ROLE OF MECHANICAL PRESSURE IN PERMEATION OF A SOLVENT THROUGH GELS

In a system consisting of gel network and solvent, mechanical pressure and network stress can be transformed from one to the other through t he frictional drag between the network and the solvent. In addition, m echanical pressure contributes to the total stress. The application of these well-known principles to concrete physical situations involves surprisingly subtle issues and, unless both roles of the pressure are properly taken into account, may lead to erroneous conclusions. To ill ustrate this point, we analyse the fundamental elastohydrodynamic proc esses which underlie several recent theoretical works and show how the y depend on the geometries of set-up of gel, surrounding solvent and s ubstrate that supports the gel sample.