Investigation of swelling behavior of functional hydrogels with modified hydrophilic/hydrophobic balance in organic solvents and aqueous solutions

Examining the effects of modification on the functional properties of hydrogels, and therefore on their swelling behavior, is an important research topic. In this study, poly(vinylimidazole) (pV) hydrogel was partially quaternized over imidazole nitrogens with alkyl halides with different chain lengths and gel structures with different hydrophilic/hydrophobic properties were obtained. The swelling behavior of the gels in distilled water, salt solutions and different organic solvents was investigated. Homopolymer pV was synthesized in aqueous medium by free radical solution polymerization, and quaternization reactions were carried out in ethanol solvent under riflux conditions. Gels were characterized by spectroscopic (FTIR), microscopic (SEM-EDX) and thermal (TGA) methods. The dependence of the swelling process on pH and ionic strength was investigated by swelling experiments in aqueous media. While pV had the highest equilibrium swelling rate under pH 2 conditions, the swelling capacity of the homopolymer decreased significantly with increasing pH. On the other hand, some quaternized gels maintained a high equilibrium swelling ratio at all pHs studied due to decreased pH sensitivity. While modified gels containing long alkyl chains swelled minimally in water, they exhibited significant swelling behavior especially in ethanol, dimethylsulphoxide, N,N-dimethylformamide ve dichloromethane. At this point, besides the physicochemical properties of the gel, the polarity of the solvent was also effective.