Salt-induced homoaggregation of poly(N-isopropylacrylamide) microgels

Microgels of poly(N-isopropylacrylamide), copolymerized with acrylic acid and cross-linked with methylene bisacrylamide, swell at temperatures below 32 degreesC. Such swollen particles deswell at high salt concentrations, where electrostatic stabilization is eliminated. This results in a system where the strength of the van der Waals attraction, driving homo aggregation, is controlled independently by both temperature and salt concentration. In this paper, the locus of stability for these particles at different temperatures and salt concentrations was determined. Small-angle light scattering studies of the homoaggregating particles revealed a system that changes from diffusion-limited to a mechanism involving particle rearrangement over a small temperature range.