A theoretical explanation of the lowering of frictional forces with layer height of long chain polar lubricants

Assuming the anisotropic elastic constants of stearic acid as a function of layer height to be as determined by Akhmatov and Panova, the shear strengths of mono layers and multi layers are calculated. A computer programme describing the slip of a monolayer of an orthorhombic fatty acid crystal system about the methyl end groups is adapted to represent layer height by the use of a range of interaction potentials. Although the computed shear strengths are too high in magnitude compared with experimental results, as expected from strength calculations of an ideal crystal system, the correct trend of behaviour between multilayers and monolayers is shown.