Study On The Effect Of Non-uniform Electric Field On The Electrocoalescence Of Nano-droplets

How to efficiently use an electrostatic field to drive droplet coalescence has become a common concern in frontier fields such as industrial production,electronic communication,and aerospace.In fact,the electrocoalescence process of droplets is realized by means of a uniform electric field.Attracted by static electricity,the droplets are polarized and drawn towards each other.Although uniform electric field can promote the coalescence of nano-droplets,it still has some limitations:(1)smaller coalescence range;(2)larger energy consumption.Therefore,in this paper,by a molecular dynamics method,the law of electrodynamic behavior and the microcosmic mechanism of the formation of nano-droplets in the process of electrostatic polymerization under non-uniform electric field are analyzed from the microscopic perspective.The main research contents of this paper are as follows:Firstly,the electrocoalescence process of single component nano-droplets(namely pure water droplets)under non-uniform electric field was studied.The effects of uniform and non-uniform electric fields on droplet coalescence were compared,and the mechanism of non-uniform electric fields was analyzed.The results show that the droplet coalescence efficiency under non-uniform electric field is twice as high as that under uniform electric field,while the average electric field intensity is only 1/2 of that under a uniform electric field.In the non-uniform electric field,a non-zero resultant force(dielectrophoretic force)is generated on the droplet due to the different electric field intensity at both ends of the droplet,which promotes the droplet migration.Under the effect of the strong electric field,the dielectrophoretic force can be clearly observed to promote droplets coalescence.In addition,by increasing the electric field gradient,it is found that the dielectrophoretic force will accelerate the droplet coalescence.However,when the electric field gradient increases to a certain extent,the dielectrophoretic force acting on the droplet will rapidly increase in a nonlinear manner,and due to the strong tensile effect,the droplet will form a chain-like structure,or even form a droplet secondary dispersion.Secondly,the electrocoalescence process of salt ion nano-droplet was studied under the action of the non-uniform electric field.For multi-component droplets containing salt ions,the presence of ions will change the electrocoalescence process of droplets.As the ions in the droplet will form a symmetrical distribution similar to the structure of the double electron layer,the one side with high electric field intensity is the adsorption layer,and the other side with low electric field intensity is the diffusion layer.The ions in the adsorption layer will drive the diffusion layer ions to migrate under the strong electrophoresis force,thus,the ions strengthen electrocoalescence process.At the same time,the process of electrocoalescence of salt ion droplets with different strength and gradient of the non-uniform electric field is analyzed.The results show that similar to the uniform electric field,increasing the intensity and gradient of the electric field can promote the coalescence efficiency of the droplet.The reason is that the larger Coulombic force makes the ions more easily get rid of the bondage of the ion cluster and forms a double-layer structure.However,increasing the electric field gradient only accelerates the formation of a double-layer structure and does not affect the distribution of ions in the droplet.It is found that under the critical electric field intensity,the droplet will undergo secondary coalescence due to the action of the non-uniform electric field.Therefore,the phenomenon of droplet partial coalescence and rebound can be effectively avoided by using the non-uniform electric field on droplet electrostatic polymerization.Finally,the effect of different concentration of salt ions on droplet electrocoalescence under the action of the non-uniform electric field was analyzed.The electrostatic coalescence of droplets with different concentration of salt ions was studied.The results showed that for the droplets with a low concentration(c<1.32mol/L),due to the small number of ions,the interaction between particles needed to be overcome is also small,so the number of ions migrating from the diffusion layer to the adsorption layer is large.Therefore,the increase of ion concentration increases the asymmetry of ions,which is conducive to the further formation of the double layer.For the droplet with high concentration(c>1.32mol/L),the interaction force between particles is enhanced,but the formation of the double-layer structure is restricted.As the concentration of ions increased,the ions gradually formed a symmetrical distribution,which greatly reduced the size of the dielectrophoretic force.