LONG-CHAIN AMPHIPHILE MONOLAYERS ON AN ANISOTROPIC SUBSTATE - A COMPUTER-SIMULATION STUDY

We report the results of Monte Carlo and molecular dynamics simulations of the properties of monolayers of long-chain amphiphile molecules supported on an anisotropic substrate. The calculations were undertaken to illustrate the nature of the several signatures of the anisotropic substrate surface potential in the properties of the monolayer. The calculations reported are for the case where the surface is the basal plane of a tetrahedral lattice; the symmetry of the potential of this surface is fundamentally linear with a zigzag modulation. We show, for example, that in the low-density regime the long-chain amphiphile molecules are stretched along the symmetry axis of the surface potential and contracted perpendicular to that direction. In the high-density regime the model monolayer displays several interesting properties, dependent on temperature and area per molecule: collective tilting along the symmetry axis of the surface potential, different packing of head groups and long chains (implying a defect structure in the monolayer), packing in multiple sublattices which are rotated with respect to one another, etc. These model calculations clearly show that we can expect both obvious and subtle structural effects to be induced in a monolayer of long-chain amphiphile molecules by an anisotropic surface potential.