Dresden 2014 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 28: (Hydro) Gels and Elastomers

CPP 28.1: Hauptvortrag

Mittwoch, 2. April 2014, 09:30–10:00, ZEU 222

Rheo-imaging of Polymer Networks — •Norbert Willenbacher — Karlsruhe Institute of Technology, Germany

Combining mechanical rheometry and multi-particle tracking (MPT) optical microrheology provides insight into polymer network structure.

High absolute values but weak concentration dependence of shear moduli are generic features of Intermediate filament networks, which play a crucial role in metazoan cell mechanics. MPT experiments reveal uniform mesh sizes (0.1-1μm), but modulus values obtained from MPT are orders of magnitude lower than those from bulk rheometry. This discrepancy is attributed to a strong entropic contribution of stretched filament strands since attractive interactions at filament contact points prevent thermal equilibration. Addition of surfactant does not affect network mesh size, but allows filament strand equilibration, and the discrepancy between MPT and bulk rheometry vanishes.

Acrylate microgels, which are used as thickeners in a broad variety of commercial products, with similar chemical composition, but different molecular architecture have been investigated. Emulsion polymerization products form uniform networks (mesh size below 100nm). In contrast, the microgel system from solution polymerization is extremely inhomogeneous. Tracer particle mobility varies by orders of magnitude. Tracers diffuse freely within microgel particles, but are elastically trapped in overlap regions. A heterogeneous microstructure with a characteristic length scale of about 10μm can be directly visualized based on spatial distribution of tracer particle mobility.