Molecular Dynamics Study of Partial Monolayer Ordering of Chain Molecules

We present the results of a molecular dynamics study of a partial monolayer of self-assembled octadecanethiol molecules. The correlations between various statistical measures of surface induced chain ordering are examined. These include the density profile, chain morphology, tilt angle distributions, and gauche defect distributions. Particular attention is focused on the significance of the strength of the alkane chain surface interaction, as well as the role of temperature, on the type and degree of disorder which we observe. Our simulations are in accord with experimental evidence which indicates that the quality, in the sense of reproducibility in the laboratory, of dense films increases as the coupling of the chain molecules with the surface decreases. We believe that our findings have general implications for the establishment of experimental protocols for self-assembled surface films of organic molecules with varying degrees of prescribed disorder.