We study the partitioning of cosolute particles in a thin film of a
semi-flexible 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.Comment: Macromolecules (2017
