An interpenetrating polymer network (IPN) hydrogel based on poly(propylene glycol) and poly(acrylic acid) was prepared by UV irradiation. The swelling behavior of the IPN hydrogel was studied by the immersion of the gel in aqueous NaCl solutions of various concentrations. The swelling ratio decreased with an increase in the NaCl concentration. The electrically sensitive behavior of the IPN hydrogel in electric fields was also investigated. The IPN hydrogel also showed a stepwise bending behavior that depended on the electric stimulus. The bending angle and bending speed of the IPN hydrogel were greatest in 0.6 wt % aqueous NaCl and increased with an increase in the applied voltage.

ABSTRACT:Interpenetrating polymer network (IPN) hydrogels composed of poly(vinyl alcohol) (PVA) and monomer, N-isopropylacrylamide (NIPAAm), diallyldimethylammonium chloride (DADMAC), or methacrylic acid (MAA) were prepared by using the sequential-IPN method. The equilibrium swelling ratios of PVA/NIPAAm (VANP), PVA/DADMAC (VADC), and PVA/MAA (VAMA) are 412, 370, and 297 at 25°C, respectively. VANP had the highest swelling ratio in time-dependent swelling behavior, whereas the swelling ratio of VAMA had the lowest. The n values of VANP, VADC, and VAMA are 0.72, 0.81, and 0.96, respectively. Transport of all IPN hydrogels is anomalous and their transport mechanisms are dominated by a combination of diffusion-controlled and relaxation-controlled systems. VAMA has the highest activation energy and VANP has the lowest activation energy. The values of all IPN hydrogels are from 4.66 to 16.49 kJ/mol, which proves that all IPN hydrogels are hydrophilic.

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Temperature-responsive semi-interpenetrating polymer networks (semi-IPNs) constructed with chitosan and polyacrylonitrile (PAN) were crosslinked with glutaraldehyde. The semi-IPN determined the sorption behavior of water at several temperatures and at a relative humidity (RH) of 95% using a dynamic vapor sorption (DVS) system. Water diffusion coefficients of semi-IPNs were calculated according to the Fickian Law at several temperatures and exhibited a relatively water uptake, 0.1-0.4 at room temperature. The water uptake of hydrogels depended on temperature. The apparent activation energy was dependent of the composition of the semi-IPN with value of 32.8 -34.8 kJmol Ϫ1 .