Temperature‐Responsive Photonic Devices Based on Cholesteric Liquid Crystals

• Published in: Advanced photonics research Vol. 2; no. 7
• Main Authors: Zhang, Weixin, Froyen, Arne A. F., Schenning, Albertus P. H. J., Zhou, Guofu, Debije, Michael G., de Haan, Laurens T.
• Format: Journal Article
• Language: English
• Published: Hoboken John Wiley & Sons, Inc 01.07.2021; Wiley-VCH
• Subjects: cholesteric liquid crystals; Crystals; Handedness; Light; Phase transitions; photonic crystals; photonic devices; Polymers; temperature-responsive reflective colors
• ISSN: 2699-9293; 2699-9293
• DOI: 10.1002/adpr.202100016

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 dynamic reflection color changes upon variation of temperature, is 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 are fabricated into different forms of photonic devices, including cells, coatings, free‐standing films, and 3D objects. Temperature‐responsive devices developed from CLCs are integrated for application in temperature sensors, energy‐saving smart windows, smart labels, actuators, and adding aesthetically pleasing features to common objects. Herein, the device capabilities of the different material systems of temperature‐responsive CLCs are summarized: 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. In addition, the potential of each material system for future device applications and product developments is envisioned. Temperature‐responsive cholesteric liquid crystals are an important class of photonic materials that show dynamic reflection properties upon temperature changes. The mechanisms that induce such temperature responses are discussed and related to the different molecular systems. A summary of design strategies, opportunities, challenges, and possible device structures is presented with a focus on photonic applications.