Flow-Induced Twist-Compression in a Twisted Nematic Cell

An optical convergent-beam guided-wave technique is used to explore in detail the dynamic flow effects in a twisted nematic cell. During switch-on it is found that the dynamic flow compresses the director twist to regions close to the cell walls. For high fields this twist compression takes the cell far beyond the Mauguin limit and it no longer effectively guides the polarization of the light through the cell. This results in a very fast switch to a transient dark state.

Figure 1

The experimental setup for the convergent beam system.

Figure 2

The dynamic data of $T_{pp}$ after switch-on of an applied electric field to (a) 2.9 V, (b) 4.7 V, and (c) 6.8 V.

Figure 3

Fitted director profiles at different times after switch-on of 6.8-V ac to the cell.

Figure 4

Models using the fitted parameters for the cell of (a) the velocity profile at different times after switch-on of 6.8-V ac to the cell. (b) The relationship between the director twist and the velocity profile at 5 ms.