A Simple Method to Measure Pretilt Angles of Inverse Twisted Nematic Liquid Crystal Cells

Abstract

We have developed a simple optical method based on measurements of phase retardation[1] versus out-of-plane cell rotation angle and data analyzed by extended Jones matrix method to obtain pretilt angles of inverse twisted nematic (ITN) and tilted homeotropic liquid crystal (LC) cells. In our Jones-matrix calculations, we have assumed a constant pretilt angle as the LC-director tilt angles throughout the ITN cell as well as the tilted homeotropic cell. We have compared the measured pretilt angles of the ITN cell with those of an accompanying tilted homeotropic (ATH) cell. The results showed increasing discrepancies between them with increasing rubbing depth for LC alignments. However, these discrepancies could be explained by assuming that the surface-LC tilt angle of the ITN cell was equal to the measured pretilt angle of the ATH cell to generate a convex-type LC-director-deformation profile within the ITN cell based on Oseen-Frank elastic continuum theory with infinite anchoring energies. The average of the LC-director tilt angles over this profile was equivalent to the measured pretilt angle of the ITN cell.

P‐121: Electro‐Optical Properties of Inverse Twisted Nematic Cells with Different Pretilt Angles

“…We changed the rubbing depth on the rubbing cloth to vary the pretilt angles of ITN cells. We have measured the phase retardation versus out-of-plane cell rotation angle and data analyzed by extended Jones matrix method to obtain pretilt angles of ITN cells [6]. Two substrates with rubbing directions perpendicular to each other were assembled into ITN cells by using ball spacers of average diameter at 9 μm.…”

“…In this paper, we report the E-O effects by controlling pretilt angles of ITN cells from 89° ~ 83° measured from cell substrates by increasing the rubbing depth after the rubbing cloth touches the polyimide (PI) alignment film. The pretilt angles of ITN cells were measured by an out-of-plane crystalrotation method and fitting the data with calculated results by extended Jones matrix method [6]. We have investigated the E-O characteristics of ITN LC cells within stated range of pretilt angles.…”