Molecular dynamics simulation for bilayers of alkyl thiol molecules at solid-solid interfaces

We present the results of molecular dynamics simulations for three different systems of bilayers of long-chain alkyl thiol [S(CH2)(15)CH3] molecules on an solid-solid interface using the extended collapsed atom model for the chain-molecule. It is found that there exist two possible transitions: a continuous transition characterized by a change in molecular interaction between sites of different chain molecules with increasing area per molecule and a sudden transition from an ordered lattice-like state to a Liquid-like state due to the lack of interactions between sites of chain molecules on different surfaces with increasing distance between two solid surfaces. The third system displays a smooth change in probability distribution characterized by the increment of gauche structure in the near-tail part of the chain with increasing area per molecule. The analyses of energetic results and chain conformation results demonstrate the characteristic change of chain structure of each system.