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The need for tunable and responsive hydrogels in numerous applications has motivated intense research efforts. A novel strategy for the formation of tunable hydrogels is based on phase-separation of ion-rich regions from the aqueous environment, called ionic coacervation, which occurs on mixing two ABA triblock copolymers with oppositely charged anionic and cationic A-blocks. Charged ionic nanoclusters are useful species having unique characteristics such as surface plasmon resonance, catalytic activity, electronic, and/or magnetic properties, and can be easily prepared with a tunable degree of surface ionization. We propose to utilize this surface charge to couple the charged ionic nanoclusters through ionic coacervation into responsive hybrid hydrogels. Both polyoxometalates (POM) and charged gold nanoparticles (AuNP) were prepared and added to the copolyelectrolytes. The effects of composition, concentration, particle size and temperature on the resulting materials properties were probed. We observed strong attractive interactions occurring between POM anionic nanoclusters and the cationic ABA copolyelectrolytes; moreover, ionic interactions were also observed between the like charged anionic POM clusters and the anionic ABA copolyelectrolyte. The hybrid inorganic/organic materials were thermally responsive and have reversibly undergone color switching through UV light induced reduction of the POM clusters. AuNP of varying size and surface charge were synthesized so that the ionic interactions could be modulated. They should be localized in the ionic domains, providing higher concentration and spatial organization within the coacervate hydrogels, features which should lead to interesting optical properties.
We found that noncovalent ionic interactions may be used as a general means to prepare hybrid inorganic/organic hydrogels.