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The increased production of nanomaterials in recent years has been unprecedented. Given their potential toxicity, understanding the mechanisms controlling the transport of nanoparticles in the subsurface is important. In this study, a technique was developed for using a Laser Scanning Cytometer (LSC) to visualize and quantify the stable attachment of nano-scale particles. Experiments using three different size particles, 510 nm, 210 nm and 57 nm, in conjunction with a flow cell system containing saturated glass beads under varied injection duration, solution chemistry, Darcy velocity and solids content were performed. A technique for using the LSC data to develop spatial distributions of attached particles was developed. The ability to provide quantifiable data and a spatial distribution of nanoparticle attachment at the pore-scale is unique and provides direct insight into the fundamental mechanisms governing nanoparticle transport.
The experimental results show attachment decreases with decreasing particle size. The increase in injection duration for the 510 nm particles indicates a likely maximum retention capacity (Smax). Blocking effects are observed for the 57 nm particles in which attached particles block the available attachment sites and slow the rate of attachment. Secondary minimum attachment plays a minor role for the attachment of both the 510 nm and 57 nm particles and is independent of particle size. Only about 10% of the attachment is attributed to secondary minimum attachment. Change of Darcy velocity has no profound influence on the attachment of the 57 nm particles indicating diffusion-dominated attachment. Diffusion control is further confirmed by the spatial distributions of attached 57 nm particles showing attaching on downstream glass bead areas. Investigations of initial solids content reveal the importance of particle (aqueous) - particle (attached) interactions. For the 510 nm and 210 nm particles, there exists a critical initial solids content above which the attachment decreases with increasing initial solids content. This trend does not occur for the 57 nm particles which exhibit increasing attachment with increasing solids content due to much weaker repulsive interaction energy.
Advisor: Yusong Li