Silver nanoparticle monolayers on poly(ethylene imine) covered mica produced by colloidal self-assembly

Monodisperse silver particles were synthesized according to the method of Creighton et al. by reduction of AgNO(3) solutions with NaBH(4) in the presence of polyvinyl alcohol as the stabilizing agent. Bulk characteristics of silver nanoparticles in aqueous solutions were carried out by measuring their extinction spectrum, fluorescence, diffusion coefficients using the PCS method and the electrophoretic mobilities. The average hydrodynamic diameter of PVA covered silver particles was 44 nm, being fairly independent of ionic strength and pH in the range of 3-9. It was also shown that the hydrodynamic radius did not change within prolonged storage of suspensions (up to 75 days), indicating that the sols were quite stable. A similar value of 45±8 nm was determined from SEM measurements. The electrophoretic mobility measurements showed that the zeta potential of silver nanoparticles was insensitive to pH and decreased with the ionic strength, attaining -45 mV for I=10(-5) M and -25 mV for I=10(-2) M. Additionally, the kinetics of silver particle deposition on mica modified by adsorption of a saturated layer of poly(ethylene imine) (PEI) was studied. Surface concentration was determined directly by counting the number of particles over various surface areas using the atomic force microscopy working in the semicontact mode. The maximum surface concentration for I=10(-3)M was 102 μm(-2), which corresponds to the coverage degree of 16%. The kinetic run and the maximum coverage value was in a good agreement with theoretical predictions stemming from the random sequential adsorption (RSA) model. This kinetic run allowed one to determine the size of Ag core, which was 20 nm and the thickness of the PVA layer, equal to 12 nm.