Dielectric Properties of Collapsing Hydrogels

Dielectric spectra were measured for the polymer gel of N -isopropylacrylamide (NIPA) and copolymer gels of N -isopropylacrylamide and sodium styrenesulfonate (NIPA−SS) in the swollen and collapsing states in the frequency range from 100 kHz to 2 MHz. Dispersions were observed for the NIPA gel in the collapsing state and NIPA−SS gels in both the collapsing and swollen states. The characteristics of dispersions in the collapsing gels were different from the characteristics in the swollen gels, while the former characteristics are very similar in NIPA and NIPA−SS. The similarity between dispersions observed for NIPA and NIPA−SS gels indicates that counterions of NIAP−SS gels bind tightly to the ionized groups and cannot move freely in the collapsing gels. The analysis of the dispersions reveals that water molecules inside the collapsing gels are surrounded by the gel chains and form electrically disconnected clusters.