Issue 1, 2019

Shear flow simulations of smectic liquid crystals based on the Gay–Berne fluid and the soft sphere string-fluid

Abstract

We have studied the shear flow of the smectic A phase of three coarse grained liquid crystal model systems, namely two versions of the Gay–Berne fluid and the soft sphere string-fluid. At low shear rates, the orientation where the smectic layers are parallel to the shear plane and the orientation parallel to the vorticity plane are both stable in all the systems. In one of the Gay–Berne fluids, there is a transition from the orientation parallel to the shear plane to the orientation parallel to the vorticity plane. At higher shear rates, a nonequilibrium nematic phase is obtained in all the systems in the same way as in linear alkanes under shear. If the initial configuration is an equilibrium smectic A phase or a nematic phase with the molecules parallel to the streamlines, the orientation parallel to the shear plane is attained at low shear rates in the Gay–Berne fluids. In order to analyze the stability of the different orientations, the torque acting on the liquid crystal is calculated. It consists of an elastic torque caused by deformations due to the shape of the simulation cell and the periodic boundary conditions and a shear-induced torque. The elastic torque stabilizes both the orientation parallel to the shear plane and the orientation parallel to the vorticity plane because the liquid crystal is deformed if it is turned away from these orientations. The shear-induced torque, on the other hand, always turns the liquid crystal to the orientation parallel to the vorticity plane where the viscosity and the irreversible energy dissipation rate are minimal. Since the latter torque is proportional to the square of the shear rate, rather high shear rates are required for it to overwhelm the elastic torque. However, the elastic torque decreases with the system size so that it is likely that the shear-induced torque will dominate in large systems and that the orientation parallel to the vorticity plane will be attained at low or even zero shear rate.

Graphical abstract: Shear flow simulations of smectic liquid crystals based on the Gay–Berne fluid and the soft sphere string-fluid

Article information

Article type
Paper
Submitted
09 Aug 2018
Accepted
26 Nov 2018
First published
26 Nov 2018

Phys. Chem. Chem. Phys., 2019,21, 292-305

Shear flow simulations of smectic liquid crystals based on the Gay–Berne fluid and the soft sphere string-fluid

S. Sarman, Y. Wang and A. Laaksonen, Phys. Chem. Chem. Phys., 2019, 21, 292 DOI: 10.1039/C8CP05077E

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements