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

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.