Enhanced solar modulation ability of smart windows based on hydroxypropyl cellulose mixed with nonionic surfactants

Thermo-responsive smart windows have attracted considerable attention due to their solar modulation ability and energy-saving performances. Researchers focus on ionic surfactants to adjust the lower critical solution temperatures (LCSTs). However, few researchers explored the effect and mechanism of nonionic surfactants. Hydroxypropyl cellulose (HPC) is an excellent thermo-responsive candidate for smart windows due to its nontoxicity and zero energy input. Herein, the effect of nonionic surfactants on HPC optical properties was investigated. The solar spectrum transmittance was evaluated as a function of nonionic surfactant types and concentrations. The addition of polyvinylpyrrolidone (PVP) significantly improved solar modulation ability(ΔT_sol). The enhancement was due to the formation of larger aggregates of HPC and PVP molecules. The optimal PVP loading was 1.5 wt%, which resulted in a 69.75% ΔT_sol improvement and a 1.35 °C reduction in the LCST compared with pure HPC solution. PVP would serve as a cost-effective additive to improve HPC optical properties. Heating conditions also made contributions to HPC phase separation. The energy-saving experiment verified a 4.89 °C reduction in room temperature, which confirmed the energy-saving performance. This research explains the relationship between HPC and nonionic surfactants and extends the application of HPC to smart windows.