Broadband Light Management with Thermochromic Hydrogel Microparticles for Smart Windows

Control of solar transmission through windows promises to reduce building energy consumption. However, the ability of current chromogenic technologies to regulate solar gain with the tunable extinction of phase-change materials is still far from optimum. We report a strategy for optimizing the transmittance modulation range of temperature-responsive hydrogel particles by means of tuning the light-scattering behaviors through controlling particle size and internal structure. An emerging thermochromic material, poly(N-isopropylacrylamide)-2-aminoethylmethacrylate hydrochloride (pNIPAm-AEMA) microparticles, was synthesized to demonstrate this strategy. The average size of pNIPAm-AEMA microparticles varies from 1,388 nm at 25 degrees C to 546 nm at 35 degrees C, contributing to an unprecedented infrared transmittance modulation of 75.6%. A high luminous transmittance of 87.2% at 25 degrees C had also been accomplished. An investigation of the tunable scattering behaviors of pNIPAm-AEMA particles provided mechanistic insight into light management by this class of materials, the application field of which is beyond energy-saving smart windows.