Phase transitions in ionic gels

Abstract

Abstract It has been reported that under certain conditions the polymer network of acrylamide gels immersed in acetone—water mixtures undergoes a discrete transition in equilibrium volume with changes in acetone concentration or temperature. In the present work, the physical and chemical basis of this phase transition is identified. The magnitude of the collapse can increase substantially when a small percentage of the acrylamide groups of the gel network is converted to ionizable acrylic acid. A discrete collapse in volume of up to 350 times is observed in such a gel. The volume collapse is also observed if the pH or the ionic strength of the gel fluid is varied. In addition, this phase transition can be induced by placing the gel in an electric field, Using a mean field equation of state for an ionic gel, the effect of ionization of the gel network on the volume transition is clarified.