Dynamic Refractive Index-Matching for Adaptive Thermoresponsive Smart Windows

Thermoresponsive smart windows (TRSWs) take great advantages in energy-efficient buildings and on-demand devices owing to their self-adaptiveness and external energy consumption-free nature. Currently used TRSWs largely rely on thermal-induced phase transitions in single-material systems, however, the intrinsic characteristics of which may not be suited for practical window utilization, such as poor luminous transparency and fixed critical temperature (T_c ). Herein, an adaptive TRSW based on dynamic refractive index (RI) matching between two phases is demonstrated, which is facilely fabricated by embedding ethylene glycol solution microdroplets into polydimethylsiloxane (PDMS) via a one-step emulsification approach, realizing a smart temperature response in PDMS. The TRSW presents high transparency (≈92%) and bidirectional transparency-temperature response (≈20% at 73 °C, ≈40% at 8 °C). Moreover, the RI dispersion generates a unique effect of wavelength selectivity with temperature. Notably, the effective optical-temperature response with variable T_c could be tuned over a wide range of 13-68 °C by adjusting the EGS concentration. The proposed strategy with dynamic RI matching allows TRSW construction to extend beyond phase transitional materials and greatly broadens the applicable scope of TRSWs, which is promising in the fields of smart optical devices such as smart windows, anti-counterfeiting, optical switches, and optical selection.