The effects of gas and particle properties on thermophoresis

This paper extends a companion paper on measurements of the thermophoretic force for solid and liquid spheres in air. Using electrodynamic levitation to maintain a microsphere in the space between heated and cooled plates, the effects of the system parameters, gas and particle thermal conductivities, the magnitude of the temperature gradient and other variables are explored. Experimental data obtained using helium, air and carbon dioxide with nickel, polystyrene latex and glass solid spheres and with dioctyl phthalate liquid droplets are compared with available theories. The polarity and charge density of the microparticle are shown to have a large effect on the thermophoretic force, particularly in helium.