Effects of molecular structure on frictional properties of Langmuir-Blodgett monolayers

Molecular dynamics simulations have been used to study shear friction in Langmuir-Blodgett monolayers of carboxylic acids. The effects of partial fluorination of hydrocarboxylic acids, of introduction of ether linkages into perfluorocarboxylic acids, and of chain length on frictional properties such as frictional mechanism and frictional coefficients were investigated. The frictional coefficient of the semifluorocarboxylic acid monolayer changed with the fluorination ratio of the hydrocarboxylic acid. Furthermore, the frictional coefficients of hydrocarboxylic acids with a carbon chain length from 12 to 20 were found to be independent of this length. The qualitative aspects of the simulation results were consistent with reported experimental results. The simulation results were discussed in relation to excess root mean square fluctuations of the potential energy under shear from the equilibrium energy value.