title: Design of Aerosol Particle Coating: Thickness, Texture and Efficiency.
abstract: Core-shell particles preserve the performance (e.g. magnetic, plasmonic or opacifying) of a core material while modifying its surface with a shell that facilitates (e.g. by blocking its reactivity) their incorporation into a host liquid or polymer matrix. Here coating of titania (core) aerosol particles with thin silica shells (films or layers) is investigated at non-isothermal conditions by a trimodal aerosol dynamics model, accounting for SiO2generation by gas phase and surface oxidation of hexamethyldisiloxane (HMDSO) vapor, coagulation and sintering. After TiO2particles have reached their final primary particle size (e.g. upon completion of sintering during their flame synthesis), coating starts by uniformly mixing them with HMDSO vapor that is oxidized either in the gas phase or on the particles' surface resulting in SiO2aerosols or deposits, respectively. Sintering of SiO2deposited onto the core TiO2particles takes place transforming rough into smooth coating shells depending on process conditions. The core-shell characteristics (thickness, texture and efficiency) are calculated for two limiting cases of coating shells: perfectly smooth (e.g. hermetic) and fractal-like. At constant TiO2core particle production rate, the influence of coating weight fraction, surface oxidation and core particle size on coating shell characteristics is investigated and compared to pertinent experimental data through coating diagrams. With an optimal temperature profile for complete precursor conversion, the TiO2aerosol and SiO2-precursor (HMDSO) vapor concentrations have the strongest influence on product coating shell characteristics.
authors.affiliation: Particle Technology Laboratory, Institute of Process Engineering, Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zürich, Switzerland.
authors.forename: B
authors.initials: B
authors.lastname: Buesser
authors.forename: S E
authors.initials: SE
authors.lastname: Pratsinis
keywords: condensation; hermetic layering; nanoparticle encapsulation; particle formation; population balance; powder technology