Mussel-inspired hydrogels with UCST for temperature-controlled reversible adhesion

Achieving on-demand adhesion on different surfaces remains an adaunting challenge for polymer adhesives. Herein, we report a temperature-controlled adhesion strategy of hydrogels based on the reversible exposure and shielding of adhesive promoters regulated by microphase separation. The hydrogels are constructed by the physical crosslinking (hydrogen bonding and ion interaction) of a ternary random copolymer (PQAM) derived from the copolymerization of catechol containing quaternary ammonium salt monomer (QCA), acrylic acid (AA), and acrylamide (AAm). The physically crosslinked polymer networks can effectively toughen the hydrogels, resulting in tensile fracture strength, elongation, and energy up to 43.3 kPa, 1223%, and 9.5 kJ/m2, respectively. PQAM hydrogels exhibit upper critical solution temperature (UCST) behavior, and the transition temperature can be easily adjusted from 42.1 to 49.0 °C by changing the content of PQCA. PQAM hydrogels are non-transparent and non-adhesive at temperatures below UCST, while become transparent and highly adhesive at temperatures above UCST. By simply controlling the temperature, PQAM hydrogels can repeatedly attach to and detach from various substrates (including glass, plastics, ceramic, and metals) with an optimal adhesion strength up to 35.5 kPa. The strategy of hiding adhesive promoters may be interesting in the design of smart adhesives.