Nanostructural heterogeneity in polymer networks and gels

Many polymer networks and gels display nanostructural heterogeneity in the form of spatially inhomogeneous crosslinking densities, along with additional topological defects such as dangling chain ends, crosslinker–crosslinker shortcuts, and chains forming loops. In this review, we summarize and interrelate existing studies on the origin of this heterogeneity and on its characterization by scattering techniques, microscopies, and NMR spectroscopy. We also outline some recent investigations on the impact of polymer-network nanostructural heterogeneity on the elasticity, swelling, and permeability of polymer gels.