Bentor Joseph, Gabbard Chase, Bostwick Joshua B, Xuan Xiangchun
Department of Mechanical Engineering, Clemson University, Clemson, South Carolina 29634-0921, United States.
Langmuir. 2024 Sep 11. doi: 10.1021/acs.langmuir.4c02334.
The nonlinear electric field dependence of particle electrophoresis has been demonstrated to occur in Newtonian fluids for highly charged particles under large electric fields. It has also been predicted to arise from the rheological effects of non-Newtonian fluids even at small electric fields. We present in this work an experimental verification of nonlinear electrophoresis in shear thinning xanthan gum solutions through a straight rectangular microchannel. The addition of polymer into a Newtonian buffer solution is found to change the electric field dependence from linear to superlinear for electroosmotic, electrokinetic, and electrophoretic velocities. The nonlinear index of each of these electrokinetic phenomena increases with the increasing polymer or buffer concentration, among which electrophoresis exhibits the strongest nonlinearity. Both these observed trends are captured by a dimensionless electrokinetic shear thinning number that depends on the power-law index of fluid viscosity and the Debye length.
在大电场下，已证明在牛顿流体中，高电荷粒子的粒子电泳存在非线性电场依赖性。据预测，即使在小电场下，非牛顿流体的流变效应也会导致这种现象。在这项工作中，我们通过一个直的矩形微通道，对剪切变稀的黄原胶溶液中的非线性电泳进行了实验验证。发现在牛顿缓冲溶液中添加聚合物会使电渗、电动和电泳速度的电场依赖性从线性变为超线性。这些电动现象的非线性指数均随聚合物或缓冲液浓度的增加而增加，其中电泳表现出最强的非线性。这两种观察到的趋势都可以通过一个无量纲的电动剪切变稀数来描述，该数取决于流体粘度的幂律指数和德拜长度。
