Polyelectrolyte complex-based thermochromic hydrogels containing carbonized polymer dots for smart windows with fast response, excellent solar modulation ability, and high durability

Abstract

Thermochromic smart windows have gained increasing popularity in light modulation and energy management in buildings. However, the fabrication of flexible thermochromic smart windows with high luminous transmittance (T_lum), tailorable critical temperature (τ_c), strong solar modulation ability (ΔT_sol), and long-term durability remains a huge challenge. In this study, hydrogel-based thermochromic smart windows are fabricated by sandwiching thermochromic hydrogels of polyallylamine hydrochloride, polyacrylic acid, and carbonized polymer dots (CPDs) complexes between two pieces of transparent substrates. Benefiting from the incorporation of nanosized CPDs, the thermochromic hydrogel has an ultrahigh T_lum of ~98.7%, a desirable τ_c of ~24.2 °C, a ΔT_sol of ~89.3% and a rapid transition time of ~3 s from opaque state to transparent state. Moreover, the thermochromic hydrogel exhibits excellent anti-freezing ability, tight adhesion toward various substrates, and excellent self-healing capability. The self-healing capability enables the fabrication of large-area smart windows by welding multiple hydrogel pieces. The smart windows retain their original thermochromic properties after being stored under ambient conditions for at least 147 days or undergoing 10,000 uninterrupted heating/cooling cycles. The model houses with smart windows can achieve a temperature reduction of 9.2 °C, demonstrating the excellent indoor temperature modulation performance of the smart windows.

Keywords

carbonized polymer dots / polyelectrolyte complexes / smart windows / thermochromic hydrogels

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