Conformations of homopolymer chains and their phase behavior in a simple supercritical solvent

Using a simple molecular model and the configurational-bias Monte Carlo method combined with the parallel tempering technique, solvent driven changes in conformations of a homopolymer chain in a simple supercritical solvent are systematically investigated. The solvent is modelled as a square-well fluid, and two types of chain are considered: the flexible chain of tangentially touching (i) hard spheres (purely repulsive chain) and (ii) square-well spheres (purely attractive chain). The mean square end-to-end distance and radius of gyration are the main quantities computed and used to characterize the changes in conformations in dependence on the temperature and density of the solvent. It is found that the attractive chain exhibits both the upper and lower critical solution temperatures, whereas the repulsive chain exhibits only the upper critical solution temperature.