Zenithal alignment of liquid crystal on homeotropic polyimide film irradiated by ion beam

Abstract

We investigate the pretilt characteristics of a nematic liquid crystal [LC] in terms of ion beam exposure conditions on the homeotropic polyimide alignment layer. The pretilt angle of LCs in the case of high-energy ion beam treatment was decreased considerably almost the same to that of the homogenous alignment layer though we used homeotropic polyimide film at first. Increasing irradiating energy, we could control the pretilt from 90° to 1° with several steps. We believe that this is because the side chain with hydrophobicity in the used polyimide is broken by ion beam exposure. To confirm it, contact angle measurement was carried out. With this result, we can easily control the LC pretilt in the pixel with appropriate exposure conditions which is critical to achieve excellent electrooptic characteristics and good image quality.

The domain mixing effect on the electro-optical properties of liquid crystals using polyimide doped with reactive mesogen

“…Figure 4(a,b) shows the voltage-dependent transmittance characteristics and the threshold voltages of the different LC cells as a function of the RM concentration. The UV light exposure intensity was identically maintained in all the experiments so as to eliminate any difference between the LC cells arising from the decomposition of the PI molecules by the UV light exposure, except for the formation of the LCP microdomains [14]. In the 0-2.5 wt% RM concentration range, the threshold voltage decreased to 2.32 V (from about 2.80 V for the unexposed case with no RM), whereas at above 5.0 wt% it increased monotonically with increasing RM concentration.…”

“…The LC alignment is predominantly governed by surface conditions such as the surface topography and the anchoring energy. Several methods of imposing the surface conditions on the LC alignment, such as polymer stabilization [12,13], ultraviolet (UV) light treatment [14,15], and insertion of an additional layer [16,17], have been suggested to improve the EO performance of LCD. Some of these methods, however, often encounter uniformity issues, such as light leakage in the off-state due to the predefined pretilt of the LC and poor transmittance, while others lead to the poor long-term stability of the LC alignment and the complexity of the fabrication process.…”

Precise local control of liquid crystal pretilt on polymer layers by focused ion beam nanopatterning

“…It is quantitatively characterized by the pretilt angle between the director and the surface plane. Surfaces stabilizing pretilted alignments remain rare and require more complex fabrication techniques such as patterning with nanogrooves [13–15] and nanoslits [16], ion-beam irradiation of specific inorganic [17] and polymer [18] substrates, subjecting of photo-controlled aligning polymers to near-threshold doses of ultraviolet radiation [19], formation of surface microdomains from segregating mixtures of vertically and planar aligning polymers [20–21], or stacking of nanolayers of such polymers [22]. The techniques yield homogeneous pretilt angles sufficient for conventional flat-display applications but are very inconvenient for establishing spatially inhomogeneous states.…”