Manipulating Nanoparticle Size within Polyelectrolyte Multilayers via Electroless Nickel Deposition

Palladium nanoparticles within polyelectrolyte multilayers of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) were prepared as seeds for further growth by electroless nickel deposition. The seeds were generated by binding tetraaminepalladium from aqueous solution to PAA carboxylic acid functionalities in the polymer film and subsequent reduction. Nickel was electrolessly deposited on the small, 2-nm-diameter catalytic particles. By manipulation of the rate and duration of the electroless deposition, a nickel shell of arbitrary thickness could be grown; up to 14-nm-diameter particles were obtained. Elemental analyses showed that the composition of the electrolessly deposited material, nickel with several weight percent boron, was similar to that obtained from macroscopic surface electroless nickel plating. The electroless chemistry facilitated control over nanoparticle size independent of the process of nanoparticle nucleation and hence particle concentration.