Condensed-Matter Physics & Materials Science Seminar

"Topological defects and Colloidal Particles in Liquid Crystals: Three-Dimensional Imaging and Patterns"

Presented by Oleg Lavrentovich, Kent State University

Tuesday, November 21, 2006, 11:00 am — Small Seminar Room, Bldg. 510

Topological defects and colloidal particles in liquid crystals: Three-dimensional imaging and patterns
Oleg D. Lavrentovich
Liquid Crystal Institute and Chemical Physics Interdisciplinary Program,Kent State Univ., Kent,OH 44242 odl@lci.kent.edu
Orientational order is a universal feature of numerous soft-matter systems, most notably liquid crystals. These systems are extremely flexible, producing a rich variety of complex 3D structures that are easily changed by external factors such as an electric field. Non-destructive techniques to study and control these patterns are in a great demand. This presentation discusses how a tightly focused laser beam can serve as a tool to both image and to manipulate complex patterns of the director.
(1) To image the 3D configuration of molecular orientation, we use the technique of fluorescence confocal polarizing microscopy (FCPM) based on the property of an anisotropic medium to align an anisometric fluorescent dye molecule. In polarized light, the measured fluorescence signal is determined by the spatial orientation of the molecules rather than by concentration gradients of dye. We apply the technique to a variety of complex 3D director structures in liquid crystals, such as gliding and sliding dislocations, undulations, formation of colloidal crystals at the nematic-air interface, etc.
(2) Colloidal particles dispersed in liquid crystals interact through elastic distortions of the host medium. We use optical tweezers to characterize the anisotropic colloidal forces and elastic properties of topological defects in the liquid crystal medium.

Hosted by: R. Pindak/B. Ocko

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