Temperature responsive self-assembled hydroxybutyl chitosan nanohydrogel based on homogeneous reaction for smart window

Chitosan (CS) based self-assembled nanohydrogels are considered as promising platform for biomedicine, petrochemical, agricultural and food applications due to their unique biodegradability, nano-interface effect, and intelligent responsiveness. However, the most CS derivatives are prepared in heterogeneous system, which is unstable and environmentally unfriendly. In this work, a series of hydroxybutyl chitosan (HBC) was synthesized based on a green and homogeneous system (potassium hydroxide (KOH)/urea), which given this derivative interesting temperature responsive phase transformation behavior. HBC could change from dissolved state into nanohydrogel state in deionized water, when the temperature exceed its critical phase change temperature, and this process could be repeated more than 50 cycles (one cycle/day) without coagulation. The nanohydrogels solution exhibited concentration and temperature-dependent ultraviolet absorption and visible light regulation, which had great application potential in smart windows. This study provided a novel preparation method and extended the application of chitosan-based temperature responsive self-assembled nanohydrogels.