Lubricity of High Water Content Aqueous Gels

Aqueous gels such as biopolymer gels, mucus, and high water content hydrogels are often qualitatively described as lubricious. In hydrogels, mesh size, ξ , has been found to be a controlling parameter in friction coefficient. In the tribology of aqueous gels, we suggest that the Weissenberg number ( Wi ) is a useful parameter to define different regimes, and following the original formulations in rheology, Wi is given by the polymer relaxation time ( ηξ 3 / k B T ) multiplied by the shear rate due to fluid shear through a single mesh ( V / ξ ): Wi = ηVξ 2 / k B T . At sliding speeds below a Weissenberg number of approximately 0.1, Wi