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The relation between the transition temperature of typical nematic liquid crystal mixtures and the dynamic properties of twisted nematic (TN) cells are presented. The extrapolated response time at nematic-isotropic transition temperature is of use as a relative response time in the comparison of liquid crystal materials with each other. The glass transition temperature of liquid crystal mixtures is one of the best indicators of the dynamic properties of TN-cells. The linear relation between the reciprocal ATg and the logarithm of the reciprocal response time led us to believe that we could improve the response time of TN-cells by producing liquid crystal materials with lower Tg's. We assumed that the lower limit for the response time of TN-cells at 25°C is about 10-20 rns from the above relation.

The critical conditions governing twist domain generation in twisted nematic cells was investigated theoretically with respect to chiral additives and pretilt angles. It was found that a critical margin twist angle (δc) was greatly affected by even a small change in the size of a pretilt angle. The theoretical analysis was supported by the results of experiments that were carried out with various combinations of cell materials, for example, rubbed organic films and organic sealants. This investigation proved that pretilt angle measurement is a useful means of selecting the combination of materials that will result in completely domain-free twisted nematic cells.

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