Optical textures of biological liquid crystal: cellulose and gelatin aqueous solutions

Jieh-Wen Tsung^1*, Bo-Hsien Wu¹, Li-Yan Hung¹

¹Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu, Taiwan

* Presenter:Jieh-Wen Tsung, email:jiehwen.tsung@nycu.edu.tw

Cellulose is the main substance found in plant cell walls, which supports the plant, keeping it stiff and strong. Gelatin is derived from collagen, which constructs the skin and bones of animals. Both biological molecules form long chain of crystal-amorphous periodic nano structure, showing structural birefringence. In water, the long chain of nano crystals self-assemble into twisted fibers, showing the optics of chiral nematic liquid crystal (CLC). CLC settles into three kinds of stable states, which are planar, fingerprint, and focal conic domains. Planar texture shows Bragg diffraction, which reflects circularly polarized light when the wavelength is the same as the CLC pitch and when the light and CLC have the same handness. The fingerprint texture is translucent with glitter. The focal conic domains are highly scattering, leading to a hazy paper-like texture. Switching between the metallic/translucent/hazy looks leads to fascinating technologies such as electronic ink, energy-saving smart windows, and colorimetric sensors. The goal of this research is creating the three stable states with biological CLC. The configuration of liquid crystal should be determined by the phases and boundary conditions. With polarized optical microscope, the 3D structure of the twisted fibers are analyzed, and the location of the crystal-amorphous periodic nano structure can be identified. In case of cellulose chiral liquid crystal, planar texture with oily streaks, fingerprint texture embedded in double twisted fibrils, and focal conic domains are identified experimentally. The self-assembled twisted fibrils align and fix the nano crystals. The cellulose chiral liquid crystal shows brilliant stable visible color appearance in room temperature in daylight. Photopolymerized collagen molecules assemble into chiral structures as well. The lithography was performed under a microscope with a micro-LED projector. The pattern was directly projected on the collagen for localized curing. The cured collagen shows birefringence and self-assembled periodical nanostructures. Cellulose and collagen have excellent biocompatibility, biodegradability and bioactivity. Utilizing the metallic/translucent/hazy optical appearance and self-assembled natural photonic crystals, they are excellent for eco-friendly pigments, displays, sensors, and wearable optoelectronics.

Keywords: liquid crystal, photonic crystal, metamaterial, microscopy, sustainable eco-fiendly optoelectronics