Numerical Simulation Of The Active Particle Brownian Motion Based On Lattice Boltzmann Method

Janus particles as a typical representative of active Brownian particle have gotten too much concern in the field of scientific research in recent years. It is synthetic particle which is composed by two-parts of different physical or chemical properties. Since Janus particles can produce different types of "mobility" under the effect of the gradient around the field by using the differences nature in their own of both sides. it is also known as active Janus particles or self-propelled Janus particles. This characteristic of self-propelled Janus particles make it in the field of micro systems, biological, environmental, medical and other important application.Based on mesoscopic lattice Boltzmann method(LBM) and the basic theory of Brownian motion, an efficient numerical method for studying the Brownian motion of active particles was established. The validity of the method was verified through a series of numerical simulation, and on the basis of the method, the paper studied the Brownian motion characteristic of concentration gradient-driven active Janus particles.Choosing cylindrical particles(diameter is 10 lattice units) for the study, firstly, with the help of the LBM and Ghost Fluid(GF) immersed boundary method, the simulation investigated the pure Brownian motion of ordinary microparticles by means of modifying Brown force to revise the motion equation(Langevin equation) of particle. And the reasonableness and effectiveness of this method was verified by taking different temperatures and different initial velocity to simulate pure Brownian motion. A new simulation model for simulating the Brownian motion of micro-particles was established, which considered LBM and GF immersed boundary method. The simulation results showed that in the case of different temperatures and different initial velocity, the conventional cylindrical micro-particles can eventually be stable and achieve consistent thermal equilibrium with the surrounding fluid under the influence of Brownian force, which was in line with the theory of Brownian motion. The mean square displacement(MSD) and statistical time interval of the particle motion accorded with a linear relationship, which met Einstein’s Brownian motion theory equation.Furthermore, on this basis, the above established simulation model was used to research the superposition of self-propelled motion and Brownian motion of active Janus particles. For the self-propelled characteristics of Janus particles, the diffusiophoresis force was added in the motion equation. And with reference to the experimental parameters, the above method was used to simulate the motion characteristics of Janus particles. The results read that the motion characteristics of simulation met experimental phenomenon for different diffusiophoresis force sizes, and on the other side, the bigger the diffusiophoresis force was, the smaller the directional angle changed. Comparison with experimental data, the size of the diffusiophoresis force of Janus particles for different concentrations fuel was obtained. This work provided a strong support for movement mechanism and control research of subsequent experiments and numerical work of Janus particle.