The swelling behaviour of thermoresponsive hydrogel/silica nanoparticle composites

A new responsive nanocomposite material consisting of a poly-(N-isopropylacrylamide) hydrogel and "super-crosslinking'' silica nanoparticles was prepared by mixing both components in solution, spincoating a thin film, and photocrosslinking by UV irradiation. Detailed analysis of the thermal response of these water-swollen films by means of surface plasmon resonance and optical waveguide spectroscopy revealed that the composite is very stable and has excellent responsive properties; it is of high optical homogeneity; admixture of the nanoparticles (up to 50%-wt) does not affect the critical volume collapse temperature; and swell-collapse cycles are highly reproducible and display only limited hysteresis. Thus, the composite is promising as a scaffold for further functionalisation and incorporation in sensors or actuators.