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Broad-Band Dielectric Spectroscopy of Liquid Crystals Confined in Random and Cylindrical Pores

Published online by Cambridge University Press:  10 February 2011

G.P. Sinha  and
F.M. Aliev
G.P. Sinha
Affiliation:
Department of Physics and Materials Research Center, PO BOX 23343, University of Puerto Rico, San Juan, PR 00931–3343, USA
F.M. Aliev
Affiliation:
Department of Physics and Materials Research Center, PO BOX 23343, University of Puerto Rico, San Juan, PR 00931–3343, USA
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Abstract

Using dielectric spectroscopy in the frequency range 0.1 Hz-1.5 GHz, we investigated the influence of confinement on the dynamic properties of polar nematic liquid crystals (LC) dispersed in porous matrices with randomly oriented, interconnected pores as well as in parallel cylindrical pores with different, pores sizes. The confinement has a strong influence on the dielectric properties of LC which resulted in the appearance of a low frequency relaxational process (f ≤ 10 KHz) absent in bulk and a strong modification of modes due to the molecular rotation around short axis and librational motion. The differences between bulk and confined behavior are: (a) - the dielectrically active modes in confined LC are not frozen even at temperatures about 20 degrees below the bulk crystallization temperature; (b) - in the temperature range corresponding to the anisotropie phase in pores, lnτ, where τ is the relaxation time corresponding to the molecular rotation around short axis, is not a linear function of 1/T and there is an evidence for smectic type order formation at sufficiently low T; (c) - the retardation factor g = τ/τis is ≃ 1.5, where as the typical value of g in bulk nematic liquid crystals is ≃ 4; (d) - smooth and small changes in T at phase transition in pores suggest that the “isotropie” phase of LC in pores is not bulk like isotropie phase with complete disorder in molecular orientations, and some degree of orientation order still persists.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 464: Symposium FF – Dynamics in Small Confining Systems III , 1996 , 195
Copyright
Copyright © Materials Research Society 1997

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