04/06/2011
MaierSaupe theory is the canonical mean field description of thermotropic nematic liquid crystals. In this paper, we examine the predictions of the theory in four spatial dimensions. Representations of the order parameter tensor and the existence of new phases are discussed. The phase diagram, based on numerical solution of the selfconsistent equations and Landau theory, is presented. Orientational order decreases as the number of spatial dimensions is increased.
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01/15/2013
In their paper, using the principle of energy conservation, F. Castles, S. M. Morris, and H. J. Coles [AIP Advances 1, 032120 (2011)] establish inequalities involving the elastic and dielectric constants and flexoelectric coefficients of liquid crystals. They then argue that recently measured values of flexoelectric coefficients by Harden et al. do not obey these inequalities, hence they violate the principle of energy conservation. In this comment, we point out that in their calculation, Castles et al. use an inappropriate value for an elastic constant, hence their conclusions, predicated on the outcome of this calculation, are not justified. Copyright 2013 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4774285]
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10/04/2004
In this work, we have studied the temperature dependence of a cholesteric liquidcrystal laser coupled to an optical fiber, with a view towards optical fiber sensor applications. To stabilize the laser emission, we developed a procedure to align the liquid crystal placed in the fiber. Unexpected oscillations in the laser emission were observed as the temperature was varied, which can be understood in terms of the competition between bulk and surface anchoring torques. (C) 2004 American Institute of Physics.
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03/15/2011
In this paper, we present a simple one tensor mean field model of biaxial nematic liquid crystals. The salient feature of our approach is that material parameters appear explicitly in the order parameter tensor. We construct the free energy from a mean field potential based on anisotropic dispersion interactions, identify the order parameter tensor and its elements, and obtain selfconsistent equations, which are then solved numerically. The results are illustrated in a 3D ternary phase diagram. The phase behavior can be simply related to molecular parameters. The results may be useful for designing molecules that show a thermotropic biaxial phase.
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06/15/2011
We have constructed a hypothetical charge pump which converts solar energy into DC electricity. The output is generated by cyclic changes in the capacitance of a circuit, which transfers charge from a low to a high voltage. The electric field across the capacitor must be of the order of 10(8)Vm(1) to compete with efficiencies of photovoltaics. We have modeled the output using a liquid crystal elastomer as the working substance. Efficiencies of 1  4% are obtained, and are enhanced by careful choices in the capacitor geometries and the operating voltages of the charge pump. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3581134]
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01/01/1998
We consider the size of domains formed in ordered systems in the presence of quenched random fields. We argue that below the critical dimension, the, domain size shows a nonmonotonic dependence on the correlation length of the random field. If the random field is slowly varying in space, the order parameter follows the field, and the domain size is comparable to the correlation length. If the field is rapidly varying, the domain size becomes larger than the correlation length, and diverges as the correlation length of the random field goes to zero.
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01/01/2011
We consider a continuum model describing the dynamic behavior of nematic liquid crystal elastomers (LCEs) and implement a numerical scheme to solve the governing equations. In the model, the Helmholtz free energy and Rayleigh dissipation are used, within a Lagrangian framework, to obtain the equations of motion. The free energy consists of both elastic and liquid crystalline contributions, each of which is a function of the material displacement and the orientational order parameter. The model gives dynamics for the material displacement, the scalar order parameter and the nematic director, the latter two of which correspond to the orientational order parameter tensor. Our simulations are carried out by solving the governing equations using an implicitexplicit scheme and the Chebyshev polynomial method. The simulations show that the model can successfully capture the shape changing dynamics of LCEs that have been observed in experiments, and also track the evolution of the order parameter tensor.
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01/01/1998
We derive the amplitude equation, in the weakly nonlinear regime, for an optical wave packet that propagates in an initially undistorted nematic liquid crystal. By using the dyad representation Q(ij), we find the retarded and nonlocal equation for the nematic configuration and solve it in Fourier space. This allows us to calculate the amplitude dependent dispersion relation for a nematic liquid crystal in a given initial undistorted stationary state. We consider a linearly polarized wave packet that travels along the principal axis of the nematic dielectric tensor. We find a nonlinear Schrodinger equation for the amplitude, which includes an additional quadratic term with dissipation. [S1063651X(98)093106].
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01/01/2006
We have developed a fully nonlocal model to describe the dynamic behavior of nematic liquidcrystal elastomers. The free energy, incorporating both elastic and nematic contributions, is a function of the material displacement vector and the orientational order parameter tensor. The free energy cost of spatial variations of these order parameters is taken into account through nonlocal interactions rather than through the use of gradient expansions. We also give an expression for the Rayleigh dissipation function. The equations of motion for displacement and orientational order are obtained from the free energy and the dissipation function by the use of a Lagrangian approach. We examine the free energy and the equations of motion in the limit of longwavelength and smallamplitude variations of the displacement and the orientational order parameter. We compare our results with those in the literature. If the scalar order parameter is held fixed, we recover the usual viscoelastic theory for nematic liquid crystals.
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01/01/2007
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