Award Date

5-1-2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

First Committee Member

Hui Zhao

Second Committee Member

Yingtao Jiang

Third Committee Member

Yi-Tung Chen

Fourth Committee Member

Kwang Kim

Fifth Committee Member

Pengtao Sun

Number of Pages

106

Abstract

In this project we are interested in electrokinetics phenomenon (i.e., study of electrical charges in a liquid matter) and focus on three families of this phenomenon, dielectrophoresis, electro-osmosis and streaming current. For the first work, at concentrated electrolytes, the ion-ion electrostatic correlations effect is considered as an important factor in electrokinetics. In this project, we compute, in theory and simulation, the dipole moment for a spherical particle (charged, dielectric) under the presence of an alternating electric field using the modified continuum Poisson-Nernst-Planck (PNP) model by Bazant et al. (Phys. Rev. Lett. 106, 2011) [25]. We investigate the dependency of the dipole moment in terms of the frequency and its variation with such quantities such as zeta potential, electrostatic correlation length, and double layer thickness. With thin electric double layers, we develop simple models through performing an asymptotic analysis to the modified PNP model. We also present numerical results for an arbitrary Debye screening length and electrostatic correlation length. From the results, we find a complicated impact of electrostatic correlations on the dipole moment. For instance, with increasing the electrostatic correlation length, the dipole moment decreases and reaches a minimum, and then it goes up. This is because of initially decreasing of surface conduction and it’s finally increasing due to the impact of ion-ion electrostatic correlations on ion’s convection and migration. Also, we show that in contrast to the standard PNP model, the modified PNP model can qualitatively explain the data from the experimental results in multivalent electrolytes.

For the second study, Ion-ion electrostatic correlations are recognized to play a significant role in the presence of concentrated multivalent electrolytes. To account for their impact on ionic current rectification phenomenon in conical nanopores, we use the modified continuum Poisson-Nernst-Planck (PNP) equations by Bazant et al. [Phys. Rev. Lett. 106, 046102 (2011)]. Coupled with the Stokes equations, the effects of the electroosmotic flow (EOF) are also included. We thoroughly investigate the dependence of the ionic current rectification ratios as a function of the double layer thickness and the electrostatic correlation length. By considering the electrostatic correlations, the modified PNP model successfully captures the ionic current rectification reversal in nanopores filled with lanthanum chloride LaCl3. This finding qualitatively agrees with the experimental observations that cannot be explained by the standard PNP model, suggesting that ion-ion electrostatic correlations are responsible for this reversal behavior. The modified PNP model not only can be used to explain the experiments, but also go beyond to provide a design tool for nanopore applications involving multivalent electrolytes.

The third part of this project deals with applying modified PNP equations to compute streaming current which is generated by a pressure-driven liquid flow in nanochannels. Streaming currents are the results of the transport of counterions in the electric double layer, when a pressure gradient is applied. The accumulated counterions at the end of the reservoir are inducing the streaming potential. Streaming current can provide an effective tool to convert hydrostatic pressure differences into electrical energy. In this project, by using modified PNP, we compute streaming current and potential in a silica nanochannel. The efficiency of nanochannel is increasing as the correlation length is getting higher. As the correlation length is increasing the negative ions are depleted inside the nanochannel and the ionic current is mainly consisting of cations. So, at higher correlation length the smaller the thickness of the EDL, the higher the efficiency is.

Keywords

Electrokinetics phenomenon; Dielectrophoresis,; Electro-osmosis; Streaming current

Disciplines

Mechanical Engineering

File Format

pdf

File Size

1.6 MB

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/


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