Film Disjoining Pressure Research Articles

The modified Thomson equation in the theory of heterogeneous vapor nucleation on charged solid particles

Thermodynamic theory of heterogeneous vapor nucleation on charged nanosized solid particles is considered and formulas for the condensate chemical potential in the droplet and the nucleation activation barrier are derived. A modified Thomson equation for the pressure of vapor saturated over a liquid droplet formed around the spherical charged particle is proposed. This equation determines the saturated vapor pressure as a function of the particle size, charge magnitude and sign, and the droplet radius. The approach assumes that the droplet liquid film between the particle and the vapor phase is polarized in the central electric field of the charged particle and is thin, i.e., surface layers of the film at the boundaries with the particle and the vapor phase are overlapped and the arising disjoining pressure affects the droplet state. It is shown that the film disjoining pressure, the Maxwell stress of the film in the central electric field of the particle, the degree of the particle wetting, and the particle size interplay in determination of the threshold value of vapor supersaturation ratio at barrierless nucleation. The threshold values of the vapor supersaturation ratio were found for different model isotherms of the disjoining pressure and different relations between size and charge of the solid particles.

The modified Thomson equation in the theory of heterogeneous vapor nucleation on charged solid particles

Thermodynamic theory of heterogeneous vapor nucleation on charged nanosized solid particles is considered and formulas for the condensate chemical potential in the droplet and the nucleation activation barrier are derived. A modified Thomson equation for the pressure of vapor saturated over a liquid droplet formed around the spherical charged particle is proposed. This equation determines the saturated vapor pressure as a function of the particle size, charge magnitude and sign, and the droplet radius. The approach assumes that the droplet liquid film between the particle and the vapor phase is polarized in the central electric field of the charged particle and is thin, i.e., the surface layers of the film at the boundaries with the particle and the vapor phase are overlapped and the arising disjoining pressure affects the droplet state. It is shown that the film disjoining pressure, the Maxwell stress of the film in the central electric field of the particle, the degree of the particle wetting, and the particle size interplay in determination of the threshold value of vapor supersaturation ratio at barrierless nucleation. The threshold values of the vapor supersaturation ratio are found for different model isotherms of the disjoining pressure and different relations between size and charge of the solid particles.

Properties of foam films stabilized with tetraethylammonium perfluorooctane-sulfonate

Properties of single foam films prepared with tetraethylammonium perfluorooctane-sulfonate (TAPOS) were studied. Film thickness was measured as a function of NH 4Cl concentration in the film forming solution. The dependence of the film disjoining pressure versus the film thickness (disjoining pressure isotherms) and the mean lifetime of the films were studied. The dependence of the film thickness on the electrolyte concentration showed the presence of an electrostatic double layer at the film surfaces. The electrostatic double layer component of the disjoining pressure was screened at a NH 4Cl concentration higher than 0.2 M where Newton black films (NBFs) of 6 nm thickness were formed. These films are bilayers of amphiphile molecules and contain almost no free water. The disjoining pressure isotherms of the foam films formed with 0.001 M TAPOS were measured at two different NH 4Cl concentrations (0.005 and 0.0005 M). The Deryaguin–Landau–Verwey–Overbeek (DLVO) theory describes well the isotherms with an electrostatic double layer potential of ∼140 mV. The mean lifetime, a measure of the stability of the NBFs, was measured depending on surfactant concentrations. The observation of NBF was possible above a minimum TAPOS concentration of 9.4 × 10 −5 M. Above this concentration, the lifetime increases exponentially. The dependence of the film lifetime on surfactant concentration is explained by the theory for NBF-rupture by nucleation mechanism of formation of microscopic holes.

Stability analysis of ultrathin lubricant films via surface energy measurements and molecular dynamics simulations

The stability of nanoscale lubricant films was analyzed via both surface energy measurements and molecular dynamics (MD) simulations. Using the sessile method, the contact angles of deionized water and n-dodecane on Zdol lubricant films were measured to examine the dispersive and polar surface energy as well as the nanofilm stability. By calculating the free energy from MD simulations, we investigated surface energy of the lubricant film. Furthermore, the film disjoining pressure and the stability diagram were constructed from MD simulations to examine the layering structures in spreading phenomena. Our analysis exclusively focuses on the effects of the end-functionality and molecular weight.

On the Theory of the Stability of Dipole Molecule Solution Interlayers in Apolar Solvents: 4. A Localized Adsorption at the Dipole Orientation Parallel to the Interface

Image forces and their contribution to the disjoining pressure of solution films at the orientation of dipole molecules of adsorbed component parallel to the film interfaces are analyzed. Expressions for the calculation of the correlation attraction of adsorbed monolayers under various conditions of adsorption on opposite film boundaries are obtained. Relation for calculating the contribution of interaction between the adsorbed monolayers and their images to the film disjoining pressure is derived. Numerical estimates of the disjoining pressure arising due to aforementioned interactions are made.

Depletion and Structural Forces between Two Macrosurfaces Immersed in a Bidisperse Colloidal Suspension

Recent experiments on the thinning of liquid films formed from colloidal suspensions carried out in our laboratory [Nikolov, A., and Wasan, D. T., J. Colloid Interface Sci.133, 1 (1989); Langmuir8, 2985 (1992)] have revealed the pronounced effect of the presence of bidisperse-sized particles on the film stability. To shed more light on the role of the size bidispersity on the film properties, we performed a statistical mechanics study of a model system that consists of a binary hard-sphere mixture with a size ratio of 1 : 10 between two planar surfaces. The variations of the particle local densities, excess surface coverage, film disjoining pressure, and film interaction energy per unit area with separation between the surfaces in the presence of monodisperse and bidisperse particles have been investigated. A repulsive depletion interaction (depletion stabilization) between the surfaces in the case of a bidisperse suspension has been observed at separations of about one layer of the larger particles.

A Simple Calculation of Structural and Depletion Forces for Fluids/Suspensions Confined in a Film

By use of the analytic result for the Laplace transform of the radial distribution function for two large hard spheres dispersed in a fluid of the smaller hard spheres, simple equations for the film interaction energy and film disjoining pressure, due to the structural and depletion forces, are derived. The proposed equations satisfy some known exact results and explicitly express the energy and pressure as a function of the film thickness and volume fraction of the small hard spheres. The predicted results for the film energy and film disjoining pressure are compared with existing computer simulation data. The proposed simple analytical expressions can be applied to understand the stability of liquid films containing colloidal particles and the stability of suspensions, foams, and emulsions.

Direct measurement of disjoining pressure in black foam films II. Films from nonionic surfactants

Experiments are reported with foam films from two different polyoxyethylenic nonionic surfactants of relatively short and long polyoxyethylene chains. The direct measurement of the film disjoining pressure was combined with measurements of the film thickness dependence on the electrolyte concentration. The results obtained are discussed in connection with: (i) the type of black films observed, (ii) the influence of the POE chain length on the film properties, (iii) the agreement between the disjoining pressure isotherms obtained and the theoretical ones, (iv) the relationship between the charge and potential of the interacting diffuse double layers.

Direct measurement of disjoining pressure in black foam films. I. Films from an ionic surfactant

Disjoining pressure isotherms for microscopic foam films were measured directly, using an apparatus where the film disjoining pressure was balanced by

Some problems of gibbs' two dividing surfaces: Thermodynamics of multicomponent foam films

The system of a multicomponent foam film in equilibrium with a bulk liquid (meniscus) and a gas phase is considered. A rigorous thermodynamic scheme of describing this kind of systems is presented. The idealized system is introduced by making use of two dividing surfaces separating two bulk phases — the gas phase and the liquid phase of the meniscus. It is shown that the problems of the surface thermodynamics of small phases have been first developed by Gibbs. The conditions of the mechanical equilibrium of the system considered are examined in order to join the experimental method of liquid film investigations with the thermodynamic theory. Thermodynamical and riechanical definitions of the film disjoining pressure, tension, film surface tension, contact angle are presented. The problem of the independent thermodynamic variables, important for the comparison between the experimental data and the thermodynamic theory, is also discussed. Some fundamental Gibbs—Duhem equations are obtained. They correspond to suitable independent, experimental variables. A number of experimentally determinable quantities, that follow from those equations, are examined in detail and an emphasis is laid both on the possibilities for their physical interpretation and their comparison with similar quantities, obtained by model calculations.