Cosolute Partitioning in Polymer Networks: Effects of Flexibility and Volume Transitions

We study the partitioning of cosolute particles in a thin film of a semiflexible polymer network by a combination of coarse-grained (implicit-solvent) stochastic dynamics simulations and mean-field theory. We focus, on a wide range of solvent qualities and cosolute-network interactions for selected polymer flexibilities. Our investigated ensemble (isothermal-isobaric) allows the network to undergo a volume transition from extended to collapsed state while the cosolutes can distribute in bulk and network, correspondingly. We find a rich topology of equilibrium states, of the network and transitions between them; qualitatively depending on solvent quality, polymer flexibility, and cosolute-network interactions. In particular, we find a novel cosolute-induced collapsed state, where strongly attractive cosolutes bridge network monomers albeit the latter interact mutually repulsive. Finally,the cosolutes' global partitioning landscape, computed as, a function of solvent-quality and cosolute-network interactions, exhibits very different topologies depending on polymer flexibility. The simulation results are supported, by theoretical predictions obtained with a two-component mean-field approximation for the Helmholtz free, energy that considers the chain, elasticity and the particle interactions in terms of a virial expansion. Our findings have implications On the interpretation of transport processes and permeability in hydrogel films, as realized in filtration or macromolecular carrier systems.