Regensburg 2010 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 42: Colloids and Complex Liquids I
CPP 42.6: Vortrag
Donnerstag, 25. März 2010, 12:30–12:45, H39
Sedimentation equilibrium of colloidal platelets in an aligning magnetic field — •Matthias Schmidt1,2 and Hendrik Reich3 — 1Theoretische Physik II, Universität Bayreuth, D-95440 Bayreuth, Germany — 2H. H. Wills Physics Laboratory, University of Bristol, Royal Fort, Tyndall Avenue, Bristol BS8 1TL, United Kingdom — 3Deutscher Wetterdienst, Frankfurter Str. 135, D-63067 Offenbach, Germany
We consider colloidal platelets under the influence of gravity and an external aligning (magnetic) field. The system is studied using a fundamental measures density functional theory for model platelets of circular shape and vanishing thickness. In the gravity-free case the bulk phase diagram exhibits paranematic-nematic phase coexistence that vanishes at an upper critical point upon increasing the strength of the aligning field. Equilibrium sedimentation profiles display a paranematic-nematic interface, that moves to smaller (larger) height upon increasing the strength of gravity (the aligning field). The density near the bottom of the system decreases upon increasing the strength of the aligning field. Using a simple model for the birefringence properties of equilibrium states, we simulate the colour variation with height, as can be observed in samples between crossed polarizers.