Abstract
Common adhesives stick to a wide range of materials immediately after they are applied to the surfaces. To prevent indiscriminate sticking, smart adhesive materials that adhere to a specific target surface only under particular conditions are desired. Here we report a polymer hydrogel modified with both β-cyclodextrin (βCD) and 2,2′-bipyridyl (bpy) moieties (βCD–bpy gel) as a functional adhesive material responding to metal ions as chemical stimuli. The adhesive property of βCD–bpy gel based on interfacial molecular recognition is expressed by complexation of metal ions to bpy that controlled dissociation of supramolecular cross-linking of βCD–bpy. Moreover, adhesion of βCD–bpy gel exhibits selectivity on the kinds of metal ions, depending on the efficiency of metal–bpy complexes in cross-linking. Transduction of two independent chemical signals (metal ions and host–guest interactions) is achieved in this adhesion system, which leads to the development of highly orthogonal macroscopic joining of multiple objects.
Highlights
Common adhesives stick to a wide range of materials immediately after they are applied to the surfaces
A polymer hydrogel modified with cyclodextrins as host moieties showed chemically selective adhesion ability to a specific counterpart that possessed complementary hydrophobic guest moieties through host–guest interaction
Polyacrylamide was selected as the main chain in this study because interactions of –CONH2 groups with cyclodextrins[13] or metal ions[42] are known to be small. bCD–bpy gel was prepared by radical copolymerization of acrylamide (AAm), mono(6-deoxyacrylamido)-b-cyclodextrin13, 5-acrylamidomethyl-50-methyl-2,20-bipyridine and N,N 0-methylenebisacrylamide (MBAAm) in dimethyl sulfoxide (DMSO), followed by the replacement with H2O and used as a hydrogel
Summary
Common adhesives stick to a wide range of materials immediately after they are applied to the surfaces. We report a polymer hydrogel modified with both b-cyclodextrin (bCD) and 2,20-bipyridyl (bpy) moieties (bCD–bpy gel) as a functional adhesive material responding to metal ions as chemical stimuli. We have found adhesion phenomena between soft materials through molecular recognition[13,14,15,16,17] In this case, a polymer hydrogel modified with cyclodextrins as host moieties showed chemically selective adhesion ability to a specific counterpart that possessed complementary hydrophobic guest moieties through host–guest interaction. In the pursuit of smart adhesive materials that stick to a desired target in response to specific stimuli, we have conceived to control molecular recognition ability of hosts in adhesive materials by modifying them with suitable inhibitory guests whose inclusion properties can be switchable. The adhesive ability of bCD–bpy gel varies with the kinds of metal ions, whose chemical selectivity is explained by the gel’s property change depending on the resulting metal–bpy complexes
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