This video shows direct observation of colloid microspheres of 2 mm diameter being transported in a microscopic granular media domain of glass beads that are approximately 1 mm diameter. The main flow direction is from bottom left to top right. Colloids show as bright white dots. Under unfavorable conditions colloids spend a significant time in the near‑surface fluid domain prior to attachment or re‑entrainment back to bulk fluid; there is frequent slow colloid motion along the grain surface, with a subset of the colloids becoming attached. In contrast, under favorable conditions, attachment occurs immediately once the colloid enters the near‑surface fluid domain; there is no action at the grain surface other than the sudden appearance of the attached colloid as can be viewed here.
A discussion of the material in this video is provided in Section 5.1.1 ‘Colloid Motion in Near Surface Fluid Domain in Pore Scale Experiments’ of the Groundwater Project book ‘Colloid (Nano- and Micro-Particle) Transport and Surface Interaction in Groundwater’, the PDF can be downloaded at that link.
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Citation: Johnson, W.P. & Pazmiño, E.F. (2023). Colloid Attachment to Porous Medium Under Unfavorable Conditions. Video of The Groundwater Project, Guelph, Ontario, Canada.