Collapse kinetic of composites based on copolymers of acrylic acid and acrylamide filled with bentonite in aqueous solutions of polyvalent metals

Polymer polyelectrolyte hydrogel composites of acrylic acid and acrylamide copolymer filled with different amounts of bentonite (from 1 to 5 wt.%) were synthesized. Collapse kinetics of hydrogel composites was studied in solutions of different concentrations of polyvalent metal salts at a constant temperature of 25 °C. The mass of water given away from hydrogels into the solution was determined by gravimetric method. It has been found that the presence of bentonite in the polyelectrolyte hydrogel composites prevents to some extent collapse in electrolyte solutions, due to steric and electrostatic interactions between the filler particles. These interactions preclude further collapse of hydrogels. The Peleg's kinetic model, most precisely describing experimental data, was applied to calculation of kinetic constants of polymer hydrogels collapse. It is shown that the initial collapse rate and the kinetic constant of collapse and swelling depend non-monotonically on the concentration (ionic strength) in the electrolyte solution. At the identical concentration of salts in the solution the kinetic constant of hydrogel collapse is independent of the radius of ions of metals of the studied salts.