From Plasma Chemistry to Adhesion Strength : Mechanical Characterization of Pure Versus Mixed Aminosilane Films for Bonding Polyurea to Aluminum

Abstract

Reliably bonding fast-curing polyurea adhesives (PUA) to aluminum requires replacing wet primers with dry, in-line solutions. This study investigated atmospheric pressure plasma jet (APPJ) coatings using (3-aminopropyl)triethoxysilane (APTES). Contrary to expectations, plasma co-polymerization of APTES with functional co-monomers reduced adhesion. Instead, pure plasma-polymerized APTES films (APTESpp) proved superior, quadrupling lap-shear strength on Al-6063 from ~2.7 to ~11.2 MPa. Chemical derivatization XPS revealed a “threshold effect”: once sufficient amines exist for covalent coupling, adhesion depends on the interphase's cross-linking and anchoring rather than maximized nitrogen content. Simple APTESpp deposition using air as the process gas emerges as a robust industrial primer, validated by an 8-h continuous stress test.