Ma Hsien Chen, Keh Huan J
Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan, ROC.
J Colloid Interface Sci. 2007 Sep 15;313(2):686-96. doi: 10.1016/j.jcis.2007.05.007. Epub 2007 Jun 13.
A theoretical study is presented for the steady diffusioosmotic flow of an electrolyte solution in a fine capillary slit with each of its inside walls coated with a layer of polyelectrolytes generated by an imposed tangential concentration gradient. In this solvent-permeable and ion-penetrable surface charge layer, idealized polyelectrolyte segments are assumed to be distributed at a uniform density. The electric double layer and the surface charge layer may have arbitrary thicknesses relative to the gap width between the slit walls. The Poisson-Boltzmann equation and a modified Navier-Stokes/Brinkman equation are solved numerically to obtain the electrostatic potential, dynamic pressure, tangentially induced electric field, and fluid velocity as functions of the lateral position in the slit in a self-consistent way, with the constraint of no net electric current arising from the cocurrent diffusion, electric migration, and diffusioosmotic convection of the electrolyte ions. The existence of the surface charge layers can lead to a diffusioosmotic flow quite different from that in a capillary with bare walls. The effect of the lateral distribution of the induced tangential electric field and the relaxation effect due to ionic convection in the slit on the diffusioosmotic flow are found to be very significant in practical situations.
本文提出了一项理论研究，针对一种电解质溶液在细毛细管狭缝中的稳态扩散渗透流动，该狭缝的每个内壁都涂有一层由施加的切向浓度梯度产生的聚电解质。在这个溶剂可渗透且离子可穿透的表面电荷层中，假设理想化的聚电解质链段以均匀密度分布。相对于狭缝壁之间的间隙宽度，双电层和表面电荷层可以具有任意厚度。通过数值求解泊松 - 玻尔兹曼方程和修正的纳维 - 斯托克斯/布林克曼方程，以自洽的方式获得静电势、动压、切向感应电场和流体速度作为狭缝中横向位置的函数，并满足电解质离子的共流扩散、电迁移和扩散渗透对流不产生净电流的约束条件。表面电荷层的存在会导致一种与裸壁毛细管中的扩散渗透流动截然不同的流动。发现在实际情况中，狭缝中感应切向电场的横向分布以及离子对流引起的弛豫效应对扩散渗透流动的影响非常显著。
