Dresden 2006 – wissenschaftliches Programm
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CPP: Chemische Physik und Polymerphysik
CPP 1: Thin Films and Surfaces I
CPP 1.4: Vortrag
Montag, 27. März 2006, 10:30–10:45, ZEU Lich
Pretransitional Wetting Structures at a Thermotropic Liquid Crystal/Water Interface — •Christian Bahr — Max Planck Institute for Dynamics and Self-Organization, Bunsenstr. 10, 37073 Göttingen
Recently, theoretical interest has emerged concerning colloidal interactions between spherical particles, which are suspended in the isotropic phase of nematic liquid crystals and are covered with a nematic wetting layer [1]. A corresponding experimental system could consist of an emulsion of water droplets in an isotropic liquid crystal. It is not known, however, if at isotropic liquid crystal/water interfaces nematic wetting layers exist or what properties they have. We present here an ellipsometric study of such an interface near the nematic – isotropic phase transition. Approaching the transition temperature TNI from above, a nematic wetting layer appears at the interface if the water phase contains a surfactant inducing a homeotropic alignment of the nematic phase. On further approaching TNI, the thickness of the nematic layer shows a pronounced increase and a possible logarithmic divergence at TNI. The detailed behavior is significantly influenced by the concentration of the surfactant. The experimental results can be described by a mean-field model in which the surfactant concentration tunes the magnitude of an ordering interface potential.
[1] H. Stark, Phys. Rev. E 66, 041705 (2002); J. Fukuda, H. Stark, H. Yokoyama, Phys. Rev. E 69, 021714 (2004); M. Huber and H. Stark, Europhys. Lett. 69, 135 (2005).