Swelling, Shrinking, Deformation, and Oscillation of Polyampholyte Gels Based on Vinyl 2-Aminoethyl Ether and Sodium Acrylate

Abstract

The behavior of amphoteric hydrogels based on vinyl 2-aminoethyl ether and sodium acrylate under the influence of pH, ionic and solvent composition, temperature, and dc electric field has been studied. The excess of positive or negative charges causes the swelling of polyampholyte networks. At the isoelectric point (IEP) the polyampholyte gel is in shrunken state due to the formation of intraionic contacts. An antipolyelectrolyte effect is observed at the IEP: the gel considerably swells in the presence of neutral salt. The condensation of bulky anions to positively charged groups of polyampholyte gels enhances the shrinking rate. The shrinking process can be described by apparent first-order kinetics. Polyampholyte gel shrinks with the increasing of temperature when the overall charge is neutral (IEP), while it shrinks effectively with addition of acetone when the overall charge is negative. In dependence of the network net charge, the ionic strength of the external solution, and the direction of dc electric field, the polyampholyte specimen can bend, shrink, swell, and oscillate. Under the same conditions, positively and negatively charged precursors of polyampholytes only swell or shrink. Shrinking and swelling of amphoteric gels are determined by the concentration of mobile ions inside and outside of gel. To interpret the oscillation phenomenon the Donnan equilibrium and water hydrolysis are utilized. The realization of antipolyelec-trolyte or polyampholyte and polyelectrolyte effects is probably the driving force of gel behavior. The oscillation-relaxation regimes are characterized by numerical value of 1/τ (where τ is the relaxation period). The phase portraits of all oscillation-relaxation curves are in good agreement with the Faraday law.