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    An experimental optimization study for concentration and laser power effects in the fullerene-C60 and azo dye doped guest-host liquid crystal systems
    (Elsevier Science Bv, 2009) Okutan, M.; Koysal, O.; San, S. E.; Yakuphanoglu, F.
    The current-voltage characteristics of a famous guest-host liquid crystal system have been investigated under dark and laser illumination conditions. Dependency of current modulation with respect to concentration and laser power gives some optimization possibilities and estimations on the reorientation mechanisms of the liquid crystals. The current-voltage character of pure E7 is almost unchanged with laser pumping, while the fullerene and dye doping are enhancing effects in their individual and collective usage. The negative resistance effect was observed for some certain concentrations of the dye and C-60, and this peculiarity is shown to be switched with laser illumination. The mobility of the doped LC samples was calculated by transient current measurements and its dependency on the dye concentration and the laser power was investigated. It is evaluated that the effect of methyl red is a critical parameter in photoconductivity applications of liquid crystals. (c) 2009 Elsevier B.V. All rights reserved
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    Effect of an azo dye (DR1) on the dielectric parameters of a nematic liquid crystal system
    (Elsevier, 2007) Ozder, S.; Okutan, M.; Koysal, O.; Goktas, H.; San, S. E.
    The dielectric parameters and relaxation properties of azo dye (DR1) doped E7 and pure E7 liquid crystal (LC) have been investigated in a wide frequency range of 10k-10MHz through the dielectric spectroscopy method at room temperature. Dielectric anisotropy (Delta epsilon) property of the LC changes from the positive type to negative type and dielectric anisotropy values decrease with doping of DR1. The relaxation frequency f(r) of E7 and E7/DR1 LC was calculated by means of Cole-Cole plots. Influence of bias voltage on the dielectric parameters has also been investigated. (c) 2006 Elsevier B.V. All rights reserved.
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    Temperature dependency of impedance spectroscopy behaviors in side-chain liquid crystalline polymer
    (Elsevier, 2009) Okutan, M.; Koysal, O.; San, S. E.; Senturk, E.
    In this paper, the electrical properties of side-chain liquid crystalline polymer (SLCP) are investigated by impedance spectroscopy technique. We report the measurement of dielectric and conductivity for SLCP from 1 kHz to 10 MHz within the temperature range from 300 to 370 K. The DC conductivity obeys Arrhenius law and it gives a small deviation at 315 K. The activation energies are equal to 0.20 eV and 0.75 eV for high and low temperatures, respectively. The frequency dependence of conductivity satisfies the power law, sigma(AC) = Aw(5), with s = 0.50-0.57. The evaluated power law exponent s exhibits nearly linear decreasing behavior with temperature. This suggests that the Correlated Barrier Hopping (CBH) model is the operating mechanism. (C) 2009 Elsevier B.V. All rights reserved.
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    The electrical properties of a fullerene and CI Acid Red 2 (methyl red) doped E7 nematic liquid crystal
    (Elsevier Sci Ltd, 2010) Okutan, M.; San, S. E.; Koysal, O.; Senturk, E.
    The electrical properties of a C.I. Acid Red 2 (4-dimethylaminoazobenzene-2'-carboxylic acid) and fullerene mixture of the nematic liquid crystal E7 were studied using complex dielectric spectroscopy as a function of the frequency of the applied AC-DC signal at various temperatures. Both the real and imaginary components of the dielectric constant decreased with increased frequency of the applied field whilst the AC conductivity increased with increasing frequency of the applied field. The alternating current conductivity sigma(omega) varied with angular frequency, omega as omega(s), with s <= 1, suggesting that a dominant hopping conduction process operated. The temperature dependence of both the AC conductivity and the exponents can be reasonably well interpreted using a correlated barrier hopping model. (C) 2009 Elsevier Ltd. All rights reserved.