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

• Main Author: Sargin, Saniye Pinar
• Format: Others
• Language: English; en
• Published: 2000
• Online Access: http://tuprints.ulb.tu-darmstadt.de/32/1/PTez1son.pdf; Sargin, Saniye Pinar <http://tuprints.ulb.tu-darmstadt.de/view/person/Sargin=3ASaniye_Pinar=3A=3A.html> : Model Studies on the Phase Behavior of 4-cyano-4'-n-pentyloxybiphenyl. [Online-Edition] Technische Universität, Darmstadt [Ph.D. Thesis], (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.