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Showing papers on "Surface tension published in 2014"


Journal ArticleDOI
TL;DR: This work suggests that the wetting properties of surface oxides—which are ubiquitous on most metals and semiconductors—are intrinsic “surfactants” that can be harnessed to induce previously unidentified electrohydrodynamic phenomena for manipulating liquid metal alloys based on gallium.
Abstract: We present a method to control the interfacial tension of a liquid alloy of gallium via electrochemical deposition (or removal) of the oxide layer on its surface. In sharp contrast with conventional surfactants, this method provides unprecedented lowering of surface tension (∼500 mJ/m2 to near zero) using very low voltage, and the change is completely reversible. This dramatic change in the interfacial tension enables a variety of electrohydrodynamic phenomena. The ability to manipulate the interfacial properties of the metal promises rich opportunities in shape-reconfigurable metallic components in electronic, electromagnetic, and microfluidic devices without the use of toxic mercury. This work suggests that the wetting properties of surface oxides—which are ubiquitous on most metals and semiconductors—are intrinsic “surfactants.” The inherent asymmetric nature of the surface coupled with the ability to actively manipulate its energetics is expected to have important applications in electrohydrodynamics, composites, and melt processing of oxide-forming materials.

289 citations


Journal ArticleDOI
TL;DR: The derived equation, which expresses the splash threshold velocity as a function of the material properties of the two fluids involved, the drop radius, and the mean free path of the molecules composing the surrounding gaseous atmosphere is thoroughly validated experimentally at normal atmospheric conditions.
Abstract: Making use of experimental and theoretical considerations, in this Letter we deduce a criterion to determine the critical velocity for which a drop impacting a smooth dry surface either spreads over the substrate or disintegrates into smaller droplets. The derived equation, which expresses the splash threshold velocity as a function of the material properties of the two fluids involved, the drop radius, and the mean free path of the molecules composing the surrounding gaseous atmosphere, has been thoroughly validated experimentally at normal atmospheric conditions using eight different liquids with viscosities ranging from μ=3×10(-4) to μ=10(-2) Pa s, and interfacial tension coefficients varying between σ=17 and σ=72 mN m(-1). Our predictions are also in fair agreement with the measured critical speed of drops impacting in different gases at reduced pressures given by Xu et al. [Phys. Rev. Lett. 94, 184505 (2005).

246 citations


Journal ArticleDOI
TL;DR: In this article, the effect of applied linear energy density (LED) on the temperature distribution, melt pool dimensions, behaviors of gaseous bubbles and resultant densification activity has been investigated.

238 citations


Journal ArticleDOI
04 Jun 2014-Langmuir
TL;DR: It is demonstrated that, dependent on dynamics of formation and resulting morphology of the liquid metal-substrate interface, GaInSn adhesion can occur in two modes, and it is demonstrated how these two adhesion modes limit microcontact printing of GaIn Sn patterns but can be exploited to repeatedly print individual sub-200 nm liquid metal drops.
Abstract: Gallium-based liquid metals are of interest for a variety of applications including flexible electronics, soft robotics, and biomedical devices. Still, nano- to microscale device fabrication with these materials is challenging because, despite having surface tension 10 times higher than water, they strongly adhere to a majority of substrates. This unusually high adhesion is attributed to the formation of a thin oxide shell; however, its role in the adhesion process has not yet been established. In this work, we demonstrate that, dependent on dynamics of formation and resulting morphology of the liquid metal–substrate interface, GaInSn adhesion can occur in two modes. The first mode occurs when the oxide shell is not ruptured as it makes contact with the substrate. Because of the nanoscale topology of the oxide surface, this mode results in minimal adhesion between the liquid metal and most solids, regardless of substrate’s surface energy or texture. In the second mode, the formation of the GaInSn–substrat...

198 citations


Journal ArticleDOI
TL;DR: In this article, a modified VLE was used to study the phase behavior of reservoir fluids in unconventional reservoirs, and the multiple-mixing-cell (MMC) algorithm and the modified procedure were used to determine the minimal miscibility pressure (MMP) of a synthetic oil and Bakken oil with carbon dioxide (CO2) and mixtures of CO2 and methane gas.
Abstract: Numerous studies indicate that the pressure/volume/temperature (PVT) phase behavior of fluids in large pores (designated “unconfined” space) deviates from phase behavior in nanopores (designated “confined” space). The deviation in confined space has been attributed to the increase in capillary force, electrostatic interactions, van der Waals forces, and fluid structural changes. In this paper, conventional vapor/liquid equilibrium (VLE) calculations are modified to account for the capillary pressure and the critical-pressure and -temperature shifts in nanopores. The modified VLE is used to study the phase behavior of reservoir fluids in unconventional reservoirs. The multiple-mixing-cell (MMC) algorithm and the modified VLE procedure were used to determine the minimal miscibility pressure (MMP) of a synthetic oil and Bakken oil with carbon dioxide (CO2) and mixtures of CO2 and methane gas. We show that the bubblepoint pressure, gas/oil interfacial tension (IFT), and MMP are decreased with confinement (nanopores), whereas the upper dewpoint pressure increases and the lower dewpoint pressure decreases.

183 citations


Journal ArticleDOI
TL;DR: In this paper, the correlation between the contact angle, the spreading, the surface tension and the surface energy of fourteen frequently used engineering materials belonging to four different classes of materials (steel, DLC coatings, ceramics, and polymers) wetted with four different liquids: three oils (a non-polar synthetic oil of two different viscosities and a polar natural-based oil) and water.

174 citations


Journal ArticleDOI
15 Oct 2014-Fuel
TL;DR: In this paper, high-speed imaging is performed using long-distance microscopy and diffused back-illumination to resolve ligament structures and droplets in the near nozzle region.

166 citations


Journal ArticleDOI
TL;DR: A review of surface rheology can be found in this article, focusing on recent advances and giving examples of phenomena in which surface Rheology plays an important role, including surface compression elasticity and viscosity.
Abstract: When surfactants adsorb at liquid surfaces, they not only decrease the surface tension, they also confer rheological properties to the surfaces. The most common rheological parameters are the surface compression elasticity and viscosity and the surface shear viscosity. These parameters usually depend on the timescale of the deformation, owing to surface relaxations, and on its amplitude, owing to nonlinear responses. In addition, surfactants can exchange between the bulk and surface, in a way that depends on the amount of bulk surfactant locally available. This complexity explains why the topic has progressed slowly over the years. This review describes the current knowledge, focusing on recent advances, and gives examples of phenomena in which surface rheology plays an important role.

150 citations


Journal ArticleDOI
TL;DR: Single H2 nanobubble nucleation is studied at Pt nanodisk electrodes of radii less than 50 nm, where H2 is produced through electrochemical reduction of protons in a strong acid solution and the effects of different surfactants are consistent with the classic nucleation theory.
Abstract: Single H2 nanobubble nucleation is studied at Pt nanodisk electrodes of radii less than 50 nm, where H2 is produced through electrochemical reduction of protons in a strong acid solution. The critical concentration of dissolved H2 required for nanobubble nucleation is measured to be ∼0.25 M. This value is ∼310 times larger than the saturation concentration at room temperature and pressure and was found to be independent of acid type (e.g., H2SO4, HCl, and H3PO4) and nanoelectrode size. The effects of different surfactants on H2 nanobubble nucleation are consistent with the classic nucleation theory. As the surfactant concentration in H2SO4 solution increases, the solution surface tension decreases, resulting in a lower nucleation energy barrier and consequently a lower supersaturation concentration required for H2 nanobubble nucleation. Furthermore, amphiphilic surfactant molecules accumulate at the H2/solution interface, hindering interfacial H2 transfer from the nanobubble into the solution; consequentl...

147 citations


Journal ArticleDOI
TL;DR: Fluorosurfactants are the most effective compounds to lower the surface tension of aqueous solutions, but their wetting properties as related to low energy hydrocarbon solids are inferior to hydrocarbon trisiloxane surfactants, although the latter demonstrate higher surface tension in aQueous solutions.

144 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of both low and high salinity water on the surface properties of crude oil-brine/solid surfaces were investigated and two main surface properties including contact angle and interfacial tension were measured using a pendant drop apparatus.
Abstract: It has been already well established that adjusting the salinity of displacing fluid critically affects the oil recovery efficiency during secondary and tertiary oil recovery processes. In this investigation, systematic experiments are designed and conducted to find the effects of both low and high salinity water on the surface properties of crude oil–brine/solid surfaces. In this respect, the effects of the major salts including NaCl, CaCl2, and MgCl2 are tested in the concentration range of 0–45 000 ppm on fluid/solid and fluid/fluid interactions for a crude oil/water/rock system. Two main surface properties including contact angle and interfacial tension (IFT) are measured using a pendant drop apparatus. The obtained results demonstrate the critical effects of heavy oil components on the interfacial properties. High film stability in some cases resulted in small contact angle changes, mostly in the range of the strongly water wet condition, for different brine salinity.

Journal ArticleDOI
TL;DR: In this paper, the authors consider polyelectrolyte solutions which, under suitable conditions, phase separate into a liquid-like coacervate phase and a coexisting supernatant phase that exhibit an extremely low interfacial tension.
Abstract: We consider polyelectrolyte solutions which, under suitable conditions, phase separate into a liquid-like coacervate phase and a coexisting supernatant phase that exhibit an extremely low interfacial tension. Such interfacial tension provides the basis for most coacervate-based applications, but little is known about it, including its dependence on molecular weight, charge density, and salt concentration. By combining a Debye–Huckel treatment for electrostatic interactions with the Cahn–Hilliard theory, we derive explicit expressions for this interfacial tension. In the absence of added salts, we find that the interfacial tension scales as N–3/2(η/ηc–1)3/2 near the critical point of the demixing transition, and that it scales as η1/2 far away from it, where N is the chain length and η measures the electrostatic interaction strength as a function of temperature, dielectric constant, and charge density of the polyelectrolytes. For the case with added salts, we find that the interfacial tension scales with t...

Journal ArticleDOI
TL;DR: In this paper, an experimental study in a T-junction microfluidic device, allowing large ranges of interfacial tension between the two immiscible fluids, viscosity ratios, channel geometries, and their impact on droplet formation was conducted.
Abstract: Precise control of monodisperse micron-sized liquid droplet emulsions produced in a microfluidic T-junction has far reaching implications in several mechanical, biomedical, and optical applications. This paper is an experimental study in a T-junction microfluidic device, allowing large ranges of interfacial tension between the two immiscible fluids, viscosity ratios, channel geometries, and their impact on droplet formation. Classification of the droplet formation regimes, droplet in T-junction (DTJ), droplet in channel (DC), and parallel flow (PF), is further clarified based on experiments in this study and in the literature. Our experiments show that the droplet volume decreases and the production frequency increases as the channel aspect ratio (h/w c) is increased, consistent with conservation laws. In addition, the transition flow rate ratio (Q d/Q c) for a given capillary number decreases with decreasing aspect ratio for both DTJ–DC and DC–PF transitions, with subscripts d and c referring to the dispersed and continuous phases. Larger viscosity ratios (μ d/μ c) and interfacial tension values also tend to decrease this transition flow rate ratio for a given capillary number. The viscosity ratio, interfacial tension, and channel geometry have an impact on the DTJ–DC and DC–PF droplet transition regions, and a new parameter, the dimensionless interfacial tension (Ω), is used to further characterize these transition locations. Using this parameter, the channel aspect ratio, flow rate ratio, and viscosity ratio, we develop empirical correlations for predicting the DC–PF transition regions for both the squeezing and dripping regimes. These correlations predict the capillary number at which the DC–PF transition will occur with less than 8.5 % error in the dripping regime and less than 2.8 % in the squeezing regime.

Journal ArticleDOI
TL;DR: Large-scale molecular dynamics simulations are used to study the behavior of supercritical CO2 and aqueous fluids on both the hydrophilic and hydrophobic basal surfaces of kaolinite, a common clay mineral, to influence long-term mineralization of injected carbon dioxide.
Abstract: Capture and subsequent geologic storage of CO2 in deep brine reservoirs plays a significant role in plans to reduce atmospheric carbon emission and resulting global climate change. The interaction of CO2 and brine species with mineral surfaces controls the ultimate fate of injected CO2 at the nanoscale via geochemistry, at the pore-scale via capillary trapping, and at the field-scale via relative permeability. We used large-scale molecular dynamics simulations to study the behavior of supercritical CO2 and aqueous fluids on both the hydrophilic and hydrophobic basal surfaces of kaolinite, a common clay mineral. In the presence of a bulk aqueous phase, supercritical CO2 forms a nonwetting droplet above the hydrophilic surface of kaolinite. This CO2 droplet is separated from the mineral surface by distinct layers of water, which prevent the CO2 droplet from interacting directly with the mineral surface. Conversely, both CO2 and H2O molecules interact directly with the hydrophobic surface of kaolinite. In th...

Journal ArticleDOI
TL;DR: In this article, the authors have studied air-water and oil-water interfacial tensions of systems containing both surfactants and ZrO 2 nanoparticles and showed that nanoparticles are surface active at oil-air interface with negligible tendency toward adsorption at air-Water interface.

Journal ArticleDOI
15 Jan 2014-Langmuir
TL;DR: It is argued that models of dynamic surface or interfacial tension appropriate for molecular species break down when the adsorption energy greatly exceeds the mean energy of thermal fluctuations and validated alternative models extending the application of generalized random sequential adsOrption theory to nanoparticle adsorptions at fluid interfaces.
Abstract: Adsorption-driven self-assembly of nanoparticles at fluid interfaces is a promising bottom-up approach for the preparation of advanced functional materials and devices. Full realization of its potential requires quantitative understanding of the parameters controlling the self-assembly, the structure of nanoparticles at the interface, the barrier properties of the assembly, and the rate of particle attachment. We argue that models of dynamic surface or interfacial tension (DST) appropriate for molecular species break down when the adsorption energy greatly exceeds the mean energy of thermal fluctuations and validate alternative models extending the application of generalized random sequential adsorption theory to nanoparticle adsorption at fluid interfaces. Using a model colloidal system of hydrophobic, charge-stabilized ethyl cellulose nanoparticles at neutral pH, we demonstrate the potential of DST measurements to reveal information on the energy of adsorption, the adsorption rate constant, and the energy of particle-interface interaction at different degrees of nanoparticle coverage of the interface. These findings have significant implications for the quantitative description of nanoparticle adsorption at fluid interfaces.

Journal ArticleDOI
TL;DR: In this paper, the mass transfer characteristics during CO 2 bubble absorption and diffusion processes in nanofluid with Al 2 O 3 nanoparticles were analyzed and the effect of the nanoparticles on mass transfer enhancement was measured.

Journal ArticleDOI
TL;DR: In this paper, an improved smoothed particle hydrodynamics (SPH) method for modeling viscous liquid drop is presented by using a hyperbolicshaped kernel function which possesses non-negative second derivatives.

Journal ArticleDOI
TL;DR: A new and complex relationship between the composition of an organic aerosol and its hygroscopicity is revealed, suggesting that organic surface films might strongly influence cloud droplet formation as well as the multiphase chemistry of organic aerosols.
Abstract: Although many organic molecules commonly found in the atmosphere are known to be surface-active in macroscopic aqueous solutions, the impact of surface partitioning of organic molecules to a microscopic aqueous droplet interface remains unclear. Here we measure the droplet size formed, at a relative humidity (∼99.9%) just below saturation, on submicrometer particles containing an ammonium sulfate core and an organic layer of a model compound of varying thickness. The 12 model organic compounds are a series of dicarboxylic acids (C3 to C10), cis-pinonic, oleic, lauric, and myristic acids, which represent a broad range in solubility from miscible (malonic acid) to insoluble. The variation in droplet size with increasing organic aerosol fraction cannot be explained by assuming the organic material is dissolved in the bulk droplet. Instead, the wet droplet diameters exhibit a complex and nonlinear dependence on organic aerosol volume fraction, leading to hygroscopic growth that is in some cases smaller and in others larger than that predicted by bulk solubility alone. For palmitic and stearic acid, small droplets at or below the detection limit of the instrument are observed, indicating significant kinetic limitations for water uptake, which are consistent with mass accommodation coefficients on the order of 10(-4). A model based on the two-dimensional van der Waals equation of state is used to explain the complex droplet growth with organic aerosol fraction and dry diameter. The model suggests that mono- and dicarboxylic acids with limited water solubility partition to the droplet surface and reduce surface tension only after a two-dimensional condensed monolayer is formed. Two relatively soluble compounds, malonic and glutaric acid, also appear to form surface phases, which increase hygroscopicity. There is a clear alternation in the threshold for droplet growth observed for odd and even carbon number diacids, which is explained in the model by differences in the excluded molecular areas of even (∼40 A(2)/molecule) and odd (∼20 A(2)/molecule) diacids. These differences are consistent with the odd diacids arranged at the droplet interface in "end-to-end" configurations with only one acid group in contact with the aqueous phase, which is in contrast to even carbon numbered diacids forming "folded" films with both acid groups in contact with the bulk phase. Organic matter produced by the ozonolysis of α-pinene forms surface films that exhibit similar behavior and become thinner with oxidation, allowing for greater water uptake. These results reveal a new and complex relationship between the composition of an organic aerosol and its hygroscopicity, suggesting that organic surface films might strongly influence cloud droplet formation as well as the multiphase chemistry of organic aerosols.

Journal ArticleDOI
15 May 2014
TL;DR: The surface tension of water is almost independent of pH between pH 1 and 13 when the pH is adjusted by addition of HCl or NaOH, but the surface tension becomes pH dependent around pH 7 in millimolar NaCl or KCl solutions.
Abstract: Despite the strong adsorption of hydroxide ions, the surface tension of water is almost independent of pH between pH 1 and 13 when the pH is adjusted by addition of HCl or NaOH. This is consistent with the Gibbs adsorption isotherm which measures the surface excess of all species in the double layer, if hydronium ions and hydroxide ions are adsorbed and sodium and chloride ions are not. The surface tension becomes pH dependent around pH 7 in millimolar NaCl or KCl solutions, for now sodium ions can replace hydronium ions as counterions to the adsorbed hydroxide ions.

Journal ArticleDOI
11 Apr 2014-Langmuir
TL;DR: This work uses lubrication theory to derive an evolution equation for the interface that accounts for capillarity and thermocapillarity, and simulates the spreading of droplets of fluids whose surface tension-temperature curves exhibit a turning point.
Abstract: We study the thermocapillary-driven spreading of a droplet on a nonuniformly heated substrate for fluids associated with a non-monotonic dependence of the surface tension on temperature. We use lubrication theory to derive an evolution equation for the interface that accounts for capillarity and thermocapillarity. The contact line singularity is relieved by using a slip model and a Cox-Voinov relation; the latter features equilibrium contact angles that vary depending on the substrate wettability, which, in turn, is linked to the local temperature. We simulate the spreading of droplets of fluids whose surface tension-temperature curves exhibit a turning point. For cases wherein these turning points correspond to minima, and when these minima are located within the droplet, then thermocapillary stresses drive rapid spreading away from the minima. This gives rise to a significant acceleration of the spreading whose characteristics resemble those associated with the "superspreading" of droplets on hydrophobic substrates. No such behavior is observed for cases in which the turning point corresponds to a surface tension maximum.

Journal ArticleDOI
TL;DR: A lattice Boltzmann phase-field model is developed to simulate immiscible thermocapillary flows with consideration of fluid-surface interactions and an interfacial force of potential form is proposed to model the interfacial tension force and the Marangoni stress.

Journal ArticleDOI
TL;DR: A numerical solution of the problem of indentation of an elastic half-space by a rigid sphere showing the transition between the classical Johnson-Kendall-Roberts (JKR) deformation and a liquid-like deformation in the absence of external load and gravity is presented.
Abstract: In problems of indentation of an elastic half-space by a rigid sphere, the effects of surface tension outside the contact zone are not accounted for by classical theories of contact mechanics. However surface tension plays a dominant role in determining the mechanics of this adhesive contact when the half-space becomes very compliant and the sphere is very small. Using a finite element method (FEM), we present a numerical solution of such a problem, showing the transition between the classical Johnson–Kendall–Roberts (JKR) deformation and a liquid-like deformation in the absence of external load and gravity. The numerical model is in good agreement with previous experiments [R. W. Style et al., Nat. Commun., 2013, 4, 2728].

Journal ArticleDOI
TL;DR: In this article, a number of steady-state numerical simulations of condensation of R134a at mass fluxes of 400 kg m−2 s−1 and 800 kgm−2 S−1 inside a 1-mm square cross section minichannel are proposed and compared against simulations in a circular cross section channel with the same hydraulic diameter.
Abstract: A number of steady-state numerical simulations of condensation of R134a at mass fluxes of 400 kg m−2 s−1 and 800 kg m−2 s−1 inside a 1-mm square cross section minichannel are proposed here and compared against simulations in a circular cross section channel with the same hydraulic diameter. The volume of fluid (VOF) method is used to track the vapor–liquid interface, and the effects of interfacial shear stress, surface tension, and gravity are taken into account. A uniform wall temperature is fixed as a boundary condition. At both mass velocities the liquid film and the vapor core are treated as turbulent; a low-Re form of the SST k-ω model has been used for the modeling of turbulence through both the liquid and vapor phases. Numerical simulations are validated against experimental data. The influence of the surface tension on the shape of the vapor–liquid interface may provide some heat transfer enhancement in a square cross section minichannel, but this depends on the mass flux and it may be not signifi...

Journal ArticleDOI
TL;DR: It was found that surface wettability does not affect the duration of inertial wetting, whereas the viscosity of the liquid does, and a viscous wetting regime only on surfaces with an equilibrium contact angle smaller than a critical angle θ(c) depending on viscosities.
Abstract: In this paper, we experimentally investigated the dynamic spreading of liquid drops on solid surfaces. Drop of glycerol water mixtures and pure water that have comparable surface tensions (62.3-72.8 mN/m) but different viscosities (1.0-60.1 cP) were used. The size of the drops was 0.5-1.2 mm. Solid surfaces with different lyophilic and lyophobic coatings (equilibrium contact angle θ(eq) of 0°-112°) were used to study the effect of surface wettability. We show that surface wettability and liquid viscosity influence wetting dynamics and affect either the coefficient or the exponent of the power law that describes the growth of the wetting radius. In the early inertial wetting regime, the coefficient of the wetting power law increases with surface wettability but decreases with liquid viscosity. In contrast, the exponent of the power law does only depend on surface wettability as also reported in literature. It was further found that surface wettability does not affect the duration of inertial wetting, whereas the viscosity of the liquid does. For low viscosity liquids, the duration of inertial wetting corresponds to the time of capillary wave propagation, which can be determined by Lamb's drop oscillation model for inviscid liquids. For relatively high viscosity liquids, the inertial wetting time increases with liquid viscosity, which may due to the viscous damping of the surface capillary waves. Furthermore, we observed a viscous wetting regime only on surfaces with an equilibrium contact angle θ(eq) smaller than a critical angle θ(c) depending on viscosity. A scaling analysis based on Navier-Stokes equations is presented at the end, and the predicted θ(c) matches with experimental observations without any additional fitting parameters.

Posted Content
TL;DR: In this article, the full irrotational water waves system with surface tension and no gravity in dimension two (the capillary waves system), and prove global regularity and modified scattering for suitably small and localized perturbations of a flat interface.
Abstract: We consider the full irrotational water waves system with surface tension and no gravity in dimension two (the capillary waves system), and prove global regularity and modified scattering for suitably small and localized perturbations of a flat interface. An important point of our analysis is to develop a sufficiently robust method, based on energy estimates and dispersive analysis, which allows us to deal with strong singularities arising from time resonances in the applications of the normal form method and nonlinear scattering. As a result, we are able to consider a suitable class of perturbations with finite energy, but no other momentum conditions. Part of our analysis relies on a new treatment of the Dirichlet-Neumann operator in dimension two which is of independent interest. As a consequence, the results in this paper are self-contained.

Journal ArticleDOI
TL;DR: In this article, the authors report surface tension measurements, coexisting densities, concentration profiles along the interfacial region, surface activities, and relative Gibbs adsorption isotherms for binary mixtures of carbon dioxide (CO2) + n-decane (n-C10H22) at 344.15 K and carbon dioxide(CO 2)+ n-eicosane (N-C20H42) at 323.15K over a pressure range from 0.1 MPa to 10.35 MPa.
Abstract: We report surface tension measurements, coexisting densities, concentration profiles along the interfacial region, surface activities, and relative Gibbs adsorption isotherms for binary mixtures of carbon dioxide (CO2) + n-decane (n-C10H22) at 344.15 K and carbon dioxide (CO2) + n-eicosane (n-C20H42) at 323.15 K over a pressure range from 0.1 MPa to 10.35 MPa. The results are obtained by employing a broad approach that integrates experiments with both theory and molecular simulations to gain an enhanced multiscale description of the interfacial region. Measurements are based on the use of a high-pressure pendant drop tensiometer coupled to a high-pressure densimeter. Theoretical modeling is carried out using the Square Gradient Theory based on a version of the Statistical Associated Fluid Theory (SAFT-VR Mie) equation of state. At the molecular level, Molecular Dynamics is employed and molecules are represented by the SAFT-γ coarse-grained force field. The novelty here is that both the theory and the simu...

Journal ArticleDOI
TL;DR: In this paper, the authors derived closed-form expressions for the translational speed of a spheroidal particle in the limit of small capillary, Peclet and Reynolds numbers.
Abstract: We study the Marangoni propulsion of a spheroidal particle located at a liquid–gas interface. The particle asymmetrically releases an insoluble surface-active agent and so creates and maintains a surface tension gradient leading to the self-propulsion. Assuming that the surface tension has a linear dependence on the concentration of the released agent, we derive closed-form expressions for the translational speed of the particle in the limit of small capillary, Peclet and Reynolds numbers. Our derivations are based on the Lorentz reciprocal theorem, which eliminates the need to develop the detailed flow field.

Journal ArticleDOI
TL;DR: The adsorption of the mixtures of soy glycinin with a biosurfactant stevioside at the air-water interface was studied to understand its relation with foaming properties, and the strong synergy in reducing surface tension and the plateau in surface elasticity for mixed 11S-STE layers formed from the weakly interacting mixtures were clearly observed.
Abstract: The adsorption of the mixtures of soy glycinin (11S) with a biosurfactant stevioside (STE) at the air–water interface was studied to understand its relation with foaming properties. A combination of several techniques such as dynamic surface tension, dilatational rheology, fluorescence spectroscopy, and isothermal titration calorimetry (ITC) was used. In the presence of intermediate STE concentrations (0.25–0.5%), the weak binding of STE with 11S in bulk occurred by hydrophobic interactions, which could induce conformational changes of 11S, as evidenced by fluorescence and ITC. Accordingly, the strong synergy in reducing surface tension and the plateau in surface elasticity for mixed 11S–STE layers formed from the weakly interacting mixtures were clearly observed. This effect could be explained by the complexation with STE, which might facilitate the partial dissociation and further unfolding of 11S upon adsorption, thus enhancing the protein–protein and protein–STE interfacial interactions. These surface...

Journal ArticleDOI
TL;DR: In this paper, the equilibrium shape of liquid drops on elastic substrates is determined by minimizing elastic and capillary free energies, focusing on thick incompressible substrates, governed by three length scales: the size of the drop R, the molecular size a and the ratio of surface tension to elastic modulus γ/E.
Abstract: The equilibrium shape of liquid drops on elastic substrates is determined by minimizing elastic and capillary free energies, focusing on thick incompressible substrates. The problem is governed by three length scales: the size of the drop R, the molecular size a and the ratio of surface tension to elastic modulus γ/E. We show that the contact angles undergo two transitions upon changing the substrate from rigid to soft. The microscopic wetting angles deviate from Young’s law when γ/(Ea)≫1, while the apparent macroscopic angle only changes in the very soft limit γ/(ER)≫1. The elastic deformations are worked out for the simplifying case where the solid surface energy is assumed to be constant. The total free energy turns out to be lower on softer substrates, consistent with recent experiments.