Repeatable adhesion by proton donor-acceptor interaction of polymer brushes

Abstract

Polymer brushes having proton donor and acceptor type functional groups were prepared on silicon wafers by surface-initiated atom transfer radical polymerization of 2-hydroxyethyl methacrylate (HEMA), 4-hydroxystyrene (4HS), 2-vinylpyridine (2VP), and 4-vinylpyridine (4VP), respectively. Two silicon wafers, one prepared with a poly(HEMA) brush and one with a poly(4VP) brush, were jointed in a 1-cm2 contact area using 5-μL of methanol under a pressure of 120 N at room temperature and successively air-dried to form hydrogen bonds at the brush interface, yielding a lap shear adhesion strength of 337 kPa. Furthermore, poly(4HS) and poly(4VP) brushes also adhered more firmly with 5-μL of methanol to yield a lap shear adhesion strength of 843 kPa due to the phenolic OH group with a larger dipole moment compared to aliphatic OH. In addition, the adhered specimens smoothly debonded in methanol within 20 min at 298 K. The two separated substrates adhered again with a small amount of methanol. Repeatable adhesion and debonding was successfully achieved by proton donor and acceptor type polymer brushes.