Interface Effect On Electrokinetic Motion Of An Oil Droplet And A Solid Particle In An Aqueous Solution

The fundamental study on the electrokinetic behavior of an oil droplet and a solid particle in an aqueous solution under an applied electric field has the important scientific significance,and facilitates the development of the separation,concentration and detection technology of the oil in oily sewage from ships and the marine pollutants based on an electric field.This dissertation took oil droplets and particles at various interfaces as research objects and studied the electrokinetic motion of an oil droplet near an air-water interface,attached to an air-water interface from below,and near a horizontal solid surface,as well as the electrokinetic motion of a spherical solid particle at an oil-water interface.The specific contents are as following:(1)A numerical study on the electrokinetic motion of a charged oil droplet near a charged air-water interface is presented in this dissertation.First,the separation distance between the oil droplet and the air-water interface is calculated,and then the electrokinetic velocity of the droplet is simulated utilizing a three-dimensional numerical model.The numerical results indicate that when the water area is infinite,a negatively charged oil droplet near a negatively charged air-water interface moves in the opposite direction of the direct current electric field.(2)The electrokinetic motion of an oil droplet attached to an air-water interface from below is numerically studied by a three-dimensional numerical model and the effects of the mobile air-water interface and the mobile oil-water interface on the electrokinetic motion of the attached oil droplet are investigated and discussed.The results show that when an oil droplet submerged in an infinite water and an air-water interface are all negatively charged,the oil droplet attached to the air-water interface from below moves in the opposite direction to that of the external direct current electric field,and its moving velocity increases with the increase of the absolute values of the negative zeta potentials at both the air-water interface and the oil-water interface.(3)The translational velocity of a negatively charged oil droplet in an aqueous solution near a negatively charged solid surface under a direct current electric field is numerically investigated.The equilibrium separation distance between the charged oil droplet and the charged solid surface is calculated under different parameters and the translational motion of the droplet near the solid surface is simulated via a three-dimensional mathematical model.The results indicate that the velocity of the droplet is higher under a larger zeta potential of the solid surface and a smaller zeta potential of the droplet.When the absolute value of the negative zeta potential of the droplet is larger than that of the solid surface,the droplet will move in opposite direction of the electric field.It is also found that the droplet translational velocity increases with the decrease of the separation distance between the oil droplet and the solid surface.(4)This dissertation also analyzed and derived the electric force actting on a charged spherical particle at an oil-water interface under a direct current electric field.A three-dimensional transient numerical model is developed to investigate the electrokinetic motion of a charged spherical particle at an oil-water interface.The simulation results show that for a negatively charged micro-particle aborbed in a negatively charged oil-water interface in a microchannel,when the absolute value of the negative zeta potential of the particle is much smaller than that of the oil-water interface,the particle moves in the same direction of the electric field;otherwise,the moving direction of the particle is switched.Under the same conditions,when the region of the aboved particle-oil-water system is infinite,the particle moves in the opposite direction of the electric field.By comparison,the simulation results and experimental results match well,which demonstrates the validity and accuracy of the numerical model.The study in this dissertation enriches the theory of the electrokinetic motion of oil droplets and solid particles in the water and provides an important theoretical basis for the practical application of the technique in such as oil separation and recovery,sewage disposal,new material synthesis and liquid-liquid extraction.