Characterization of a Langmuir-Blodgett monolayer using molecular dynamics calculations

Molecular dynamics calculations have been used to explore the structure and dynamics of a monolayer of long-chain molecules supported on a planar substrate. The simulation system consisted of a periodically replicated array of 90 flexible-chain molecules, each with 20 pseudo-atoms, interacting with each other via potentials appropriate to the liquid alkanes and with the substrate via a 9–3 potential. At room temperature and a surface density of 20.8 Å2/chain, the system consists of highly ordered all-trans chains, with few conformational defects, canted at ≈40° with respect to the surface normal. Results are presented for the pseudo-atom density distribution of the film normal to the surface, the structure factor parallel to the surface, and the density of states for the low-frequency lattice vibrations. The effect of heating the system is also discussed.