# A Molecular Meanfield Model for the Biaxial Rectangular Discotic Phase with Herring-Bone Packing of Tilted Molecules

01 May 1995-Molecular Crystals and Liquid Crystals (Taylor & Francis Group)-Vol. 264, Iss: 1, pp 165-179

TL;DR: In this article, a molecular mean field model for a rectangular columnar to hexagonal columnar phase transition is presented, assuming the molecules basically to be biaxial objects.

Abstract: A molecular meanfield model for a rectangular columnar to hexagonal columnar phase transition, as observed in case of the HAT series, is presented here assuming the molecules basically to be biaxial objects The theory is developed for a rectangular lattice having herring-bone packing of the tilted molecules Various types of phase diagrams for a homologous series are reproduced for different values of molecular biaxiality Some of them are very similar to the experimentally observed cases but others, particularly involving biaxial nematic phase, are not yet observed It is shown that a gradual lowering of biaxiality with the addition of flexible chain segments can lead to the full phase sequence observed in the HAT series

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TL;DR: In this paper, the structures of columnar mesophases that depend on the presence of either N-H⋯O, or H-O-Bonds (subsumed under the term ‘N|H|O-bonds') are reviewed.

Abstract: The structures of supramolecular columnar mesophases that depend on the presence of either N–H⋯O, or N⋯H–O– hydrogen bonds (subsumed under the term ‘N|H|O-bonds’) are reviewed. The thesis is supported that supramolecular mesogenes bridge different fields of liquid crystal research, offering the opportunity to create a unified picture of thermotropic, and lyotropic mesomorphism. With the examples of N|H|O hydrogen bond mesogenes the molecular structures of the respective mesogenes are presented, and general principles to rationally construct such molecules are discussed. A connection is drawn to systems from isolated columns as found in low molecular weight organogels. Perspectives, and outlooks for possible applications of N|H|O hydrogen bonded columnar phases are given.

117 citations

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TL;DR: The results point to the formation of dynamical structural defects along the columns in stacks of liquid-crystalline tetraalkoxy-substituted, metal-free phthalocyanines.

Abstract: We present a joint molecular dynamics (MD)/kinetic Monte Carlo (KMC) study aimed at the atomistic description of charge transport in stacks of liquid-crystalline tetraalkoxy-substituted, metal-free phthalocyanines. The molecular dynamics simulations reproduce the major structural features of the mesophases, in particular, a phase transition around 340 K between the rectangular and hexagonal phases. Charge transport simulations based on a Monte Carlo algorithm show an increase by 2 orders of magnitude in the hole mobility when accounting for the rotational and translational dynamics. The results point to the formation of dynamical structural defects along the columns.

82 citations

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01 Jan 1984TL;DR: McMillan's mean field model of smectic A is extended so that the translational order parameter is now periodic in two dimensions as discussed by the authors, and the theory is developed for a face-centered rectangular lattice composed of liquid-like columns, taking the molecular cores to be circular discs normal to columnar axes but with an asymmetrical disposition of the chains.

Abstract: McMillan’s mean field model of smectic A is extended so that the translational order parameter is now periodic in two dimensions. The theory is developed for a face-centered rectangular lattice composed of liquid-like columns, taking the molecular cores to be circular discs normal to the columnar axes but with an asymmetrical disposition of the chains. When the axial ratio b/a = √3, the rectangular lattice reduces to a hexagonal one and the theory becomes essentially identical to that proposed very recently by Feldkamp, Handschy and Clark.

12 citations

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TL;DR: In this paper, group theoretical techniques are used to discuss the disordered hexagonal columnar-disordered rectangular columnar (D hd −D rd ) liquid crystal phase transition in HAT series.

Abstract: Group theoretical techniques are used to discuss the disordered hexagonal columnar-disordered rectangular columnar (D hd −D rd ) liquid crystal phase transition in HAT series. On the basis of Landau theory the transition is predicted to be second order. The Ginzburg-Landau-Wilson Hamiltonian corresponds to a universality class with an n=3 component order parameter and with cubic anisotropy. The critical behaviour near the D hd −D rd transition is discussed by referring to the renormalization group results of Aharony and other authors and we present evidence in favour of the critical value of n, n c , being greater than 3. It is also predicted that a second order transition from the D hd phase to an as yet experimentally undiscovered phase is possible Analyse de la transition en appliquant les techniques de la theorie des groupes

8 citations

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8 citations

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TL;DR: In this article, a mean field model for a rectangular columnar to hexagonal columnar phase transition, assuming that the molecules are biaxial in both the phases, is presented, taking the molecular cores to be tilted in a particular direction with respect to the column axis by the same angle at each lattice site.

Abstract: A mean field model for a rectangular columnar to hexagonal columnar phase transition, assuming thatthe molecules are biaxial in both the phases, is presented. The theory is developed for a face centeredrectangular lattice taking the molecular cores to be tilted in a particular direction with respect to thecolumn axis by the same angle at each lattice site. Phase diagrams for a homologous series for twovalues of biaxiality parameter are presented. With increasing temperature a phase sequence rectangular-hexagonal-nematic-isotropic is found for shorter members while for higher members of a homologousseries the nematic phase is absent in the calculated phase sequence.

7 citations

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TL;DR: In this article, the phase diagram of a discotic system is reproduced in a single particle potential model and the equivalence of the variational method and the particle potential approach is discussed.

Abstract: In an earlier work the present authors extended the variational method of Lee et al. for rod-like molecules to obtain the phase diagram of a discotic liquid crystal system. In the present work, the phase diagram of a discotic system is reproduced in a single particle potential model. It is seen that the single particle potential approach reproduces results very similar to those of the variational method but with considerable ease in computation. The equivalence of the two approaches is discussed.

5 citations