Electrically controllable and thermally responsive liquid-crystal smart window

Guan-Fu Sung^1*, Po-Chang Wu¹, Wei Lee²

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

* Presenter:Guan-Fu Sung, email:grant.sung418@gmail.com

Cholesteric liquid crystals (CLCs) are important for display and sensing due to their optical and dielectric anisotropy that is susceptible to stimuli such as the electric field and temperature. A CLC in the periodically helical structure is characterized by the selective reflection following Bragg’s law. Although CLCs are promising in window applications, virtually all suggested mechanisms can allow to operate only either actively or passively. In the case of recently suggested thermo- or photo-sensitive CLCs for the employment of smart windows, there exists a serious weakness of lacking human-based consideration for a habitant living in a specific climate zone. In this work, an intriguing dual-mode CLC device was manifested, enabling the transparency to be automatically adjustable in response to the temperature while simultaneously allowing a user to take the control in its automation and for fully on-demand function. The principle originates in the voltage-controllable extent of the electrohydrodynamic (EHD) effect in CLC, causing temperature-dependent dynamic scattering and, in turn, the transmission switchable and tunable by the frequency and amplitude of applied voltage. The characteristic Bragg reflection band designated to occur in the near-infrared region offers a value-added benefit to partially reject the undesired thermal radiation in the transparent state.

Keywords: Smart window, Liquid crystal, Electrohydrodynamic effect, Bragg's reflection