Date of Award

8-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

School of Materials Science and Engineering

Committee Member

Dr. O. Thompson Mefford, Committee Chair

Committee Member

Dr. Brian Powell

Committee Member

Dr. Igor Luzinov

Committee Member

Dr. Marek Urban

Committee Member

Dr. Christopher Kitchens

Abstract

The use of iron oxide nanoparticles for a variety of applications has grown over the past few decades. Manipulation of surface chemistry of these materials is critical to customizing the properties of the particles for desired applications. Ligand exchange is a common and versatile tool for surface modification. There are many factors which affect ligand exchange including ligand chain length, number of binding groups, binding group chemistry, and particle aging and oxidation. Furthermore, ligand exchange may not always occur to completion. Therefore, it is important to characterize the surface of the particles to determine the extent of exchange. Current techniques to confirm and monitor ligand exchange can be limited in sensitivity and versatility, and often these techniques must be used in combination to thoroughly characterize the exchange. To address this issue, radioanalytical techniques were developed to quantify ligand exchange on iron oxide nanoparticles and investigate the factors which affect ligand exchange. Oleic acid coated iron oxide nanoparticles were synthesized via thermal decomposition with trace amounts of 14C-oleic acid on the surface. The particles were modified via ligand exchange with a variety of hydrophilic ligands. The modified particles were measured using liquid scintillation counting (LSC) to determine the activity and ultimately, the total number of 14C-oleic acid chains remaining after exchange. These techniques were used to determine effects of head group chemistry with polymeric ligands and effects of head group chemistry, number of binding groups, and ligand exchange reaction parameters with small molecule ligands. Results revealed catechols displace the most oleic acid during exchange. Furthermore, multidenticity, or multiple binding groups, increases the displacement of the oleic acid. Particle aging and oxidation was investigated using these techniques. Unlabeled, oleic acid coated particles which were aged in solution for 2, 7, and 30 days were mixed with 14C-oleic acid in exchange reactions. Results revealed that aging of the particles at 30 days effected an increase in the amount of 14C-oleic acid adsorbed on the particles after exchange. Kinetic analysis of these results indicated an increase in the desorption rate constant and a decrease in the adsorption rate constant with age but with no profound change in the overall reaction rates. A follow-up study with oxidized particles suggested that this behavior may be due to oxidation during aging. Overall, the results signify an increase in the number of available binding sites, possibly due to formation of a defective oxide shell during aging and/or oxidation.

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