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Soft Matter and Biological Physics

Eur. Phys. J. E 4, 435-443

Theoretical investigations of rotational phenomena and dielectric properties in a nematic liquid crystal

A.V. Zakharov and A. Maliniak

Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University, S-10691 Stockholm, Sweden


(Received 22 March 2000 and Received in final form 8 October 2000)

The molecular dynamics (MD) simulation, based on a realistic atom-atom interaction potential, was performed on 4-n-pentyl-4'-cyanobiphenyl (5CB) in the nematic phase. The rotational viscosity coefficients (RVCs) $\gamma_i$, (i = 1,2) and the ratio of the RVCs $\lambda = - \gamma_2/\gamma_1$ were investigated. Furthermore, static and frequency-dependent dielectric constants $\epsilon_{\parallel}$ and $\epsilon_{\perp}$ were calculated using parameters obtained from the MD simulation. Time correlation functions were computed and used to determine the rotational diffusion coefficient, $D_{\perp}$. The RVCs and $\lambda$ were evaluated using the existing statistical-mechanical approach (SMA), based on a rotational diffusion model. The SMA rests on a model in which it is assumed that the reorientation of an individual molecule is a stochastic Brownian motion in a certain potential of mean torque. According to the SMA, $\gamma_i$ are dependent on the orientational order and rotational diffusion coefficients. The former was characterized using: i) orientational distribution function (ODF), and ii) a set of order parameters, both derived from analyses of the MD trajectory. A reasonable agreement between the calculated and experimental values of $\gamma_i$ and $\lambda$ was obtained.

61.30.-v - Liquid crystals.
61.30.Cz - Theory and models of liquid crystal structure.

© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2001