Molecular-dynamics calculations have been carried out for a system of long-chain molecules supported on a physisorbing planar substrate and constrained to a surface density characteristics of that observed in lipid and fatty acid monolayers at the air-water interface. Results are presented for the density distribution normal to the surface, the structure factor parallel to the surface, and the number of chain conformational defects as the surface area per chain is increased at room temperature. The driving force for the observed structural and conformational changes appears to be related to the tendency for the alkyl-chain methylene groups to close-pack.

• Received 16 December 1987

DOI:https://doi.org/10.1103/PhysRevLett.60.2152