Temperature-responsive photonic devices based on cholesteric liquid crystals

Cholesteric liquid crystals (CLCs) are a major class of photonic materials that display selective reflection properties arising from their helical ordering. The temperature response of CLCs, comprising of dynamic reflection color changes upon variation of temperature, can be exploited using material systems consisting of small mesogenic molecules, polymer‐dispersed liquid crystals (PDLCs), polymer‐stabilized liquid crystals (PSLCs), or liquid‐crystalline polymers. Taking advantage of the easy processability and flexibility of the molecular design, these temperature‐responsive CLCs have been fabricated into different forms of photonic devices, including cells, coatings, free‐standing films, and three‐dimensional objects. Temperature‐responsive devices developed from CLCs could be integrated for application in temperature sensors, energy‐saving smart windows, smart labels, actuators, and adding aesthetically pleasing features to common objects. This review summarizes the device capabilities of the different material systems of temperature‐responsive CLCs: small mesogenic molecules, PDLCs, PSLCs, and CLC polymers. For each system, examples of different device forms are presented, with their temperature responsiveness and the underlying mechanisms discussed. Additionally, the potential of each material system for future device applications and product developments is envisioned