Tuning properties of silver particle monolayers via controlled adsorption-desorption processes

Abstract

Using the well-defined silver particle suspension, systematic studies of adsorption kinetics on mica modified by poly(allylamine hydrochloride) (PAH) were carried out. The coverage of adsorbed particles was directly determined by AFM and SEM imaging. The dependence of the coverage on adsorption time, bulk suspension concentration, and ionic strength was systematically studied. It was confirmed that adsorption was diffusion controlled, with the initial rate proportional to the bulk concentration of particles. On the other hand, for long adsorption times, the saturation coverage was attained, which increased systematically with the ionic strength of the particle suspension. The adsorption kinetic runs were adequately reflected for the entire range of times and bulk concentration by the random sequential adsorption (RSA) model. Additionally, particle desorption kinetics from previously formed monolayers were studied. The decrease in the surface coverage of particles as a function of time was measured, which allowed one to determine the equilibrium adsorption constant K(a). The binding energy of silver particles (energy minimum depth) derived form these measurements varied between -16.9 kT and -17.8 kT, which suggests that it is mainly controlled by electrostatic interactions. Knowing the equilibrium adsorption constant, a particle adsorption isotherm was theoretically derived using the RSA model. Experimental data obtained for various bulk concentration of particles were in agreement with these theoretical predictions. These measurements suggest that it is feasible to produce uniform silver particle monolayers of desired coverage in the self-assembly process of particles.