Synthesis and quantitative characterization of non-conductive colloidal particle multilayers

We have studied theoretically and experimentally layer by layer assembled multilayers of monodisperse colloidal particles. More specifically, we have determined the effect of variations in the single-layer surface coverage on the properties of the multilayers. We have mimicked the layer by layer self-assembling process at a solid-liquid interface using the extended random sequential adsorption model of hard spheres. We have simulated ten multilayers: one with a constant single-layer coverage of 0.3 and nine others with variable single-layer coverages. We have kept the mean single-layer surface coverage of the nine multilayers at 0.3. For each of the multilayers, we have determined its mean thickness, porosity, tortuosity, and equivalent thickness of stagnant solution layer. We have found that, for not too large variations in the single-layer coverage, their effect on the mean multilayer parameters is minor. We have also tested our theoretical results experimentally. We have produced five multilayers of polystyrene latex particles of the diameter 800 nm on the surface of gold disk electrodes. For each of the multilayers, we have conducted measurements of the limiting diffusion current at the rotating electrodes to determine the layer’s transport parameters. We have also used an ultra micro balance to determine the mass and mean single-layer surface coverage of each multilayer. We have found a good agreement between the numerical simulations and experiments at the surface coverage below 0.45. Our experimental results have also suggested that at higher surface coverages the colloidal particle multilayers have collapsed forming heterogeneous structures. We have demonstrated the applicability of the cyclic voltammetry and rotating disk electrode techniques for the characterization of colloidal particle multilayers.

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