Effect of Viscosity on the Collision Dynamics and Oxidation of Individual Ag Nanoparticles

We experimentally and theoretically explore the effect of viscosity on the collision dynamics and oxidation of colloidal Ag nanoparticles (NPs) at a Au microdisk electrode. Building on a previously reported random walk simulation of NP collisions, we introduce continuum approximations of the ensemble-averaged transient NP collision frequency and faradaic current arising from a one-dimensional random walk. The theoretical models incorporate mass-dependent particle speed from classical kinetic theory and radius/viscosity-dependent diffusivity from Einstein’s diffusion relations. We demonstrate that the measured cumulative average charge from the oxidation of individual Ag NPs scales with the square root of the diffusion coefficient, in agreement with both random walk simulations and analytical approximations. Our findings indicate that single-NP diffusion controls the average rate of electron transfer at the electrode/solution interface.