Berlin 2012 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 16: Poster: Colloids and Complex Liquids

CPP 16.21: Poster

Dienstag, 27. März 2012, 18:15–20:45, Poster A

Magneto-optical Technique for Detecting the Biaxial Nematic Liquid Crystal Phase — •Tanya Ostapenko¹, Cuiyu Zhang², Samuel Sprunt¹, Antal Jákli², and James Gleeson¹ — ¹Department of Physics, Kent State University, Kent, Ohio 44242, USA — ²Chemical Physics Interdisciplinary Program and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA

The existence of the biaxial nematic liquid crystal phase (N_b) has been the subject of much discussion since it was first predicted [1]. The geometry of the liquid crystal mesogen is important and it is thought that banana-shaped, or bent-core, liquid crystals will have an N_b phase. Recently, there have been attempts to find a bent-core liquid crystal that exhibits this phase, but there have been many conflicting reports about whether the N_b phase has been positively identified. One reason for the discrepancy is that there is currently no way to rule out surface effects or anchoring transitions, both of which may give a false positive identification of a uniaxial-biaxial nematic transition. Optical techniques usually rely on a sample cell rubbing treatment to align the sample, but optical misidentification could occur if the material is in a tilted uniaxial phase, which appears the same as a homeotropically-aligned biaxial phase. We have developed a technique that uses a magnetic field to align the uniaxial director, thus widening its application to any bent-core nematic material.

[1] M.J. Freiser. Phys. Rev. Lett. 24, 19, 1041-1043 (1970).