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

Abstract

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.

Mechanism and regulation of LCST behavior in poly(hydroxypropyl acrylate)-based temperature-sensitive hydrogels

“…Although there have been attempts to modulate the LCST range of hydrogels by copolymerization with hydrophilic/hydrophobic monomers, those changes are very limited or the preparation methods are complex. [28][29][30][31][32] The transition rate refers to the time it takes for a material to go from the onset of phase change to the end of the phase change. Some research studies have obtained faster response rates by conguring small size microgels into low concentration solutions; 24,[33][34][35][36][37] however, it would bring the risk of liquid leakage.…”