Surface dynamic friction of polymer gels

The sliding friction of various kinds of hydrogels has been studied and it was Found that the frictional behaviors of the hydrogels do not conform to Amonton's law F = mu W which well describes the friction of solids. The frictional force and its dependence on the load are quite different depending on the chemical structures of the gels, surface properties of the opposing substrates, and the measurement condition. The gel friction is explained in terms of interfacial interaction, either attractive or repulsive, between the polymer chain and the solid surface. According to this model, the friction is ascribed to the viscous flow of solvent at the interface in the repulsive case. In the attractive case, the force to detach the adsorbing chain from the substrate appears as friction. The surface adhesion between glass particles and gels measured by AFM showed a good correlation with the friction, which supported the repulsion-adsorption model proposed by the authors.