CAREER: solute-mediated transport of colloids in porous media

Predicting the motion of small micron-size particles known as colloids in porous media is relevant to many technological, environmental, and biomedical applications, from microplastic spreading in the soil to drug delivery to tumors. The colloidal particles are often suspended in flow through a porous medium in these applications. These flows also produce variations in the concentration of a solute such as a salinity gradient in coastal zones or a contaminant gradient in soil near a discharge. This project will use a combination of experiments, numerical simulations, and theoretical modeling to determine the effects of chemical gradients on the motion of colloids in porous media. The project will integrate research with education and outreach activities, involving high-school and undergraduate students in museum demonstrations of experimental modules related to microplastic spreading in soil, synthetic trees, and extraction of energy from salinity gradients. Predicting and controlling the transport of colloids in porous media is essential in a broad range of problems from filtration and wastewater treatment to contaminant spreading and remediation in subsurface flows. Colloids in these environments are often exposed to chemical gradients, which can lead to their diffusiophoretic migration. This project will use experiments, simulations, and modeling to systematically probe the role of flow velocity disorder, solute gradients, and the 2D/3D nature of the problem on the dispersion and transport of colloids through porous media. This is a multiscale problem, from the nanometric Debye layer next to solid surfaces, where surface charge and zeta potential impacts the diffusioosmotic flows, to the macroscopic dispersion of colloids over the scale of the porous medium. The combination of experiments and simulations probe a wide range of length and timescales, isolating and highlighting the role of key physicochemical ingredients such as surface properties at the nanoscale on the dispersion of colloids at macroscopic scales. Results will advance our fundamental understanding of colloid transport in porous media and lead to predictive models that describe, control, and guide colloids in the presence of flow and solute gradients. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.