Isotropic-nematic transition in an external field
TL;DR: In this article, the effects of an external field on the isotropic-nematic transition in liquid-crystalline substances were studied using the "orientationally averaged pair correlations" approximation.
Abstract: We study the effects of an external field on the isotropic-nematic transition in liquid-crystalline substances. The theoretical technique employed is called the "orientationally averaged pair correlations" approximation. It takes into detailed account spatial correlations between the molecules while treating orientational order in a mean-field-like manner. The results obtained for MBBA ($4\ensuremath{-}\mathrm{m}\mathrm{e}\mathrm{t}\mathrm{h}\mathrm{o}\mathrm{x}\mathrm{y}\mathrm{b}\mathrm{e}\mathrm{n}\mathrm{z}\mathrm{y}\mathrm{l}\mathrm{i}\mathrm{d}\mathrm{e}\mathrm{n}\mathrm{e}\ensuremath{-}4\ensuremath{'}\ensuremath{-}n\ensuremath{-}\mathrm{b}\mathrm{u}\mathrm{t}\mathrm{y}\mathrm{l}\mathrm{a}\mathrm{n}\mathrm{i}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}$) are compared to those of the Maier-Saupe theory and the Landau-de Gennes theory. We determine the paranematic-nematic coexistence curve, the temperature-external field phase diagram, the Cotton-Mouton coefficient, the maximum supercooling temperature, critical exponents, and the relation between the transition temperature and the electric field in laser-induced isotropic-nematic transitions. These results are compared to experimental data. Their implications are discussed.
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TL;DR: A review of the wide variety of predictions that results from a Landau-type of description of the nematic-isotropic phase transition is given in this paper, which includes a discussion of the nature of the order parameter and of the various types of possible phases.
291 citations
TL;DR: In this article, the discharge modes of a thermionic low pressure discharge (p < 1Pa) were investigated with the one-dimensional particle-in-cell simulation codes PDP1 and XPDP1, and the simulation results provided a model approach for stable discharge modes, hysteresis, and for nonlinear relaxation-oscillations.
Abstract: The discharge modes of a thermionic low pressure discharge (p<1Pa) are investigated with the one‐dimensional particle‐in‐cell simulation codes PDP1 and XPDP1 [C. K. Birdsall, IEEE Trans. Plasma Sci. 19, 65 (1991)]. The simulation results provide a model approach for stable discharge modes, hysteresis, and for nonlinear relaxation‐oscillations. During this potential‐relaxation instability, nonlinear structures, e.g. electron holes and double layers, are observed. A Pierce–Buneman‐mode is suggested as a trigger mechanism for the onset of the instability. The detailed oscillation process can be subdivided into three distinct phases: expansion phase, double layer phase, and relaxation phase. This allows one to explain the parameter dependencies of the oscillation frequency. For a periodically driven discharge, mode‐locking in a period‐2 state is found and explained by the model. The mode‐locking phenomenon is studied systematically. The results of the simulations are well confirmed by experimental observations presented in Part II of this paper [T. Klinger et al., Phys. Plasmas 2, 1822 (1995)].
36 citations
TL;DR: According to the Maier-Saupe theory, the order induced by a magnetic field in a liquid crystal above the nematic-isotropic transition varies with temperature as (T − T ∗ ) -1 as mentioned in this paper.
26 citations
TL;DR: In this paper, magnetically induced birefringence measurements were performed in the isotropic phase of methoxybenzylidene butylaniline (MBBA).
Abstract: Magnetically induced birefringence measurements were performed in the isotropic phase of methoxybenzylidene butylaniline (MBBA). Over the entire temperature range studied, $\ensuremath{\Delta}n$ was found to be linear in ${H}^{2}$ to fields over 10 T. This result is consistent with the Landau model of the nematic-isotropic transition, and strongly inconsistent with the results of Keyes and Shane [Phys. Rev. Lett. 42, 722 (1979)] in a similar experiment. Their results indicate both the approach of a field-induced critical point and tricritical behavior near the phase transition.
23 citations
TL;DR: In this article, the effect of electric field on the measured order parameter of a liquid crystal is considered, and it is pointed out that an external field may influence the apparent degree of order by changing the microscopic order parameter, and by quenching director fluctuations.
Abstract: The effect of an electric field on the measured order parameter of a liquid crystal is considered. It is pointed out that an external field may influence the apparent degree of order by changing the microscopic order parameter, and by quenching director fluctuations. In nematic liquid crystal the latter dominates, but for smectic phases the effects of field-induced molecular order may be observable. Measurements are reported of the electric field-induced birefringence in nematic 44′-n-pentylcyanobiphenyl (5CB) and the nematic and smectic phases of 44′-n-octylcynobiphenyl (8CB). The modular dependence of induced order on electric field strength predeicted for nematics is experimentally confirmed by Fourier analysis of the electro-optic response. At low field strength, and in the smectic phase, the induced order varies as the square of the field strength, and the dependece on cell thickness is not as predicted by continuum theory. By introducing two scaling parameters into the theory it is possible...
15 citations