Swelling behavior of radiation-polymerized polyampholytic two-component gels: Dynamic and equilibrium swelling kinetics

Abstract

Polyampholytic hydrogels, with varying degrees of crosslinking and ionic content, were prepared by radiation polymerization of p-sodium styrene sulfonate (SSS) and vinyl benzyl trimethylammoniumchloride (VBT). These gels were investigated for their dynamic and equilibrium swelling kinetics. Dynamic swelling of these gels established that the gels containing equal amounts of SSS and VBT strictly follow Fickian diffusion. The hydrogels containing excess of SSS followed the case II type of diffusion, whereas those containing excess of VBT followed anomalous diffusion. Equilibrium swelling kinetics of these gels in aqueous system, ethanol–water mixture, at different pHs, and in the presence of solutions of biological interest was studied. It was seen that gels containing equal amounts of SSS and VBT show the lowest equilibrium swelling. Swelling of the polyampholytic gel decreased with an increase in the radiation dose imparted and the amount of crosslinking agent incorporated in the gel. The gels having an excess of VBT showed higher equilibrium swelling in comparison to those having an excess of SSS. Differential scanning calorimetry (DSC) studies showed that crosslinking of the gels decreases equilibrium swelling but increases the bonded nonfreezable water content of the gels. The organic solvents like ethanol cause abrupt collapse of the polyampholyte gels containing excess of SSS and those containing equal amounts of both the monomers at some critical ratio of water and ethanol in swelling medium. However, the deswelling in the water–ethanol mixture was gradual for gels containing an excess of VBT and the extent of deswelling was also low for these gels in comparison to other gels. The swelled gels of all compositions deswelled when they were transferred to solutions at pH in the range 2–12. Biologically important solutes like urea, glucose, and surfactants like Triton-X tend to further swell the polymer matrices, whereas NaCl causes their deswelling. The additive effect is more prominent for polyampholyte gels containing excess of either of the monomers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 730–742, 2003