Study On Driving Force Of Pt-SiO₂ Janus Particle Based On Lattice Boltzmann Method

Manufacture of nano-and microscale motor has always been a desire of the people.The micro particle system driven by the self-generated gradient is one of the typical representations.These particles are known as Janus particles.Janus particles have two distinguished surfaces/chemistries on the two sides.Due to the difference in the nature of the two sides,there will establish asymmetric electric field,concentration field,temperature field and other gradient field around the particles.The asymmetric force will be formed with the effect of these self-generated gradient fields and drive particle movement.Janus motors have important prospects in the targeted transport of drugs and autonomous vectors in microfluidic devices.In this paper,we chose the micron Pt-SiO2-type Janus particle as the research object,focusing on the self-propulsion of the single particle.The lattice Boltzmann method is a modern mesoscopic method based on the microscopic particle characteristics of the fluid that makes it more intuitive to deal with the interaction of the fluid and solid.It is more advantageous in the description of this micro-interface dynamic problem – the self-propulsion of Janus particle.Through this method,we study,analyze and summarize the law of motion.Diffusiophoresis,the motive force of particle movemen,is derived from the unbalanced impact of the solute molecules on the Janus particles.It is difficult to establish the model of driving force with commonly macroscopic and microscopic methods.Therefore,the calculation method of dffusiophoresis has always been the focus and difficult problem of Janus particle subject.In this paper,Firstly the osmotic propulsion mechanism proposed by Córdova-Figueroa is used to calculate the diffusiophoresis.The diffusiophoresis was calculated by simulating the flow field and concentration field.And the motion of self-propelled Janus and different initial concentration simulation results were analyzed.The results show that diffusiophoresis value is basically the same no matter the flow velocity is 0 or not,so the effect of the flow field on diffusiophoresis can be neglected.As the concentration of the solution increases exponentially,the value of diffusiophoresis increases,but the growth rate is decreased.For the same particle size,the diffusiophoresis is proportional to the particle surface reaction rate.Based on the momentum theorem,the method of calculating the diffusiophoresis produced by concentration diffusion is proposed.The self-propelled motion of 2?m Janus particles is simulated and analyzed.The simulation error is corrected by introducing a coefficient ?,and the reason of the change of the coefficient is analyzed and discussed.Moreover,this diffusiophoresis model is modified by comparing between the fluid resistance from the experiments and simulations.The results are compared with the experimental data,which verifies the validity of the diffusiophoresis model.Through the further application of this model and ignoring the effects of the wall,five different shapes of Janus particles with the same volume are compared in simulations.The results show that the self-diffusiophoresis is mainly determined by axis projection area.In addition,the reaction area of the particle also impacts on the value of the diffusiophoresis.