The thesis is divided into two parts: (1) microfluidic modeling of blood cell flow in constricted microvasculature and (2) the kinetic study of self-assembly of Au nanorods with different lengths. The passive mechanism of the flow of neutrophils was studied by using poly(dimethyl siloxane) microchannels with circular cross-sections as model blood vessels and agarose microgels as model cells. Their velocity and pressure profiles at various locations inside the microchannel with constrictions were studied as functions of (a) the initial velocity of the microgels, (b) the degree at which the channel-at-large tapered into the constriction, and (c) the size of microgels. Previously, our group proposed that the kinetics of self-assembly of Au nanorods resembles that of the reaction-controlled step-growth polymerization. To investigate factors that affect the reactivity of functional groups, self-assembly experiments were performed for nanorods with different lengths and their kinetics was analyzed.

The thesis is divided into two parts: (1) microfluidic modeling of blood cell flow in constricted microvasculature and (2) the kinetic study of self-assembly of Au nanorods with different lengths. The passive mechanism of the flow of neutrophils was studied by using poly(dimethyl siloxane) microchannels with circular cross-sections as model blood vessels and agarose microgels as model cells. Their velocity and pressure profiles at various locations inside the microchannel with constrictions were studied as functions of (a) the initial velocity of the microgels, (b) the degree at which the channel-at-large tapered into the constriction, and (c) the size of microgels. Previously, our group proposed that the kinetics of self-assembly of Au nanorods resembles that of the reaction-controlled step-growth polymerization. To investigate factors that affect the reactivity of functional groups, self-assembly experiments were performed for nanorods with different lengths and their kinetics was analyzed.

Thesis (M.S.) -- Mississippi State University. Department of Chemistry. / Title from title screen. Includes bibliographical references.

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This thesis presents an alternative approach for pre-concentrating heavy metals in aqueous environments using electro spun polymer nanofiber sorbents. The conditions for electrospinning polyethersulfone, polystyrene, polysulfone and polyamide-6 were optimized. The morphologies and porosities of the electrospun nanofibers were studied using SEM and BET nitrogen gas adsorptions. The nanofibers had mesoporous morphologies with specific surface areas up to 58 m2/g. The electro spun nanofiber sorbents were characterized in terms of their tunability for both uptake and release of heavy metals. The usability of the sorbent was also assessed. The sorbents showed fast adsorption kinetics for heavy metals « 20 min for As, Cu, Ni and Pb) in different aqueous environments. The adsorption characteristics of the sorbents best fitted the Freundlich isotherm and followed the first order kinetics. The efficiencies of adsorption and desorption of heavy metals on both imidazolyl-functionalized polystyrene and amino-functionalized polysulfone sorbents were more than 95% up to the fifth cycle of usage. Reusability improved dramatically (up to 10 runs of usage) when mechanically stable amino-functionalized nylon-6 electro spun nanofibers were used. The capacity of the amino-functionalized nylon-6 sorbent to pre-concentrate heavy metals compared very favourably with those of aqua regia and HN03+H202 digestions especially in less complex matrices. Due to their highly porous nature, the electro spun nanofibers exhibited high adsorption capacities (up to 50 mg/g) for heavy metal ions. The loading capacities achieved with the imidazolyl-functionalized sorbent were higher than those for amino-functionalized mesoporous silica and biomass-based sorbents. The electro spun nanofiber sorbents presents an efficient and cost effective alternative for preconcentrating heavy metals in aqueous environments.

<p>  </p> <p>A staggering number of problems in materials chemistry relate to controlling the assembly of matter at <10 nm scales, including those with applications in nanoelectronics, energy harvesting, and biomedical device design. It is difficult to achieve precise chemical patterning at the short length scales required for such applications using traditional top-down fabrication methods (<em>e.g., </em>lithographic techniques). On the other hand, biological systems create high-resolution chemical patterns with remarkable efficiency, by assembling simple molecular building blocks with nm-scale features (<em>e.g.,</em> nucleotides, amino acids, lipids) into structurally complex motifs capable of carrying out the diverse functions required for life. </p> <p>Drawing inspiration from the diverse structures and functions of lipids in biological membranes, this work uses lipids to create high-resolution chemical patterns at interfaces, control the growth and self-assembly of nanocrystals, and to facilitate interactions that precisely template nanocrystals at chemically patterned surfaces.</p> <p>Functional alkanes assemble into striped phase monolayers on highly oriented pyrolytic graphite (HOPG), in which the alkyl chains are oriented parallel to the substrate, expressing both the polar and nonpolar regions of the amphiphile at the environmental interface. The same is true for diyne phosphoethanolamine (dPE), a phospholipid with a zwitterionic headgroup. When assembled into striped phases on HOPG, the headgroup zwitterions of dPE are confined in 1-nm-wide rows of functional groups with a pitch of ~7 nm, resulting in ordered arrays of orientable dipoles at the HOPG surface. The chemistry of dimensionally confined functional groups is distinct from bulk solution phase chemistry, and in this case enables powerful directing effects which can be used to template the adsorption of ultranarrow gold nanowires (AuNWs) in precise alignment with the template stripes. </p> <p>Technical grade oleylamine (<em>cis</em>-9-octadecen-1-amine, OLAm, 70% purity) serves as the capping ligand for the AuNWs used in this work, and additionally plays an important role in the assembly of AuNWs at dPE/HOPG surfaces. While technical-grade reagents enable cost-effective and scalable production of materials, variation in the composition of impurities between different batches have significant impacts on nanocrystal morphology and assembly. We show that thermal transitions of alkyl chain impurities (<em>trans</em> and saturated chains) in AuNW ligand shells can be used to regulate AuNW assembly at chemically patterned interfaces. </p> <p>Characterization of OLAm reagents by 1H NMR and mass spectrometry reveals significant and highly variable fractions elaidylamine (ELAm, <em>trans</em>-9-octadecen-1-amine) and octadecylamine (ODAm) between different batches of OLAm. To understand the phase behavior of mixtures of the C18 alkylamines commonly found in technical grade OLAm, we synthesize isomerically pure OLAm and its <em>trans</em> isomer, elaidylamine (ELAm), to generate binary and ternary mixtures with (ODAm), which is commercially available in high purity. Differential scanning calorimetry reveals limited miscibility of the C18 chains, and demonstrates the significant impact of chain composition on the physical properties of mixtures of alkyl chains (<em>e.g.,</em> tech. grade OLAm). Finally, we examine the impacts of <em>trans</em> and saturated alkyl chains on AuNW synthesis. We find that inclusion of ODAm and ELAm in the ligand blend used for AuNW synthesis each result in shorter AuNWs than those synthesized with pure OLAm. We also observe enhanced stability of surface adsorbed AuNWs conferred by <em>trans </em>and saturated chains. </p>

<p>    </p> <p>Surface functionalization of metallic nanoparticles is an attractive route to tailor the ensemble geometry and redox properties of active sites in heterogeneous catalysts. However, it is challenging to generate well-defined interfaces through conventional impregnation and one-pot colloidal synthesis methods. In this work, we utilize ligand exchange reactions for post synthetic surface modification of colloidal nanoparticles to generate unique core-shell and surface alloy structures. We use halometallate and metal chalcogenide complexes to create surface sites that are active for electrocatalytic hydrogen evolution reaction (HER). </p> <p>We synthesize a self-limiting monolayer of metal chalcogenides on colloidal Au nanoparticles through biphasic ligand exchange reaction between ammonium tetrathiomolybdate (NH₄)₂MoS₄ complex and Au nanoparticles. Through a combination of spectroscopy techniques and computational methods, we show that strong Au-S interactions introduce electronic and geometric distortion to the geometry and bond metrics of MoS₄^2-complex. Moreover, proximal MoS₄ units adsorbed on the Au surface interlink to form small MoSx oligomers with highly active bridging disulfide sites. Consequently, these core-shell AuMoS₄ nanoparticles exhibit significantly higher HER activity than MoS₄^2- supported on non-interacting carbon supports under highly acidic electrolyte conditions. Although post catalysis characterization reveals partial hydrolysis of surface adsorbed MoSx species, stable HER activity under bulk electrolysis condition indicates that active sites remain persistent. </p> <p>In an effort to extend these ligand exchange reactions to create metal/metal interfaces on other coinage metal nanoparticles such as Ag, we design metal-ligand coordination complexes to mitigate undesired galvanic replacement reactions. By varying the strength and number of coordinating ligands, we fine-tune the redox potential of oxidized noble metal precursors and confine the deposition of noble metals to a few surface layers of the Ag nanoparticles. We utilize organic amine and phosphine ligands to generate Ag@AgM core-shell nanoparticles, where M = Pd, Pt, and Au. Surface alloy or pure metal shells of Pd and Pt on Ag nanoparticles generated through this ligand-based strategy exhibited high precious metal atom utilization in electrocatalytic hydrogen evolution reaction. </p>

Two batches of CdSe QDs with different sizes were synthesized for immobilizing in polyisoprene (PI), polymethylmethacrylate (PMMA), and low-density polyethylene (LDPE). The combinations of QDs and polymer substrates were evaluated for their analytical fit-for-use in applicable immunoassays. Hydrogen peroxide standards were injected into the flow injection analyzer (FIA) constructed to simulate enzyme-generated hydrogen peroxide reacting with bis-(2,4,6-trichlorophenyl) oxalate. Linear correlations between hydrogen peroxide and chemilumenscent intensities yielded regression values greater than 0.9750 for hydrogen peroxide concentrations between 1.0 x 10-4 M and 1.0 x 10-1 M. The developed technique’s LOD was approximately 10 ppm. Variability of the prepared QD-polymer products was as low as 3.2% throughout all preparations.Stability of the preparations was tested during a 30-day period that displayed up to a four-fold increase in the first 10 days. The preparations were decently robust to the FIA system demonstrating up to a 15.20% intensity loss after twenty repetitive injections.

<p>  </p> <p>From applications in nanoscale electronics to regenerative medicine, there is a strong need for control assembly processes at nanometer length scales.1,2 In this work, we investigate the application of microscale droplet delivery as a rapid and scalable approach to pattern the molecular assembly of nanoscale chemical patterns on highly oriented pyrolytic graphite (HOPG). Furthermore, it was also observed that variations in the blend of alkyl impurities present in technical-grade OLAm reagents influenced the temperature-dependent assembly behavior.13 This suggests a likely role of alkyl chain phase transitions in the ligand shell, particularly in more complex mixtures and for anisotropic nanocrystals.</p> <p>Oleylamine (OLAm) is a common technical-grade reagent used in nanocrystal synthesis. Most nanocrystal synthesis is done using technical grade Oleylamine (70% purity). Higher purity reagents are not readily available because in certain instances, technical grades are obtained from natural substances, resulting in differing impurities compared to those generated during preparative reactions using pure raw materials.3 Technical grade reagents of OLAm contain 70% of the cis chain OLAm and 30% of an unspecified mixture of Elaidylamine (ELAm) , Octadecylamine (ODAm) and segments of various lengths and saturated alkyl chains.4,5 Here, we use Differential Scanning Calorimetry thermograms to investigate the miscibility of binary mixtures of OLAm/ELAm, OLAm/ODAm, and ELAm/ODAm. Ternary mixtures of the lipids showed clear peaks for the trans and saturated impurities.</p> <p>We patterned graphite surfaces with amphiphiles via inkjet printing to quickly generate 1-nm-wide functional patterns. Inkjet printing allowed for long-scale hierarchical patterning. We investigated various ink formulations and the resulting printing quality of functional monolayers on 2D crystalline materials. </p>