PNIPAM-based ionic hydrogels for enhanced privacy smart windows and flexible sensor

Abstract

The thermochromic materials are widely used in the smart window field because they can efficiently regulate solar radiation with temperature changes. Currently, most smart windows switch back and forth between opaque and transparent states to control solar radiation, which is very disadvantageous for the visibility of enclosed environments. Herein, in a binary solvent of ethylene glycol-water (EW), we are developing a series of thermoresponsive ion hydrogels suitable for smart windows by in-situ free radical polymerization of the thermoresponsive monomer N-isopropylacrylamide (NIPAM) and ionic monomers (amphiphilic, anionic, cationic). These smart windows exhibit excellent one-way transparency for privacy protection, allowing observation from a relatively dark private space to a public space outside the smart window during the day, while preventing a view from the relatively bright public space into the private space. Furthermore, these hydrogels demonstrate efficient blocking of ultraviolet / near-infrared radiation, low temperature resistance (∼ −40 °C), wide temperature range thermal responsiveness (∼ −25–60 °C), enabling effective regulation of solar heat radiation. Additionally, the anionic-NIPAM complex hydrogel possesses a high diffusion coefficient of water and excellent conductivity of 13.38 mS cm−1, which can be expanded its application in the field of flexible ion-conductive sensors.