Langmuir, Vol.17, No.21, 6610-6615, 2001
Selective electroless nickel plating on polyelectrolyte multilayer platforms
Polyelectrolyte multilayers (PEMs) fabricated by the layer-by-layer adsorption of poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) are used to selectively bind palladium catalysts for electroless nickel Plating. Depending on the PH conditions used during multilayer processing and the polyelectrolyte adsorbed last, the surface of the PAH/PAA-based multilayers can be tuned to contain primarily PAA, primarily PAH, or a mixture of PAA and PAR functionalities (i.e., carboxylic acids or amines). The palladium-complex ions of tetraaminepalladium chloride (Pd(NH3)(4)Cl-2) or sodium tetrachloropalladate (Na2PdCl4) bind selectively ky ion exchange only to surfaces of PAA or PAH, respectively. Substrates that are coated with regions of PAA-topped and PAH-topped multilayers, fabricated at a PAR PH of 7.5 and a PAA PH of 3.5, bind [Pd(NH3)(4)](2+) only on the PAA regions. Upon immersion into an electroless nickel plating bath, only the PAA-topped regions of the substrate, activated by the Pd complex, promote nickel plating while the PAH-topped regions resist plating. By using [PdCl4](2-), the PAR regions are selectively plated instead. Moreover, the facile patternability of PEMs is demonstrated using the inkjet printing of a PAA solution onto a PAR-topped multilayer film. Tetraaminepalladium ion binding and nickel plating are confined to the printed PAA pattern. Because of their surface tunable capabilities and therefore ease of selective activation, conformal coverage, facile processing, adherent coating, and patternability, PAH/PAA-based multilayers are ideal platforms for selective electroless plating.