(382c) Mesoscale Simulations of Surface-Grafted Polymers in Binary Solvent Mixtures: Effects of Cononsolvency

One puzzling phenomenon about polymer conformation in mixtures of good solvents is the cononsolvency effect -- polymers in a good solution undergo reentrant coil-to-globule-to-coil transition upon addition of a (small amount of) good cosolvent. In this study, we first show that computer simulations employing a mesoscale soft model is able to reproduce the reentrant coil-to-globule-to-coil transition of a single polymer dissolved in mixtures of two good solvents, provided that solvents are treated explicitly. This result offers support to the increasingly accepted belief that cononsolvency of polymers is a generic effect that is independent of chemically specific details of polymers and solvents. The model is then applied to investigate morphological responses of polymer brushes to the solvent composition. It is found that brush height and brush profile may exhibit sensitive dependence on the solvent composition even when both solvents are individually perfectly miscible with polymers. The self-consistent field calculations based on the same model are further conducted to provide information on the free-energy changes that underlying the observed morphological responses. This study expands our understanding of the complicate role played by solvents in controlling conformation and phase behavior of polymers in solvent mixtures. On the application side, the study expands the strategy toolbox of designing stimuli-responsive homopolymer brushes beyond conventional methods of swapping good-bad solvents.