Thermophoresis of Janus particles at large Knudsen numbers

Abstract

The force and torque on a Janus sphere moving in a rarefied gas with a thermal gradient are calculated. The regime of large Knudsen number is considered, with the momenta of impinging gas molecules either obtained from a Chapman-Enskog distribution or from a binary Maxwellian distribution between two opposing parallel plates at different temperature. The reflection properties at the surface of the Janus particle are characterized by accommodation coefficients having constant but dissimilar values on each hemisphere. It is shown that the Janus particle preferentially orients such that the hemisphere with a larger accommodation coefficient points towards the lower temperature. The thermophoretic velocity of the particle is computed, and the influence of the thermophoretic motion on the magnitude of the torque responsible for the particle orientation is studied. The analytical calculations are supported by Direct Simulation Monte Carlo results, extending the scope of the study towards smaller Knudsen numbers. The results shed light on the efficiency of oriented deposition of nanoparticles from the gas phase onto a cold surface. arXiv:1807.04987v1 [physics.flu-dyn]

On the motion of slightly rarefied gas induced by a discontinuous surface temperature

“…It was shown that the parallel alignment of flat plates also have a pumping effect when appropriately heated (Taguchi & Aoki 2015;Baier et al 2017). Actually, flows related to discontinuous surface temperature have been a subject of recent studies such as the thermally-driven pumps (e.g., Donkov et al 2011;Lotfian & Roohi 2019) and the thermophoresis (Aoki et al 2014) (see also Baier et al (2018)). Despite its theoretical and practical interest, however, the understanding of these flows is far behind due to the lack of general theory.…”

Drag and lift coefficients of ellipsoidal particles under rarefied flow conditions

“…In their formulation the surface of the particle is approximated by a triangulated mesh. Baier et al [44] investigated the thermophoretic force experienced by spherical Janus particles in presence of an external thermal gradient. Chinnappan et al [45] addressed the transport dynamics of ellipsoidal particles in the free-molecular gas flow regime.…”

A Magnetically and Electrically Powered Hybrid Micromotor in Conductive Solutions: Synergistic Propulsion Effects and Label‐Free Cargo Transport and Sensing

“…[7] However, motion of micromotors, e.g., metallo-dielectric Janus particles (JPs), actuated by an alternating current (AC) electric field is quenched with increasing solution conductivity [9] and practically ceases at solution conductivities exceeding, [10,11] ≈0.3 mS cm −1 . In order to manipulate JPs and still maintain cargo manipulation and localized electroporation capabilities offered by the electric field, in high conductivity solutions, it is essential to propel the JP using other methods, such as thermophoresis, [12] optics, [13] chemical, [14] and catalytic reaction, [15] or magnetism. [16] In biological systems, the solutions required to ensure prolonged survival are highly conductive.…”