Simulation of diffusiophoresis force and the confinement effect of Janus particles with the continuum method

The Janus particle is a special class of colloidal particle that has different surface characteristics on its two hemispheres. In the microsystem field, an interesting application is the Janus particle's self-propulsion. Diffusiophoresis (DFP) provides one possible mechanism to explain this phenomenon. In this paper, we used the continuum model to simulate DFP and to study the confinement effect of Janus particles travelling on the substrate. In the experiment, we noticed a special quasi-1D motion, in which the DFP force is dominant and particles move at a constant velocity within a short interval approximately along a straight line. This enables us to adopt a reference frame to numerically study the distributions of the flow field and concentration field and hence to evaluate the different forces. Because the confinement effect has a great influence on the magnitude of forces, the gaps were calculated accurately according to the force balance principle. Meanwhile, the fitting coefficients to match the experimental and numerical results were suggested. This result may help us to get a better understanding of self-propulsion and is also beneficial for designing a DFP-based micro-device.