Showing papers on "Surface tension published in 1992"
TL;DR: In this paper, a force density proportional to the surface curvature of constant color is defined at each point in the transition region; this force-density is normalized in such a way that the conventional description of surface tension on an interface is recovered when the ratio of local transition-reion thickness to local curvature radius approaches zero.
7,863 citations
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TL;DR: The Surface Evolver is a computer program that minimizes the energy of a surface subject to constraints that is represented as a simplicial complex.
Abstract: The Surface Evolver is a computer program that minimizes the energy of a surface subject to constraints. The surface is represented as a simplicial complex. The energy can include surface tension, gravity and other forms. Constraints can be geometrical constraints on vertex positions or constraints on integrated quantities such as body volumes. The minimization is done by evolving the surface down the energy gradient. This paper describes the mathematical model used and the operations available to interactively modify the surface.
2,241 citations
TL;DR: A surface having a spatial gradient in its surface free energy was capable of causing drops of water placed on it to move uphill after an imbalance in the forces due to surface tension acting on the liquid-solid contact line on the two opposite sides of the drop.
Abstract: A surface having a spatial gradient in its surface free energy was capable of causing drops of water placed on it to move uphill. This motion was the result of an imbalance in the forces due to surface tension acting on the liquid-solid contact line on the two opposite sides ("uphill" or "downhill") of the drop. The required gradient in surface free energy was generated on the surface of a polished silicon wafer by exposing it to the diffusing front of a vapor of decyltrichlorosilane, Cl(3)Si(CH(2))(9)CH(3). The resulting surface displayed a gradient of hydrophobicity (with the contact angle of water changing from 97 degrees to 25 degrees ) over a distance of 1 centimeter. When the wafer was tilted from the horizontal plane by 15 degrees , with the hydrophobic end lower than the hydrophilic, and a drop of water (1 to 2 microliters) was placed at the hydrophobic end, the drop moved toward the hydrophilic end with an average velocity of approximately 1 to 2 millimeters per second. In order for the drop to move, the hysteresis in contact angle on the surface had to be low (
1,446 citations
TL;DR: The present calculations explain the trend exhibited by the surface energies of the alkali, alkaline earth, divalent rare-earth, 3d, 4d, and 5d transition and noble metals, as derived from the surface tension of liquid metals.
Abstract: We have performed an ab initio study of the surface energy and the work function for six close-packed surfaces of 40 elemental metals by means of a Green's-function technique, based on the linear-muffin-tin-orbitals method within the tight-binding and atomic-sphere approximations. The results are in excellent agreement with a recent full-potential, all-electron, slab-supercell calculation of surface energies and work functions for the 4d metals. The present calculations explain the trend exhibited by the surface energies of the alkali, alkaline earth, divalent rare-earth, 3d, 4d, and 5d transition and noble metals, as derived from the surface tension of liquid metals. In addition, they give work functions which agree with the limited experimental data obtained from single crystals to within 15%, and explain the smooth behavior of the experimental work functions of polycrystalline samples as a function of atomic number. It is argued that the surface energies and work functions calculated by present day ab initio methods are at least as accurate as the experimental values.
1,080 citations
TL;DR: The Kinetic Theory of Gases as discussed by the authors describes the physical structure of surfaces and their properties, including surface curvature, surface tension, and surface mobility, as well as surface chemistry.
Abstract: SURFACE STRUCTURE, THERMODYNAMICS, AND MOBILITY. Atomic Structure of Surfaces. Electronic Structure of Surfaces. Surface Tension. Thermodynamics of One-Component Systems. Thermodynamics of Multicomponent Systems. Surface Mobility. GAS-SURFACE INTERACTIONS. The Kinetic Theory of Gases. Molecular Beam Formation. Gas Scattering. Adsorption-The Kinetic View. Physical Adsorption. Chemisorption. Surface Chemical Reactions. ENERGETIC PARTICLE-SURFACE INTERACTIONS. Electron-Surface Interactions. Ion-Surface Interactions. Photon-Surface Interactions. CRYSTAL GROWTH. Crystal Nucleation and Growth. Index.
464 citations
TL;DR: In this paper, the weighted relaxation spectra τH(τ) of polystyrene (PS)/poly(methylmethacrylate) blends show an additional peak with a characteristic relaxation time that is correlated with the interfacial tension.
Abstract: When shear oscillations are performed with melts of polystyrene (PS)/poly(methylmethacrylate) (PMMA) blends the total deformation has a large elastic portion at low frequencies. This finding is caused by the interfacial tension acting between the two phases of the blends. A simple model allows one to describe the influence of the interfacial tension on the storage and the loss moduli in a broad frequency range for all mixing ratios of the blend components. The weighted relaxation spectra τH(τ) of such blends show an additional peak with a characteristic relaxation time that is correlated with the interfacial tension. From this characteristic relaxation time the interfacial tension α between the melts of PS and PMMA can be determined. The resulting α=(1.9±0.3)×10−3 N/m at 170 °C is in good agreement with the value obtained from recovery following melt elongation of the blends.
296 citations
TL;DR: In this article, a simple method is described for the determination of contact angles (0) on powdered materials such as clay particles, by depositing the particles from a liquid suspension onto glass slides, by sedimentation, followed by drying.
Abstract: A simple method is described for the determination of contact angles (0) on powdered materials such as clay particles. This is done by depositing the particles from a liquid suspension onto glass slides, by sedimentation, followed by drying. The dried thin-layer plates are then subjected to wicking in a number of liquids using the Washhurn equation to determine cos . However, one other unknown in the Washburn equation, i.e. the average interstitial pore radius R, must first be determined. This is done by wicking with low-energy spreading liquids, such as alkanes. It could be shown with spherical monosized polymer particles, as well as with clay particles, that spreading liquids pre-wet the surfaces of the particles over which they subsequently spread. Thus, it can be demonstrated that spreading coefficients, in the sense of Harkins, play no role in this type of spreading and cos 0 equals unity in the Washburn equation for all values of γ1, for all spreading liquids (L). Results were obtained by thin layer...
227 citations
TL;DR: In this article, the surface tension of a liquid can be split into polar and dispersive components, and these same components can be obtained for a solid surface by the measurement of contact angles.
216 citations
TL;DR: In this paper, the authors used molecular dynamics simulations to predict the equilibrium liquid-vapor interface structure and surface tension of n-alkanes decane and eicosanes, C 10 H 22 and C 20 H 42, respectively.
Abstract: Molecular dynamics simulations are used to predict the equilibrium liquid-vapor interface structure and surface tension of n-alkanes decane and eicosanes, C 10 H 22 and C 20 H 42 , respectively. The model treats each methyl and methylene group as one united Lennard-Jones atom. Realistic bond lengths, bond angle potentials, and torsional potentials are included in the simulation. The simulations predict that although the total mass density profile is monotonic, the density profile of the chain centers of mass and central segments is strongly peaked. The outer edge of the surface is dominated by chain ends
193 citations
TL;DR: In this paper, a sample of triblock copolym Synperonic F127 was purified and the micellisation and gelation properties of aqueous solutions of purified and unpurified copolymers were investigated by surface tension measurement, static and dynamic light scattering, differential scanning calorimetry and NMR spectroscopy.
Abstract: A sample of triblock copoly(oxyethylene/oxypropylene/oxyethylene) Synperonic F127 was purified. The micellisation and gelation properties of aqueous solutions of purified and unpurified copolymers were investigated by surface tension measurement, static and dynamic light scattering, differential scanning calorimetry and NMR spectroscopy. Generally, the results obtained for the two samples were similar: an exception was the surface tension. Endothermic standard enthalpies of micellisation were obtained over a wide concentration range, with corresponding endothermic standard enthalpies of gelation in the high concentration range. Considered on an equivalent basis, i.e. kJ mol–1(chains), gelation was found to be an almost athermal process compared to micellisation. Based on the presented evidence, particularly that from DSC, and considering other recent studies, it was concluded that the thermal gelation of F127 (i.e. gelation on raising the temperature) resulted essentially from the packing of spherical micelles. A small thermal event at the gelation point was ascribed to a disorder–order discontinuity.
189 citations
TL;DR: In this article, the authors provided an analysis of the flow in the neighbourhood of the cusp, via an idealized problem which is solved completely: the cylinders are represented by a vortex dipole and the solution is obtained by complex variable techniques.
Abstract: When two cylinders are counter-rotated at low Reynolds number about parallel horizontal axes below the free surface of a viscous fluid, the rotation being such as to induce convergence of the flow on the free surface, then above a certain critical angular velocity Ωc, the free surface dips downwards and a cusp forms. This paper provides an analysis of the flow in the neighbourhood of the cusp, via an idealized problem which is solved completely: the cylinders are represented by a vortex dipole and the solution is obtained by complex variable techniques. Surface tension effects are included, but gravity is neglected. The solution is analytic for finite capillary number [Cscr ], but the radius of curvature on the line of symmetry on the free surface is proportional to exp (−32π[Cscr ]) and is extremely small for [Cscr ] [gsim ] 0.25, implying (in a real fluid) the formation of a cusp. The equation of the free surface is cubic in (x, y) with coefficients depending on [Cscr ], and with a cusp singularity when [Cscr ] = ∞.The influence of gravity is considered through a stability analysis of the free surface subjected to converging uniform strain, and a necessary condition for the development of a finite-amplitude disturbance of the free surface is obtained.An experiment was carried out using the counter-rotating cylinders as described above, over a range of capillary numbers from zero to 60; the resulting photographs of a cross-section of the free surface are shown in figure 13. For Ω Ωc, the downward-pointing cusp forms, and its structure shows good agreement with the foregoing theory.
TL;DR: In this paper, the possible crest-forms of permanent waves of small amplitude which exist on the free surface of a two-dimensional fluid layer under the influence of gravity and surface tension when the Froude number is close to 1 were determined.
Abstract: In this paper we determine the possible crest-forms of permanent waves of small amplitude which exist on the free surface of a two-dimensional fluid layer under the influence of gravity and surface tension when the Froude number is close to 1. The Bond number b, measuring surface tension, is assumed to satisfy b < ⅓. We find one-parameter families of periodic waves of two different types, quasiperiodic waves and solitary waves with oscillations at infinity. The existence of true solitary waves is established for a sequence of systems approximating the full Euler equations in every algebraic order of − 1.
TL;DR: Comparison with the liquid-vapor interfacial tensions of the model liquids studied here indicates that the surface free energies extracted for atomic-size cavities cannot be accurately identified with the macroscopic surface tensions of these systems.
Abstract: Observation of the size distribution of transient cavities in computer simulations of water, n-hexane, and n-dodecane under benchtop conditions shows that the sizes of cavities are more sharply defined in liquid water but the most-probable-size cavities are about the same size in each of these liquids. The calculated solvent atomic density in contact with these cavities shows that water applies more force per unit area of cavity surface than do the hydrocarbon liquids. This contact density, or "squeezing" force, reaches a maximum near cavity diameters of 2.4 angstroms. The results for liquid water are compared to the predictions of simple theories and, in addition, to results for a reference simple liquid. The numerical data for water at a range of temperatures are analyzed to extract a surface free energy contribution to the work of formation of atomic-size cavities. Comparison with the liquid-vapor interfacial tensions of the model liquids studied here indicates that the surface free energies extracted for atomic-size cavities cannot be accurately identified with the macroscopic surface tensions of the systems.
TL;DR: In this article, a series of surface tension measurements were performed to study the self-association of asphaltenes, and a distinctive discontinuous point was observed for surface tension as a function of the asphalte's concentration.
TL;DR: In this article, the curvature dependence of the liquid-vapor surface tension is described in the limit of small curvatures by Tolman's length, and a pressure tensor expression is obtained from an analysis of the pressure difference over the interface of a liquid drop that does not suffer from the previously encountered inconsistencies.
Abstract: The curvature dependence of the liquid–vapor surface tension is described in the limit of small curvatures by Tolman’s length. Measurements of it, either experimentally or in a simulation, have not yet given a clear idea of its magnitude, even its sign is being debated. Previous attempts to relate Tolman’s length to a pressure tensor have led to ill‐defined expressions. From an analysis of the pressure difference over the interface of a liquid drop, a pressure tensor expression is obtained for Tolman’s length that does not suffer from the previously encountered inconsistencies. This pressure difference is studied in a simulation of liquid drops, leading to an estimate of Tolman’s length. It appears to be small and bounds are given on it.
TL;DR: In this paper, the physical and chemical structures of gels dried from aprotic solvents were studied by a series of techniques (29 Si MAS-NMR, nitrogen adsorption, SAXS, elemental analysis, TGA).
Abstract: A two-step acid/base-catalyzed silica gel has been aged in alcohol and water baths followed by various aprotic solvents with a wide range of surface tensions. Low temperature (CO 2 ) and high temperature (ethanol) aerogels were also prepared. The physical and chemical structures of gels dried from aprotic solvents were studied by a series of techniques ( 29 Si MAS-NMR, nitrogen adsorption, SAXS, elemental analysis, TGA). The aprotic solvents isolated the effects of pore fluid surface tension during drying since they do not participate in condensation and other reactions. For aprotic solvents, a linear decrease in xerogel surface area was observed with increasing surface tension. Pore volume and pore size distribution followed a similar trend. Depending upon whether the gel had been washed in ethanol or water prior to the aprotic solvent, the final pore volume was changed significantly for a given surface tension. This indicates that both surface area and pore volume may be independently controlled.
TL;DR: In this paper, the dynamics of a thin film of Newtonian fluid coating the inner surface of an elastic circular tube is analyzed and nonlinear evolution equations for the film thickness and wall position are derived using lubrication theory, but an accurate representation of the curvatures of both the liquid and wall interfaces is employed which is valid for thick films.
Abstract: The dynamics of a thin film of Newtonian fluid coating the inner surface of an elastic circular tube is analysed. This problem is motivated by an interest in the closure of small airways of the lungs either by formation of a liquid bridge, the collapse of the airway wall or a combination of both processes. Liquid bridge formation is due to the destabilization of the liquid film that coats the inner surface of airways, while wall collapse can be due to either the high surface tension of the air–liquid interface or the flexibility of the wall.Nonlinear evolution equations for the film thickness and wall position are derived using lubrication theory, but an accurate representation of the curvatures of both the liquid and wall interfaces is employed which is valid for thick films. These approximations allow closure to be predicted. In addition, these approximations are justified by comparison with rigid-wall results obtained by solving the full Navier–Stokes equations and because fluid inertia only becomes important in the very late stages of closure. The linear stability of these equations is examined using normal-mode analysis for infinitesimal disturbances and the nonlinear stability is investigated by solving the governing equations numerically using the method of lines. Solutions show that there is a critical film thickness, strongly dependent on fluid and wall properties, above which unstable waves grow to form liquid bridges. The critical film thickness decreases with increasing surface tension or wall compliance since waves grow faster. Even for relatively stiff airways, the volume of fluid in the liquid lining required for closure can be approximately 70% of the volume for the rigid-tube case. Wall damping is an important effect only when the airway is sufficiently compliant. Airway closure occurs more rapidly with increasing unperturbed film thickness, surface tension and wall flexibility and decreasing wall damping.
TL;DR: Surface tension-area relations from pulmonary surfactant were obtained with a new apparatus that contains a leak free captive bubble of controllable size and surface tension and area are interrelated in the captive bubble which may promote low and stable surface tensions.
TL;DR: In this article, a single-shot flash photography was used to photographically record the deformation and spreading of a droplet on a porous porphyriac surface, which was found to be independent of surface temperature during the early period of impact.
TL;DR: In this paper, the dynamic surface properties of three widely different protein systems are investigated using different experimental techniques: static drop experiments, modulus experiments, stress relaxation experiments, and to a lesser degree, aspiration and sweeping experiments.
TL;DR: The surface tension of normal liquid alkanes (chain lengths between 15 and 18 carbon atoms) has been measured as a function of temperature as mentioned in this paper, which is consistent with a surface-induced phase transition in which the conformational degrees of freedom of molecules close to the surface are inhibited.
Abstract: The surface tension of normal liquid alkanes (chain lengths between 15 and 18 carbon atoms) has been measured as a function of temperature. In all cases the tension exhibits a well-defined change in behavior at a temperature close to, but distinct from, the melting point. The phenomena are consistent with a surface-induced phase transition in which the conformational degrees of freedom of molecules close to the surface are inhibited. Various properties of the transition vary smoothly with alkane chain length.
TL;DR: In this paper, the Cahn-Hilliard density gradient theory was used in conjunction with the Flory, Orwoll, and Vrij (FOV) and the Sanchez and Lacombe (SL) equations of state theories to predict surface tension with bulk pressure-volume-temperature data.
TL;DR: In this article, a homopolymer containing C 8 F 17 segments and C 4 F 9 substituents was prepared and homo-and copolymerized with styrene by radical initiation.
Abstract: Styrene monomers carrying C 4 F 9 and C 8 F 17 substituents were prepared and homo- and copolymerized with styrene by radical initiation. A decrease in the T g with increasing the fraction of fluorocarbon substituents was observed. Side-chain crystallization was observed for the homopolymer containing C 8 F 17 segments. This polymer exhibited a remarkably low critical surface tension by dynamic contact angle measurements, indicating the formation of a highly ordered layer of fluorocarbon degments at the polymer surface
Patent•
05 Mar 1992TL;DR: In this paper, a method for removing a liquid from a surface of a substrate, which is placed in a centrifuge and subjected therein to a rotary movement, is described, the substrate being rotated at such a speed that the liquid is centrifuged from the surface.
Abstract: A method is set forth of removing a liquid (3) from a surface (2) of a substrate (1), which is placed in a centrifuge (4) and is then subjected therein to a rotary movement, the substrate being rotated at such a speed that the liquid is centrifuged from the surface. According to the invention, the substrate is brought into contact in the centrifuge with a vapour of a material which is miscible with the liquid and which, when mixed therewith, yields a mixture having a surface tension which is lower than that of the liquid. Due to this step, the quantity of material remaining on the surface is strongly reduced.
TL;DR: The results indicate that SP-A enhances phospholipid adsorption during dynamic cycling and may enhance elimination of non-DPPC lipids during cycling.
Abstract: The effect of surfactant concentration and supplementation with surfactant-associated protein A (SP-A) on the surface activity of lipid extract surfactant (LES) was examined using a captive bubble technique. Adsorption of LES is strongly concentration dependent over the range of 50-1,000 micrograms/ml. Addition of SP-A to LES at low concentrations in the presence of calcium dramatically increases the rate of adsorption. In quasistatic cycling experiments, samples containing SP-A require less compression to achieve low surface tensions even during the first compression cycle. Calculated film compressibilities at 15 mN/m indicate that SP-A alters the surfactant monolayer behavior such that in a small number of cycles the compressibility is indistinguishable from that of pure DPPC. Furthermore, SP-A reduces the incidence of bubble "clicking," suggesting a stabilization of the monolayer at low surface tensions. In dynamic cycling experiments, SP-A reduces compression of the film area required to achieve a low surface tension of approximately 1 mN/m. SP-A eliminated the plateau just below 25 mN/m normally observed during the compression phase with low concentrations of LES and the shoulder observed at approximately 35 mN/m during expansion. In the presence of SP-A and, to a lesser extent with high concentrations of LES, there is a marked lag in the increase in surface tension during the initial part of the dynamic expansion loop, with surface tensions remaining near 1 mN/m for approximately 10% of the increase in bubble area. The results indicate that SP-A enhances phospholipid adsorption during dynamic cycling and may enhance elimination of non-DPPC lipids during cycling.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: In this paper, a computationally simple procedure is described to model effects of oil entrapment on three-phase permeability-saturation-capillary pressure relations, which are assumed to be nonhysteretic and are characterized by Van Genuchten's parametric model; scaling factors equal to the ratio of water surface tension to oil surface tension and to oil-water interfacial tension; and the maximum oil saturation which would occur following water flooding of oil saturated soil.
Abstract: A computationally simple procedure is described to model effects of oil entrapment on three-phase permeability-saturation-capillary pressure relations. The model requires knowledge of airwater saturation-capillary pressure relations, which are assumed to be nonhysteretic and are characterized by Van Genuchten's parametric model; scaling factors equal to the ratio of water surface tension to oil surface tension and to oil-water interfacial tension; and the maximum oil (also referred to as nonwetting liquid in a three-phase medium) saturation which would occur following water flooding of oil saturated soil. Trapped nonwetting liquid saturation is predicted as a function of present oil-water and air-oil capillary pressures and minimum historical water saturation since the occurrence of oil at a given location using an empirically-based algorithm. Oil relative permeability is predicted as a simple function of apparent water saturation (sum of actual water saturation and trapped oil saturation) and free oil saturation (difference between total oil and trapped oil saturation), and water relative permeability is treated as a unique function of actual water saturation. The proposed method was implemented in a two-dimensional finite-element simulator for three-phase flow and component transport, MOFAT. The fluid entrapment model requires minimal additional computational effort and computer storage and is numerically robust. The applicability of the model is illustrated by a number of hypothetical one- and two-dimensional simulations involving infiltration and redistribution with changes in water-table elevations. Results of the simulations indicate that the fraction of a hydrocarbon spill that becomes trapped under given boundary conditions increases as a nonlinear function of the maximum trapped nonwetting liquid saturation. Dense organic liquid plumes may exhibit more pronounced effects of entrapment due to the more dynamic nature of flow, even under static water table conditions. Disregarding nonwetting fluid entrapment may lead to significant errors in predictions of immiscible plume migration.
TL;DR: In this article, the in-plane and out-of-plane orientational motions of acridine orange at the interface of water and several hydrocarbon liquids were investigated for n-hexadecane, isopropycyclohexane, cis-decalin, and transdecalin.
Abstract: The first study of a molecular reorientation at a liquid/liquid interface is described. The in-plane and out-of-plane orientational motions are investigated for acridine orange at the interface of water and several hydrocarbon liquids: n-hexadecane, isopropycyclohexane, cis-decalin, and trans-decalin. The results reveal that the hydrocarbon viscosity has no direct influence on the in-plane reorientation of acridine orange. The results also reveal measurable differences in the out-of-plane orientational distribution, which is attributed to surface roughness. The roughness is unrelated to surface tension, suggesting that the surface roughness sensed by the probe is due to molecularity rather than to thermal capillary waves. 22 refs., 6 figs., 2 tabs.
TL;DR: Several fluid mechanical instabilities associated with buoyancy, surface tension and rotational forces in the Czochralski melt convection are described in this article, which obviates the need of the axisymmetric assumptions and the extensive computing required to obtain the statistics of a three-dimensional flow.
TL;DR: In this article, the anionic surfactant sodium dodecyl sulfate (SDS) was used to study the adhesion of SDS to various materials, a schematic molecular model of the SDS was used which optimally correlates with its critical micelle concentration (c.m.c.) values under various conditions.
Abstract: To study the adhesion of the anionic surfactant sodium dodecyl sulfate (SDS) to various materials, a schematic molecular model of SDS was used which optimally correlates with its critical micelle concentration (c.m.c.) values under various conditions. Using the surface tension components and parameters of (a) the SDS apolar and polar moieties and (b) the polymeric surfaces of cellulose and nylon, the energy of adhesion of SDS to these polymeric surfaces as well as to a typical low-energy material (greasy dirt) in the guise of hexadecane was determined. It could be quantitatively shown (using a surface-thermodynamic approach) that SDS, in water, adheres more strongly to the low-energy (greasy dirt) compounds than to the polymeric materials. The c.m.c. of SDS was derived directly from the surface tension components and parameters of its apolar and polar moieties, and the ζ potential of its polar heads. The c.m.c. values obtained using this model correlate well with the published c.m.c. values obtained exper...