Simulating Surface-Grafted Polymers in Solvent Mixtures: Effects of Cononsolvency

One puzzling phenomenon about polymer conformations in a mixture of solvents is the cononsolvency effect -- polymers in a good solvent undergo reentrant coil-to-globule-to-coil transition upon addition of a good cosolvent. Recent studies have suggested the generic nature of the cononsolvency effect independent of chemically specific details of the polymer and solvents. In this study, we first reinforce such claim by showing that a coarse-grained soft model frequently used in studying polymers is able to reproduce the reentrant transition at the single-chain level, provided that solvents are treated explicitly. In our Monte Carlo simulations, the coil-to-globule-to-coil transition occurs as the chemical potential of polymers in solution decreases upon increasing the cosolvent fraction, ruling out increasingly worse solvent quality as the cause of collapse. To further our microscopic understanding, we apply the soft model to studying conformational responses of surface-grafted polymers under the cononsolvency effect. By analyzing the inter-polymer density correlations, we illustrate the highly correlated nature of polymer clustering mediated by the cosolvents. Conformational responses of high grafting density brushes will also be discussed in the context of smart sensor surfaces.