Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Breedveld, Victor; Committee Chair: Hess, Dennis; Committee Member: Aidun, Cyrus; Committee Member: Deng, Yulin; Committee Member: Singh, Preet. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Ground Penetrating Radar (GPR) methods have been used to evaluate the presence, extent, and spatial variability of hydrophobic soils in Southern California Watersheds. It has been shown that high frequency ground penetrating radar equipment, under certain conditions, has the ability to determine the presence, depth, and persistence of post fire hydrophobic soils. As part of this study an extensive investigation was undertaken to not only evaluate the capability of this approach but also to understand under what conditions the method can be applied successfully and what are the limitations of the approach. The investigation includes use of computer simulations and modeling, laboratory investigations in sand boxes with native soils, and multiple field trials spanning a five year time period. Of particular significance is the finding that using GPR it is possible to: locate the interface between the uppermost burnt soil layer, and soil horizons below; quantify the depth at which the hydrophobic layer forms; and quantify the spatial extent of the layer. As part of this study best practice methods for both field and lab experimentation have also been developed and are presented in the body of the thesis. Based on this study it is concluded that the use of GPR can provide a much more accurate and comprehensive method of evaluating the nature of hydrophobic layers in such environments than the current point specific manual methods. As a result the use of GPR has significantly advanced our capacity to assess the potential for increased erosion and the generation of debris flows in such environments after rainfall events.

Modern agriculture, the basis of our civilization, provides sustenance for over 7.9 billion people. However, considering the increasing global population and rising living standards, our food production must to grow by ~50% by 2050. Further constraints of limited arable land, freshwater resources, and the threatening effects of climate change, put our food security at risk and call for multifaceted technological intervention. Currently, irrigated agriculture, while only accounting for 20% of cultivated land, contributes 33%-40% of the total food production. Therefore, irrigated agriculture in arid and semi-arid lands can help us address this complex food–water–climate challenge. However, aridlands are characterized by low precipitation, immense evapotranspiration losses, which is often compensated unsustainably by colossal amounts of freshwater. Evaporation from the topsoil in aridlands remains inadequately tackled. For instance, while plastic mulches have been demonstrated to restrict evaporation, their cost, fragility, lack of reuse, and eventual disposal in landfills limit widespread acceptance. In response, we have conceptualized, developed, and field-tested superhydrophobic sand (SHS), a bio-inspired enhancement of common sand with a nanoscale coating of wax. When a 5-10 mm mulch of SHS is applied on top of subsurface-irrigated soil, the evaporation is dramatically reduced; higher soil moisture boosts plant health, biomass, and yields. Our multi-year field trials of SHS application on tomato (Solanum lycopersicum), barley (Hordeum vulgare), and wheat (Triticum aestivum) crops have consistently demonstrated significant enhancement in grain yields ranging from 17%–73%. In this dissertation, we present our translational surface science research spanning materials development and characterization, mass transfer studies and mathematical modeling, and greenhouse and field experiments. To gain insights into the mulching capacity of water-repellent granular media such as SHS, we present an encompassing novel modeling approach based on particle–particle and liquid–particle forces to accurately capture the fate of evaporating liquid marbles. Then, we explain the origins of SHS superhydrophobicity and provide mechanistic insights into SHS mulching action. Subsequently, we present the data from the field trials to demonstrate how SHS shifts the water balance towards higher crop yields. We close the dissertation with SHS lifecycle analysis and environmental impact and practicality considerations.

Abstract: Greener synthetic routes for producing organic molecules are desirable to reduce environmental pollution and lower manufacturing costs.2 In this context, Sharpless & co-workers reported that it is possible to achieve dramatic rate enhancements in a number of cycloaddition reactions, if they were conducted in vigorously mixed oil-water emulsions instead of bulk organic solvents.1 These interfacial reactions – which came to be known as “on-water” reactions – thus present a tantalizing prospect for green chemistry. However, despite many experimental and theoretical studies along this theme, a clear understanding of the governing factors and mechanisms remains unavailable. For instance, proposed mechanisms vary from dangling hydrogen bonds stabilizing transition states, to the specific adsorption of hydroxide ions at the water-organic interface, and the partial dissolution of reactants in water leading to products.3,4,5Additional effects include sharp variations in dielectric constants and hydration levels across the interface and hydrodynamic effects during vigorous stirring. In this thesis, we investigate a Diels-Alder reaction between two water-insoluble reactants – trans,trans-2,4-hexadienyl acetate and N-propylmaleimide– to disentangle the contributions of bulk reactions from interfacial reactions. We compare the conversion of reactants into products in the following scenarios: pure reactants (i) mixed into each other (neat condition), (ii) dissolved in hexane, (iii) dissolved in hexane and vigorously stirred with water (1:1 v/v), and (iv) dissolved in hexane and vigorously stirred in water-methanol mixtures. In addition to vigorously-stirred emulsions that produce polydisperse emulsions, we designed and developed microfluidic devices that allowed us to precisely controlled the water-organic interfacial area. With this6 device, we pin-point interfacial effects on the reaction rates.

In recent years super-hydrophobic micro-patterned substrates (SHS) have been successfully used for the suspension of a few biological molecules, allowing the further characterization in a background-free environment by label-free techniques such as Raman spectroscopy, SEM and TEM in one device. This result is due to the combined action of laminar flow and shear stress exerted on the molecules contained in a drop that is spotted on top of the SHS and slowly evaporates. This new method is here proposed for the label-free formation and background-free characterization of amyloid fibers. Amyloids are insoluble aggregates formed by proteins that convert from a misfolded form into highly-organized β-sheet structures that could accumulate in different organs and compromise their normal physiological functions. Known amyloid-related diseases, named amyloidosis, are for instance Alzheimer, Parkinson, and type 2 diabetes. In classical crystallography, the study of the amyloid aggregates structure is often hampered by the laborious and time consuming sample preparation techniques. Therefore the need of a quick reproducible technique, has emerged. The amyloid fibers investigated in this work are derived from a lysozyme protein and a Tau-derived short peptide, both known to be related to two forms of amyloidosis. With this technique we demonstrate that threads of protein fibers are deposited on the substrate helped by the patterning of the SHS and its properties, and by characterizing them with Raman spectroscopy technique we revealed that they are anisotropic structures of amyloid nature. This type of sample preparation technique arises from the effect of the evaporation on the SHS, and opens up new possibilities for the formation of oriented fibers of amyloids and more in general, of proteins, ready for a substrate-free characterization, while classic crystallographic methods could have a limitation.

This research focused on development of nanoparticle- based therapeutics against amyloid fibrils. Amyloid fibrils are associated with various diseases such as Parkinson’s, Huntington’s, mad cow disease, Alzheimer’s, and cataracts. Amyloid fibrils develop when proteins change their shape from a native form to a pathogenic “misfolded” form. The misfolded proteins have the ability to recruit more native proteins into the pathogenic forms, which self-assemble into amyloid fibrils that are hallmarks of the various protein-misfolding diseases listed above. Amyloid fibrils are highly resistant to degradation, which may contribute to the symptoms of amyloid diseases. Synthetic drugs, natural compounds, and antibodies are widely explored for potential to stop pathogenic protein assembly or to promote fibril degradation and clearance, but to date have had little success in relieving symptoms in clinical trials. In this research, I have synthesized fluorine-containing silica nanoparticles (NPs), and tested their fibril-inhibiting activity against amyloid fibrils formed by a non-pathogenic protein, β-lactoglobulin (BLG). These fluoro-silica NPs prevented BLG amyloid formation, whereas non-fluorinated nanoparticle analogs did not inhibit fibrillation under the same reaction conditions. The fluoro-silica NPs interacted with the BLG protein in a manner that prevented the protein from adopting a form that could self-assemble into fibrils. Additional applications of the NPs were explored as small-molecule drug-delivery systems; such that multiple functionalities could be introduced into a single nano- therapeutic.

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A new processing technique, known as hydrophobic displacement, was explored as a means of simultaneously removing both mineral matter and surface moisture from coal in a single process. Previous thermodynamic analysis suggests that coal moisture will be spontaneously displaced by any oil with a contact angle greater than ninety degrees in water. Based on these results, six methods of hydrophobic displacement were evaluated: hand shaking, screening, air classification, centrifugation, filtration, and displacement. In the first five methods hydrophobic displacement took place during the cleaning stage. A recyclable non-polar liquid (i.e. pentane) was used to agglomerate coal fines followed by a physical separation step to remove the coal agglomerates from the mineral-laden slurry. Bench-scale tests were performed to identify the conditions required to create stable agglomerates. Only the last method, displacement, did not utilized agglomeration and performed hydrophobic displacement during dewatering, not cleaning. A procedure was also developed for determining moisture content from evaporation curves so that the contents of water and pentane remaining in a sample could be accurately distinguished. Two primary coal samples were evaluated in the test program, i.e., dry pulverized 80 mesh x 0 clean coal and 100 mesh x 0 flotation feed. These samples were further screened or aged (oxidized) to provide additional test samples. The lowest moisture, 7.5%, was achieved with centrifugation of the pulverized 80 mesh x 0 clean coal sample. Centrifugation provided the most reliable separation method since it consistently produced low moisture, high combustible recoveries, and high ash rejections. Hand shaking produced the next lowest moisture at 16.2%; however, the low moistures were associated with a drop in combustible recovery. There was also a great deal of error in this process due to its arbitrary nature. Factors such as oxidation, size distribution, and contact angle hysteresis influenced the concentrate moistures, regardless of the method utilized. / Master of Science

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