Modulating thermochromic properties of thermally adaptive PNIPAM hydrogels for energy-saving smart windows

Organic polymers, especially poly-N-isopropylacrylamide (PNIPAM), have gradually become an emerging material choice for thermally changing intelligent windows because of their advantages such as low critical solution temperature (LCST), phase transition behavior, easy synthesis, low cost, and adjustable optical properties. This study focuses on modifying PNIPAM thermochromic hydrogels by incorporating hydroxypropyl cellulose (HPC) and polyacrylamide (PAM) to enhance their phase transition behavior, mechanical properties, and thermal responsiveness. Different compositions of PNIPAM-HPC and PNIPAM-PAM hydrogels were synthesized via free radical polymerization, and their properties were systematically analyzed. Experimental results reveal that PAM makes the window much more difficult to create a transition into visual opaque position. Additionally, HPC is beneficial to make the windows transit easier, but not really for recyclable and reversible use. The study further identifies key research directions, including enhancement of cycling stability and integration with photothermal nanomaterials to boost responsiveness, paving the way for the development of advanced adaptive building envelopes that dynamically balance energy conservation with occupant comfort requirements.