Swelling, shrinking, deformation, and oscillation of polyampholyte gels based on vinyl 2-aminoethyl ether and sodium acrylate

The behavior of amphoteric hydrogels based on vinyl 2-aminoethyl ether and sodium acrylate under the influence of pH, ionic and solvent composition, t emperature, and de electric field has been studied. The excess of positive or negative charges causes the swelling of polyampholyte networks, At the i soelectric point (IEP) the polyampholyte gel is in shrunken state due to th e formation of intraionic contacts. An "antipolyelectrolyte" effect is obse rved at the IEP: the gel considerably swells in the presence of neutral sal t. The condensation of bulky anions to positively charged groups of polyamp holyte gels enhances the shrinking rate. The shrinking process can be descr ibed by apparent first-order kinetics. Polyampholyte gel shrinks with the i ncreasing of temperature when the overall charge is neutral (IEP), while it shrinks effectively with addition of acetone when the overall charge is ne gative. In dependence of the network net charge, the ionic strength of the external solution, and the direction of de electric field, the polyampholyt e specimen can bend, shrink, swell, and oscillate. Under the same condition s, positively and negatively charged precursors of polyampholytes only swel l or shrink. Shrinking and swelling of amphoteric gels are determined by th e concentration of mobile ions inside and outside of gel. To inter pl rt th e oscillation phenomenon the Donnan equilibrium and water hydrolysis are ut ilized. The realization of "antipolyelectrolyte" or polyampholyte and polye lectrolyte effects is probably the driving force of gel behavior. The oscil lation-relaxation regimes are characterized by numerical value of 1/tau (wh ere tau is the relaxation period). The phase portraits of all oscillation-r elaxation curves are in good agreement with the Faraday law.