Optically Bistable Switching Glazing Achieved by Memory Function of Grafted Hydrogels.

Active switching glazings driven by electrical energy have been widely used for the on-demand control of the optical transmittance of smart windows; however, continuous electrical energy consumption is necessary to maintain the optical state. In this work, to minimize the energy consumption during operation of switchable windows, we have developed an optically bistable switching glazing based on the memory function in the volume change of the hydrogels. By grafting a multicomponent copolymer that has a chemical composition gradient of three different monomers onto the methyl cellulose backbone, the prepared hydrogel exhibits a smooth transition during heating and a large thermal hysteresis in the swelling behavior during cooling. On the basis of the novel thermal behavior of the triangular shape in volume phase transitions, an optically bistable window capable of retaining a switched state as well as stepwise activation, depending on the applied current, can be prepared. The developed bistable glazing is expected to provide energy-saving devices for on-demand solar control and variation in visibility.