Bello M S, de Besi P, Rezzonico R, Righetti P G, Casiraghi E
Faculty of Pharmacy, University of Milan, Italy.
Electrophoresis. 1994 May;15(5):623-6. doi: 10.1002/elps.1150150186.
The classical von Smoluchowski equation predicts that the electroosmotic mobility generated by the wall zeta potential could be suppressed if the viscosity of the solution adjacent to the wall were extremely high. When performing runs in capillaries filled with polymer solutions (2% methyl cellulose solutions with viscosities of 25 cP), however, one consistently finds that the quenching of electroosmotic mobility is substantially less than predicted by the von Smoluchowski relationship. The electroosmotic flow is progressively suppressed with subsequent electrophoretic runs, suggesting a "dynamic coating" of the polymers onto the capillary wall. This progressive reduction of electroosmotic mobility tends to a plateau value which is still substantially higher than the value derived on the basis of the von Smoluchowski relationship. The following explanation is proposed: due to the very high shear rate in the electric double layer, the polymer molecules change their orientation and/or conformation, which lowers the fluid viscosity in this region. A scaling equation for electroosmotic mobility taking into account the non-Newtonian properties of polymer solutions is derived. It predicts electric field dependence of the electroosmotic mobility as the shear rate in the double layer is proportional to the electric field. Experimental measurements confirm the dependence of the electroosmotic mobility on the electric field.
经典的冯·斯莫卢霍夫斯基方程预测，如果壁面附近溶液的粘度极高，由壁面zeta电位产生的电渗迁移率可能会受到抑制。然而，当在充满聚合物溶液（粘度为25 cP的2%甲基纤维素溶液）的毛细管中进行实验时，人们始终发现电渗迁移率的猝灭程度远低于冯·斯莫卢霍夫斯基关系所预测的程度。随着后续的电泳实验，电渗流逐渐受到抑制，这表明聚合物在毛细管内壁上形成了“动态涂层”。这种电渗迁移率的逐渐降低趋于一个平稳值，该值仍然远高于基于冯·斯莫卢霍夫斯基关系得出的值。现提出以下解释：由于双电层中极高的剪切速率，聚合物分子改变了其取向和/或构象，从而降低了该区域的流体粘度。推导了一个考虑聚合物溶液非牛顿性质的电渗迁移率标度方程。由于双电层中的剪切速率与电场成正比，该方程预测了电渗迁移率与电场的相关性。实验测量证实了电渗迁移率与电场的相关性。
