Numerical Simulation About Janus Particles’ Self-electrophoresis Through The Coupling Of Multiphysical Fields

Janus particles are the typical active particles whose surfaces have two different chemical or physical properties. They can construct the gradients of concentration field,temperature field, light intensity field, or other fields across two sides of Janus particles by their asymmetric properties. Under these gradients, Janus particles own swimming motility, or Janus particles are self-driven. This phenomenon has some important applications in biology, medicine, environment, micro fluid and other fields.In this article, we studied self-electrophoresis of Janus particle using numerical simulation. Janus particles’ self-electrophoresis is decided by some different physical fields and the particles’ motion is the typical problem that couples flow field and electric field. Similarly, electroosmotic flow is the same problem that couples the similar physical fields. The numerical simulation of electroosmotic flow is more straightforward than that of Janus particles. So this paper begins with the electroosmotic flow in simple microchannel. The coupling between the flow field and the electric field is established and the validity of the numerical model was verified. Next, the problem of Janus particles self-electrophoresis was studied based on this platform.In this article, we used multiphysical fields coupling simulation platform, Comsol Multiphysics. First of all, the two dimensional rectangular numerical simulation research of electroosmotic flow was done. The electroosmotic mechanism is introduced.For the fixed geometry size of channel, we studied the effects of various physical fields,such as electric potential distribution of electric double layer(Poisson equation), the applied external electric field(Laplace equation) and laminar flow field(Navier-Stokes equation). This article does not consider the effect of dilute matter transfer in electroosmotic flow. The potential distribution of electric double layer is determines by the spatial potential density, which applied external electric field to coupling thevolume force in laminar flow. This can produce electroosmotic flow phenomenon.Respectively, change the zeta potential and the strength of the external electric field and study it. The results show that reducing zeta potential on surface will cause the rearrangement of the electric potential inside the pore distribution. It will lead to the enhancement of the spatial charge density. When the external electric field’s intensity is unchanged, electric field force will increase and the speed of electroosmotic flow becomes higher. Increasing the intensity of the external electric field gradually and neglecting its effect on the electric potential of the double electric layer, the solution is driven by the increased driven force, and the speed of the electroosmotic flow is accelerated, which is consistent with the existed conclusions.This article used the coupling model of multiphysical fields to study Janus particles’ self-electrophoresis. The particles are composed of Pt and Au, and own bipolar rod-like structures. When they are suspended in the H2O2 solution, it will create a self-generated electric field in the both poles. Due to the asymmetry of electrochemical characteristics, it can create a driven force and prompt Janus particles to do spontaneous electrophoretic motion in solution. In this article, according to the principle of relative frame, the relationship between the physical fields of Janus particles is explained by the coupled Poisson-Nernst-Planck-Stokes equation. Then, we introduced the electrokinetic equation(Frumkin-corrected-Butler-Volmer equation) to characterize the electrochemical reaction strength of the surface on the particles.Through the comparison of simulation results with the different concentration of H2O2,it was found that when the concentration of H2O2 is higher, the zeta potential on the surface of Janus particles is decreased. The electrophoretic velocity becomes faster.These studies provide a reliable method for the depth study the complex selfpropulsion problem of micro- or nano-particles.