Bidirectional Temperature-Responsive Thermochromic Hydrogels With Adjustable Light Transmission Interval for Smart Windows

Abstract

Thermochromic smart windows have been widely developed for solar regulation to save building energy. However, most current smart windows still exhibit a single responsiveness to a specific temperature, which is not conducive to daytime energy saving or nighttime privacy protection. Herein, a low-temperature response is achieved by pre-initiation of the monomer acrylamide (AAm) and acrylic acid (AA) in the synthesis of P(AAm-co-AA). Then, N-isopropyl acrylamide and AAm are introduced into P(AAm-co-AA) to form a pre-polymerized precursor solution. The liquid precursor solution can be encapsulated within two quartz glasses and synthesized in situ to prepare smart windows, which exhibit a high visible light transmittance of 84.4%, excellent solar modulation of 69.5%, and bidirectional temperature responsiveness (cold and hot). In addition, the upper critical solution temperature and the lower critical solution temperature of the hydrogel and the light transmission interval between the two temperatures can be flexibly adjusted to adapt to different climates and individual user needs. The designed smart window maintains a high light transmission within the human body's comfort temperature range. The bidirectional temperature response window achieves the dual functions of energy saving and privacy protection, making it an ideal smart window candidate with good prospects for practical applications.