Physical crosslinked hydrogel-derived smart windows: anti-freezing and fast thermal responsive performance

Area of Science:

• Materials Science
• Polymer Science

Background:

• Thermochromic hydrogels are smart materials with applications in smart windows, sensing, and camouflage.
• Previous hydrogel smart windows relied on covalent crosslinking, involving complex, multi-step preparation and often compromising structural integrity and antifreezing capabilities.
• Research has primarily focused on luminous transmittance and solar modulation, neglecting crucial practical aspects like structural integrity and cold-weather performance.

Purpose of the Study:

• To develop a novel, physically crosslinked hydrogel-derived smart window with enhanced structural integrity and antifreezing properties.
• To overcome the limitations of traditional covalent crosslinking methods in hydrogel smart window fabrication.
• To create a facile synthesis route for thermochromic hydrogels suitable for practical applications.

Main Methods:

• In situ free radical polymerization (FRP) of N-isopropylacrylamide (NIPAM) in a glycerol-water (GW) binary solvent system.
• Utilizing noncovalent crosslinking to form the hydrogel network.
• Characterization of thermochromic properties, luminous transmittance, solar modulation, freezing tolerance, response time, and structural integrity.

Main Results:

• Facile synthesis of noncovalent crosslinked PNIPAM GW solutions.
• Achieved outstanding freezing tolerance (approximately -18 °C).
• Demonstrated a high luminous transmittance (90%) and solar modulation ability (60.8%), with a fast response time (approximately 10 s) and good structural integrity.

Conclusions:

• The developed physical hydrogel offers a promising alternative to traditional covalent methods for creating smart windows.
• This approach provides a new strategy for designing heat-stimulated smart hydrogels with improved practical performance, particularly for energy-saving applications.
• The material exhibits excellent freezing tolerance, high optical performance, and robust structural integrity, making it suitable for real-world deployment.