FORCE RELAXATION OF SINGLE SPHERICAL GEL BEADS UNDER COMPRESSION

A spherical bead, when submitted to an uniaxial compression between tw o parallel pistons, exhibits solvent migration effects both inside and outside the gel. We describe here some experiments of force relaxatio n on a strained bead, at different swelling ratio. We present a theore tical description that allows to determine the shear and the compressi on modulus, and the critical force one has to apply in order to deswel l a bead which is swollen below its equilibrium ratio. We also show th at mechanical tests do not allow for a direct observation of the deswe lling force. (C) 1998 Elsevier Science Ltd. All rights reserved.