TITLE

Mechanism of quasi-one-dimensional electronic conductivity in discotic liquid crystals

AUTHOR(S)
Boden, N.; Bushby, R. J.; Clements, J.
PUB. DATE
April 1993
SOURCE
Journal of Chemical Physics;4/1/1993, Vol. 98 Issue 7, p5920
SOURCE TYPE
Academic Journal
DOC. TYPE
Article
ABSTRACT
Recently, it has been shown that a new class of quasi-one-dimensional conductors can be created by doping discotic liquid crystals with appropriate oxidants. This paper reports the elucidation of the mechanism of conduction in these new materials. In particular, the ac conductivity of 2,3,6,7,10,11-hexahexyloxytriphenylene (HAT6) doped with the Lewis acid AlCl3, has been measured as a function of frequency (10-3–107 Hz), and temperature in its crystalline solid (K), hexagonal discotic liquid crystal (Dho), and isotropic liquid (I) phases. In all three phases the conductivity is independent of frequency at low frequencies, but shows a power law dependence on frequency [σ(ω)∼ωs, s∼0.7–0.8] at higher frequencies. This behavior is characteristic of charge carrier transport by a hopping mechanism. The conductivity data have been analyzed in terms of the Scher and Lax theory to obtain the parameters describing this process. In macroscopically aligned K and Dho phases, the conductivity measured along the column axes is approximately 103 greater than that in the perpendicular direction. The conduction along the columns is identified with a single charge transport process in which the carriers hop between localized states (radical cations) associated with AlCl4--counterions linearly distributed off-axis along the columns. The charge carrier diffusion coefficient is independent of the concentration of dopant and has the value D||∼3.4×10-10 m2 s-1 in the Dho phase at 343 K. In the isotropic melt phase, the conductivity measurements reveal the involvement of two distinct processes. One of these is identified with charge migration along supramolecular ‘‘stacks’’ some 200 nm in length, whilst the other appears to be associated with carriers hopping between these stacks. The conductivity behavior of the unaligned Dho and K phases is very similar to that of the isotropic liquid phase implying...
ACCESSION #
7609799

 

Related Articles

  • Observation of surface and bulk phase transitions in nematic liquid crystals. Boamfa, M. I.; Kim, M. W.; Maan, J. C.; Rasing, Th. // Nature;1/9/2003, Vol. 421 Issue 6919, p149 

    The behaviour of liquid crystal (LC) molecules near a surface is of both fundamental and technological interest: it gives rise to various surface phase-transition and wetting phenomena[SUP1-14], and surface-induced ordering of the LC molecules is integral to the operation of LC...

  • Simple model of induced smectic phases in binary mixtures of liquid crystals. de Jeu, Wim H.; Longa, Lech; Demus, Dietrich // Journal of Chemical Physics;6/1/1986, Vol. 84 Issue 11, p6410 

    The origin of the occurrence of induced smectic phases (ISP) in binary mixtures of liquid crystals is discussed. First the experimental evidence is reviewed, which leads to a division in strong complexing (electron–donor–acceptor complex as indicated by a charge–transfer...

  • Curvature-related molecular segregation in lyotropic aggregates of potassium palmitate and benzyl alcohol: A 2H NMR study. Pope, J. M.; Doane, J. W. // Journal of Chemical Physics;9/1/1987, Vol. 87 Issue 5, p3201 

    The ternary system potassium palmitate/benzyl alcohol/water has been studied by 2H NMR of selectively 2H labeled amphiphiles. At low temperatures the samples comprise a mixture of cylindrical aggregates (Rα) and pure potassium palmitate gel (Lβ), which transforms first to a liquid...

  • Order parameter and packing studies in nematic and smectic A phases by x-ray diffraction. Haase, W.; Fan, Z. X.; Müller, H. J. // Journal of Chemical Physics;9/1/1988, Vol. 89 Issue 5, p3317 

    X-ray diffraction measurements have been made on the nematic phase of T15 (4-cyano-4’-n-pentyl-p-terphenyl), as well as on the nematic and smectic A phases of RNO2 [4’-nitrophenyl-4-(4’-n-hexyloxy-benzoyloxy)-cinnamate]. The x-ray equipment used allows comparably high...

  • Liquid crystals take the temperature in tests. Beard, Jonathan // New Scientist;8/14/93, Vol. 139 Issue 1886, p20 

    Reports on research involving liquid crystals and how they change color with accompanying temperature changes. Heat transfer in aero-propulsion systems; Linear relationship between temperature to color in the crystals; Calibrated crystal's behavior as a temperature gauge.

  • Thermal variation of surface tension at liquid crystal–isotropic liquid interface. Mohandas, K. P.; George, A. K. // Journal of Chemical Physics;3/15/1992, Vol. 96 Issue 6, p4779 

    The surface tension of two nematic liquid crystals bounded by an isotropic liquid (glycerin) was measured as a function of temperature. A spinning drop technique was used for the measurements. Unlike monotonically decreasing dependence found in most isotropic liquids, the surface...

  • Optical birefringence and temperature range of the biaxial nematic phase in a lyotropic liquid crystal. Galerne, Y.; Neto, A. M. Figueiredo; Liebert, L. // Journal of Chemical Physics;2/1/1986, Vol. 84 Issue 3, p1732 

    A linear relation is found between the cube of the optical birefringence and the temperature range of the biaxial nematic phase in the lyotropic mixtures of potassium laurate, l-decanol, D2O. Such a relation which is consistent with the Landau model of the uniaxial to biaxial nematic phase...

  • Temperature-independent hole mobility in discotic liquid crystals. Kreouzis, T.; Donovan, K. J.; Boden, N.; Bushby, R. J.; Lozman, O. R.; Liu, Q. // Journal of Chemical Physics;1/22/2001, Vol. 114 Issue 4 

    Experimental measurements are presented of the hole mobilities of four conjugated discotic systems, forming columnar liquid crystals, as a function of temperature. The measurements cover the crystalline/glassy phase and mesophase of these materials. It is a remarkable fact that the mobility is...

  • Accurate determination of the temperature and frequency dependent smectic C biaxial permittivity... Brown, Carl V.; Jones, J. Cliff // Journal of Applied Physics;9/15/1999, Vol. 86 Issue 6, p3333 

    Focuses on a study which measured the temperature and frequency dependent smectic C bend and splay elastic constants and permittivities for a smectic C liquid crystal mixture. Smectic C alignment geometries and theory; Experimental procedures; Results and discussion; Conclusions.

Share

Read the Article

Courtesy of THE LIBRARY OF VIRGINIA

Sorry, but this item is not currently available from your library.

Try another library?
Sign out of this library

Other Topics