Kinetics of silver nanoparticle deposition onto poly(ethylene imine) modified mica determined by AFM and SEM measurements

Abstract

A stable silver nanoparticle sol was synthesized via the reduction of silver nitrate using sodium borohydride in the presence of polyvinyl alcohol serving as the stabilizing agent. Bulk characteristics of this sol involved the solid weight content, the extinction spectrum, diffusion coefficient (hydrodynamic diameter) measured by dynamic light scattering (DLS) and the electrophoretic mobility. The average diameter of silver nanoparticles measured by scanning electron microscopy (SEM) and atomic force microscopy (AFM) was 19 and 18 nm, respectively. On the other hand, the hydrodynamic diameter of particles, determined via the diffusion coefficients measurements was 25 nm, being fairly independent of ionic strength. The electrophoretic mobility measurements revealed that the zeta potential of nanoparticles increased with the ionic strength, from −43 mV for I = 10 −4 M to −12 mV for I = 3 × 10 −2 M. Using the sol, the kinetics of silver particle deposition on mica modified by a PEI sublayer was studied under diffusion-controlled transport conditions. The surface concentration of particles was determined by a directly enumeration using AFM and SEM technique. The measurements were performed for various ionic strengths ranging from 10 −4 to 3 × 10 −2 M. Both the kinetics of particle deposition (for the time reaching 24 h) and the maximum surface concentration were determined. It was found that for higher ionic strength the maximum coverage exceeded 0.2, and the monolayers were uniform in a macroscopic scale. It was also proven that the monolayers were stable over a prolonged time period. The kinetic data were quantitatively interpreted in terms of the random sequential adsorption (RSA) model using the effective hard particle concept. It was concluded that by applying the self-assembling process exploited in our work, uniform silver particle monolayers of controlled density can be produced in a reliable way.