Modulation of an Si-O-Si structure in uniformly photochromic microcapsules for solar heat and daylight management

Abstract

Photochromic microcapsules adjust to sunlight adaptively and using them to fill windows is an attractive option for constructing smart windows that can manage solar heat and daylight. However, fabricating high-durability polymer-composite photochromic microcapsules for use in outdoor glass windows remains challenging, requiring high contrast ratio, high transparency, and low haze. Herein, we synthesized a novel poly(urea-siloxane) shell monomer containing Si-O-Si bonds and successfully prepared a photochromic microcapsule by modulating the mass ratios of shell monomers and emulsifiers. The photochromic poly(urea-siloxane)-based microcapsule-coated glass (PCPUS MCG) showed high luminance transmittance (83.66 %) and low haze (20.31 %). The as-prepared PCPUS MCG exhibited self-adaptive sunlight control without additional energy input, with strong solar modulation ability (Δτsol of 38.30 %). Furthermore, the response indoor air temperature was reduced by approximately 3.7 °C in a field test using a model house equipped with PCPUS MCG windows, showing promising energy-saving potential compared with conventional windows. Therefore, uniform photochromic-microcapsule modification using Si-O-Si bonds warrants attention in future energy-saving window designs.