Responsive properties and triggered disassembly of supramolecular microgels: a key role of the structure.

Abstract

Although understanding structure–property relationships in microgels is crucial, it remains limited due to the challenges associated with both controlling and quantitatively characterizing the distribution of crosslinkers within the network. Here, multi-responsive supramolecular poly(N-isopropylacrylamide) (PNIPAM) microgels have been synthesized with either “ultra” core-shell (via batch synthesis) or quasi homogeneous (via continuous feeding) distributions of a metallosupramolecular charged crosslinker (SC), while maintaining a constant size. The SC presents two main advantages. First, its color and its high electronic contrast allow an easy and precise quantification of both its final content and its spatial distribution in the microgel network respectively. It is found that microgels with a quasi-homogeneous SC distribution exhibit a lower swelling ratios upon decreasing the temperature and/or the salt concentration. Second, the triggered SC cleavage through chemical oxidation allows the microgel disassembly. Both the SC cleavage kinetics and the resulting microgel disassembly are faster when the initial SC distribution is quasi-homogeneous. Furthermore, the molar mass of the disassembled polymer chains can be closely correlated to the initial microgel structure. Overall, this work highlights that the microgel structure is a key parameter in understanding their behavior and optimizing their applications.