Conformation Transition of a Homopolymer Chain in Binary Mixed Solvents

On the basis of a minimal lattice model, we apply the Wang–Landau Monte Carlo (MC) algorithm and a Flory-type mean-field theory to investigate the conformation of a homopolymer chain in a mixture of binary solvents A and B. This MC method enables us to accurately locate the conformation transitions and to determine their nature over a large parameter space. We find that in a good solvent A, adding a small amount of better solvent B causes a continuous collapse transition when the difference in the solvent quality is large. Increasing the fraction of solvent B results in a smooth reswelling of the chain. We explain these findings by the delicate interplay among the mixing entropy of binary solvents, the chain conformational entropy, and the competition in the interactions between the monomer and the two solvents.