Surface alignment of liquid crystal multilayers evaporated on photoaligned polyimide film observed by surface profiler

Abstract

The investigation of the surface alignment of liquid crystal (LC) multilayers evaporated on photoaligned polyimide vertical alignment (PI-VA) film was carried out by means of the novel three-dimensional (3D) surface profiler. We report the first use of the surface profiler to visualize a microscopic image of the monolayer arrangement of LC molecules in contact with the surface of photo-treated PI-VA film. The photoinduced anisotropy of partially UV-exposed PI-VA film can be visualized as a topological image of LC multilayers. It seems that the topology of LC multilayers is indicating the orientational distribution of LC molecules on the treated film. It was found that the periodically photoaligned PI-VA film surface can align an adsorbed LC monolayer and the LC molecular alignment can be extended to the bulk via the epitaxylike LC-LC interaction, i.e. a short-range molecular interaction. With regard to the unexposed PI-VA film surface, noticeable anisotropy in the monolayer alignment was not observed, indicating that the long-range elastic interaction may be responsible for the bulk alignment. The appearance of small droplets in the masked region may be presumably related to the dewetting phenomena. q

Investigation of the liquid crystal alignment layer: effect on electrical properties

“…Indeed, the capacitance values C 0 and C 1 are of the order of nF and µF, respectively, which is in agreement with the literature [1][2][3]. This is also the case for the high resistance values (order of magnitude of MHz).…”

“…In a liquid crystal device (LCD), polymer layers play an important role in molecular alignment and charge injection [1,2]. It is known that the dielectric anisotropy of nematic liquid crystals (NLCs) plays an important role in the application of the electrical effect to display devices [3].…”

Semi-Alicyclic Polyimides: Insights into Optical Properties and Morphology Patterning Approaches for Advanced Technologies

“…One possibility is that alignment is induced by grooves formed mechanically on the polymer surface by the rubbing process [65]. An alternative concept is that alignment acts through the van der Waals interactions between LC molecules and the polymer molecules, since rubbing causes the anisotropic orientation of the polymer molecules [66][67][68]. In this context, there are fewer studied aspects, such as the nature and the texture of the fabric fiber and the polymer surface hardness, which are factors that have to be considered in explaining the LC alignment.…”

Synthesis and Study of Copolymers Bearing Two Coumarin Side Groups in Monomer Unit: Toward Photoalignment of Liquid Crystals

“…[59,60] These photosensitive species exhibit angularly dependent absorption of linearly polarized light and are able to create an anisotropic surface. [61][62][63] Each type of photoactive polymers has some advantages and disadvantages, but as a whole, photo-crosslinked polymers based on the photodimerization have now emerged as the most relevant one for applications, combining good photoalignment behaviors of LCs in terms of high anchoring energy and controllable pretilt angles as well as excellent thermal and optical stability. It is worth mentioning that one of the two commercial photoalignment materials is the polyvinylcinnamate (PVC) sold by Rolic (Switzerland).…”