Gel-Solvent Friction

The science of gel draws much attention after the discovery of the volume phase transition of gel. Among others, the information on the dynamics of gel is of importance to understand the kinetic behaviors of the volume phase transition of the gel. It is well established that the dynamics of gel is governed mainly by the collective diffusion of the polymer network of gel and the collective diffusion itself is determined by the balance between two forces. One is the elastic force due to the deformation of three-dimensional polymer network of gel, and the other is the frictional drag force between the polymer network of gel and the gel fluid. In early stage of the study in gels, the elastic properties of gel attract much attention, and, hence, considerable effort has been devoted to clarify the elastic behaviors of gel. The elastic properties of various gels under various experimental conditions are gained and reported so far. In contrast, much attention has not been paid to the frictional properties of gel since the experimental method in obtaining the reliable values of the friction coefficient has not been established until recently. The systematic studies on the frictional properties of gel begun only recently. Here, we would like to overviewthe earlier studies on the frictional property of gels including why the frictional study of gel is difficult and how we can solve the difficulty to obtain the reliable values of the friction coefficient of gel. The recent advancement on the frictional study of colloid gel will also be reviewed.