7 research outputs found

    Core charge distribution and self assembly of columnar phases: the case of triphenylenes and azatriphenylenes

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    <p>Abstract</p> <p>Background</p> <p>The relation betweeen the structure of discotic molecules and columnar properties, a crucial point for the realization of new advanced materials, is still largely unknown. A paradigmatic case is that hexa-alkyl-thio substituted triphenylenes present mesogenic behavior while the corresponding azatriphenylenes, similar in shape and chemical structure, but with a different core charge distribution, do not form any liquid crystalline mesophase. This study is aimed at investigating, with the help of computer simulations techniques, the effects on phase behaviour of changes of the charge distribution in the discotic core.</p> <p>Results</p> <p>We described the shape and the pair, dispersive and electrostatic, interactions of hexa alkyl triphenylenes by uniaxial Gay-Berne discs with embedded point charges. Gay-Berne parameters were deduced by fitting the dispersive energies obtained from an atomistic molecular dynamics simulation of a small sample of hexa-octyl-thio triphenylene molecules in columnar phase, while a genetic algorithm was used to get a minimal set of point charges that properly reproduces the ab anitio electrostatic potential. We performed Monte Carlo simulations of three molecular models: the pure Gay-Berne disc, used as a reference, the Gay-Berne disc with hexa-thio triphenylene point charges, the Gay-Berne disc with hexa-thio azatriphenylene point charges. The phase diagram of the pure model evidences a rich polymorphism, with isotropic, columnar and crystalline phases at low pressure, and the appearance of nematic phase at higher pressure.</p> <p>Conclusion</p> <p>We found that the intermolecular electrostatic potential among the cores is fundamental in sta-bilizing/destabilizing columnar phases; in particular the triphenylene charge distribution stabilizes the columnar structure, while the azatriphenylene distribution suppresses its formation in favor of the nematic phase. We believe the present model could be successfully employed as the basis for coarse-grained level simulations of a wider class of triphenylene derivatives.</p

    Monte Carlo simulation of the nematic-vapour interface for a Gay-Berne liquid crystal RID E-3129-2010

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    The nematic-vapour interface of the Gay-Berne liquid crystal model has been studied by Monte Carlo simulation. When the anisotropy parameter kappa' is set to 1.25, a film of particles in a rectangular box has been shown to exhibit nematic-vapour coexistence. Analysis of the orientational ordering across the sample reveals that the anchoring is planar, that is, the preferred alignment is in a direction parallel to the interface. No nematic wetting of the film in the isotropic phase is observed, although there is a strong tendency for the molecules near the surface to be parallel to the interface even at temperatures higher than the isotropic-nematic-vapour triple point. (C) 1997 Published by Elsevier Science B.V

    Molecular Organization and Construction of the Fungal Cell Wall

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    Fungal Cell Wall Synthesis and Assembly

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