Recent experimental observations on combined electrokinetic and shear flows of colloidal suspensions in rectangular cross-section microfluidic channels have shown unusual cross-stream colloidal particle migration and dynamic assembly. Although a new electrophoresis-induced lift force has been postulated to cause the lateral migration of colloidal particles, little is known about how fluid properties and flow conditions impact this force and therefore subsequent colloidal particle migration. Furthermore, no experimental quantification of this electrophoresis-induced lift force is available. We report several key advances by demonstrating that the kinematic viscosity of the fluid can be used to modulate the spatial distribution of particles over the entire microchannel cross-section, with suppression of the colloidal particle migration observed with increase in fluid kinematic viscosity. Colloidal particle migration of ∼10 μm from not only the top and bottom microchannel walls but also from the side walls is shown with the corresponding electrophoresis-induced lift force of up to ∼30 fN. The breadth of flow conditions tested capture the channel Reynolds number in the 0.1–1.1 range, with inertial migration of colloidal particles shown in flow regimes where the migration was previously thought to be ineffective, if not for the electrophoresis-induced lift force. The ability of the electrophoresis-induced lift force to migrate colloidal particles across the entire microchannel cross-section establishes a new paradigm for three-dimensional control of colloidal particles within confined microchannels.

中文翻译：

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动电流和剪切流相结合控制胶体颗粒在微通道横截面的分布

最近对矩形横截面微流体通道中胶体悬浮液的动电和剪切流组合的实验观察显示出不寻常的跨流胶体颗粒迁移和动态组装。尽管一种新的电泳引起的升力被认为会引起胶体颗粒的横向迁移，但人们对流体特性和流动条件如何影响该力以及随后的胶体颗粒迁移知之甚少。此外，还没有对这种电泳引起的升力进行实验量化。我们报告了几项关键进展，证明流体的运动粘度可用于调节整个微通道横截面上颗粒的空间分布，随着流体运动粘度的增加观察到胶体颗粒迁移的抑制。显示~10 μm 的胶体颗粒不仅从顶部和底部微通道壁迁移，而且从侧壁迁移，相应的电泳诱导升力高达~30 fN。测试的流动条件范围捕获了 0.1-1.1 范围内的通道雷诺数，在流动状态中显示了胶体颗粒的惯性迁移，如果没有电泳引起的升力，以前认为迁移是无效的。电泳引起的升力使胶体颗粒在整个微通道横截面迁移的能力为有限微通道内胶体颗粒的三维控制建立了新的范例。