Unravelling the Governing Factors for Cholesteric Self-Assembly of Polysaccharides

Thanks to their earth abundance and their ability to self-assemble in photonic crystals that can selectively reflect circularly polarized light, cholesteric polysaccharides have been investigated as the basis for colorimetric sensors responding to humidity, pressure, temperature, and other stimuli. However, cholesteric self-assembly requires a gel-like state, achieved by suspending the biopolymer in a strongly hydrogen-bonding solvent. Efforts to stabilize the cholesteric order in the solid-state have relied on controlled solvent evaporation or polymerization. However, the effects of polysaccharide chemistry and solvent-polymer interaction on the formation and solid-state retention of the cholesteric phase remain understudied. In this talk, we explain how different thermodynamic and chemical factors influence the self-assembly and optical properties of cholesteric mesophases constructed from suspensions of polysaccharides, such as cellulose ethers. Through a systematic data analysis framework we developed, we elucidate structure-property relationships linking solubility, viscosity, and hydrogen bonding to the cholesteric pitch and resulting optical properties. Then, we discuss how chemical factors such as molecular weight and repeat-unit chemistry affect kinetics of liquid-crystalline self-assembly and stabilization of the cholesteric order in a solid form. These relationships are expected to assist in the large-scale deployment of polysaccharide-based sensors with direct colorimetric assessment of temperature, mechanical strain, or humidity.