Research On Motion Characteristics Of Micro-particle Swarm Based On Fluctuating Lattice Boltzmann Method

Janus particles are synthetic micro-nanoparticles composed of two parts that differ in physical or chemical properties.Due to its asymmetrical structure,Janus particles can convert the energy in the environment into their own mechanical energy,which in turn can be self-driven.The self-driven properties of Janus particles have great potential applications in microenergy systems,drug targeted transport,biotrendivity,environmental management,and self-assembly.For the micro-nano-scale Janus particles,under the unbalanced collision of surrounding fluid molecules,the random motion will never stop,so the actual motion is the superposition of random Brownian motion and autonomous motion.In the actual preparation and application process,Janus particles often exist in the form of groups.Therefore,mastering the group's movement characteristics and the interaction mechanism during the movement process are the main basis for popularization and application.The motion of the group Janus particles was numerically simulated by lattice Boltzmann method in order to explore its motion characteristics and interaction mechanism.Firstly,the lattice Boltzmann method was used to numerically simulate the free settlement of single particle,two particles and particle group under gravity.By simulating the free settlement of single particles under gravity,and comparing the simulated values with the experimental values,the validity of the LBM model and the effectiveness of the half-way boundary conditions for processing the flow-solid boundary were verified.By simulating the free sedimentation of double particles and group particles,the effectiveness of the particle collision model was verified,and we have a preliminary understanding of the interaction mechanism between particles and the characteristics of group motion.Secondly,the Brownian motion of Janus particles was numerically simulated by using the fluctuating lattice Boltzmann(FLB)method.We numerically simulated the Brownian motion of a single spherical Janus particle,and verified the validity and accuracy of the FLB method by analyzing its mean square velocity,mean square angular velocity,mean square displacement and diffusion coefficient.Subsequently,the Brownian motion of group particles with different volume fractions was simulated by FLB method.It was found that the Brownian motion of the group particles still satisfied the energy equalization Theorem,and the average diffusion coefficient of the population particles decreased with the increase of the volume fraction.Finally,the FLB method was used to simulate the self-propulsion of Janus particles.By simulating the self-propulsion of a single spherical Janus particle,and comparing the simulated results of mean square displacement and diffusion coefficient with the experimental results in the earlier stage of our research group,the validity and accuracy of FLB method in simulating the self-propulsion of Janus particle were confirmed.Subsequently,the motion of group Janus particle under different driving forces was simulated by FLB method.The results show that the self-propulsion of the group Janus particles has similar kinematic characteristics as the self-propulsion of single Janus particle.In addition,the study of the translational characteristic time under different driving forces shows that as the diffusion force increases,the faster the particles change from the Brownian motion stage to the directional motion stage.