Effect of chain hydrophobicity on volume change behavior of ionic gels in binding of hydrophobic counterions

The effect of the hydrophobicity of gel chains on the volume changes of ion ic gels in binding of the Dodecylpyridinium (DP) ions was examined. The stu dy was carried out for a series of copolymer gels, acrylate-methylacrylate, acrylate-ethylacrylate, acrylate-n-propylacrylate, and acrylate-n -butylac rylate(BA), in which the molar ratios of acrylate to the alkyl acrylate wer e 1. The distinctive two regimes; the regime HYS where the volume changes w ith hysteresis and the regime TRL where it changes in a transition-like man ner without hysteresis, were found in the volume change with the concentrat ion of DP ion (C-out). The hysteresis was more prominent for the more hydro phobic gel and/or the gel in the solution of lower salt concentration. Subs tantial plateau regions were found between HYS and TRL in the volume change of the more hydrophobic gel. The hysteresis was also exhibited for the cha nge in degree of binding of counterion, beta, with C-out. The dissociation rate of DP ion in immersing the gel bound by DP ions into the solution of h igher salt concentration is affected by the hydrophobicity of gel chain mor e than by the osmotic pressure.