Date of Award

8-7-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Dr Gangli Wang

Abstract

Solid-state nanopores, nanopipettes, and other nano-channel type structures have been of significant interest due to potential applications in separation, energy storage, energy conversion, sensing, imaging and localized delivery of stimulus. At the nanoscale interfacial properties of the substrate have significant impacts on fundamental transport processes, and interesting phenomena are observed such as current rectification and frequency dependent responses such as pinched hysteresis loops and cross points in conductivity measurements.

It well known that the role of cations and anions in the respective contributions to the overall conductivity will depend on the charge sign on the substrate of interest but directly observing the behavior of ions is not currently accessible by available techniques. The electroosmotic flow (EOF) which is convoluted with migration and diffusive transport is difficult to quantify in nano-apertures and approaches such as using dyes to measure flow rate occur in apertures on the micrometer scale. We use finite element modeling of a nanopore system, by solving the Poisson-Nernst Planck and Navier-Stokes governing equations to elucidate the mechanism of ion transport behaviors in the dynamic transport regime. The determination and differentiation of the role of different nanostructures in terms of shape, half cone angle and radius/dimension on the ion transport is hampered by difficulty of fine control of fabrication experimentally. Using finite element modeling we elucidate the role of individual structure, surface and solution parameters on the ion transport behaviors of counter- and co-ions individually.

This dissertation starts with an introduction on electrokinetic transport in the field of nanofluidics; chapter 2 quantifies the contribution of cations and anions to the ion redistribution process in nano-apertures; chapter 3 quantifies the EOF contribution to the ion transport in nano-apertures; chapter 4 demonstrates the mechanisms behind the EOF transport signatures; chapter 5 discusses ion redistribution and EOF in asymmetric concentration systems; and chapter 6 conclusions and future perspectives of these discoveries. The structure and fluid flow have a significant effect on individual ion behavior in the dynamic transport regime and in the case of flow there is a unique signature created by an electroosmotic flow which can be used to identify devices were flow is a significant component of the ion transport. Using this parameter such as selectivity and power generation can be optimized for applications such as energy extraction from a salinity gradient and water desalination.

DOI

https://doi.org/10.57709/12577823

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