Force relaxation of single spherical gel beads under compression

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