Abstract
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.
Highlights
Cholesteric liquid crystals (CLCs) are a major class of photonic materials that of solar light: many wavelengths are invisidisplay 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), polymerstabilized liquid crystals (PSLCs), or liquid-crystalline polymers
This Review presents an overview of recent developments in temperature-responsive CLC devices using small mesogenic molecules, PSLC, PDLC, and polymeric CLC systems
Summary
Electromagnetic waves of different wavelengths are perceived by most eyes as different colors; this perception is ubiquitous to daily life as humans rely on light for visual recognition of objects, reception of signals, and appreciation of aesthetics. An alternative configuration is the polymer-dispersed liquid crystal (PDLC) system, in which the LC phase is encapsulated within a nonmesogenic polymer binder.[49] Small mesogenic molecules, PSLCs, PDLCs, and polymers of CLC systems each have their own unique features related to working mechanisms and resulting temperature responses, suggesting different application suitability. This Review presents an overview of recent developments in temperature-responsive CLC devices using small mesogenic molecules, PSLC, PDLC, and polymeric CLC systems. Alternative systems with optical responses including complete loss of reflectivity and/or diffraction effects are outside the scope of this Review
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