Liquid-crystal twist cell dynamics with backflow

Abstract

We describe and present results of a numerical method we have used to solve the hydrodynamic equations with negligible rates of change of momentum and angular momentum, but without other approximations, in a liquid‐crystal twist cell. We verify that the ’’bounce’’ in transmission of normally incident light that is observed when the electric potential across the cell is turned off is an effect of shear flow (backflow) which causes temporary reverse rotation of directors in the middle of the cell. It is not an inertial effect. Inertial effects would have transient times much shorter than the times associated with the optical bounce. When fluid flow is omitted, as in our previous papers, molecules do not tilt backward and the ’’optical bounce’’ occurs only for light that is obliquely incident in one quadrant. A qualitative explanation of the optics of the bounce is given, in addition to numerical results.