Humidity responsive self-healing based on intermolecular hydrogen bonding and metal-ligand coordination

Here, we report the fabrication of a self-healing, colorful polyelectrolyte multilayer (PEM) composite film with humidity responsive properties, based on intermolecular hydrogen bonding and metal-ligand coordination. The synthetic strategy involves the fabrication of multilayer chitosan (CS)/polyacrylic acid (PAA) film with a layer-by-layer (LbL) self-assembly technique, followed by immersing the resulting CS/PAA PEM film in a cobalt chloride solution. According to the theory calculation and experimental results, cobalt chloride annealing treatment plays a critical role in rebuilding the reversible interactions that facilitate the PEM film to heal the mechanical damages and endow the PEM film with the property of reversibly changing its color in different conditions of humidity. Such a metal induced, humidity responsive, self-healing PEM film may broaden the application of the self-healing materials.