Surface friction of hydrogels

The sliding fiction of various kinds of hydrogels has been studied and it w as found that the frictional behaviors of the hydrogels do not conform to A monton's law F = mu W, which well describes the friction of solids. The fri ctional force and its dependencies on the load are quite different dependin g on the chemical structures of the gels, surface properties of the opposin g substrates, and the measurement condition. The gel friction is explained in terms of interfacial interaction, either attractive or repulsive, betwee n the polymer chain and the solid surface. According to this model, the fri ctional force is ascribed to the viscous flow of solvent at the interface i n the repulsive case. In the attractive case, the force to detach the adsor bing chain from the substrate appears as friction. Surface adhesion between glass particles and gels measured by AFM showed a good correlation with th e friction, which support the repulsion-adsorption model proposed by author s.