The volume change and volume phase transition temperature of hydrogels were investigated in variation of the temperature, ionic concentration, pH and salt concentration. The NIPAAm (N-isopropylacrylamide), IPSMA(N-isopropyl acrylamide-co- sodium methacrylate) and IPSA(N-isopropylacrylamide-co-sodium acrylate) hydrogels were synthesized by radical and inverse emulsion polymerization. Equilibrium swelling curves were observed by microscope, and volume phase transition temperature were determined by microscope and DSC(differential scanning calorimetry).
NIPAAm hydrogel undergoes a sharp yet continuous volume change, whereas IPSMA and IPSA show a sharp discontinuous volume change. Volume change and volume phase transition temperature increased with the amount of sodium methacrylate and sodium acrylate in IPSMA and IPSA hydrogels. The volume change of IPSMA hydrogel was larger than that of IPSA.
There was no effect of pH in the volume change and volume phase transition temperature, but the volume decreased with NaCl concentrations.
In diffusion experiment, the diffusivity of 4-acetamidophenol through NIPAAm gel membrane decreased discontinuously in the range of the volume phase transition temperature.
