Role of Dispersion Interactions Between Hydrocarbon Chains in Boundary Lubrication

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Abstract
A model utilizing simple structural defect theory in molecular monolayers quantitatively accounts for the relationship between measured friction coefficients at monolayer coverage and additive properties such as enthalpy of fusion, chain length, chain symmetry, and solubility in hydrocarbon media. This model is an extension of a recent model of boundary lubrication for a simple two-component lubricant (i.e., base lubricant and one additive) relating friction coefficient to surface coverage. For a given polar end group, it is shown that the lateral cohesive interactions between the hydrocarbon chains in the monolayer play the major role in reducing friction and that the sum total of these interactions approximates the enthalpy of fusion. The coupling between friction coefficient at monolayer coverage and solubility directly follows from thermodynamics.