Study on the effect of positive nematic liquid crystalline physical parameters on EHD properties

Abstract

ABSTRACT The paper investigated the effects of viscous, elastic and dielectric parameters on the EHD performance of a positive nematic liquid crystal 5CB using CFD (CFD stands for Computational Fluid Dynamics) method. The governing equations including the continuity, momentum and angular momentum equation are presented. The constitutive equations for viscoelastic deformation and shear stress were established based on the L-E and O-F theories. The variables of micro-flow velocity, 5CB molecular director angular velocity, etc were chosen as the EHD (EHD is the abbreviation for electrohydrodynamic dynamics) feature quantities. The application of a DC electric field can cause continuous stable micro-flow in LC cell. The magnitude and direction of micro-flow are coupled with the angular velocity of the 5CB directors and are also influenced by viscoelastic parameters. The relaxation time is inversely proportional to the electric field intensity and dielectric parameters, proportional to the viscous parameters, and independent of the elastic parameters. Using the micro-PIV experiments, the numerical simulation results were tested. A stable approximate antisymmetric ‘S’ type flow profile was obtained in the 5CB cell which is in good agreement with the simulation result. The conclusions can lay a theoretical foundation for further study and application of liquid crystalline microfluidic driving methods.