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High-frequency dielectric relaxation of liquid crystals: THz time-domain spectroscopy of liquid crystal colloids
University of Exeter (at the time of publication Euan Hendry was at FOM Institute for Atomic and Molecular Physics, Amsterdam); Japan Science & Technology Agency; FOM Institute for Atomic and Molecular Physics
Optical Society of America
Terahertz time-domain spectroscopy has been used to study the dielectric relaxation of pure 4’–n-pentyl–4–cyanobiphenyl (5CB) liquid crystal (LC) and its mixtures with 10 µm SiO2 particles in the frequency range 0.2–2 THz. For the pure sample, we find that spatial inhomogeneities consisting of oriented domains, comparable in size to our probe area (~1 mm2), cause a large scatter in the measured dielectric function, due to varying contributions from the ordinary and extraordinary components. In the LC/particle mixtures, ordering of the LC at the surface of the SiO2 particles results in a break-up of these domains, giving rise to a spatially much more homogeneous dielectric response. The inferred dielectric function can be interpreted using effective medium theory and the Debye relaxation model. We observe this stabilizing effect for interparticle distances < ~30 µm, setting a lower limit for the size of oriented domains in the bulk LC.
Copyright © 2006 Optical Society of America. This paper was published in Optics Express and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-14-23-11433 . Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.
14 (23), pp. 11433-11441