Thermochromic polymer blends

Context & scaleApproximately 50% of the energy used in building envelopes is dedicated to heating, cooling, and lighting interior spaces. Over 50% of interior overheating in office rooms, automobile interiors, greenhouses, and similar areas is caused by sunlight passing through transparent surfaces like windows. Smart window technology holds significant potential for energy savings while maintaining aesthetics. However, current responsive materials for smart windows either need power to function or suffer from oxidation and durability issues. To address these issues, we propose a three-component, ultra-thin thermochromic polymer film. This polymer blend offers enhanced durability, accessible thermochromic temperature ranges (25°C–35°C), high room temperature transmittance (>85%), and substantial solar modulation (63.5%). In summary, the proposed system introduces a new category of thermochromic smart materials with superior durability and effectiveness compared to existing options.Highlights•A scalable salted polymer blend system that demonstrates excellent thermochromic properties•Thermochromism observed across an accessible temperature window (RT–35°C)•Temperature-dependent transmittance arises from miscibility and phase separation•The thermochromic polymer film exhibits remarkable reversibility and durabilitySummarySmart windows using thermochromic materials provide an excellent thermal management system over broad temperature ranges, leading to significant energy savings. Existing thermochromic materials face challenges, including difficulty in application, degradation during use, and limited durability. Here, we report a simple salted polymer blend system, consisting of poly(dimethylsiloxane), poly(ethylene oxide), and lithium perchlorate, that shows excellent thermochromic properties across an accessible temperature window and remarkable durability. The reversible temperature dependence of optical transmittance of the films arises due to the miscibility of the constituent polymers at room temperature, leading to high transparency, and the gradual phase separation and opaqueness with temperature rise. The easy-to-fabricate, stable polymer system can be a viable and cost-effective alternative to inorganic thermochromic materials such as vanadium dioxide for many applications.Graphical abstract