Continuum Monte Carlo simulation at constant pressure of stiff chain molecules at surfaces

Continuum Monte Carlo simulations at constant pressure are performed on short chain molecules at surfaces. The rodlike chains, consisting of seven effective monomers, are attached at one end to a flat two dimensional substrate. It is found that the model exhibits phases similar to the liquid condensed and liquid expanded phases of Langmuir monolayers. The model is investigated here for a wide range of pressures and temperatures using a special form of constant pressure simulation compatible with the symmetry breaking during tilting transitions in the liquid condensed phases. At low pressures, the chains undergo a tilting transition exhibiting tilt directions towards nearest and also next nearest neighbors depending on temperature. At elevated temperatures and low pressure the film enters a fluidlike phase similar to the liquid expanded phase observed in experiment. (C) 1996 American Institute of Physics.