Electric and magnetic fields in photoalignment of liquid crystals

• Published in: Journal of the Society for Information Display 2015-05, Vol.23 (5), p.223-231
• Main Authors: Semina, Olga, Dubtsov, Alexander, Shmeliova, Dina, Pasechnik, Sergey, Chigrinov, Vladimir
• Format: Article
• Language: English
• Subjects: azo-dye film; easy axis; electric (magnetic) fields; Glass substrates; light irradiation; Magnetic fields; nematic liquid crystal; photoalignment
• ISSN: 1071-0922; 1938-3657
• DOI: 10.1002/jsid.383

The results of investigation of slow surface dynamics (easy axis gliding), induced by secondary illumination of photoaligned substrates with linearly polarized UV or blue light in the presence of electric (magnetic) fields, are presented for the first time. The initial surface orientation of nematic liquid crystal (NLC) was provided, in accordance with the standard photoalignment technique, via preliminary UV treatment of the glass substrates coated by sulfonic azo‐dye SD1 film. The experiments fulfilled for the two geometries, A and B, corresponding to the normal (A) and parallel (B) orientation of fields relatively to liquid crystal (LC) layer, revealed different effects induced by electric (magnetic) fields. For geometry A, strong electric field applied, in combination with a linearly polarized blue light, to the planar layer in a sandwich‐like LC cell with two photoaligned substrates results in simultaneous reorientation of easy axis on both substrates. It demonstrates the possibility of an azimuthal rotation of monodomain planar samples of LCs. For geometry B, usage of “in‐plane” electric (magnetic) fields in the cell, composed of photoaligned and rubbed substrates, speeds up reorientation process of NLC easy axis respectively to pure light‐induced reorientation. It provides electric control of operating times in previously proposed optical rewritable technology. We studied slow surface dynamics of nematic liquid crystals under secondary UV (blue) light irradiation at photoalignment process in the presence of electric (magnetic) field. It was shown that electric and magnetic fields provide opportunity to reorient the easy axis on both photoaligned substrates, speed up reorientation process, decrease the easy axis disordering and can modify optical rewritable technology.