Diverse processes—e.g., environmental pollution, groundwater remediation, oil recovery, filtration, and drug delivery—involve the transport of colloidal particles in porous media. Using confocal microscopy, we directly visualize this process in situ and thereby identify the fundamental mechanisms by which particles are distributed throughout a medium. At high injection pressures, hydrodynamic stresses cause particles to be continually deposited on and eroded from the solid matrix—notably, forcing them to be distributed throughout the entire medium. By contrast, at low injection pressures, the relative influence of erosion is suppressed, causing particles to localize near the inlet of the medium. Unexpectedly, these macroscopic distribution behaviors depend on imposed pressure in similar ways for particles of different charges, although the pore-scale distribution of deposition is sensitive to particle charge. These results reveal how the multiscale interactions between fluid, particles, and the solid matrix control how colloids are distributed in a porous medium.

各种过程（例如环境污染，地下水修复，采油，过滤和药物输送）涉及胶体颗粒在多孔介质中的运输。使用共聚焦显微镜，我们可以直接在原位观察该过程，从而确定颗粒在整个介质中分布的基本机理。在高注入压力下，流体动力应力会导致颗粒连续沉积在固体基质上并从固体基质中侵蚀出来，特别是迫使颗粒在整个介质中分布。相比之下，在低注入压力下，腐蚀的相对影响得到了抑制，导致颗粒位于介质入口附近。出乎意料的是，对于不同电荷的粒子，这些宏观分布行为以相似的方式取决于施加的压力，尽管沉积的孔尺度分布对粒子电荷敏感。这些结果揭示了流体，颗粒和固体基质之间的多尺度相互作用如何控制胶体在多孔介质中的分布方式。