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A mode coupling theory description of the short- and long-time dynamics of nematogens in the isotropic phase

J. Chem. Phys. 124, 014902 (2006); doi:10.1063/1.2145679

Published 3 January 2006

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Jie Li, Hu Cang, Hans C. Andersen, and M. D. Fayer
Department of Chemistry, Stanford University, Stanford, California 94305
Optical heterodyne-detected optical Kerr effect (OHD-OKE) experimental data are pre-sented on nematogens 4-(trans-4[prime]-n-octylcyclohexyl)isothiocyanatobenzene (8-CHBT), and 4-(4[prime]-pentyl-cyclohexyl)-benzonitrile (5-PCH) in the isotropic phase. The 8-CHBT and 5-PCH data and previously published data on 4[prime]-pentyl-4-biphenylcarbonitrile (5-CB) are analyzed using a modification of a schematic mode coupling theory (MCT) that has been successful in describing the dynamics of supercooled liquids. At long time, the OHD-OKE data (orientational relaxation) are well described with the standard Landau-de Gennes (LdG) theory. The data decay as a single exponential. The decay time diverges as the isotropic to nematic phase transition is approached from above. Previously there has been no theory that can describe the complex dynamics that occur at times short compared to the LdG exponential decay. Earlier, it has been noted that the short-time nematogen dynamics, which consist of several power laws, have a functional form identical to that observed for the short time behavior of the orientational relaxation of supercooled liquids. The temperature-dependent orientational dynamics of supercooled liquids have recently been successfully described using a schematic mode coupling theory. The schematic MCT theory that fits the supercooled liquid data does not reproduce the nematogen data within experimental error. The similarities of the nematogen data to the supercooled liquid data are the motivation for applying a modification of the successful MCT theory to nematogen dynamics in the isotropic phase. The results presented below show that the new schematic MCT theory does an excellent job of reproducing the nematogen isotropic phase OHD-OKE data on all time scales and at all temperatures. ©2006 American Institute of Physics
History: Received 22 August 2005; accepted 31 October 2005; published 3 January 2006
Permalink: http://link.aip.org/link/?JCPSA6/124/014902/1
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KEYWORDS and PACS

Keywords
PACS
  • 64.70.Md
    Transitions in liquid crystals
  • 42.70.Df
    Liquid crystals (optical materials)
  • 61.30.Gd
    Orientational order of liquid crystals in electric and magnetic fields
  • 42.65.Hw
    Optical phase conjugation; photorefractive and Kerr effects
  • 61.20.Gy
    Theory and models of liquid structure
  • YEAR: 2006

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PUBLICATION DATA

ISSN:
0021-9606 (print)   1089-7690 (online)
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AIP is a member of CrossRef AIP

REFERENCES (41)
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