Study of the PVA hydrogel behaviour in 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid

Abstract

The present paper aims at studying the behaviour of the poly(vinyl alcohol) (PVA) cryogel in the presence of 1-butyl-3-methylimidazolium tetrafluoroborate ((BMIM) + (BF4) - ) aqueous solutions with various concentrations. The gravimetric method showed that the swollen PVA cryogels exhibit mechanically active behaviour. PVA cryogels showed shrinking in the presence of ionic liquid, (IL), and re-swelling in the presence of distilled water. The re-swelling is not com- pletely reversible, due to the influence of the IL ions on the gel morphology. The Fourier transform infrared (FTIR) spectra have indicated no chemical interaction between the PVA and the studied IL, but highlighted the gel crystallinity change as a function of IL concentration, as well as changes in the bound water amount. Rheological analyses showed dominating plastifying effect of the cation at a lower IL concentration and dominating kosmotropic effect of the anion at a higher IL concentration. A phenomenological kinetic equation that takes into account both fluxes of matters, in and out of the gel, is proposed, explaining the alteration of the gel properties when it comes in contact with BMIMBF4 solutions.