Modern Problems of the Physics of Liquid Systems by Leonid A. Bulavin & Limei Xu

Author:Leonid A. Bulavin & Limei Xu
Language: eng
Format: epub
ISBN: 9783030217556
Publisher: Springer International Publishing

Another photoinduced alignment mechanism involves breaking polyimide chains with UV light [46]. Initially, the PI chains are randomly oriented in the plane of the film. Upon UV irradiation, the PI chains that are parallel to the UV polarization decompose. The remaining chains oriented perpendicular to the polarization of light remain intact. Thus, the direction of LC alignment due to van der Waals forces is parallel to the maximum density of unbroken polyimide chains [26]. One of the major limitation of photodegradation is the small value of the orientational order parameter, its accurate control and high sensitivity to UV exposure time (Fig. 7.7) [26, 144]. Additionally, the by-products may contaminate the system by reducing the thermal stability of the alignment layer, producing ions that may cause image sticking or flickers [156, 166].

Fig. 7.7Order parameter of LC cells as a function of UV exposure time.

Adapted from [144]. Copyright (2001) Elsevier

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