Correlative nanomechanical mapping and super-resolution optical microscopy in PDMS/PMMA interpenetrating networks*

Efforts in polymer compatibilization aim to overcome macrophase separation, which leads to poor mechanical properties in polymer blends. Interpenetrating polymer networks (IPNs) increase the compatibility of polymers by kinetically trapping the microstructure, resulting in stronger, tougher materials. A common assumption in IPNs is that complete phase separation occurs, but this assumption has not been rigorously tested. We investigate the molecular distribution of the opposing polymers within the microstructure by correlating peak force quantitative nanomechanical mapping (PF-QNM) with super-resolution optical microscopy (SROM) in PDMS/PMMA IPNs to directly relate mechanical modulus to PDMS fraction in each phase. Images from PF-QNM are generated by extracting the modulus from different locations on the sample. For SROM, a photoswitchable dye is labeled on the PDMS molecules, thus providing a measure of PDMS concentration throughout the sample. These two techniques are then spatially correlated, showing that incomplete phase separation occurs. PF-QNM/SROM correlative imaging is an effective tool for quantifying compatibility in multi-component polymer materials.