Alignment and optical properties of retarder film made of photoreactive calamitic liquid crystals

How the alignment and optical properties of liquid crystal polymer (LCP) film, formed by photo-polymerization of reactive LCs, are affected by the alignment layer (AL) structure, the LC-aligning method, and the polymerization conditions has been investigated. It has turned out that the alignment characteristics of LCP film greatly depend on the nature of AL and the polymerization condition and that its optical properties are governed by the degree of the in-plane alignment of LC molecules. In the case of in-air photo-polymerization, a higher intensity of UV irradiation at a fixed exposure dosage has induced the higher degree of polymerization of LCP film and thus the better thermal stability than a lower intensity. The rubbed AL has induced the higher degree of the in-plane alignment, with the tilted optic axis, and subsequently produced the better optical properties. On the other hand, photoalignment has generated the inferior LC alignment, with no tilt of the optic axis, indicating its low capability for aligning LC molecules.