Abstract
Sol-gel transition of polymer gels is a transition between a liquid phase (sol) and a solid phase (gel). The static properties of such gels seem to be well described by the percolation theory ; on contrary, viscoelastic properties present a large variety of behaviours at the sol-gel threshold. To study the precursor chemical structure effects on the dynamic properties of polymers at the sol-gel transition, we synthesized two polydimethylsiloxane (PDMS) systems. Our first results tend to show that crosslinker chemical structure influences the critical exponent values, characteristic of the sol-gel transition. After a comparison with the literature results, the first interpretation we propose points out two transitions, defining three behaviour domains. The percolation mechanism seems to be determined by the ratio of the number of Kuhn segments between branched points to the one between entanglements. In order to study the dynamic behaviour of such gels at high frequencies, we developed an ultrasonic characterization method. This method, coupled with classical rheological one, allowed us to characterize the honey, standard viscoelastic material, on a large frequency range.