Coupled influences of particle shape, surface property and flow hydrodynamics on rod-shaped colloid transport in porous media

Authors: MA, HUILIAN - University Of Utah; Bolster, Carl; JOHNSON, WILLIAM - University Of Utah; LI, KE - University Of Utah; PAZMINO, EDDY - University Of Utah; CAMACHO, KATHRYN - University Of California; ANSELMO, AARON - University Of California; MITRAGOTRI, SAMIR - University Of California

Submitted to: Journal of Colloid and Interface Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/2020
Publication Date: 5/25/2020
Citation: Ma, H., Bolster, C.H., Johnson, W.P., Li, K., Pazmino, E., Camacho, K.M., Anselmo, A.C., Mitragotri, S. 2020. Coupled influences of particle shape, surface property and flow hydrodynamics on rod-shaped colloid transport in porous media. Journal of Colloid and Interface Science. 577:471-480. https://doi.org/10.1016/j.jcis.2020.05.022.
DOI: https://doi.org/10.1016/j.jcis.2020.05.022

Interpretive Summary: Understanding the movement of colloidal-sized particles through through porous media is important for modeling the movement of bacteria, clays, and other small particles through soil. While many natural (including bacteria) or engineered colloidal particles are often non-spherical in shape, most models assume a spherical shape. Non-spherical colloids, however, are expected to behave differently than spherical particles when moving through pore spaces. In this study, polystyrene microspheres were stretched to rod-shaped particles of two different aspect ratios (2:1, 6:1). The transport and retention behaviors of rods versus spheres were investigated in packed quartz sand columns and impinging jet systems. Rods were observed to undergo rotating and tumbling motions in response to fluid shear from experiments and simulations. However, no distinct retention trends between rods and spheres were observed from column studies, despite BSA-coating on particles, Fe-coating on sand or velocity change. This was primarily due to the super-hydrophobic nature of colloid surfaces acquired from stretching process, which in hydrophilic sand columns, dominated particle-surface charge interactions. Simulations using colloids with randomly distributed charge patches qualitatively produced the observed insensitivity in retention respecting aspect ratio under low charge coverage (<30%). Hence, particle shape influences were strongly coupled with colloid surface properties and flow hydrodynamics.

Technical Abstract: Natural or engineered colloidal particles are often non-spherical in shape. In contrast to the widely-used "homogeneous sphere" assumption, the non-spherical particle shape is expected to alter particle-fluid surface interactions, which in turn affect particle transport and retention. Polystyrene microspheres were stretched to rod-shaped particles of two aspect ratios (2:1, 6:1). The transport and retention behaviors of rods versus spheres were investigated in packed quartz sand columns and impinging jet systems. In parallel, a 3D trajectory model was employed to simulate particle translation and rotation, and to elucidate the role and underlying mechanisms of particle shape impact on transport. Rods were observed to undergo rotating and tumbling motions in response to fluid shear from experiments and simulations. However, no distinct retention trends between rods and spheres were observed from column studies, despite BSA-coating on particles, Fe-coating on sand or velocity change. This was primarily due to the super-hydrophobic nature of colloid surfaces acquired from stretching process, which in hydrophilic sand columns, dominated particle-surface charge interactions. Simulations using colloids with randomly distributed charge patches qualitatively produced the observed insensitivity in retention respecting aspect ratio under low charge coverage (<30%). Hence, particle shape influences were strongly coupled with colloid surface properties and flow hydrodynamics.