A Dye-Free Method To Manufacture LCDs

AsianScientist (Nov. 22, 2017) – In a study published in Science Advances, scientists in Japan have developed a highly precise, dye-free and light-dependent method to produce flexible liquid crystal displays (LCDs).

Current two-dimensional techniques used in the manufacture of LCDs typically involve using polarized light to uniformly irradiate a film that contains photoresponsive dye molecules. The net liquid crystal alignment is thus controlled by the interaction between the dye dipole and the polarization axis of the light. However, strong dyes discolor or degrade the optical and stability properties of the displays. A dye-free method is therefore highly desired in the engineering industry.

At present, only two approaches to dye-free methods have been explored. The first is a two-step alignment method, in which the liquid crystal materials are coated over a very thin dye-containing photoalignment layer and then aligned or fixed by polymerization. The second approach aligns the liquid crystals over a surface topography template through lithography, nanoimprinting, or inkjet techniques, among others. Both methods are costly and time-consuming.

In this study, a research group led by Professor Atsushi Shishido at the Tokyo Institute of Technology used scanning wave photopolymerization to precisely align liquid crystals. The spatial and temporal scanning of focused guided light triggered mass flow resulting in alignment of the liquid crystals with the incident light patterns.

This method generatse arbitrary alignment patterns with fine control over large areas in a wide variety of liquid crystal materials, without the need for strong dyes or additional processing steps. Additionally, the researchers can produce LCDs of unlimited complexity in two dimensions that, in principal, would only be restricted by light diffraction limits.

Scanning wave photopolymerization can be readily introduced into existing photoproduction facilities, allowing for great economic advantages. However, it is currently applicable only to photopolymerizable liquid crystal systems with a thickness below tens of micrometers. The researchers speculate that with some improvement, their technique will be applicable to other material systems, such as nanorods, nanocarbons and proteins.
The article can be found at: Hisano et al. (2017) Scanning Wave Photopolymerization Enables Dye-free Alignment Patterning of Liquid Crystals.

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Source: Tokyo Institute of Technology; Photo: Atsushi Shishido.
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