Phase‐Changing Sodium Carboxymethylcellulose‐As An Electrolyte for Electro‐Thermochromic Smart Window with Synergistic Optical Modulation

Abstract Smart windows are gaining attention for their exceptional ability to regulate light and heat dynamics effectively. The main objective of developing dual‐responsive smart window materials lies in enhancing building applications and optimizing energy efficiency. Materials that exhibit dual responsiveness have already been reported in the literature. However, these materials have not garnered substantial research interest primarily due to prevailing economic and technological constraints. This study introduces a new methodology that uses a phase‐changing material as an electrolyte to design and customize smart windows based on individual preferences and requirements. In this paper, carboxymethyl cellulose sodium salt‐grafted copolymerpoly(2‐(dimethylamino) ethyl methacrylate)‐(N‐isopropylacrylamide)[CMC‐Na‐pDN] as an electrolyte and 1,1'‐Bis(2‐hydroxyethyl)‐4'4'‐dipyridinium hexafluorophosphate [HOEV] as a chromophore are synthesized and used to fabricate a gel‐based electro/thermochromic device (ETD). ETD exhibits dual‐chromism characteristics, transitioning from a colorless state to a purplehue at 25°C when 2V is applied. Furthermore, the purple color undergoes a transformation to blue coloration when the temperature exceeds 40°C. These phenomena arise due to the synergistic effect between its electrochromicreaction and thermochromic behavior. The ETD device exhibits a high optical constrast ∼82.5%, with a coloration efficiency (CE) of 333.1 cm 2 C −1 and cyclic stability of >2000 cycles.