Pretilt angle measurement

Figure 5.11 Schematic diagram of the crystal rotation method of pretilt angle measurement.

Several works on the temperature dependence of pretilt angles have been reported. For example, Bouchiat and Langevin-Cruchon 2 have measured pretilt angles at the free surface of MBBA as a function of temperature. The theoretical study of this dependence at the free surface has been given by Parsons. 3 xhe temperature dependence of the pretilt angle at the interface between glass plates and LC films was obtained first by Kahn with twisted nematic samples and then by Toda et al.l5 with non-twisted ones. 

In this paper, we describe the measurement of the temperature dependence of the pretilts for twisted as well as non-twisted nematic samples, using some conventional nematic LCs. In order to have a unified understanding of the temperature dependence of the pretilts of the different samples, an adequate normalization of both the pretilts and the nematic temperature range has been made. Then the differences in the changes of the temperature-dependent pretilt angles between non-twisted and twisted samples were compared. 

In order to compare the temperature dependence of the pretilt angle for the twisted and the non-twisted samples, twisted cells were made using the same treated glass plates which had been used for the measurements by the MCN method. Thus, as soon as the temperature dependence of the pretilt angle for the non-twisted cell was measured, the cell was taken apart, rinsed with an organic solvent to remove LC, and dried, then the twisted cell was reassembled. 

In order to compare the non-twisted and twisted sample, pretilt angles in all samples are normalized by the angle at the temperature of 30 C as shown in Fig. 7. The temperature dependence of all measured values could almost be fit to a single curve. 

The temperature dependence of pretilt angles, showing the lack of influence of the organic solvent. This measurement was performed three times for the non-twisted samples. 

D. Subacius, V. M. Pergamenshchik, and O. D. Lavrentovicha, Measurement of polar anchoring coefficient for nematic cell with high pretilt angle, Appl. Phys. Lett. 67 (2), 214 (1995)... 

M.-P. Cuminal and M. Brunet, A technique for measurement of pretilt angles arising from alignment layers, Liq. Cryst., 22, 185 (1997). 

Accordingly, the following new sections have been added elastic deformation of liquid crystals in Chapter 1, polarisation conversion with narrow and broadband quarter-wave plates in Chapter 3, and measurement of anchoring strength and pretilt angle in Chapter 5. 

To observe chemical changes in the rubbed surface, Lee and Paek measured the polarity of a rubbed surface by using water contact angle measurements, and discussed a correlation between the pretilt angle and the polarity of the rubbed surface [44,62]. The measurement method is illustrated in Fig. 2.2. 

It is known that memory angle depends on surface pretilt angle. The temperature dependences of the memory angles of the CIU and C2U states were measured for all cells, and are shown in Figs 5.1.17(a)-(c). The solid lines represent the... 

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