Self-propulsion of Janus particles in the free molecular regime

Abstract

The self-propulsion of a Janus particle suspended in a dilute gas at equilibrium is investigated in the free molecular regime. The Janus particle consists of two hemispheres with different momentum accommodation factors; the particle and the surrounding gas are held at different constant temperatures. Based on the gas kinetic theory, we calculate the particle's self-propulsion and drag force. We conclude that self-propulsion occurs only under the condition that the particle is hotter/colder than the suspension gas, and the self-propulsion force is proportional to the difference of the momentum accommodation factors and directed along the symmetry axis. The drag force, instead, is corrected by a term proportional to the average of the momentum accommodation factors. Our analytical results are confirmed by numerical Monte Carlo simulations.

Drag on nanoparticles in a liquid: from slip to stick boundary conditions

“…8 The transport properties of particles in gases have been well investigated [9][10][11][12] and the mechanism has been recognized based on the gas kinetic theory. [13][14][15] In liquids, however, a general theoretical description of the nanoparticle transport is still lacking, 16,17 despite the fact that considerable progress has been achieved over the past decades. [18][19][20] A particle moving in a fluid experiences a drag force, which governs the particle transport.…”