Flow modelling and rheological characterization of nematic liquid crystals between concentric cylinders

Abstract

Liquid crystals (LCs) have good load-bearing properties and the ability to lower friction, wear and temperature between rubbing surfaces. The steady flow of thermotropic flow-aligning nematic liquid crystalline materials was studied numerically between two concentric cylinders with small gap sizes. The rheological behaviour and flow characterisation of LCs for different inner cylinder rotational velocities and anchoring angles at the boundaries were also investigated. The Leslie–Ericksen theory was implemented to model the LC microstructures. Continuity and momentum equations were simultaneously solved with the microstructure equation. Considering the nature of the governing equations for LCs, the relaxation method was selected to solve this set of nonlinear ordinary differential equations (ODEs). The orientation angle distribution and apparent viscosity were presented as a function of the rotational velocity and shear rate. Rheological characterisation of N-(4-Methoxybenzylidene)-4-butylaniline (MBBA) was performed using a rotary rheometer and the results were compared with those of numerical simulations. Furthermore, it was shown that the preferred orientation of the molecules of liquid crystalline materials in vicinity of solid surfaces gives them an advantage over isotropic Newtonian fluids by reducing the amount of resistance torque on the inner cylinder.