Viscoelastic Behavior of Scarcely Crosslinked Poly(dimethyl siloxane) Gels: 2. Effects of Sol Component and Network Strand Length

Abstract

Linear viscoelastic behavior was examined for poly(dimethyl siloxane) (PDMS) gels scarcely crosslinked through the double-liquid reaction. The gel sample after the sol extraction exhibited the fast and slow relaxation processes characterized with the power-law behavior of the dynamic loss modulus, G" ∝ω0.5 and G" ∝ω0.8 at high and low angular frequencies ω. The fast relaxation was essentially the same as that in the gel before the sol extraction and attributed to the constraint release (CR)-Rouse relaxation of individual gel strands having a considerable length distribution. In contrast, the slow relaxation, being related to cooperative CR involving neighboring gel strands, appeared to become faster after the sol extraction than before. This puzzling result may have reflected a spatial heterogeneity of the crosslinking density, although this hypothesis has not been proven yet. For the as-prepared PDMS gels containing the sol chains, an increase of the crosslinking density was found to extend the CR-Rouse relaxation tail to low frequencies compared to the more scarcely crosslinked strands after the sol extraction. Thus, the CR motion of the strands appeared to be more strongly affected by the crosslinking density than by the sol chains.