Berlin 2012 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 35: Focus: Rheology I (joint focus with DRG)
CPP 35.4: Vortrag
Donnerstag, 29. März 2012, 16:00–16:15, C 243
In situ large amplitude oscillatory shear (LAOS) experiments on rod-like viruses and colloidal platelets — •Pavlik Lettinga1, Peter Holmqvist1, Simon Rogers1, Pierre Ballesta1, Dina Kleshchenok2, Bernd Struth3, and Joachim Kohlbrecher4 — 1Forschungszentrum Jülich, Jülich,Germany — 2van 't Hoff Laboratory, Utrecht University, The Netherlands — 3Desy, Hamburg, Germany — 4PSI, Villigen, Switserland
Highly anisotropic particles are by nature susceptible to external fields. In particular shear forces can cause a pronounced shear thinning, where a highly viscous unordered system is sheared into a low viscous ordered system. The rheological and structural responses of the system at the onset of shear thinning can be conveniently studied by large amplitude oscillatory shear in combination with in situ scattering techniques. Here we study two systems around the isotropic - nematic: dispersions of rod-like (fd) viruses in combination with time-resolved small-angle neutron scattering and dispersions of gibbsite platelets in combination with time-resolved small-angle X-ray scattering. Viewing the responses as indicating a sequence of physical processes, we identify, for the rod-dispersions, a region of purely elastic response accompanied by an increase in the orientational ordering. By yielding this is followed in sequence by a region of fluid-like behavior at an almost constant ordering. The platelet dispersions display, for a broad range of frequencies, a transition from singlet feature in the scattering at small strain amplitude to a doublet at large strain amplitude. This critical strain for reorienting the platelets is not reflected in the bulk rheology.