Volume phase transition process and spin diffusion in heterogeneous structure of acrylamide gels studied by pulsed NMR

Both ionized and non-ionized acrylamide gels in acetone-water mixture were studied by pulsed NMR. We investigated (i) dependence of the spin-spin relaxation time T-2 of the gels on the composition of the solvent, (ii) temporal changes of T-2 during the volume phase transition process for the ionized gels, and (iii) domain sizes of heterogeneous structures in the non-ionized gels caused by abrupt changes of the environment using the spin diffusion phenomenon. The results of the concentration dependence of T-2 showed that molecular mobility of both the solvent and the network was further depressed as the acetone content was increased in the contracted state although the volume change was small. These results show that the interaction parameter between the solvent and the network polymer has more influence on the mobility than the volume of the system. The shrinking and the swelling process of gels undergoing volume phase transition were different from each other. This reflects the behavior that the swelling and shrinking start on the boundary of the samples. The obtained domain sizes of the heterogeneous structure indicate that solid-like regions are formed on a smaller scale in the dense phase of the network.