Adhesion Interface Created by Surface-grafted Polymers

Two silicon wafers bearing a polystyrene（PS）brush or a poly（methyl methacrylate）（PMMA）brush were jointed using a small amount of toluene and successive thermal annealing at 408 K to give a lap shear adhesion strength of 1.3～1.7 MPa. The adhesion strength was significantly affected by the molecular weight, molecular weight distribution, and graft density of the brushes, because the intermixing of the opposite polymer brushes at the interface was a major factor for the adhesion, which was characterized by neutron reflectivity measurement. Instead of polymer brushes fabricated on a flat substrates, dip-coating film of poly（n-butyl methacrylate）-grafted silica nanoparticles（SiNP-g-poly（BMA））on silicon wafers were also used as the adhesive layer to join the substrates by thermal annealing at 333 K. The lap shear adhesion strength was 0.3～0.5 MPa, which was relatively lower strength compared with adhesion by PS or PMMA brushes, because poly（BMA）physically adsorbed on the flat silicon wafers without chemical interaction such as covalent bonds. Coumarin-terminated SiNP-g-poly（BMA）were prepared to demonstrate photo controllable adhesion of transparent glass substrates. Adhesion strength was increased by UV irradiation with 365 nm of wavelength and reduced with λ= 254 nm, due to the photo reversible dimerization and dissociation reaction of coumarin group.