Preparation and properties of broadband reflective cholesteric-phase liquid crystal films based on chiral and achiral bilayer structures

Abstract

Cholesteric phase liquid crystal films capable of selectively reflecting incident light over a wide range of wavelengths have significant potential for optical applications. However, the preparation of cholesteric phase liquid crystal films which reflect a wider broadband using simple methods has been a technical challenge. In this study, we have successfully fabricated a bilayer liquid crystal film with chiral and non-chiral layers by simply superimposing a layer of nematic liquid crystals to a cholesteric phase liquid crystal layer. Due to the synergistic effect between the diffusion rate and the polymerization rate of the polymerizable monomer in the bilayer structure, the pitch distribution of the polymerized bilayer liquid crystal film is not uniform, and the final cholesteric-phase liquid crystal film obtained can reflect circularly polarized light over a wide wavelength range of more than 1500 nm. We briefly tested the infrared shielding performance of this bilayer-structured liquid crystal film. The glass with the bilayer structured cholesteric phase liquid crystal film was heated up significantly slower than the unsampled blank glass. The final temperature difference between the two glasses reaches 33 °C within the same irradiation time (10 min). This result indicates that the film has excellent IR reflective properties for IR light. This study not only provides a new strategy for the preparation of cholesteric phase liquid crystal films, but also offers a new idea for the preparation of smart windows with IR shielding properties for optical applications.