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Iron (Fe) exerts strong control over environmental biogeochemistry. As the fourth most abundant element, Fe is present in nearly all earth environments, where it plays important roles in governing the transformation and movement of organic and inorganic constituents, and in microbial respiration. Consequently, the body of work on Fe biogeochemistry is vast. This study is specifically concerned with the dynamic changes in the oxidation state of Fe (i.e., redox cycling) and their impact on the inorganic, organic and microbial components in soil. I constructed a special apparatus to fluctuate redox potential on soil slurries while concurrently sampling a wide range of biogeochemical variables (pH, redox potential, major and trace elements, CO2 release, DNA community composition charges, etc.). Previous research has documented redox fluctuations along a climate gradient in Hawaii and a primary goal of this dissertation was to reconstruct these redox fluctuations, subjected to experimental constraints afforded by a laboratory setting, with minimal disruption to the biogeochemical processes controlling Fe redox cycling. By recasting the spatial and temporal characteristics of in situ Fe redox cycling in the laboratory, I was able to form testable hypotheses regarding the importance of Fe redox oscillations to soil mineral transformations, colloid composition/dynamics and microbial community structure. A second goal of this dissertation was to explore the utility of Fe isotopic composition for providing information on soil weathering processes along age and climate gradients at the field scale in Hawaii. This portion of the study tested emerging theories of Fe isotope fractionation during mineral dissolution using well-characterized sequences in soil weathering intensity.The principal findings of the laboratory redox fluctuation experiments are that Fe redox oscillations: (1) trigger an increase in the crystallinity of Fe-oxides; (2) mobilize colloids containing refractory elements (e.g., Zr, Nb, U, etc.); (3) reveal redox sensitive rare earth element (REE) anomalies in the aqueous phase; and (4) induce changes in the microbial community favoring microbes capable of growth under both oxic and anoxic conditions. The principal finding of the Fe isotope measurements is that isotopic composition is directly related to weathering intensity in the field, consistent with theoretical predictions.

This dissertation work addresses two important aspects of nanotechnology - stable dispersion and self-assembly of colloidal nanostructures. Three distinctly different types of nano-scaled materials have been studied: 0-dimensional ZnO quantum dots (QDs), 1-dimensional carbon nanotubes (CNTs), and 2-dimensional alpha-zirconium phosphate (ZrP) nanoplatelets. Specifically, highly crystalline ZrP layered compounds with differences in diameters have been synthesized and fully exfoliated into monolayer platelets with uniform thickness, followed by their self-assembly into liquid crystalline structures, i.e., nematic and smectic. A novel colloidal approach to debundle and disperse CNTs has been developed by utilizing nanoplatelets to gather and concentrate sonication energy onto nanotube bundles. In such a fashion, CNTs are fully exfoliated into individual tubes through physical means to preserve their exceptional physical properties. Moreover, monodisperse ZnO QDs with high purity have been synthesized through a simple colloidal approach. Exfoliated ZrP nanoplatelets are used to tune the dispersion of ligand-free ZnO QDs from micron-sized aggregates to an individual QD level depending on the ratio between nanoplatelets and QDs. Dynamic analysis suggests that the dispersion mechanism mainly involves the change of QD dispersion free energy due to the presence of nanoplatelets, so that QDs can interact favorably with the surrounding media. In addition, the nanoplatelet-assisted dispersion approach has been utilized to disperse QDs and CNTs into polymeric matrices. Dispersion - property relationship in polymer nanocomposites has been systematically investigated with emphasis on optical properties for QDs and mechanical properties for CNTs.

Humic-based organic compounds containing phenol or benzoic acid groups strongly compete with phosphates for specific binding sites on the surface of these colloidal particles. To study the interactions between phenol groups and the surface binding sites of unmodified or modified colloidal particles, chemical force spectrometry (CFS) was used as a tool to measure the adhesion force between an atomic force microscopy (AFM) tip terminated with a phenol self-assembled monolayer and colloidal particles under varying pH conditions. Two modification methods, co-precipitation and post-precipitation, were used to simulate the naturally-occurring phosphate and humic-acid adsorption process. The pH dependence of adhesion forces between phenol-terminated tip and colloidal particles could be explained by an interplay of electrostatic forces, the surface loading of the modifying phosphate or humic acid species and ionic hydrogen bonding. Polydimethylsiloxane (PDMS) is a widely-used polymer in microfluidic devices. PDMS surfaces are commonly modified to make it suitable for specific microfluidic devices. We studied the surface modification of PDMS using four perfluoroalkyl-triethoxysilane molecules of differing length of perfluorinated alkyl chain. The results show that the length of fluorinated alkyl chain has important effects on the density of surface modifying molecules, surface topography and surface zeta potential. The perfluorinated overlayer makes PDMS more efficient at supporting electroosmotic flow, which has potential applications in microfluidic devices. The kinetic study of RNase A, lysozyme C, α-lactalbumin and myoglobin at different concentrations adsorbed on the self-assembled monolayers of 1-octanethiol (OT-Au) and 1H, 1H, 2H, 2H-perfluorooctyl-1-thiol (FOT-Au) has been carried out. The results show a positive relationship between the lower protein concentration and the increased adsorption rate constant (ka) on both surfaces. At low concentrations, the protein adsorption on an OT-Au surface has greater ka than it on a FOT-Au surface. Comparing ka values for four proteins on OT-Au and FOT-Au surface demonstrates that hard proteins (lysozyme and RNase A) have larger ka than soft proteins (α-lactalbumin and myoglobin) on both surfaces. The discussion is based on the hydrophobicity of OT-Au and FOT-Au surfaces, as well as average superficial hydrophobicity, flexibility, size, stability, and surface induced conformation change of proteins. / Thesis (Ph.D, Chemistry) -- Queen's University, 2011-10-14 21:08:31.617

Globular proteins are important ingredients in many food formulations because of their nutritional value and their various functional properties such as gel formation. Proteins form gels by polymerization into a three-dimensional matrix. The rheological properties of the resulting viscoelastic solids can be obtained by Instron measurements. In the present work, gels were obtained by heating solutions of bovine serum albumin (BSA) in D$ sb2$O and egg albumin in H$ sb2$O under different conditions (i.e., pH, salt concentration, protein concentration, time of heating and temperature), and their gel strengths were measured by a compression test (Universal Testing Machine LRX). The Fourier transform infrared (FTIR) spectra of the same gel samples were recorded in order to investigate the changes in protein structure at the molecular level accompanying gel formation. Intermolecular $ beta$-sheet formation was found to increase as gel formation progresses at the expense of intramolecular $ beta$-sheet and $ alpha$-helix structures. For BSA, maximum gel strength was obtained around pH 7. The addition of salt had little effect on the gel strength while increase in protein concentration, time of heating and temperature increased the gel strength. The rate of denaturation of BSA and ovalbumin and of mixtures of these proteins in the ratios 9:1, 1:1, and 1:9 was also investigated by measuring the peak height of an aggregation band at 1618 cm$ sp{-1}$; some inhibitory effects of BSA on ovalbumin aggregation were observed. Correlations between the measured gel strengths and the amide I band profile in the FTIR spectra were examined using partial-least-squares (PLS) regression. These studies reveal that gel strengths of a particular protein gel could be adequately predicted from their infrared spectra without the need to carry out the rheological compression measurements.

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This dissertation investigates the emulsification of aqueous liquid in immiscible organic liquid in various microfluidic environments, and addresses both experimental characterization and theoretical interpretation of the dynamics and design guidelines, as well as an application of microfluidic emulsification in fabrication of disk-like colloidal particle suspensions for studying its sedimentation behavior. In an attempt to understand the dynamics of drop formation in flow-focusing microfluidic channels, especially for an explanation of a transition from unique drop size to bimodal oscillating drop sizes as observed in the experiments, numerical simulation is developed to use the volume-of-fraction method to model the drop formation, and the simulation results help to interpret the transition in the theory of saddle-node transition in drop formation, as well as show the importance of selecting proper orifice length in flow-focusing microfluidic channel design. The electric technique for controlling of microfluidic emulsification is explored by a detailed study on low-frequency alternating-current electro-flow-focusing (EFF) emulsification in microfluidic channels. It is found that the droplet size variation is not a monotonic function of the electric field as in the case of direct-current EFF emulsification, which originates from the relaxation oscillation of the flow rate through the Taylor cone, and a power-law droplet size distribution was obtained at the voltage ramping-up stage. This emulsification process was modeled in analog to the charge accumulation and release in a resistor-capacitor electric circuit with an adjustable resistor, and the simulated data exhibit good agreement with the experiments. As an application of the microfluidic emulsification, a method of fabricating disk-like wax colloidal particle suspensions using electrospray is reported. Based on this technique, the first measurement of the hindrance function for sedimentation and creaming of disk-shaped colloids via the analytical centrifugation is reported. Disks align with the external flow right above the volume fraction of a few percent and this effect is extremely sensitive to the aspect ratio of disks. Due to this alignment effect, disk sedimentation/creaming demonstrate distinct trends in dilute and semi-dilute region.

Particulate P constitutes a significant portion of the total P found in surface runoff water. Water dispersed P-containing particles can travel long distances via surface runoff and reach water bodies causing decrease in water quality. The main objective of the study was to evaluate the potential facilitation of P transport by the water dispersed soil colloids (WDC) using three KY soils with a long-term record of poultry manure, and fertilizer P applications. Sequential fractionation for both whole soils and colloidal samples revealed that the WDC had a greater total and labile P content than the soil as a whole. Also, application of manure and fertilizer P seemed to decrease colloidal organic P fractions and increase the inorganic P fractions over the period of a growing season (May to September). Laboratory settling kinetics experiments were set up for the clay-colloidal fractions of the soils. It was shown that particulate P fractions paralleled WDC settling kinetics whereas dissolved P fractions remained in solution even after 36 hours. Field taken intact soil cores were leached with colloidal suspensions to test the effect of WDC on the vertical P movement. Results illustrated the preferential flow of particulate P though the macropores. When water was applied to the manure amended soil, dissolved P levels increased significantly over the control. WDC additions lowered dissolved P levels to the manure-amended columns, by sorbing to the WDC particles, but still greater than the dissolved P levels of the columns that had not been applied with manure.

Hydrogel materials have become a heavily studied as materials for interfacing with biology both for laboratory investigations and the development of devices for biomedical applications. These polymers are water swellable and can be made responsive to many different stimuli by choice of monomers, co-monomers, and cross-linkers or functionalization with pendent ligands, substrates, or charged groups. The high water content, low moduli and potential responsively of these polymers make good candidates for biomaterials. A specific type of hydrogel called a microgel or a hydrogel micro/nanoparticle has similar properties to bulk hydrogel materials. Many of the interesting results and utility of the microgels in bioapplications are due to their inherent softness of the material. Here, the softness, flexibility, and conformability of these water swollen particles is used to create an interesting sensor platform, studied in the context of a microgel passing through a pore, and used as an emulsifier to create a drug delivery platform. The unifying theme of this dissertation is the softness of microgels which is critical for all of these experiments. However, the study of individual microgel softness is challenging and complex, since the softness is composed of two different components. The first is that the microgel is a swollen polymer which can be deswollen by an external stimuli or force. The second is that the microgel is a volume conserving elastic colloid which can deform without deswelling under the certain conditions. Throughout, this dissertation will discuss the ramifications of the complex softness of microgels in each experimental result and potential application.

The growing demand for simulated fish products coupled with the declining stocks of traditional fish species for making these products, have increased efforts aimed at developing novel procedures to put non-traditional fish species like bluefish (Pomatomus saltatrix) and tilapia (Tilapia nilotica) to better economic use. Two procedures which fulfill both objectives are (i) application of high hydrostatic pressure, and (ii) utilization of protease inhibitor to control fresh fish spoilage due to microbial activity and/or autolysis by endogenous enzymes. High hydrostatic pressure has been used to formulate gels with superior functional properties, while $ alpha sb2$-macroglobulin, a broad spectrum protease inhibitor, has been added to control proteolysis in fish gels during processing and storage. / In this study, high pressure was applied at levels of 300 to 3,742 atm for 30 min to formulate gels from bluefish meat paste, and the properties of the resulting gels were compared with those of heat-induced gels formulated at 90$ sp circ$C for 20 min or 60$ sp circ$C for 60 min. / The effects of $ alpha sb2$-macroglobulin and cooking temperatures on the properties of tilapia gels were also studied. (Abstract shortened by UMI.)