California's almond industry, valued at $2.3 billion per year, depends on the pollinator services of honey bees, although pollination by other insects, mainly solitary wild bees, is being investigated as an alternative because of recent declines in the number of honey bee colonies. Our objective is to model the movements of honey bees and determine the conditions under which they will forage in less favorable areas of a tree and its surroundings when other pollinators are present. We hypothesize that foraging in less favorable areas leads to increased movement between trees and increased cross pollination between varieties which is required for successful nut production. We use the Shigesada-Kawasaki-Teramoto model (1979) which describes the density of two species in a two-dimensional environment of variable favorableness with respect to intrinsic diffusions and intra- and interspecific interactions of species. The model is applied to almond pollination by honey bees and other pollinators with environmental favorableness based on the distribution of flowers in trees. Using the spectral-Galerkin method in a rectangular domain, we numerically approximated the two-dimensional nonlinear parabolic partial differential system arising in the model. When cross-diffusion or interspecific effects of other pollinators was high, honey bees foraged in less favorable areas of the tree. High cross-diffusion also resulted in increased activity in honey bees in terms of accelerations, decelerations, and changes in direction, indicating rapid redistribution of densities to an equilibrium state. Empirical analysis of the number of honey bees and other visitors in two-minute intervals to almond trees shows a negative relationship, indicating cross-diffusion effects in nature with the potential to increase movement to a different tree with a more favorable environment, potentially increasing nut production.

Carbon nanotubes (CNTs) exhibit unique and fascinating intrinsic electrical, optical, thermal or mechanical properties that lead to a plethora of potential applications in composite materials, electronics, energy storage, medicine, among others. However, the manipulation of nanotubes is not trivial and there are significant difficulties to overcome before achieving their full potential in applications. Because of their high aspect ratio and strong tube-to-tube van der Waals interactions, nanotubes form bundles and ropes that are difficult to disperse in liquids. In this thesis, the topic of dispersing carbon nanotubes in water was addressed by several experimental methods such as nuclear magnetic resonance (NMR) diffusometry and light/electron microcopy. The main goal was to obtain molecular information on how the dispersants interact with carbon nanotubes. In dispersions of single-walled carbon nanotubes (SWNTs) in water, only a small fraction of the polymeric dispersant (Pluronic F127) was shown to be adsorbed at the CNT surface. Regarding dynamic features, the residence time of F127 on the SWNT surface was measured to be in the order of hundred milliseconds, and the lateral diffusion coefficient of the polymer along the nanotube surface proved to be an order of magnitude slower than that in the solution. The surface coverage of SWNTs by F127 was also investigated and the competitive adsorption of F127 and the protein bovine serum albumin, BSA, was assessed. F127 was found to bind stronger to the CNT surface than BSA does. Low molecular weight dispersants, viz. surfactants, were also investigated. Using carefully controlled conditions for the sonication and centrifugation steps, reproducible sigmoidal dispersibility curves were obtained, that exhibited an interesting variation with molecular properties of the surfactants. Various metrics that quantify the ability of different surfactants to disperse CNTs were obtained. In particular, the concentration of surfactant required to attain maximal dispersibility depends linearly on alkyl chain length, which indicates that the CNT-surfactant association, although hydrophobic in nature, is different from a micellization process. No correlation between dispersibility and the critical micellization concentration, cmc, of the surfactants was found. For gemini surfactants of the n-s-n type with spacer length s and hydrophobic tail length n, the dispersibility of multiwalled carbon nanotubes (MWNTs) also followed sigmoidal curves that were compared to those obtained with single-tailed homologues. The increase in spacer length caused an increase in the dispersion efficiency. The observations indicate a loose type of monolayer adsorption rather than the formation of micelle-like aggregates on the nanotube surface. With the future goal of embedding nanotubes in liquid crystal (LC) phases and thereby creating nanocomposites, the effect of the spacer length on the thermotropic behavior of the gemini 12-s-12 surfactant was investigated. Different mesophases were observed and a non-monotonic effect of the spacer length was found and rationalized within a model of the surfactant packing in the solid state. The relative binding strength of simple surfactants to CNTs was assessed by the amount of F127 they displace from the CNT surface upon addition. Anionic surfactants were found to replace more F127, which was interpreted as a sign of stronger binding to CNT. The data collected for all surfactants showed a good correlation with their critical dispersibility concentration that suggests the existence of a surface coverage threshold for dispersing nanotubes. On the macroscopic scale, the formation of weakly bound CNT aggregates in homogeneous dispersions was found to be induced by vortex-shaking. These aggregates could quickly and easily be re-dispersed by mild sonication. This counterintuitive behavior was related to the type of dispersant used and of the duration of mechanical agitation and was explained as a result of loose coverage by the dispersant. / <p>This Ph.D thesis was completed under the Thesis Co-supervision Agreement between KTH Royal Institute of Technology and the University of Port. QC 20151105</p>

Title: Investigation of matter transport by means of PFG NMR Author: Mikuláš Peksa Department of low temperature physics Supervisor: doc. RNDr. Jan Lang, Ph.D. Assistant Supervisor: RNDr. Milan Kočiřík, CSc. (ÚFCH JH AV ČR) Abstract: Estimation of transport-structural parameters such as porosity, tortuosity and surface-to-volume ratio of pores in beds of glass beads is the main goal of this study. These parameters were estimated for 5 samples with different distributions of sizes. The second goal is to probe a possibility to use the same approach to describe the self-diffusion in water solution of LiCl confined in two porous materials based on Al2O3 and glass, respectively. The last goal is the measurement of self-diffusion of water molecules in mesoporous geopolymeric material. Its capability of water transport at long scales have been documented. The measurements of apparent self-diffusion coefficients by means of NMR spectroscopy with pulsed field gradients was major methodology of this work. Keywords: porous material, porosity, tortuosity, self-diffusion, NMR

Here, we report on slow Li self-diffusion in lithium containing metal oxide compounds with special emphasis on the influence of structural disorder on diffusion.

Here we investigate the organic ionic plastic crystal (OIPC) 1,2-bis[N-(N\'-hexylimidazolium-d2(4,5))]C2H4 2PF6- in one of its solid plastic crystal phases by means of multi-nuclear solid-state (SS) NMR and pulsed-field-gradient (PFG) NMR. We quantify distinct cation and anion diffusion coefficients as well as the diffusion activation energies (Ea) in this dicationic imidazolium-based OIPC. Our studies suggest a change in transport mechanism for the cation upon varying thermal and magnetic treatment (9.4 T), evidenced by changes in cation and anion Ea. Moreover, variable temperature 2H SSNMR lineshapes further support a change in local molecular environment upon slow cooling in B0. Additionally, we quantify the percentage of mobile anions as a function of temperature from variable temperature 19F SSNMR, where two distinct spectral features are present. We also comment on the pre-exponential factor (D0), giving insight into the number of degrees of freedom for both cation and anion as a function of thermal treatment. In conjunction with previously reported conductivity values for this class of OIPCs and the Stokes-Einstein relation, we propose that ion conduction is dominated by anion diffusion between crystallites (i.e., grain boundaries). Using our experimentally determine diffusion coefficient and previously reported PF6- hydrodynamic radius (rH), viscous (" = 4.1 Pa " s) ionic liquid (IL) is present with a cation rH of 0.34 nm. NMR measurements are very powerful in elucidating fundamental OIPC properties and allow a deeper understanding of ion transport within such materials. / Master of Science

α-Al2O3 is an important refractory material which has numerous technical applications: as an in situ growing self-healing oxide scale, as a massive material and as reinforcement fibres in composites. For modelling diffusion controlled processes (creep, sintering, alpha-alumina scale growth on aluminium bearing Fe or Ni base alloys) it is necessary to study self-diffusion of the constituent elements.

Understanding transport of water molecules and salt ions from a molecular level up to macroscopic length scales is critical to the design of novel materials for many applications, including separations membranes for fuel cell and desalination applications, as well as rechargeable battery technology. This work aims to investigate and develop new models correlating the dynamics and structure of polymeric materials, to the transport of small molecules within them, using a variety of Nuclear Magnetic Resonance (NMR) techniques. We present three studies through which we utilize two chemically similar membranes: hydroxyethyl acrylate-co-ethyl acrylate (HEA-co-EA) and hydroxymethyl methacrylate-co-methyl methacrylate (HEMA-co-MMA), which greatly differ in glass transition temperature, in order to understand the fundamental relationships from polymer chain dynamics and small molecule diffusion. From observations of the micron scale diffusion of these materials we find that the more dynamic, rubbery HEA-co-EA exhibits lower water to salt selectivity than HEMA-co-MMA, and that this difference arises from nanoscale morphology of the materials. From this, we propose a new model for hydrophilic pathways inside polymeric materials consisting of nanometer scale interconnected pathways are interrupted by micron scale arrangements of so-called "dead ends". We also for the first time show the separation of material tortuosity into two regimes, ranging from the nanometer-bulk and micron-bulk length scales. We further separate the contributions of structure from chemical interactions in the chemically similar desalination materials by investigating the local activation energy of diffusion in both materials, as well as aqueous solutions of the hydrophilic monomers analogous to the internal membrane environment. We find that the effects of local geometric confinement are very similar between the two materials, however the intermolecular interactions between water and the hydrophilic monomers, with respect to water transport, are significantly different between the two hydrophilic species. Geometric confinement accounts for a 5 ± 1 kJ/mol increase in diffusive activation energy from solution to membrane for both chemistries, and a 4 ± 1 kJ/mol difference in activation energy is seen between the two chemistries in both solution and membrane form. We propose that the entropic contributions to transport, are strongly impacted by the rigid environment of the HEMA material, and is related to the increased water-salt selectivity, as well as the increasing selectivity with increased ionic size observed compared to the HEA system. Using Dynamic NMR spectroscopy, we further investigate the differences seen in water-monomer intermolecular proton exchange by NMR. We utilize an iterative least-squares solving method to fit our exchange lineshape to a model of an uncoupled, two-site exchange lineshape in order to obtain rate and equilibrium population data from -50 to 70 °C. We find that, similar to the diffusive activation energy, the HEA-water system shows reduced enthalpy and entropy of the transition state compared to HEMA-water, such that there is faster exchange between HEMA and water at all temperatures measured, in addition to more biased populations in the HEA-water system. / Doctor of Philosophy / Understanding transport of water molecules and salt ions from a molecular level up to macroscopic length scales is critical to the design of novel materials for many applications, including separations membranes for fuel cell and desalination applications, as well as rechargeable battery technology. This work aims to investigate and develop new models correlating the dynamics and structure of polymeric materials, to the transport of small molecules within them, using a variety of Nuclear Magnetic Resonance (NMR) techniques. We will present three studies in which we seek to further understand the relationships between a material's physical and chemical properties, with the behavior of small molecules like water absorbed within the material. NMR spectroscopy, while not the standard method for characterizing desalination membranes, allows us to specifically probe direct effects on molecular motion of polymer structure from the microscopic level to the bulk, a feat not easily achieved by any other single technique. The first study presented within focuses on the differences in micrometer scale structure in two near identical sets of materials; differing only in that one is rubbery with flexible polymer chains, and the other is rigid with relatively immobile polymer chains. The second study takes these two materials and investigates them through a different lens, probing the molecular scale differences in water motions imparted by the flexible versus rigid polymer chains. The third and final study looks into the fundamental differences seen in how the two chemistries used to create the polymers in the first two studies interact with water molecules through a different NMR technique. These three studies together represent a series of methods and techniques that can be applied to many other classes of polymer materials, such as those destined for use in fuel cells and rechargeable batteries, in order to better understand the fundamental forces at work in those systems to aid in the design of the next generation's materials.

This dissertation focuses on the fundamental understanding of liquid dynamics confined in polymer membranes. Such knowledge guides the development of better polymer membranes for practical applications and contributes to the general understanding of confined liquid dynamics in various nanoporous materials. First, we investigate the membrane transport by experimental measurements on a PFSA membrane and computer modeling of the confined liquid molecules. We probe the nano-scale environment in the ionomer membrane by determining the activation energy of diffusion. We notice two structural features of the PFSA membrane that dominate membrane transport. At relatively high hydrations, the nano-scale phase-separation creates bulk-like water in the ionomer membrane and prompts fast transport of mobile species. At relatively low hydrations, the nanoconfinement of the polymer matrix leads to the ordering of confined water and prompts a high energy barrier for transport. We then delve deeper into the confinement effect by molecular modeling of various nanoconfining geometries, including carbon nanotubes, parallel graphene sheets, and parallel rigid rods. We notice retarded water dynamics under hydrophobic confinement regardless of the geometry. We further investigate the confined water by determining the residence time of water around water, which evaluates the timescale of associations between water molecules. We learn that a decreasing confinement size prompts longer associations among water molecules. Further, we propose that the prolonged associations are responsible for the retarded water dynamics under hydrophobic confinement. Next, we turn our attention to the effect of interactions between mobile species (mostly water molecules) and a confining surface. In ionomer membranes, interactions between mobile species and the ionic groups dominate the water-surface interactions. We start by looking at water-ion interactions in bulk solutions. Using solutions at varying concentrations, we notice a temperature-concentration superposition behavior from diffusion coefficients of water molecules and ions in the solutions in both experimental and computational results. Observation of this superposition behavior in bulk solutions is unprecedented. The temperature-concentration superposition parallels the well-known time-temperature superposition. We are able to extract the offset of reciprocal temperature, which fits well to a Williams-Landel-Ferry type equation. The temperature-concentration superposition points to the new perspective that the effect of ions on water dynamics can be similar to the effect of lowering temperature. We further investigate the effect of ions by modeling ions/charges onto confining geometries. Remarkably, we reveal that the presence of ions can break the ordered water structure induced by confinement. The hydrophobic confinement prompts the ordering of water molecules, which leads to slower diffusion and higher activation energy. The presence of ions/charges on the confining surface has multiple effects on the dynamics of confined water. First, the ions associate strongly with neighboring water molecules while breaking the hydrogen-bonding network between water molecules. Second, the disruption of the hydrogen-bonding network leads to decreased activation energy of diffusion and enhanced water mobility. At relatively high ion density, the water-ion interactions overcome the structure-breaking effect and lead to retarded water diffusion. Overall, the studies presented in this dissertation augment our understanding of water transport in nanostructures by revealing the rich behavior of liquid-water dynamics under both hydrophobic and ionic confinement. / Doctor of Philosophy / Polymer separations membranes contribute to important applications such as fuel cells and water desalination. Optimizing the separation ability of polymer membranes improves their practical performance. The transport property of a polymer membrane depends on its nanoscale and microscale structures. This dissertation focuses on the nanoscale structure-transport relations in ionic polymer membranes. We utilize nuclear magnetic resonance techniques and molecular dynamics simulations to probe the transport properties. We investigate the effects of membrane nanostructure and water-ion interactions on the dynamics of confined water. Such knowledge not only guides the development of high-performance membranes but also contributes to the fundamental understanding of liquid dynamics in nanoporous materials.

Investigation and characterization of polymeric materials are necessary to obtain in-depth understanding of their behavior and properties, which can fuel further development. To illuminate these molecular properties and their coupling to macroscopic behavior, we have performed nuclear magnetic resonance (NMR) studies on a variety of chemical systems. In addition to versatile "traditional" NMR measurements, we took advantage of specialized techniques, such as "rheo-NMR," 2H NMR, and NMR self-diffusion experiments to analyze alignment, orientational order, elaborate rheological behavior, and ion transport in polymer films and complex fluids. We employed self-diffusion and quadrupolar deuterium NMR methods to water-swollen channels in Nafion ionomer films commonly used in fuel cells and actuators. We also correlated water uptake and anisotropic diffusion with differing degrees and types of alignment in Nafion films based on membrane processing methods. Further, we made quantitative measurements of bulk channel alignment in Nafion membranes and determined anisotropic properties such as the biaxiality parameter using these methods. Additionally, our studies made the first direct comparison of directional transport (diffusion) with quantitative orientational order measurements for ionomer membranes. These results lend insight to the importance of water content in ionomer device performance, and showed that increased control over the direction and extent of orientational order of the hydrophilic channels could lead to improved materials design. We used the same techniques, with the addition of "rheo-NMR" and solution rheology measurements, to study the complex rheological behavior of cetyltrimethylammonium bromide wormlike micelle solutions, which behave as nematic liquid crystals at sufficiently high concentration. Amphiphilic solutions of this type are used in myriad applications, from fracturing fluids in oil fields to personal care products. We investigated the phase behavior and dynamics of shear and magnetic field alignment, and made the first observations of a novel bistable shear-activated phase in these solutions. Our first reports of the complex Leslie-Ericksen viscoelastic parameters in wormlike micelles and measurements of diffusion anisotropy show the potential for increased control and understanding of materials used in tissue engineering, oil extraction, personal care products, and advanced lubricants. / Ph. D.

Fundamental understanding of water transport and morphology is critical for improving ion conductivity in polymer electrolyte membranes (PEMs). Herein, we present comprehensive water transport measurements comparing anion-exchange membranes (AEMs) based on ammonium-functionalized poly(phenylene oxide) and cation-exchange membranes (CEMs) based on sulfonated poly(ether sulfone). We investigate the influence of counter ions, alkyl side chain, and degree of functionalization on water transport in AEMs and CEMs using pulsed-field-gradient (PFG) NMR diffusometry. Water diffusion in both AEMs and CEMs exhibit specific trends as a function of water uptake (wt%), indicating morphological similarities across common chemical structures. Furthermore, restricted diffusion reveals micron-scale heterogeneity of the hydrophilic network in both CEMs and AEMs. We propose a model wherein the hydrophilic network in these membranes has micron-scale distributions of local nm-scale dead ends, leading to changes in tortuosity as a function of water content, counterion type, and polymer structure. We furthermore parse tortuosity into two regimes, corresponding to nm-to-bulk and µm-to-bulk ranges, which reveal the importance of multi-scale morphological structures that influence bulk transport. This study provides new insights into polymer membrane morphology from nm to µm scales with the ultimate goal of controlling polymeric materials for enhanced fuel cells and other separations applications / MS