Controlled structure and properties of thermoresponsive nanoparticle-hydrogel composites

Nanocomposite materials consisting of colloidal metal nanoparticles embedded in synthetic polymer hydrogels have attracted attention due to potential applications in catalysis, photonics, electronics, optics, and biomedicine.([1]) Here we describe a method for synthesizing nanocomposite materials consisting of colloidal gold (Au) nanoparticles embedded in thermoresponsive poly(N-isopropylacrylamide) (PNIPAm) hydrogels. By incorporating thiol groups that have affinity to both Au3+ ions and colloidal Au into the PNIPAm hydrogels, we demonstrate specific control over the size, morphology, and long-term stability of the Au nanoparticles by adjusting the concentration of thiols in the hydrogel side chains. Compared with the non-Au-containing PNIPAm hydrogels, the Au-PNIPAm nanocomposite hydrogels display remarkably different bulk properties of equilibrium swelling and thermoresponsive phase transition, which are related to the size and morphology, and possibly the surface charge, of the Au nanoparticles.