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
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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77 citations
TL;DR: In this paper, it was pointed out that the usual one-parameter approximation for the order parameter tensor in nematic liquid crystals is not always adequate, and that a twoparameter description is indicated by experiments, and it was shown that for p-azoxyanisole at 120°C, the two parameters have the values; S ¯ = 0.52, D ¯ =0.07, where S ¯ is the usual nematic order parameter and D ¯ describes the difference in the tendency of the two transverse molecular axes to be oriented along the average
Abstract: It is pointed out that the usual one-parameter approximation for the order parameter tensor in nematic liquid crystals is not always adequate, and that a two-parameter description is indicated by experiments. From previously published data we find that for p-azoxyanisole at 120°C, the two parameters have the values; S ¯ = 0.52, D ¯ = 0.07, where S ¯ is the usual nematic order parameter and D ¯ describes the difference in the tendencies of the two transverse molecular axes to be oriented along the average nematic director.
64 citations
TL;DR: In this paper, the feasibility of x-ray scattering studies of freely suspended strands of discotic liquid crystals (of triphenylene hexa-n-dodecanoate) was demonstrated.
Abstract: We demonstrate the feasibility of x-ray scattering studies of freely suspended strands of discotic liquid crystals (of triphenylene hexa-n-dodecanoate). We are able to grow strands, which are stable for days, of diameter >50 ..mu..m with a few single crystal domains. Unexpectedly, we find that the quasi two-dimensional structural phase transition from columnar D2 to columnar D1 corresponds to the orientational ordering of columns of molecules with the molecules tilted at finite angles to the column axis in both phases.
61 citations
03 Jun 1983-Philosophical transactions - Royal Society. Mathematical, physical and engineering sciences
TL;DR: Based on the x-ray data, a structure is proposed in which the discs are stacked one on top of the other in columns that constitute a hexagonal arrangement, but the spacing between the discs in each column is irregular as discussed by the authors.
Abstract: Thermotropic mesomorphism has been observed in pure compounds consisting of simple disc-like molecules, viz., benzene-hexa-n-alkanoates. Thermodynamic, optical and x-ray studies indicate that the mesophase is a highly ordered lamellar type of liquid crystal. Based on the x-ray data, a structure is proposed in which the discs are stacked one on top of the other in columns that constitute a hexagonal arrangement, but the spacing between the discs in each column is irregular. Thus the structure has translational periodicity in two dimensions and liquid-like disorder in the third.
49 citations
TL;DR: In this article, it was shown that triphenylene hexa-n$-dodecanoate can be stretched into strands of diameter \ensuremath{gtrsim}1 \ensuresm{m}m, with the disk-shaped molecules arranged into columns along the strand axis.
Abstract: Observations of stable, freely suspended liquid-crystal strands are reported. Liquid crystals of triphenylene hexa-$n$-dodecanoate can be stretched into strands of diameter \ensuremath{\gtrsim}1 \ensuremath{\mu}m, with the disk-shaped molecules arranged into columns along the strand axis. In the $D1$ phase ($Tl110\ifmmode^\circ\else\textdegree\fi{}$ C) the molecules are tilted with respect to the strand axis, the tilt orientation behaving as a one-dimensional nematiclike field, interrupted by jumps in orientation between degenerate stable positions relative to the column lattice.
39 citations