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Model Studies on the Phase Behavior of 4-cyano-4'-n-pentyloxybiphenyl

Sargin, Saniye Pinar (2000)
Model Studies on the Phase Behavior of 4-cyano-4'-n-pentyloxybiphenyl.
Technische Universität Darmstadt
Ph.D. Thesis, Primary publication

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Item Type: Ph.D. Thesis
Type of entry: Primary publication
Title: Model Studies on the Phase Behavior of 4-cyano-4'-n-pentyloxybiphenyl
Language: English
Referees: Haase, Prof. Dr. W.
Advisors: Brickmann, Prof. Dr. J.
Date: 4 February 2000
Place of Publication: Darmstadt
Date of oral examination: 31 January 2000

The term liquid crystal signifies a state of aggregation that is intermediate between the crystalline solid and the amorphous liquid. A substance in this state is strongly anisotropic in some of its properties and yet shows a certain degree of fluidity, which in some cases is comparable to that of an ordinary liquid. Compounds like 4-cyano-4'-n-alkyloxybiphenyl (nOCB), 4-cyano-4'-n-alkylbiphenyl (nCB), where n stands for the number of carbon atoms in the alkoxy (or in the alkyl) group, are known to be rod-shaped molecules, which have an elongated, anisotropic geometry allowing for prefential alignment along one spatial direction. Computer simulations of molecules like 5OCB with the use of realistic atom potentials are restricted to short simulation times due to the expensiveness of computer time. Therefore, there is a need for the use of less complex models in the Molecular Dynamics (MD) and the Monte Carlo (MC) simulatios of the liquid crystalline systems. The aim of this work is to examine the influence of the force field parameters on the isotropic and the liquid crystalline phase behavior of the model system for 5OCB by means of MD simulation. The representation of the phenyl ring as a sphere, formed by a united atom, the inclusion or the exclusion of the electrostatic interactions, and the treatment of the 5OCB molecule as a semiflexible model or as a rigid body model are the main simplifications carried out in this work. Those simplifications allow a longer simulation time while analyzing the dynamical properties as well as the structural properties of both the isotropic and the liquid crystalline phases for 5OCB as a function of temperature and the density ; such as diffusion coefficient, the orientational order parameter, and the radial, angular, and time correlation functions.

Alternative Abstract:
Alternative AbstractLanguage

Das Ziel der vorliegenden Arbeit bestand in der Untersuchung des Einflusses der Kraftfeld-Parameter auf das Verhalten der isotropen und flüssigkristallinen Phase des Modellsystems 5OCB mit hilfe von MD-Simulationen. Die Phasenabfolge des 5OCB verläuft von der kristallinen über eine nematische zur isotropen Phase. Die Untersuchung des Phasenverhaltens des 5OCBs mit MD-Simulationen unter Berücksichtigung sämtlicher molekularer Freiheitsgrade ist durch den hohen Rechenaufwund auf eine kurze Simulationszeit begrenzt. Deswegen wurde in der hier vorgestellten Arbeit eine Reihe von Vereinfachungen am Modellsystem zur Beschreibung des Phasenverhaltens des 5OCB eingeführt. Dazu zählen die Beschreibung des Phenylrings in Rahmen eines united atom-Ansatzes durch eine Kugel, die Vernachlässigung der elektro- statischen Wechselwirkungen und die Behandlung des 5OCB Moleküls als Starrkörper oder teilflexibles Modell.

URN: urn:nbn:de:tuda-tuprints-323
Classification DDC: 500 Science and mathematics > 540 Chemistry
Divisions: 07 Department of Chemistry
Date Deposited: 17 Oct 2008 09:20
Last Modified: 07 Dec 2012 11:46
URI: https://tuprints.ulb.tu-darmstadt.de/id/eprint/32
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