脉冲电场O/W乳状液破乳的分子动力学模拟

Molecular Dynamics Simulation of Pulsed Electric Field O/W Emulsion Demulsification

采用分子动力学方法研究了水包油(O/W)型乳状液体系中重油油滴在脉冲电场中的聚集行为.通过改变电场占空比的模拟参数,探讨了一定电场强度下的油滴聚集行为,以及电场破乳时电场强度参数与占空比参数之间的联系.同时利用静电势分布、相互作用势能以及结合构象统计等分析方法,从微观角度说明在电场作用下油滴的电荷分布与聚集机制.模拟结果表明,在近0.40~0.75 V/nm范围内电场强度下,距离一定的重油滴聚集,低电场强度可通过增加占空比促使油滴聚集,且占空比随电场强度的增大而减小;油滴在电场中发生形变,油滴电荷出现两极化分布,带负电沥青质分子引导油滴朝电场反方向移动;无电场下聚集过程中沥青质处于两油滴界面,范德华作用力为油滴聚集的主要作用力,同时油滴界面沥青质分子与周围分子形成π-π结合构象,增强了油滴间的相互作用力.

The aggregation behavior of two heavy oil droplets in an O/W emulsion system in a pulsed electric field was studied by molecular dynamics method.By changing the simulation parameters of duty cycle,the aggregation of oil droplets under certain electric field intensity and the relation between electric field intensity parameters and duty cycle parameters during electric field demulsification were discussed.At the same time,the charge distribution and the accumulation mechanism of oil droplets in the electric field were explained from the microscopic point of view by analysis methods of electrostatic potential distribution,interaction poten⁃tial energy and adsorption structure statistics.The simulation results showed that:(1)the duty cycle could be adjusted to control the applied time of electric field.Oil droplets accumulate at electric field in the range of 0.40-0.75 V/nm,and the duty cycle decreases with the increase of electric field intensity;(2)the oil drop⁃lets deforme and the charge is polarized in the electric field,and the negatively charged asphaltene molecules guid the droplet to move in the opposite direction of the electric field;(3)the asphaltenes are at the interface of two oil droplets in the process of aggregation without electric field,and van der Waals action is the main force for oil droplets'aggregation.Meanwhile,asphaltenes at the interface of oil droplets form π-π binding conformation with surrounding molecules,which enhances the interaction between oil droplets.