Investigations into the deswelling dynamics and thermodynamics of thermoresponsive microgel composite films

We report on the deswelling behavior of microcomposite hydrogel films composed of poly(N-isopropylacrylamide) (pNIPAm). These films were synthesized first by formation of pNIPAm microgel particles via precipitation polymerization, followed by polymerization of these particles into a pNIPAm thin film gel matrix immobilized on a glass slide. The deswelling behavior of these composite films was studied by temperature-dependent light scattering (i.e., turbidity). In conventional (not microstructured) films the scattering increases and plateaus as the temperature is increased beyond the lower critical solution temperature (LCST) of pNIPAm. In contrast to these conventional films, microgel composite films display an increase in turbidity until the LCST, followed by a rapid turbidity decrease beyond the LCST. It is also observed that the rate at which scattering decreases depends on the concentration of the hydrogel particles in the film. Together, these results offer insight into the morphological changes occurring during the deswelling processes in composite hydrogel thin films.