CHARACTERIZATION OF A COLLOIDAL PD(II)-BASED CATALYST DISPERSION FOR ELECTROLESS METAL-DEPOSITION

An aqueous Pd(II) dispersion, useful as a catalyst for the selective e lectroless deposition of nickel metal at ligand-bearing surfaces, is p repared by the hydrolysis of PdCl42- at pH 5 in an approximately 0.01 mol dm(-3) NaCl solution. The catalyst dispersion is characterized by W-visible absorption spectroscopy, electroless metallization, ultracen trifugation, and electrophoresis. The dispersion is found to consist o f a distribution of anionic and uncharged Pd(II) species ranging in ty pe from monomeric to colloidal. The species responsible for the initia tion of electroless metal deposition at the ligand surface are identif ied as colloidal. Atomic force microscopy indicates that the colloidal catalysts are bound at the surface and range in diameter from approxi mately 4 to 53 nm with an average size of 30 +/- 12 nm. The behavior o f the catalyst dispersion is consistent with a model in which colloid formation is initiated by polymerization of monomeric precursors gener ated by successive hydrolytic Cl- loss from PdCl42-, and deprotonation of the corresponding aquo-Pd(II) complex(es).