Berlin 2008 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 17: SYMPOSIUM Driven Soft Matter II

CPP 17.2: Hauptvortrag

Dienstag, 26. Februar 2008, 14:30–15:00, C 130

Viscoelasticity of gels — •Annette Zippelius and Peter Müller — Institut für Theoretische Physik, Georg-August-Universität, D-37077 Göttingen

We study shear relaxation of randomly crosslinked macromolecular networks. The sol phase is characterized by a stretched exponential decay of shear relaxation, which can be traced to the random connectivity of molecular clusters such that weakly connected regions dominate the relaxation of shear. The transition from the sol to the gel is - like the glass transition - characterized by a diverging static shear viscosity, if the transition point is approached from the fluid side, respectively by a vanishing shear modulus, if the approach is from the amorphous solid side. The critical behaviour can be calculated exactly within the Rouse model, including the coefficients of normal stresses. A variational principle can be used to derive an exact lower bound for the static shear viscosity in the presence of excluded volume interactions. The divergence of the lower bound is stronger than in the Rouse model, proving the relevance of excluded volume interactions for the dynamic critical behaviour.