AbstractsEarth & Environmental Science

The objective of this project is to synthesize biodegradable micro- and nanoparticles based on calcium carbonate to be used for water treatment purposes. Calcite is a naturally occurring mineral in natural aqueous environments which mitigates the negative environmental impact of these materials versus previously used silver nanoparticles. Polycationic natural and synthetic polymers have been shown to interact electrostatically with bacteria and kill them. Thus, single calcite crystals and the mineral particles are coated with selected polyelectrolytes. A multilayer approach is employed to increase the coverage of the calcite surfaces and slow-down mineral dissolution. The polyelectrolyte multilayer significantly decreases the dissolution of the calcite, so the overall particle will dissolve very slowly over time. Polyallylamine-g-perfluorophenylazide (PAAm-PFPA) is the first polymer layer which allows the attachment of a variety of polyelectrolytes due to covalent bonding by nitrene insertion reactions when exposed to UV light. The adsorbed mass of polyelectrolytes on the mineral is measured with a Quartz Crystal Microbalance (QCM) and multiple beam interferometry. Atomic Force Microscopy (AFM) is used to measure the interaction forces between the coated mineral particles as well as the long-term resistance of the polymers grafted to the mineral subjected to shear. Our measurements indicate that the polymers should stabilize the particles in solution. Under the investigated shear conditions the polymer coating does not wear. The outlook of this project is to prove the antibacterial action of the coated mineral particles. For this purpose, AFM with fluorescence microscopy is the main experimental technique to be used. Escherichia coli (E. coli), a rod-shaped member of the coliform group was chosen for the preliminary studies and fixed to a substrate while a colloidal microsphere was coated with the polymer coating. The preliminary results suggest that instead, a cell probe should be employed to measure interactions with the coated substrate. However, adsorption measurements with the QCM indicate that there is strong yet slow adsorption of E. coli to the polyelectrolyte multilayer unreversed by rinsing which shows promise for bacterial-particle interactions. Advisors/Committee Members: Espinosa-Marzal, Rosa (advisor).