Reversible adhesive-free nanoscale adhesion utilizing oppositely charged polyelectrolyte brushes

Two prepared silicon wafers bearing cationic and anionic polyelectrolyte brushes were joined with 2 mu L of water under 0.098 MPa of pressure at room temperature. The bonded area was fixed at 5 x 10 mm(2). A lap shear strength of 1.52 MPa was achieved through the adhesion of poly[2-(methacryloyloxy)ethyl trimethylammonium chloride] and poly(3-sulfopropyl methacrylate potassium salt) brush substrates due to electrostatic attractive interactions between the positively and negatively charged polymers. In contrast, the lap shear strength of bonded polymer brushes with like charges was only 0.027-0.072 MPa. The polyelectrolyte brushes remained on the substrates even after their separation in the lap shear test; and the brush substrates readhered in the presence of a small amount of water. Furthermore, the adhering substrates were smoothly debonded in aqueous NaCl solution due to the electrostatic interaction of the hydrated salt ions. However, the substrates did not separate in deionized water. In summary, reversible nanoscale adhesion was achieved using oppositely charged polyelectrolyte brushes combined with aqueous solution.