Regensburg 2007 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 3: Colloids and Nanoparticles I: Structure
CPP 3.4: Vortrag
Montag, 26. März 2007, 11:00–11:15, H47
Director Tumbling of Nematic Wormlike Micelles Under Shear: Time-Resolved Rheo-NMR Experiments — Nikolay Sinyavsky1, Isabel Quijada-Garrido2, and •Claudia Schmidt3 — 1Department of Physics, Baltic State Academy, Molodiozhnaya str. 6, 36029 Kaliningrad, Russia — 2Instituto de Ciencia y Tecnologia de Polimeros, Consejo Superior de Investigaciones Científicas, Juan de la Cierva 3, 28006 Madrid, Spain — 3Department Chemie, Universität Paderborn, Warburger Str. 100, 33098 Paderborn, Germany
Nematic liquid crystals show a complex flow behavior due to the coupling between orientation and flow. Some materials show a stable director orientation in steady shear flow (flow aligning), while for others no stable director orientation exists (tumbling). Director tumbling gives rise to oscillations of shear and normal stresses in rheological experiments and can be detected by optical methods, for example by microscopy or birefringence measurements. We have used deuterium NMR spectroscopy to observe shear-induced director orientations [1,2]. In the lyotropic system cetylpyridinium chloride/hexanol/brine, which forms a nematic phase of wormlike micelles, time-resolved observations of the director orientation by means of deuterium NMR spectroscopy of D2O have been possible for the first time. The time-dependence of the director orientations in both shear start-up and flow-reversal experiments will be presented.
[1] D. A. Grabowski, C. Schmidt, Macromolecules, 27, 2632 (1994).
[2] C. Schmidt, in: Modern Magnetic Resonance, Vol. 3, Springer, New York, 2006.