动电学效应下微流动近壁面带电离子受力分析

Forces for Charged Ions near Wall of Micro-channel under Electro-kinetics Effects

应用离子分布的Boltzmann定律和Poisson方程研究了微流动中通道近壁面电势的分布,采用Derjaguin理论计算了动电学效应下带电离子受到的双电层作用力,应用Hamaker-DeBoer近似式得到了离子与壁面间的范德瓦尔力,同时也考虑到离子重力的影响,揭示了三种力对带电离子流动特性的影响。研究结果表明:无量纲间距d*≤0.2时,离子重力的影响可以忽略,带电离子主要受范德瓦尔力和双电层作用力的作用,且二力均随d*增大而减小,d*≤0.02时,范德瓦尔力起主要作用,当0.02<d*≤0.2时,双电层作用力逐渐起主导作用;d*>0.2时,重力、范德瓦尔力及双电层作用力都趋于零,均可忽略。

The Boltzmann theory and Poisson equation were used to analyze the distribution of electric potential near the wall in micro-channel flow. The variety of electric double layer interaction force under electro-kinetic effect was calculated with Derjaguin method, the Van Der Waals force between ions and the wall was evaluated by Hamaker-De Boer approximately model. The gravitation of ions was considered, and the effects of three forces on flow characteristics were analyzed. The results showo that (1) In the region d*≤0.2, the influence of gravitation could be neglected, the electric double layer interaction force and Van Der Waals force play a significant role near the wall, and they both decrease with the increase of d*. The influence of Van Der Waals force is mainly concentrated in the region d*≤0.02 while the electric double layer interaction force begins playing a dominant role in the region 0.02<d*≤0.2. (2) The gravitation and Van der Waals force as well as the electric double layer interaction force are infinitesimal and could be neglected in the region d*>0.2.