Discrete model studies of two grafted polyelectrolyte polymer hydrogels pressed in contact.

The interaction between two grafted polymer gels was investigated. We studied a defect-free network of diamond-like topology containing 8 tetra-functional nodes linked by 16 non-crossing chains. In order to explain the very low friction coefficient observed for polyelectrolyte hydrogels, we computed the monomer density profile of these polymer gels, the interpenetration between two polymer gels (defined as the percentage of monomers belonging to one gel which have penetrated the second gel), the normal force per unit area, and the radial distribution function of the interacting monomers. Low monomer density in the interface region separating the two gels and low interpenetration of the gels similar to that found in our simulations are likely to be responsible for the small friction coefficients observed for polyelectrolyte polymer gels.