MOLECULAR-DYNAMICS SIMULATION OF THE EFFECTS OF TEMPERATURE ON A DENSE MONOLAYER OF LONG-CHAIN MOLECULES

Molecular dynamics calculations have been used to study the effects of temperature on a dense monolayer of hydrocarbon molecules. The simulation system consisted of 90 flexible chains with headgroups and had periodic boundary conditions in the plane of the surface. The interaction potentials were chosen to model a monolayer of chemisorbed alkyl thiol molecules [S(CH 2)15CH3] on a Au (111) surface; molecules that self-assemble from solution to form a triangular lattice at a fixed surface density of 21.4 Å2 per chain. Simulations at different temperatures reveal distinct phases with different kinds of disorder. Nonequilibrium molecular dynamics techniques have been used to investigate the transition from the high-temperature state, in which the molecular planes undergo reorientational motion, to a low-temperature, orientationally ordered state. Possible correlations between the rotational phase transition and the appearance of conformational defects are also explored. © 1990 American Institute of Physics.