PHASE-TRANSITION IN SWOLLEN GELS .20. THE DIELECTRIC BEHAVIOR OF SWOLLEN POLY(N,N-DIETHYLACRYLAMIDE) GELS IN THE COLLAPSE REGION

Dielectric behavior of two networks: a non-ionized poly(N,N-diethylacrylamide) network (N1) and an ionized network (N2) prepared by copolymerization of N,N-diethylacrylamide with 3 mol% of sodium methacrylate swollen in deionized water was studied in the frequency range 10 Hz to 500 kHz and in the temperature interval 20 to 80 degrees C. From the frequency dependences of the components of complex permittivity epsilon* (epsilon* = epsilon' - i epsilon'') of both networks, it follows that a loss-relaxation Debye region exists at low frequencies; the results can be explained neither by the de conductivity nor by the effect of the electric double layer polarization. While both components of the complex permittivity decrease with increasing temperature for the non-ionized network, for the ionized network both epsilon' and epsilon'' increase with temperature and two small steep rises at temperatures 35 and 52 degrees C can be seen. The rise in permittivity, epsilon*, observed for the network N2 at 52 degrees C, corresponds to the jumpwise decrease in the volume of the gel connected with the phase transition. This transition is accompanied by the ordering of clusters of water molecules which interact with the polymer chain. The second rise observed at 35 degrees C is probably connected with the side chains clustering.