Temperature-responsive ‘cloud’ with controllable self-assembled particle size for smart window application

Abstract

The thermochromic material for smart window applications should simultaneously have the following comprehensive properties, namely, high visible light transmittance, low near-infrared (NIR) light transmittance, easy fluidity during casting, comfortable low phase transition temperature for the human body, and stability above the phase transition temperature. However, these performance requirements are difficult to meet simultaneously. We report a strategy for achieving the above performances simultaneously using controllable self-assembled particles from a thermochromic graft copolymer solution. By oxidoreduction (REDOX) between persulfate and hydroxyl groups on the glucose unit of sodium carboxymethyl cellulose (CMC), the thermochromic copolymer poly (2-(dimethylamino) ethyl methacrylate)-(N-isopropylacrylamide) (pDN) were grafted to CMC to prepare a target thermochromic copolymer of C-g-pDN. Owing to the introduction of positively charged ions, the self-assembled particles of C-g-pDN had a size ranging from 200 to 20,000 nm. Among them, the particle size of 248 to 4774 nm accounted for 80.1%, which is equivalent to the wide band of NIR light. On the basis of the ingenious structure of C-g-pDN, an ultralow NIR light transmittance (0.8%) above LCST and an ultrahigh luminous transmittance (95.7%) at 20 °C were realized. Also, the smart windows containing C-g-pDN have excellent luminous modulation up to 95.7%. At the same time, the smart windows were illuminated with infrared and xenon lamps. The results showed that the smart windows have excellent scattering performance to both NIR light and sunlight and can effectively reduce the indoor temperature to the human body's comfortable temperature, and do not affect the normal indoor lighting.