Thermoresponsive Three-Stage Optical Modulation of a Self-Healing Composite Hydrogel

A self-healing composite hydrogel with thermoresponsive three-stage optical adjustment (opaque-transparent-translucent) is achieved by combining polyampholyte hydrogel (PAH) with a small amount of poly( N -isopropylacrylamide) (PNIPAM) nanogels. The PAH has an upper critical solution temperature to dominate the initial optical stage of reversible opaque-transparent transition and also offers its self-healing properties via reversible ionic bonds. Meanwhile, the PNIPAM shows a lower critical solution temperature by hydrophilic-hydrophobic phase transition and synergistic clustering of PAH, which controls the subsequent optical stage of reversible transparent-translucent transition. Therefore, the PAH/PNIPAM composite hydrogel shows a reversible three-stage optical modulation by controlling temperature from low (<15 °C) to medium (15–30 °C) to high (>30 °C) via double phase transition behavior of PAH/PNIPAM. Through different analytical methods, the synergistic thermoreposensive effects of PNIPAM nanogels and the bulk PAH are demonstrated. Finally, a prototype of a smart window is designed to demonstrate one of its potential applications.