Influence of supporting polyelectrolyte layers on the coverage and stability of silver nanoparticle coatings

Deposition mechanisms of citrate-stabilized silver nanoparticles 15 nm in diameter on cationic polyelectrolyte supporting layers were evaluated. Initially, the bulk and the electrokinetic properties of cationic polyelectrolytes and their monolayers on mica were determined using in situ streaming potential measurements. Analogously, the size distribution, stability and electrokinetic properties of silver particles were studied using transmission electron microscopy (TEM) and microelectrophoretic measurements. Afterward, the kinetics of silver particle deposition was quantitatively evaluated by a direct enumeration procedure exploiting the atomic force microscopy (AFM) and scanning electron microscopy (SEM) micrographs. Using this method the kinetics of particle adsorption was determined for various polyelectrolyte supporting layers as a function of ionic strength. These experiments were interpreted in terms of the random sequential adsorption (RSA) model. It was found that the highest coverage of 0.35 was obtained for silver monolayers deposited on poly(allylamine hydrochloride) (PAH)-modified mica in the case of higher ionic strength. The release kinetics of nanoparticles was also studied using the SEM and AFM imaging method. Using these experimental data the equilibrium adsorption constant and the binding energy of nanoparticles were calculated by exploiting the RSA approach. The investigations showed that the most stable silver monolayers are obtained for the poly-L-lysine (PLL) supporting layers where the 50% of particle is released after 441h, whereas in the case of PEI the release time was only 9h. These results are consistent with the model of discrete electrostatic interactions among ion pairs. Additionally, the obtained results have practical implication indicating that it is feasible to regulate the rate of silver nanoparticle release by a proper choice of the polyelectrolyte forming the supporting layer.