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Description
Thiol functionalization is one potentially useful way to tailor physical and chemical properties of graphene oxides (GOs) and reduced graphene oxides (RGOs). Despite the ubiquitous presence of thiol functional groups in diverse chemical systems, efficient thiol functionalization has been challenging for GOs and RGOs, or for carbonaceous materials in general. In this work, thionation of GOs has been achieved in high yield through two new methods that also allow concomitant chemical reduction/thermal reduction of GOs; a solid-gas metathetical reaction method with boron sulfides (BxSy) gases and a solvothermal reaction method employing phosphorus decasulfide (P4S10). The thionation products, called "mercapto reduced graphene oxides (m-RGOs)", were characterized by employing X-ray photoelectron spectroscopy, powder X-ray diffraction, UV-Vis spectroscopy, FT-IR spectroscopy, Raman spectroscopy, electron probe analysis, scanning electron microscopy, (scanning) transmission electron microscopy, nano secondary ion mass spectrometry, Ellman assay and atomic force microscopy. The excellent dispersibility of m-RGOs in various solvents including alcohols has allowed fabrication of thin films of m-RGOs. Deposition of m-RGOs on gold substrates was achieved through solution deposition and the m-RGOs were homogeneously distributed on gold surface shown by atomic force microscopy. Langmuir-Blodgett (LB) films of m-RGOs were obtained by transferring their Langmuir films, formed by simple drop casting of m-RGOs dispersion on water surface, onto various substrates including gold, glass and indium tin oxide. The m-RGO LB films showed low sheet resistances down to about 500 kΩ/sq at 92% optical transparency. The successful results make m-RGOs promising for applications in transparent conductive coatings, biosensing, etc.
ContributorsJeon, Kiwan (Author) / Seo, Dong-Kyun (Thesis advisor) / Jones, Anne K (Committee member) / Yarger, Jeffery (Committee member) / Arizona State University (Publisher)
Created2013
Description
Glycosaminoglycans (GAGs) are a class of complex biomolecules comprised of linear, sulfated polysaccharides whose presence on cell surfaces and in the extracellular matrix involve them in many physiological phenomena as well as in interactions with pathogenic microbes. Decorin binding protein A (DBPA), a Borrelia surface lipoprotein involved in the infectivity of Lyme disease, is responsible for binding GAGs found on decorin, a small proteoglycan present in the extracellular matrix. Different DBPA strains have notable sequence heterogeneity that results in varying levels of GAG-binding affinity. In this dissertation, the structures and GAG-binding mechanisms for three strains of DBPA (B31 and N40 DBPAs from B. burgdorferi and PBr DBPA from B. garinii) are studied to determine why each strain has a different affinity for GAGs. These three strains have similar topologies consisting of five α-helices held together by a hydrophobic core as well as two long flexible segments: a linker between helices one and two and a C-terminal tail. This structural arrangement facilitates the formation of a basic pocket below the flexible linker which is the primary GAG-binding epitope. However, this GAG-binding site can be occluded by the flexible linker, which makes the linker a negative regulator of GAG-binding. ITC and NMR titrations provide KD values that show PBr DBPA binds GAGs with higher affinity than B31 and N40 DBPAs, while N40 binds with the lowest affinity of the three. Work in this thesis demonstrates that much of the discrepancies seen in GAG affinities of the three DBPAs can be explained by the amino acid composition and conformation of the linker. Mutagenesis studies show that B31 DBPA overcomes the pocket obstruction with the BXBB motif in its linker while PBr DBPA has a retracted linker that exposes the basic pocket as well as a secondary GAG-binding site. N40 DBPA, however, does not have any evolutionary modifications to its structure to enhance GAG binding which explains its lower affinity for GAGs. GMSA and ELISA assays, along with NMR PRE experiments, confirm that structural changes in the linker do affect GAG-binding and, as a result, the linker is responsible for regulating GAG affinity.
ContributorsMorgan, Ashli M (Author) / Wang, Xu (Thesis advisor) / Allen, James (Committee member) / Yarger, Jeffery (Committee member) / Arizona State University (Publisher)
Created2015
Description
Transition metal oxides are used for numerous applications, includingsemiconductors, batteries, solar cells, catalysis, magnetic devices, and are commonly
observed in interstellar media. However, the atomic-scale properties which dictate the
overall bulk material activity is still lacking fundamental details. Most importantly, how
the electron shells of metals and O atoms mix is inherently significant to reactivity. This
thesis compares the binding and excited state properties of highly correlated first-row
transition metal oxides using four separate transition metal systems of Ti, Cr, Fe and Ni.
Laser ablation coupled with femtosecond pump-probe spectroscopy is utilized to resolve
the time-dependent excited state relaxation dynamics of atomically precise neutral
clusters following 400 nm (3.1 eV) photoexcitation. All transition metal oxides form
unique stable stoichiometries with excited state dynamics that evolve due to oxidation,
size, or geometry. Theoretical calculations assist in experimental analysis, showing
correlations between charge transfer characteristics, electron and hole localization, and
magnetic properties to the experimentally determined excited state lifetimes.
This thesis finds that neutral Ti and Cr form stable stoichiometries of MO2 (M =
Ti, Cr) which easily lose up to two O atoms, while neutral Fe and Ni primarily form MO
(M = Fe, Ni) geometries with suboxides also produced. TiO2 clusters possess excited
state lifetimes that increase with additional cluster units to ~600 fs, owing to a larger
delocalization of excited charge carriers with cluster size. CrO2 clusters show a unique
inversed metallic behavior with O content, where the fast (~30 fs) metallic relaxation
component associated with electron scattering increases with higher O content, connected
to the percent of ligand-to-metal charge transfer (LMCT) character and higher density of
states. FeO clusters show a decreased lifetime with size, reaching a plateau of ~150 fs at
the size of (FeO)5 related to the density of states as clusters form 3D geometries. Finally,
neutral (NiO)n clusters all have similar fast lifetimes (~110 fs), with suboxides possessing
unexpected electronic transitions involving s-orbitals, increasing excited state lifetimes
up to 80% and causing long-lived states lasting over 2.5 ps. Similarities are drawn
between each cluster system, providing valuable information about each metal oxide
species and the evolution of excited state dynamics as a result of the occupied d-shell.
The work presented within this thesis will lead to novel materials of increased reactivity
while facilitating a deeper fundamental understanding on the effect of electron
interactions on chemical properties.
ContributorsGarcia, Jacob M. (Author) / Sayres, Scott G (Thesis advisor) / Yarger, Jeffery (Committee member) / Steimle, Timothy (Committee member) / Arizona State University (Publisher)
Created2021
Description
Water-soluble, adenosine triphosphate (ATP)-stabilized palladium nanoparticles have been synthesized by reduction of palladium salt in the presence of excess ATP. They have been characterized by electron microscopy, energy dispersive X-ray spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, and X-ray diffraction in order to determine particle size, shape, composition and crystal structure. The particles were then subsequently attached to a glassy carbon electrode (GCE) in order to explore their electrochemical properties with regard to hydrogen insertion in 1 M sodium hydroxide. The particles were found to be in the size range 2.5 to 4 nm with good size dispersion. The ATP capping ligand allowed the particles to be air-stable and re-dissolved without agglomeration. It was found that the NPs could be firmly attached to the working electrode via cycling the voltage repeatedly in a NP/phosphate solution. Further electrochemical experiments were conducted to investigate the adsorption and absorption of hydrogen in the NPs in 1 M sodium hydroxide. Results for cyclic voltammetry experiments were consistent with those for nanostructured and thin-film palladium in basic solution. Absorbed hydrogen content was analyzed as a function of potential. The maximum hydrogen:Pd ratio was found to be ~0.7, close the theoretical maximum value for β phase palladium hydride.
ContributorsLamb, Timothy (Author) / Buttry, Daniel A (Thesis advisor) / Yarger, Jeffery (Committee member) / Ros, Alexandra (Committee member) / Arizona State University (Publisher)
Created2013
Description
An evolving understanding of elastomeric polymer nanocomposites continues to expand commercial, defense, and industrial products and applications. This work explores the thermomechanical properties of elastomeric nanocomposites prepared from bisphenol A diglycidyl ether (BADGE) and three amine-terminated poly(propylene oxides) (Jeffamines). The Jeffamines investigated include difunctional crosslinkers with molecular weights of 2,000 and 4,000 g/mol and a trifunctional crosslinker with a molecular weight of 3,000 g/mol. Additionally, carbon nanotubes (CNTs) were added, up to 1.25 wt%, to each thermoset. The findings indicate that the Tg and storage modulus of the polymer nanocomposites can be controlled independently within narrow concentration windows, and that effects observed following CNT incorporation are dependent on the crosslinker molecular weight.
Polymer matrix composites (PMCs) offer design solutions to produce smart sensing, conductive, or high performance composites for a number of critical applications. Nanoparticle additives, in particular, carbon nanotubes and metallic quantum dots, have been investigated for their ability to improve the conductivity, thermal stability, and mechanical strength of traditional composites. Herein we report the use of quantum dots (QDs) and fluorescently labeled carbon nanotubes (CNTs) to modify the thermomechanical properties of PMCs. Additionally, we find that pronounced changes in fluorescence emerge following plastic deformation, indicating that in these polymeric materials the transduction of mechanical force into the fluorescence occurs in response to mechanical activation.
Segmented ionenes are a class of thermoplastic elastomers that contain a permanent charged group within the polymer backbone and a spacer segment with a low glass transition temperature (Tg) to provide flexibility. Ionenes are of interest because of their synthetic versatility, unique morphologies, and ionic nature. Using phase changing ionene-based nanocomposites could be extended to create reversible mechanically, electrically, optically, and/or thermally responsive materials depending on constituent nanoparticles and polymers. This talk will discuss recent efforts to utilize the synthetic versatility of ionenes (e.g., spacer composition of PTMO or PEG) to prepare percolated ionic domains in microphase separated polymers that display a range of thermomechanical properties. Furthermore, by synthesizing two series of ionene copolymers with either PEG or PTMO spacers at various ratios with 1,12-dibromododecane will yield a range of ion contents (hard contents) and will impact nanoparticle dispersion.
Polymer matrix composites (PMCs) offer design solutions to produce smart sensing, conductive, or high performance composites for a number of critical applications. Nanoparticle additives, in particular, carbon nanotubes and metallic quantum dots, have been investigated for their ability to improve the conductivity, thermal stability, and mechanical strength of traditional composites. Herein we report the use of quantum dots (QDs) and fluorescently labeled carbon nanotubes (CNTs) to modify the thermomechanical properties of PMCs. Additionally, we find that pronounced changes in fluorescence emerge following plastic deformation, indicating that in these polymeric materials the transduction of mechanical force into the fluorescence occurs in response to mechanical activation.
Segmented ionenes are a class of thermoplastic elastomers that contain a permanent charged group within the polymer backbone and a spacer segment with a low glass transition temperature (Tg) to provide flexibility. Ionenes are of interest because of their synthetic versatility, unique morphologies, and ionic nature. Using phase changing ionene-based nanocomposites could be extended to create reversible mechanically, electrically, optically, and/or thermally responsive materials depending on constituent nanoparticles and polymers. This talk will discuss recent efforts to utilize the synthetic versatility of ionenes (e.g., spacer composition of PTMO or PEG) to prepare percolated ionic domains in microphase separated polymers that display a range of thermomechanical properties. Furthermore, by synthesizing two series of ionene copolymers with either PEG or PTMO spacers at various ratios with 1,12-dibromododecane will yield a range of ion contents (hard contents) and will impact nanoparticle dispersion.
ContributorsWang, Meng, Ph.D (Author) / Green, Matthew D (Thesis advisor) / Green, Alexander (Committee member) / Yarger, Jeffery (Committee member) / Arizona State University (Publisher)
Created2019