Phase instability of inhomogeneous gels crosslinked within the spinodal region

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Abstract
We consider theoretically the gels crosslinked in the early stage of spinodal decomposition. A weakly crosslinked and homogeneous gel is brought into the thermodynamically unstable state, and additional crosslinks are introduced while the spinodal decomposition takes place. The inhomogenization of gel is ‘‘recorded’’ as position dependent distribution of chain conformations. The model is based on the theory of permanent set and that of nonequilibrium thermodynamics of gels. We investigate the effect of the rate of crosslinking on the process of spinodal decomposition. We also analyze the stability of the inhomogeneous gel thus processed. Our study shows that the spinodal instability may still occur in an inhomogeneous ‘‘opaque’’ gel, and a possible experimental test is proposed.