Swelling behaviour of a polyelectrolyte network under load

The kinetics of swelling of a strongly charged hydrogel is studied. The influence of external load on the rate of swelling and on the equilibrium degree of swelling is experimentally investigated. With the help of a sensitive technique it is shown that two different mechanisms governing the process of swelling may be clearly determined. The first one (at the beginning of swelling) is connected with the 'ordinary' swelling of a neutral network, and the second one corresponds to the largest part of the kinetic curve and is connected with additional electrostatic interactions. The dynamics of hydrogel swelling, which corresponds to strong electrostatic interactions, is analysed by the equation of motion of the hydrogel boundary. The mathematical approach is based on the modern theory of the qualitative solution of differential equations. It allows one to obtain a correlation between static and dynamic parameters of the swelling process and the dependence of these parameters on applied load. (C) Elsevier Science Ltd.