Enhancement of adhesion to heterogeneously patterned substrates

Organofunctional silanes have long been used as promoters of adhesion between polymers and mineral oxide surfaces. The present work reports adhesion results obtained using binary combinations of adhesion-promoting and non-adhesion-promoting silanes patterned onto an oxide adherend surface. The effects of pattern shape, texture (feature size) and the fractional coverage of the adhesion promoter are explored for the bonding of poly(vinyl butyral) (PVB) to aluminum (oxide) surfaces using combinations of γ-aminopropyl triethoxysilane (APS), an adhesion promoter and octadecyl trichlorosilane (ODTS), a non-adhesion promoter for this system. Climbing drum peel tests reveal that adhesion depends on feature size, shape and area ratio of the silanes, in many cases resulting in a reduction of adhesion compared with that for a pure APS film, but in other cases producing enhancements of as much as 80%. Among the conditions examined thus far, the greatest adhesion was achieved using square islands, 12 mm × 12 mm in size, surrounded by 1.5 mm wide borders of non-adhesive. Adhesion enhancement is attributed to arrest and confinement of crack propagation. As the crack propagates through a heterogeneous surface, it will blunt at the end of an adhesive patch, and must re-nucleate at the start of the next adhesive domain.