Smectic model for liquid films on solid surfaces. Part 1.—Application to monolayer boundary lubrication

Abstract

A qualitative theory of films of hydrocarbon solutions of fatty acids described in a previous publication correlates many experimental data. According to this theory the fatty acid molecules and solvent molecules are arranged in layered structures similar to those in smectic mesophases. A simplified method for calculating the attractive energy between two such layers is described. The fatty acid molecules are assumed to behave as hard rods of constant electric polarizability and diamagnetic susceptibility. A potential describing the interaction between two rods is derived and used in a lattice sum calculation to compute the total energy of interaction of two layers as a function of average separation of molecules within a layer, relative position of the two layers and the distance between layers. Calculation of frictional force and coefficient of friction by means of this model show good agreement with a similar calculation of Cameron if the proper assumption about the relative magnitude of energy as a function of relative position is made.