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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 55: Flow-Induced Structures in Complex Fluids (with DRG, Deutsche Rheologische Gesellschaft, and DY)

CPP 55.12: Vortrag

Mittwoch, 18. März 2015, 18:15–18:30, C 264

Soft Solid Rheology Near the Gel Point — •Horst Henning Winter — University of Massachusetts Amherst

For most amorphous materials that undergo gelation, the powerlaw relaxation time spectrum, H(tau)~tau^-n for tau,min<tau<tau,max, governs the rheology only in a narrow window very close to the gel point. Soon beyond the gel point, the soft solid develops a very rich viscoelastic behavior for the evolving material states with increasing connectivity. Typical rheological features of the evolving soft solid are a growing relaxation modulus and accelerated relaxation processes for the structural components that can still relax. Time-resolved rheology measurements, in combination with time-cure superposition, on two model materials show this soft solid behavior. One model material (self-exfoliating clay-polymer composite) represents physical gelation and the other one (crosslinking polyurethane) represents chemical gelation. The relaxation characteristics near the gel point are different for the two materials. For the physically gelling material, the modulus growth was found to be inversely proportional to the relaxation time decay. For chemical gelation, the modulus grows only with a factor of about 0.7. During the next couple of months, more gelling materials are going to be included in the study since it is unclear how widespread the observed viscoelastic pattern occurs.