charged ions, but in the experiments described here multiply charged ions are produced by laser ablation of analyte incorporated into a common MALDI matrix, 2,5-dihydroxybenzoic acid, using standard solvent-based sample preparation protocols. Laser ablation is known to produce matrix clusters in MALDI provided a threshold energy is achieved. We propose that these clusters (liquid droplets) are highly charged, and under conditions that produce sufficient matrix evaporation, ions are field-evaporated from the droplets similarly to ESI. Because of the multiple charging, advanced mass spectrometers with limited mass-to-charge range can be used for protein characterization. Thus, using an Orbitrap mass spectrometer, low femtomole quantities of proteins produce full-range mass spectra at 100,000 mass resolution with <5-ppm mass accuracy and with 1-s acquisition. Furthermore, the first example of protein fragmentation using electron transfer dissociation with MALDI is presented.

  1. Evaporation of inclined water droplets.

    PubMed

    Kim, Jin Young; Hwang, In Gyu; Weon, Byung Mook

    2017-02-16

    When a drop is placed on a flat substrate tilted at an inclined angle, it can be deformed by gravity and its initial contact angle divides into front and rear contact angles by inclination. Here we study on evaporation dynamics of a pure water droplet on a flat solid substrate by controlling substrate inclination and measuring mass and volume changes of an evaporating droplet with time. We find that complete evaporation time of an inclined droplet becomes longer as gravitational influence by inclination becomes stronger. The gravity itself does not change the evaporation dynamics directly, whereas the gravity-induced droplet deformation increases the difference between front and rear angles, which quickens the onset of depinning and consequently reduces the contact radius. This result makes the evaporation rate of an inclined droplet to be slow. This finding would be important to improve understanding on evaporation dynamics of inclined droplets.

  2. Evaporation of inclined water droplets

    NASA Astrophysics Data System (ADS)

    Kim, Jin Young; Hwang, In Gyu; Weon, Byung Mook

    2017-02-01

    When a drop is placed on a flat substrate tilted at an inclined angle, it can be deformed by gravity and its initial contact angle divides into front and rear contact angles by inclination. Here we study on evaporation dynamics of a pure water droplet on a flat solid substrate by controlling substrate inclination and measuring mass and volume changes of an evaporating droplet with time. We find that complete evaporation time of an inclined droplet becomes longer as gravitational influence by inclination becomes stronger. The gravity itself does not change the evaporation dynamics directly, whereas the gravity-induced droplet deformation increases the difference between front and rear angles, which quickens the onset of depinning and consequently reduces the contact radius. This result makes the evaporation rate of an inclined droplet to be slow. This finding would be important to improve understanding on evaporation dynamics of inclined droplets.

  3. Evaporation of inclined water droplets

    PubMed Central

    Kim, Jin Young; Hwang, In Gyu; Weon, Byung Mook

    2017-01-01

    When a drop is placed on a flat substrate tilted at an inclined angle, it can be deformed by gravity and its initial contact angle divides into front and rear contact angles by inclination. Here we study on evaporation dynamics of a pure water droplet on a flat solid substrate by controlling substrate inclination and measuring mass and volume changes of an evaporating droplet with time. We find that complete evaporation time of an inclined droplet becomes longer as gravitational influence by inclination becomes stronger. The gravity itself does not change the evaporation dynamics directly, whereas the gravity-induced droplet deformation increases the difference between front and rear angles, which quickens the onset of depinning and consequently reduces the contact radius. This result makes the evaporation rate of an inclined droplet to be slow. This finding would be important to improve understanding on evaporation dynamics of inclined droplets. PMID:28205642

  4. Droplet microfluidics based microseparation systems.

    PubMed

    Xiao, Zhiliang; Niu, Menglei; Zhang, Bo

    2012-06-01

    Lab on a chip (LOC) technology is a promising miniaturization approach. The feature that it significantly reduced sample consumption makes great sense in analytical and bioanalytical chemistry. Since the start of LOC technology, much attention has been focused on continuous flow microfluidic systems. At the turn of the century, droplet microfluidics, which was also termed segmented flow microfluidics, was introduced. Droplet microfluidics employs two immiscible phases to form discrete droplets, which are ideal vessels with confined volume, restricted dispersion, limited cross-contamination, and high surface area. Due to these unique features, droplet microfluidics proves to be a versatile tool in microscale sample handling. This article reviews the utility of droplet microfluidics in microanalytical systems with an emphasize on separation science, including sample encapsulation at ultra-small volume, compartmentalization of separation bands, isolation of droplet contents, and related detection techniques.

  5. a Theoretical Model of a Superheated Liquid Droplet Neutron Detector.

    NASA Astrophysics Data System (ADS)

    Harper, Mark Joseph

    Neutrons can interact with the atoms in superheated liquid droplets which are suspended in a viscous matrix material, resulting in the formation of charged recoil ions. These ions transfer energy to the liquid, sometimes resulting in the droplets vaporizing and producing observable bubbles. Devices employing this mechanism are known as superheated liquid droplet detectors, or bubble detectors. The basis of bubble detector operation is identical to that of bubble chambers, which have been well characterized by researchers such as Wilson, Glaser, Seitz, and others since the 1950's. Each of the microscopic superheated liquid droplets behaves like an independent bubble chamber. This dissertation presents a theoretical model which considers the three principal aspects of detector operation: nuclear reactions, charged particle energy deposition, and thermodynamic bubble formation. All possible nuclear reactions were examined and those which could reasonably result in recoil ions sufficiently energetic to vaporize a droplet were analyzed in detail. Feasible interactions having adequate cross sections include elastic and inelastic scattering, n-proton, and n-alpha reactions. Ziegler's TRansport of Ions in Matter (TRIM) code was used to calculate the ions' stopping powers in various compounds based on the ionic energies predicted by standard scattering distributions. If the ions deposit enough energy in a small enough volume then the entire droplet will vaporize without further energy input. Various theories as to the vaporization of droplets by ionizing radiation were studied and a novel method of predicting the critical (minimum) energy was developed. This method can be used to calculate the minimum required stopping power for the ion, from which the threshold neutron energy is obtainable. Experimental verification of the model was accomplished by measuring the response of two different types of bubble detectors to monoenergetic thermal neutrons, as well as to neutrons

  6. Solvent reorganization of electron transitions in viscous solvents

    SciTech Connect

    Ghorai, Pradip K.; Matyushov, Dmitry V.

    2006-04-14

    We develop a model of electron transfer reactions at conditions of nonergodicity when the time of solvent relaxation crosses the observation time window set up by the reaction rate. Solvent reorganization energy of intramolecular electron transfer in a charge-transfer molecule dissolved in water and acetonitrile is studied by molecular dynamics simulations at varying temperatures. We observe a sharp decrease of the reorganization energy at a temperature identified as the temperature of structural arrest due to cage effect, as discussed by the mode-coupling theory. This temperature also marks the onset of the enhancement of translational diffusion relative to rotational relaxation signaling the breakdown of the Stokes-Einstein relation. The change in the reorganization energy at the transition temperature reflects the dynamical arrest of the slow, collective relaxation of the solvent related to the relaxation of the solvent dipolar polarization. An analytical theory proposed to describe this effect agrees well with both the simulations and experimental Stokes shift data. The theory is applied to the analysis of charge-transfer kinetics in a low-temperature glass former. We show that the reorganization energy is substantially lower than its equilibrium value for the low-temperature portion of the data. The theory predicts the possibility of discontinuous changes in the dependence of the electron transfer rate on the free energy gap when the reaction switches between ergodic and nonergodic regimes.

  7. Analyzing Benzene and Cyclohexane Emulsion Droplet Collisions on Ultramicroelectrodes.

    PubMed

    Li, Yan; Deng, Haiqiang; Dick, Jeffrey E; Bard, Allen J

    2015-11-03

    We report the collisions of single emulsion oil droplets with extremely low dielectric constants (e.g., benzene, ε of 2.27, or cyclohexane, ε of 2.02) as studied via emulsion droplet reactor (EDR) on an ultramicroelectrode (UME). By applying appropriate potentials to the UME, we observed the electrochemical effects of single-collision signals from the bulk electrolysis of single emulsion droplets. Different hydrophobic redox species (ferrocene, decamethyl-ferrocene, or metalloporphyrin) were trapped in a mixed benzene (or cyclohexane) oil-in-water emulsion using an ionic liquid as the supporting electrolyte and emulsifier. The emulsions were prepared using ultrasonic processing. Spike-like responses were observed in each i-t response due to the complete electrolysis of all of the above-mentioned redox species within the droplet. On the basis of these single-particle collision results, the collision frequency, size distribution, i-t decay behavior of the emulsion droplets, and possible mechanisms are analyzed and discussed. This work demonstrated that bulk electrolysis can be achieved in a few seconds in these attoliter reactors, suggesting many applications, such as analysis and electrosynthesis in low dielectric constant solvents, which have a much broader potential window.

  8. Anisotropic particle synthesis inside droplet templates on superhydrophobic surfaces.

    PubMed

    Rastogi, Vinayak; García, Antonio A; Marquez, Manuel; Velev, Orlin D

    2010-01-18

    We demonstrate how droplet templates dispensed on superhydrophobic substrates can be used to fabricate both shape-anisotropic ("doughnut") and composition-anisotropic ("patchy magnetic") supraparticles. The macroscopic shape of the closely-packed particle assemblies is guided by the droplet meniscus. Aqueous droplets of monodisperse microsphere suspensions dispensed on the substrates initially acquire near-spherical shape due to a high contact angle. During the solvent evaporation, however, silica suspension droplets undergo shape transitions (concaving) guiding the structure of the final assemblies into doughnut supraparticles. Composition anisotropy is achieved by drying a droplet containing a mixed suspension of latex and magnetic nanoparticles, while exposing it to magnetic field gradients. Depending on the pattern of the magnetic fields, the magnetic nanoparticles segregate into single, bilateral, or trilateral, patched spherical supraparticles. The physical effects leading to the development of anisotropy are discussed. Unlike the conventional wet self-assembly (WSA) methods where the final structures need to be extracted from the liquid environment, this efficient one-step procedure produces ready to use "dry" supraparticles.

  9. Maze Solving by Chemotactic Droplets

    SciTech Connect

    Lagzi, Istvan; Soh, Siowling; Wesson, Paul J.; Browne, Kevin P.; Grzybowski, Bartosz A.

    2010-01-11

    Droplets emitting surface-active chemicals exhibit chemotaxis toward low-pH regions. Such droplets are self-propelled and navigate through a complex maze to seek a source of acid placed at one of the maze’s exits. In doing so, the droplets find the shortest path through the maze. Chemotaxis and maze solving are due to an interplay between acid/base chemistry and surface tension effects.

  10. Gelled MMH hypergolic droplet investigation

    NASA Astrophysics Data System (ADS)

    Solomon, Yair

    Gelled propellants are promising candidates for certain future rocket applications, offering potential improvements in performance and/or safety over conventional liquid and solid systems. In particular, gelled hypergolic propellants can eliminate some handling difficulties by reducing leakage hazard. Before such systems can be developed, however, a fundamental understanding of combustion of the gel droplet is required. This study addresses the combustion behavior of monomethyl hydrazine (MMH) droplet gelled with both hydroxypropyl cellulose (HPC) and fumed silica in an environment of gaseous nitrogen dioxide. All MMH/HPC gel droplets displayed swelling and jetting that are typical to hydrocarbon gels with an organic gelling agent. Burning rates were measured for droplet diameters from 1.8 to 3.2 mm at three ambient pressures of 1.72, 2.06 and 2.89 bar. It was found that the droplet burning rate is dependent on the droplet diameter similarly to liquid MMH. Over the investigated pressure range, no dependence of burning rate on pressure was found. The combustion of MMH/HPC gel was compared to MMH/tetraglyme to examine the influence the type of gelling agent. Droplets of MMH and liquid tetraglyme showed increasing swelling frequencies and volume fluctuations during combustion while the MMH and HPC droplets exhibited a more constant burning history. The MMH/Silica gels showed a different combustion mechanism with the formation of a rigid silica structure, micro-explosions, and up to a 50% reduction in droplet volume during combustion.

  11. Uranium droplet core nuclear rocket

    NASA Technical Reports Server (NTRS)

    Anghaie, Samim

    1991-01-01

    Uranium droplet nuclear rocket is conceptually designed to utilize the broad temperature range ofthe liquid phase of metallic uranium in droplet configuration which maximizes the energy transfer area per unit fuel volume. In a baseline system dissociated hydrogen at 100 bar is heated to 6000 K, providing 2000 second of Isp. Fission fragments and intense radian field enhance the dissociation of molecular hydrogen beyond the equilibrium thermodynamic level. Uranium droplets in the core are confined and separated by an axisymmetric vortex flow generated by high velocity tangential injection of hydrogen in the mid-core regions. Droplet uranium flow to the core is controlled and adjusted by a twin flow nozzle injection system.

  12. Small droplets on superhydrophobic substrates.

    PubMed

    Gross, Markus; Varnik, Fathollah; Raabe, Dierk; Steinbach, Ingo

    2010-05-01

    We investigate the wetting behavior of liquid droplets on rough hydrophobic substrates for the case of droplets that are of comparable size to the surface asperities. Using a simple three-dimensional analytical free-energy model, we have shown in a recent letter [M. Gross, F. Varnik, and D. Raabe, EPL 88, 26002 (2009)] that, in addition to the well-known Cassie-Baxter and Wenzel states, there exists a further metastable wetting state where the droplet is immersed into the texture to a finite depth, yet not touching the bottom of the substrate. Due to this new state, a quasistatically evaporating droplet can be saved from going over to the Wenzel state and instead remains close to the top of the surface. In the present paper, we give an in-depth account of the droplet behavior based on the results of extensive computer simulations and an improved theoretical model. In particular, we show that releasing the assumption that the droplet is pinned at the outer edges of the pillars improves the analytical results for larger droplets. Interestingly, all qualitative aspects, such as the existence of an intermediate minimum and the "reentrant transition," remain unchanged. We also give a detailed description of the evaporation process for droplets of varying sizes. Our results point out the role of droplet size for superhydrophobicity and give hints for achieving the desired wetting properties of technically produced materials.

  13. Monodisperse, submicrometer droplets via condensation of microfluidic-generated gas bubbles.

    PubMed

    Seo, Minseok; Matsuura, Naomi

    2012-09-10

    Microfluidics (MFs) can produce monodisperse droplets with precise size control. However, the synthesis of monodisperse droplets much smaller than the minimum feature size of the microfluidic device (MFD) remains challenging, thus limiting the production of submicrometer droplets. To overcome the minimum micrometer-scale droplet sizes that can be generated using typical MFDs, the droplet material is heated above its boiling point (bp), and then MFs is used to produce monodisperse micrometer-scale bubbles (MBs) that are easily formed in the size regime where standard MFDs have excellent size control. After MBs are formed, they are cooled, condensing into dramatically smaller droplets that are beyond the size limit achievable using the original MFD, with a size decrease corresponding to the density difference between the gas and liquid phases of the droplet material. Herein, it is shown experimentally that monodisperse, submicrometer droplets of predictable sizes can be condensed from a monodisperse population of MBs as generated by MFs. Using perfluoropentane (PFP) as a representative solvent due to its low bp (29.2 °C), it is demonstrated that monodisperse PFP MBs can be produced at MFD temperatures >3.6 °C above the bp of PFP over a wide range of sizes (i.e., diameters from 2 to 200 μm). Independent of initial size, the generated MBs shrink rapidly in size from about 3 to 0 °C above the bp of PFP, corresponding to a phase change from gas to liquid, after which they shrink more slowly to form fully condensed droplets with diameters 5.0 ± 0.1 times smaller than the initial size of the MBs, even in the submicrometer size regime. This new method is versatile and flexible, and may be applied to any type of low-bp solvent for the manufacture of different submicrometer droplets for which precisely controlled dimensions are required.

  14. Stoddard solvent poisoning

    MedlinePlus

    These products contain Stoddard solvent: Dry cleaning fluids Paints Paint thinner Stoddard solvent ( mineral spirits ) Toners used in copy machines This list may not include all products containing Stoddard solvent.

  15. Interface-tracking electro-hydrodynamic model for droplet coalescence

    NASA Astrophysics Data System (ADS)

    Crowl Erickson, Lindsay; Noble, David

    2012-11-01

    Many fluid-based technologies rely on electrical fields to control the motion of droplets, e.g. micro-fluidic devices for high-speed droplet sorting, solution separation for chemical detectors, and purification of biodiesel fuel. Precise control over droplets is crucial to these applications. However, electric fields can induce complex and unpredictable fluid dynamics. Recent experiments (Ristenpart et al. 2009) have demonstrated that oppositely charged droplets bounce rather than coalesce in the presence of strong electric fields. Analytic hydrodynamic approximations for interfaces become invalid near coalescence, and therefore detailed numerical simulations are necessary. We present a conformal decomposition finite element (CDFEM) interface-tracking method for two-phase flow to demonstrate electro-coalescence. CDFEM is a sharp interface method that decomposes elements along fluid-fluid boundaries and uses a level set function to represent the interface. The electro-hydrodynamic equations solved allow for convection of charge and charge accumulation at the interface, both of which may be important factors for the pinch-off dynamics in this parameter regime.

  16. Bending instability of electrically charged liquid jets of polymer solutions in electrospinning

    NASA Astrophysics Data System (ADS)

    Reneker, Darrell H.; Yarin, Alexander L.; Fong, Hao; Koombhongse, Sureeporn

    2000-05-01

    Nanofibers of polymers were electrospun by creating an electrically charged jet of polymer solution at a pendent droplet. After the jet flowed away from the droplet in a nearly straight line, it bent into a complex path and other changes in shape occurred, during which electrical forces stretched and thinned it by very large ratios. After the solvent evaporated, birefringent nanofibers were left. In this article the reasons for the instability are analyzed and explained using a mathematical model. The rheological complexity of the polymer solution is included, which allows consideration of viscoelastic jets. It is shown that the longitudinal stress caused by the external electric field acting on the charge carried by the jet stabilized the straight jet for some distance. Then a lateral perturbation grew in response to the repulsive forces between adjacent elements of charge carried by the jet. The motion of segments of the jet grew rapidly into an electrically driven bending instability. The three-dimensional paths of continuous jets were calculated, both in the nearly straight region where the instability grew slowly and in the region where the bending dominated the path of the jet. The mathematical model provides a reasonable representation of the experimental data, particularly of the jet paths determined from high speed videographic observations.

  17. Droplet formation and scaling in dense suspensions

    PubMed Central

    Miskin, Marc Z.; Jaeger, Heinrich M.

    2012-01-01

    When a dense suspension is squeezed from a nozzle, droplet detachment can occur similar to that of pure liquids. While in pure liquids the process of droplet detachment is well characterized through self-similar profiles and known scaling laws, we show here the simple presence of particles causes suspensions to break up in a new fashion. Using high-speed imaging, we find that detachment of a suspension drop is described by a power law; specifically we find the neck minimum radius, rm, scales like near breakup at time τ = 0. We demonstrate data collapse in a variety of particle/liquid combinations, packing fractions, solvent viscosities, and initial conditions. We argue that this scaling is a consequence of particles deforming the neck surface, thereby creating a pressure that is balanced by inertia, and show how it emerges from topological constraints that relate particle configurations with macroscopic Gaussian curvature. This new type of scaling, uniquely enforced by geometry and regulated by the particles, displays memory of its initial conditions, fails to be self-similar, and has implications for the pressure given at generic suspension interfaces. PMID:22392979

  18. Coalescence-induced droplet actuation

    NASA Astrophysics Data System (ADS)

    Sellier, Mathieu; Verdier, Claude; Nock, Volker

    2011-11-01

    This work investigates a little explored driving mechanism to actuate droplets: the surface tension gradient which arises during the coalescence of two droplets of liquid having different compositions and therefore surface tensions. The resulting surface tension gradient gives rise to a Marangoni flow which, if sufficiently large, can displace the droplet. In order to understand, the flow dynamics arising during the coalescence of droplets of different fluids, a model has been developed in the lubrication framework. The numerical results confirm the existence of a self-propulsion window which depends on two dimensionless groups representing competing effects during the coalescence: the surface tension contrast between the droplets which promotes actuation and species diffusion which tends to make the mixture uniform thereby anihilating Marangoni flow and droplet motion. In parallel, experiments have been conducted to confirm this self-propulsion behaviour. The experiment consists in depositing a droplet of distilled water on a ``hydrophilic highway.'' This stripe was obtained by plasma-treating a piece of PDMS shielded in some parts by glass coverslips. This surface functionalization was found to be the most convenient way to control the coalescence. When a droplet of ethanol is deposited near the ``water slug,'' coalescence occurs and a rapid motion of the resulting mixture is observed. The support of the Dumont d'Urville NZ-France Science & Technology program is gratefully acknowledged.

  19. Experiments examining drag in linear droplet packets

    NASA Astrophysics Data System (ADS)

    Nguyen, Q. V.; Dunn-Rankin, D.

    1992-01-01

    This paper presents an experimental study of vertically traveling droplet packets, where the droplets in each packet are aligned linearly, one behind another. The paper describes in detail, an experimental apparatus that produces repeatable, linearly aligned, and isolated droplet packets containing 1 6 droplets per packet. The apparatus is suitable for examining aerodynamic interactions between droplets within each packet. This paper demonstrates the performance of the apparatus by examining the drag reduction and collision of droplets traveling in the wake of a lead droplet. Comparison of a calculated single droplet trajectory with the detailed droplet position versus time data for a droplet packet provides the average drag reduction experienced by the trailing droplets due to the aerodynamic wake of the lead droplet. For the conditions of our experiment (4 droplet packet, 145 μm methanol droplets, 10 m/s initial velocity, initial droplet spacing of 5.2 droplet diameters, Reynolds number approx. 80) the average drag on the first trailing droplet was found to be 75% of the drag on the lead droplet.

  20. Points, skyrmions and torons in chiral nematic droplets

    NASA Astrophysics Data System (ADS)

    Posnjak, Gregor; Čopar, Simon; Muševič, Igor

    2016-05-01

    Chiral nematic droplets with perpendicular surface alignment of liquid crystalline molecules frustrate the helical structure into convoluted 3D textures with complex topology. We observe the droplets with fluorescent confocal polarising microscopy (FCPM), and reconstruct and analyse for the first time the topology of the 3D director field using a novel method of director reconstruction from raw data. We always find an odd number of topological defects, which preserve the total topological charge of the droplet of +1 regardless of chirality. At higher chirality, we observe up to 5 point hedgehog defects, which are elastically stabilized with convoluted twisted structures, reminiscent of 2D skyrmions and toron-like structure, nested into a sphere.

  1. Points, skyrmions and torons in chiral nematic droplets

    PubMed Central

    Posnjak, Gregor; Čopar, Simon; Muševič, Igor

    2016-01-01

    Chiral nematic droplets with perpendicular surface alignment of liquid crystalline molecules frustrate the helical structure into convoluted 3D textures with complex topology. We observe the droplets with fluorescent confocal polarising microscopy (FCPM), and reconstruct and analyse for the first time the topology of the 3D director field using a novel method of director reconstruction from raw data. We always find an odd number of topological defects, which preserve the total topological charge of the droplet of +1 regardless of chirality. At higher chirality, we observe up to 5 point hedgehog defects, which are elastically stabilized with convoluted twisted structures, reminiscent of 2D skyrmions and toron-like structure, nested into a sphere. PMID:27198649

  2. Interactions of PAMAM dendrimers with negatively charged model biomembranes.

    PubMed

    Yanez Arteta, Marianna; Ainalem, Marie-Louise; Porcar, Lionel; Martel, Anne; Coker, Helena; Lundberg, Dan; Chang, Debby P; Soltwedel, Olaf; Barker, Robert; Nylander, Tommy

    2014-11-13

    We have investigated the interactions between cationic poly(amidoamine) (PAMAM) dendrimers of generation 4 (G4), a potential gene transfection vector, with net-anionic model biomembranes composed of different ratios of zwitterionic phosphocholine (PC) and anionic phospho-L-serine (PS) phospholipids. Two types of model membranes were used: solid-supported bilayers, prepared with lipids carrying palmitoyl-oleoyl (PO) and diphytanoyl (DPh) acyl chains, and free-standing bilayers, formed at the interface between two aqueous droplets in oil (droplet interface bilayers, DIBs) using the DPh-based lipids. G4 dendrimers were found to translocate through POPC:POPS bilayers deposited on silica surfaces. The charge density of the bilayer affects translocation, which is reduced when the ionic strength increases. This shows that the dendrimer-bilayer interactions are largely controlled by their electrostatic attraction. The structure of the solid-supported bilayers remains intact upon translocation of the dendrimer. However, the amount of lipids in the bilayer decreases and dendrimer/lipid aggregates are formed in bulk solution, which can be deposited on the interfacial layers upon dilution of the system with dendrimer-free solvent. Electrophysiology measurements on DIBs confirm that G4 dendrimers cross the lipid membranes containing PS, which then become more permeable to ions. The obtained results have implications for PAMAM dendrimers as delivery vehicles to cells.

  3. Surface Interaction of Water-in-Oil Emulsion Droplets with Interfacially Active Asphaltenes.

    PubMed

    Shi, Chen; Zhang, Ling; Xie, Lei; Lu, Xi; Liu, Qingxia; He, Jiajun; Mantilla, Cesar A; Van den Berg, Frans G A; Zeng, Hongbo

    2017-02-07

    Adsorption of interfacially active components at the water/oil interface plays critical roles in determining the properties and behaviors of emulsion droplets. In this study, the droplet probe atomic force microscopy (AFM) technique was applied, for the first time, to quantitatively study the interaction mechanism between water-in-oil (W/O) emulsion droplets with interfacially adsorbed asphaltenes. The behaviors and stability of W/O emulsion droplets were demonstrated to be significantly influenced by the asphaltene concentration of organic solution where the emulsions were aged, aging time, force load, contact time, and solvent type. Bare water droplets could readily coalesce with each other in oil (i.e., toluene), while interfacially adsorbed asphaltenes could sterically inhibit droplet coalescence and induce interfacial adhesion during separation of the water droplets. For low asphaltene concentration cases, the adhesion increased with increasing asphaltene concentration (≤100 mg/L), but it significantly decreased at relatively high asphaltene concentration (e.g., 500 mg/L). Experiments in Heptol (i.e., mixture of toluene and heptane) showed that the addition of a poor solvent for asphaltenes (e.g., heptane) could enhance the interfacial adhesion between emulsion droplets at relatively low asphaltene concentration but could weaken the adhesion at relatively high asphaltene concentration. This work has quantified the interactions between W/O emulsion droplets with interfacially adsorbed asphaltenes, and the results provide useful implications into the stabilization mechanisms of W/O emulsions in oil production. The methodology in this work can be readily extended to other W/O emulsion systems with interfacially active components.

  4. Spontaneous Formation of Water Droplets at Oil-Solid Interfaces

    PubMed Central

    Yang, Zhongqiang; Abbott, Nicholas L.

    2010-01-01

    We report observations of spontaneous formation of micrometer-sized water droplets within micrometer-thick films of a range of different oils (isotropic and nematic 4-cyano-4’-pentylbiphenyl (5CB), and silicone, olive and corn oil) that are supported on glass substrates treated with octadecyltrichlorosilane (OTS) and immersed under water. Confocal imaging was used to determine that the water droplets nucleate and grow at the interface between the oils and OTS-treated glass with a contact angle of ~130°. A simple thermodynamic model based on macroscopic interfacial energetic arguments consistent with the contact angle of 130°, however, fails to account for the spontaneous formation of the water droplets. ζ-potential measurements performed with OTS-treated glass (− 59.0 ± 16.4 mV) and hydrophobic monolayers formed on gold films (2.0 ± 0.7 mV), when combined with the observed absence of droplet formation under films of oil supported on the latter surfaces, suggest that the charge of the oil-solid interface promotes partitioning of water to the interfacial region. The hydrophobic nature of the OTS-treated glass promotes dewetting of water accumulated in the interfacial region into droplets (a thin film of water is seen to form on bare glass). The inhibitory effect on droplet formation of both salt (NaCl) and sucrose (0.1mM to 500mM) added to the aqueous phase was similar, indicating that both solutes lower the chemical potential of the bulk water (osmotic effect) sufficiently to prevent partitioning of the water to the interface between the oil and supporting substrates. These results suggest that charged, hydrophobic surfaces can provide routes to spontaneous formation of surface-supported, water-in-oil emulsions. PMID:20712383

  5. Solvent Reaction Field Potential inside an Uncharged Globular Protein: A Bridge between Implicit and Explicit Solvent Models?

    PubMed Central

    Baker, Nathan A.; McCammon, J. Andrew

    2008-01-01

    The solvent reaction field potential of an uncharged protein immersed in Simple Point Charge/Extended (SPC/E) explicit solvent was computed over a series of molecular dynamics trajectories, intotal 1560 ns of simulation time. A finite, positive potential of 13 to 24 kbTec−1 (where T = 300K), dependent on the geometry of the solvent-accessible surface, was observed inside the biomolecule. The primary contribution to this potential arose from a layer of positive charge density 1.0 Å from the solute surface, on average 0.008 ec/Å3, which we found to be the product of a highly ordered first solvation shell. Significant second solvation shell effects, including additional layers of charge density and a slight decrease in the short-range solvent-solvent interaction strength, were also observed. The impact of these findings on implicit solvent models was assessed by running similar explicit-solvent simulations on the fully charged protein system. When the energy due to the solvent reaction field in the uncharged system is accounted for, correlation between per-atom electrostatic energies for the explicit solvent model and a simple implicit (Poisson) calculation is 0.97, and correlation between per-atom energies for the explicit solvent model and a previously published, optimized Poisson model is 0.99. PMID:17949217

  6. Investigation of droplet collisions for solutions with different solids content

    NASA Astrophysics Data System (ADS)

    Kuschel, Matthias; Sommerfeld, Martin

    2013-02-01

    The collision behaviour of droplets and the collision outcome are investigated for high viscous polymer solutions. For that purpose, two droplet chains produced by piezoelectric droplet generators are directed towards each other at a certain angle so that individual droplet pairs collide. For recording the collision event, one double-image and one high-speed CCD camera were used. One camera is positioned perpendicular to the collision plane recording the outcome of the collision, and the second camera is aligned parallel to the collision plane to assure that the droplet chains are exactly in one plane. A new approach for tracking droplets in combination with an extended particle tracking velocimetry algorithm has been developed. Time-resolved series of pictures were used to analyse the dynamics of droplet collisions. The three different water soluble substances were saccharose and 1-Ethenyl-2-pyrrolidone (PVP) with different molecular weights (K17, K30). The solvent was demineralised water. The solids contents ranged from 20 to 60 %, 5 to 25 % and 5 to 35 %, yielding dynamic viscosities in the range of 2-60 mPa s. Results were collected for different pairs of impact angles and Weber numbers in order to establish common collision maps for characterising the outcomes. Here, relative velocities between 0.5 and 4 m/s and impact parameters in the interval from 0 to 1 for equal-sized droplets (Δ = 1) have been investigated. Additionally, satellite formation will be discussed exemplarily for K30. A comparison with common models of different authors (Ashgriz and Poo in J Fluid Mech 221:183-204, 1990; Estrade et al. in Int J Heat Fluid Flow 20:486-491, 1999) mainly derived for low viscous droplets revealed that the upper limit of their validity is given by an Ohnesorge number of Oh = 0.115 and a capillary number of Ca = 0.577. For higher values of these non-dimensional parameters and hence higher dynamic viscosities, these models are unable to predict correctly the

  7. Lossless droplet transfer of droplet-based microfluidic analysis

    SciTech Connect

    Kelly, Ryan T; Tang, Keqi; Page, Jason S; Smith, Richard D

    2011-11-22

    A transfer structure for droplet-based microfluidic analysis is characterized by a first conduit containing a first stream having at least one immiscible droplet of aqueous material and a second conduit containing a second stream comprising an aqueous fluid. The interface between the first conduit and the second conduit can define a plurality of apertures, wherein the apertures are sized to prevent exchange of the first and second streams between conduits while allowing lossless transfer of droplets from the first conduit to the second conduit through contact between the first and second streams.

  8. Solvent wash solution

    DOEpatents

    Neace, J.C.

    1984-03-13

    A process is claimed for removing diluent degradation products from a solvent extraction solution, which has been used to recover uranium and plutonium from spent nuclear fuel. A wash solution and the solvent extraction solution are combined. The wash solution contains (a) water and (b) up to about, and including, 50 vol % of at least one-polar water-miscible organic solvent based on the total volume of the water and the highly-polar organic solvent. The wash solution also preferably contains at least one inorganic salt. The diluent degradation products dissolve in the highly-polar organic solvent and the organic solvent extraction solvent do not dissolve in the highly-polar organic solvent. The highly-polar organic solvent and the extraction solvent are separated.

  9. Solvent wash solution

    DOEpatents

    Neace, James C.

    1986-01-01

    Process for removing diluent degradation products from a solvent extraction solution, which has been used to recover uranium and plutonium from spent nuclear fuel. A wash solution and the solvent extraction solution are combined. The wash solution contains (a) water and (b) up to about, and including, 50 volume percent of at least one-polar water-miscible organic solvent based on the total volume of the water and the highly-polar organic solvent. The wash solution also preferably contains at least one inorganic salt. The diluent degradation products dissolve in the highly-polar organic solvent and the organic solvent extraction solvent do not dissolve in the highly-polar organic solvent. The highly-polar organic solvent and the extraction solvent are separated.

  10. Colloidal transport phenomena of milk components during convective droplet drying.

    PubMed

    Fu, Nan; Woo, Meng Wai; Chen, Xiao Dong

    2011-10-15

    Material segregation has been reported for industrial spray-dried milk powders, which indicates potential material migration during drying process. The relevant colloidal transport phenomenon and the underlying mechanism are still under debate. This study extended the glass-filament single droplet drying technique to observe not only the drying behaviour but also the dissolution behaviour of the correspondingly dried single particle. At progressively longer drying stage, a solvent droplet (water or ethanol) was attached to the semi-dried milk particle and the interaction between the solvent and the particle was video-recorded. Based on the different dissolution and wetting behaviours observed, material migration during milk drying was studied. Fresh skim milk and fresh whole milk were investigated using water and ethanol as solvents. Fat started to accumulate on the surface as soon as drying was started. At the initial stage of drying, the fat layer remained thin and the solubility of the semi-dried milk particle was much affected by lactose and protein present underneath the fat layer. Fat kept accumulating at the surface as drying progressed and the accumulation was completed by the middle stage of drying. The results from drying of model milk materials (pure sodium caseinate solution and lactose/sodium caseinate mixed solution) supported the colloidal transport phenomena observed for the milk drying. When mixed with lactose, sodium caseinate did not form an apparent solvent-resistant protein shell during drying. The extended technique of glass-filament single droplet approach provides a powerful tool in examining the solubility of individual particle after drying.

  11. Bacterial encountering with oil droplet

    NASA Astrophysics Data System (ADS)

    Sheng, Jian; Molaei, Mehdi

    2014-11-01

    Encountering of microorganisms with rising oil droplets in aqueous environments is the first and one of the critical steps in the biodegradation of crude oil. Several factors such as droplet sizes, rising velocity, surfactant, and motility of bacteria are expected to affect the encounter rate. We establish well controlled microfluidic devices by applying layer-by-layer technique that allows us to produce horizontal micro droplets with different sizes. The encounter rates of passive particles, motile and non-motile bacteria with these droplets are measured by high speed microscopy. The effects of mobility and motility of these particles on encounter rates are assessed quantitatively. Meanwhile, we visualize reorientation of the particle due to flow filed around the oil droplet. Results show that the motile bacteria have higher probabilities to interact with an oil droplet compare to the passive particles. Ongoing analyses focus on the effect of shear rates, angular dispersion, curvatures of streamlines, and the swimming velocity of bacteria. The ratios of the encounter area to the entire droplet surface at various flow regimes will also been measured. GoMRI.

  12. Droplet resonator based optofluidic microlasers

    NASA Astrophysics Data System (ADS)

    Kiraz, Alper; Jonáš, Alexandr; Aas, Mehdi; Karadag, Yasin; Brzobohatý, Oto; Ježek, Jan; Pilát, Zdeněk.; Zemánek, Pavel; Anand, Suman; McGloin, David

    2014-03-01

    We introduce tunable optofluidic microlasers based on active optical resonant cavities formed by optically stretched, dye-doped emulsion droplets confined in a dual-beam optical trap. To achieve tunable dye lasing, optically pumped droplets of oil dispersed in water are stretched by light in the dual-beam trap. Subsequently, resonant path lengths of whispering gallery modes (WGMs) propagating in the droplet are modified, leading to shifts in the microlaser emission wavelengths. We also report lasing in airborne, Rhodamine B-doped glycerolwater droplets which were localized using optical tweezers. While being trapped near the focal point of an infrared laser, the droplets were pumped with a Q-switched green laser. Furthermore, biological lasing in droplets supported by a superhydrophobic surface is demonstrated using a solution of Venus variant of the yellow fluorescent protein or E. Coli bacterial cells expressing stably the Venus protein. Our results may lead to new ways of probing airborne particles, exploiting the high sensitivity of stimulated emission to small perturbations in the droplet laser cavity and the gain medium.

  13. Droplets, Bubbles and Ultrasound Interactions.

    PubMed

    Shpak, Oleksandr; Verweij, Martin; de Jong, Nico; Versluis, Michel

    2016-01-01

    The interaction of droplets and bubbles with ultrasound has been studied extensively in the last 25 years. Microbubbles are broadly used in diagnostic and therapeutic medical applications, for instance, as ultrasound contrast agents. They have a similar size as red blood cells, and thus are able to circulate within blood vessels. Perfluorocarbon liquid droplets can be a potential new generation of microbubble agents as ultrasound can trigger their conversion into gas bubbles. Prior to activation, they are at least five times smaller in diameter than the resulting bubbles. Together with the violent nature of the phase-transition, the droplets can be used for local drug delivery, embolotherapy, HIFU enhancement and tumor imaging. Here we explain the basics of bubble dynamics, described by the Rayleigh-Plesset equation, bubble resonance frequency, damping and quality factor. We show the elegant calculation of the above characteristics for the case of small amplitude oscillations by linearizing the equations. The effect and importance of a bubble coating and effective surface tension are also discussed. We give the main characteristics of the power spectrum of bubble oscillations. Preceding bubble dynamics, ultrasound propagation is introduced. We explain the speed of sound, nonlinearity and attenuation terms. We examine bubble ultrasound scattering and how it depends on the wave-shape of the incident wave. Finally, we introduce droplet interaction with ultrasound. We elucidate the ultrasound-focusing concept within a droplets sphere, droplet shaking due to media compressibility and droplet phase-conversion dynamics.

  14. Asymmetric Wettability Directs Leidenfrost Droplets

    SciTech Connect

    Agapov, Rebecca L; Boreyko, Jonathan B; Briggs, Dayrl P; Srijanto, Bernadeta R; Retterer, Scott T; Collier, Pat; Lavrik, Nickolay V

    2014-01-01

    Leidenfrost phenomena on nano- and microstructured surfaces are of great importance for increasing control over heat transfer in high power density systems utilizing boiling phenomena. They also provide an elegant means to direct droplet motion in a variety of recently emerging fluidic systems. Here, we report the fabrication and characterization of tilted nanopillar arrays (TNPAs) that exhibit directional Leidenfrost water droplets under dynamic conditions, namely on impact with Weber numbers 40 at T 325 C. The batch fabrication of the TNPAs was achieved by glancing-angle anisotropic reactive ion etching of a thermally dewet platinum mask, with mean pillar diameters of 100 nm and heights of 200-500 nm. In contrast to previously implemented macro- and microscopic Leidenfrost ratchets, our TNPAs induce no preferential directional movement of Leidenfrost droplets under conditions approaching steady-state film boiling, suggesting that the observed droplet directionality is not a result of asymmetric vapor flow. Using high-speed imaging, phase diagrams were constructed for the boiling behavior upon impact for droplets falling onto TNPAs, straight nanopillar arrays, and smooth silicon surfaces. The asymmetric impact and directional trajectory of droplets was exclusive to the TNPAs for impacts corresponding to the transition boiling regime, revealing that asymmetric wettability upon impact is the mechanism for the droplet directionality.

  15. Electrically Controllable Microparticle Synthesis and Digital Microfluidic Manipulation by Electric-Field-Induced Droplet Dispensing into Immiscible Fluids.

    PubMed

    Um, Taewoong; Hong, Jiwoo; Im, Do Jin; Lee, Sang Joon; Kang, In Seok

    2016-08-18

    The dispensing of tiny droplets is a basic and crucial process in a myriad of applications, such as DNA/protein microarray, cell cultures, chemical synthesis of microparticles, and digital microfluidics. This work systematically demonstrates droplet dispensing into immiscible fluids through electric charge concentration (ECC) method. It exhibits three main modes (i.e., attaching, uniform, and bursting modes) as a function of flow rates, applied voltages, and gap distances between the nozzle and the oil surface. Through a conventional nozzle with diameter of a few millimeters, charged droplets with volumes ranging from a few μL to a few tens of nL can be uniformly dispensed into the oil chamber without reduction in nozzle size. Based on the features of the proposed method (e.g., formation of droplets with controllable polarity and amount of electric charge in water and oil system), a simple and straightforward method is developed for microparticle synthesis, including preparation of colloidosomes and fabrication of Janus microparticles with anisotropic internal structures. Finally, a combined system consisting of ECC-induced droplet dispensing and electrophoresis of charged droplet (ECD)-driven manipulation systems is constructed. This integrated platform will provide increased utility and flexibility in microfluidic applications because a charged droplet can be delivered toward the intended position by programmable electric control.

  16. Electrically Controllable Microparticle Synthesis and Digital Microfluidic Manipulation by Electric-Field-Induced Droplet Dispensing into Immiscible Fluids

    NASA Astrophysics Data System (ADS)

    Um, Taewoong; Hong, Jiwoo; Im, Do Jin; Lee, Sang Joon; Kang, In Seok

    2016-08-01

    The dispensing of tiny droplets is a basic and crucial process in a myriad of applications, such as DNA/protein microarray, cell cultures, chemical synthesis of microparticles, and digital microfluidics. This work systematically demonstrates droplet dispensing into immiscible fluids through electric charge concentration (ECC) method. It exhibits three main modes (i.e., attaching, uniform, and bursting modes) as a function of flow rates, applied voltages, and gap distances between the nozzle and the oil surface. Through a conventional nozzle with diameter of a few millimeters, charged droplets with volumes ranging from a few μL to a few tens of nL can be uniformly dispensed into the oil chamber without reduction in nozzle size. Based on the features of the proposed method (e.g., formation of droplets with controllable polarity and amount of electric charge in water and oil system), a simple and straightforward method is developed for microparticle synthesis, including preparation of colloidosomes and fabrication of Janus microparticles with anisotropic internal structures. Finally, a combined system consisting of ECC-induced droplet dispensing and electrophoresis of charged droplet (ECD)-driven manipulation systems is constructed. This integrated platform will provide increased utility and flexibility in microfluidic applications because a charged droplet can be delivered toward the intended position by programmable electric control.

  17. Electrically Controllable Microparticle Synthesis and Digital Microfluidic Manipulation by Electric-Field-Induced Droplet Dispensing into Immiscible Fluids

    PubMed Central

    Um, Taewoong; Hong, Jiwoo; Im, Do Jin; Lee, Sang Joon; Kang, In Seok

    2016-01-01

    The dispensing of tiny droplets is a basic and crucial process in a myriad of applications, such as DNA/protein microarray, cell cultures, chemical synthesis of microparticles, and digital microfluidics. This work systematically demonstrates droplet dispensing into immiscible fluids through electric charge concentration (ECC) method. It exhibits three main modes (i.e., attaching, uniform, and bursting modes) as a function of flow rates, applied voltages, and gap distances between the nozzle and the oil surface. Through a conventional nozzle with diameter of a few millimeters, charged droplets with volumes ranging from a few μL to a few tens of nL can be uniformly dispensed into the oil chamber without reduction in nozzle size. Based on the features of the proposed method (e.g., formation of droplets with controllable polarity and amount of electric charge in water and oil system), a simple and straightforward method is developed for microparticle synthesis, including preparation of colloidosomes and fabrication of Janus microparticles with anisotropic internal structures. Finally, a combined system consisting of ECC-induced droplet dispensing and electrophoresis of charged droplet (ECD)-driven manipulation systems is constructed. This integrated platform will provide increased utility and flexibility in microfluidic applications because a charged droplet can be delivered toward the intended position by programmable electric control. PMID:27534580

  18. Thermocapillary Convection in Liquid Droplets

    NASA Technical Reports Server (NTRS)

    1986-01-01

    The purpose of this video is to understand the effects of surface tension on fluid convection. The fluid system chosen is the liquid sessile droplet to show the importance in single crystal growth, the spray drying and cooling of metal, and the advance droplet radiators of the space stations radiators. A cross sectional representation of a hemispherical liquid droplet under ideal conditions is used to show internal fluid motion. A direct simulation of buoyancy-dominant convection and surface tension-dominant convection is graphically displayed. The clear differences between two mechanisms of fluid transport, thermocapillary convection, and bouncy dominant convection is illustrated.

  19. Shrinking instability of toroidal droplets.

    PubMed

    Fragkopoulos, Alexandros A; Pairam, Ekapop; Berger, Eric; Segre, Phil N; Fernández-Nieves, Alberto

    2017-03-14

    Toroidal droplets are inherently unstable due to surface tension. They can break up, similar to cylindrical jets, but also exhibit a shrinking instability, which is inherent to the toroidal shape. We investigate the evolution of shrinking toroidal droplets using particle image velocimetry. We obtain the flow field inside the droplets and show that as the torus evolves, its cross-section significantly deviates from circular. We then use the experimentally obtained velocities at the torus interface to theoretically reconstruct the internal flow field. Our calculation correctly describes the experimental results and elucidates the role of those modes that, among the many possible ones, are required to capture all of the relevant experimental features.

  20. Single Stage Contactor Testing Of The Next Generation Solvent Blend

    SciTech Connect

    Herman, D. T.; Peters, T. B.; Duignan, M. R.; Williams, M. R.; Poirier, M. R.; Brass, E. A.; Garrison, A. G.; Ketusky, E. T.

    2014-01-06

    The Modular Caustic Side Solvent Extraction (CSSX) Unit (MCU) facility at the Savannah River Site (SRS) is actively pursuing the transition from the current BOBCalixC6 based solvent to the Next Generation Solvent (NGS)-MCU solvent to increase the cesium decontamination factor. To support this integration of NGS into the MCU facility the Savannah River National Laboratory (SRNL) performed testing of a blend of the NGS (MaxCalix based solvent) with the current solvent (BOBCalixC6 based solvent) for the removal of cesium (Cs) from the liquid salt waste stream. This testing utilized a blend of BOBCalixC6 based solvent and the NGS with the new extractant, MaxCalix, as well as a new suppressor, tris(3,7dimethyloctyl) guanidine. Single stage tests were conducted using the full size V-05 and V-10 liquid-to-liquid centrifugal contactors installed at SRNL. These tests were designed to determine the mass transfer and hydraulic characteristics with the NGS solvent blended with the projected heel of the BOBCalixC6 based solvent that will exist in MCU at time of transition. The test program evaluated the amount of organic carryover and the droplet size of the organic carryover phases using several analytical methods. The results indicate that hydraulically, the NGS solvent performed hydraulically similar to the current solvent which was expected. For the organic carryover 93% of the solvent is predicted to be recovered from the stripping operation and 96% from the extraction operation. As for the mass transfer, the NGS solvent significantly improved the cesium DF by at least an order of magnitude when extrapolating the One-stage results to actual Seven-stage extraction operation with a stage efficiency of 95%.

  1. Droplet spectral broadening in marine stratus

    SciTech Connect

    Hudson, J.G.; Yum, Seong Soo

    1997-11-15

    Broadening of the cloud droplet (diameter < 50 {mu}m) spectrum with increased droplet size was found to depend on the vertical profiles of cloud water. Clouds with liquid water profiles resembling adiabatic conditions displayed constant spectral widths. Other clouds displayed broader droplet spectra and increasing broadness with mean droplet sizes. Less than adiabatic cloud liquid water profiles may be accounted for by conversion to drops (diameter > 50 {mu}m, i.e., drizzle). Broad droplet spectra were most closely associated with drizzle drops. Both the concentration, C and slope, k, of the cloud condensation nuclei (CCN) spectra were theoretically found to affect droplet spectral width. For individual cloud parcels a higher C and lower k each contributed to broader droplet spectra. When mixing among cloud parcels with different updrafts was considered, the predictions deviated especially at larger mean droplet diameters. Variations in updraft velocity result in differences in droplet concentrations and mean droplet sizes. The predictions for this internal mixing process showed greater droplet spectral widths for CCN spectra with higher k, especially at the larger mean droplet diameters. Instead of the individual parcel predictions of narrower droplet spectra at larger mean droplet sizes, internal mixing predicted increasing droplet spectral width with increasing mean droplet size. These predictions are consistent with the observations. First, when only cloud parcels with small mean droplet diameters (< 1 {mu}m) were considered, the polluted clouds that formed on CCN with higher C and lower k displayed broader droplet spectra than clean clouds. Cloud parcels with large mean droplet diameters (>12 {mu}m) and large {sigma} were observed only in clean conditions where k was high. Increasing droplet spectral width with mean droplet diameter (especially > 12 {mu}m) is typical of many observations here and elsewhere.

  2. MALDI-TOF imaging mass spectrometry of artifacts in "dried droplet" polymer samples.

    PubMed

    Weidner, Steffen; Knappe, Patrick; Panne, Ulrich

    2011-07-01

    Matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) imaging of polystyrenes with various molecular masses was applied to study spatial molecular mass distribution of polymers in sample spots prepared by the "dried droplet" method. When different solvents and target surfaces were examined, a segregation of single homologous polymers was observed depending upon the evaporation rate of the solvent. For the observed patterns left by the evaporating droplet, a hypothesis is offered taking into account different hydrodynamic interactions and diffusion. The results illustrate that spot preparation using the conventionally "dried droplet" method is prone to artifacts and should be avoided for reliable and reproducible MALDI mass spectrometry experiments with regards to the determination of molecular masses and mass distributions.

  3. Diffusiophoresis of a charged drop

    NASA Astrophysics Data System (ADS)

    Yang, Fan; Shin, Sangwoo; Stone, Howard

    2016-11-01

    Diffusiophoresis describes the motion of colloids in an electrolytic solution under a concentration gradient. Most of the previous studies in diffusiophoresis have dealt with motion of rigid particles. Here, we study the diffusiophoresis of fluid particles analytically and experimentally. We obtain the analytical solution of the diffusiophoretic velocity of fluid particles by perturbation methods. Using charged oil droplets, we measure the droplet speed under solute concentration gradient and compare it with the analytical solution. Our findings have potential applications for oil recovery and drug delivery.

  4. Decompressing Emulsion Droplets Favors Coalescence

    NASA Astrophysics Data System (ADS)

    Bremond, Nicolas; Thiam, Abdou R.; Bibette, Jérôme

    2008-01-01

    The destabilization process of an emulsion under flow is investigated in a microfluidic device. The experimental approach enables us to generate a periodic train of droplet pairs, and thus to isolate and analyze the basic step of the destabilization, namely, the coalescence of two droplets which collide. We demonstrate a counterintuitive phenomenon: coalescence occurs during the separation phase and not during the impact. Separation induces the formation of two facing nipples in the contact area that hastens the connection of the interfaces prior to fusion. Moreover, droplet pairs initially stabilized by surfactants can be destabilized by forcing the separation. Finally, we note that the fusion mechanism is responsible for a cascade of coalescence events in a compact system of droplets where the separation is driven by surface tension.

  5. Droplet depinning in a wake

    NASA Astrophysics Data System (ADS)

    Hooshanginejad, Alireza; Lee, Sungyon

    2017-03-01

    Pinning and depinning of a windswept droplet on a surface is familiar yet deceptively complex for it depends on the interaction of the contact line with the microscopic features of the solid substrate. This physical picture is further compounded when wind of the Reynolds number greater than 100 blows over pinned drops, leading to the boundary layer separation and wake generation. In this Rapid Communication, we incorporate the well-developed ideas of the classical boundary layer to study partially wetting droplets in a wake created by a leader object. Depending on its distance from the leader, the droplet is observed to exhibit drafting, upstream motion, and splitting, due to the wake-induced hydrodynamic coupling that is analogous to drafting of moving bodies. We successfully rationalize the onset of the upstream motion regime using a reduced model that computes the droplet shape governed by the pressure field inside the wake.

  6. Droplet combustion at reduced gravity

    NASA Technical Reports Server (NTRS)

    Dryer, F. L.; Williams, F. A.

    1988-01-01

    The current work involves theoretical analyses of the effects identified, experiments in the NASA Lewis drop towers performed in the middeck areas of the Space Shuttle. In addition, there is laboratory work associated with the design of the flight apparatus. Calculations have shown that some of the test-matrix data can be obtained in drop towers, and some are achievable only in the space experiments. The apparatus consists of a droplet dispensing device (syringes), a droplet positioning device (opposing, retractable, hollow needles), a droplet ignition device (two matched pairs of retractable spark electrodes), gas and liquid handling systems, a data acquisition system (mainly giving motion-picture records of the combustion in two orthogonal views, one with backlighting for droplet resolution), and associated electronics.

  7. The life of lipid droplets

    PubMed Central

    Walther, Tobias C.; Farese, Robert V.

    2009-01-01

    Lipid droplets are the least characterized of cellular organelles. Long considered simple lipid storage depots, these dynamic and remarkable organelles have recently been implicated in many biological processes, and we are only now beginning to gain insights into their fascinating lives in cells. Here we examine what we know of the life of lipid droplets. We review emerging data concerning their cellular biology and present our thoughts on some of the most salient questions for investigation. PMID:19041421

  8. Magnetic droplets and dynamical skyrmions

    NASA Astrophysics Data System (ADS)

    Akerman, Johan

    2015-03-01

    Nanocontact spin-torque oscillators (NC-STOs) provide an excellent environment for studying nano-magnetic phenomena such as localized and propagating auto-oscillatory spin wave (SW) modes. The recent experimental observation of magnetic droplet solitons in NC-STOs with perpendicular magnetic anisotropy (PMA) free layers, and the numerical and experimental demonstrations of spin transfer torque (STT) nucleated skyrmions in similar magnetic thin films add two interesting and useful nanoscale magnetic objects. Due to the competition between exchange, anisotropy, and, in the case of skyrmions, the Dzyaloshinskii-Moriya interaction (DMI), the droplet and the skyrmion are extremely compact, on the order of 10-100 nm. One of the main differences between a magnetic dissipative droplet soliton and a skyrmion is that the former is a dynamical object with all its spins precessing around an effective field and stabilized by STT, exchange, and PMA, while the latter has static spins and an internal structure stabilized by DMI, exchange, and PMA. The dissipative droplet is furthermore a non-topological soliton, while the skyrmion is topologically protected. In this work I will report on our most recent droplet experiments, including droplet collapse at very high fields, droplets excited in nano-wire based NC-STOs, and studies of the field-current droplet nucleation boundary. I will also demonstrate numerically and analytically that STT driven precession can stabilize so-called dynamical skyrmions even in the absence of DMI, and I will describe their very promising properties in detail. From a more fundamental perspective, precession is hence a third independent possibility to stabilize a skyrmion, without the need for the conventional stabilization from either dipolar energy or DMI.

  9. Arrested of coalescence of emulsion droplets of arbitrary size

    NASA Astrophysics Data System (ADS)

    Mbanga, Badel L.; Burke, Christopher; Blair, Donald W.; Atherton, Timothy J.

    2013-03-01

    With applications ranging from food products to cosmetics via targeted drug delivery systems, structured anisotropic colloids provide an efficient way to control the structure, properties and functions of emulsions. When two fluid emulsion droplets are brought in contact, a reduction of the interfacial tension drives their coalescence into a larger droplet of the same total volume and reduced exposed area. This coalescence can be partially or totally hindered by the presence of nano or micron-size particles that coat the interface as in Pickering emulsions. We investigate numerically the dependance of the mechanical stability of these arrested shapes on the particles size, their shape anisotropy, their polydispersity, their interaction with the solvent, and the particle-particle interactions. We discuss structural shape changes that can be induced by tuning the particles interactions after arrest occurs, and provide design parameters for the relevant experiments.

  10. The liquid droplet heat exchanger

    NASA Astrophysics Data System (ADS)

    Bruckner, A. P.

    Direct contact heat exchange between a gas and a molten metal dispersed into droplets offers an attractive new approach to increasing the efficiency and decreasing the specific weight of thermal power cycles for space applications. The ability of a droplet heat exchanger to transfer heat directly from a liquid metal to a working gas over a wide temperature range circumvents many of the material limitations of conventional tube type heat exchangers and does away with complicated plumbing systems and their tendency toward simple point failure. Droplet heat exchangers offer large surface to volume ratios in a compact geometry, very low pressure drop and high effectiveness. In the simplest configuration the molten material is sprayed axially through a counterflowing, high pressure inert working gas in an insulated cylindrical chamber. The droplets transfer heat directly to the gas by convection as they traverse the heat exchanger and are subsequently collected for recycling through the heat source. A number of suitable liquid metals and eutectic alloys having negligibly low vapor pressures in the temperature range of 350-1300 K were identified. Experimental studies of droplet formation with mercury demonstrated that near perfect control of droplet size can be easily achieved.

  11. Sintering of polydisperse viscous droplets

    NASA Astrophysics Data System (ADS)

    Wadsworth, Fabian B.; Vasseur, Jérémie; Llewellin, Edward W.; Dingwell, Donald B.

    2017-03-01

    Sintering—or coalescence—of compacts of viscous droplets is driven by the interfacial tension between the droplets and the interstitial gas phase. The process, which occurs in a range of industrial and natural settings, such as the manufacture of ceramics and the welding of volcanic ash, causes the compact to densify, to become stronger, and to become less permeable. We investigate the role of droplet polydispersivity in sintering dynamics by conducting experiments in which populations of glass spheres with different size distributions are heated to temperatures above the glass transition interval. We quantify the progress of sintering by tracking changes in porosity with time. The sintering dynamics is modeled by treating the system as a random distribution of interstitial gas bubbles shrinking under the action of interfacial tension only. We identify the scaling between the polydispersivity of the initial droplets and the dynamics of bulk densification. The framework that we develop allows the sintering dynamics of arbitrary polydisperse populations of droplets to be predicted if the initial droplet (or particle) size distribution is known.

  12. What Protein Charging (and Supercharging) Reveal about the Mechanism of Electrospray Ionization

    NASA Astrophysics Data System (ADS)

    Ogorzalek Loo, Rachel R.; Lakshmanan, Rajeswari; Loo, Joseph A.

    2014-10-01

    Understanding the charging mechanism of electrospray ionization is central to overcoming shortcomings such as ion suppression or limited dynamic range, and explaining phenomena such as supercharging. Towards that end, we explore what accumulated observations reveal about the mechanism of electrospray. We introduce the idea of an intermediate region for electrospray ionization (and other ionization methods) to account for the facts that solution charge state distributions (CSDs) do not correlate with those observed by ESI-MS (the latter bear more charge) and that gas phase reactions can reduce, but not increase, the extent of charging. This region incorporates properties (e.g., basicities) intermediate between solution and gas phase. Assuming that droplet species polarize within the high electric field leads to equations describing ion emission resembling those from the equilibrium partitioning model. The equations predict many trends successfully, including CSD shifts to higher m/z for concentrated analytes and shifts to lower m/z for sprays employing smaller emitter opening diameters. From this view, a single mechanism can be formulated to explain how reagents that promote analyte charging ("supercharging") such as m-NBA, sulfolane, and 3-nitrobenzonitrile increase analyte charge from "denaturing" and "native" solvent systems. It is suggested that additives' Brønsted basicities are inversely correlated to their ability to shift CSDs to lower m/z in positive ESI, as are Brønsted acidities for negative ESI. Because supercharging agents reduce an analyte's solution ionization, excess spray charge is bestowed on evaporating ions carrying fewer opposing charges. Brønsted basicity (or acidity) determines how much ESI charge is lost to the agent (unavailable to evaporating analyte).

  13. What Protein Charging (and Supercharging) Reveal about the Mechanism of Electrospray Ionization

    PubMed Central

    Loo, Rachel R. Ogorzalek; Lakshmanan, Rajeswari

    2014-01-01

    Understanding the charging mechanism of electrospray ionization is central to overcoming shortcomings such as ion suppression or limited dynamic range and explaining phenomena such as supercharging. Towards that end, we explore what accumulated observations reveal about the mechanism of electrospray. We introduce the idea of an intermediate region for electrospray ionization (and other ionization methods) to account for the facts that solution charge state distributions (CSDs) do not correlate to those observed by ESI– MS (the latter bear more charge) and that gas phase reactions can reduce, but not increase the extent of charging. This region incorporates properties, e.g., basicities, intermediate between solution and gas phase. Assuming that droplet species polarize within the high electric field leads to equations describing ion emission resembling those from the equilibrium partitioning model. The equations predict many trends successfully, including CSD shifts to higher m/z for concentrated analytes and shifts to lower m/z for sprays employing smaller emitter opening diameters. From this view, a single mechanism can be formulated to explain how reagents that promote analyte charging (“supercharging”) such as m–NBA, sulfolane, and 3–nitrobenzonitrile increase analyte charge from “denaturing” and “native” solvent systems. It is suggested that additives’ Brønsted basicities are inversely correlated to their ability to shift CSDs to lower m/z in positive ESI, as are Brønsted acidities for negative ESI. Because supercharging agents reduce an analyte's solution ionization, excess spray charge is bestowed on evaporating ions carryingfewer opposing charges. Brønsted basicity (or acidity) determines how much ESI charge is lost to the agent (unavailable to evaporating analyte). PMID:25135609

  14. Liquid droplet radiator development status. [waste heat rejection devices for future space vehicles

    NASA Technical Reports Server (NTRS)

    White, K. Alan, III

    1987-01-01

    Development of the Liquid Droplet Radiator (LDR) is described. Significant published results of previous investigators are presented, and work currently in progress is discussed. Several proposed LDR configurations are described, and the rectangular and triangular configurations currently of most interest are examined. Development of the droplet generator, collector, and auxiliary components are discussed. Radiative performance of a droplet sheet is considered, and experimental results are seen to be in very good agreement with analytical predictions. The collision of droplets in the droplet sheet, the charging of droplets by the space plasma, and the effect of atmospheric drag on the droplet sheet are shown to be of little consequence, or can be minimized by proper design. The LDR is seen to be less susceptible than conventional technology to the effects of micrometeoroids or hostile threats. The identification of working fluids which are stable in the orbital environments of interest is also made. Methods for reducing spacecraft contamination from an LDR to an acceptable level are discussed. Preliminary results of microgravity testing of the droplet generator are presented. Possible future NASA and Air Force missions enhanced or enabled by a LDR are also discussed. System studies indicate that the LDR is potentially less massive than heat pipe radiators. Planned microgravity testing aboard the Shuttle or space station is seen to be a logical next step in LDR development.

  15. Solvents in novolak synthesis

    NASA Astrophysics Data System (ADS)

    Sobodacha, Chet J.; Lynch, Thomas J.; Durham, Dana L.; Paradis, Valerie R.

    1993-09-01

    Novolac resins may be prepared with or without a solvent present. We have found that solvent power greatly affects the properties of the finished resin and thus gives the resist chemist another variable with which to `fine-tune' resist properties. Using designed experiments, we investigated the effect of solvent power, as measured by Hansen's Solubility Parameters, of a number of solvents and solvent mixtures on the final properties of the novolac resin. We found that the relative molecular weight (RMW) and dissolution rate of a novolac resin can be varied by selection of a solvent or solvent mixture with the appropriate polarity and hydrogen- bonding characteristics. The solvent polarity and hydrogen-bonding characteristics may affect the stability of the cresol/formaldehyde transition state, thus causing the observed changes in RMW and dissolution rate.

  16. Solvent Recycling for Shipyards

    DTIC Science & Technology

    1993-05-01

    alternatives to solvent cleaning. Typical equipment types that can be effectively cleaned with recycled solvents include spray guns paint hoses pumps...in place of solvent-based coatings; or equipment changes, such as the use of airless or HVLP systems to reduce paint consumption and overspray...Using mechanical cleaning methods instead of solvent cleaning Change from conventional painting to solventless processes such as thermal spray or powder

  17. NEPTUNIUM SOLVENT EXTRACTION PROCESS

    DOEpatents

    Dawson, L.R.; Fields, P.R.

    1959-10-01

    The separation of neptunium from an aqueous solution by solvent extraction and the extraction of neptunium from the solvent solution are described. Neptunium is separated from an aqueous solution containing tetravalent or hexavalent neptunium nitrate, nitric acid, and a nitrate salting out agent, such as sodium nitrate, by contacting the solution with an organic solvent such as diethyl ether. Subsequently, the neptunium nitrate is extracted from the organic solvent extract phase with water.

  18. Uniform-droplet spray forming

    SciTech Connect

    Blue, C.A.; Sikka, V.K.; Chun, Jung-Hoon; Ando, T.

    1997-04-01

    The uniform-droplet process is a new method of liquid-metal atomization that results in single droplets that can be used to produce mono-size powders or sprayed-on to substrates to produce near-net shapes with tailored microstructure. The mono-sized powder-production capability of the uniform-droplet process also has the potential of permitting engineered powder blends to produce components of controlled porosity. Metal and alloy powders are commercially produced by at least three different methods: gas atomization, water atomization, and rotating disk. All three methods produce powders of a broad range in size with a very small yield of fine powders with single-sized droplets that can be used to produce mono-size powders or sprayed-on substrates to produce near-net shapes with tailored microstructures. The economical analysis has shown the process to have the potential of reducing capital cost by 50% and operating cost by 37.5% when applied to powder making. For the spray-forming process, a 25% savings is expected in both the capital and operating costs. The project is jointly carried out at Massachusetts Institute of Technology (MIT), Tuffs University, and Oak Ridge National Laboratory (ORNL). Preliminary interactions with both finished parts and powder producers have shown a strong interest in the uniform-droplet process. Systematic studies are being conducted to optimize the process parameters, understand the solidification of droplets and spray deposits, and develop a uniform-droplet-system (UDS) apparatus appropriate for processing engineering alloys.

  19. Reduced Graphene Oxide Membranes for Ultrafast Organic Solvent Nanofiltration.

    PubMed

    Huang, Liang; Chen, Ji; Gao, Tiantian; Zhang, Miao; Li, Yingru; Dai, Liming; Qu, Liangti; Shi, Gaoquan

    2016-10-01

    Solvated reduced graphene oxide (S-rGO) membranes are stable in organic solvents, and strong acidic, alkaline, or oxidative media. They show high rejections to small molecules with charges the same as that of S-rGO coatings or neutral molecules larger than 3.4 nm, while retaining their high permeances to organic solvents.

  20. Solvents and sustainable chemistry

    PubMed Central

    Welton, Tom

    2015-01-01

    Solvents are widely recognized to be of great environmental concern. The reduction of their use is one of the most important aims of green chemistry. In addition to this, the appropriate selection of solvent for a process can greatly improve the sustainability of a chemical production process. There has also been extensive research into the application of so-called green solvents, such as ionic liquids and supercritical fluids. However, most examples of solvent technologies that give improved sustainability come from the application of well-established solvents. It is also apparent that the successful implementation of environmentally sustainable processes must be accompanied by improvements in commercial performance. PMID:26730217

  1. Solvent recycle/recovery

    SciTech Connect

    Paffhausen, M.W.; Smith, D.L.; Ugaki, S.N.

    1990-09-01

    This report describes Phase I of the Solvent Recycle/Recovery Task of the DOE Chlorinated Solvent Substitution Program for the US Air Force by the Idaho National Engineering Laboratory, EG G Idaho, Inc., through the US Department of Energy, Idaho Operations Office. The purpose of the task is to identify and test recovery and recycling technologies for proposed substitution solvents identified by the Biodegradable Solvent Substitution Program and the Alternative Solvents/Technologies for Paint Stripping Program with the overall objective of minimizing hazardous wastes. A literature search to identify recycle/recovery technologies and initial distillation studies has been conducted. 4 refs.

  2. Droplets merging through wireless ultrasonic actuation.

    PubMed

    Nayak, Praveen Priyaranjan; Kar, Durga Prasanna; Bhuyan, Satyanarayan

    2016-01-01

    A new technique of droplets merging through wireless ultrasonic actuation has been proposed and experimentally investigated in this work. The proposed method is based on the principle of resonant inductive coupling and piezoelectric resonance. When a mechanical vibration is excited in a piezoelectric plate, the ultrasonic vibration transmitted to the droplets placed on its surface and induces merging. It has been observed that the merging rate of water droplets depends on the operating frequency, mechanical vibration of piezoelectric plate, separation distance between the droplets, and volume of droplets. The investigated technique of droplets merging through piezoelectric actuation is quite useful for microfluidics, chemical and biomedical engineering applications.

  3. Eliminating the interferences from TRIS buffer and SDS in protein analysis by fused-droplet electrospray ionization mass spectrometry.

    PubMed

    Shieh, I-Fan; Lee, Chi-Yang; Shiea, Jentaie

    2005-01-01

    Multiply charged protein ions were detected from the solutions containing a high concentration of tris(hydroxymethyl) aminomethane buffer (TRIS) and sodium dodecyl sulfate (SDS) using fused-droplet electrospray ionization mass spectrometry (FD-ESI/MS). The sample aerosols were generated at ambient temperature with a pneumatic nebulizer commonly used to produce sample aerosols in an atmospheric pressure chemical ionization (APCI) source. The aerosols were carried by nitrogen gas to the tip of a capillary where charged methanol droplets had been continuously generated by electrospraying an acidic methanol solution. The neutral sample aerosols then fused with the charged methanol droplets and electrospray ionization proceeded from the newly formed fused droplets to generate multiply charged protein ions. Because of its low solubility in methanol, TRIS molecules (concentration as high as 1 M) were efficiently excluded from the newly formed droplets and the protein ion signals were detected and observed in the mass spectra. To remove the interferences from SDS, equal moles of positively charged cetyltrimethylammonium bromide (CTAB) was added into the SDS containing sample solution to form the dodecyl sulfate-cetyltrimethylammonium ion pair (DS-CTA). The DS-CTA ion pair has a low polarity and solubility in methanol and is excluded from the fused droplet. Protein ions were still detected from the solution containing 10(-2) M of SDS.

  4. Application of light scattering in studies of transport, thermodynamics, light absorption, and electric properties of single droplets

    NASA Astrophysics Data System (ADS)

    Tu, Haohua

    2001-12-01

    coefficient of an extremely nonvolatile system at room conditions. It is reported that a charged droplet might not explode even above Rayleigh limit and droplet electron emission might happen well below the theoretical expectation.

  5. Droplet burning at zero G

    NASA Technical Reports Server (NTRS)

    Williams, F. A.

    1978-01-01

    Questions of the importance and feasibility of performing experiments on droplet burning at zero gravity in Spacelab were studied. Information on the physics and chemistry of droplet combustion, with attention directed specifically to the chemical kinetics, heat and mass transfer, and fluid mechanics of the phenomena involved, are presented. The work was divided into three phases, the justification, the feasibility, and the conceptual development of a preliminary design. Results from the experiments performed revealed a few new facts concerning droplet burning, notably burning rates in excess of theoretical prediction and a phenomenon of flash extinction, both likely traceable to accumulation of carbon produced by gas-phase pyrolysis in the fuel-rich zone enclosed by the reaction surface. These experiments also showed that they were primarily due to timing difficulties.

  6. Vibration-Induced Droplet Atomization

    NASA Technical Reports Server (NTRS)

    Smith, M. K.; James, A.; Vukasinovic, B.; Glezer, A.

    1999-01-01

    Thermal management is critical to a number of technologies used in a microgravity environment and in Earth-based systems. Examples include electronic cooling, power generation systems, metal forming and extrusion, and HVAC (heating, venting, and air conditioning) systems. One technique that can deliver the large heat fluxes required for many of these technologies is two-phase heat transfer. This type of heat transfer is seen in the boiling or evaporation of a liquid and in the condensation of a vapor. Such processes provide very large heat fluxes with small temperature differences. Our research program is directed toward the development of a new, two-phase heat transfer cell for use in a microgravity environment. In this paper, we consider the main technology used in this cell, a novel technique for the atomization of a liquid called vibration-induced droplet atomization. In this process, a small liquid droplet is placed on a thin metal diaphragm that is made to vibrate by an attached piezoelectric transducer. The vibration induces capillary waves on the free surface of the droplet that grow in amplitude and then begin to eject small secondary droplets from the wave crests. In some situations, this ejection process develops so rapidly that the entire droplet seems to burst into a small cloud of atomized droplets that move away from the diaphragm at speeds of up to 50 cm/s. By incorporating this process into a heat transfer cell, the active atomization and transport of the small liquid droplets could provide a large heat flux capability for the device. Experimental results are presented that document the behavior of the diaphragm and the droplet during the course of a typical bursting event. In addition, a simple mathematical model is presented that qualitatively reproduces all of the essential features we have seen in a burst event. From these two investigations, we have shown that delayed droplet bursting results when the system passes through a resonance

  7. Snell's law and walking droplets

    NASA Astrophysics Data System (ADS)

    Bush, John; Pucci, Giuseppe; Aubin, Benjamin; Brun, Pierre-Thomas; Faria, Luiz

    2016-11-01

    Droplets walking on the surface of a vibrating bath have been shown to exhibit a number of quantum-like features. We here present the results of a combined experimental and theoretical investigation of such droplets crossing a linear step corresponding to a reduction in bath depth. When the step is sufficiently large, the walker reflects off the step; otherwise, it is refracted as it crosses the step. Particular attention is given to an examination of the regime in which the droplet obeys a form of Snell's Law, a behavior captured in accompanying simulations. Attempts to provide theoretical rationale for the dependence of the effective refractive index on the system parameters are described. Supported by NSF through CMMI-1333242.

  8. Walking droplets in linear channels

    NASA Astrophysics Data System (ADS)

    Filoux, Boris; Hubert, Maxime; Schlagheck, Peter; Vandewalle, Nicolas

    2017-01-01

    When a droplet is placed onto a vertically vibrated bath, it can bounce without coalescing. Upon an increase of the forcing acceleration, the droplet is propelled by the wave it generates and becomes a walker with a well-defined speed. We investigate the confinement of a walker in different rectangular cavities, used as waveguides for the Faraday waves emitted by successive droplet bounces. By studying the walker velocities, we discover that one-dimensional confinement is optimal for narrow channels of width of D ≃1.5 λF . Thereby, the walker follows a quasilinear path. We also propose an analogy with waveguide models based on the observation of the Faraday instability within the channels.

  9. A QSPR study on the solvent-induced frequency shifts of acetone and dimethyl sulfoxide in organic solvents

    NASA Astrophysics Data System (ADS)

    Ou, Yu Heng; Chang, Chia Ming; Chen, Ying Shao

    2016-06-01

    In this study, solvent-induced frequency shifts (SIFS) in the infrared spectrum of acetone and dimethyl sulfoxide in organic solvents were investigated by using four types of quantum-chemical reactivity descriptors. The results showed that the SIFS of acetone is mainly affected by the electron-acceptance chemical potential and the maximum nucleophilic condensed local softness of organic solvents, which represent the electron flow and the polarization between acetone and solvent molecules. On the other hand, the SIFS of dimethyl sulfoxide changes with the maximum positive charge of hydrogen atom and the inverse of apolar surface area of solvent molecules, showing that the electrostatic and hydrophilic interactions are main mechanisms between dimethyl sulfoxide and solvent molecules. The introduction of the four-element theory model-based quantitative structure-property relationship approach improved the assessing quality and provided a basis for interpreting the solute-solvent interactions.

  10. A QSPR study on the solvent-induced frequency shifts of acetone and dimethyl sulfoxide in organic solvents.

    PubMed

    Ou, Yu Heng; Chang, Chia Ming; Chen, Ying Shao

    2016-06-05

    In this study, solvent-induced frequency shifts (SIFS) in the infrared spectrum of acetone and dimethyl sulfoxide in organic solvents were investigated by using four types of quantum-chemical reactivity descriptors. The results showed that the SIFS of acetone is mainly affected by the electron-acceptance chemical potential and the maximum nucleophilic condensed local softness of organic solvents, which represent the electron flow and the polarization between acetone and solvent molecules. On the other hand, the SIFS of dimethyl sulfoxide changes with the maximum positive charge of hydrogen atom and the inverse of apolar surface area of solvent molecules, showing that the electrostatic and hydrophilic interactions are main mechanisms between dimethyl sulfoxide and solvent molecules. The introduction of the four-element theory model-based quantitative structure-property relationship approach improved the assessing quality and provided a basis for interpreting the solute-solvent interactions.

  11. Film boiling of mercury droplets

    NASA Technical Reports Server (NTRS)

    Baumeister, K. J.; Schoessow, G. J.; Chmielewski, C. E.

    1975-01-01

    Vaporization times of mercury droplets in Leidenfrost film boiling on a flat horizontal plate are measured in an air atmosphere. Extreme care was used to prevent large amplitude droplet vibrations and surface wetting; therefore, these data can be compared to film boiling theory. Diffusion from the upper surface of the drop appears as a dominant mode of mass transfer from the drop. A closed-form analytical film boiling theory is developed to account for the diffusive evaporation. Reasonable agreement between data and theory is seen.

  12. Microstructures of undercooled germanium droplets

    NASA Technical Reports Server (NTRS)

    Devaud, G.; Turnbull, D.

    1987-01-01

    Undercoolings at crystal nucleation onset of liquid Ge droplets are measured and the microstructures of the droplets are examined. Undercooling values ranging from 150-415 + or 20 C were obtained. It is observed that for the samples undercooled less than 300 C prior to solidification the grain size was greater than 100 microns; for samples undercooled between 300-400 C the grain size was between 50-100 microns; and for samples undercooled greater than 400 C the grain size was 10-20 microns. Consideration is given to dendritic growth and interfacial undercooling. It is noted that there is a correlation between undercooling and as-crystallized grain structure.

  13. Film boiling of mercury droplets

    NASA Technical Reports Server (NTRS)

    Baumeister, K. J.; Schoessow, G. J.; Chmielewski, C. E.

    1975-01-01

    Vaporization times of mercury droplets in Leidenfrost film boiling on a flat horizontal plate are measured in an air atmosphere. Extreme care was used to prevent large amplitude droplet vibrations and surface wetting; therefore, these data can be compared to film boiling theory. For these data, diffusion from the upper surface of the drop is a dominant mode of mass transfer from the drop. A closed-form analytical film boiling theory is developed to account for the diffusive evaporation. Reasonable agreement between data and theory is seen.

  14. Charge fluctuations in nanoscale capacitors.

    PubMed

    Limmer, David T; Merlet, Céline; Salanne, Mathieu; Chandler, David; Madden, Paul A; van Roij, René; Rotenberg, Benjamin

    2013-09-06

    The fluctuations of the charge on an electrode contain information on the microscopic correlations within the adjacent fluid and their effect on the electronic properties of the interface. We investigate these fluctuations using molecular dynamics simulations in a constant-potential ensemble with histogram reweighting techniques. This approach offers, in particular, an efficient, accurate, and physically insightful route to the differential capacitance that is broadly applicable. We demonstrate these methods with three different capacitors: pure water between platinum electrodes and a pure as well as a solvent-based organic electrolyte each between graphite electrodes. The total charge distributions with the pure solvent and solvent-based electrolytes are remarkably Gaussian, while in the pure ionic liquid the total charge distribution displays distinct non-Gaussian features, suggesting significant potential-driven changes in the organization of the interfacial fluid.

  15. Charge Fluctuations in Nanoscale Capacitors

    NASA Astrophysics Data System (ADS)

    Limmer, David T.; Merlet, Céline; Salanne, Mathieu; Chandler, David; Madden, Paul A.; van Roij, René; Rotenberg, Benjamin

    2013-09-01

    The fluctuations of the charge on an electrode contain information on the microscopic correlations within the adjacent fluid and their effect on the electronic properties of the interface. We investigate these fluctuations using molecular dynamics simulations in a constant-potential ensemble with histogram reweighting techniques. This approach offers, in particular, an efficient, accurate, and physically insightful route to the differential capacitance that is broadly applicable. We demonstrate these methods with three different capacitors: pure water between platinum electrodes and a pure as well as a solvent-based organic electrolyte each between graphite electrodes. The total charge distributions with the pure solvent and solvent-based electrolytes are remarkably Gaussian, while in the pure ionic liquid the total charge distribution displays distinct non-Gaussian features, suggesting significant potential-driven changes in the organization of the interfacial fluid.

  16. Materials science: Droplets leap into action

    NASA Astrophysics Data System (ADS)

    Vollmer, Doris; Butt, Hans-Jürgen

    2015-11-01

    What could cause a water droplet to start bouncing on a surface? It seems that a combination of evaporation and a highly water-repellent surface induces droplet bouncing when ambient pressure is reduced. See Letter p.82

  17. Ice and water droplets on graphite: A comparison of quantum and classical simulations

    SciTech Connect

    Ramírez, Rafael; Singh, Jayant K.; Müller-Plathe, Florian; Böhm, Michael C.

    2014-11-28

    Ice and water droplets on graphite have been studied by quantum path integral and classical molecular dynamics simulations. The point-charge q-TIP4P/F potential was used to model the interaction between flexible water molecules, while the water-graphite interaction was described by a Lennard-Jones potential previously used to reproduce the macroscopic contact angle of water droplets on graphite. Several energetic and structural properties of water droplets with sizes between 10{sup 2} and 10{sup 3} molecules were analyzed in a temperature interval of 50–350 K. The vibrational density of states of crystalline and amorphous ice drops was correlated to the one of ice Ih to assess the influence of the droplet interface and molecular disorder on the vibrational properties. The average distance of covalent OH bonds is found 0.01 Å larger in the quantum limit than in the classical one. The OO distances are elongated by 0.03 Å in the quantum simulations at 50 K. Bond distance fluctuations are large as a consequence of the zero-point vibrations. The analysis of the H-bond network shows that the liquid droplet is more structured in the classical limit than in the quantum case. The average kinetic and potential energy of the ice and water droplets on graphite has been compared with the values of ice Ih and liquid water as a function of temperature. The droplet kinetic energy shows a temperature dependence similar to the one of liquid water, without apparent discontinuity at temperatures where the droplet is solid. However, the droplet potential energy becomes significantly larger than the one of ice or water at the same temperature. In the quantum limit, the ice droplet is more expanded than in a classical description. Liquid droplets display identical density profiles and liquid-vapor interfaces in the quantum and classical limits. The value of the contact angle is not influenced by quantum effects. Contact angles of droplets decrease as the size of the water droplet

  18. Droplet centrifugation, droplet DNA extraction, and rapid droplet thermocycling for simpler and faster PCR assay using wire-guided manipulations

    PubMed Central

    2012-01-01

    A computer numerical control (CNC) apparatus was used to perform droplet centrifugation, droplet DNA extraction, and rapid droplet thermocycling on a single superhydrophobic surface and a multi-chambered PCB heater. Droplets were manipulated using “wire-guided” method (a pipette tip was used in this study). This methodology can be easily adapted to existing commercial robotic pipetting system, while demonstrated added capabilities such as vibrational mixing, high-speed centrifuging of droplets, simple DNA extraction utilizing the hydrophobicity difference between the tip and the superhydrophobic surface, and rapid thermocycling with a moving droplet, all with wire-guided droplet manipulations on a superhydrophobic surface and a multi-chambered PCB heater (i.e., not on a 96-well plate). Serial dilutions were demonstrated for diluting sample matrix. Centrifuging was demonstrated by rotating a 10 μL droplet at 2300 round per minute, concentrating E. coli by more than 3-fold within 3 min. DNA extraction was demonstrated from E. coli sample utilizing the disposable pipette tip to cleverly attract the extracted DNA from the droplet residing on a superhydrophobic surface, which took less than 10 min. Following extraction, the 1500 bp sequence of Peptidase D from E. coli was amplified using rapid droplet thermocycling, which took 10 min for 30 cycles. The total assay time was 23 min, including droplet centrifugation, droplet DNA extraction and rapid droplet thermocycling. Evaporation from of 10 μL droplets was not significant during these procedures, since the longest time exposure to air and the vibrations was less than 5 min (during DNA extraction). The results of these sequentially executed processes were analyzed using gel electrophoresis. Thus, this work demonstrates the adaptability of the system to replace many common laboratory tasks on a single platform (through re-programmability), in rapid succession (using droplets), and with a high level of

  19. Sophisticated compound droplets on fiber networks

    NASA Astrophysics Data System (ADS)

    Weyer, Floriane; Lismont, Marjorie; Dreesen, Laurent; Vandewalle, Nicolas

    2015-11-01

    Droplets on fibers are part of our everyday lives. Indeed, many phenomena involve drops and fibers such as the formation of dew droplets on a spiderweb, the trapping of water droplets on cactus spines or the dyeing of cotton or wool fibers. Therefore, this topic has been widely studied in the recent years and it appears that droplets on fibers can be the starting point for an open digital microfluidics. We study the behavior of soapy water droplets on a fiber array. When a droplet slides along a vertical fiber and encounters a horizontal fiber, it can either stick there or continue its way. In the latter case, the droplet releases a tiny residue. We study the volume of these residues depending on the geometry of the node. By using this technique, a large number of small droplets can be trapped at the nodes of a fiber array. These residues can be encapsulated and collected by an oil droplet in order to create a multicompound droplet. Moreover, by using optical fibers, we can provoke and detect the fluorescence of the inner droplets. Fibers provide therefore an original way to study compound droplets and multiple reactions. F. Weyer is financially supported by an FNRS grant. This work is also supported by the FRFC 2.4504.12.

  20. Water droplet impact on elastic superhydrophobic surfaces

    PubMed Central

    Weisensee, Patricia B.; Tian, Junjiao; Miljkovic, Nenad; King, William P.

    2016-01-01

    Water droplet impact on surfaces is a ubiquitous phenomenon in nature and industry, where the time of contact between droplet and surface influences the transfer of mass, momentum and energy. To manipulate and reduce the contact time of impacting droplets, previous publications report tailoring of surface microstructures that influence the droplet - surface interface. Here we show that surface elasticity also affects droplet impact, where a droplet impacting an elastic superhydrophobic surface can lead to a two-fold reduction in contact time compared to equivalent rigid surfaces. Using high speed imaging, we investigated the impact dynamics on elastic nanostructured superhydrophobic substrates having membrane and cantilever designs with stiffness 0.5–7630 N/m. Upon impact, the droplet excites the substrate to oscillate, while during liquid retraction, the substrate imparts vertical momentum back to the droplet with a springboard effect, causing early droplet lift-off with reduced contact time. Through detailed experimental and theoretical analysis, we show that this novel springboarding phenomenon is achieved for a specific range of Weber numbers (We >40) and droplet Froude numbers during spreading (Fr >1). The observation of the substrate elasticity-mediated droplet springboard effect provides new insight into droplet impact physics. PMID:27461899

  1. Solute and solvent dynamics in confined equal-sized aqueous environments of charged and neutral reverse micelles: a combined dynamic fluorescence and all-atom molecular dynamics simulation study.

    PubMed

    Guchhait, Biswajit; Biswas, Ranjit; Ghorai, Pradip K

    2013-03-28

    Here a combined dynamic fluorescence and all-atom molecular dynamics simulation study of aqueous pool-size dependent solvation energy and rotational relaxations of a neutral dipolar solute, C153, trapped in AOT (charged) and IGPAL (neutral) reverse micelles (RMs) at 298 K, is described. RMs in simulations have been represented by a reduced model where SPC/E water molecules interact with a trapped C153 that possesses realistic charge distributions for both ground and excited states. In large aqueous pools, measured average solvation and rotation rates are smaller for the neutral RMs than those in charged ones. Interestingly, while the measured average solvation and rotation rates increase with pool size for the charged RMs, the average rotation rates for the neutral RMs exhibit a reverse dependence. Simulations have qualitatively reproduced this experimental trend and suggested interfacial location for the solute for all cases. The origin for the subnanosecond Stokes shift dynamics has been investigated and solute-interface interaction contribution quantified. Simulated layer-wise translational and rotational diffusions of water molecules re-examine the validity of the core-shell model and provide a resolution to a debate regarding the origin of the subnanosecond solvation component in dynamic Stokes shift measurements with aqueous RMs but not detected in ultrafast IR measurements.

  2. Shock wave-droplet interaction

    NASA Astrophysics Data System (ADS)

    Habibi Khoshmehr, Hamed; Krechetnikov, Rouslan

    2016-11-01

    Disintegration of a liquid droplet under the action of a shock wave is experimentally investigated. The shock wave-pulse is electromagnetically generated by discharging a high voltage capacitor into a flat spiral coil, above which an isolated circular metal membrane is placed in a close proximity. The Lorentz force arising due to the eddy current induced in the membrane abruptly accelerates it away from the spiral coil thus generating a shock wave. The liquid droplet placed at the center of the membrane, where the maximum deflection occurs, is disintegrated in the process of interaction with the shock wave. The effects of droplet viscosity and surface tension on the droplet destruction are studied with high-speed photography. Water-glycerol solution at different concentrations is used for investigating the effect of viscosity and various concentrations of water-sugar and water-ethanol solution are used for studying the effect of surface tension. Here we report on how the metamorphoses, which a liquid drop undergoes in the process of interaction with a shock wave, are affected by varied viscosity and surface tension.

  3. Helium Droplets Doped with Sulfur and C60

    PubMed Central

    2014-01-01

    Clusters of sulfur are grown by passing superfluid helium nanodroplets through a pickup cell filled with sulfur vapor. In some experiments the droplets are codoped with C60. The doped droplets are collided with energetic electrons and the abundance distributions of positively and negatively charged cluster ions are recorded. We report, specifically, distributions of Sm+, Sm–, and C60Sm– containing up to 41 sulfur atoms. We also observe complexes of sulfur cluster anions with helium; distributions are presented for HenSm– with n ≤ 31 and m ≤ 3. The similarity between anionic and cationic C60Sm± spectra is in striking contrast to the large differences between spectra of Sm+ and Sm–. PMID:26045732

  4. Electrically Controllable Microparticle Synthesis and Digital Microfluidic Manipulation by Electric-Field-Induced Droplet Dispensing into Immiscible Fluids

    NASA Astrophysics Data System (ADS)

    Um, Taewoong; Hong, Jiwoo; Kang, In Seok

    2016-11-01

    The dispensing of tiny droplets is a basic and crucial process in a myriad of applications, such as DNA/protein microarray, cell cultures, chemical synthesis of microparticles, and digital microfluidics. This work demonstrates the droplet dispensing into immiscible fluids through electric charge concentration (ECC) method. Three main modes (i.e., attaching, uniform and bursting modes) are exhibited as a function of flow rates, applied voltage and gap distance between the nozzle and the oil surface. Through a conventional nozzle with diameter of a few millimeters, charged droplets with volumes ranging from a few μL to a few tens of nL can be uniformly dispensed into the oil chamber without reduction in nozzle size. Based on the features of the proposed method (e.g., formation of droplets with controllable polarity and amount of electric charge in water and oil system), a simple and straightforward method is developed for microparticle synthesis, including preparation for colloidosomes and fabrication of Janus microparticles with anisotropic internal structures. Finally, a combined system consisting of ECC-induced droplet dispensing and electrophoresis of charged droplet (ECD)-driven manipulation systems is constructed. This work was supported by the BK21Plus Program for advanced education of creative chemical engineers of the National Research Foundation of Korea (NRF) Grant funded by the Korea government (MSIP).

  5. Spreading of Thin Droplets of Perfect and Leaky Dielectric Liquids on Inclined Surfaces.

    PubMed

    Corbett, Andrew; Kumar, Satish

    2016-07-05

    The spreading of droplets may be influenced by electric fields, a situation that is relevant to applications such as coating, printing, and microfluidics. In this work we study the effects of an electric field on the gravity-driven spreading of two-dimensional droplets down an inclined plane. We consider both perfect and leaky dielectric liquids, as well as perfectly and partially wetting systems. In addition to the effects of electric fields, we examine the use of thermocapillary forces to suppress the growth of the capillary ridge near the droplet front. Lubrication theory is applied to generate a set of coupled partial differential equations for interfacial height and charge, which are then solved numerically with a finite-difference method. Electric fields increase the height of the capillary ridge in both perfect and leaky dielectric droplets due to electrostatic pressure gradients that drive liquid into the ridge. In leaky dielectrics, large interfacial charge gradients in the contact-line region create shear stresses that also enhance ridge growth and the formation of trailing minor ridges. The coalescence of these ridges can significantly affect the long-time thinning rate of leaky dielectric droplets. In partially wetting liquids, electric fields promote the splitting of smaller droplets from the primary droplet near the receding contact line due to the interplay between electrostatic forces and disjoining pressure. Cooling from below and heating from above generates thermocapillary forces that counteract the effects of electric fields and suppress the growth of the capillary ridge. The results of this work have important implications for manipulating the spreading of droplets down inclined surfaces.

  6. Time resolved spectroscopy of 2-(dimethylamine)fluorene. Solvent effects and photophysical behavior

    NASA Astrophysics Data System (ADS)

    Sánchez, Francisco G.; Díaz, Aurora N.; Algarra, Manuel; Lovillo, Josefa; Aguilar, Alfonso

    2011-12-01

    The effect of different solvents on the fluorescent properties of 2-(dimethylamine)fluorene (DAF) were studied. In aprotic solvents we detected a strongly emissive intramolecular charge transfer (ICT) state that decayed by intersystem crossing to triplet. In proton-accepting solvents DAF exhibits in the excited state an intramolecular proton transfer. An ionized species is postulated, which simultaneously twists to a rotated conformation in the excited state. Thus, the specific solvent interactions supplement but do not replace the twist mechanism and accompany the charge transfer accepted as the prerequisite for twisted intramolecular charged transfer (TICT) state formation.

  7. Induction Charge Detector with Multiple Sensing Stages

    NASA Technical Reports Server (NTRS)

    Gamero-Castano, Manuel

    2008-01-01

    An induction charge detector with multiple sensing stages has been conceived for use in characterizing sprayed droplets, dust particles, large ionized molecules, and the like. Like related prior single-stage devices, each stage yields a measurement of the electric charge and the time of flight of the particle. In effect, an n-stage sensor yields n independent sets of such measurements from the same particle. The benefit of doing this is to increase the effective signal-to-noise ratio and thereby lower the charge-detection limit and the standard error of the charge measurement.

  8. Formation and Levitation of Unconfined Droplet Clusters

    NASA Technical Reports Server (NTRS)

    Liu, S.; Ruff, G. A.

    1999-01-01

    Combustion experiments using arrays of droplets seek to provide a link between single droplet combustion phenomena and the behavior of complex spray combustion systems. Both single droplet and droplet array studies have been conducted in microgravity to better isolate the droplet interaction phenomena and eliminate or reduce the confounding effects of buoyancy-induced convection. In most experiments involving droplet arrays, the droplets are supported on fibers to keep them stationary and close together before the combustion event. The presence of the fiber, however, disturbs the combustion process by introducing a source of heat transfer and asymmetry into the configuration. As the number of drops in a droplet array increases, supporting the drops on fibers becomes less practical because of the cumulative effect of the fibers on the combustion process. The overall objective of this research is to study the combustion of well-characterized drop clusters in a microgravity environment. Direct experimental observations and measurements of the combustion of droplet clusters would fill a large gap in our current understanding of droplet and spray combustion and provide unique experimental data for the verification and improvement of spray combustion models. This paper describes current work on the design and performance of an apparatus to generate and stabilize droplet clusters using acoustic and electrostatic forces.

  9. Passive droplet sorting using viscoelastic flow focusing.

    PubMed

    Hatch, Andrew C; Patel, Apurva; Beer, N Reginald; Lee, Abraham P

    2013-04-07

    We present a study of passive hydrodynamic droplet sorting in microfluidic channels based on intrinsic viscoelastic fluid properties. Sorting is achieved by tuning the droplets' intrinsic viscous and viscoelastic properties relative to the continuous oil phase to achieve a positive or negative lateral migration toward high or low shear gradients in the channel. In the presence of weakly viscoelastic fluid behavior, droplets with a viscosity ratio, κ, between 0.5-10 were found to migrate toward a high shear gradient near the channel walls. For all other κ-values, or Newtonian fluids, droplets would migrate toward a low shear gradient at the channel centerline. It was also found that for strongly viscoelastic fluids with low interfacial tension, droplets would migrate toward the edge even with κ-values lower than 0.5. The resulting bi-directional lateral droplet migration between different droplets allows size-independent sorting. Still, their sorting efficiencies are dependent on droplet size, intrinsic fluid elasticity, viscosity, droplet deformability, and overall fluid shear rates. Based on these findings, we demonstrate >200 Hz passive droplet sorting frequencies and achieve >100 fold enrichment factors without the need to actively sense and/or control active mechanisms. Using a low viscosity oil phase of 6.25 cPs, we demonstrate sorting discrimination of 1 cPs and 5 cPs aqueous droplets with κ-values of 0.2 and 0.8 respectively.

  10. Thermophoresis of water droplets inside carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Zambrano, Harvey; Walther, Jh; Oyarzua, Elton; Rojano, Andres

    2016-11-01

    Carbon Nanotubes (CNTs) offer unique possibilities as fluid conduits with applications ranging from lab on a chip devices to encapsulation media for drug delivery. CNTs feature high mechanical strength, chemical and thermal stability and biocompatibility therefore they are promising candidates for nanodevice fabrication. Thermal gradients have been proposed as mechanism to drive particles, fullerenes and droplets inside CNTs. Here, by conducting Molecular Dynamics (MD) simulations, we study thermophoresis of water droplets inside CNTs. We systematically change the size of the droplets, the axial thermal gradient and CNT chirality. We find that the droplet motion in the armchair CNTs exhibits two clearly delimited stages, a regime wherein the droplet is accelerated and subsequently, a regime wherein the droplet moves with constant velocity. Inside the zig zag CNTs, the droplet accelerates during a very short time and then it moves with constant velocity. We compute the net force during the droplet acceleration and find a correlation between the droplet acceleration and the magnitude of the thermal gradient without any dependence on the droplet size. Moreover, we conduct velocity constrained MD simulations to determine the friction and thermophoretic forces acting on the droplet. We acknowledge partial funding from FONDECYT through the Project No. 11130559 and from VRID Universidad de Concepcion.

  11. Dynamics of droplet motion under electrowetting actuation.

    PubMed

    Annapragada, S Ravi; Dash, Susmita; Garimella, Suresh V; Murthy, Jayathi Y

    2011-07-05

    The static shape of droplets under electrowetting actuation is well understood. The steady-state shape of the droplet is obtained on the basis of the balance of surface tension and electrowetting forces, and the change in the apparent contact angle is well characterized by the Young-Lippmann equation. However, the transient droplet shape behavior when a voltage is suddenly applied across a droplet has received less attention. Additional dynamic frictional forces are at play during this transient process. We present a model to predict this transient behavior of the droplet shape under electrowetting actuation. The droplet shape is modeled using the volume of fluid method. The electrowetting and dynamic frictional forces are included as an effective dynamic contact angle through a force balance at the contact line. The model is used to predict the transient behavior of water droplets on smooth hydrophobic surfaces under electrowetting actuation. The predictions of the transient behavior of droplet shape and contact radius are in excellent agreement with our experimental measurements. The internal fluid motion is explained, and the droplet motion is shown to initiate from the contact line. An approximate mathematical model is also developed to understand the physics of the droplet motion and to describe the overall droplet motion and the contact line velocities.

  12. SOLVENT EXTRACTION OF NEPTUNIUM

    DOEpatents

    Butler, J.P.

    1958-08-12

    A process is described for the recovery of neptuniunn from dissolver solutions by solvent extraction. The neptunium containing solution should be about 5N, in nitric acid.and about 0.1 M in ferrous ion. The organic extracting agent is tributyl phosphate, and the neptuniunn is recovered from the organic solvent phase by washing with water.

  13. Solvent-free synthesis

    EPA Science Inventory

    This chapter gives a brief introduction about solvent-free reactions whose importance can be gauged by the increasing number of publications every year during the last decade. The mechanistic aspects of the reactions under solvent-free conditions have been highlighted. Our observ...

  14. Active droplet sorting in microfluidics: a review.

    PubMed

    Xi, Heng-Dong; Zheng, Hao; Guo, Wei; Gañán-Calvo, Alfonso M; Ai, Ye; Tsao, Chia-Wen; Zhou, Jun; Li, Weihua; Huang, Yanyi; Nguyen, Nam-Trung; Tan, Say Hwa

    2017-02-28

    The ability to manipulate and sort droplets is a fundamental issue in droplet-based microfluidics. Various lab-on-a-chip applications can only be realized if droplets are systematically categorized and sorted. These micron-sized droplets act as ideal reactors which compartmentalize different biological and chemical reagents. Array processing of these droplets hinges on the competence of the sorting and integration into the fluidic system. Recent technological advances only allow droplets to be actively sorted at the rate of kilohertz or less. In this review, we present state-of-the-art technologies which are implemented to efficiently sort droplets. We classify the concepts according to the type of energy implemented into the system. We also discuss various key issues and provide insights into various systems.

  15. Enhanced Droplet Control by Transition Boiling

    NASA Astrophysics Data System (ADS)

    Grounds, Alex; Still, Richard; Takashina, Kei

    2012-10-01

    A droplet of water on a heated surface can levitate over a film of gas produced by its own evaporation in the Leidenfrost effect. When the surface is prepared with ratchet-like saw-teeth topography, these droplets can self-propel and can even climb uphill. However, the extent to which the droplets can be controlled is limited by the physics of the Leidenfrost effect. Here, we show that transition boiling can be induced even at very high surface temperatures and provide additional control over the droplets. Ratchets with acute protrusions enable droplets to climb steeper inclines while ratchets with sub-structures enable their direction of motion to be controlled by varying the temperature of the surface. The droplets' departure from the Leidenfrost regime is assessed by analysing the sound produced by their boiling. We anticipate these techniques will enable the development of more sophisticated methods for controlling small droplets and heat transfer.

  16. 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.

  17. Alternative Green Solvents Project

    NASA Technical Reports Server (NTRS)

    Maloney, Phillip R.

    2012-01-01

    Necessary for safe and proper functioning of equipment. Mainly halogenated solvents. Tetrachloride, Trichloroethylene (TCE), CFC-113. No longer used due to regulatory/safety concerns. Precision Cleaning at KSC: Small % of total parts. Used for liquid oxygen (LOX) systems. Dual solvent process. Vertrel MCA (decafluoropentane (DFP) and trons-dichloroethylene) HFE-7100. DFP has long term environmental concerns. Project Goals: a) Identify potential replacements. b) 22 wet chemical processes. c) 3 alternative processes. d) Develop test procedures. e) Contamination and cleaning. f) Analysis. g) Use results to recommend alternative processes. Conclusions: a) No alternative matched Vertrel in this study. b) No clear second place solvent. c) Hydrocarbons- easy; Fluorinated greases- difficult. d) Fluorinated component may be needed in replacement solvent. e) Process may need to make up for shortcoming of the solvent. f) Plasma and SCC02 warrant further testing.

  18. Integrated microfluidic system capable of size-specific droplet generation with size-dependent droplet separation.

    PubMed

    Lee, Sangmin; Hong, Seok Jun; Yoo, Hyung Jung; Ahn, Jae Hyun; Cho, Dong-il Dan

    2013-06-01

    Droplet-based microfluidics is receiving much attention in biomedical research area due to its advantage in uniform size droplet generation. Our previous results have reported that droplet size plays an important role in drug delivery actuated by flagellated bacteria. Recently, many research groups have been reported the size-dependent separation of emulsion droplets by a microfluidic system. In this paper, an integrated microfluidic system is proposed to produce and sort specificsized droplets sequentially. Operation of the system relies on two microfluidic transport processes: initial generation of droplets by hydrodynamic focusing and subsequent separation of droplets by a T-junction channel. The microfluidic system is fabricated by the SU-8 rapid prototyping method and poly-di-methyl-siloxane (PDMS) replica molding. A biodegradable polymer, poly-capro-lactone (PCL), is used for the droplet material. Using the proposed integrated microfluidic system, specific-sized droplets which can be delivered by flagellated bacteria are successfully generated and obtained.

  19. Droplet actuator analyzer with cartridge

    NASA Technical Reports Server (NTRS)

    Smith, Gregory F. (Inventor); Sturmer, Ryan A. (Inventor); Paik, Philip Y. (Inventor); Srinivasan, Vijay (Inventor); Pollack, Michael G. (Inventor); Pamula, Vamsee K. (Inventor); Brafford, Keith R. (Inventor); West, Richard M. (Inventor)

    2011-01-01

    A droplet actuator with cartridge is provided. According to one embodiment, a sample analyzer is provided and includes an analyzer unit comprising electronic or optical receiving means, a cartridge comprising self-contained droplet handling capabilities, and a wherein the cartridge is coupled to the analyzer unit by a means which aligns electronic and/or optical outputs from the cartridge with electronic or optical receiving means on the analyzer unit. According to another embodiment, a sample analyzer is provided and includes a sample analyzer comprising a cartridge coupled thereto and a means of electrical interface and/or optical interface between the cartridge and the analyzer, whereby electrical signals and/or optical signals may be transmitted from the cartridge to the analyzer.

  20. Recent developments in droplet epitaxy

    SciTech Connect

    Mano, Takaaki; Jo, Masafumi; Kuroda, Takashi; Abbarchi, Marco; Noda, Takeshi; Sakoda, Kazuaki

    2014-05-15

    The droplet epitaxy allows for self-assembly of lattice-matched GaAs quantum dots (QDs) with high quality and high uniformity. In this article, we show our efforts to realize the GaAs QDs with excellent optical properties. After the optimization of the several growth processes, we achieved current-injection lasing in the GaAs QDs. In addition, formation of further advanced nanostructure is presented.

  1. Separation of gas from solvent by membrane technology

    SciTech Connect

    Beaupre, R.F.; Jung, D.Y.

    1991-02-26

    This patent describes the method of separating a charge rich liquid containing gas dissolved in solvent. It comprises: maintaining the charge rich liquid containing gas dissolved in solvent therefore in liquid phase in contact with a gas-permeable, essentially solvent impermeable membrane of pore size of less than about 1000 A and molecular weight cutoff of below about 1,000 selected from the group consisting of cellulose acetate membrane, hydrolyzed cellulose membrane, and polyethyleneimine membrane, and; maintaining a pressure drop across the gas-permeable essentially solvent-impermeable membrane; passing the gas from the charge rich liquid containing gas dissolved in solvent therefore at the higher pressure side of the membrane through the membrane thereby forming lean liquid containing decreased quantities of gas dissolved in solvent on the higher pressure side of the membrane and, on the lower pressure side of the membrane, gas containing decreased quantities of liquid; recovering lean liquid containing decreased quantities of gas dissolved in solvent from the high pressure side of the membrane; and recovering gas containing decreased quantities of liquid from the lower pressure side of the membrane.

  2. SOLVENT EXTRACTION PROCESS

    DOEpatents

    Jonke, A.A.

    1957-10-01

    In improved solvent extraction process is described for the extraction of metal values from highly dilute aqueous solutions. The process comprises contacting an aqueous solution with an organic substantially water-immiscible solvent, whereby metal values are taken up by a solvent extract phase; scrubbing the solvent extract phase with an aqueous scrubbing solution; separating an aqueous solution from the scrubbed solvent extract phase; and contacting the scrubbed solvent phase with an aqueous medium whereby the extracted metal values are removed from the solvent phase and taken up by said medium to form a strip solution containing said metal values, the aqueous scrubbing solution being a mixture of strip solution and an aqueous solution which contains mineral acids anions and is free of the metal values. The process is particularly effective for purifying uranium, where one starts with impure aqueous uranyl nitrate, extracts with tributyl phosphate dissolved in carbon tetrachloride, scrubs with aqueous nitric acid and employs water to strip the uranium from the scrubbed organic phase.

  3. Splash Suppression by Solvent Viscosity in Dense Suspension Impact

    NASA Astrophysics Data System (ADS)

    Zhang, Wendy; Dodge, Kevin; Peters, Ivo; Klein Schaarsberg, Martin; Jaeger, Heinrich

    2015-03-01

    When a dense suspension droplet impacts a hard surface, it will either break apart (``splash'') or remain in a compact configuration without ejecting any particles. We use experiments and discrete particle simulations in which relative particle motions are penalized by lubrication-flow drag to analyze the influence of solvent viscosity on splashing. We find that suspension splash is driven by particle inertia. It can be suppressed in 2 different ways. At low solvent viscosity, lubrication drag due to viscous flow has a negligible effect. Splash is suppressed by surface tension overcoming particle inertia. At high solvent viscosity, lubrication drag alone suppresses splashing. Because impact produces an expanding flow that stretches the suspension radially, suppression in the high-viscosity regime is largely accomplished by lubrication-flow drag preventing initially nearby particle pairs from separating fully. Energy dissipation by viscous flow during collisions plays a smaller role. Present Address: Physics of Fluids Group, University of Twente.

  4. Vortices catapult droplets in atomization

    SciTech Connect

    Jerome, J. John Soundar Zaleski, Stéphane; Hoepffner, Jérôme; Marty, Sylvain; Matas, Jean-Philippe

    2013-11-15

    A droplet ejection mechanism in planar two-phase mixing layers is examined. Any disturbance on the gas-liquid interface grows into a Kelvin-Helmholtz wave, and the wave crest forms a thin liquid film that flaps as the wave grows downstream. Increasing the gas speed, it is observed that the film breaks up into droplets which are eventually thrown into the gas stream at large angles. In a flow where most of the momentum is in the horizontal direction, it is surprising to observe these large ejection angles. Our experiments and simulations show that a recirculation region grows downstream of the wave and leads to vortex shedding similar to the wake of a backward-facing step. The ejection mechanism results from the interaction between the liquid film and the vortex shedding sequence: a recirculation zone appears in the wake of the wave and a liquid film emerges from the wave crest; the recirculation region detaches into a vortex and the gas flow over the wave momentarily reattaches due to the departure of the vortex; this reattached flow pushes the liquid film down; by now, a new recirculation vortex is being created in the wake of the wave—just where the liquid film is now located; the liquid film is blown up from below by the newly formed recirculation vortex in a manner similar to a bag-breakup event; the resulting droplets are catapulted by the recirculation vortex.

  5. Vortices catapult droplets in atomization

    NASA Astrophysics Data System (ADS)

    Jerome, J. John Soundar; Marty, Sylvain; Matas, Jean-Philippe; Zaleski, Stéphane; Hoepffner, Jérôme

    2013-11-01

    A droplet ejection mechanism in planar two-phase mixing layers is examined. Any disturbance on the gas-liquid interface grows into a Kelvin-Helmholtz wave, and the wave crest forms a thin liquid film that flaps as the wave grows downstream. Increasing the gas speed, it is observed that the film breaks up into droplets which are eventually thrown into the gas stream at large angles. In a flow where most of the momentum is in the horizontal direction, it is surprising to observe these large ejection angles. Our experiments and simulations show that a recirculation region grows downstream of the wave and leads to vortex shedding similar to the wake of a backward-facing step. The ejection mechanism results from the interaction between the liquid film and the vortex shedding sequence: a recirculation zone appears in the wake of the wave and a liquid film emerges from the wave crest; the recirculation region detaches into a vortex and the gas flow over the wave momentarily reattaches due to the departure of the vortex; this reattached flow pushes the liquid film down; by now, a new recirculation vortex is being created in the wake of the wave—just where the liquid film is now located; the liquid film is blown up from below by the newly formed recirculation vortex in a manner similar to a bag-breakup event; the resulting droplets are catapulted by the recirculation vortex.

  6. Grating droplets with a mesh

    NASA Astrophysics Data System (ADS)

    Soto, Dan; Le Helloco, Antoine; Clanet, Cristophe; Quere, David; Varanasi, Kripa

    2016-11-01

    A drop thrown against a mesh can pass through its holes if impacting with enough inertia. As a result, although part of the droplet may remain on one side of the sieve, the rest will end up grated through the other side. This inexpensive method to break up millimetric droplets into micrometric ones may be of particular interest in a wide variety of applications: enhancing evaporation of droplets launched from the top of an evaporative cooling tower or preventing drift of pesticides sprayed above crops by increasing their initial size and atomizing them at the very last moment with a mesh. In order to understand how much liquid will be grated we propose in this presentation to start first by studying a simpler situation: a drop impacting a plate pierced with a single off centered hole. The study of the role of natural parameters such as the radius drop and speed or the hole position, size and thickness allows us to discuss then the more general situation of a plate pierced with multiple holes: the mesh.

  7. Droplet Core Nuclear Rocket (DCNR)

    NASA Technical Reports Server (NTRS)

    Anghaie, Samim

    1991-01-01

    The most basic design feature of the droplet core nuclear reactor is to spray liquid uranium into the core in the form of droplets on the order of five to ten microns in size, to bring the reactor to critical conditions. The liquid uranium fuel ejector is driven by hydrogen, and more hydrogen is injected from the side of the reactor to about one and a half meters from the top. High temperature hydrogen is expanded through a nozzle to produce thrust. The hydrogen pressure in the system can be somewhere between 50 and 500 atmospheres; the higher pressure is more desirable. In the lower core region, hydrogen is tangentially injected to serve two purposes: (1) to provide a swirling flow to protect the wall from impingement of hot uranium droplets: (2) to generate a vortex flow that can be used for fuel separation. The reactor is designed to maximize the energy generation in the upper region of the core. The system can result in and Isp of 2000 per second, and a thrust-to-weight ratio of 1.6 for the shielded reactor. The nuclear engine system can reduce the Mars mission duration to less than 200 days. It can reduce the hydrogen consumption by a factor of 2 to 3, which reduces the hydrogen load by about 130 to 150 metric tons.

  8. Droplet impact on a fiber

    NASA Astrophysics Data System (ADS)

    Kim, Sung-Gil; Kim, Taehong; Kim, Wonjung

    2015-11-01

    We present the results of a combined experimental and theoretical investigation of drop impact on a fiber. We use high-speed videography to characterize the dynamics of drops impacting fibers. Our systematical experiments reveal that the outcome of droplet collision critically depends on the relative magnitude of inertial to capillary forces and the ratio of the thickness of fiber to the diameter of the drop. We identify three outcomes of the collision using a non-dimensional regime map. The selection among the modes of single capturing, single drop falling, and divided drop falling is explained through a scale analysis of forces. We also examine the droplet retention on the fiber after impact. For each mode, we suggest the mathematical models to predict the amount of residual water on the fiber. Our study can be extended to predicting the remaining droplet, the critical problem in air filtration, water collection, and fiber coating. This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIP) (2009-0083510).

  9. Interfacial Instabilities on a Droplet

    NASA Astrophysics Data System (ADS)

    Jalaal, Maziyar; Mehravaran, Kian

    2013-11-01

    The fragmentation of droplets is an essential stage of several natural and industrial applications such as fuel atomization and rain phenomena. In spite of its relatively long history, the mechanism of fragmentation is not clear yet. This is mainly due to small length and time scales as well as the non-linearity of the process. In the present study, two and three-dimensional numerical simulations have been performed to understand the early stages of the fragmentation of an initially spherical droplet. Simulations are performed for high Reynolds and a range of relatively high Weber numbers (shear breakup). To resolve the small-scale instabilities generated over the droplet, a second-order adaptive finite volume/volume of fluids (FV/VOF) method is employed, where the grid resolution is increased with the curvature of the gas-liquid interface as well as the vorticity magnitude. The study is focused on the onset and growth of interfacial instabilities. The role of Kelvin-Helmholtz instability (in surface wave formation) and Rayleigh-Taylor instability (in azimuthal transverse modulation) are shown and the obtained results are compared with the linear instability theories for zero and non-zero vorticity layers. Moreover, the analogy between the fragmentation of a single drop and a co-axial liquid jet is discussed. The current results can be used for the further development of the current secondary atomization models.

  10. The mechanism of formation of the droplets on the electrodes under the impact of the high power density streams

    NASA Astrophysics Data System (ADS)

    Goncharov, V. D.; Sorokin, K. S.; Yashkardin, R. V.; Fiskin, E. M.

    2016-07-01

    The article contains a brief description of functioning principles of the device for creating ultradispersive powders of metals under the impact of electrically charged streams with power density about 108 W/cm2. The results of atomic forced microscopy (AFM) measurements of surfaces of the electrodes exposed to dispergate the microdroplets, which allowed to study the droplets formation steps are presented. The results of AFM surfaces of the substrate surfaces to be inflicted by the dispergated droplets are presented. The dependency of the particles sizes on the distance between the electrode and substrate allows to consider the main mechanism of division the dispergated from the electrode surface droplets the Rayleigh instability.

  11. Evaluation of permanently charged electrofibrous filters

    SciTech Connect

    Biermann, A.H.; Lum, B.Y.; Bergman, W.

    1982-10-18

    These studies showed that loading the permanently charged filters with captured aerosols will lead to a neutralization of the filter charge. The transfer from the captured aerosol to the fiber surface and the subsequent neutralization of fiber charge. The increased efficiency is due to the additional mechanical capture by the particle deposits. The minimum efficiency obtained during the loading of solid aerosols is determined by the aerosol charge, with highly charged aerosols producing a lower minimum. Permanently charged filters lose their fiber charge when exposed to organic solvents or ionic water solutions. The fiber charge neutralization was minimized by coating the charged fibers with a polymer. Several different coating techniques were examined. Unfortunately, preventing the neutralization of fiber charge is not sufficient to prevent a deterioration of filter efficiency.

  12. Droplet interactions during combustion of unsupported droplet clusters in microgravity: Numerical study of droplet interactions at low Reynolds number

    NASA Astrophysics Data System (ADS)

    Ciobanescu Husanu, Irina N.

    2005-09-01

    The present work developed a numerical model to study the combustion of well-characterized drop clusters in microgravity environment using direct numerical simulation by the means of Fire Dynamic Simulator---a CFD model of fire-driven fluid flow. The computational research investigated the combustion of clusters of droplets of different sized and asymmetric three-dimensional configurations in zero gravity environments for zero relative Reynolds numbers. One of the aspects studied is droplet interaction during evaporation and combustion over the lifetime of the droplet. The model developed accounts for variable gas-phase thermophysical properties, unity Lewis number, Stefan velocities and includes the gas-phase radiative transfer (solved by a finite volume method) for finite rate reaction. Mass burning rates are calculated for each droplet in an array and compared to mass burning rate of similar single droplet, the ratio of these two being a correction factor eta. Single droplet combustion has been studied to evaluate and validate the model output. It was found that single droplet combustion does follow the d2-law, mass burning rates being in excellent qualitative agreement with current theories and experimental data. Direct numerical results of multiple droplet combustion were obtained and compared with a point source method as well as with experimental and numerical models developed in the past. Data obtained with proposed method provided results consistent with and in qualitative agreement with multiple droplets combustion theories and experimental investigations. Quantitatively, the numerical model results were in the range of 85% to 95% of the results provided by the investigations found in the literature for droplet array combustion models and in the range of 85% to 90% when compared with single droplet combustion models. The numerical simulation along with the future proposed experiment described in the project is a unique combination of investigative methods

  13. Solvent-Augmented Mineralization of Pyrene by a Mycobacterium sp

    PubMed Central

    Jimenez, I. Y.; Bartha, R.

    1996-01-01

    The biodegradation of polycyclic aromatic hydrocarbon pollutants is constrained, in part, by their solid physical state and very low water solubility. Searching for ways to overcome these limitations, we isolated from soil a bacterium capable of growing on pyrene as a sole source of carbon and energy. Acid-fast stain, morphology, and fatty acid profile identified it as a Mycobacterium sp. In a mineral salts solution, the isolate mineralized 50% of a 250-(mu)g/ml concentration of [(sup14)C]pyrene in 2 to 3 days. Detergent below the critical micelle concentration increased the pyrene mineralization rate to 154%, but above the critical micelle concentration, the detergent severely inhibited pyrene mineralization. The water-miscible solvent polyethylene glycol was inhibitory. The hydrophobic solvents heptamethylnonane, decalin, phenyldecane, and diphenylmethane were also inhibitory at several concentrations tested, but the addition of paraffin oil, squalene, squalane, tridecylcyclohexane, and cis-9-tricosene at 0.8% (vol/vol) doubled pyrene mineralization rates by the Mycobacterium sp. without being utilized themselves. The Mycobacterium sp. was found to have high cell surface hydrophobicity and adhered to the emulsified solvent droplets that also contained the dissolved pyrene, facilitating its mass transfer to the degrading bacteria. Cells physically adhering to solvent droplets metabolized pyrene 8.5 times as fast as cells suspended in the aqueous medium. An enhanced mass transfer of polycyclic aromatic hydrocarbon compounds to microorganisms by suitable hydrophobic solvents might allow the development of solvent-augmented biodegradation techniques for use in aqueous or slurry-type bioreactors. PMID:16535350

  14. Vibration-induced droplet atomization

    NASA Astrophysics Data System (ADS)

    Vukasinovic, Bojan

    The atomization of liquid drops is investigated experimentally using laser vibrometry, high-speed imaging, and particle tracking techniques. The spray is generated by a novel vibration-induced droplet atomization (VIDA) process in which a sessile drop is atomized by an underlying vibrating thin metal diaphragm, resulting in rapid ejection of small secondary droplets from the free surface of the primary drop. Under some conditions, the primary drop can be atomized extremely rapidly by a bursting-like mechanism (e.g., a 0.1 ml water drop can be atomized in 0.4 seconds). The present research has focused on four major areas: global characteristics of VIDA process, instability modes and free surface dynamics of the forced drop, mechanisms of the interface breakup, and parametric characterization of the ensuing spray. Prior to atomization, the drop free surface undergoes three transitions: from axisymmetric standing waves to azimuthal waves, to a newly-observed lattice mode, and to a disordered pre-ejection state. The droplet ejection results from localized collapse of surface troughs and initiation and ultimate breakup of momentary liquid spikes. Breakup begins with capillary pinch-off from spike tips and can be followed by additional pinching of liquid droplets. For a relatively low-viscosity liquid, e.g., water, a capillary-wave instability of the spike is observed in some cases, while for a very viscous liquid, e.g., a glycerin/water solution, the first breakup occurs near the stem of the spike, with or without subsequent breakup of the detached, elongated thread. Different mechanisms dominating the primary breakup of the spike are operative in the low- and high-viscosity ejection regimes. When ejection of the secondary droplets is triggered, the evolution and rate of atomization depend on the coupled dynamics of the primary drop and the vibrating diaphragm. Due to these dynamics, the process can be either self-intensifying or self-decaying. The resulting VIDA spray

  15. [Micro-droplet characterization and its application for amino acid detection in droplet microfluidic system].

    PubMed

    Yuan, Huiling; Dong, Libing; Tu, Ran; Du, Wenbin; Ji, Shiru; Wang, Qinhong

    2014-01-01

    Recently, the droplet microfluidic system attracts interests due to its high throughput and low cost to detect and screen. The picoliter micro-droplets from droplet microfluidics are uniform with respect to the size and shape, and could be used as monodispensed micro-reactors for encapsulation and detection of single cell or its metabolites. Therefore, it is indispensable to characterize micro-droplet and its application from droplet microfluidic system. We first constructed the custom-designed droplet microfluidic system for generating micro-droplets, and then used the micro-droplets to encapsulate important amino acids such as glutamic acid, phenylalanine, tryptophan or tyrosine to test the droplets' properties, including the stability, diffusivity and bio-compatibility for investigating its application for amino acid detection and sorting. The custom-designed droplet microfluidic system could generate the uniformed micro-droplets with a controllable size between 20 to 50 microm. The micro-droplets could be stable for more than 20 h without cross-contamination or fusion each other. The throughput of detection and sorting of the system is about 600 micro-droplets per minute. This study provides a high-throughput platform for the analysis and screening of amino acid-producing microorganisms.

  16. Evaporation of multi-component mixtures and shell formation in spray dried droplets

    NASA Astrophysics Data System (ADS)

    Valente, Pedro; Duarte, Íris; Porfirio, Tiago; Temtem, Márcio

    2015-11-01

    Drug particles where the active pharmaceutical ingredient (APIs) is dispersed in a polymer matrix forming an amorphous solid dispersion (ASD) is a commonly used strategy to increase the solubility and dissolution rate of poorly water soluble APIs. However, the formation and stability of an amorphous solid dispersion depends on the polymer/API combination and process conditions to generate it. The focus of the present work is to further develop a numerical tool to predict the formation of ASDs by spray drying solutions of different polymer/API combinations. Specifically, the evaporation of a multi-component droplet is coupled with a diffusion law within the droplet that minimizes the Gibbs free energy of the polymer/API/solvents system, following the Flory-Huggins model. Prior to the shell formation, the evaporation of the solvents is modelled following the simplified approach proposed by Abramzon & Sirignano (1989) which accounts for the varying relative velocity between the droplet and the drying gas. After shell formation, the diffusion of the solvents across the porous shell starkly modifies the evaporative dynamics.

  17. CHLORINATED SOLVENT PLUME CONTROL

    EPA Science Inventory

    This lecture will cover recent success in controlling and assessing the treatment of shallow ground water plumes of chlorinated solvents, other halogenated organic compounds, and methyl tert-butyl ether (MTBE).

  18. Micellar interactions in water-AOT based droplet microemulsions containing hydrophilic and amphiphilic polymers

    NASA Astrophysics Data System (ADS)

    Appel, Markus; Spehr, Tinka Luise; Wipf, Robert; Moers, Christian; Frey, Holger; Stühn, Bernd

    2013-11-01

    We investigate the influence of addition of hydrophilic and amphiphilic polymer on percolation behavior and micellar interactions in AOT-based water-in-oil droplet microemulsions. We focus on two series of samples having constant molar water to surfactant ratio W = 20 and constant droplet volume fraction Φ = 30%, respectively. From dielectric spectroscopy experiments, we extract the bending rigidity of the surfactant shell by percolation temperature measurements. Depending on droplet size, we find stabilization and destabilization of the surfactant shell upon addition of hydrophilic poly(ethylene glycol) (PEG) (Mn = 3100 g mol-1) and amphiphilic poly(styrene)-b-poly(ethylene glycol) copolymer with comparable length of the hydrophilic block. Complementary small angle X-ray scattering experiments corroborate the finding of stabilization for smaller droplets and destabilization of larger droplets. Subsequent analysis of dielectric spectra enables us to extract detailed information about micellar interactions and clustering by evaluating the dielectric high frequency shell relaxation. We interpret the observed results as a possible modification of the inter-droplet charge transfer efficiency by addition of PEG polymer, while the amphiphilic polymer shows a comparable, but dampened effect.

  19. Electrodynamic behavior and interface instability of double emulsion droplets under high electric field

    NASA Astrophysics Data System (ADS)

    Abbasi, Muhammad Salman; Song, Ryungeun; Kim, Jaehoon; Lee, Jinkee

    2016-11-01

    In this paper, numerical solution of electro-dynamic behavior and interface instability of double emulsion droplet is presented. Level set method and leaky dielectric model coupled with Navier-Stokes equation are used to solve the electrodynamic problem. The method is validated against the theoretical analysis and the simulation results of the other researchers. Double emulsion droplet with inner droplet (core) and outer droplet (shell) phases immersed in continuous phase is subjected to high electric field. Shell/continuous and core/shell interfaces of the droplet undergo prolate-oblate or oblate-prolate deformation depending on the extent of the penetration of electric potential and sense of charge distribution at the interfaces. The deformation of the shell deviates from theory at larger volume fraction of core for oblate-prolate case whereas it follows theory for prolate-oblate case. The interfaces showing oblate-prolate deformation split away at the poles whereas, for prolate-oblate, they split at the equator. The re-union of the two split parts under high electric field results with production of daughter droplet at the core. The large decrease in critical electric field for oblate-prolate case shows their less interface stability at larger volume fraction of core. When the core is eccentric, the electric field drives it towards the shell center or to the shell/continuous interface depending on electrical parameters.

  20. Bouncing droplets on a billiard table.

    PubMed

    Shirokoff, David

    2013-03-01

    In a set of experiments, Couder et al. demonstrate that an oscillating fluid bed may propagate a bouncing droplet through the guidance of the surface waves. I present a dynamical systems model, in the form of an iterative map, for a droplet on an oscillating bath. I examine the droplet bifurcation from bouncing to walking, and prescribe general requirements for the surface wave to support stable walking states. I show that in addition to walking, there is a region of large forcing that may support the chaotic motion of the droplet. Using the map, I then investigate the droplet trajectories in a square (billiard ball) domain. I show that in large domains, the long time trajectories are either non-periodic dense curves or approach a quasiperiodic orbit. In contrast, in small domains, at low forcing, trajectories tend to approach an array of circular attracting sets. As the forcing increases, the attracting sets break down and the droplet travels throughout space.

  1. Supercritical droplet combustion and related transport phenomena

    NASA Technical Reports Server (NTRS)

    Yang, Vigor; Hsieh, K. C.; Shuen, J. S.

    1993-01-01

    An overview of recent advances in theoretical analyses of supercritical droplet vaporization and combustion is conducted. Both hydrocarbon and cryogenic liquid droplets over a wide range of thermodynamic states are considered. Various important high-pressure effects on droplet behavior, such as thermodynamic non-ideality, transport anomaly, and property variation, are reviewed. Results indicate that the ambient gas pressure exerts significant control of droplet gasification and burning processes through its influence on fluid transport, gas-liquid interfacial thermodynamics, and chemical reactions. The droplet gasification rate increases progressively with pressure. However, the data for the overall burnout time exhibit a considerable change in the combustion mechanism at the criticl pressure, mainly as a result of reduced mass diffusivity and latent heat of vaporization with increased pressure. The influence of droplet size on the burning characteristics is also noted.

  2. Electropermanent magnet actuation for droplet ferromicrofluidics

    PubMed Central

    Padovani, José I.; Jeffrey, Stefanie S.; Howe, Roger T.

    2016-01-01

    Droplet actuation is an essential mechanism for droplet-based microfluidic systems. On-demand electromagnetic actuation is used in a ferrofluid-based microfluidic system for water droplet displacement. Electropermanent magnets (EPMs) are used to induce 50 mT magnetic fields in a ferrofluid filled microchannel with gradients up to 6.4 × 104 kA/m2. Short 50 µs current pulses activate the electropermanent magnets and generate negative magnetophoretic forces that range from 10 to 70 nN on 40 to 80 µm water-in-ferrofluid droplets. Maximum droplet displacement velocities of up to 300 µm/s are obtained under flow and no-flow conditions. Electropermanent magnet-activated droplet sorting under continuous flow is demonstrated using a split-junction microfluidic design. PMID:27583301

  3. Impact of Viscous Droplets on Superamphiphobic Surfaces

    NASA Astrophysics Data System (ADS)

    Zhao, Binyu; Chen, Longquan; Deng, Xu

    2016-11-01

    Superamphiphobic coating is promising for various applications in industry, e.g. self-cleaning windows, where the impingement of droplets on surfaces is commonly encountered. In this work, we experimentally investigated the impact of droplets with similar surface tension (63-72 mN/m) but much different viscosity (1-150 mPa s) on superamphiphobic surfaces. We found that droplets can rebound from the superamphiphobic surfaces when the impact velocity is larger than a critical value, which linearly increases with the liquid viscosity. Droplet with higher viscosity spreads, retracts slower, and eventually rebounds lower and fewer times than that of low viscous droplet. These findings have important implications for surface engineers to use superamphiphobic coatings. Furthermore, we measured the maximum spreading factors for droplet impact on superamphiphobic surfaces and proposed a simple model based on energy conversation to describe its relationship to the Weber number and Reynolds number.

  4. A parameterization of cloud droplet nucleation

    SciTech Connect

    Ghan, S.J.; Chuang, C.C.; Penner, J.E.

    1994-01-01

    Droplet nucleation is a fundamental cloud process. The number of aerosols activated to form cloud droplets influences not only the number of aerosols scavenged by clouds but also the size of the cloud droplets. Cloud droplet size influences the cloud albedo and the conversion of cloud water to precipitation. Global aerosol models are presently being developed with the intention of coupling with global atmospheric circulation models to evaluate the influence of aerosols and aerosol-cloud interactions on climate. If these and other coupled models are to address issues of aerosol-interactions, the droplet nucleation process must be adequately represented. Ghan et al. have introduced a droplet nucleation parameterization for a single aerosol type that offers certain advantages over the popular Twomey parameterization. Here we describe the generalization of that parameterization to the case of multiple aerosol types, with estimation of aerosol mass as well as number activated.

  5. Electroporation of cells in microfluidic droplets.

    PubMed

    Zhan, Yihong; Wang, Jun; Bao, Ning; Lu, Chang

    2009-03-01

    Droplet-based microfluidics has raised a lot of interest recently due to its wide applications to screening biological/chemical assays with high throughput. Despite the advances on droplet-based assays involving cells, gene delivery methods that are compatible with the droplet platform have been lacking. In this report, we demonstrate a simple microfluidic device that encapsulates cells into aqueous droplets and then electroporates the encapsulated cells. The electroporation occurs when the cell-containing droplets (in oil) flow through a pair of microelectrodes with a constant voltage established in between. We investigate the parameters and characteristics of the electroporation. We demonstrate delivering enhanced green fluorescent protein (EGFP) plasmid into Chinese hamster ovary (CHO) cells. We envision the application of this technique to high-throughput functional genomics studies based on droplet microfluidics.

  6. Oscillatory combustion of liquid monopropellant droplets

    NASA Technical Reports Server (NTRS)

    Chanin, S. P.; Faeth, G. M.

    1976-01-01

    A theoretical investigation was conducted on the open-loop combustion response of monopropellant droplets and sprays to imposed pressure oscillations. The theoretical model was solved as a perturbation analysis through first order, yielding linear response results. Unsteady gas phase effects were considered in some cases, but the bulk of the calculations assumed a quasi-steady gas phase. Calculations were conducted using properties corresponding to hydrazine decomposition. Zero-order results agreed with earlier measurements of hydrazine droplet burning in combustion gases. The droplet response was greatest (exceeding unity in some cases) for large droplets with liquid phase temperature gradients; at frequencies near the characteristic frequency of the liquid phase thermal wave. The response of a spray is less than that of its largest droplet, however, a relatively small percentage of large droplets provides a substantial response (exceeding unity in some cases).

  7. Continuous countercurrent membrane column for the separation of solute/solvent and solvent/solvent systems

    DOEpatents

    Nerad, Bruce A.; Krantz, William B.

    1988-01-01

    A reverse osmosis membrane process or hybrid membrane - complementary separator process for producing enriched product or waste streams from concentrated and dilute feed streams for both solvent/solvent and solute/solvent systems is described.

  8. An Investigation of the Behavior of Solvent based Polycaprolactone ink for Material Jetting

    PubMed Central

    He, Yinfeng; Wildman, Ricky D.; Tuck, Chris J.; Christie, Steven D. R.; Edmondson, Steven

    2016-01-01

    An initial study of processing bioresorbable polycaprolactone (PCL) through material jetting was conducted using a Fujifilm Dimatix DMP-2830 material printer. The aim of this work was to investigate a potential solvent based method of jetting polycaprolactone. Several solvents were used to prepare a PCL solvent based ink and 1, 4-dioxane was chosen with the consideration of both solubility and safety. The morphology of PCL formed under different substrate temperatures, droplet spacings were investigated. Multi-layer PCL structures were printed and characterized. This work shows that biodegradable polycaprolactone can be processed through material jetting. PMID:26868530

  9. SOLVENT EXTRACTION OF RUTHENIUM

    DOEpatents

    Hyman, H.H.; Leader, G.R.

    1959-07-14

    The separation of rathenium from aqueous solutions by solvent extraction is described. According to the invention, a nitrite selected from the group consisting of alkali nitrite and alkaline earth nitrite in an equimolecular quantity with regard to the quantity of rathenium present is added to an aqueous solution containing ruthenium tetrantrate to form a ruthenium complex. Adding an organic solvent such as ethyl ether to the resulting mixture selectively extracts the rathenium complex.

  10. Supercritical solvent coal extraction

    NASA Technical Reports Server (NTRS)

    Compton, L. E. (Inventor)

    1984-01-01

    Yields of soluble organic extract are increased up to about 50% by the supercritical extraction of particulate coal at a temperature below the polymerization temperature for coal extract fragments (450 C.) and a pressure from 500 psig to 5,000 psig by the conjoint use of a solvent mixture containing a low volatility, high critical temperature coal dissolution catalyst such as phenanthrene and a high volatility, low critical temperature solvent such as toluene.

  11. Droplet Deformation Prediction With the Droplet Deformation and Breakup Model (DDB)

    NASA Technical Reports Server (NTRS)

    Vargas, Mario

    2012-01-01

    The Droplet Deformation and Breakup Model was used to predict deformation of droplets approaching the leading edge stagnation line of an airfoil. The quasi-steady model was solved for each position along the droplet path. A program was developed to solve the non-linear, second order, ordinary differential equation that governs the model. A fourth order Runge-Kutta method was used to solve the equation. Experimental slip velocities from droplet breakup studies were used as input to the model which required slip velocity along the particle path. The center of mass displacement predictions were compared to the experimental measurements from the droplet breakup studies for droplets with radii in the range of 200 to 700 mm approaching the airfoil at 50 and 90 m/sec. The model predictions were good for the displacement of the center of mass for small and medium sized droplets. For larger droplets the model predictions did not agree with the experimental results.

  12. Droplet Deformation Prediction with the Droplet Deormation and Break Up Model (DDB)

    NASA Technical Reports Server (NTRS)

    Vargas, Mario

    2012-01-01

    The Droplet Deformation and Breakup Model was used to predict deformation of droplets approaching the leading edge stagnation line of an airfoil. The quasi-steady model was solved for each position along the droplet path. A program was developed to solve the non-linear, second order, ordinary differential equation that governs the model. A fourth order Runge-Kutta method was used to solve the equation. Experimental slip velocities from droplet breakup studies were used as input to the model which required slip velocity along the particle path. The center of mass displacement predictions were compared to the experimental measurements from the droplet breakup studies for droplets with radii in the range of 200 to 700 mm approaching the airfoil at 50 and 90 m/sec. The model predictions were good for the displacement of the center of mass for small and medium sized droplets. For larger droplets the model predictions did not agree with the experimental results.

  13. Influence of adduct stereochemistry and hydrogen-bonding solvents on photoinduced charge transfer in a covalent benzo[a]pyrene diol epoxide-nucleoside adduct on picosecond time scales

    SciTech Connect

    O'Connor, D. ); Shafirovich, V.Y.; Geacintov, N.E. )

    1994-09-29

    Photoinduced electron transfer occurs with different rate constants upon picosecond laser pulse excitation of the stereoisomeric (+)-trans- and (-)-cis-benzo[a]pyrene diol epoxide-N[sup 2]-deoxyguanosine covalently linked adducts (BPDE-N[sup 2]-dG, bond with 10S absolute configuration) in polar solvents (N,N[prime]-dimethylformamide (DMF), and the hydrogen-bonding liquids H[sub 2]O, D[sub 2]O, formamide (FA), and N-methylformamide (NMF)). In the case of (+)-trans-BPDE-dG in DMF, photoinduced electron transfer occurs in the normal Marcus region, from dG to the pyrenyl residue singlet with a rate constant k[sub s] = (9.1 [+-] 0.9) x 10[sup 9] s[sup [minus]1], which is followed by a slower recombination (k[sub r] = (1.8 + 0.5) x 10[sup 9] s[sup [minus]1]) in the inverted Marcus region. In the cis-stereoisomeric adduct, both rate constants are enhanced by a factor of approximately 5. The presence of the hydrogen-bonding network in NMF and FA exerts opposite effects on these rate constants, decreasing k[sub s] and increasing k[sub r] by factors of 2-5. In aqueous solutions these effects are even more pronounced, and radical ions are not observed since k[sub r] [much gt] k[sub s]. A kinetic isotope effect on the delay of the pyrenyl singlets in H[sub 2]O and D[sub 2]O (k[sub s](H[sub 2]O)/k[sub s](D[sub 2]O) = 1.3-1.5) suggests that a proton-coupled electron transfer mechanism may be operative in aqueous solutions. 51 refs., 10 figs., 2 tabs.

  14. Cleaning without chlorinated solvents

    SciTech Connect

    Thompson, L.M.; Simandl, R.F.

    1994-12-31

    Because of health and environmental concerns, many regulations have been passed in recent years regarding the use of chlorinated solvents. The Oak Ridge Y-12 Plant has had an active program to find alternatives for these solvents used in cleaning applications for the past 7 years. During this time frame, the quantity of solvents purchased has been reduced by 92%. The program has been a twofold effort. Vapor degreasers used in batch cleaning-operations have been replaced by ultrasonic cleaning with aqueous detergent, and other organic solvents have been identified for use in hand-wiping or specialty operations. In order to qualify these alternatives for use, experimentation was conducted on cleaning ability as well as effects on subsequent operations such as welding, painting and bonding. Cleaning ability was determined using techniques such as X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared Spectroscopy (FTIR) which are capable of examining monolayer levels of contamination on a surface. Solvents have been identified for removal of rust preventative oils, lapping oils, machining coolants, lubricants, greases, and mold releases. Solvents have also been evaluated for cleaning urethane foam spray guns, swelling of urethanes and swelling of epoxies.

  15. Cleaning without chlorinated solvents

    NASA Technical Reports Server (NTRS)

    Thompson, L. M.; Simandl, R. F.

    1995-01-01

    Because of health and environmental concerns, many regulations have been passed in recent years regarding the use of chlorinated solvents. The Oak Ridge Y-12 Plant has had an active program to find alternatives for these solvents used in cleaning applications for the past 7 years. During this time frame, the quantity of solvents purchased has been reduced by 92 percent. The program has been a twofold effort. Vapor degreasers used in batch cleaning operations have been replaced by ultrasonic cleaning with aqueous detergent, and other organic solvents have been identified for use in hand-wiping or specialty operations. In order to qualify these alternatives for use, experimentation was conducted on cleaning ability as well as effects on subsequent operations such as welding, painting, and bonding. Cleaning ability was determined using techniques such as x-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) which are capable of examining monolayer levels of contamination on a surface. Solvents have been identified for removal of rust preventative oils, lapping oils, machining coolants, lubricants, greases, and mold releases. Solvents have also been evaluated for cleaning urethane foam spray guns, swelling of urethanes, and swelling of epoxies.

  16. Droplet immobilization within a polymeric organogel improves lipid bilayer durability and portability.

    PubMed

    Venkatesan, Guru A; Sarles, Stephen A

    2016-05-24

    The droplet interface bilayer (DIB) is a promising technique for assembling lipid membrane-based materials and devices using water droplets in oil, but it has largely been limited to laboratory environments due to its liquid construction. With a vision to transform this lab-based technique into a more-durable embodiment, we investigate the use of a polymer-based organogel to encapsulate DIBs within a more-solid material matrix to improve their handling and portability. Specifically, a temperature-sensitive organogel formed from hexadecane and poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) triblock copolymer is used to replace the liquid solvent that surrounds the lipid-coated droplets to establish a novel liquid-in-gel DIB system. Through specific capacitance measurements and single-channel recordings of the pore forming peptide alamethicin, we verify that the structural and functional membrane properties are retained when DIBs are assembled within SEBS organogel. In addition, we demonstrate that organogel encapsulation offers improved handling of droplets and yields DIBs with a near 3× higher bilayer durability, as quantified by the lateral acceleration required to rupture the membrane, compared to liquid-in-liquid DIBs in oil. This encapsulated DIB system provides a barrier against contamination from the environment and offers a new material platform for supporting multilayered DIB-based devices as well as other digital microfluidic systems that feature water droplets in oil.

  17. Two-dimensional self-assembly of amphiphilic porphyrins on a dynamically shrinking droplet surface.

    PubMed

    Numata, Munenori; Takigami, Yusuke; Hirose, Naoya; Sakai, Ryoichiro

    2014-03-14

    Developing a new field of molecular self-assembly in the sub-micrometer regime-with precision as high as that used to make discrete nano-sized molecular architectures through molecular design-is a major challenge for supramolecular chemistry. At present, however, there is no effective strategy for controlling the assembling molecules when their quantity is greater than one thousand. Herein, we propose a potential solution by exploiting a novel supramolecular system in conjunction with dynamically shrinking oil droplets, enabling more than a thousand component molecules to organize simultaneously into the form of sub-micrometer-scale ring structures. In our developed system, amphiphilic porphyrins, having potential two-dimensional assembling ability, were compartmentalized into droplets with narrow distributions and molecular numbers. These droplets were subsequently transformed into discrete ring-like structures during the process of solvent removal from the inner organic layer, i.e., shrinking the droplets. Unique self-assembled structures, which are not accessible through conventional supramolecular strategies, can be selectively created depending on the initial stage of the droplet.

  18. A multiphase ion-transport analysis of the electrostatic disjoining pressure: implications for binary droplet coalescence

    NASA Astrophysics Data System (ADS)

    Mason, Lachlan; Gebauer, Felix; Bart, Hans-Jörg; Stevens, Geoffrey; Harvie, Dalton

    2016-11-01

    Understanding the physics of emulsion coalescence is critical for the robust simulation of industrial solvent extraction processes, in which loaded organic and raffinate phases are separated via the coalescence of dispersed droplets. At the droplet scale, predictive collision-outcome models require an accurate description of the repulsive surface forces arising from electrical-double-layer interactions. The conventional disjoining-pressure treatment of double-layer forces, however, relies on assumptions which do not hold generally for deformable droplet collisions: namely, low interfacial curvature and negligible advection of ion species. This study investigates the validity bounds of the disjoining pressure approximation for low-inertia droplet interactions. A multiphase ion-transport model, based on a coupling of droplet-scale Nernst-Planck and Navier-Stokes equations, predicts ion-concentration fields that are consistent with the equilibrium Boltzmann distribution; indicating that the disjoining-pressure approach is valid for both static and dynamic interactions in low-Reynolds-number settings. The present findings support the development of coalescence kernels for application in macro-scale population balance modelling.

  19. Dispersion of Droplet Clouds in Turbulence.

    PubMed

    Bocanegra Evans, Humberto; Dam, Nico; Bertens, Guus; van der Voort, Dennis; van de Water, Willem

    2016-10-14

    We measure the absolute dispersion of clouds of monodisperse, phosphorescent droplets in turbulent air by means of high-speed image-intensified video recordings. Laser excitation allows the initial preparation of well-defined, pencil-shaped luminous droplet clouds in a completely nonintrusive way. We find that the dispersion of the clouds is faster than the dispersion of fluid elements. We speculate that preferential concentration of inertial droplet clouds is responsible for the enhanced dispersion.

  20. Droplet Vaporization in a Supercritical Microgravity Environment

    NASA Technical Reports Server (NTRS)

    Curtis, E. W.; Farrell, P. V.

    1987-01-01

    A model is presented which describes single liquid droplet vaporization at nearly critical liquid pressures and temperatures. A modified Redlich-Kwong equation of state is used to evaluate the fugacities and liquid and vapor mole fractions at the interface under the assumption of interface equilibrium. Results obtained for different droplet sizes and conditions indicate significant differences in behavior in comparison with low-pressure quasi-steady droplet vaporization.

  1. Combustion of Unconfined Droplet Clusters in Microgravity

    NASA Technical Reports Server (NTRS)

    Ruff, G. A.; Liu, S.

    2001-01-01

    Combustion experiments using arrays of droplets seek to provide a link between single droplet combustion phenomena and the behavior of complex spray combustion systems. Both single droplet and droplet array studies have been conducted in microgravity to better isolate the droplet interaction phenomena and eliminate or reduce the confounding effects of buoyancy-induced convection. In most experiments involving droplet arrays, the droplets are supported on fibers to keep them stationary and close together before the combustion event. The presence of the fiber, however, disturbs the combustion process by introducing a source of heat transfer and asymmetry into the configuration. As the number of drops in a droplet array increases, supporting the drops on fibers becomes less practical because of the cumulative effect of the fibers on the combustion process. To eliminate the effect of the fiber, several researchers have conducted microgravity experiments using unsupported droplets. Jackson and Avedisian investigated single, unsupported drops while Nomura et al. studied droplet clouds formed by a condensation technique. The overall objective of this research is to extend the study of unsupported drops by investigating the combustion of well-characterized drop clusters in a microgravity environment. Direct experimental observations and measurements of the combustion of droplet clusters would fill a large gap in our current understanding of droplet and spray combustion and provide unique experimental data for the verification and improvement of spray combustion models. In this work, the formation of drop clusters is precisely controlled using an acoustic levitation system so that dilute, as well as dense clusters can be created and stabilized before combustion in microgravity is begun. This paper describes the design and performance of the 1-g experimental apparatus, some preliminary 1-g results, and plans for testing in microgravity.

  2. Droplet vaporization in a supercritical microgravity environment

    NASA Astrophysics Data System (ADS)

    Curtis, E. W.; Farrell, P. V.

    1987-10-01

    A model is presented which describes single liquid droplet vaporization at nearly critical liquid pressures and temperatures. A modified Redlich-Kwong equation of state is used to evaluate the fugacities and liquid and vapor mole fractions at the interface under the assumption of interface equilibrium. Results obtained for different droplet sizes and conditions indicate significant differences in behavior in comparison with low-pressure quasi-steady droplet vaporization.

  3. Modulation of Buckling Dynamics in Nanoparticle Laden Droplets Using External Heating.

    PubMed

    Pathak, Binita; Basu, Saptarshi

    2016-03-22

    Dynamics of contact free (levitated) drying of nanofluid droplets is ubiquitous in many application domains ranging from spray drying to pharmaceutics. Controlling the final morphology (macro to micro scales) of the dried out sample poses some serious challenges. Evaporation of solvent and agglomeration of particles leads to porous shell formation in acoustically levitated nanosilica droplets. The capillary pressure due to evaporation across the menisci at the nanoscale pores causes buckling of the shell which leads to ring and bowl shaped final structures. Acoustics plays a crucial role in flattening of droplets which is a prerequisite for initiation of buckling in the shell. Introduction of mixed nanocolloids (sodium dodecyl sulfate + nanosilica) reduces evaporation rate, disrupts formation of porous shell, and enhances mechanical strength of the shell, all of which restricts the process of buckling. Although buckling is completely arrested in such surfactant added droplets, controlled external heating using laser enhances evaporation through the pores in the shell due to thermally induced structural changes and rearrangement of SDS aggregates which reinitializes buckling in such droplets. Furthermore, inclusion of anilinium hydrochloride into the nanoparticle laden droplets produces ions which adsorb and modify the morphology of sodium dodecyl sulfate crystals and reinitializes buckling in the shell (irrespective of external heating conditions). The kinetics of buckling is determined by the combined effect of morphology of the colloidal particles, particle/aggregate diffusion rate within the droplet, and the rate of evaporation of water. The buckling dynamics leads to cavity formation which grows subsequently to yield final structures with drastically different morphological features. The cavity growth is controlled by evaporation through the nanoscale pores and exhibits a universal trend irrespective of heating rate and nanoparticle type.

  4. Pyrolysis of Large Black Liquor Droplets

    NASA Technical Reports Server (NTRS)

    Bartkus, Tadas P.; T'ien, James S.; Dietrich, Daniel L.; Wessel, Richard A.

    2007-01-01

    This paper presents the results of experiments involving the pyrolysis of large black liquor droplets in the NASA KC-135 reduced gravity aircraft. The reduced gravity environment facilitated the study of droplets up to 9 mm in diameter extending the results of previous studies to droplet sizes that are similar to those encountered in recovery boilers. Single black liquor droplets were rapidly inserted into a 923 K oven. The primary independent variables were the initial droplet diameter (0.5 mm to 9 mm), the black liquor solids content (66.12% - 72.9% by mass), and the ambient oxygen mole fraction (0.0 - 0.21). Video records of the experiments provided size and shape of the droplets as a function of time. The results show that the particle diameter at the end of the drying stage (D(sub DRY) ) increases linearly with the initial particle diameter (D(sub O)). The results further show that the ratio of the maximum swollen diameter (D(sub MAX)) to D(sub O) decreases with increasing D(sub O) for droplets with D(sub O) less than 4 mm. This ratio was independent of D(sub O) for droplets with D(sub O) greater than 4 mm. The particle is most spherical at the end of drying, and least spherical at maximum swollen size, regardless of initial sphericity and droplet size.

  5. Pyrolysis of Large Black Liquor Droplets

    NASA Technical Reports Server (NTRS)

    Bartkus, Tadas P.; Dietrich, Daniel L.; T'ien, James S.; Wessel, Richard A.

    2007-01-01

    This paper presents the results of experiments involving the pyrolysis of large black liquor droplets in the NASA KC-135 reduced gravity aircraft. The reduced gravity environment facilitated the study of droplets up to 9 mm in diameter extending the results of previous studies to droplet sizes that are similar to those encountered in recovery boilers. Single black liquor droplets were rapidly inserted into a 923 K oven. The primary independent variables were the initial droplet diameter (0.5 mm to 9 mm), the black liquor solids content (66.12% - 72.9% by mass), and the ambient oxygen mole fraction (0.0 - 0.21). Video records of the experiments provided size and shape of the droplets as a function of time. The results show that the particle diameter at the end of the drying stage (D(sub DRY)) increases linearly with the initial particle diameter (D(sub O)). The results further show that the ratio of the maximum swollen diameter (D(sub MAX)) to D(sub O) decreases with increasing D(sub O) for droplets with D(sub O) less than 4 mm. This ratio was independent of D(sub O) for droplets with D(sub O) greater than 4 mm. The particle is most spherical at the end of drying, and least spherical at maximum swollen size, regardless of initial sphericity and droplet size.

  6. A Theory of Shape-Shifting Droplets

    NASA Astrophysics Data System (ADS)

    Haas, Pierre; Goldstein, Raymond; Smoukov, Stoyan; Denkov, Nikolai

    2016-11-01

    Recent observations of cooled oil emulsion droplets uncovered a remarkable array of shape transformations: the initially spherical droplets flatten into polygonal shapes, first hexagons, then triangles or quadrilaterals that ultimately grow thin protrusions from their corners. These transformations are driven by a partial phase transition of the bulk liquid phase. In this talk, we explore theoretically the simplest geometric competition between this phase transition and surface tension in planar polygons. We recover the experimental sequence of shapes and predict shape statistics in qualitative agreement with experiments. Extending the model to capture some of the three-dimensional structure of the droplets, we analyse the topological transition of droplet puncture observed in experiments.

  7. 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.

  8. Liquid Droplets on a Highly Deformable Membrane

    NASA Astrophysics Data System (ADS)

    Schulman, Rafael; Dalnoki-Veress, Kari

    2015-11-01

    We present measurements of the deformation produced by micro-droplets atop thin elastomeric and glassy free-standing films. Due to the Laplace pressure, the droplets deform the elastic membrane thereby forming a bulge. Thus, there are two angles that define the droplet/membrane geometry: the angle the liquid surface makes with the film and the angle the deformed bulge makes with the film. The contact line geometry is well captured by a Neumann construction which includes contributions from interfacial and mechanical tensions. Finally, we show that a droplet atop a film with biaxial tension assumes an equilibrium shape which is elongated along the axis of high tension.

  9. Droplet evaporation with complexity of evaporation modes

    NASA Astrophysics Data System (ADS)

    Hwang, In Gyu; Kim, Jin Young; Weon, Byung Mook

    2017-01-01

    Evaporation of a sessile droplet often exhibits a mixed evaporation mode, where the contact radius and the contact angle simultaneously vary with time. For sessile water droplets containing polymers with different initial polymer concentrations, we experimentally study their evaporation dynamics by measuring mass and volume changes. We show how diffusion-limited evaporation governs droplet evaporation, regardless of the complexity of evaporation behavior, and how the evaporation rate depends on the polymer concentration. Finally, we suggest a unified expression for a diffusion-limited evaporation rate for a sessile droplet with complexity in evaporation dynamics.

  10. Tin droplets for LPP EUV sources

    NASA Astrophysics Data System (ADS)

    Rollinger, Bob; Bozinova, Luna; Gambino, Nadia; Abhari, Reza S.

    2012-03-01

    The tin droplet generator is a key component of EUV LPP sources. Small tin droplets, when combined with a high power laser, form a regenerative target with high CE. A major challenge associated with today's EUV sources is energy stability, which directly correlates with the stability of the fuel delivery system. The LEC droplet dispenser is now in its 5th generation design, with several years of development, including studies of different nozzle types, excitation mechanisms, thermal management approaches and contamination control systems. The dispenser produces droplets in the frequency range required for both metrology and HVM EUV sources. The two relevant instability modes are drop-to-drop jitter and lateral instabilities. The low frequency content of the lateral droplet displacement is compensated by a newly implemented dispenser positioning system. The drop-to-drop jitter, which is studied over 2000 s, equals 11.2% (3σ) of the mean droplet spacing, which makes individual droplet laser triggering necessary. The lateral instabilities, which are mainly relevant in the plane perpendicular to the laser axis, are determined to be in the range of 7.1% (3σ) of the droplet diameter. The lateral displacements are recorded over 2.2 hrs. The related EUV temporal energy stability (open-loop) is estimated to be 0.35% (3σ) for the worst case scenario, a laser spot size which matches the droplet diameter.

  11. Coffee Stain Effect with Liquid Droplets

    NASA Astrophysics Data System (ADS)

    Mitra, Sushanta; Das, Siddhartha

    2012-11-01

    We discuss the dynamics of immiscible bidispersed oil droplets that are suspended in an evaporating water sessile drop. Therefore, in contrast to classical coffee stain problem, the depositing ``particles'' are replaced by microscopic oil droplets - hence, we discuss a liquid-droplet coffee stain phenomenon. We show experimentally that unlike colloidal particles in a classical coffee stain problem, liquid oil droplets cannot reach the three phase contact line (TPCL) due to the aversion of the oil droplets to form finite oil-air interface in water medium. Therefore, the oil droplets get positioned at a finite distance from the TPCL. We call this distance the ``enclosure'' distance, which being a function of the droplet size, triggers a spontaneous size-based oil droplet separation. In addition, the ``enclosure'' effect is a function of the surface energies of the oil droplet and the rate of evaporation. We develop a theory to describe this effect, and the results show excellent agreement with the experimental findings. NSERC Banting Postdoctoral Fellowship for S. Das.

  12. Fiber Supported Droplet Combustion-2 (FSDC-2)

    NASA Technical Reports Server (NTRS)

    Colantonio, Renato; Dietrich, Daniel; Haggard, John B., Jr.; Nayagan, Vedha; Dryer, Frederick L.; Shaw, Benjamin D.; Williams, Forman A.

    1998-01-01

    Experimental results for the burning characteristics of fiber supported, liquid droplets in ambient Shuttle cabin air (21% oxygen, 1 bar pressure) were obtained from the Glove Box Facility aboard the STS-94/MSL-1 mission using the Fiber Supported Droplet Combustion - 2 (FSDC-2) apparatus. The combustion of individual droplets of methanol/water mixtures, ethanol, ethanol/water azeotrope, n-heptane, n-decane, and n-heptane/n-hexadecane mixtures were studied in quiescent air. The effects of low velocity, laminar gas phase forced convection on the combustion of individual droplets of n-heptane and n-decane were investigated and interactions of two droplet-arrays of n-heptane and n-decane droplets were also studied with and without gas phase convective flow. Initial diameters ranging from about 2mm to over 6mm were burned on 80-100 micron silicon fibers. In addition to phenomenological observations, quantitative data were obtained in the form of backlit images of the burning droplets, overall flame images, and radiometric combustion emission measurements as a function of the burning time in each experiment. In all, 124 of the 129 attempted experiments (or about twice the number of experiments originally planned for the STS-94/MSL-1 mission) were conducted successfully. The experimental results contribute new observations on the combustion properties of pure alkanes, binary alkane mixtures, and simple alcohols for droplet sizes not studied previously, including measurements on individual droplets and two-droplet arrays, inclusive of the effects of forced gas phase convection. New phenomena characterized experimentally for the first time include radiative extinction of droplet burning for alkanes and the "twin effect" which occurs as a result of interactions during the combustion of two-droplet arrays. Numerical modeling of isolated droplet combustion phenomenon has been conducted for methanol/water mixtures, n-heptane, and n-heptane/n-hexadecane mixtures, and results

  13. Quantitative DNA Analysis Using Droplet Digital PCR.

    PubMed

    Vossen, Rolf H A M; White, Stefan J

    2017-01-01

    Droplet digital PCR (ddPCR) is based on the isolated amplification of thousands of individual DNA molecules simultaneously, with each molecule compartmentalized in a droplet. The presence of amplified product in each droplet is indicated by a fluorescent signal, and the proportion of positive droplets allows the precise quantification of a given sequence. In this chapter we briefly outline the basis of ddPCR, and describe two different applications using the Bio-Rad QX200 system: genotyping copy number variation and quantification of Illumina sequencing libraries.

  14. Lipid-induced structural turnover of water droplets to liquid crystal droplets

    NASA Astrophysics Data System (ADS)

    Sidiq, Sumyra; Pal, Santanu Kumar

    2014-04-01

    For the first time direct observation of structural turnover of water droplets to liquid crystal (LC) droplets with radial LC ordering was observed in presence of surfactants and lipids. Study of interactions between enzymes with the topological defects in the LC mediate the response of these droplets suggesting new principles for the design of chemical and biological sensors.

  15. Walking droplets in confined domains

    NASA Astrophysics Data System (ADS)

    Sáenz, Pedro; Bush, John

    2016-11-01

    A millimetric liquid drop can walk spontaneously along the surface of a vibrating fluid bath, propelled by a resonant interaction with its own wave field. These walking droplets exhibit features previously thought to be exclusive to the microscopic quantum realm. We here explore experimentally the dynamics and statistics of this macroscopic wave-particle system in confined domains, or 'corrals'. Particular attention is given to characterizing the influence of the corral geometry on the emergent probability distributions. The relation to analogous quantum systems (specifically, quantum corrals, the quantum mirage and scarring in Bose-Einstein condensates) is discussed. NSF support via CMMI-1333242.

  16. Cluster Study of Anion Specificity in Solutions: From Molecular-Like Species to Nano-Sized Droplets

    NASA Astrophysics Data System (ADS)

    Wang, Xue-Bin

    2015-03-01

    In this talk, I will present our cluster approach using size-selected, low-temperature photoelectron spectroscopy and ab initio calculations to study a variety of complex anion solvation across the Hofmeister series. Pronounced anion specific effects and rich solute-solvent, solvent-solvent interactions have been discovered en-route to solvation evolution from molecular-like species to nano-sized droplets. We found significant solute anisotropy effects in preferably selecting solvent network to align solute permanent dipole with the solvent electric field in hydrated neutral clusters. Thermodynamic advantage of organic acids in facilitating formation of bisulfate ion clusters, an important issue related to atmospheric chemistry and aerosol particle formation will also be discussed. This work was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences.

  17. Droplet Vaporization In A Levitating Acoustic Field

    NASA Technical Reports Server (NTRS)

    Ruff, G. A.; Liu, S.; Ciobanescu, I.

    2003-01-01

    Combustion experiments using arrays of droplets seek to provide a link between single droplet combustion phenomena and the behavior of complex spray combustion systems. Both single droplet and droplet array studies have been conducted in microgravity to better isolate the droplet interaction phenomena and eliminate or reduce the effects of buoyancy-induced convection. In most experiments involving droplet arrays, the droplets are supported on fibers to keep them stationary and close together before the combustion event. The presence of the fiber, however, disturbs the combustion process by introducing a source of heat transfer and asymmetry into the configuration. As the number of drops in a droplet array increases, supporting the drops on fibers becomes less practical because of the cumulative effect of the fibers on the combustion process. To eliminate the effect of the fiber, several researchers have conducted microgravity experiments using unsupported droplets. Jackson and Avedisian investigated single, unsupported drops while Nomura et al. studied droplet clouds formed by a condensation technique. The overall objective of this research is to extend the study of unsupported drops by investigating the combustion of well-characterized drop clusters in a microgravity environment. Direct experimental observations and measurements of the combustion of droplet clusters would provide unique experimental data for the verification and improvement of spray combustion models. In this work, the formation of drop clusters is precisely controlled using an acoustic levitation system so that dilute, as well as dense clusters can be created and stabilized before combustion in microgravity is begun. While the low-gravity test facility is being completed, tests have been conducted in 1-g to characterize the effect of the acoustic field on the vaporization of single and multiple droplets. This is important because in the combustion experiment, the droplets will be formed and

  18. A Comprehensive Model of Electric-Field-Enhanced Jumping-Droplet Condensation on Superhydrophobic Surfaces.

    PubMed

    Birbarah, Patrick; Li, Zhaoer; Pauls, Alexander; Miljkovic, Nenad

    2015-07-21

    Superhydrophobic micro/nanostructured surfaces for dropwise condensation have recently received significant attention due to their potential to enhance heat transfer performance by shedding positively charged water droplets via coalescence-induced droplet jumping at length scales below the capillary length and allowing the use of external electric fields to enhance droplet removal and heat transfer, in what has been termed electric-field-enhanced (EFE) jumping-droplet condensation. However, achieving optimal EFE conditions for enhanced heat transfer requires capturing the details of transport processes that is currently lacking. While a comprehensive model has been developed for condensation on micro/nanostructured surfaces, it cannot be applied for EFE condensation due to the dynamic droplet-vapor-electric field interactions. In this work, we developed a comprehensive physical model for EFE condensation on superhydrophobic surfaces by incorporating individual droplet motion, electrode geometry, jumping frequency, field strength, and condensate vapor-flow dynamics. As a first step toward our model, we simulated jumping droplet motion with no external electric field and validated our theoretical droplet trajectories to experimentally obtained trajectories, showing excellent temporal and spatial agreement. We then incorporated the external electric field into our model and considered the effects of jumping droplet size, electrode size and geometry, condensation heat flux, and droplet jumping direction. Our model suggests that smaller jumping droplet sizes and condensation heat fluxes require less work input to be removed by the external fields. Furthermore, the results suggest that EFE electrodes can be optimized such that the work input is minimized depending on the condensation heat flux. To analyze overall efficiency, we defined an incremental coefficient of performance and showed that it is very high (∼10(6)) for EFE condensation. We finally proposed mechanisms

  19. Efficient photochemical oxidation of anisole in protic solvents: electron transfer driven by specific solvent-solute interactions.

    PubMed

    Lewandowska, Anna; Hug, Gordon L; Hörner, Gerald; Pedzinski, Tomasz; Filipiak, Piotr; Marciniak, Bronislaw

    2010-07-12

    The dynamics of the bimolecular quenching of triplet excited benzophenone by anisole was studied by nanosecond flash photolysis. We carried out a detailed study of the solvent dependence of the reaction rates and efficiencies in a number of protic and non-protic solvents. These studies were augmented by theoretical modelling and experimental investigation of solute/solvent interactions in the triplet excited and the ground state, respectively. The triplet quenching that follows Stern-Volmer kinetics in all cases is profoundly dependent on the nature of the solvent, with the highest reactivity being consistently found in protic solvents. The results in non-protic solvents are compatible with unproductive quenching via a charge-transfer state, whereas the generally fast quenching in protic solvents is accompanied by efficient formation of free-radical products. Analysis of the solvent dependence in terms of Marcus theory reveals the impact of specific solvation of benzophenone by protic solvents on the ET driving force and kinetics. Specific solvation is found to support efficient free radical ion formation in media of moderate and low polarity as well.

  20. Vortices catapult droplets in atomization

    NASA Astrophysics Data System (ADS)

    John Soundar Jerome, J.; Marty, Sylvain; Matas, Jean-Philippe; Zaleski, Stephane; Hoepffner, Jerome

    2013-11-01

    A droplet ejection mechanism in planar two-phase mixing layers is examined. Any disturbance on the gas-liquid interface grows into a Kelvin-Helmholtz wave and the wave crest forms a thin liquid film that flaps as the wave grows downstream. Increasing the gas speed, it is observed that the film breaks-up into droplets which are eventually thrown into the gas stream at large angles. In a flow where most of the momentum is in the horizontal direction, it is surprising to observe these large ejection angles. Our experiments and simulations show that a recirculation region grows downstream of the wave and leads to vortex shedding similar to the wake of a backward-facing step. The ejection mechanism results from the interaction between the liquid film and the vortex shedding sequence: a recirculation zone appears in the wake of the wave and a liquid film emerges from the wave crest; the recirculation region detaches into a vortex and the gas flow over the wave momentarily reattaches due to the departure of the vortex; this reattached flow pushes the liquid film down; by now, a new recirculation vortex is being created in the wake of the wave-just where the liquid film is now located; the liquid film is blown-up from below by the newly formed recirculation vortex in a manner similar to a bag-breakup event.

  1. Droplet turbulence interactions under subcritical and supercritical conditions

    NASA Technical Reports Server (NTRS)

    Coy, E. B.; Greenfield, S. C.; Ondas, M. S.; Song, Y.-H.; Spegar, T. D.; Santavicca, D. A.

    1993-01-01

    The goal of this research is to experimentally characterize the behavior of droplets in vaporizing liquid sprays under conditions typical of those encountered in high pressure combustion systems such as liquid fueled rocket engines. Of particular interest are measurements of droplet drag, droplet heating, droplet vaporization, droplet distortion, and secondary droplet breakup, under both subcritical and supercritical conditions. The paper presents a brief description of the specific accomplishments which have been made over the past year.

  2. Solvent Polarity Effect on Nonradiative Decay Rate of Thioflavin T.

    PubMed

    Stsiapura, Vitali I; Kurhuzenkau, Siarhei A; Kuzmitsky, Valery A; Bouganov, Oleg V; Tikhomirov, Sergey A

    2016-07-21

    It has been established earlier that fluorescence quantum yield of thioflavin T (ThT)-a probe widely used for amyloid fibrils detection-is viscosity-dependent, and photophysical properties of ThT can be well-described by the fluorescent molecular rotor model, which associates twisted internal charge transfer (TICT) reaction with the main nonradiative decay process in the excited state of the dye. Solutions of ThT in a range of polar solvents were studied using steady-state fluorescence and sub-picosecond transient absorption spectroscopy methods, and we showed that solvent effect on nonradiative transition rate knr cannot be reduced to the dependence on viscosity only and that ∼3 times change of knr can be observed for ThT in aprotic solvents and water, which correlates with solvent polarity. Different behavior was observed in alcohol solutions, particularly in longer n-alcohols, where TICT rate was mainly determined by rotational diffusion of ThT fragments. Quantum-chemical calculations of S0 → S1 transition energy were performed to get insight of polar solvent contribution to the excited-state energy stabilization. Effect of polar solvent on electronic energy levels of ThT was simulated by applying homogeneous electric field according to the Onsager cavity model. Static solvent effect on the excited-state potential energy surface, where charge transfer reaction takes place, was not essential to account for experimentally observed TICT rate differences in water and aprotic solvents. From the other side, nonradiative decay rate of ThT in water, ethylene glycol, and aprotic solvents was found to follow dynamics of polar solvation knr ∼ τS(-1), which can explain dependence of the TICT rate on both polarity and viscosity of the solvents.

  3. Safe battery solvents

    DOEpatents

    Harrup, Mason K.; Delmastro, Joseph R.; Stewart, Frederick F.; Luther, Thomas A.

    2007-10-23

    An ion transporting solvent maintains very low vapor pressure, contains flame retarding elements, and is nontoxic. The solvent in combination with common battery electrolyte salts can be used to replace the current carbonate electrolyte solution, creating a safer battery. It can also be used in combination with polymer gels or solid polymer electrolytes to produce polymer batteries with enhanced conductivity characteristics. The solvents may comprise a class of cyclic and acyclic low molecular weight phosphazenes compounds, comprising repeating phosphorus and nitrogen units forming a core backbone and ion-carrying pendent groups bound to the phosphorus. In preferred embodiments, the cyclic phosphazene comprises at least 3 phosphorus and nitrogen units, and the pendent groups are polyethers, polythioethers, polyether/polythioethers or any combination thereof, and/or other groups preferably comprising other atoms from Group 6B of the periodic table of elements.

  4. Separation by solvent extraction

    DOEpatents

    Holt, Jr., Charles H.

    1976-04-06

    17. A process for separating fission product values from uranium and plutonium values contained in an aqueous solution, comprising adding an oxidizing agent to said solution to secure uranium and plutonium in their hexavalent state; contacting said aqueous solution with a substantially water-immiscible organic solvent while agitating and maintaining the temperature at from -1.degree. to -2.degree. C. until the major part of the water present is frozen; continuously separating a solid ice phase as it is formed; separating a remaining aqueous liquid phase containing fission product values and a solvent phase containing plutonium and uranium values from each other; melting at least the last obtained part of said ice phase and adding it to said separated liquid phase; and treating the resulting liquid with a new supply of solvent whereby it is practically depleted of uranium and plutonium.

  5. Solvent resistant copolyimide

    NASA Technical Reports Server (NTRS)

    Chang, Alice C. (Inventor); St. Clair, Terry L. (Inventor)

    1995-01-01

    A solvent resistant copolyimide was prepared by reacting 4,4'-oxydiphthalic anhydride with a diaimine blend comprising, based on the total amount of the diamine blend, about 75 to 90 mole percent of 3,4'-oxydianiline and about 10 to 25 mole percent p-phenylene diamine. The solvent resistant copolyimide had a higher glass transition temperature when cured at 350.degree. , 371.degree. and 400.degree. C. than LaRC.TM.-IA. The composite prepared from the copolyimide had similar mechanical properties to LaRC.TM.-IA. Films prepared from the copolyimide were resistant to immediate breakage when exposed to solvents such as dimethylacetamide and chloroform. The adhesive properties of the copolyimide were maintained even after testing at 23.degree., 150.degree., 177.degree. and 204.degree. C.

  6. Halogenated solvent remediation

    DOEpatents

    Sorenson, Jr., Kent S.

    2008-11-11

    Methods for enhancing bioremediation of ground water contaminated with nonaqueous halogenated solvents are disclosed. An illustrative method includes adding an electron donor for microbe-mediated anaerobic reductive dehalogenation of the halogenated solvents, which electron donor enhances mass transfer of the halogenated solvents from residual source areas into the aqueous phase of the ground water. Illustrative electron donors include C.sub.2-C.sub.4 carboxylic acids and hydroxy acids, salts thereof, esters of C.sub.2-C.sub.4 carboxylic acids and hydroxy acids, and mixtures thereof, of which lactic acid, salts of lactic acid--such as sodium lactate, lactate esters, and mixtures thereof are particularly illustrative. The microbes are either indigenous to the ground water, or such microbes can be added to the ground water in addition to the electron donor.

  7. Halogenated solvent remediation

    DOEpatents

    Sorenson, Kent S.

    2004-08-31

    Methods for enhancing bioremediation of ground water contaminated with nonaqueous halogenated solvents are disclosed. A preferred method includes adding a composition to the ground water wherein the composition is an electron donor for microbe-mediated reductive dehalogenation of the halogenated solvents and enhances mass transfer of the halogenated solvents from residual source areas into the aqueous phase of the ground water. Illustrative compositions effective in these methods include surfactants such as C.sub.2 -C.sub.4 carboxylic acids and hydroxy acids, salts thereof, esters of C.sub.2 -C.sub.4 carboxylic acids and hydroxy acids, and mixtures thereof. Especially preferred compositions for use in these methods include lactic acid, salts of lactic acid, such as sodium lactate, lactate esters, and mixtures thereof. The microbes are either indigenous to the ground water, or such microbes can be added to the ground water in addition to the composition.

  8. Synchronous universal droplet logic and control

    NASA Astrophysics Data System (ADS)

    Katsikis, Georgios; Cybulski, James S.; Prakash, Manu

    2015-07-01

    Droplets are versatile digital materials; they can be produced at high throughput, perform chemical reactions as miniature beakers and carry biological entities. Droplets have been manipulated with electric, optical, acoustic and magnetic forces, but all these methods use serial controls to address individual droplets. An alternative is algorithmic manipulation based on logic operations that automatically compute where droplets are stored or directed, thereby enabling parallel control. However, logic previously implemented in low-Reynolds-number droplet hydrodynamics is asynchronous and thus prone to errors that prevent scaling up the complexity of logic operations. Here we present a platform for error-free physical computation via synchronous universal logic. Our platform uses a rotating magnetic field that enables parallel manipulation of arbitrary numbers of ferrofluid droplets on permalloy tracks. Through the coupling of magnetic and hydrodynamic interaction forces between droplets, we developed AND, OR, XOR, NOT and NAND logic gates, fanouts, a full adder, a flip-flop and a finite-state machine. Our platform enables large-scale integration of droplet logic, analogous to the scaling seen in digital electronics, and opens new avenues in mesoscale material processing.

  9. Orientation Dependence of Jumping Droplet Condensation

    NASA Astrophysics Data System (ADS)

    Berrier, Austin; Boreyko, Jonathan; Nature-Inspired Fluids; Interfaces Team

    2015-11-01

    On nanostructured superhydrophobic surfaces, microscopic condensate exhibits out-of-plane jumping that minimizes the average droplet size for maximal phase-change heat transfer. This jumping-droplet phenomenon occurs independently of gravity and is due to surface energy being partially converted to kinetic energy upon coalescence events. Although the initial departure of the jumping droplets is independent of gravity, the subsequent trajectories exhibit a dependence upon the orientation of the substrate. The drop size distribution of jumping-droplet condensation growing on a superhydrophobic substrate was characterized for both horizontal and vertical surface orientations. With the horizontal orientation, jumping condensate returns to the substrate by gravity. While this can result in chain reactions with other droplets to trigger further jumping events, eventually the rebounding droplets become too large to jump and are stuck on the surface. In contrast, droplets jumping off a vertically oriented surface do not return to the substrate. For this reason, the maximum droplet diameters during condensation growth were found to be significantly larger on the horizontally oriented superhydrophobic surface than on the vertical orientation.

  10. Analysis of coalescence behavior for compressed droplets

    NASA Astrophysics Data System (ADS)

    Choi, Sung Woong; Lee, Dong Eon; Lee, Woo Il; Kim, Han Sang

    2017-03-01

    Coalescence of droplets is a significant phenomenon, and it has been adapted to many applications such as raindrop formation, emulsion polymerization, ink-jet printing, coating, and multiphase flows. In this study, the morphological characteristics of two compressed adjacent droplets between two parallel plates were investigated to study the phenomenon of coalescence of droplets. By controlling the distance of the dispensed droplets, various results for coalescence of droplets were evaluated, especially, from the view of the minor axis, major axis, and meniscus liquid bridge of the coalesced droplet. Experimental results show that the length of the meniscus liquid bridge rapidly increases and then the rate of increase slows with time. The increase rate of the major and minor axes is largely influenced by the meniscus liquid bridge, which is mainly due to the curvature between the droplets. The numerical modeling of the coalescence of the two compressed droplets between two parallel plates was presented and simulation was conducted to realize the coalescence behavior. Comparison with numerical simulation showed that there was a good agreement with the experimental results.

  11. Binary droplet collision at high Weber number

    NASA Astrophysics Data System (ADS)

    Pan, Kuo-Long; Chou, Ping-Chung; Tseng, Yu-Jen

    2009-09-01

    By using the techniques developed for generating high-speed droplets, we have systematically investigated binary droplet collision when the Weber number (We) was increased from the range usually tested in previous studies on the order of 10 to a much larger value of about 5100 for water (a droplet at 23 m/s with a diameter of 0.7 mm). Various liquids were also used to explore the effects of viscosity and surface tension. Specifically, beyond the well-known regimes at moderate We’s, which exhibited coalescence, separation, and separation followed by satellite droplets, we found different behaviors showing a fingering lamella, separation after fingering, breakup of outer fingers, and prompt splattering into multiple secondary droplets as We was increased. The critical Weber numbers that mark the boundaries between these impact regimes are identified. The specific impact behaviors, such as fingering and prompt splattering or splashing, share essential similarity with those also observed in droplet-surface impacts, whereas substantial variations in the transition boundaries may result from the disparity of the boundary conditions at impacts. To compare the outcomes of both types of collisions, a simple model based on energy conservation was carried out to predict the maximum diameter of an expanding liquid disk for a binary droplet collision. The results oppose the dominance of viscous drag, as proposed by previous studies, as the main deceleration force to effect a Rayleigh-Taylor instability and ensuing periphery fingers, which may further lead to the formations of satellite droplets.

  12. Dynamic Morphologies of Microscale Droplet Interface Bilayers

    SciTech Connect

    Mruetusatorn, Prachya; Boreyko, Jonathan B; Sarles, Stephen A; Venkatesan, Guru; Hayes, Douglas G; Collier, Pat

    2014-01-01

    Droplet interface bilayers (DIBs) are a powerful platform for studying the dynamics of synthetic cellular membranes; however, very little has been done to exploit the unique dynamical features of DIBs. Here, we generate microscale droplet interface bilayers ( DIBs) by bringing together femtoliter-volume water droplets in a microfluidic oil channel, and characterize morphological changes of the DIBs as the droplets shrink due to evaporation. By varying the initial conditions of the system, we identify three distinct classes of dynamic morphology. (1) Buckling and Fission: When forming DIBs using the lipid-out method (lipids in oil phase), lipids in the shrinking monolayers continually pair together and slide into the bilayer to conserve their mass. As the bilayer continues to grow, it becomes confined, buckles, and eventually fissions one or more vesicles. (2) Uniform Shrinking: When using the lipid-in method (lipids in water phase) to form DIBs, lipids uniformly transfer from the monolayers and bilayer into vesicles contained inside the water droplets. (3) Stretching and Unzipping: Finally, when the droplets are pinned to the wall(s) of the microfluidic channel, the droplets become stretched during evaporation, culminating in the unzipping of the bilayer and droplet separation. These findings offer a better understanding of the dynamics of coupled lipid interfaces.

  13. Determination of charge on asphaltene nanoaggregates in air using electrostatic force microscopy.

    PubMed

    Gaikwad, Ravi; Hande, Aharnish; Das, Siddhartha; Mitra, Sushanta K; Thundat, Thomas

    2015-01-20

    In this paper, we provide measurement of charge of asphaltene nanoaggregates in air using electrostatic force microscopy. We obtain the average surface charge density of the nanoaggregates as 43.7 nC/cm(2). Among the different aspects of asphaltene, one of the least known is its charge and the effect of solvent and compositional variability (of asphaltene) in dictating this charge. For aqueous systems, asphaltene charge demonstrates a strong dependence on the pH and the salt concentration, indicating that a possible ionization of the surface groups leads to this charging. On the contrary, for asphaltene in nonpolar media (e.g., toluene and heptane), it is believed that asphaltene native charge is central in dictating this charging. This native charge is the solvent-independent charge or the asphaltene charge in air. Our measurements, therefore, provide the first direct quantification (i.e., a quantification of charge not from the measurement of the asphaltene mobilities, which in turn requires specification of the nonuniform asphaltene size distribution) of this asphaltene native charge by conducting the measurements in air. Similar measurements in a solvent may introduce a solvent-dependent value, thereby forbidding not only the exact quantification of this native charge but also the understanding of the specific role of the solvent. This measurement, therefore, will provide a useful starting point to quantify the mechanism of asphaltene charging in nonpolar solvents with important ramifications in deciphering the role of asphaltene in transport and handling of crude and heavy oils.

  14. Droplet freezing, docking, and the exchange of immiscible phase and surfactant around frozen droplets.

    PubMed

    Sgro, Allyson E; Chiu, Daniel T

    2010-07-21

    This paper describes a platform for cooling microfluidic chips so as to freeze aqueous droplets flowing in oil. Using a whole-chip cooling chamber, we can control the ambient temperature surrounding a microfluidic chip and induce cooling and freezing inside the channels. When combined with a droplet generation and droplet docking chip, this platform allows for the facile freezing of droplets immobilized in resistance-based docks. Depending on the design and shape of the docks, the frozen droplets can either be trapped stably in the docks or be released because deformed non-frozen aqueous droplets turn spherical when frozen, and thus can become dislodged from the docks. Additionally, using this chamber and chip combination we are able to exchange immiscible phases and surfactants surrounding the frozen droplets. The materials and methods are inexpensive and easily accessible to microfluidics researchers, making this a simple addition to an existing microfluidic platform.

  15. Fiber-Supported Droplet Combustion Experiment-2

    NASA Technical Reports Server (NTRS)

    Colantonio, Renato O.

    1998-01-01

    A major portion of the energy produced in the world today comes from the burning of liquid hydrocarbon fuels in the form of droplets. Understanding the fundamental physical processes involved in droplet combustion is not only important in energy production but also in propulsion, in the mitigation of combustion-generated pollution, and in the control of the fire hazards associated with handling liquid combustibles. Microgravity makes spherically symmetric combustion possible, allowing investigators to easily validate their droplet models without the complicating effects of gravity. The Fiber-Supported Droplet Combustion (FSDC-2) investigation was conducted in the Microgravity Glovebox facility of the shuttles' Spacelab during the reflight of the Microgravity Science Laboratory (MSL- 1R) on STS-94 in July 1997. FSDC-2 studied fundamental phenomena related to liquid fuel droplet combustion in air. Pure fuels and mixtures of fuels were burned as isolated single and duo droplets with and without forced air convection. FSDC-2 is sponsored by the NASA Lewis Research Center, whose researchers are working in cooperation with several investigators from industry and academia. The rate at which a droplet burns is important in many commercial applications. The classical theory of droplet burning assumes that, for an isolated, spherically symmetric, single-fuel droplet, the gas-phase combustion processes are much faster than the droplet surface regression rate and that the liquid phase is at a uniform temperature equal to the boiling point. Recent, more advanced models predict that both the liquid and gas phases are unsteady during a substantial portion of the droplet's burning history, thus affecting the instantaneous and average burning rates, and that flame radiation is a dominant mechanism that can extinguish flames in a microgravity environment. FSDC-2 has provided well-defined, symmetric droplet burning data including radiative emissions to validate these theoretical

  16. Charged particle accelerator grating

    DOEpatents

    Palmer, Robert B.

    1986-01-01

    A readily disposable and replaceable accelerator grating for a relativistic particle accelerator. The grating is formed for a plurality of liquid droplets that are directed in precisely positioned jet streams to periodically dispose rows of droplets along the borders of a predetermined particle beam path. A plurality of lasers are used to direct laser beams into the droplets, at predetermined angles, thereby to excite the droplets to support electromagnetic accelerating resonances on their surfaces. Those resonances operate to accelerate and focus particles moving along the beam path. As the droplets are distorted or destroyed by the incoming radiation, they are replaced at a predetermined frequency by other droplets supplied through the jet streams.

  17. Charged particle accelerator grating

    DOEpatents

    Palmer, Robert B.

    1986-09-02

    A readily disposable and replaceable accelerator grating for a relativistic particle accelerator. The grating is formed for a plurality of liquid droplets that are directed in precisely positioned jet streams to periodically dispose rows of droplets along the borders of a predetermined particle beam path. A plurality of lasers are used to direct laser beams into the droplets, at predetermined angles, thereby to excite the droplets to support electromagnetic accelerating resonances on their surfaces. Those resonances operate to accelerate and focus particles moving along the beam path. As the droplets are distorted or destroyed by the incoming radiation, they are replaced at a predetermined frequency by other droplets supplied through the jet streams.

  18. Settling of fixed erythrocyte suspension droplets

    NASA Technical Reports Server (NTRS)

    Omenyi, S. N.; Snyder, R. S.

    1983-01-01

    It is pointed out that when particles behave collectively rather than individually, the fractionation of micron-size particles on the basis of size, density, and surface characteristics by centrifugation and electrophoresis is hindered. The formation and sedimentation of droplets containing particles represent an extreme example of collective behavior and pose a major problem for these separation methods when large quantities of particles need to be fractionated. Experiments are described that measure droplet sizes and settling rates for a variety of particles and droplets. Expressions relating the particle concentration in a drop to measurable quantities of the fluids and particles are developed. The number of particles in each droplet is then estimated, together with the effective droplet density. Red blood cells from different animals fixed in glutaraldehyde provide model particle groups.

  19. Droplet microfluidics in (bio)chemical analysis.

    PubMed

    Basova, Evgenia Yu; Foret, Frantisek

    2015-01-07

    Droplet microfluidics may soon change the paradigm of performing chemical analyses and related instrumentation. It can improve not only the analysis scale, possibility for sensitivity improvement, and reduced consumption of chemical and biological reagents, but also the speed of performing a variety of unit operations. At present, microfluidic platforms can reproducibly generate monodisperse droplet populations at kHz or higher rates with droplet sizes suitable for high-throughput experiments, single-cell detection or even single molecule analysis. In addition to being used as microreactors with volume in the micro- to femtoliter range, droplet based systems have also been used to directly synthesize particles and encapsulate biological entities for biomedicine and biotechnology applications. This minireview summarizes various droplet microfluidics operations and applications for (bio)chemical assays described in the literature during the past few years.

  20. Removal of biofilms by impinging water droplets

    NASA Astrophysics Data System (ADS)

    Cense, A. W.; van Dongen, M. E. H.; Gottenbos, B.; Nuijs, A. M.; Shulepov, S. Y.

    2006-12-01

    The process of impinging water droplets on Streptococcus mutans biofilms was studied experimentally and numerically. Droplets were experimentally produced by natural breakup of a cylindrical liquid jet. Droplet diameter and velocity were varied between 20 and 200 μm and between 20 and 100 m/s, respectively. The resulting erosion process of the biofilm was determined experimentally with high-speed recording techniques and a quantitative relationship between the removal rate, droplet size, and velocity was determined. The shear stress and the pressure on the surface during droplet impact were determined by numerical simulations, and a qualitative agreement between the experiment and the simulation was obtained. Furthermore, it was shown that the stresses on the surface are strongly reduced when a water film is present.

  1. Capillary droplet propulsion on a fibre.

    PubMed

    Haefner, Sabrina; Bäumchen, Oliver; Jacobs, Karin

    2015-09-21

    A viscous liquid film coating a fibre becomes unstable and decays into droplets due to the Rayleigh-Plateau instability (RPI). Here, we report on the generation of uniform droplets on a hydrophobized fibre by taking advantage of this effect. In the late stages of liquid column breakup, a three-phase contact line can be formed at one side of the droplet by spontaneous rupture of the thinning film. The resulting capillary imbalance leads to droplet propulsion along the fibre. We study the dynamics and the dewetting speed of the droplet as a function of molecular weight as well as temperature and compare to a force balance model based on purely viscous dissipation.

  2. Soot agglomeration in isolated, free droplet combustion

    NASA Technical Reports Server (NTRS)

    Choi, M. Y.; Dryer, F. L.; Green, G. J.; Sangiovanni, J. J.

    1993-01-01

    Under the conditions of an isolated, free droplet experiment, hollow, carbonaceous structures, called soot spheres, were observed to form during the atmospheric pressure, low Reynolds number combustion of 1-methylnaphthalene. These structures which are agglomerates composed of smaller spheroidal units result from both thermophoretic effects induced by the envelope flame surrounding each drop and aerodynamic effects caused by changes in the relative gas/drop velocities. A chemically reacting flow model was used to analyze the process of sootshell formation during microgravity droplet combustion. The time-dependent temperature and gas property field surrounding the droplet was determined, and the soot cloud location for microgravity combustion of n-heptane droplets was predicted. Experiments showed that the sooting propensity of n-alkane fuel droplets can be varied through diluent substitution, oxygen-index variations, and ambient pressure reductions.

  3. Droplet mixers: Microfluidics, mixing measures and optimization

    NASA Astrophysics Data System (ADS)

    Stone, Zachary; Stone, Howard

    2003-11-01

    Rapid mixing is essential in a variety of microfluidic applications but is often difficult to achieve at low Reynolds numbers. Inspired by a recently developed microdevice that mixes reagents in droplets, which simply flow along a periodic serpentine channel (Song, Tice and Ismagilov, 2003), we investigate a model ``droplet mixer". The model consists of a spherical droplet immersed in a periodic sequence of distinct external flows, which are superpositions of uniform and shear flows. We label the fluid inside the droplet with two colors and visualize mixing with a method we call ``backtrace imaging", which allows us to render cross-sections of the droplet at arbitrary times during the mixing cycle. To analyze our results, we present a simple measure of mixing, which allows us to locate sets of parameters that optimize mixing over a small number of flow cycles. We also consider shear flows in multiple directions and the effect of random variations in the durations of external flows.

  4. Autophagy and Lipid Droplets in the Liver.

    PubMed

    Martinez-Lopez, Nuria; Singh, Rajat

    2015-01-01

    Autophagy is a conserved quality-control pathway that degrades cytoplasmic contents in lysosomes. Autophagy degrades lipid droplets through a process termed lipophagy. Starvation and an acute lipid stimulus increase autophagic sequestration of lipid droplets and their degradation in lysosomes. Accordingly, liver-specific deletion of the autophagy gene Atg7 increases hepatic fat content, mimicking the human condition termed nonalcoholic fatty liver disease. In this review, we provide insights into the molecular regulation of lipophagy, discuss fundamental questions related to the mechanisms by which autophagosomes recognize lipid droplets and how ATG proteins regulate membrane curvature for lipid droplet sequestration, and comment on the possibility of cross talk between lipophagy and cytosolic lipases in lipid mobilization. Finally, we discuss the contribution of lipophagy to the pathophysiology of human fatty liver disease. Understanding how lipophagy clears hepatocellular lipid droplets could provide new ways to prevent fatty liver disease, a major epidemic in developed nations.

  5. The Lipid-Droplet Proteome Reveals that Droplets Are a Protein-Storage Depot

    SciTech Connect

    Cermelli, Silvia; Guo, Yi; Gross, Steven P.; Welte, Michael

    2006-09-19

    Lipid droplets are ubiquitous organelles that are among the basic building blocks of eukaryotic cells. Despite central roles for cholesterol homeostasis and lipid metabolism, their function and protein composition are poorly understood. Results: We purified lipid droplets from Drosophila embryos and analyzed the associated proteins by capillary LC-MS-MS. Important functional groups include enzymes involved in lipid metabolism, signaling molecules, and proteins related to membrane trafficking. Unexpectedly, histones H2A, H2Av, and H2B were present. Using biochemistry, genetics, real-time imaging, and cell biology, we confirm that roughly 50% of certain embryonic histones are physically attached to lipid droplets, a localization conserved in other fly species. Histone association with droplets starts during oogenesis and is prominent in early embryos, but it is undetectable in later stages or in cultured cells. Histones on droplets are not irreversibly trapped; quantitation of droplet histone levels and transplantation experiments suggest that histones are transferred from droplets to nuclei as development proceeds. When this maternal store of histones is unavailable because lipid droplets are mislocalized, zygotic histone production starts prematurely. Conclusions: Because we uncover a striking proteomic similarity of Drosophila droplets to mammalian lipid droplets, Drosophila likely provides a good model for understanding droplet function in general. Our analysis also reveals a new function for these organelles; the massive nature of histone association with droplets and its developmental time-course suggest that droplets sequester maternally provided proteins until they are needed. We propose that lipid droplets can serve as transient storage depots for proteins that lack appropriate binding partners in the cell. Such sequestration may provide a general cellular strategy for handling excess proteins.

  6. Two Droplets on Wire Approaching Ignition

    NASA Technical Reports Server (NTRS)

    2003-01-01

    The Fiber-Supported Droplet Combustion (FSDC) uses two droplets positioned on the fiber wire, instead of the usual one. Two droplets more closely simulates the environment in engines, which ignite many fuel droplets at once. The behavior of the burning was also unexpected -- the droplets moved together after ignition, generating quite a bit of data for understanding the interaction of fuel droplets while they burn. This MPEG movie (1.3 MB) shows a time-lapse of this burn (3x speed). Because FSDC is backlit (the bright glow behind the drops), you carnot see the glow of the droplets while they burn -- instead, you see them shrink! The small blobs left on the wire after the burn are the beads used to center the fuel droplet on the wire. This image was taken on STS-94, July 12, 1997, MET:10/19:13 (approximate). FSDC-2 studied fundamental phenomena related to liquid fuel droplet combustion in air. Pure fuels and mixtures of fuels were burned as isolated single and dual droplets with and without forced air convection. The FSDC guest investigator was Forman Williams, University of California, San Diego. The experiment was part of the space research investigations conducted during the Microgravity Science Laboratory-1R mission (STS-94, July 1-17 1997). Advanced combustion experiments will be a part of investigations planned for the International Space Station. (1.3MB, 12-second MPEG, screen 320 x 240 pixels; downlinked video, higher quality not available) A still JPG composite of this movie is available at http://mix.msfc.nasa.gov/ABSTRACTS/MSFC-0300178.html.

  7. Droplet migration characteristics in confined oscillatory microflows

    NASA Astrophysics Data System (ADS)

    Chaudhury, Kaustav; Mandal, Shubhadeep; Chakraborty, Suman

    2016-02-01

    We analyze the migration characteristics of a droplet in an oscillatory flow field in a parallel plate microconfinement. Using phase field formalism, we capture the dynamical evolution of the droplet over a wide range of the frequency of the imposed oscillation in the flow field, drop size relative to the channel gap, and the capillary number. The latter two factors imply the contribution of droplet deformability, commonly considered in the study of droplet migration under steady shear flow conditions. We show that the imposed oscillation brings an additional time complexity in the droplet movement, realized through temporally varying drop shape, flow direction, and the inertial response of the droplet. As a consequence, we observe a spatially complicated pathway of the droplet along the transverse direction, in sharp contrast to the smooth migration under a similar yet steady shear flow condition. Intuitively, the longitudinal component of the droplet movement is in tandem with the flow continuity and evolves with time at the same frequency as that of the imposed oscillation, although with an amplitude decreasing with the frequency. The time complexity of the transverse component of the movement pattern, however, cannot be rationalized through such intuitive arguments. Towards bringing out the underlying physics, we further endeavor in a reciprocal identity based analysis. Following this approach, we unveil the time complexities of the droplet movement, which appear to be sufficient to rationalize the complex movement patterns observed through the comprehensive simulation studies. These results can be of profound importance in designing droplet based microfluidic systems in an oscillatory flow environment.

  8. Control of droplet morphology for inkjet-printed TIPS-pentacene transistors

    USGS Publications Warehouse

    Lee, Myung Won; Ryu, Gi Seong; Lee, Young Uk; Pearson, Christopher; Petty, Michael C.; Song, Chung Kun

    2012-01-01

    We report on methods to control the morphology of droplets of 6,13-bis(triisopropyl-silylethynyl) pentacene (TIPS-PEN), which are then used in the fabrication of organic thin film transistors (OTFTs). The grain size and distribution of the TIPS-PEN were found to depend on the temperature of the droplets during drying. The performance of the OTFTs could be improved by heating the substrate and also by changing the relative positions of the inkjet-printed droplets. In our experiments, the optimum substrate temperature was 46 °C in air. Transistors with the TIPS-PEN grain boundaries parallel to the current flow between the source and drain electrodes exhibited charge carrier mobilities of 0.44 ± 0.08 cm2/V s.

  9. Accounting for changes in particle charge, dry mass and composition occurring during studies of single levitated particles.

    PubMed

    Haddrell, Allen E; Davies, James F; Yabushita, Akihiro; Reid, Jonathan P

    2012-10-11

    The most used instrument in single particle hygroscopic analysis over the past thirty years has been the electrodynamic balance (EDB). Two general assumptions are made in hygroscopic studies involving the EDB. First, it is assumed that the net charge on the droplet is invariant over the time scale required to record a hygroscopic growth cycle. Second, it is assumed that the composition of the droplet is constant (aside from the addition and removal of water). In this study, we demonstrate that these assumptions cannot always be made and may indeed prove incorrect. The presence of net charge in the humidified vapor phase reduces the total net charge retained by the droplet over prolonged levitation periods. The gradual reduction in charge limits the reproducibility of hygroscopicity measurements made on repeated RH cycles with a single particle, or prolonged experiments in which the particle is held at a high relative humidity. Further, two contrasting examples of the influence of changes in chemical composition changes are reported. In the first, simple acid-base chemistry in the droplet leads to the irreversible removal of gaseous ammonia from a droplet containing an ammonium salt on a time scale that is shorter than the hygroscopicity measurement. In the second example, the net charge on the droplet (<100 fC) is high enough to drive redox chemistry within the droplet. This is demonstrated by the reduction of iodic acid in a droplet made solely of iodic acid and water to form iodine and an iodate salt.

  10. Stochastic kinetics reveal imperative role of anisotropic interfacial tension to determine morphology and evolution of nucleated droplets in nematogenic films

    NASA Astrophysics Data System (ADS)

    Bhattacharjee, Amit Kumar

    2017-01-01

    For isotropic fluids, classical nucleation theory predicts the nucleation rate, barrier height and critical droplet size by ac- counting for the competition between bulk energy and interfacial tension. The nucleation process in liquid crystals is less understood. We numerically investigate nucleation in monolayered nematogenic films using a mesoscopic framework, in par- ticular, we study the morphology and kinetic pathway in spontaneous formation and growth of droplets of the stable phase in the metastable background. The parameter κ that quantifies the anisotropic elastic energy plays a central role in determining the geometric structure of the droplets. Noncircular nematic droplets with homogeneous director orientation are nucleated in a background of supercooled isotropic phase for small κ. For large κ, noncircular droplets with integer topological charge, accompanied by a biaxial ring at the outer surface, are nucleated. The isotropic droplet shape in a superheated nematic background is found to depend on κ in a similar way. Identical growth laws are found in the two cases, although an unusual two-stage mechanism is observed in the nucleation of isotropic droplets. Temporal distributions of successive events indi- cate the relevance of long-ranged elasticity-mediated interactions within the isotropic domains. Implications for a theoretical description of nucleation in anisotropic fluids are discussed.

  11. Stochastic kinetics reveal imperative role of anisotropic interfacial tension to determine morphology and evolution of nucleated droplets in nematogenic films

    PubMed Central

    Bhattacharjee, Amit Kumar

    2017-01-01

    For isotropic fluids, classical nucleation theory predicts the nucleation rate, barrier height and critical droplet size by ac- counting for the competition between bulk energy and interfacial tension. The nucleation process in liquid crystals is less understood. We numerically investigate nucleation in monolayered nematogenic films using a mesoscopic framework, in par- ticular, we study the morphology and kinetic pathway in spontaneous formation and growth of droplets of the stable phase in the metastable background. The parameter κ that quantifies the anisotropic elastic energy plays a central role in determining the geometric structure of the droplets. Noncircular nematic droplets with homogeneous director orientation are nucleated in a background of supercooled isotropic phase for small κ. For large κ, noncircular droplets with integer topological charge, accompanied by a biaxial ring at the outer surface, are nucleated. The isotropic droplet shape in a superheated nematic background is found to depend on κ in a similar way. Identical growth laws are found in the two cases, although an unusual two-stage mechanism is observed in the nucleation of isotropic droplets. Temporal distributions of successive events indi- cate the relevance of long-ranged elasticity-mediated interactions within the isotropic domains. Implications for a theoretical description of nucleation in anisotropic fluids are discussed. PMID:28054600

  12. Morphological transitions and buckling characteristics in a nanoparticle-laden sessile droplet resting on a heated hydrophobic substrate.

    PubMed

    Bansal, Lalit; Miglani, Ankur; Basu, Saptarshi

    2016-04-01

    In this work, we have established the evaporation-liquid flow coupling mechanism by which sessile nanofluid droplets on a hydrophobic substrate evaporate and agglomerate to form unique morphological features under controlled external heating. It is well understood that evaporation coupled with internal liquid flow controls particle transport in a spatiotemporal sense. Flow characteristics inside the heated droplet are investigated and found to be driven by the buoyancy effects. Velocity magnitudes are observed to increase by an order at higher temperatures with similar looking flow profiles. The recirculating flow induced particle transport coupled with collision of particles and shear interaction between them leads to the formation of dome shaped viscoelastic shells of different dimensions depending on the surface temperature. These shells undergo sol-gel transition and subsequently undergo buckling instability leading to the formation of daughter cavities. With an increase in the surface temperature, droplets exhibit buckling from multiple sites over a larger sector in the top half of the droplet. Irrespective of the initial nanoparticle concentration and substrate temperature, growth of a daughter cavity (subsequent to buckling) inside the droplet is found to be controlled by the solvent evaporation rate from the droplet periphery and is shown to exhibit a universal trend.

  13. Solvent effects on the electronic absorption spectra and acid strength of some substituted pyridinols

    NASA Astrophysics Data System (ADS)

    Hashem, Elham Y.; Saleh, Magda S.

    2002-01-01

    The electronic absorption spectra of some substituted pyridinols in organic solvents of different polarities are studied. Also, the solvent effects on the intramolecular charge transfer bands are discussed using various solvent parameters. The acid-base equilibria of the compounds used are studied spectrophotometrically in various mixed aqueous solvents at 25 °C and 0.1 M ionic strength (NaClO 4). Furthermore, the influence of the solvents on the dissociation constants and tautomeric equilibria of a pyridinol derivatives are discussed. The effect of molecular structure of the pyridinols on the p K's is also examined.

  14. ONSITE SOLVENT RECOVERY

    EPA Science Inventory

    This study evaluated the product quality, waste reduction/pollution prevention, and economic aspects of three technologies for onsite solvent recovery. The technologies were (1) atmospheric batch distillation, (2) vacuum heat-pump distillation, and (3) low-emission vapor degreas...

  15. DESIGNING GREENER SOLVENTS

    EPA Science Inventory

    Computer-aided design of chemicals and chemical mixtures provides a powerful tool to help engineers identify cleaner process designs and more-benign alternatives to toxic industrial solvents. Three software programs are discussed: (1) PARIS II (Program for Assisting the Replaceme...

  16. Organic solvent topical report

    SciTech Connect

    Cowley, W.L.

    1998-04-30

    This report is the technical basis for the accident and consequence analyses used in the Hanford Tank Farms Basis for Interim Operation. The report also contains the scientific and engineering information and reference material needed to understand the organic solvent safety issue. This report includes comments received from the Chemical Reactions Subcommittee of the Tank Advisory Panel.

  17. Organic solvent topical report

    SciTech Connect

    COWLEY, W.L.

    1999-05-13

    This report provides the basis for closing the organic solvent safety issue. Sufficient information is presented to conclude that risk posed by an organic solvent fire is within risk evaluation guidelines. This report updates information contained in Analysis of Consequences of Postulated Solvent Fires in Hanford Site Waste Tanks. WHC-SD-WM-CN-032. Rev. 0A (Cowley et al. 1996). However, this document will not replace Cowley et al (1996) as the primary reference for the Basis for Interim Operation (BIO) until the recently submitted BIO amendment (Hanson 1999) is approved by the US Department of Energy. This conclusion depends on the use of controls for preventing vehicle fuel fires and for limiting the use of flame cutting in areas where hot metal can fall on the waste surface.The required controls are given in the Tank Waste Remediation System Technical Safety Requirements (Noorani 1997b). This is a significant change from the conclusions presented in Revision 0 of this report. Revision 0 of this calcnote concluded that some organic solvent fire scenarios exceeded risk evaluation guidelines, even with controls imposed.

  18. Directional Movement of Droplets in Grooves: Suspended or Immersed?

    PubMed Central

    Xu, Wei; Lan, Zhong; Peng, Benli; Wen, Rongfu; Chen, Yansong; Ma, Xuehu

    2016-01-01

    The behavior of droplets trapped in geometric structures is essential to droplet manipulation applications such as for droplet transport. Here we show that directional droplet movement can be realized by a V-shaped groove with the movement direction controlled by adjusting the surface wettability of the groove inner wall and the cross sectional angle of the groove. Experiments and analyses show that a droplet in a superhydrophobic groove translates from the immersed state to the suspended state as the cross sectional angle of the groove decreases and the suspended droplet departs from the groove bottom as the droplet volume increases. We also demonstrate that this simple grooved structure can be used to separate a water-oil mixture and generate droplets with the desired sizes. The structural effect actuated droplet movements provide a controllable droplet transport method which can be used in a wide range of droplet manipulation applications. PMID:26743167

  19. Directional Movement of Droplets in Grooves: Suspended or Immersed?

    NASA Astrophysics Data System (ADS)

    Xu, Wei; Lan, Zhong; Peng, Benli; Wen, Rongfu; Chen, Yansong; Ma, Xuehu

    2016-01-01

    The behavior of droplets trapped in geometric structures is essential to droplet manipulation applications such as for droplet transport. Here we show that directional droplet movement can be realized by a V-shaped groove with the movement direction controlled by adjusting the surface wettability of the groove inner wall and the cross sectional angle of the groove. Experiments and analyses show that a droplet in a superhydrophobic groove translates from the immersed state to the suspended state as the cross sectional angle of the groove decreases and the suspended droplet departs from the groove bottom as the droplet volume increases. We also demonstrate that this simple grooved structure can be used to separate a water-oil mixture and generate droplets with the desired sizes. The structural effect actuated droplet movements provide a controllable droplet transport method which can be used in a wide range of droplet manipulation applications.

  20. Combustion of interacting droplet arrays in a microgravity environment

    NASA Technical Reports Server (NTRS)

    Dietrich, Daniel L.

    1995-01-01

    This research program involves the study of one and two dimensional arrays of droplets in a buoyant-free environment. The purpose of the work is to extend the database and theories that exist for single droplets into the regime where droplet interactions are important. The eventual goal being to use the results of this work as inputs to models on spray combustion where droplets seldom burn individually; instead the combustion history of a droplet is strongly influenced by the presence of the neighboring droplets. Throughout the course of the work, a number of related aspects of isolated droplet combustion have also been investigated. This paper will review our progress in microgravity droplet array combustion, advanced diagnostics (specifically L2) applied to isolated droplet combustion, and radiative extinction large droplet flames. A small-scale droplet combustion experiment being developed for the Space Shuttle will also be described.

  1. Fluoropolymer surface coatings to control droplets in microfluidic devices.

    PubMed

    Riche, Carson T; Zhang, Chuchu; Gupta, Malancha; Malmstadt, Noah

    2014-06-07

    We have demonstrated the application of low surface energy fluoropolymer coatings onto poly(dimethylsiloxane) (PDMS) microfluidic devices for droplet formation and extraction-induced merger of droplets. Initiated chemical vapor deposition (iCVD) was used to pattern fluoropolymer coatings within microchannels based on geometrical constraints. In a two-phase flow system, the range of accessible flow rates for droplet formation was greatly enhanced in the coated devices. The ability to controllably apply the coating only at the inlet facilitated a method for merging droplets. An organic spacer droplet was extracted from between a pair of aqueous droplets. The size of the organic droplet and the flow rate controlled the time to merge the aqueous droplets; the process of merging was independent of the droplet sizes. Extraction-induced droplet merging is a robust method for manipulating droplets that could be applied in translating multi-step reactions to microfluidic platforms.

  2. Visualization of Electrohydrodynamic Effects and Time Scale Analysis for Impinging Spray Droplets of HFE-7000

    SciTech Connect

    Kreitzer, Paul J.; Kuhlman, John M.

    2008-01-21

    Spray cooling is becoming a leading technique for removing excess heat from high heat flux electronics. Electrohydrodynamic effects have been found to result in significant variation in spray behavior once the applied voltage level is increased enough to reach the Rayleigh limit. In the present work the dielectric coolant HFE-7000 has been used to study spray cooling heat transfer across a thick film resistor heater mounted to a 16 mm diameter pedestal. Heater power levels have been varied from 0 to 80 Watts, with spray flow rates varied from 2 GPH to 6 GPH (2.1x10{sup -6} m{sup 3}/s to 6.3x10{sup -6} m{sup 3}/s). Applied voltage levels between 0 kV and 30 kV with both positive and negative polarity have been applied directly to the brass spray nozzle, resulting in contact charging of the spray. A high-speed video camera was used to study behavior of both the impinging spray and the liquid film that formed on the heater surface. The contact charging was observed to lead to electrostatic atomization or 'breakup' of the droplets. Time scale estimates of the various physical processes within the spray and the liquid film based on the average droplet size have indicated that the time between droplet impacts falling into a crater from a previous droplet is the shortest time scale, which will limit the amount of heat transfer that may take place during spray cooling. However, the observed time between large droplet impacts onto the same heater surface location is comparable to the computed time to heat and vaporize a large drop, indicating a new explanation for the onset of spray cooling CHF: localized dryout of the original large droplet impact craters.

  3. Spreading of a granular droplet

    NASA Astrophysics Data System (ADS)

    Clement, Eric; Sanchez, Ivan; Raynaud, Franck; Lanuza, Jose; Andreotti, Bruno; Aranson, Igor

    2008-03-01

    The influence of controlled vibrations on the granular rheology is investigated in a specifically designed experiment in which a granular film spreads under the action of horizontal vibrations. A nonlinear diffusion equation is derived theoretically that describes the evolution of the deposit shape. A self-similar parabolic shape (the``granular droplet'') and a spreading dynamics are predicted that both agree quantitatively with the experimental results. The theoretical analysis is used to extract effective friction coefficients between the base and the granular layer under sustained and controlled vibrations. A shear thickening regime characteristic of dense granular flows is evidenced at low vibration energy, both for glass beads and natural sand. Conversely, shear thinning is observed at high agitation.

  4. Freezing of stratospheric aerosol droplets

    NASA Astrophysics Data System (ADS)

    Luo, Beiping; Peter, Thomas; Crutzen, Paul

    Theoretical calculations are presented for homogeneous and heterogeneous freezing of sulfuric acid droplets under stratospheric conditions, based on classical nucleation theory. In contrast to previous results it is shown that a prominent candidate for freezing, sulfuric acid tetrahydrate (SAT ≡ H2SO4·4H2O), does not freeze homogeneously. The theoretical results limit the homogeneous freezing rate at 200 K to much less than 1 cm-3s-1, a value that may be estimated from bulk phase laboratory experiments. This suggests that the experimental value is likely to be a measure of heterogeneous, not homogeneous nucleation. Thus, under statospheric conditions, freezing of SAT can only occur in the presence of suitable nuclei; however, even for heterogeneous nucleation experimental results impose strong constraints. Since a nitric acid trihydrate (NAT) embryo probably needs a solid body for nucleation, these results put an important constraint on the theory of NAT formation in polar stratospheric clouds.

  5. Numerical simulations of pendant droplets

    NASA Astrophysics Data System (ADS)

    Pena, Carlos; Kahouadji, Lyes; Matar, Omar; Chergui, Jalel; Juric, Damir; Shin, Seungwon

    2015-11-01

    We simulate the evolution of a three-dimensional pendant droplet through pinch-off using a new parallel two-phase flow solver called BLUE. The parallelization of the code is based on the technique of algebraic domain decomposition where the velocity field is solved by a parallel GMRes method for the viscous terms and the pressure by a parallel multigrid/GMRes method. Communication is handled by MPI message passing procedures. The method for the treatment of the fluid interfaces uses a hybrid Front Tracking/Level Set technique which defines the interface both by a discontinuous density field as well as by a local triangular Lagrangian mesh. This structure allows the interface to undergo large deformations including the rupture and coalescence of fluid interfaces. EPSRC Programme Grant, MEMPHIS, EP/K0039761/1.

  6. Self-propelled droplet behavior during condensation on superhydrophobic surfaces

    NASA Astrophysics Data System (ADS)

    Chu, Fuqiang; Wu, Xiaomin; Zhu, Bei; Zhang, Xuan

    2016-05-01

    Self-propelled droplet motion has applications in various engineering fields such as self-cleaning surfaces, heat transfer enhancement, and anti-icing methods. A superhydrophobic surface was fabricated using two simultaneous chemical reactions with droplet condensation experiments performed on the horizontal superhydrophobic surface to characterize the droplet behavior. The droplet behavior is classified into three types based on their motion features and leftover marks as immobile droplet coalescence, self-propelled droplet jumping, and self-propelled droplet sweeping. This study focuses on the droplet sweeping that occurs due to the ultra-small rolling angle of the superhydrophobic surface, where the resulting droplet sweeps along the surface, merging with all the droplets it meets and leaving a long, narrow, clear track with a large droplet at the end of the track. An easy method is developed to predict the droplet sweeping direction based on the relative positions of the droplets just before coalescence. The droplet sweeping always absorbs dozens of droplets and is not limited by the surface structures; thus, this sweeping has many useful applications. In addition, the relationships between the droplet behavior and the number of participating droplets are also analyzed statistically.

  7. Small GTPase Rab40c Associates with Lipid Droplets and Modulates the Biogenesis of Lipid Droplets

    PubMed Central

    Tan, Ran; Wang, Weijie; Wang, Shicong; Wang, Zhen; Sun, Lixiang; He, Wei; Fan, Rong; Zhou, Yunhe; Xu, Xiaohui; Hong, Wanjin; Wang, Tuanlao

    2013-01-01

    The subcellular location and cell biological function of small GTPase Rab40c in mammalian cells have not been investigated in detail. In this study, we demonstrated that the exogenously expressed GFP-Rab40c associates with lipid droplets marked by neutral lipid specific dye Oil red or Nile red, but not with the Golgi or endosomal markers. Further examination demonstrated that Rab40c is also associated with ERGIC-53 containing structures, especially under the serum starvation condition. Rab40c is increasingly recruited to the surface of lipid droplets during lipid droplets formation and maturation in HepG2 cells. Rab40c knockdown moderately decreases the size of lipid droplets, suggesting that Rab40c is involved in the biogenesis of lipid droplets. Stimulation for adipocyte differentiation increases the expression of Rab40c in 3T3-L1 cells. Rab40c interacts with TIP47, and is appositionally associated with TIP47-labeled lipid droplets. In addition, over-expression of Rab40c causes the clustering of lipid droplets independent of its GTPase activity, but completely dependent of the intact SOCS box domain of Rab40c. In addition, Rab40c displayed self-interaction as well as interaction with TIP47 and the SOCS box is essential for its ability to induce clustering of lipid droplets. Our results suggest that Rab40c is a novel Rab protein associated with lipid droplets, and is likely involved in modulating the biogenesis of lipid droplets. PMID:23638186

  8. Solvent-Ion Interactions in Salt Water: A Simple Experiment.

    ERIC Educational Resources Information Center

    Willey, Joan D.

    1984-01-01

    Describes a procedurally quick, simple, and inexpensive experiment which illustrates the magnitude and some effects of solvent-ion interactions in aqueous solutions. Theoretical information, procedures, and examples of temperature, volume and hydration number calculations are provided. (JN)

  9. Internal Charging

    NASA Technical Reports Server (NTRS)

    Minow, Joseph I.

    2014-01-01

    (1) High energy (>100keV) electrons penetrate spacecraft walls and accumulate in dielectrics or isolated conductors; (2) Threat environment is energetic electrons with sufficient flux to charge circuit boards, cable insulation, and ungrounded metal faster than charge can dissipate; (3) Accumulating charge density generates electric fields in excess of material breakdown strenght resulting in electrostatic discharge; and (4) System impact is material damage, discharge currents inside of spacecraft Faraday cage on or near critical circuitry, and RF noise.

  10. Droplet vaporization in supercritical pressure environments

    NASA Astrophysics Data System (ADS)

    Farrell, Patrick V.; Peters, Bruce D.

    For most liquid-fueled combustion systems the behavior of the fuel as it is introduced to the combustion zone, often by spray injection, will have a significant impact on combustion. The subsequent combustion may be affected to a considerable degree by the initial spread of the liquid, break-up of larger fuel sheets and droplets into droplets of various sizes, droplet vaporization, and diffusion of gaseous fuel. Among the many factors which affect spray break-up and droplet vaporization are the environmental conditions into which the spray is introduced. For both diesel engines and rockets the environment pressure and temperature may be above the critical pressure and temperature of the injected fuel. In a compression-ignition internal combustion engine, the environment consists primarily of air, at pressures from 20 to 100 atmospheres and temperatures ranging from 900 to 1500 K. Even higher pressures are encountered in turbocharged diesels. A typical diesel reference fuel, dodecane, has a thermodynamic critical pressure of about 17 atmospheres, and a critical temperature of 600 K. Fuel is injected into a diesel engine environment in which ambient pressures exceed the critical pressure. While droplet temperatures are subcritical at first, they may rise to the critical temperature or higher. This paper will survey current understanding of supercritical pressure droplet vaporization. Specifically, the topics covered will include: liquid phase behavior; vapor phase behavior; thermodynamic and transport properties; droplet distribution and break-up; micro-explosions; and effects of microgravity.

  11. Three dimensional force balance of asymmetric droplets

    NASA Astrophysics Data System (ADS)

    Kim, Yeseul; Lim, Su Jin; Cho, Kun; Weon, Byung Mook

    2016-11-01

    An equilibrium contact angle of a droplet is determined by a horizontal force balance among vapor, liquid, and solid, which is known as Young's law. Conventional wetting law is valid only for axis-symmetric droplets, whereas real droplets are often asymmetric. Here we show that three-dimensional geometry must be considered for a force balance for asymmetric droplets. By visualizing asymmetric droplets placed on a free-standing membrane in air with X-ray microscopy, we are able to identify that force balances in one side and in other side control pinning behaviors during evaporation of droplets. We find that X-ray microscopy is powerful for realizing the three-dimensional force balance, which would be essential in interpretation and manipulation of wetting, spreading, and drying dynamics for asymmetric droplets. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2016R1D1A1B01007133).

  12. Mechanical vibration of viscoelastic liquid droplets

    NASA Astrophysics Data System (ADS)

    Sharp, James; Harrold, Victoria

    2014-03-01

    The resonant vibrations of viscoelastic sessile droplets supported on different substrates were monitored using a simple laser light scattering technique. In these experiments, laser light was reflected from the surfaces of droplets of high Mw poly acrylamide-co-acrylic acid (PAA) dissolved in water. The scattered light was allowed to fall on the surface of a photodiode detector and a mechanical impulse was applied to the drops using a vibration motor mounted beneath the substrates. The mechanical impulse caused the droplets to vibrate and the scattered light moved across the surface of the photodiode. The resulting time dependent photodiode signal was then Fourier transformed to obtain the mechanical vibrational spectra of the droplets. The frequencies and widths of the resonant peaks were extracted for droplets containing different concentrations of PAA and with a range of sizes. This was repeated for PAA loaded water drops on surfaces which displayed different values of the three phase contact angle. The results were compared to a simple model of droplet vibration which considers the formation of standing wave states on the surface of a viscoelastic droplet. We gratefully acknowledge the support of the Leverhulme trust under grant number RPG-2012-702.

  13. Lipid droplet dynamics in skeletal muscle.

    PubMed

    Bosma, Madeleen

    2016-01-15

    The skeletal muscle is subjected to high mechanical and energetic demands. Lipid droplets are an important source of energy substrates for the working muscle. Muscle cells contain a variety of lipid droplets, which are fundamentally smaller than those found in adipocytes. This translates into a greater lipid droplet surface area serving as the interface for intracellular lipid metabolism. The skeletal muscle has a high plasticity, it is subjected to major remodeling following training and detraining. This coincides with adaptations in lipid droplet characteristics and dynamics. The majority of lipid droplets in skeletal muscle are located in the subsarcolemmal region or in-between the myofibrils, in close vicinity to mitochondria. The vastly organized nature of skeletal muscle fibers limits organelle mobility. The high metabolic rate and substrate turnover in skeletal muscle demands a strict coordination of intramyocellular lipid metabolism and LD dynamics, in which lipid droplet coat proteins play an important role. This review provides insights into the characteristics, diversity and dynamics of skeletal muscle lipid droplets.

  14. Bi-Component Droplet Combustion Experiment Designed

    NASA Technical Reports Server (NTRS)

    Dietrich, Daniel L.

    2002-01-01

    The combustion of liquid fuels is a major source of energy in the world today, and the majority of these fuels are burned in the form of a spray. The research at the NASA Glenn Research Center in droplet combustion has the overall goal of providing a better understanding of spray combustion by studying the smallest element in a spray, the single droplet. The Bi-Component Droplet Combustion Experiment (BCDCE) extends the work at Glenn from pure, or single-component, fuels to an idealized liquid fuel composed of two completely miscible components. The project is a collaborative effort between Glenn and Prof. B.D. Shaw of the University of California, Davis. The BCDCE project is planned to fly onboard the International Space Station in the Multi-User Droplet Combustion Apparatus. The unique feature of this experiment is that it will be the first droplet combustion experiment to perform a detailed characterization of the flow inside a liquid fuel droplet. The experiment will use a relatively new technique called Digital Particle Imaging Velocimetry (DPIV) to characterize the liquid flow. In this technique, very small (approx. 5-mm diameter) particles are dispersed throughout a liquid droplet. These particles are illuminated by a thin laser sheet. Images of the particle motion are recorded on a computer, which then tracks the motion of the particles to determine the flow characteristics.

  15. Statistical steady state in turbulent droplet condensation

    NASA Astrophysics Data System (ADS)

    Siewert, Christoph; Bec, Jérémie; Krstulovic, Giorgio

    2017-01-01

    Motivated by systems in which droplets grow and shrink in a turbulence-driven supersaturation field, we investigate the problem of turbulent condensation in a general manner. Using direct numerical simulations we show that the turbulent fluctuations of the supersaturation field offer different conditions for the growth of droplets which evolve in time due to turbulent transport and mixing. Based on that, we propose a Lagrangian stochastic model for condensation and evaporation of small droplets in turbulent flows. It consists of a set of stochastic integro-differential equations for the joint evolution of the squared radius and the supersaturation along the droplet trajectories. The model has two parameters fixed by the total amount of water and the thermodynamic properties, as well as the Lagrangian integral timescale of the turbulent supersaturation. The model reproduces very well the droplet size distributions obtained from direct numerical simulations and their time evolution. A noticeable result is that, after a stage where the squared radius simply diffuses, the system converges exponentially fast to a statistical steady state independent of the initial conditions. The main mechanism involved in this convergence is a loss of memory induced by a significant number of droplets undergoing a complete evaporation before growing again. The statistical steady state is characterised by an exponential tail in the droplet mass distribution. These results reconcile those of earlier numerical studies, once these various regimes are considered.

  16. Spraying mode effect on droplet formation and ion chemistry in electrosprays.

    PubMed

    Nemes, Peter; Marginean, Ioan; Vertes, Akos

    2007-04-15

    Depending on the spraying conditions and fluid properties, a variety of electrospray regimes exists. Here we explore the changes in ion production that accompany the transitions among the three axial spraying modes, the burst mode, the pulsating Taylor cone mode, and the cone-jet mode. Spray current oscillation and phase Doppler anemometry measurements, fast imaging of the electrified meniscus, and mass spectrometry are utilized to study the formation, size, velocity, and chemical composition of droplets produced in the three modes. High-speed images indicate that the primary droplets are produced by varicose waves and lateral kink instabilities on the liquid jet emerging from the Taylor cone, whereas secondary droplets are formed by fission. Dramatic changes in the droplet size distributions result from the various production and breakup mechanisms observed at different emitter voltages and liquid flow rates. We demonstrate that droplet fission can be facilitated by space charge effects along the liquid jet and in the plume. Compared to the other two regimes, a significantly enhanced signal-to-noise ratio, a lower degree of analyte oxidation, and milder fragmentation are observed for the cone-jet mode.

  17. Photoacoustic spectral characterization of perfluorocarbon droplets

    NASA Astrophysics Data System (ADS)

    Strohm, Eric; Gorelikov, Ivan; Matsuura, Naomi; Kolios, Michael

    2012-02-01

    Perfluorocarbon droplets containing optical absorbing nanoparticles have been developed for use as theranostic agents (for both imaging and therapy) and as dual-mode contrast agents. Droplets can be used as photoacoustic contrast agents, vaporized via optical irradiation, then the resulting bubbles can be used as ultrasound imaging and therapeutic agents. The photoacoustic signals from micron-sized droplets containing silica coated gold nanospheres were measured using ultra-high frequencies (100-1000 MHz). The spectra of droplets embedded in a gelatin phantom were compared to a theoretical model which calculates the pressure wave from a spherical homogenous liquid undergoing thermoelastic expansion resulting from laser absorption. The location of the spectral features of the theoretical model and experimental spectra were in agreement after accounting for increases in the droplet sound speed with frequency. The agreement between experiment and model indicate that droplets (which have negligible optical absorption in the visible and infrared spectra by themselves) emitted pressure waves related to the droplet composition and size, and was independent of the physical characteristics of the optical absorbing nanoparticles. The diameter of individual droplets was calculated using three independent methods: the time domain photoacoustic signal, the time domain pulse echo ultrasound signal, and a fit to the photoacoustic model, then compared to the diameter as measured by optical microscopy. It was found the photoacoustic and ultrasound methods calculated diameters an average of 2.6% of each other, and 8.8% lower than that measured using optical microscopy. The discrepancy between the calculated diameters and the optical measurements may be due to the difficulty in resolving the droplet edges after being embedded in the translucent gelatin medium.

  18. Fog droplet distribution functions for lidar.

    PubMed

    Mallow, J V

    1982-04-15

    The interpretation of lidar data on fog has been limited by two obstacles: approximations in the form of the Mie scattering cross sections for water droplets, and droplet size distribution functions whose relationship to the experiment has not been clear. This paper develops a method for generating distribution functions from experimental data. These functions are then used with newly available Mie cross sections to obtain backscattering and extinction coefficients for singly scattered ruby laser pulses in fog. The results show what experimental lidar accuracies are needed to uniquely determine fog droplet size distribution.

  19. Fog droplet distribution functions for lidar

    SciTech Connect

    Mallow, J.V.

    1982-04-15

    The interpretation of lidar data on fog has been limited by two obstacles: approximations in the form of the Mie scattering cross sections for water droplets, and droplet size distribution functions whose relationship to the experiment has not been clear. This paper develops a method for generating distribution functions from experimental data. These functions are then used with newly available Mie cross sections to obtain backscattering and extinction coefficients for singly scattered ruby laser pulses in fog. The results show what experimental lidar accuracies are needed to uniquely determine fog droplet size distribution.

  20. Orbiting droplets on a vibrated bath

    NASA Astrophysics Data System (ADS)

    Sampara, Naresh; Burger, Loic; Gilet, Tristan; Microfluidics, university of liege Team

    2015-11-01

    A millimeter-sized oil droplet can bounce on a vertically vibrated liquid bath for unlimited time. It may couple to the surface wave it emits; leading to horizontal self-propulsion called walking. When several walkers coexist close to one another, they either repel or attract each other, in response to the superposition of the waves they generate. Attraction leads to various bound states, including droplets that orbit around each other. We have experimentally investigated the variety of quantized orbital motions exhibited by two, three and more identical walkers, as a function of forcing acceleration. Each motion is quantified in terms of droplet and wave energy.

  1. DESIGNING ENVIRONMENTALLY BENIGN SOLVENT SUBSTITUTES

    EPA Science Inventory

    Since the signing of 1987 Montreal Protocol, reducing and eliminating the use of harmful solvents has become an internationally imminent environmental protection mission. Solvent substitution is an effective way to achieve this goal. The Program for Assisting the Replacement of...

  2. On the coupling of solvent characteristics to the electronic structure of solute molecules.

    PubMed

    Bogatko, Stuart; Cauët, Emilie; Geerlings, Paul; De Proft, Frank

    2014-02-28

    We present the results of a theoretical investigation focusing on the solvent structure surrounding the -1, 0 and +1 charged species of F, Cl, Br and I halogen atoms and F2, Cl2, Br2 and I2 di-halogen molecules in a methanol solvent and its influence on the electronic structure of the solute molecules. Our results show a large stabilizing effect arising from the solute-solvent interactions. Well-formed first solvation shells are observed for all species, the structure of which is strongly influenced by the charge of the solute species. Detailed analysis reveals that coordination number, CN, solvent orientation, θ, and solute-solvent distance, d, are important structural characteristics which are coupled to changes in the electronic structure of the solute. We propose that the fundamental chemistry of any solute species is generally regulated by these solvent degrees of freedom.

  3. The effects of turbulence on droplet drag and secondary droplet breakup

    NASA Technical Reports Server (NTRS)

    Song, Y.-H.; Coy, E.; Greenfield, S.; Ondas, M.; Prevish, T.; Spegar, T.; Santavicca, D.

    1994-01-01

    The objective of this research is to obtain an improved understanding of the behavior of droplets in vaporizing sprays, particularly under conditions typical of those in high pressure rocket sprays. Experiments are conducted in a variety of high pressure, high temperature, optically-accessible flow systems, including one which is capable of operation at pressures up to 70 atm, temperatures up to 600 K, gas velocities up to 30 m/sec and turbulence intensities up to 40 percent. Single droplets, 50 to 500 micron in diameter, are produced by an aerodynamic droplet generator and transversely injected into the flow. Measurements are made of the droplet position, size, velocity and temperature and of the droplet's vapor wake from which droplet drag, dispersion, heating, vaporization and breakup are characterized.

  4. Effect of monoglyceride structure and cholesterol content on water permeability of the droplet bilayer.

    PubMed

    Michalak, Zuzanna; Muzzio, Michelle; Milianta, Peter J; Giacomini, Rosario; Lee, Sunghee

    2013-12-23

    The process of water permeation across lipid membranes has significant implications for cellular physiology and homeostasis, and its study may lead to a greater understanding of the relationship between the structure of lipid bilayer and the role that lipid structure plays in water permeation. In this study, we formed a droplet interface bilayer (DIB) by contacting two aqueous droplets together in an immiscible solvent (squalane) containing bilayer-forming surfactant (monoglycerides). Using the DIB model, we present our results on osmotic water permeabilities and activation energy for water permeation of an associated series of unsaturated monoglycerides as the principal component of droplet bilayers, each having the same chain length but differing in the position and number of double bonds, in the absence and presence of a varying concentration of cholesterol. Our findings suggest that the tailgroup structure in a series of monoglyceride bilayers is seen to affect the permeability and activation energy for the water permeation process. Moreover, we have also established the insertion of cholesterol into the droplet bilayer, and have detected its presence via its effect on water permeability. The effect of cholesterol differs depending on the type of monoglyceride. We demonstrate that the DIB can be employed as a convenient model membrane to rapidly explore subtle structural effects on bilayer water permeability.

  5. Numerical methods and calculations for droplet flow, heating and ignition

    NASA Technical Reports Server (NTRS)

    Dwyer, H. A.; Sanders, B. R.; Dandy, D.

    1982-01-01

    A numerical method was devised and employed to solve a variety of problems related to liquid droplet combustion. The basic transport equations of mass, momentum and energy were formulated in terms of generalized nonorthogonal coordinates, which allows for adaptive griding and arbitrary particle shape. Example problems are solved for internal droplet heating, droplet ignition and high Reynolds number flow over a droplet.

  6. Solvent Immersion Imprint Lithography

    SciTech Connect

    Vasdekis, Andreas E.; Wilkins, Michael J.; Grate, Jay W.; Kelly, Ryan T.; Konopka, Allan; Xantheas, Sotiris S.; Chang, M. T.

    2014-06-21

    The mechanism of polymer disolution was explored for polymer microsystem prototyping, including microfluidics and optofluidics. Polymer films are immersed in a solvent, imprinted and finally brought into contact with a non-modified surface to permanently bond. The underlying polymer-solvent interactions were experimentally and theoretically investigated, and enabled rapid polymer microsystem prototyping. During imprinting, small molecule integration in the molded surfaces was feasible, a principle applied to oxygen sensing. Polystyrene (PS) was employed for microbiological studies at extreme environmental conditions. The thermophile anaerobe Clostridium Thermocellum was grown in PS pore-scale micromodels, revealing a double mean generation lifetime than under ideal culture conditions. Microsystem prototyping through directed polymer dissolution is simple and accessible, while simultaneous patterning, bonding, and surface/volume functionalization are possible in less than one minute.

  7. Thermodynamic and kinetic theory of nucleation, deliquescence and efflorescence transitions in the ensemble of droplets on soluble particles.

    PubMed

    Shchekin, Alexander K; Shabaev, Ilya V; Hellmuth, Olaf

    2013-02-07

    Thermodynamic and kinetic peculiarities of nucleation, deliquescence and efflorescence transitions in the ensemble of droplets formed on soluble condensation nuclei from a solvent vapor have been considered. The interplay of the effects of solubility and the size of condensation nuclei has been analyzed. Activation barriers for the deliquescence and phase transitions and for the reverse efflorescence transition have been determined as functions of the relative humidity of the vapor-gas atmosphere, initial size, and solubility of condensation nuclei. It has been demonstrated that, upon variations in the relative humidity of the atmosphere, the crossover in thermodynamically stable and unstable variables of the droplet state takes place. The physical meaning of stable and unstable variables has been clarified. The kinetic equations for establishing equilibrium and steady distributions of binary droplets have been solved. The specific times for relaxation, deliquescence and efflorescence transitions have been calculated.

  8. Selectively splitting a droplet using superhydrophobic stripes on hydrophilic surfaces.

    PubMed

    Song, Dong; Song, Baowei; Hu, Haibao; Du, Xiaosong; Zhou, Feng

    2015-06-07

    Superhydrophobic patterns were fabricated on hydrophilic surfaces by selective painting. The impinging process of water droplets on these hybrid surfaces was investigated. The droplet can be split by impinging on the hydrophilic surface with a single stripe at a high velocity. The time to split the droplet is independent of the impact velocity and it is smaller than the contact time of a droplet impinging on the fully superhydrophobic surface. The volume ratios of the split mini-droplets could be precisely controlled by adjusting the landing position of the original droplet. The droplet could be split uniformly into more mini-marbles by increasing the stripe numbers.

  9. A review of droplet resonators: Operation method and application

    NASA Astrophysics Data System (ADS)

    Wang, Yan; Li, Hanyang; Zhao, Liyuan; Wu, Bing; Liu, Shuangqiang; Liu, Yongjun; Yang, Jun

    2016-12-01

    Droplet resonators hold promise as a special class of optical cavities for numerous applications in micro-optical. Owing to liquid surface tension, droplet resonators possess nearly perfect spherical geometry and exceptionally smooth surfaces that prompt more and more meritorious applications to be exploit. Herein, we survey two typical operation methods of the droplet resonators, passive and active droplet resonator. Besides, droplet applications as high-performance lasers and sensors have been discussed. Although these applications have brought us tremendous value, the research for droplet resonators are still in its infancy, added potential application and intrinsic investigation of the droplet resonators should be developed in the future work.

  10. Interaction Effects on Combustion of Alcohol Droplet Pairs

    NASA Astrophysics Data System (ADS)

    Okai, Keiichi; Ono, Yutaka; Moriue, Osamu; Shiba, Seiji; Araki, Mikiya; Nomura, Hiroshi; Shiga, Seiichi; Tsue, Mitsuhiro; Kono, Michikata

    Experimental investigation was conducted on two droplet-array combustion of methanol and methanol/dodecanol mixture fuels in microgravity. For methanol, effects of ambient pressure and droplet spacing were examined. Results show that the droplet lifetime decreases with increasing spacing at relatively low pressure and the droplet lifetime becomes independent of spacing at higher-subcritical and supercritical pressures. For methanol/dodecanol mixture, effects of pressure, fuel composition were investigated in terms of occurrence of disruption. Disruption of droplet during combustion was demonstrated both for single droplet and droplet pairs.

  11. Quasistatic packings of droplets in flat microfluidic channels

    NASA Astrophysics Data System (ADS)

    Kadivar, Erfan

    2016-02-01

    As observed in recent experiments, monodisperse droplets self-assemble spontaneously in different ordered packings. In this work, we present a numerical study of the droplet packings in the flat rectangular microfluidic channels. Employing the boundary element method, we numerically solve the Stokes equation in two-dimension and investigate the appearance of droplet packing and transition between one and two-row packings of monodisperse emulsion droplets. By calculating packing force applied on the droplet interface, we investigate the effect of flow rate, droplet size, and surface tension on the packing configurations of droplets and transition between different topological packings.

  12. Charging machine

    DOEpatents

    Medlin, John B.

    1976-05-25

    A charging machine for loading fuel slugs into the process tubes of a nuclear reactor includes a tubular housing connected to the process tube, a charging trough connected to the other end of the tubular housing, a device for loading the charging trough with a group of fuel slugs, means for equalizing the coolant pressure in the charging trough with the pressure in the process tubes, means for pushing the group of fuel slugs into the process tube and a latch and a seal engaging the last object in the group of fuel slugs to prevent the fuel slugs from being ejected from the process tube when the pusher is removed and to prevent pressure liquid from entering the charging machine.

  13. PARIS II: DESIGNING GREENER SOLVENTS

    EPA Science Inventory

    PARIS II (the program for assisting the replacement of industrial solvents, version II), developed at the USEPA, is a unique software tool that can be used for customizing the design of replacement solvents and for the formulation of new solvents. This program helps users avoid ...

  14. Hazardous solvent substitution

    SciTech Connect

    Twitchell, K.E.

    1995-11-01

    Eliminating hazardous solvents is good for the environment, worker safety, and the bottom line. However, even though we are motivated to find replacements, the big question is `What can we use as replacements for hazardous solvents?`You, too, can find replacements for your hazardous solvents. All you have to do is search for them. Search through the vendor literature of hundreds of companies with thousands of products. Ponder the associated material safety data sheets, assuming of course that you can obtain them and, having obtained them, that you can read them. You will want to search the trade magazines and other sources for product reviews. You will want to talk to users about how well the product actually works. You may also want to check US Environmental Protection Agency (EPA) and other government reports for toxicity and other safety information. And, of course, you will want to compare the product`s constituent chemicals with the many hazardous constituency lists to ensure the safe and legal use of the product in your workplace.

  15. Effects of droplet interactions on droplet transport at intermediate Reynolds numbers

    NASA Technical Reports Server (NTRS)

    Shuen, J. S.

    1986-01-01

    Effects of droplet interactions on drag, evaporation, and combustion of a planar droplet array, oriented perpendicular to the approaching flow, are studied numerically. The three-dimensional Navier-Stokes equations, with variable thermophysical properties, are solved using finite-difference techniques. Parameters investigated include the droplet spacing, droplet Reynolds number, approaching stream oxygen concentration, and fuel type. Results are obtained for the Reynolds number range of 5 to 100, droplet spacing from 2 to 24 diameters, oxygen concentrations of 0.1 and 0.2, and methanol and n-butanol fuels. The calculations show that the gasification rates of interacting droplets decrease as the droplet spacings decrease. The reduction in gasification rates is significant only at small spacings and low Reynolds numbers. For the present array orientation, the effects of interactions on the gasification rates diminish rapidly for Reynolds numbers greater than 10 and spacings greater than 6 droplet diameters. The effects of adjacent droplets on drag are shown to be small.

  16. Tetrachromacy, oil droplets and bird plumage colours.

    PubMed

    Vorobyev, M; Osorio, D; Bennett, A T; Marshall, N J; Cuthill, I C

    1998-11-01

    There is a growing body of data on avian eyes, including measurements of visual pigment and oil droplet spectral absorption, and of receptor densities and their distributions across the retina. These data are sufficient to predict psychophysical colour discrimination thresholds for light-adapted eyes, and hence provide a basis for relating eye design to visual needs. We examine the advantages of coloured oil droplets, UV vision and tetrachromacy for discriminating a diverse set of avian plumage spectra under natural illumination. Discriminability is enhanced both by tetrachromacy and coloured oil droplets. Oil droplets may also improve colour constancy. Comparison of the performance of a pigeon's eye, where the shortest wavelength receptor peak is at 410 nm, with that of the passerine Leiothrix, where the ultraviolet-sensitive peak is at 365 nm, generally shows a small advantage to the latter, but this advantage depends critically on the noise level in the sensitivity mechanism and on the set of spectra being viewed.

  17. Investigation of critical burning of fuel droplets

    NASA Technical Reports Server (NTRS)

    Faeth, G. M.

    1979-01-01

    The general problem of spray combustion was investigated. The combustion of bipropellent droplets; combustion of hydrozine fuels; and combustion of sprays were studied. A model was developed to predict mean velocities and temperatures in a combusting gas jet.

  18. 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

  19. Nucleation pressure threshold in acoustic droplet vaporization

    NASA Astrophysics Data System (ADS)

    Miles, Christopher; Doering, Charles; Kripfgans, Oliver

    2016-11-01

    We combine classical nucleation theory with superharmonic focusing to predict necessary pressures to induce nucleation in acoustic droplet vaporization. We show that linear acoustics is a valid approximation to leading order when particle displacements in the sound field are small relative the radius of the droplet. This is done by perturbation analysis of an axisymmetric compressible inviscid flow about a droplet with small surface perturbations relative to the mean radius subjected to an incoming ultrasonic wave. The necessary nucleation pressure threshold inside the droplet is calculated to be - 9 . 33 +/- 0 . 30 MPa for typical experimental parameters by employing results from classical homogeneous nucleation theory. As a result we are able to predict if a given incident pressure waveform will induce nucleation. This research was supported by the Rackham Merit Fellowship, the University of Michigan Physics department, the University of Michigan's MCubed program, and NSF awards PHY-1205219 and DMS-1515161.

  20. Swimming active droplet: A theoretical analysis

    NASA Astrophysics Data System (ADS)

    Schmitt, M.; Stark, H.

    2013-02-01

    Recently, an active microswimmer was constructed where a micron-sized droplet of bromine water was placed into a surfactant-laden oil phase. Due to a bromination reaction of the surfactant at the interface, the surface tension locally increases and becomes non-uniform. This drives a Marangoni flow which propels the squirming droplet forward. We develop a diffusion-advection-reaction equation for the order parameter of the surfactant mixture at the droplet interface using a mixing free energy. Numerical solutions reveal a stable swimming regime above a critical Marangoni number M but also stopping and oscillating states when M is increased further. The swimming droplet is identified as a pusher whereas in the oscillating state it oscillates between being a puller and a pusher.

  1. Impact of droplet on superheated surfaces

    NASA Astrophysics Data System (ADS)

    Lohse, Detlef; Staat, Hendrik J. J.; Tran, Tuan; Prosperetti, Andrea; Sun, Chao

    2012-11-01

    At impact of a liquid droplet on a smooth surface heated way above the liquid's boiling point, the droplet spreads without any surface contact, floating on its own (Leidenfrost-type) vapor layer, and then bounces back. We show that the dimensionless maximum spreading factor Γ, defined by the ratio of the maximal spreading diameter and the droplet diameter, shows a universal scaling Γ ~ Weγ with the Weber number We - regardless of surface temperature and of liquid properties - which is much steeper than that for the impact on non-heated (hydrophilic or hydrophobic) surfaces, for which γ = 1 / 4 . Based on the idea that the vapor shooting out of the gap between the droplet and the superheated surface drags the liquid outwards, we derive scaling laws for the spreading factor Γ, the vapor layer thickness, and the vapor flow velocity.

  2. Droplet Breakup in Expansion-contraction Microchannels

    PubMed Central

    Zhu, Pingan; Kong, Tiantian; Lei, Leyan; Tian, Xiaowei; Kang, Zhanxiao; Wang, Liqiu

    2016-01-01

    We investigate the influences of expansion-contraction microchannels on droplet breakup in capillary microfluidic devices. With variations in channel dimension, local shear stresses at the injection nozzle and focusing orifice vary, significantly impacting flow behavior including droplet breakup locations and breakup modes. We observe transition of droplet breakup location from focusing orifice to injection nozzle, and three distinct types of recently-reported tip-multi-breaking modes. By balancing local shear stresses and interfacial tension effects, we determine the critical condition for breakup location transition, and characterize the tip-multi-breaking mode quantitatively. In addition, we identify the mechanism responsible for the periodic oscillation of inner fluid tip in tip-multi-breaking mode. Our results offer fundamental understanding of two-phase flow behaviors in expansion-contraction microstructures, and would benefit droplet generation, manipulation and design of microfluidic devices. PMID:26899018

  3. Droplet Microfluidics for Chip-Based Diagnostics

    PubMed Central

    Kaler, Karan V. I. S.; Prakash, Ravi

    2014-01-01

    Droplet microfluidics (DMF) is a fluidic handling technology that enables precision control over dispensing and subsequent manipulation of droplets in the volume range of microliters to picoliters, on a micro-fabricated device. There are several different droplet actuation methods, all of which can generate external stimuli, to either actively or passively control the shape and positioning of fluidic droplets over patterned substrates. In this review article, we focus on the operation and utility of electro-actuation-based DMF devices, which utilize one or more micro-/nano-patterned substrates to facilitate electric field-based handling of chemical and/or biological samples. The underlying theory of DMF actuations, device fabrication methods and integration of optical and opto-electronic detectors is discussed in this review. Example applications of such electro-actuation-based DMF devices have also been included, illustrating the various actuation methods and their utility in conducting chip-based laboratory and clinical diagnostic assays. PMID:25490590

  4. Numerical Simulations of Acoustically Driven, Burning Droplets

    NASA Technical Reports Server (NTRS)

    Kim, H.-C.; Karagozian, A. R.; Smith, O. I.; Urban, Dave (Technical Monitor)

    1999-01-01

    This computational study focuses on understanding and quantifying the effects of external acoustical perturbations on droplet combustion. A one-dimensional, axisymmetric representation of the essential diffusion and reaction processes occurring in the vicinity of the droplet stagnation point is used here in order to isolate the effects of the imposed acoustic disturbance. The simulation is performed using a third order accurate, essentially non-oscillatory (ENO) numerical scheme with a full methanol-air reaction mechanism. Consistent with recent microgravity and normal gravity combustion experiments, focus is placed on conditions where the droplet is situated at a velocity antinode in order for the droplet to experience the greatest effects of fluid mechanical straining of flame structures. The effects of imposed sound pressure level and frequency are explored here, and conditions leading to maximum burning rates are identified.

  5. Dispensing nano-pico droplets of ferrofluids

    NASA Astrophysics Data System (ADS)

    Irajizad, Peyman; Farokhnia, Nazanin; Ghasemi, Hadi

    2015-11-01

    Dispensing miniature volumes of a ferrofluid is of fundamental and practical importance for diverse applications ranging from biomedical devices, optics, and self-assembly of materials. Current dispensing systems are based on microfluidics flow-focusing approaches or acoustic actuation requiring complicated structures. A simple method is presented to continuously dispense the miniature droplets from a ferrofluid reservoir. Once a jet of the ferrofluid is subjected to a constrained flux through a membrane and an inhomogeneous magnetic field, the jet experiences a curvature-driven instability and transforms to a droplet. Ferrofluid droplets in the range of 0.1-1000 nl are dispensed with tunable dispensing frequencies. A model is developed that predicts the dispensed volume of the ferrofluid droplets with an excellent agreement with the measurements.

  6. Biofilm Formation in Microscopic Double Emulsion Droplets

    NASA Astrophysics Data System (ADS)

    Chang, Connie; Weitz, David

    2012-02-01

    In natural, medical, and industrial settings, there exist surface-associated communities of bacteria known as biofilms. These highly structured films are composed of bacterial cells embedded within self-produced extracellular matrix, usually composed of exopolysaccharides, proteins, and nucleic acids; this matrix serves to protect the bacterial community from antibiotics and environmental stressors. Here, we form biofilms encapsulated within monodisperse, microscopically-sized double emulsion droplets using microfluidics. The bacteria self-organize at the inner liquid-liquid droplet interfaces, multiply, and differentiate into extracellular matrix-producing cells, forming manifold three-dimensional shell-within-a-shell structures of biofilms, templated upon the inner core of spherical liquid droplets. By using microfluidics to encapsulate bacterial cells, we have the ability to view individual cells multiplying in microscopically-sized droplets, which allows for high-throughput analysis in studying the genetic program leading to biofilm development, or cell signaling that induces differentiation.

  7. Vibrational modes of elongated sessile liquid droplets.

    PubMed

    Temperton, Robert H; Sharp, James S

    2013-04-16

    Vibrations of small (microliter) sessile liquid droplets were studied using a simple optical deflection technique. The droplets were made to elongate in one direction by taking advantage of the anisotropic wetting of the liquids on structured diffraction grating surfaces. They were vibrated by applying a puff of nitrogen gas. Motion of the droplets was monitored by scattering laser light from their surfaces. The scattered light was collected using a photodiode, and the resulting time-dependent intensity signals were Fourier-transformed to obtain the vibrational response of the drops. The vibrational spectra of elongated sessile drops were observed to contain two closely spaced peaks. A simple model that considers the frequency of capillary wave fluctuations on the surfaces of the drops was used to show that the vibrational frequencies of these peaks correspond to standing wave states that exist along the major and minor profile lengths of the droplets.

  8. Micro-droplets lubrication film thickness dynamics

    NASA Astrophysics Data System (ADS)

    Huerre, Axel; Theodoly, Olivier; Cantat, Isabelle; Leshansky, Alexander; Valignat, Marie-Pierre; Jullien, Marie-Caroline; MMN Team; LAI Team; IPR Team; Department of Chemical Engineering Team

    2014-11-01

    The motion of droplets or bubbles in confined geometries has been extensively studied; showing an intrinsic relationship between the lubrication film thickness and the droplet velocity. When capillary forces dominate, the lubrication film thickness evolves non linearly with the capillary number due to viscous dissipation between meniscus and wall. However, this film may become thin enough that intermolecular forces come into play and affect classical scalings. We report here the first experimental evidence of the disjoining pressure effect on confined droplets by measuring droplet lubrication film thicknesses in a microfluidic Hele-Shaw cell. We find and characterize two distinct dynamical regimes, dominated respectively by capillary and intermolecular forces. In the former case rolling boundary conditions at the interface are evidenced through film thickness dynamics, interface velocity measurement and film thickness profile.

  9. How faceted liquid droplets grow tails

    PubMed Central

    Guttman, Shani; Sapir, Zvi; Schultz, Moty; Butenko, Alexander V.; Ocko, Benjamin M.; Deutsch, Moshe; Sloutskin, Eli

    2016-01-01

    Liquid droplets, widely encountered in everyday life, have no flat facets. Here we show that water-dispersed oil droplets can be reversibly temperature-tuned to icosahedral and other faceted shapes, hitherto unreported for liquid droplets. These shape changes are shown to originate in the interplay between interfacial tension and the elasticity of the droplet’s 2-nm-thick interfacial monolayer, which crystallizes at some T = Ts above the oil’s melting point, with the droplet’s bulk remaining liquid. Strikingly, at still-lower temperatures, this interfacial freezing (IF) effect also causes droplets to deform, split, and grow tails. Our findings provide deep insights into molecular-scale elasticity and allow formation of emulsions of tunable stability for directed self-assembly of complex-shaped particles and other future technologies. PMID:26733673

  10. Droplet Breakup in Expansion-contraction Microchannels

    NASA Astrophysics Data System (ADS)

    Zhu, Pingan; Kong, Tiantian; Lei, Leyan; Tian, Xiaowei; Kang, Zhanxiao; Wang, Liqiu

    2016-02-01

    We investigate the influences of expansion-contraction microchannels on droplet breakup in capillary microfluidic devices. With variations in channel dimension, local shear stresses at the injection nozzle and focusing orifice vary, significantly impacting flow behavior including droplet breakup locations and breakup modes. We observe transition of droplet breakup location from focusing orifice to injection nozzle, and three distinct types of recently-reported tip-multi-breaking modes. By balancing local shear stresses and interfacial tension effects, we determine the critical condition for breakup location transition, and characterize the tip-multi-breaking mode quantitatively. In addition, we identify the mechanism responsible for the periodic oscillation of inner fluid tip in tip-multi-breaking mode. Our results offer fundamental understanding of two-phase flow behaviors in expansion-contraction microstructures, and would benefit droplet generation, manipulation and design of microfluidic devices.

  11. Manipulation of microfluidic droplets by electrorheological fluid.

    PubMed

    Zhang, Menying; Gong, Xiuqing; Wen, Weijia

    2009-09-01

    Microfluidics, especially droplet microfluidics, attracts more and more researchers from diverse fields, because it requires fewer materials and less time, produces less waste and has the potential of highly integrated and computer-controlled reaction processes for chemistry and biology. Electrorheological fluid, especially giant electrorheological fluid (GERF), which is considered as a kind of smart material, has been applied to the microfluidic systems to achieve active and precise control of fluid by electrical signal. In this review article, we will introduce recent results of microfluidic droplet manipulation, GERF and some pertinent achievements by introducing GERF into microfluidic system: digital generation, manipulation of "smart droplets" and droplet manipulation by GERF. Once it is combined with real-time detection, integrated chip with multiple functions can be realized.

  12. Effect of oil droplet size on activation energy for coalescence of oil droplets in an O/W emulsion.

    PubMed

    Miyagawa, Yayoi; Katsuki, Kazutaka; Matsuno, Ryuichi; Adachi, Shuji

    2015-01-01

    The activation energy of a reasonable order of magnitude was estimated for the coalescence of oil droplets in an O/W emulsion by formulating the balance of forces acting on a droplet that crosses over the potential barrier to coalesce with another droplet by the DLVO theory and Stokes' law. An emulsion with smaller oil droplets was shown to be more stable.

  13. Fluid Flow in An Evaporating Droplet

    NASA Technical Reports Server (NTRS)

    Hu, H.; Larson, R.

    1999-01-01

    Droplet evaporation is a common phenomenon in everyday life. For example, when a droplet of coffee or salt solution is dropped onto a surface and the droplet dries out, a ring of coffee or salt particles is left on the surface. This phenomenon exists not only in everyday life, but also in many practical industrial processes and scientific research and could also be used to assist in DNA sequence analysis, if the flow field in the droplet produced by the evaporation could be understood and predicted in detail. In order to measure the fluid flow in a droplet, small particles can be suspended into the fluid as tracers. From the ratio of gravitational force to Brownian force a(exp 4)(delta rho)(g)/k(sub B)T, we find that particle's tendency to settle is proportional to a(exp 4) (a is particle radius). So, to keep the particles from settling, the droplet size should be chosen to be in a range 0.1 -1.0 microns in experiments. For such small particles, the Brownian force will affect the motion of the particle preventing accurate measurement of the flow field. This problem could be overcome by using larger particles as tracers to measure fluid flow under microgravity since the gravitational acceleration g is then very small. For larger particles, Brownian force would hardly affect the motion of the particles. Therefore, accurate flow field could be determined from experiments in microgravity. In this paper, we will investigate the fluid flow in an evaporating droplet under normal gravity, and compare experiments to theories. Then, we will present our ideas about the experimental measurement of fluid flow in an evaporating droplet under microgravity.

  14. Laser diagnostics for microgravity droplet studies

    NASA Technical Reports Server (NTRS)

    Winter, Michael

    1993-01-01

    Rapid advances have recently been made in numerical simulation of droplet combustion under microgravity conditions, while experimental capabilities remain relatively primitive. Calculations can now provide detailed information on mass and energy transport, complex gas-phase chemistry, multi-component molecular diffusion, surface evaporation and heterogeneous reaction, which provides a clearer picture of both quasi-steady as well as dynamic behavior of droplet combustion. Experiments concerning these phenomena typically result in pictures of the burning droplets, and the data therefrom describe droplet surface regression along with flame and soot shell position. With much more precise, detailed, experimental diagnostics, significant gains could be made on the dynamics and flame structural changes which occur during droplet combustion. Since microgravity experiments become increasingly more expensive as they progress from drop towers and flights to spaceborne experiments, there is a great need to maximize the information content from these experiments. Sophisticated measurements using laser diagnostics on individual droplets and combustion phenomena are now possible. These include measuring flow patterns and temperature fields within droplets, vaporization rates and vaporization enhancement, radical species profiling in flames and gas-phase flow-tagging velocimetry. Although these measurements are sophisticated, they have undergone maturation to the degree where with some development, they are applicable to studies of microgravity droplet combustion. This program beginning in September of 1992, will include a series of measurements in the NASA Learjet, KC-135 and Drop Tower facilities for investigating the range of applicability of these diagnostics while generating and providing fundamental data to ongoing NASA research programs in this area. This program is being conducted in collaboration with other microgravity investigators and is aimed toward supplementing

  15. Solvent reorganizational red-edge effect in intramolecular electron transfer.

    PubMed Central

    Demchenko, A P; Sytnik, A I

    1991-01-01

    Polar solvents are characterized by statistical distributions of solute-solvent interaction energies that result in inhomogeneous broadening of the solute electronic spectra. This allows photoselection of the high interaction energy part of the distribution by excitation at the red (long-wavelength) edge of the absorption bands. We observe that intramolecular electron transfer in the bianthryl molecule from the locally excited (LE) to the charge-transfer (CT) state, which requires solvent relaxation and does not occur in vitrified polar solutions, is dramatically facilitated in low-temperature propylene glycol glass by the red-edge excitation. This allows one to obtain spectroscopically the pure CT form and observe its dependence upon the relaxational properties of the solvent. A qualitative potential model of this effect is presented. PMID:11607224

  16. Double emulsion solvent evaporation techniques used for drug encapsulation.

    PubMed

    Iqbal, Muhammad; Zafar, Nadiah; Fessi, Hatem; Elaissari, Abdelhamid

    2015-12-30

    Double emulsions are complex systems, also called "emulsions of emulsions", in which the droplets of the dispersed phase contain one or more types of smaller dispersed droplets themselves. Double emulsions have the potential for encapsulation of both hydrophobic as well as hydrophilic drugs, cosmetics, foods and other high value products. Techniques based on double emulsions are commonly used for the encapsulation of hydrophilic molecules, which suffer from low encapsulation efficiency because of rapid drug partitioning into the external aqueous phase when using single emulsions. The main issue when using double emulsions is their production in a well-controlled manner, with homogeneous droplet size by optimizing different process variables. In this review special attention has been paid to the application of double emulsion techniques for the encapsulation of various hydrophilic and hydrophobic anticancer drugs, anti-inflammatory drugs, antibiotic drugs, proteins and amino acids and their applications in theranostics. Moreover, the optimized ratio of the different phases and other process parameters of double emulsions are discussed. Finally, the results published regarding various types of solvents, stabilizers and polymers used for the encapsulation of several active substances via double emulsion processes are reported.

  17. Floating Droplet Array: An Ultrahigh-Throughput Device for Droplet Trapping, Real-time Analysis and Recovery

    PubMed Central

    Labanieh, Louai; Nguyen, Thi N.; Zhao, Weian; Kang, Dong-Ku

    2016-01-01

    We describe the design, fabrication and use of a dual-layered microfluidic device for ultrahigh-throughput droplet trapping, analysis, and recovery using droplet buoyancy. To demonstrate the utility of this device for digital quantification of analytes, we quantify the number of droplets, which contain a β-galactosidase-conjugated bead among more than 100,000 immobilized droplets. In addition, we demonstrate that this device can be used for droplet clustering and real-time analysis by clustering several droplets together into microwells and monitoring diffusion of fluorescein, a product of the enzymatic reaction of β-galactosidase and its fluorogenic substrate FDG, between droplets. PMID:27134760

  18. Condensed Matter and Material Sciences: Electrochemistry of Immobilized Particles and Droplets

    NASA Astrophysics Data System (ADS)

    Scholz, Fritz; Schröder, Uwe; Gulaboski, Rubin

    Immobilizing particles or droplets on electrodes is a novel and most powerful technique for studying the electrochemical reactions of three-phase systems. It gives access to a wealth of information, ranging from quantitative and phase analysis to thermodynamic and kinetic data of electrode processes. Three-phase electrodes with immobilized droplets provide information on the electrochemistry of redox liquids and of compounds dissolved in inert organic liquids. Such measurements allow the determination of the Gibbs energies of the transfer of cations and anions between immiscible solvents, and thus make it possible to assess the hydrophobicity of ions -- a property that is of great importance for pharmaceutical applications, biological studies, and for many fields of chemistry.

  19. Nanostructured Colloidal Particles by Confined Self-Assembly of Block Copolymers in Evaporative Droplets

    NASA Astrophysics Data System (ADS)

    Kim, Minsoo; Yi, Gi-Ra

    2015-06-01

    Block copolymers (BCPs) can create various morphology by self-assembly in bulk or film. Recently, using BCPs in confined geometries such as thin film (one-dimension), cylindrical template (two-dimension), or emulsion droplet (three-dimension), nanostructured BCP particles have been prepared, in which unique nanostructures of the BCP are formed via solvent annealing process and can be controlled depending on molecular weight ratio and interaction parameter of the BCPs, and droplet size. Moreover, by tuning interfacial property of the BCP particles, anisotropic particles with unique nanostructures have been prepared. Furthermore, for practical application such as drug delivery system, sensor, self-healing, metamaterial, and optoelectronic device, functional nanoparticles can be incorporated inside BCP particles. In this article, we summarize recent progress on the production of structured BCP particles and composite particles with metallic nanoparticles.

  20. Controlling droplet-based deposition uniformity of long silver nanowires by micrometer scale substrate patterning

    NASA Astrophysics Data System (ADS)

    Basu, Nandita; Cross, Graham L. W.

    2015-12-01

    We report control of droplet-deposit uniformity of long silver nanowires suspended in solutions by microscopic influence of the liquid contact line. Substrates with microfabricated line patterns with a pitch far smaller than mean wire length lead to deposit thickness uniformity compared to unpatterned substrates. For high boiling-point solvents, two significant effects were observed: The substrate patterns suppressed coffee ring staining, and the wire deposits exhibited a common orientation lying perpendicular over top the lines. The latter result is completely distinct from previously reported substrate groove channeling effects. This work shows that microscopic influence of the droplet contact line geometry including the contact angle by altered substrate wetting allows significant and advantageous influence of deposition patterns of wire-like solutes as the drop dries.

  1. Solvent effect on the spectral properties of Neutral Red

    PubMed Central

    Rauf, Muhammad A; Soliman, Ahmed A; Khattab, Muhammad

    2008-01-01

    Background The study was aimed at investigating the effect of various solvents on the absorption spectra of Neutral Red, a dye belonging to the quinone-imine class of dyes. The solvents chosen for the study were water, ethanol, acetonitrile, acetone, propan-1-ol, chloroform, nitrobenzene, ethyleneglycol, acetic acid, DMSO and DMF. Results The results have shown that the absorption maxima of dyes are dependent on solvent polarity. In non-hydrogen-bond donating solvents, solvation of dye molecules probably occurs via dipole-dipole interactions, whereas in hydrogen-bond donating solvents the phenomenon is more hydrogen bonding in nature. To estimate the contribution of the different variables on the wave number of the Neutral Red dye, regression analyses using the ECW model were compared with the π* scale model. This showed that the unified scale for estimating the solvent effect on the absorption of the Neutral Red dye is more adopted and more applicable than the π* scale model. Conclusion Absorption maxima of dyes are dependent on solvent polarity. Solvation of dye molecules probably occurs via dipole-dipole interactions in non-hydrogen-bond donating solvents, whereas in hydrogen-bond donating solvents the phenomenon is more hydrogen bonding in nature. The unified scale for estimating the solvent effect on the absorption of Neutral Red dye is more adopted and more applicable than the π* scale model. This may be due to complications from both π-π* charge transfer interactions and incomplete complexation of the solute; these effects are averaged out in the derived β and π parameters and thus limit their applicability. PMID:18799016

  2. Association of amino acids embedded in helium droplets detected by mass spectrometry

    NASA Astrophysics Data System (ADS)

    Lalanne, Matthieu R.; Achazi, Georg; Reichwald, Sebastian; Lindinger, Albrecht

    2015-12-01

    Amino acids were embedded in helium droplets. The electron impact ionization allows for detecting positively charged glycine, valine, histidine, tryptophan and their principal fragments. Monomers and polymers with up to four amino acids are reported. Heterodimers of tryptophan and valine or histidine are observed as well as heterodimers of included fragments. The ability of these associations of molecules to form complexes with water is examined.

  3. Proton transfer in histidine-tryptophan heterodimers embedded in helium droplets

    SciTech Connect

    Bellina, Bruno; Merthe, Daniel J.; Kresin, Vitaly V.

    2015-03-21

    We used cold helium droplets as nano-scale reactors to form and ionize, by electron bombardment and charge transfer, aromatic amino acid heterodimers of histidine with tryptophan, methyl-tryptophan, and indole. The molecular interaction occurring through an N–H ⋅ ⋅ ⋅ N hydrogen bond leads to a proton transfer from the indole group of tryptophan to the imidazole group of histidine in a radical cationic environment.

  4. Understanding Solvent Manipulation of Morphology in Bulk-Heterojunction Organic Solar Cells.

    PubMed

    Chen, Yuxia; Zhan, Chuanlang; Yao, Jiannian

    2016-10-06

    Film morphology greatly influences the performance of bulk-heterojunction (BHJ)-structure-based solar cells. It is known that an interpenetrating bicontinuous network with nanoscale-separated donor and acceptor phases for charge transfer, an ordered molecular packing for exciton diffusion and charge transport, and a vertical compositionally graded structure for charge collection are prerequisites for achieving highly efficient BHJ organic solar cells (OSCs). Therefore, control of the morphology to obtain an ideal structure is a key problem. For this solution-processing BHJ system, the solvent participates fully in film processing. Its involvement is critical in modifying the nanostructure of BHJ films. In this review, we discuss the effects of solvent-related methods on the morphology of BHJ films, including selection of the casting solvent, solvent mixture, solvent vapor annealing, and solvent soaking. On the basis of a discussion on interaction strength and time between solvent and active materials, we believe that the solvent-morphology-performance relationship will be clearer and that solvent selection as a means to manipulate the morphology of BHJ films will be more rational.

  5. Dictyostelium Lipid Droplets Host Novel Proteins

    PubMed Central

    Du, Xiaoli; Barisch, Caroline; Paschke, Peggy; Herrfurth, Cornelia; Bertinetti, Oliver; Pawolleck, Nadine; Otto, Heike; Rühling, Harald; Feussner, Ivo; Herberg, Friedrich W.

    2013-01-01

    Across all kingdoms of life, cells store energy in a specialized organelle, the lipid droplet. In general, it consists of a hydrophobic core of triglycerides and steryl esters surrounded by only one leaflet derived from the endoplasmic reticulum membrane to which a specific set of proteins is bound. We have chosen the unicellular organism Dictyostelium discoideum to establish kinetics of lipid droplet formation and degradation and to further identify the lipid constituents and proteins of lipid droplets. Here, we show that the lipid composition is similar to what is found in mammalian lipid droplets. In addition, phospholipids preferentially consist of mainly saturated fatty acids, whereas neutral lipids are enriched in unsaturated fatty acids. Among the novel protein components are LdpA, a protein specific to Dictyostelium, and Net4, which has strong homologies to mammalian DUF829/Tmem53/NET4 that was previously only known as a constituent of the mammalian nuclear envelope. The proteins analyzed so far appear to move from the endoplasmic reticulum to the lipid droplets, supporting the concept that lipid droplets are formed on this membrane. PMID:24036346

  6. Droplet Suspended on a Wire Begins Ignition

    NASA Technical Reports Server (NTRS)

    2003-01-01

    The Fiber Supported Droplet Combustion Experiment completing a number of successful burns on STS-94, July 11, 1997, MET:9/17:40 (approximate). The photo shows a droplet of 95% heptane and 5% hexadecane, suspended and positioned by the fiber wire, just as it is being ignited by the glowing coil beneath. Study of the physical properties of burning fuel from this experiment is expected to contribute to more efficient use of fossil fuels and reduction of combustion by-products on Earth. The sequence is from a time-lapse movie (34 seconds condensed to 12 seconds), and clearly shows particles emanating from the droplet during the burn. The droplet shrank to nothing as it was consumed. FSDC-2 studied fundamental phenomena related to liquid fuel droplet combustion in air. Pure fuels and mixtures of fuels were burned as isolated single and dual droplets with and without forced air convection. The FSDC guest investigator was Forman Williams, University of California, San Diego. The experiment was part of the space research investigations conducted during the Microgravity Science Laboratory-1R mission (STS-94, July 1-17 1997). Advanced combustion experiments will be a part of investigations plarned for the International Space Station. (1.2 MB, 11-second MPEG, screen 320 x 240 pixels; downlinked video, higher quality not available) A still JPG composite of this movie is available at http://mix.msfc.nasa.gov/ABSTRACTS/MSFC-0300180.html.

  7. Ignition of Droplet Suspended on a Wire

    NASA Technical Reports Server (NTRS)

    2003-01-01

    The Fiber Supported Droplet Combustion Experiment completing a number of successful burns on STS-94, July 11, 1997, MET:9/17:40 (approximate). The photo shows a droplet of 95% heptane and 5% hexadecane, suspended and positioned by the fiber wire, just as it is being ignited by the glowing coil beneath. Study of the physical properties of burning fuel from this experiment is expected to contribute to more efficient use of fossil fuels and reduction of combustion by-products on Earth. The sequence is from a time-lapse movie (34 seconds condensed to 12 seconds), and clearly shows particles emanating from the droplet during the burn. The droplet shrank to nothing as it was consumed. FSDC-2 studied fundamental phenomena related to liquid fuel droplet combustion in air. Pure fuels and mixtures of fuels were burned as isolated single and dual droplets with and without forced air convection. The FSDC guest investigator was Forman Williams, University of California, San Diego. The experiment was part of the space research investigations conducted during the Microgravity Science Laboratory-1R mission (STS-94, July 1-17 1997). Advanced combustion experiments will be a part of investigations plarned for the International Space Station. (133KB JPEG, 656 x 741 pixels; downlinked video, higher quality not available) The MPG from which this composite was made is available at http://mix.msfc.nasa.gov/ABSTRACTS/MSFC-0300181.html.

  8. Predicting Droplet Formation on Centrifugal Microfluidic Platforms

    NASA Astrophysics Data System (ADS)

    Moebius, Jacob Alfred

    Centrifugal microfluidics is a widely known research tool for biological sample and water quality analysis. Currently, the standard equipment used for such diagnostic applications include slow, bulky machines controlled by multiple operators. These machines can be condensed into a smaller, faster benchtop sample-to-answer system. Sample processing is an important step taken to extract, isolate, and convert biological factors, such as nucleic acids or proteins, from a raw sample to an analyzable solution. Volume definition is one such step. The focus of this thesis is the development of a model predicting monodispersed droplet formation and the application of droplets as a technique for volume definition. First, a background of droplet microfluidic platforms is presented, along with current biological analysis technologies and the advantages of integrating such technologies onto microfluidic platforms. Second, background and theories of centrifugal microfluidics is given, followed by theories relevant to droplet emulsions. Third, fabrication techniques for centrifugal microfluidic designs are discussed. Finally, the development of a model for predicting droplet formation on the centrifugal microfluidic platform are presented for the rest of the thesis. Predicting droplet formation analytically based on the volumetric flow rates of the continuous and dispersed phases, the ratios of these two flow rates, and the interfacial tension between the continuous and dispersed phases presented many challenges, which will be discussed in this work. Experimental validation was completed using continuous phase solutions of different interfacial tensions. To conclude, prospective applications are discussed with expected challenges.

  9. Burning Heptane Droplets on STS-94

    NASA Technical Reports Server (NTRS)

    2003-01-01

    Fuel ignites and burns in the Droplet Combustion Experiment (DCE) on STS-94 on July 11, 1997. This round of experiments burned heptane droplets in 1/2 atmosphere pressure consisting of oxygen and helium. During this mission, scientists have seen for the first time droplets which stop burning due to heat loss by radiation. From these data, the investigators hope to understand the physical and chemical processes that take place in droplet combustion in different environments, including conditions under which the flames extinguish, the chemistry of the combustion reaction, and the production of pollutants such as nitrogen oxides and soot particles. The DCE was designed to investigate the fundamental combustion aspects of single, isolated droplets under different pressures and ambient oxygen concentrations for a range of droplet sizes varying between 2 and 5 mm. The DCE principal investigator was Forman Williams, University of California, San Diego. The experiment was part of the space research investigations conducted during the Microgravity Science Laboratory-1R mission (STS-94, July 1-17 1997). Advanced combustion experiments will be a part of investigations plarned for the International Space Station.(983KB, 9-second MPEG, screen 320 x 240 pixels; downlinked video, higher quality not available) A still JPG composite of this movie is available at http://mix.msfc.nasa.gov/ABSTRACTS/MSFC-0300172.html.

  10. Structure of DNA cholesteric spherulitic droplet dispersions

    NASA Astrophysics Data System (ADS)

    Goldar, Arach; Thomson, Hellen; Seddon, John M.

    2008-01-01

    The aggregation of short (294-base-pair) linear double-stranded DNA molecules into cholesteric spherulitic droplets in a brine solution of polyethylene glycol has been studied using polarized light microscopy. The DNA concentration within the droplet is found to be constant and therefore the cholesteric pitch is independent of the total DNA concentration. The size of the droplets grows as a power law of the total concentration of DNA. The exponent of the power law relation is calculated using a progressive nucleation and growth model. The exponent is found to be equal to two-thirds and is in good agreement with the experimental data. By analysing fields of spherulitic droplets at low magnification using either hydrophobic or hydrophilic slides and cover-slips, we demonstrate that the positions of the droplets are correlated in solution. The long range correlation between the droplets indicates some kinetic arrest of the phase separating solution that may have been induced by the finite size of the system.

  11. Caustics and the growth of droplets

    NASA Astrophysics Data System (ADS)

    Govindarajan, Rama; Ravichandran, S.; Ray, Samriddhi; Deepu, P.

    Caustics are formed when inertial particles of very different velocities collide in a flow, and are a consequence of the dissipative nature of particle motion in a suspension. Using a model vortex-dominated flow with heavy droplets in a saturated environment, we suggest that sling caustics form only within a neighbourhood around a vortex, the square of whose radius is proportional to the product of circulation and particle inertia. Droplets starting close to this critical radius congregate very close together, resulting in large spikes in (Lagrangian) number density. Allowing for merger when droplets collide, we show that droplets starting out close to the critical radius display a much more rapid growth in size than those starting elsewhere, and a large fraction of the large droplets are those that originate within the caustics-forming region. We test these predictions in a two-dimensional simulation of turbulent flow. We hope that our study will be of interest in long-standing problems of physical interest such as the mechanism of broadening of droplet spectra in a turbulent flow. Support from the Ministry of Earth Sciences, Government of India for the project Coupled physical processes in the Bay of Bengal and monsoon air-sea interaction under OMM is gratefully acknowledged.

  12. Whole Teflon valves for handling droplets.

    PubMed

    Cybulski, Olgierd; Jakiela, Slawomir; Garstecki, Piotr

    2016-06-21

    We propose and test a new whole-Teflon gate valve for handling droplets. The valve allows droplet plugs to pass through without disturbing them. This is possible due to the geometric design, the choice of material and lack of any pulses of flow generated by closing or opening the valve. The duct through the valve resembles a simple segment of tubing, without constrictions, change in lumen or side pockets. There are no extra sealing materials with different wettability or chemical resistance. The only material exposed to liquids is FEP Teflon, which is resistant to aggressive chemicals and fully biocompatible. The valve can be integrated into microfluidic systems: we demonstrate a complex system for culturing bacteria in hundreds of microliter droplet chemostats. The valve effectively isolates modules of the system to increase precision of operations on droplets. We verified that the valve allowed millions of droplet plugs to safely pass through, without any cross-contamination with bacteria between the droplets. The valve can be used in automating complex microfluidic systems for experiments in biochemistry, biology and organic chemistry.

  13. Rayleigh wave scattering from sessile droplets

    NASA Astrophysics Data System (ADS)

    Quintero, R.; Simonetti, F.

    2013-10-01

    Radiation of energy by large-amplitude leaky Rayleigh waves is regarded as one of the key physical mechanisms regulating the actuation and manipulation of droplets in surface acoustic wave (SAW) microfluidic devices. The interaction between a SAW and a droplet is highly complex and is presently the subject of extensive research. This paper investigates the existence of an additional interaction mechanism based on the propagation of quasi-Stoneley waves inside sessile droplets deposited on a solid substrate. In contrast with the leaky Rayleigh wave, the energy of the Stoneley wave is confined within a thin fluid layer in contact with the substrate. The hypothesis is confirmed by three-dimensional finite element simulations and ultrasonic scattering experiments measuring the reflection of Rayleigh waves from droplets of different diameters. Moreover, real-time monitoring of the droplet evaporation process reveals a clear correlation between the droplet contact angle and the spectral information of the reflected Rayleigh signal, thus paving the way for ultrasonic measurements of surface tension.

  14. Mechanical vibrations of pendant liquid droplets.

    PubMed

    Temperton, Robert H; Smith, Michael I; Sharp, James S

    2015-07-01

    A simple optical deflection technique was used to monitor the vibrations of microlitre pendant droplets of deuterium oxide, formamide, and 1,1,2,2-tetrabromoethane. Droplets of different volumes of each liquid were suspended from the end of a microlitre pipette and vibrated using a small puff of nitrogen gas. A laser was passed through the droplets and the scattered light was collected using a photodiode. Vibration of the droplets resulted in the motion of the scattered beam and time-dependent intensity variations were recorded using the photodiode. These time-dependent variations were Fourier transformed and the frequencies and widths of the mechanical droplet resonances were extracted. A simple model of vibrations in pendant/sessile drops was used to relate these parameters to the surface tension, density and viscosity of the liquid droplets. The surface tension values obtained from this method were found to be in good agreement with results obtained using the standard pendant drop technique. Damping of capillary waves on pendant drops was shown to be similar to that observed for deep liquid baths and the kinematic viscosities obtained were in agreement with literature values for all three liquids studied.

  15. Studies of droplet burning and extinction

    NASA Technical Reports Server (NTRS)

    Williams, Forman A.

    1993-01-01

    A project on droplet combustion, pursued jointly with F.L. Dryer of Princeton University, has now been in progress for many years. The project involves experiments on the burning of single droplets in various atmospheres, mainly at normal atmosperic pressure and below, performed in drop towers and designed to be performed aboard space-based platforms such as the Space Shuttle or the Space Station. It also involves numerical computations on droplet burning, performed mainly at Princeton, and asymptotic analyses of droplet burning, performed mainly at UCSD. The focus of the studies rests primarily on time-dependent droplet-burning characteristics and on extinction phenomena. The presentation to be given here concerns the recent research on application of asymptotic methods to investigation of the flame structure and extinction of hydrocarbon droplets. These theoretical studies are investigating the extent to which combustion of higher hydrocarbons - heptane, in particular - can be described by four-step reduced chemistry of the kind that has achieved a good degree of success for methane flames. The studies have progressed to a point at which a number of definite conclusions can now be stated. These conclusions and the reasoning that led to them are outlined here.

  16. Gel-like double-emulsion droplets

    NASA Astrophysics Data System (ADS)

    Guzowski, Jan; Korczyk, Piotr; Garstecki, Piotr; Stone, Howard

    2015-11-01

    We experimentally study the problem of packing of micro-droplets inside a droplet of another immiscible liquid phase. We use microfluidics to encapsulate multiple monodisperse aqueous segments inside a drop of oil. For small numbers N (N<10) of the aqueous droplets and at their volume fraction in oil exceeding the close-packing threshold we observe multiple metastable structures with well-defined point-group symmetries. We attribute the observed metastability to the deformability of the droplets which leads to effective many-body interactions and energy barriers for rearrangement. By changing the composition of the oil phase we find that when the surface tensions of the droplets and of the encapsulating phase are comparable, the energy barriers are high enough to trap elongated structures or even linear chains, independently of N. However, when the surface tension of the encapsulating phase is much larger than that of the droplets, non-spherical morphologies are stable only at sufficiently high N. In such a case multiple internal interfaces can hold stresses and prevent relaxation of the global deformations which leads to a plastic, gel-like behavior. Our findings can serve as guidelines for synthesis of functional particles as well as for designing biomimetic materials, e.g. for tissue engineering. J.G. acknowledges financial support from Polish Ministry of Science provided within the framework Mobility Plus.

  17. Studies of droplet burning and extinction

    NASA Technical Reports Server (NTRS)

    Williams, F. A.

    1995-01-01

    A project on droplet combustion, pursued jointly with F. L. Dryer of Princeton University, has now been in progress for many years. The project involves experiments on the burning of single droplets in various atmospheres, mainly at normal atmospheric pressure and below, performed in drop towers and designed to be performed aboard space-based platforms such as the Space Shuttle or the Space Station and currently manifest for Spacelab in the MSL-1 flight of the Space Shuttle in April of 1997. It also involves numerical computations on droplet burning, performed mainly at Princeton, and asymptotic analyses of droplet burning, performed mainly at UCSD. The focus of the studies rests primarily on time-dependent droplet-burning characteristics and on extinction phenomena. The presentation to be given here concerns the recent research on application of asymptotic methods to investigation of the flame structure and extinction of alcohol droplets. These theoretical studies are relevant to the second of the proposed space-flight tests and are currently investigating the extent to which combustion of alcohols can be described by four-step reduced chemistry similar to that which has achieved a good degree of success for alkane flames. These studies have progressed to a point at which a number of definite conclusions can now be stated. These conclusions and the reasoning that led to them are outlined.

  18. SOLVENT FIRE BY-PRODUCTS

    SciTech Connect

    Walker, D; Samuel Fink, S

    2006-05-22

    Southwest Research Institute (SwRI) conducted a burn test of the Caustic-Side Solvent Extraction (CSSX) solvent to determine the combustion products. The testing showed hydrogen fluoride gas is not a combustion product from a solvent fire when up to 70% of the solvent is consumed. The absence of HF in the combustion gases may reflect concentration of the modifier containing the fluoride groups in the unburned portion. SwRI reported results for other gases (CO, HCN, NOx, formaldehyde, and hydrocarbons). The results, with other supporting information, can be used for evaluating the consequences of a facility fire involving the CSSX solvent inventory.

  19. Solvent replacement for green processing.

    PubMed Central

    Sherman, J; Chin, B; Huibers, P D; Garcia-Valls, R; Hatton, T A

    1998-01-01

    The implementation of the Montreal Protocol, the Clean Air Act, and the Pollution Prevention Act of 1990 has resulted in increased awareness of organic solvent use in chemical processing. The advances made in the search to find "green" replacements for traditional solvents are reviewed, with reference to solvent alternatives for cleaning, coatings, and chemical reaction and separation processes. The development of solvent databases and computational methods that aid in the selection and/or design of feasible or optimal environmentally benign solvent alternatives for specific applications is also discussed. Images Figure 2 Figure 3 PMID:9539018

  20. Modeling spreading of nematic droplets

    NASA Astrophysics Data System (ADS)

    Lin, Te-Sheng; Cummings, Linda; Kondic, Lou

    2011-03-01

    Experiments by Poulard & Cazabat on spreading droplets of nematic liquid crystal reveal a surprisingly rich variety of behavior, including at least two different emerging lengthscales resulting from a contact line instability. In earlier work we modified a lubrication model for nematic liquid crystals due to Ben Amar and Cummings, and showed that, in a qualitative sense, it can account for much of the observed behavior. In the present work we propose a new approach, that allows us to explore the effect of anchoring variations on the substrate. This in turn gives a simple way to model the presence of defects, which are always present during such liquid crystal flows. The new model leads to additional terms in the governing equation. We first explore the influence of these additional terms for some simple flow scenarios, to gain a basic understanding of their influence, before extending our simulations to the experimental geometry and comparing our results to the experiments. This work was partially supported by NSF Grant No. DMS-0908158.