Structure–property correlation of crosslinked domain hydrogels exhibiting thermoresponsive mechanical toughening and hybridization with photoluminescent carbon dots

Abstract

A hydrogel exhibiting stimuli-responsive simultaneous change in multiple properties is attractive for various applications. We have recently developed a gel with a thermoresponsive crosslinked domain (CD) structure, which underwent mechanical toughening upon heating in air with maintenance of high transparency. In this study, we evaluated the structure–property correlation of a hydrogel having a thermoresponsive CD structure prepared by a polymerization-induced self-assembly (PISA) process using reversible addition–fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide (NIPAAm) with a hydrophilic poly(N,N-dimethylacrylamide) (PDMAAm) macro-chain transfer agent (macro-CTA). The molecular weight of the macro-CTA had a slight effect on the swelling behavior of the product gels in water, while a macro-CTA with an appropriate molecular weight yielded a gel exhibiting pronounced mechanical toughening with an increased elastic modulus and elongation upon heating. The composition of the gel significantly affected its mechanical properties and transparency at a high temperature, and we found that a gel with an NIPAAm content as high as 50% maintained the transparency due to an internal structure with homogeneously dispersed CDs in the network. In addition, we successfully obtained a gel exhibiting simultaneous mechanical toughening and enhanced photoluminescence upon heating by hybridization with carbon dots.