Hybrid Active–Passive Control of an Unconventional Smart Window Based on Dye‐Doped Dual‐Frequency Liquid Crystal

Abstract

The allure of dual‐frequency liquid crystal (DFLC) stems from its unique feature of the switchable and revertible sign of dielectric anisotropy. In addition to the common frequency‐modulation method, this study focuses on manipulating the dielectric anisotropy in DFLC through change in temperature. Herein, the hybrid control of a dichroic‐dye‐doped DFLC smart window is proposed, which offers a passive‐control function by reacting to the temperature and automatically switching to one of the three distinct transmission levels: the transparent, variably gray (tinted or translucent), and opaque states. In contrast to conventional, passively controlled smart windows that typically exhibit a gray or opaque state at high temperatures and become transparent at low temperatures, the suggested smart window thermally operates in the opposite manner, presenting a unique characteristic that holds significant potential for a wide range of applications. This thermally reverse‐mode smart window allows one to actively control the degree of transparency by applied voltage at various frequencies as well. A parameter termed the “crossover temperature” is introduced as an indicator of the potency for the change in dielectric anisotropy of the DFLC by temperature. The operation scheme of the hybrid electrical‐and‐thermal control for the proposed vertically aligned dye‐doped DFLC smart window is summarized.