Collaborative Research: Real-time Investigations of Anisotropic Nanoparticle Aggregation and Consequences for Deposition in Porous Media

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Nanoparticles are prevalent in nature and widely produced in a variety of shapes and sizes in ever-increasing quantities. These nanoparticles often aggregate in water, and thus they typically transport and deposit in environmental media in the form of aggregates instead of individual nanoparticles. However, how the structure of nanoparticle aggregates influence nanoparticles' movement in the environment is not well understood. The overall objective of this project is to better understand the interactions of nanoparticulate aggregates with environmental media and how these interactions can be governed by the shape and size of the individual nanoparticles. Findings from this work can benefit the design and optimization of a broad range of engineered processes, such as filter-based water treatment, groundwater remediation, and drug delivery. This project will also benefit K-12 education through outreach activities involving videos and pictures of nanomaterials. Additional outreach programs include 1) the Summer Coding Camp, at Ohio University to introduce middle school girls to the STEM fields, and 2) various science activities offered by Nebraska Center for Materials and Nanosciences at the University of Nebraska-Lincoln to broaden the exposure of K-12 students to materials science and engineering, nanoscience, and nanotechnology. In addition, the PIs will leverage the existing REU programs at the University of Nebraska-Lincoln to train Ohio university undergraduate students during summers. In the past, nanoparticle aggregation and deposition were often studied separately, with limited research linking mobility of nanoparticles in environmental media to the structure of nanoparticle aggregates. However, new evidence suggests that anisotropic nanoparticles, the most common form of nanoparticles in the environment, often form non-compact aggregates. The formation of these non-compact aggregates cannot be explained by classic colloidal aggregation theories. Moreover, non-compact aggregates undergo unusual deposition and modify hydrodynamics in environmental porous media, which is not described by the classical filtration theory. Acquisition and integration of quantitative data from all steps involved in nanoparticle aggregation and deposition is critically needed. The research objectives of this project include: 1) Quantifying the anisotropic diffusion dynamics of nanoparticles with various aspect ratios in water; 2) Elucidating the role of the shape of primary nanoparticles on the formation kinetics and morphological structure of aggregates; and 3) Evaluating the impact of aggregate structure on the transport and deposition of aggregates in environmental porous media. Hematite nanoparticles with different aspect ratios (i.e., nanosphere, nanorod, nanodisk) will be synthesized in the study. Advanced techniques will be employed to visualize and quantify nanoparticle diffusion, aggregation, transport, and deposition in environmental matrices. Furthermore, the experimental data will be used to update classical filtration theory for predicting nanoparticle behaviors in porous media. The expected intellectual outcomes from this work will include development of a series of quantitative metrics from measurements of anisotropic diffusion, aggregate formation, and aggregate deposition and flow dynamics in porous media. These quantitative characterizations will allow us to elucidate the mechanisms which control anisotropic nanoparticle aggregation and deposition in environmental porous media. This will, in turn, improve the utility of colloidal science principles in understanding and predicting nanoparticle behaviors, such as colloid Brownian motion theory, colloid aggregation theory, and the classical filtration theory.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.