Raman scattering study of phase biaxiality in a thermotropic bent-core nematic liquid crystal.

School of Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA.
Physical Review Letters (Impact Factor: 7.73). 07/2010; 105(2):027801. DOI: 10.1103/PhysRevLett.107.109801
Source: PubMed

ABSTRACT Polarized Raman spectroscopy was used to investigate the development of orientational order and the degree of phase biaxiality in a bent-core mesogenic system. The values of the uniaxial order parameters and , and biaxial order parameters , , and , and their evolution with temperature were determined. The temperature dependence of almost all order parameters reveals a second order transition from the uniaxial to biaxial nematic phase with increasing to ∼0.22 before a first order transition to the smectic-C phase, upon cooling.

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    Physical Review E 10/2010; 82(4 Pt 1):041711. · 2.31 Impact Factor
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    ABSTRACT: We determine the bifurcation phase diagrams with isotropic (I), uniaxial (N(U)) and biaxial (N(B)) nematic phases for model bent-core mesogens using Onsager-type theory. The molecules comprise two or three Gay-Berne interacting ellipsoids of uniaxial and biaxial shape and a transverse central dipole. The Landau point is found to turn into an I-N(B) line for the three-center model with a large dipole moment. For the biaxial ellipsoids, a line of Landau points is observed even in the absence of the dipoles.
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    ABSTRACT: A molecular theory of biaxial nematic ordering in the system of bent-core molecules has been developed in the two-particle cluster approximation which enables one to take into account short-range polar correlations determined by both electrostatic dipole-dipole interaction and polar molecular shape. All orientational order parameters and short-range correlation functions are calculated numerically as functions of temperature in the uniaxial and in the biaxial nematic phases, and the results are compared with the ones obtained in the mean-field approximation and in the cluster approximation but without taking into consideration the dipole-dipole interaction. It is shown that short-range polar correlations and, in particular, the dipole-dipole correlations dramatically increase the temperature of the transition into the biaxial nematic phase and enhancing its stability range. The results are also very sensitive to the value of the opening angle of a model bent-core molecule.
    Journal of Physics Condensed Matter 03/2012; 24(14):142201. · 2.22 Impact Factor


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