Thermophoretic levitation of solid particles at atmospheric pressure

Separation and transportation of powders are important processes in various technological applications. Although mechanical, chemical, or electrical methods can provide possible solutions, operational or environmental constraints may require alternative methods. Spreading and levitation of clusters (aggregates) of fluorinated fumed silica nanoparticles placed under atmospheric pressure on a hot plate is reported. The powder spreading in the chamber continued until the temperature-dependent saturation value of the spot radius, which grew linearly with the temperature. Open space experiments clearly demonstrated levitation of the powder clouds. Qualitative physical analysis of the observed phenomena is suggested. The effect of levitation is explained by the lifting thermo-phoretic force emerging in the Knudsen layer of air. The levitation of the powder under atmospheric pressure becomes possible due to the combination of low adhesion of the fluorinated fumed silica clusters to the substrate, low density of the particles and clusters, and their high specific surface area.