Special Discussions of The Faraday Society 

About: Special Discussions of The Faraday Society is an academic journal. The journal publishes majorly in the area(s): Contact angle & Viscosity. Over the lifetime, 22 publications have been published receiving 497 citations.

Composition and energy relationships for some thin lipid films, and the chain conformation in monolayers at liquid-liquid interfaces

Abstract: Optically black films have been formed in aqueous media from solutions of glyceryl mono-oleate in aliphatic hydrocarbons. The thicknesses of the hydrocarbon cores of the films were estimated from electrical capacitance measurements and the compositions from interfacial tension data. The thicknesses and the compositions were found to be interrelated in a simple way and were markedly dependent on the chain length of the hydrocarbon solvent.An electrical potential applied across a liquid film subjects it to a large compressive force under which most types of film became significantly thinner. From thickness measurements in applied fields the strengths of the steric interactions which stabilize the films were calculated. From a knowledge of the steric interaction, together with an estimate of the London-van der Waals forces from contact angle measurements, the curve of potential energy against film thickness has been calculated for one system. The magnitude of the steric interaction at a given film thickness varies considerably for films of different solvent content. As a consequence, a general picture of the time-average conformations of the hydrocarbon chains of glyceryl mono-oleate in the black films and at different hydrocarbon/water interfaces may be deduced.

Measurement of forces between colloidal particles

Abstract: Apparatus has been constructed for the measurement of the pressure created by disperse systems as a function of the volume concentration of the disperse phase. Experiments with sodium montmorillonite as the colloidal system have enabled the force to be obtained as a function of the distance between the plates down to distances of the order of 10 A. The results have been compared with those expected theoretically on the basis of the DLVO theory. The forces obtained at distances of less than 50 A are much greater than those predicted by the theory and the additional force appears to arise from solvation effects in the thin liquid film between the particles. This has been confirmed by carrying out measurements in the presence of a non-ionic surface-active agent, a known stabilizing agent, where the repulsive forces due to solvation are enhanced.

Cohesive properties of thin films of liquids adhering to a solid surface

Abstract: The process of forming and rupturing a thin liquid film at a solid surface is described thermodynamically for both high and low energy solid surfaces. In part 1 the build-up of thin films on high-energy surfaces from the first monolayer is considered and reviewed. Components of the surface free energy of formation of the thin film (disjoining pressure) are defined. For curved surfaces the disjoining forces should be combined with the Laplace capillary pressure to give a correct form of the Kelvin equation. It is suggested from the early work of Bangham and Deryaguin that thin liquid layers have anomalous physical properties. These studies are discussed in relation to the thickness of the liquid films.In part 2, new experimental evidence of the critical rupture thickness of thin liquid films on low energy surface is presented. A number of pure liquids rupture spontaneously on low energy surfaces such as wax or polytetrafluoroethylene at very great thicknesses (0.01 cm). The effects of aqueous salt and surfactant solutions suggest these long-range forces are electrical in origin.

Contact between a gas bubble and a solid surface and froth flotation

Abstract: The process of formation of the contact silica surface/air when pressing a liquid meniscus on to the solid/liquid interface is investigated. The kinetics of expansion of the contact area and the final states characterized by contact angles in both directions (by spreading and withdrawing of the contact) are examined. Preliminary data about the effect of surfactants on the velocity of expansion of the contact and on the contact angle and its hysteresis are presented. The new methods applied in the investigations are described. The results are compared with flotation experiment data.

Measurement of viscosity of liquids in quartz capillaries

Abstract: A method is developed for measuring radii of microcapillaries and the viscosity of liquids in them. The viscosity of water, benzene, and carbon tetrachloride was measured in quartz capillaries of radius r= 0.5–0.04 µm. The viscosity of water in such capillaries is elevated (by 40 % in capillaries 0.04 µm radius), but the viscosity of non-polar CCl4 and benzene remains normal. The temperature dependence of the increased viscosity of water is studied; the viscosity becomes normal at t= 60–70°C When water is drawn into a capillary with “dry” walls, the wetting angle differs from zero. In these cases the contact angle is not constant, but depends on the rate of entry of the water.