Photoalignment of nematic liquid crystal on polyamic‐acid‐based soluble polyimide with no side fragments

Abstract

Abstract— The photoalignment of nematic LC on a layer of newly synthesized UV‐sensitive polyimide without side fragments is reported. The photoaligning polymer advantageously differs from other photoaligning materials because of its extremely low sticking effect and residual DC voltage. These parameters, as well as the UV and thermal stability of the alignment, are not worse than those of rubbed polyimides. At the same time, the new material possesses all the advantages of photoaligning polymers.

Photoalignment of liquid crystals: basics and current trends

“…The essential advance in development of these materials with low sticking has been claimed recently. 86 Comparison analysis shows that the photo-crosslinking materials demonstrate the best industrial prospect. They may combine rather good photosensitivity and high resistance of LC alignment to heat and light, because of irreversible photochemistry and strongly restricted molecular motions.…”

Preparation and characterization of photo‐decomposable ester‐containing semi‐alicyclic polyimide alignment layers for potential applications in in‐plane switching thin‐film transistor liquid crystal display devices

“…The LC molecules exhibited quite low θ p values of 0.09° for PI‐I a , 0.12° for PI‐I b , and 0.15° for PI‐II a , respectively. These values were comparable or a bit lower than that of the PI (CBDA‐DDM) alignment layer 51 . It has been proven that the photo‐cleavable photoaligning PIs without movable fragments; that is the rigid backbone PI materials are of great potential interest in practical applications due to the afforded low θ p values close to 0 51 .…”

“…The measured VHR and RDC features of the LC minicells at a measurement temperature of 25°C are shown in Figures 9 and 10 respectively, as a function of the frame period and the results are given in Table 2. It has been well‐established that the VHR feature of one LC cell depends on various materials and display parameters, including the DI, dielectric constant, residual ionic conductivity, and the polarity of LC materials, as well as on the ion‐adsorption capacity of the PI alignment layers 51 . Many methodologies for achieving the high VHR values for the TFT‐LCD cells have been proposed, including the high volume resistivity of the LC and the PI alignment layers, minimal diffusion of ionic impurities from the sealant resin into the LC layer, avoidance of functional groups, such as lone pairs or strongly π‐conjugated links in LC molecules and alignment layers, and effective removal of residual ionic impurities from TFT substrates and PI alignment layers.…”

“…51 It has been proven that the photo-cleavable photoaligning PIs without movable fragments; that is the rigid backbone PI materials are of great potential interest in practical applications due to the afforded low θ p values close to 0. 51 From this point, the currently developed PI alignment layers possessing rigid-rod ester linkages might be promising candidates as alignment components. PI-II a exhibit a bit higher θ p value in the series, which might be due to the pendant movable methyl groups in the structures.…”

“…These values were comparable or a bit lower than that of the PI (CBDA-DDM) alignment layer. 51 It has been proven that the photo-cleavable photoaligning PIs without movable fragments; that is the rigid backbone PI materials are of great potential interest in practical applications due to the afforded low θ p values close to 0. 51 From this point, the currently developed PI alignment layers possessing rigid-rod ester linkages might be promising candidates as alignment components.…”