Tunable thermosensitive smart window based on a surfacetreatment-free, polymer-stabilized cholesteric liquid crystal with a high contrast ratio

Min-Han Lu^1*, Wei Lee²

¹Institute of Lighting and Energy Photonics, College of Photonics, National Yang Ming Chiao Tung University, Tainan, Taiwan
²Institute of Imaging and Biomedical Photonics, College of Photonics, National Yang Ming Chiao Tung University, Tainan, Taiwan

* Presenter:Min-Han Lu, email:p10061203@gmail.com

In view of the growing global awareness of environmental issues, smart windows have emerged as a promising solution to mitigate the rise in indoor temperatures. In this study, we present a smart-window device, which is characterized by a back-and-forth regulation between the smectic- A phase (SmA in the homeotropic state) and the chiral nematic phase (N* in the focal conic state) of a polymer-stabilized cholesteric liquid crystal (PSCLC). The incorporation of a temperature-sensitive dimer (CB7CB), possessing a symmetric bend molecular shape, enabled the attainment of a controlled gray-scale decrease in transmission with increasing temperature. The employment of an applied voltage pulse addressed the prevalent issue of temperature hysteresis in the PSCLC. The PSCLC was further doped with a black dye, resulting in a significant enhancement of the contrast ratio from 29 to 4820—a more than 160-fold increase. Our material system demonstrated a significant distinction between the transparent SmA and opaque N* states without surface orientation treatment. The experimental results can pave the way for the development of innovative and energy-efficient applications in smart windows.

Keywords: Polymer-Stabilized Cholesteric Liquid Crystal, Photopolymerization, Smart Window