A Method for Determination of Rotational Viscosity and Pretilt Angle from Transient Current in Twisted Nematic Liquid Crystal Cells

Abstract

A method for the determination of rotational viscosity γ1 and pretilt angle θ° in twisted nematic liquid crystal cells is proposed. The method is based on the analysis of transient current of a cell excited by a dc voltage pulse. The accuracy of γ1 and θ° values determined by the method is demonstrated by means of numerical calculation of exact basic equations. Experimental results for a ZLI2293 (Merck) cell are presented, and the γ1 values obtained are found to be in excellent agreement with values in the literature.

Evidence of nanodiamond-self-assembly in a liquid crystal, and the consequent impacts on the liquid crystal properties

“…The rotational viscosity for the nematic samples was obtained by measuring the transient current induced by a DC field across the planar-aligned cell configuration. [41][42][43] When a DC field (much higher than the threshold field) is applied across a planar LC cell, the induced transient current I(t) through the cell shows a time response as the nematic director undergoes planar to homeotropic orientational transition. The transient current response is given by [41][42][43] …”

“…This method is one of the most accurate methods to measure γ 1 and θ o . 43 Figure 3(a) represents γ 1 as a function of temperature for pure E7 and E7+ND hybrids, listed in the legend. Similarly, Figure 3(b) shows θ o as a function of temperature for pure E7 and E7+ND hybrids.…”

Novel Pretilt Angle Measurement Method for Twisted-Nematic Liquid-Crystal Cells by Apparent Retardation Measurement

“…Imai et al proposed the method of measuring the pretilt angle of the TN cell by analyzing the transient current profile. 6) Using this method, the pretilt angle and rotational viscosity can be evaluated from the peak value and the delay time of the transient current peak. However, it is generally difficult to measure the correct transient current profile of the TN LCD panel when applying very high voltage.…”

Technique for Local Pretilt Measurement in Nematic Liquid Crystals

“…The precision of this technique is significantly lower and still depends on the pretilt uniformity. The recently proposed transient current technique [12][13][14] enables the direct pretilt measurement in strongly distorted (e.g. twisted nematic) cells, giving the average pretilt angle in the pixel.…”

“…For uniform and well reproducible alignments it is less precise than some other techniques. 7,8,10) The proposed technique cannot be applied for strongly twisted cells, where only transient current [12][13][14] and capacitive 6) measurements are reliable. However, our technique presents also several advantages.…”