Stable thermophoretic trapping of generic particles at low pressures

Abstract: We demonstrate levitation and three-dimensionally stable trapping of a wide variety of particles in a vacuum chamber through the use of the thermophoretic force in the presence of a strong temperature gradient. Typical sizes of the trapped particles are between 10 microns and 1 mm at a pressure between 1 and 10 Torr. The trapping stability is provided by the geometry of the temperature field, as well as the transition between the free molecule and hydrodynamic regimes of the thermophoretic force. To quantitatively measure the thermophoretic force, we examine the levitation heights of spherical polyethylene spheres under various experimental conditions and determine the temperature gradient needed to levitate the particles. A good agreement between our experimental observations and theoretical calculations is obtained. Our system offers a new platform to study thermophoretic phenomena and to simulate dynamics of interacting many-body systems in a microgravity environment.