Continuum Monte Carlo Simulation at Constant Pressure of Stiff Chain Molecules at Surfaces

TL;DR

This study uses continuum Monte Carlo simulations to explore phase behaviors of short stiff chain molecules on surfaces at constant pressure, revealing phases akin to liquid condensed and expanded states with temperature and pressure variations.

Contribution

It introduces a specialized constant pressure simulation method for modeling tilting transitions in surface-bound stiff chain molecules.

Findings

Identification of tilting transitions at low pressures and varying temperatures.

Observation of fluidlike phase with surface area per molecule matching experimental liquid expanded phase.

Demonstration of phase behavior similar to Langmuir monolayers.

Abstract

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 twodimensional 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 neighbours depending on temperature. At elevated temperatures and low pressure the film enters a fluidlike phase similar to whose surface area per molecule is in rough quantitative agreement with that of the liquid expanded phase observed in experiment.