Director tilting of liquid crystals on photoisomerizable polyimide alignment layers doped with homeotropic surfactant

Abstract

Director tilting of liquid crystal (LC) molecules on photosensitive alignment layers has been investigated. The layers, polyimides with photoisomerizable groups in their main chains, were irradiated with unpolarized near-UV (UPUV) light at oblique incidence. The irradiated film was found to align LC molecules homogeneously with a negligible pretilt angle. It was found that the pretilt angle can be generated successfully by introducing surfactant lecithin and decreasing the incidence angle of the UPUV light. The LC alignment and electro-optical properties of the LC cells with the photoalignment layers were demonstrated to be suitable for twisted nematic LC, vertical alignment LC, and surface-stabilized ferroelectric LC devices.

Photoalignment of liquid crystals: basics and current trends

“…5b shows chain scission reaction of polyimides. † In addition to polyimides, [53][54][55][56][57] polysilanes, 58,59 polystyrene, polyesters and some other aromatic polymers 15 exhibit photoalignment due to the photodestruction.…”

“…They can also be mixed with the photoaligning materials. 57,60,98 Photosensitive fragments of organic photoaligning materials have aromatic groups commonly forming p conjugation with other parts of these fragments that determines the absorption spectrum of the fragments. Therefore, the rate of photodegradation of photoaligning materials is rather sensitive to the structure of these aromatic fragments.…”

Photo-Alignment Technology

“…These groups can be attached as individual side chains [90,91], as terminal groups of photosensitive side chains [72,92] or fragments of main polymer chains. They can also be blended with the photoaligning materials [76,93,94]. The method by which photosensitive fragments are connected to the polymer chain is important.…”

“…The targets of these reactions are normally aromatic fragments of main or side polymer chains. Apart from PIs [17,93,97,98], polysilanes [99,100], polystyrene, polyesters and some other aromatic polymers [101] undergo photoalignment upon photodestruction. Photodestroyable PIs usually have a sufficiently high anchoring energy of 10 −5 J/m 2 [102,103].…”

Materials Stabilized Liquid Crystal Molecules on Chemically Modulated Polystyrene Surface Using Various Ion Beam Exposure Time

“…A rubbed polymer surface includes debris left by cloth, and the generation of electrostatic charges during rubbing induces local defects, streaks, and a grating-like wavy surface due to nonuniform microgrooves that degrade the display resolution. Non-contact alternatives, including ultraviolet (UV) exposure [4,7,8], ion beam (IB) bombardment [3,5,6], and nanoimprinting lithography [9], have been reported. Of these, the UV alignment method exhibits advantages of being a clean process, and having large-scale manufacturing and multidomain capabilities; although UV stability, low anchoring energy, and alignment materials must be considered carefully.…”