Synthesis and characterization of an extremely versatile structural motif called the plum-pudding gel

The plum-pudding gel is a composite gel structure composed of responsive microgel particles randomly dispersed in a bulk gel medium. Microgel particles can be responsive to a variety of stimuli (temperature, pH, light, etc.), and the bulk gel can be any cross-linkable material. Thus an infinite variety of materials of different mechanical and responsive properties can be envisioned based on this simple structural motif. The novelty of the plum-pudding gel is that it separates the concepts of functionality and mechanical strength. The plum-pudding nature of the gel was confirmed by laser scanning confocal microscopy: the fluorescently labeled PNIPAM microgel particles resembled plums in a pudding. A model for the structure was proposed, where the growing network chains grew through the pores of the swollen microgel particles and were unaffected by their presence, resulting in an unchanged network structure at the concentrations of microgel particles studied (up to 20 mol % of the monomer content). Two examples of the diversity of the plum-pudding gel as a structural motif are illustrated. PNIPAM microgel particles are used in the first example to enhance the positive thermoresponsiveness of responsive bulk materials (NIPA-co-BAM-co-DAM gels) and in the second example to induce positive thermoresponsiveness into nonresponsive bulk gels (DAM gels).