Effective diffusivity of colloidal particle multilayers

We have studied, both theoretically and experimentally, the effective diffusivity of colloidal particle multilayers. We have synthesized the multilayers of 0.8 μm polystyrene latex particles, according to the layer-by-layer technique. We have measured their limiting diffusion current, using cyclic voltammetry with rotating disk electrode, to determine the equivalent thickness of stagnant solution layer. Next, we have performed mass measurements of each film to determine its mean surface coverage. From these measurements, we have calculated thickness of the multilayers. We have also presented results of our numerical simulations of multilayer adsorption of hard monodisperse spheres, using the extended random sequential adsorption model. We have generated five multilayers mimicking those obtained experimentally. Then, we have analyzed their porosity, tortuosity, and effective diffusivity as functions of the distance from the adsorption surface. We have shown that variation in effective diffusivity within our multilayers has negligible effect on the concentration profile of species diffusing through the supported membranes. We have also compared the thickness of the multilayers, determined experimentally and theoretically. We have found a good agreement between the experiments and numerical simulations.