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.