Rationalizing Polymer Swelling and Collapse under Attractive Cosolvent Conditions

The collapse and swelling behavior of a generic homopolymer is studied using implicit-solvent, explicit-cosolvent Langevin dynamics computer simulations for varying interaction strengths. The systematic investigation reveals that polymer swelling is maximal if both monomer–monomer and monomer–cosolute interactions are weakly attractive. In the most swollen state the cosolute density inside the coil is remarkably bulk-like and homogeneous. Highly attractive monomer–cosolute interactions, however, are found to induce a collapse of the chain, which, in contrast to the collapsed case induced by purely repulsive cosolvents, exhibits a considerably enhanced cosolute density within the globule. Thus, collapsed states, although appearing similar on a first glance, may result from very different mechanisms with distinct final structural and thermodynamic properties. Two theoretical models, the first based on an effective one-component description where the cosolutes have been integrated out and, second, a fully tw...