One-step aerosol synthesis of nanoparticle agglomerate films: simulation of film porosityand thickness

Abstract

A method is described for designing nanoparticle agglomerate films with desired filmporosity and film thickness. Nanoparticle agglomerates generated in aerosol reactors can bedirectly deposited on substrates to form uniform porous films in one step, a significantadvance over existing technologies. The effect of agglomerate morphology and depositionmechanism on film porosity and thickness are discussed. Film porosity was calculated for agiven number and size of primary particles that compose the agglomerates, and fractaldimension. Agglomerate transport was described by the Langevin equation ofmotion. Deposition enhancing forces such as thermophoresis are incorporated in themodel. The method was validated for single spherical particles using previoustheoretical studies. An S-shape film porosity dependence on the particle Peclet numbertypical for spherical particles was also observed for agglomerates, but films formedfrom agglomerates had much higher porosities than films from spherical particles.Predicted film porosities compared well with measurements reported in the literature.Film porosities increased with the number of primary particles that composean agglomerate and higher fractal dimension agglomerates resulted in denserfilms. Film thickness as a function of agglomerate deposition time was calculatedfrom the agglomerate deposition flux in the presence of thermophoresis. Thecalculated film thickness was in good agreement with measured literature values.Thermophoresis can be used to reduce deposition time without affecting the film porosity.