| Summary: | Herein, excellent hydrogel–solid adhesion over 1500 J/m2 was achieved with the synergy of energy dissipation, covalent bonds, and topological entanglements using self-assembled monolayers. Phosphonic acids were densely deposited on arbitrary substrates, followed by direct coating with polyacrylamide. Two functional end-groups of phosphonic acids based on an alkenyl group were introduced to chemically bond with the hydrogel network. The covalent bonding between the alkenyl group and the hydrogel drastically enhances the adhesion to substrates. In addition, the long alkyl chain improved the interfacial adhesion energy to 1500 J/m2. Infrared absorbance analysis demonstrated that longer alkyl chains formed more densely packed self-assembled monolayers, leading to a higher supply of chemically reactive sites to the hydrogels. Moreover, the tendency of the adhesion energy of the swollen hydrogel proves that the long alkyl chain is physically tangled with hydrogel networks, resulting in stronger adhesion.
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