Date of Award

Spring 1-1-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical & Biochemical Engineering

First Advisor

Daniel K. Schwartz

Second Advisor

Joel Kaar

Third Advisor

Thomas Perkins

Fourth Advisor

Diego Krapf

Fifth Advisor

Charles Musgrave

Abstract

The overall objective of this work was to develop new analytical methods for characterizing molecular dynamics at the solid-liquid interface. We used single-molecule imaging, based on total internal reflection fluorescence microscopy, to observe surface-active molecules at silica-aqueous interfaces and leveraged high-throughput computational tools to create massive datasets capturing broad distributions of molecular kinetics and detailed information on surface lateral heterogeneity. We developed novel statistical approaches to learn about the molecular-level physical processes in unprecedented detail. With respect to specific applications, we first demonstrated how single-molecule imaging yields a deeper understanding of chromatographic media. We used a combination of single-molecule observations and macroscopic reversed phase liquid chromatography to characterize the surface activity of a hydrophobic analyte across a range of solution conditions, focusing on how anomalous surface sites affected the adsorption kinetics and retention in the column. The other two projects described in this thesis focused on understanding molecular mobility and structure—important variables to consider in the self-assembly of nanodevices and surface coatings. Building off of our understanding of hydrophobic systems, we carefully studied surface diffusion at the interface of a hydrophobic surface and aqueous solution and found that diffusion could be rationally manipulated by changing the polarity of the solution, although the average diffusive behavior was strongly affected by the prevalence of anomalous surface sites. Finally, we developed a new surface mapping method to correlate the conformation and adsorption behavior of molecular building blocks on surfaces. We characterized alpha-helical peptides on deliberately patterned and nominally uniform surfaces of varying hydrophobicity and found that the peptide conformation and adsorption kinetics were sensitive to microscopic, lateral surface heterogeneity. In all of this work, spatial variations in surface chemistry were observed to profoundly affect surface dynamics with significant impact on self-assembly and chemical separation processes. More generally, we found that surface heterogeneity is seemingly ubiquitous and changes considerably the correct interpretation of ensemble-averaged experiments and molecular simulations.

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