Sliding gels

A set of negatively charged chains A, mixed with multi functional cationic molecules C, can generate a gel, where C acts as a cross-link. The A chains slide along the C bridges, provided that the number of AC contacts remains constant. We discuss the mechanics of these sliding gels in various situations (rigidity, solvent quality, etc). Contrary to naive expectations, we find that the sliding gels should not be particularly soft at low stresses: all the stored length has been used to swell the gel. We also consider the case of dilute solutions, with a few chains building up a “sliding branched object”, which slides towards the most open form.