Super-cooled Water in PVA Matrixes: I. An Incoherent Quasi Elastic Neutron Scattering (QENS) Study

The incoherent quasi-elastic neutron scattering study of poly(vinyl alcohol) based hydrogels was carried out to elucidate the dynamic state of water caged in polymeric matrixes with different degree of cross-linking and nature of the cross-linking agent. This investigation focuses on the determination of the relationship occurring between the diffusional parameters of water and the polymer network architecture. Analyzing the broadening factor of the dynamic structure factor, a marked supercooling of water was detected in all the matrixes under consideration. In all cases, the activation energies were about 4 kcal/mol indicating a hydrogen bond regime governing the matrix−solvent interaction. In some favorable cases, an insight on the polymer dynamics was also possible. The q-dependence of the broadening factor of polymer relaxation component revealed a behavior compatible with a bound random jump dynamics and concerning segmental motions of the chain coupled with the interaction with water.