Ultrathin, layered polyamide and polyimide coatings on aluminum

Ultrathin, passivating films are attractive for protecting metal surfaces w ithout completely masking substrate properties. Alternating polyelectrolyte deposition of layered poly(acrylic acid)/ poly(allylamine hydrochloride) ( PAA/PAH) films on Al produces ultrathin coatings that protect Al from Cl--i nduced corrosion. Although the resistance of these films is minimal, they f orm a passivating layer on the surface oxide and increase oxide resistance by 2-3 orders of magnitude. Heating of PAA/PAH yields cross-linked polyamid es that have film resistances of about 5 M Omega cm(2), even when the film is only 10-nm thick. Although the resistance of these films is high, reduct ions in corrosion current due to cross-linked films are still primarily due to passivation of the surface oxide as oxide resistance is larger than fil m resistance. Layer-by-layer covalent deposition of Gantrez/poly(allylamine ) films yields ultrathin amic acid-linked layers that can be imidized by he ating. Impedances of Al electrodes coated with Gantrez/poly(allylamine) fil ms depend on the number of deposited bilayers and increase by an order of m agnitude after imidization. These results suggest that increases in film re sistance play a role in oxide passivation by this system.