Swelling kinetics and mechanistic aspects of thermosensitive interpenetrating polymer networks

Full interpenetrating polymer networks (FIPNs) of cross-linked gelatin with polyacrylamide [Gelx-PAamx] and N-isopropylacrylamide [Gelx-PNLPAx] of several compositions were prepared, respectively. Their dynamic swelling studies as a function of temperature were monitored. The rate of swelling increased with the rise in ambient temperature for [Gelx-PAamx]. For [Gelx-NIPAx] with the increase in temperature above its LCST (lower critical solution temperature) (i.e., 32 degreesC) decreased the swelling and below its LCST increased in swelling. From the Fickian equation, the transport mechanism for [Gelx-PAamx] was determined to be anomalous, and for [Gelx-PNIPAx] below its LCST is anomalous and above, is Fickian type of diffusion. The activation energies were determined from the initial rate of swelling, which were found to be positive for [Gelx-PAamx] ranging from 36 to 55 kcal/mol, whereas for [Gelx-PNIPAx], the values were negative ranging from -331 to -55 kcal/mol. The enthalpies for these FIPNS were also estimated.