Rheology and mesoscopic structure-dynamics relations of hydrogels

The understanding of the mechanical and transport properties of complex biological hydrogels, such as mucus, require fundamental insight into the relation between macroscopic rheology and mesoscopic structure and dynamics, and how these properties are controlled by molecular features of the constituting polymer chains. In the first funding period, first single-component homopolymeric hydrogels were studied by comprehensive macro-rheological, microrheological and scattering experiments. Microrheology was established as a reliable method that is complementary to macrorheology, extending the frequency range and being applicable to smaller volumes. The experimentally observed deviations between micro- and macrorheological viscoelastic hydrogel spectra were theoretically explained in terms of a nanoscopic shell around the tracer particles within which the hydrogel viscoelasticity differs significantly from bulk. This constitutes a novel method to reveal the dynamic interactions between particles and hydrogels. This was initially done with poly(ethylene oxide) (PEO) hydrogels where the viscoelasticity arises from chain entanglements and for which we developed a coarse-grained simulation model to relate the structure factor, the viscoelastic spectrum and the particle diffusivity. These studies were then extended to multi-component hydrogels of PEO with polymethacrylic acid (PMAA), where in addition H-bonds crosslink the polymer chains, as well as mucin-resembling polyglycerol and polypeptide-based hydrogels synthesised in B03|Haag/Block and C02|Koksch/Delbianco/Keller, which exhibit mucus-like rheological behaviour. The rheological insights gained then have be successfully applied cooperation with A01|Mall/Gradzielski and C01|Seitz/Hackenberger.