A CONTACT MECHANICS METHOD FOR CHARACTERIZING THE ELASTIC PROPERTIES AND PERMEABILITY OF POLYMER GELS

When a gel in a saturated environment is suddenly brought into contact with an indenter, its mechanical response is influenced by the flow of liquid in its pores. The solvent in the gel cannot instantaneously respond by flowing out of the network, so the gel acts incompressibly. As a result, a pressure gradient forms in the liquid. Liquid flows out of the pores until the pressure drops to zero in the entire system, thereby allowing all stresses to be transferred to the network. Because of the flow of solvent in the gel, the force required to maintain a constant contact area will relax with time. Our work studies the feasibility of using an indentation test to measure this time dependent force, which is then used to determine the elastic modulus, Poisson's ratio and the permeability, Dp, of the network. A theoretical framework based on two-dimensional Hertz contact problem of a rigid cylinder indenting on a linearly elastic, isotropic gel that is saturated in its own solvent is presented. This analysis is then compared to preliminary experimental results.