Swelling and Structural Properties of Polymer Microgels: Simulations of a Coarse-Grained Model

Microgels are microscopic particles composed of crosslinked polymer networks, which swell in a solvent. The equilibrium size and shape of a microgel respond to environmental conditions, such as pH, temperature, crowding, and ionic strength, facilitating applications to drug delivery and biochemical sensors. The swelling behavior of microgels depends directly on the distribution of tetravalent crosslinkers, which can vary from isotropic to a core-shell structure. Within a model in which polymers are represented as chains of coarse-grained beads, we perform molecular dynamics simulations to investigate the dependence of compressibility and swelling on network structure and the response of the equilibrium swollen radius to solvent quality and external stimuli. Our results provide a benchmark test of the Flory-Rehner theory of polymer networks, which relates the swelling of a polymer gel to the elasticity of the network and the entropy of mixing between the solvent and polymer. The model can be extended to explore swelling of ionic, polyelectrolyte microgels and diffusion of solutes throughout the gel network, which can help to guide the design of smart, responsive particles.