Correlating Nanomechanical Mapping and Single-Molecule Localization Microscopy for Local Properties in Interpenetrating Network Elastomers

Compatibilization in multicomponent polymer systems is a strategy to combine immiscible polymers without macrophase separation, leading to mechanically strengthened materials. Macroscopic structure–property relationships are commonly explored in these systems, but they fail to capture the local detail needed to fully understand mechanical reinforcement and phase separation. To fill this need, we investigate the relationship between local modulus and composition by correlating nanomechanical mapping (NM) with single-molecule localization microscopy (SMLM) in poly(dimethylsiloxane)/poly(methyl methacrylate) (PDMS/PMMA) interpenetrating network elastomers (IPNs). Imaging the same sample areas with NM and SMLM allows us to measure and relate the modulus (from NM) and composition (from SMLM) at the nanoscale. We reveal differences in both modulus and composition between individual phase-separated PMMA domains, and we establish that these can be related through a rule of mixtures for modulus. By further examining the relationship between domain size and composition, we notice a bifurcation where larger domains are mostly composed of pure PMMA, while smaller domains have a much wider composition range. To explain this, we propose a two-stage phase separation mechanism, where nucleation and growth occurs before spinodal decomposition as the IPN is cured. Overall, the combination of NM and SMLM results in a level of microstructural understanding that has not been previously achieved.