Dynamics of charged sub-micron or colloidal particles in a microfluidic device through cross-stream migration under combined pressure gradients and electric potential gradients was demonstrated using confocal microscopy. The microfluidic device was a rectangular cross-section poly(dimethylsiloxane) or PDMS microchannel sealed with a borosilicate glass lid to form a hybrid PDMS-glass device. We postulate that the reported particle migration may arise in response to electrophoretic particle slip, i.e., the difference between the particle and fluid velocities, due to the applied electric potential gradient across the microchannel. Colloidal particle migration was observed either towards or away from the microchannel walls depending on the relative directions for the applied potential and pressure gradients. When pressure gradient driving the fluid flow and potential gradient were applied in the same direction, colloidal particles migrate away from the microchannel walls. In the case of opposite directions for the pressure and potential gradients, colloidal particles migrate towards the microchannel walls and subsequently assemble into distinct bands next to both the bottom glass and top PDMS walls. The results reported here demonstrate that the particle dynamics due to electrophoresis in Poiseuille flow within a microchannel result in non-uniform spatial distributions of colloidal particles via cross-stream migration, with the ability to assemble particles into distinct band structures at channel walls. Such manipulation, once fully realized, could lead to several microfluidics applications in material synthesis, particle separation, and biosensing.

使用共聚焦显微镜证明了在组合压力梯度和电势梯度下，通过交叉流迁移，微流体装置中带电的亚微米或胶体颗粒的动力学。微流体装置是矩形截面的聚（二甲基硅氧烷）或PDMS微通道，用硼硅酸盐玻璃盖密封以形成混合PDMS-玻璃装置。我们假设报告的粒子迁移可能是由于电泳粒子滑移而引起的，即由于跨微通道施加的电势梯度，导致粒子与流体速度之间的差异。根据所施加的电势和压力梯度的相对方向，观察到胶体粒子向微通道壁移动或向微通道壁移动。当沿相同方向施加驱动流体流动的压力梯度和电势梯度时，胶体颗粒会从微通道壁移走。在压力和电势梯度的方向相反的情况下，胶体颗粒向微通道壁迁移，随后聚集在底部玻璃和顶部PDMS壁旁边的不同条带中。此处报告的结果表明，由于微通道内Poiseuille流动中的电泳而产生的粒子动力学，会导致通过横流迁移而产生的胶体粒子空间分布不均匀，并具有在通道壁处将粒子组装成不同的能带结构的能力。这种操作一旦完全实现，可能会导致在材料合成，颗粒分离和生物传感中的多种微流控应用。