Small-angle Neutron Scattering Combined with Spin Polarization Contrast Variation Elucidates Structural Details of Multinetwork Elastomer

To elucidate the complexity of cross-linking in multinetwork elastomers (MNEs), we employed small-angle neutron scattering combined with dynamic nuclear polarization (DNP-SANS). MNEs were designed as thermoplastic elastomers with three kinds of cross-linking consisting of hydrogen, covalent, and clay plane bonds. DNP-SANS profiles were obtained with continuously changing scattering contrasts for MNEs with different cross-link densities. We clearly recognize the three matching points in scattering intensity, originating from pairs of cross-linking groups, clay, or main chains. DNP-SANS profiles were decomposed into three partial scattering functions for self-terms of cross-linking groups clay and their cross-terms. The self-term exhibits a scattering maximum due to the interplane distance of clay, which changes with the cross-link density. The cross-term between clay and cross-link was obtained as negative, indicating that the cross-linking domains are tightly correlated, localizing on the clay surface. The results indicate that DNP-SANS is a crucial technique for obtaining structural details of MNE cross-linking without chemical deuteration.