Showing papers on "Surface tension published in 2000"
TL;DR: The first reported measurements of the dynamic surface excess Gamma(t), using the overflowing cylinder in conjunction with neutron reflection, are described.
791 citations
TL;DR: In this paper, the authors describe an experimental technique for the production of highly monodisperse emulsions (with minimum achievable polydispersities < 3%), where the phase to be dispersed is introduced into a co-flowing, surfactant-laden continuous phase via a tapered capillary.
Abstract: We describe an experimental technique for the production of highly monodisperse emulsions (with minimum achievable polydispersities <3%). The phase to be dispersed is introduced into a coflowing, surfactant-laden continuous phase via a tapered capillary. Drops detach from the capillary when the streamwise forces exceed the force due to interfacial tension. Drop size is a function of the capillary tip diameter, the velocity of the continuous phase, the extrusion rate, and the viscosities and interfacial tension of the two phases. Emulsions composed of a variety of fluids and with drop sizes ranging from 2 to 200 μm have been produced using this technique.
704 citations
TL;DR: This article is devoted to an overview, comparison and discussion of recent results (both theoretical and experimental) about lateral capillary forces, when the contact of particles or other bodies with a fluid phase boundary causes perturbations in the interfacial shape.
655 citations
TL;DR: In this paper, a smoothed particle hydrodynamics (SPH) based approach is presented for simulating two-phase flows including surface tension, and several possible implementations of surface tension force are suggested and compared.
Abstract: A method for simulating two-phase flows including surface tension is presented. The approach is based upon smoothed particle hydrodynamics (SPH). The fully Lagrangian nature of SPH maintains sharp fluid–fluid interfaces without employing high-order advection schemes or explicit interface reconstruction. Several possible implementations of surface tension force are suggested and compared. The numerical stability of the method is investigated and optimal choices for numerical parameters are identified. Comparisons with a grid-based volume of fluid method for two-dimensional flows are excellent. The methods presented here apply to problems involving interfaces of arbitrary shape undergoing fragmentation and coalescence within a two-phase system and readily extend to three-dimensional problems. Boundary conditions at a solid surface, high viscosity and density ratios, and the simulation of free-surface flows are not addressed. Copyright © 2000 John Wiley & Sons, Ltd.
468 citations
TL;DR: The use of surface tensiometry and rheometry of mixed protein/surfactant mixed layers is demonstrated as a new tool in the diagnostics of various diseases and for monitoring the progress of therapies.
418 citations
TL;DR: In this paper, the critical micelle concentrations (CMC) of nine commercial nonionic surfactants (Tween 20, 22, 40, 60, and 80) were determined by surface tension and dye micellization methods.
Abstract: The critical micelle concentrations (CMC) of nine commercial nonionic surfactants (Tween 20, 22, 40, 60, and 80; Triton X-100; Brij 35, 58, and 78) and two pure nonionics [C12(EO)5 and C12(EO)8] were determined by surface tension and dye micellization methods. Commercially available nonionic surfactants (technical grade) usually contain impurities and have a broad molecular weight distribution owing to the degree of ethoxylation. It was shown that the surface tension method (Wilhelmy plate) is very sensitive to the presence of impurities. Much lower CMC values were obtained with the surface tension method than with the dye micellization method (up to 6.5 times for Tween 22). In the presence of highly surfaceactive impurities, the air/liquid interface is already saturated at concentrations well below the true CMC, leading to a wrong interpretation of the break in the curve of surface tension (γ) vs. concentration of nonionic surfactant (log C). The actual onset of micellization happens at higher concentrations, as measured by the dye micellization method. Furthermore, it was shown that when a commercial surfactant sample (Tween 20) is subjected to foam fractionation, thereby removing species with higher surface activity, the sample yields almost the same CMC values as measured by surface tension and dye micellization methods. It was found that for monodisperse pure nonionic surfactants, both CMC determination methods yield the same results. Therefore, this study indicates that precaution should be taken when determining the CMC of commercial nonionic surfactants by the surface tension method, as it indicates the surface concentration of all surface-active species at the surface only, whereas the dye method indicates the presence of micelles in the bulk solution.
300 citations
TL;DR: In this paper, the water drop penetration time (WDPT) is used to quantify the degree of soil water repellency, and the water entry pressure, hp, which is a function of both the soil water and pore size, is an important parameter for predicting infiltration and the stability of water flow.
276 citations
TL;DR: In this paper, the spatial and groupwise distribution of surface tension in a fully hydrated 256 lipid dipalmitoylphosphatidylcholine (DPPC) bilayer is determined from a 5 ns molecular dynamics simulation by resolving the normal and lateral pressures in space through the introduction of a local virial.
Abstract: The spatial and groupwise distribution of surface tension in a fully hydrated 256 lipid dipalmitoylphosphatidylcholine (DPPC) bilayer is determined from a 5 ns molecular dynamics simulation by resolving the normal and lateral pressures in space through the introduction of a local virial. The resulting surface tension is separated into contributions from different types of interactions and pairwise terms between lipid headgroups, chains and water. By additionally performing a series of five simulations at constant areas ranging from 0.605 to 0.665 nm2 (each of 6 ns length), it is possible to independently resolve the energetic contributions to surface tension from the area dependence of the interaction energies. This also enables us to calculate the remaining entropic part of the tension and the thermal expansivity. Together with the total lateral pressures this yields a full decomposition of surface tension into energetic and entropic contributions from electrostatics, Lennard-Jones and bonded interaction...
249 citations
TL;DR: In this article, the experimental contact angle patterns for 14 solid surfaces are interpreted in terms of their solid surface tensions, and an explicit form of such a relation is obtained by modifying Berthelot's rule together with experimental data.
245 citations
TL;DR: This paper reports a theoretical and experimental study of the generation of a singularity by inertial focusing, in which no break-up of the fluid surface occurs, and predicts that the surface profiles should be describable by a single universal exponent.
Abstract: Finite-time singularities—local divergences in the amplitude or gradient of a physical observable at a particular time—occur in a diverse range of physical systems. Examples include singularities capable of damaging optical fibres and lasers in nonlinear optical systems1, and gravitational singularities2 associated with black holes. In fluid systems, the formation of finite-time singularities cause spray and air-bubble entrainment3, processes which influence air–sea interaction on a global scale4,5. Singularities driven by surface tension have been studied in the break-up of pendant drops6,7,8,9 and liquid sheets10,11,12. Here we report a theoretical and experimental study of the generation of a singularity by inertial focusing, in which no break-up of the fluid surface occurs. Inertial forces cause a collapse of the surface that leads to jet formation; our analysis, which includes surface tension effects, predicts that the surface profiles should be describable by a single universal exponent. These theoretical predictions correlate closely with our experimental measurements of a collapsing surface singularity. The solution can be generalized to apply to a broad class of singular phenomena.
232 citations
TL;DR: In this article, the effect of copolymers on the breakup and coalescence of polybutadiene (PB) drops in polydimethylsiloxane (PDMS) was studied using a four-roll mill flow cell.
Abstract: The effect of copolymers on the breakup and coalescence of polybutadiene (PB) drops in polydimethylsiloxane (PDMS) is studied using a four-roll mill flow cell. Copolymers are produced at the interface by a reaction between functionalized homopolymers. They reduce the interfacial tension and thus enhance breakup; they also inhibit coalescence of drops. Under the conditions of our experiments, the latter effect is much more significant than the former. For example, the addition of copolymer sufficient to reduce the interfacial tension by only 3% relative to the bare interface value is found to reduce the critical capillary number Cac for coalescence by a factor of 6. The critical capillary number for coalescence in the absence of copolymer is also measured for the first time. It is found to scale with the drop radius a as Cac∼a−0.82±0.03 and with the viscosity ratio λ as Cac∼λ−0.41±0.06.
TL;DR: In this paper, surface tension has been used to pull different semiconductor wafers to very close contact and strong bonding, and the bonding process has been analyzed, and criteria for surface tension, wafer flatness, and elasticity have been derived.
Abstract: Liquid surface tension has been used to pull different semiconductor wafers to very close contact and strong bonding. Bonded wafers, such as GaAs/GaP, were heat treated without pressure application to achieve wafer fusion. The bonding process has been analyzed, and criteria for surface tension, wafer flatness, and elasticity have been derived.
TL;DR: In this article, the van der Waals forces between a tip and a plane in a scanning force microscope (SFM) are calculated for a fixed distance of tip and sample, as well as during retracting of the tip from the sample surface.
Abstract: The capillary and van der Waals forces between a tip and a plane in a scanning force microscope (SFM) are calculated. The forces are calculated for a fixed distance of tip and sample, as well as during retracting of the tip from the sample surface. The exact geometric shape of the meniscus is considered, with the boundary condition of fixed liquid volume during retraction. The starting volume is given by the operating and environmental conditions (surface tension, humidity, and tip geometry) at the point of lowest distance between tip and surface. The influence of the different parameters, namely, humidity, tip geometry, tip-sample starting distance, surface tension, and contact angles are studied. For each force curve also the geometric shape of the meniscus is calculated. The capillary forces are compared with van der Waals forces to understand their relative importance in various operating conditions. In addition to application in SFM, this analysis is useful in the design of surface roughness in microdevices for low adhesion in operating environments.
TL;DR: In this article, the authors measured the surface shear elasticity modulus (μ) together with the dilatational modulus of gel-like protein layers on an air/water boundary.
Abstract: We propose a simple new method for measuring the surface shear elasticity modulus (μ) together with the dilatational modulus (K) of gel-like protein layers on an air/water boundary. The stress response to compression/expansion of the interface in a Langmuir trough is measured at two different orientations of a Wilhelmy plate, collateral and perpendicular to the movable barrier in the trough. The interfacial tension is a tensorial quantity, whence the measured values depend on the direction of the length along which the stress acts. The fact that the deformation in the trough is uniaxial, i.e., a combination of dilatation and shear, is used to determine the respective two elastic moduli (K, μ). The experiment demonstrates that adsorbed layers of β-lactoglobulin (BLG), when subjected to small deformations, exhibit a predominantly elastic rheological behavior. This proves the existence of the two-dimensional gel, as a result from partial denaturation and unfolding accompanied with entanglement of the protein...
TL;DR: This work applies the Lagrangian particle method to the formation of a liquid drop, surrounded by its vapor, for a van der Waals fluid in two dimensions, and studies strongly deformed drops performing large-amplitude oscillations.
Abstract: Smoothed particle applied mechanics (SPAM), also referred to as smoothed particle hydrodynamics, is a Lagrangian particle method for the simulation of continuous flows. Here we apply it to the formation of a liquid drop, surrounded by its vapor, for a van der Waals (vdW) fluid in two dimensions. The cohesive pressure of the vdW equation of state gives rise to an attractive, central force between the particles with an interaction range which is assumed to exceed the interaction range of all the other smoothed forces in the SPAM equations of motion. With this assumption, stable drops are formed, and the vdW phase diagram is well reproduced by the simulations. Below the critical temperature, the surface tension for equilibrated drops may be computed from the pressure excess in their centers. It agrees very well with the surface tension independently determined from the vibrational frequency of weakly excited drops. We also study strongly deformed drops performing large-amplitude oscillations, which are reminiscent of the oscillations of a large ball of water under microgravity conditions. In an appendix we comment on the limitations of SPAM by studying the violation of angular momentum conservation, which is a consequence of noncentral forces contributed by the full Newtonian viscous stress tensor.
TL;DR: In this article, it has been shown that it is possible to form micrometer rings and hexagonal arrays made of nanocrystals of different sizes, shapes and materials driven by surface tension gradients that induce Benard−Marangoni instabilities in liquid films.
Abstract: By controlling solvent evaporation rates, it has been possible to form micrometer rings and hexagonal arrays made of nanocrystals of different sizes, shapes and materials. Such patterns are driven by surface tension gradients that induce Benard−Marangoni instabilities in the liquid films. The resulting self-assembled structures are consistent with theoretical prediction of hydrodynamic instabilities.
TL;DR: Trends predicted by tau D to gauge what surfactant properties are required for rapid surface tension reduction are discussed, and are shown to be in agreement with guiding principles that have been suggested from prior structure-property studies.
TL;DR: Measurements of liquid entry pressure measurements are applied to study the hydrophobicity of microporous membranes for aqueous alcohol solutions and the maximum concentration before the spontaneous wetting occurs would be predicted.
TL;DR: The full dynamics of growth and closure of macroscopic transient pores in mechanically stretched giant vesicles are studied.
Abstract: We have visualized macroscopic transient pores in mechanically stretched giant vesicles. They can be observed only if the vesicles are prepared in a viscous solution to slow down the leak-out of the internal liquid. We study here theoretically the full dynamics of growth (driven by surface tension) and closure (driven by line tension) of these large pores. We write two coupled equations of the time evolution of the radii r(t) of the hole and R(t) of the vesicle, which both act on the release of the membrane tension. We find four periods in the life of a transient pore: (I) exponential growth of the young pore; (II) stop of the growth at a maximum radius rm; (III) slow closure limited by the leak-out; (IV) fast closure below a critical radius, when leak-out becomes negligible. Ultimately the membrane is completely resealed. Notation d membrane thickness E surface stretching modulus K b Helfrich bending constant Q leak-out flux r pore radius r i pore radius at nucleation r c pore radius at zero tension r L characteristic radius of leak-out r m radius at maximum (II) r 23 pore radius at cross-over between (II) and (III) r 34 pore radius at cross-over between (III) and (IV) R vesicle radius R i initial vesicle radius R 0 vesicle radius at zero tension V L leak-out velocity V 3 slow closure velocity limited by leak-out (III) V 4 fast closure velocity at end (IV) η 2 lipid viscosity η s surface viscosity η 0 viscosity of solution σ surface tension σ 0 surface tension before pore opening τ rise time of pore growth (I) J line tension
TL;DR: In this article, a transport model describing solvent-membrane interactions, governed by viscous and surface forces, was presented, which relates the flux of a solvent mixture with easily measurable solvent and membrane properties (surface tension, viscosity and membrane hydrophobicity).
TL;DR: In this article, the surface energies of polypropylene (PP), polystyrene (PS), and on plates of a liquid crystalline polymer (LCP) were measured at 20°C.
Abstract: In the present work, contact angles formed by drops of diethylene glycol, ethylene glycol, formamide, diiodomethane, water, and mercury on a film of polypropylene (PP), on plates of polystyrene (PS), and on plates of a liquid crystalline polymer (LCP) were measured at 20°C. Then the surface energies of those polymers were evaluated using the following three different methods: harmonic mean equation and geometric mean equation, using the values of the different pairs of contact angles obtained here; and Neumann's equation, using the different values of contact angles obtained here. It was shown that the values of surface energy generated by these three methods depend on the choice of liquids used for contact angle measurements, except when a pair of any liquid with diiodomethane was used. Most likely, this is due to the difference of polarity between diiodomethane and the other liquids at the temperature of 20°C. The critical surface tensions of those polymers were also evaluated at room temperature according to the methods of Zisman and Saito using the values of contact angles obtained here. The values of critical surface tension for each polymer obtained according to the method of Zisman and Saito corroborated the results of surface energy found using the geometric mean and Neumann's equations. The values of surface energy of polystyrene obtained at 20°C were also used to evaluate the surface tension of the same material at higher temperatures and compared to the experimental values obtained with a pendant drop apparatus. The calculated values of surface tension corroborated the experimental ones only if the pair of liquids used to evaluate the surface energy of the polymers at room temperature contained diiodomethane. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1831–1845, 2000
TL;DR: In this article, the authors compared three methods of determining the pressure tensor: the method of Irving and Kirkwood (IK), an approximation thereof (IK1), and a method of Harasima (H).
Abstract: Polymeric thin films of various thicknesses, confined between two repulsive walls, have been studied by molecular dynamics simulations. Using the anisotropy of the perpendicular, PN(z), and parallel components, PT(z), of the pressure tensor the surface tension of the system is calculated for a wide range of temperature and for various film thicknesses. Three methods of determining the pressure tensor are compared: the method of Irving and Kirkwood (IK), an approximation thereof (IK1), and the method of Harasima (H). The IK- and the H-methods differ in the expression for PT(z) (z denotes the distance from the wall), but yield the same formula for the normal component PN(z). When evaluated by molecular dynamics (or Monte Carlo)-simulations PN(z) is constant, as required by mechanical stability. Contrary to that, the IK1-method leads to strong oscillations of PN(z). However, all methods give the same expression for the total pressure when integrated over the whole system, and thus the same surface tension, w...
TL;DR: In this article, a point set method for extracting the normal, curvature, and surface area from unordered data points residing on a surface is described, which relaxes front tracking's reliance on connectivity between interfacial points and allows front tracking to model topological changes at an interface naturally.
TL;DR: In this article, the surface tension of haplogranite (HPG) melts with an excess of alkalis and phosphorous was measured by measuring the two principal radii of curvature of the drop shape in vertical cross section.
Abstract: The sessile drop method has been used for measurements of the surface tension of haplogranite (HPG) melts containing an excess of alkalis and phosphorous (HPG8, HPG8 + 5 wt% Li 2 O, 5 wt% Na 2 O, 20 wt% Na 2 O, 5 wt% K 2 O, 5 wt% Rb 2 O, 5 wt% Cs 2 O, 10 wt% P 2 O 5 ) and of Armenian rhyolite in the temperature interval, 650–1665 °C, and at 1 bar pressure. Sessile drops were placed on graphite substrates in a Pyrox tube furnace purged with Ar. Drop shape was monitored with a videocamera and stored in a videorecorder. The surface tension was calculated by measuring the two principal radii of curvature of the drop shape in vertical cross section. The precision of the method was checked against the surface tension of water. The surface tension of HPG and rhyolite melt is ~280–300 ± 5 mN/m in the temperature interval 1200–1400 °C. Temperature dependence of the surface tension of haplogranite melts and rhyolite is weak and positive (dσ/d T = 0.06 to 0.09 mN/m/°C). Addition of 5 wt% of alkali oxides (except Li 2 O) results in a decrease of the surface tension of haplogranite melts. The HPG melts with 10 wt% P 2 O 5 have 30% higher surface tension than haplogranite melts with excess alkalis, and a negative temperature derivative (dσ/d T = −0.1 mN/m/°C). The HPG melts with 20 wt% Na 2 O and 5 wt% Li 2 O exhibit a decrease in surface tension with temperature (dσ/d T = −0.02 and −0.10 mN/m/°C, respectively). The surface tension of HPG8 melt saturated with water at 1–4 kbar was measured on sessile drops quenched at high pressure in an internally heated gas vessel at temperatures of 800–1200 °C. Water pressure significantly decreases the surface tension of melt from 270 mN/m at 1 bar (1000 °C) to 65 mN/m at 4 kbar. At 1 bar in “dry” conditions, dσ/d T = +0.056 mN/m/°C and at 3 kbar of water pressure, dσ/d T = +0.075 mN/m/°C. The decrease in the surface tension of HPG melt at a water pressure of several kbars is from −10 to −30 mN/m/wt% H 2 O. The increase of water content to more than 10 wt% in granite melts may not result in any significant decrease in the surface tension, which may be explained by formation of a surface sublayer having physical properties very distinct from those of the bulk.
TL;DR: In this paper, the authors explore the time scale of surface tension evolution in jets of miscible fluids injected into critical and near-critical solvents to determine whether the jets atomize into droplets or simply evolve as gaseous plumes.
Abstract: This study provides insight into the mechanisms that govern morphology in microparticles processed using precipitation by a compressed antisolvent. We explore the time scale of surface tension evolution in jets of miscible fluids injected into critical and near-critical solvents to determine whether the jets atomize into droplets or simply evolve as gaseous plumes. Classical jet breakup length equations, modified with time-dependent surface tension, accurately predict observed breakup lengths over a range of liquid miscibilities. Linear jet breakup theory can be applied successfully to near critical conditions. The aerodynamic reduction factor remains constant over a wide range of pressures. However, under miscible conditions, calculations show that surface tension in a 10-cm/s round jet of methylene chloride in carbon dioxide at 8.5 MPa and 35 °C approaches 0.01 mN/m in 1 μm. Because this distance is shorter than characteristic breakup lengths, distinct droplets never form. Rather, the jets spread in a f...
TL;DR: In this paper, the effects of gas composition, temperature, and pressure on the interfacial tension of the studied systems are reported, for five gas compositions in the temperature range of (298−373) K and pressure range of 1−30 MPa.
Abstract: Interfacial tension for (CO2 + CH4) + water systems are reported for five gas compositions in the temperature range of (298−373) K and pressure range of (1−30) MPa. The effects of gas composition, temperature, and pressure on the interfacial tension of the studied systems are reported.
TL;DR: In this article, the surface tension of the full three-dimensional Lennard-Jones potential is calculated from grand canonical Monte Carlo simulations with the finite-size scaling methodology outlined by Binder.
Abstract: The surface tension of the full three-dimensional Lennard-Jones potential is calculated from grand canonical Monte Carlo simulations with the finite-size scaling methodology outlined by Binder [Phys. Rev. A 25, 1699 (1982)]. Surface tensions are determined for the range of reduced temperatures T*=0.95–1.312 and are found to be in good agreement with molecular-dynamics calculations. A critical temperature Tc*=1.311±0.002 is established by locating the T* where the surface tension of the infinite system size vanishes. In addition, with this method it is possible to determine the critical exponent 2ν. For the Lennard-Jones fluid we found 2ν=1.42±0.08, which differs from the accepted value of 2ν=1.26.
TL;DR: In this paper, a study of the compression of monolayers of monodisperse spherical polystyrene particles at the interface between aqueous surfactant solutions and octane was performed.
Abstract: We report a study of the compression of monolayers of monodisperse spherical polystyrene particles at the interface between aqueous surfactant solutions and octane. The particle size (2.6 μm diameter) was selected so that direct in situ microscopic observation of the monolayer structure could be made during lateral compression and “collapse”. Monolayers have been formed on a miniature Langmuir trough placed on a microscope stage. Our study has focused on (a) the relationship between the monolayer collapse pressure, Πcol, and the interfacial tension, γ*, of the oil/water interface in the absence of a particle monolayer and (b) the mode of monolayer “collapse” at high surface pressure. Interfacial tensions γ* have been adjusted (in the range 50−4 mN m-1) by addition of surfactants over a range of concentration. We find that the monolayer collapses by buckling (folding) when the surface pressure is equal to the surface tension of the oil/water interface. Particle promotion out of the interface is not observe...
TL;DR: In this article, a critical review and experimental comparison between different techniques for the determination of interfacial tension are presented for a model polymer pair. And five experimental methods were applied to the model.
Abstract: A critical review and experimental comparison between different techniques for the determination of interfacial tension are presented for a model polymer pair. Five experimental methods were applie...
TL;DR: In this paper, the Cahn-Hilliard theory was combined with three equations of state (EOS) (the Peng-Robinson (PR), the Sanchez-Lacombe (SL) lattice fluid model, and the original Statistical Associating Fluid Model) in order to describe both the phase behaviour and the surface properties of different types of molecules, namely nonpolar substances (n-alkanes and aromatic compounds), alcohols and water.