Date of Award

Spring 1-1-2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy In Chemical Engineering Degree

Department

Chemical And Biomedical Engineering

First Advisor

Ao, Geyou

Second Advisor

Christopher L. Wirth, Ph.D.

Third Advisor

Orhan Talu, Ph.D.

Abstract

Stable liquid dispersions and the subsequent self-assembly of boron nitride (BN) nanostructures are a vital precursor for translating their exceptional electrical, mechanical, thermal, and optical properties into large-area assemblies with controlled properties. However, achieving individually dispersed BN nanomaterials including BN nanotubes (BNNTs) and hexagonal BN nanosheets (hBN) in almost any solvent has been hindered by strong van der Waals interactions among nanomaterials. In this dissertation work, we reported a comprehensive study on developing an efficient dispersion, self-assembly, and rheological characterization of BN nanomaterials. Particularly, we reported a highly efficient dispersions of BNNTs through noncovalent complexation while exploiting the solvent-nanotube-dispersant interactions using biopolymer DNA and various solvents including water and alcohol. The subsequent purification by membrane filtration revealed that the raw BNNT material constitutes ~ 45.2 mass % of non-nanotube impurities. Ofthe alcohols tested, isopropyl alcohol (IPA) was found to be an efficient solvent, resulting in a dispersion yield of as high as ~ 48 % nanotubes in an IPA/water mixture with 60 vol % IPA by mild bath sonication. Molecular dynamics simulations further revealed that IPA played a pseudosurfactant role in solvating BNNTs by replacing water molecules in the solvation layer while IPA is added. The dispersion techniques developed for BNNTs has been extended for aqueous dispersions of v hBN as well. Additionally, we demonstrated the formation of solid BNNT films comprised of spontaneously aligned nanotubes through drop drying of DNA-wrapped BNNTs. The overall properties of solid BNNT assemblies are directly influenced by the physical properties of nanotubes, including the tube lengths. Conventional surface deposition method by imaging dried samples on a substrate revealed inconsistencies in the average lengths of the parent BNNTs coated by DNA and SDC, due to the differential binding of DNA-BNNTs to a substrate. Therefore, we determined the nanotube lengths using an alternative method - rheological characterization - by measuring the viscosity of dilute dispersions of DNA-BNNTs, highlighting the Brownian rigid rod behavior of BNNTs. Combined, our study on the dispersion, self-assembly and rheology of BN nanomaterials paved a way for producing BN assemblies with controlled properties while offering green chemistry and multifunctionality.

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