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Novel Aliphatic Amides from Vegetable Oils as Bio-Based Phase Change Materials
Energy storage efficiency and sustainability require advanced technologies and novel materials. Recently, bio-based phase change materials (PCMs) have received significant attention for thermal energy storage (TES) uses. Vegetable oils are versatile renewable feedstocks that are well suited for the development of sustainable, functional PCMs. PCMs derived from vegetable oil, which compares favorably with paraffin waxes, the industry standard, are currently available. However, their melting points are typically below 80 °C preventing their wider integration in TES applications, particularly those requiring higher temperatures. The present work manipulated the structural building blocks of fatty acids to advantageously affect the intermolecular forces and increase the properties relevant to TES. The polar amide functional group was incorporated into fatty moieties to take advantage of the strong hydrogen bonds that it forms to increase intermolecular attractions and hence increase the phase change temperature and enthalpy as well as to improve thermal stability and thermal conductivity. A series of carefully designed lipid-derived monoamides and four series of lipid-derived diamides were synthesized via benign and simple amidation reactions. The purity of the amides and the intermolecular hydrogen bond strength were assessed using 1H NMR and FTIR. The properties relevant to TES such as thermal transition, crystal structure and polymorphism, thermal stability and thermal conductivity were measured using DSC, XRD, TGA and a thermal conductivity analyzer, respectively. The complex roles of the PCM’s constituting molecular building blocks in the phase behavior were elucidated and correlations between structure, processing conditions and macroscopic physicochemical properties, never before elucidated, were assembled in predictive relationships, drawing a unified picture of the rules that generally govern the phase behavior of lipid-derived PCMs. Practically, the prepared amides demonstrated desirable TES properties with substantial performance improvement over current bio-based PCMs. They presented increased phase change temperatures (79 - 159 °C), enthalpies of fusion (155 - 220 J/g) and thermal stability (234 - 353 °C). More importantly, the predictive structure-function relationships established in this work will allow the straightforward engineering of lipid-derived amide PCM architectures with judicious selection of molecular building blocks to extend the range of organic PCMs and deliver thermal properties desirable for TES applications. Author Keywords: LATENT HEAT THERMAL ENERGY STORAGE, LIPID-DERIVED AMIDES, PHASE CHANGE MATERIALS, RENEWABLE, SOLID LIQUID AMIDE PCMS, THERMAL PROPERTIES
I have developed and improved a coherent anti-Stokes Raman scattering (CARS) microscope based on the spectral focusing (SF) technique. The CARS microscope uses an 800 nm oscillator and a photonic crystal fibre module to generate the supercontinuum Stokes. The photonic crystal fibre was originally designed to generate light beyond 945 nm which is useful for CARS microscopy in the CH/OH frequencies but essentially prevents access to the important fingerprint region at lower frequencies. With expert and nontraditional approaches to generating supercontinuum with sufficient power at wavelengths below 945 nm, I substantially extend the usefulness of the module for SF-CARS microscopy deep into the fingerprint region. Moreover, with the invention of a dynamic supercontinuum generation scheme we call "spectral surfing," I improve both the brightness of the CARS signal and extend the accessible CARS frequency range to frequencies as low as 350 cm$^{-1}$ and as high as 3500 cm$^{-1}$---all in a single scan-window. I demonstrate the capabilities of our broadband SF-CARS system through CARS and four-wave mixing hyperspectroscopy on samples such as astaxanthin, lily pollen and glass; liquid chemicals such as benzonitrile, nitrobenzene and dimethyl sulfoxide; and on pharmaceutical samples such as acetaminophen, ibuprofen, and cetirizine. Furthermore, In search of more useful Stokes supercontinuum sources, I compare the performance of two commercial photonic crystal fibre modules for use in SF-CARS applications, ultimately finding that one module provides better spectral characteristics for static supercontinuum use, while the other provides improved characteristics when spectral surfing is implemented. Author Keywords: coherent anti-Stokes Raman scattering, nonlinear microscopy, scanning microscopy, spectroscopy, supercontinuum generation, vibrational spectroscopy
Cluster Approach Applied to the One-Dimensional Anderson-Hubbard Model
S. Johri and R. Bhatt developed a real-space renormalization group approach aimed at extracting the localized single-particle eigenstates of the Anderson model from a large system by identifying clusters of resonant site potentials. E. Campbell generalized this real-space renormalization group approach using standard perturbation theory. Both approaches were intended to approximate the single-particle density of states of the Anderson model. In this thesis, we aimed to test the potential of applying a similar real-space renormalization group approach to calculate the density of states of the interacting Anderson-Hubbard model. Our interest in the density of states of this model is due to a V-shaped zero-bias anomaly in two-dimensional systems. A real-space renormalization group approach is best applied to a one-dimensional system. We found that the zero-bias anomaly is not V-shaped in one-dimension. To test the potential of a real-space renormalization group approach, we used the cluster approach which is the same as the non-interacting renormalization group approach but without the perturbation theory and found that for strong disorder this technique could accurately calculate the density of states over a wide range of energies but deviated from exact results at the band edge, at $\omega=\pm U$ and near $\omega=0$. The first two inaccuracies will be reduced with a proper real-space renormalization group approach. We suspect that the last inaccuracy is associated with long range physics and may be difficult to recover. We also developed a technique that adjusts the identification of clusters in the cluster approach to improve the computation time of the density of states with minimal loss of accuracy in a tunable range around the Fermi level. We found that this technique significantly reduced the computation time and was able to preserve the density of states near the Fermi level, except at the smallest energies near $\omega=0$. Author Keywords: Anderson-Hubbard model, renormalization group, Strong electron correlations, Zero-bias anomaly
Phosphoric Acid Chemically Activated Waste Wood
Activated Carbon (AC) is commonly produced by gasification, but there has been increasing interest in chemical activation due to its lower activation temperatures and higher yields. Phosphoric acid, in particular, succeeds in both these areas. Phosphoric acid activated carbon (PAC) can be environmentally sustainable, and economically favourable, when the phosphoric acid used in the activation is recycled. This thesis describes the digestion and activation of waste wood using phosphoric acid, as well as methods used to recover phosphoric acid, functionalize the produced activated carbon with iron salts and then test their efficacy on the adsorption of target analytes, selenite and selenate. In order to achieve an efficient phosphoric acid based chemical activation, further understanding of the activation process is needed. A two-step phosphoric acid activation process with waste wood feed stock was examined. The filtrate washes of the crude product and the surface composition of the produced PAC were characterized using X-ray Photoelectron Spectroscopy (XPS), Fourier Transform-Infrared spectroscopy (FT-IR), Ion Chromatography (IC), and 31P Nuclear Magnetic Resonance (NMR). XPS of the unwashed PAC contained 13.3 atomic percent phosphorous, as phosphoric acid, while the washed sample contained 1.4 atomic percent phosphorous as PO43-, and P2O74-. Using 31P NMR, phosphoric acid was identified as the primary phosphorous species in the acidic 0.1 M HCl washings, with pyrophosphates also appearing in the second 0.1 M NaOH neutralizing wash, and finally a weak signal from phosphates with an alkyl component also appearing in the DI wash. IC showed high concentrations of phosphoric acid in the 0.1 M HCl wash with progressively lower concentrations in both the NaOH and DI washes. Total phosphoric acid recovery was 96.7 % for waste wood activated with 25 % phosphoric acid, which is higher than previous literature findings for phosphoric acid activation. The surface areas of the PAC were in the 1500-1900 m2g-1 range. Both pre and post activation impregnation of iron salts resulted in iron uptake. Pre-activation resulted in only iron(III) speciation while post-activation impregnation of iron(II)chloride did result in iron(II) forming on the PAC surface. The pre-activated impregnated PAC showed little to no adsorption of selenite and selenate. The post-activation impregnated iron(II)chloride removed up to 12.45 ± 0.025 mg selenium per g Iron-PAC. Competitive ions such as sulfate and nitrate had little effect on selenium adsorption. Phosphate concentration did affect the uptake. At 250 ppm approximately 75 % of adsorption capacity of both the selenate and the selenite solutions was lost, although selenium was still preferentially adsorbed. Peak adsorption occurred between a pH of 4 and 11, with a complete loss of adsorption at a pH of 13. Author Keywords: Activated Carbon, doping, Iron, phosphoric acid, selenium
Supercritical Water Chemistry
Supercritical water (SCW) exhibits unique properties that differentiates it from its low temperature behaviour. Hydrogen bonding is dramatically reduced, there is no phase boundary between liquid and gaseous states, heat capacity increases, and there is a drastic reduction of the dielectric constant. Efforts are underway for researchers to harness these properties in the applications of power generation and hazardous waste destruction. However, the extreme environment created by the high temperatures, pressures and oxidizing capabilities pose unique challenges in terms of corrosion not present in subcritical water systems. Molecular Dynamics (MD) simulations have been used to obtain mass transport, hydration numbers and the influence on water structure of molecular oxygen, chloride, ammonia and iron (II) cations in corrosion crevices in an iron (II) hydroxide passivation layer. Solvation regimes marking the transitions of solvation based versus charge meditated processes were explored by locating the percolation thresholds of both physically and hydrogen bonded water clusters. A SCW flow through reactor was used to study hydrogen evolution rates over metal oxide surfaces, metal release rates and the kinetics for the oxidation of hydrogen gas by oxygen in SCW. Insights into corrosion phenomena are provided from the MD results as well as the experimental determination of flow reactor water and hydrogen chemistry. Author Keywords: Flow Studies, Molecular Dynamics, Supercritical Water
Investigation of Using Phase Change Materials for Thermal Energy Storage in Adiabatic Compressed Air Energy Storage
There is an increasing global need for grid scale electrical energy storage to handle the implementation of intermittent renewable energy sources. Adiabatic compressed air energy storage is an emerging technology with similar performance to pumped hydro except it has the issue of heat loss during the compression stage. Previously, it has been considered to use sensible heat storage materials to store the heat created by compression in a thermal energy storage unit until energy is required, and then transfer the heat back to the air. This research proposes to instead use phase change materials to store the heat of compression, as this will reduce entropy generation and maximize roundtrip exergy efficiency. Different configurations and placements of the phase change materials are considered and exergy analyses are presented. The thermodynamic equations are derived and optimal setup conditions including amount of latent heat and melting temperatures are calculated. Author Keywords: Compressed Air Energy Storage, Energy Storage, Exergy, Phase Change Materials
Correlating density of states features with localization strength in disordered interacting systems
Johri and Bhatt found singular behavior near the band edge in the density of states as well as in the inverse participation ratio of the Anderson model. These singularities mark a transition to an energy range dominated by resonant states. We study the interacting case using an ensemble of two-site Anderson-Hubbard systems. We find the ensemble-averaged density of states and generalized inverse participation ratio have more structure than in the non-interacting case because there are more transitions and in particular the transitions depend on the ground state. Nonetheless, there are regions of sharp decline in the generalized inverse participation ratio associated with specific density of state features. Moreover these features move closer to the Fermi level with the addition of interactions making them more experimentally accessible. Unfortunately resonances unique to interacting systems cannot be specifically identified. Author Keywords: Correlated electrons, Disorder, Localization
Lipid-derived Thermoplastic Poly(ester urethane)s
Thermoplastic poly(ester urethane)s (TPEU)s derived from vegetable oils possess inferior physical properties compared to their entirely petroleum-based counterparts due to the structural limitations and lower reactivity of the precursor lipid-derived monomers. The present work shows that high molecular weight of TPEUs with enhanced performance can be obtained from lipid-derived monomers via (i) the synthesis of polyester diols with controlled molecular weights, (ii) the tuning of the functional group stoichiometry of the polyester diols and the diisocyanate during polymerization, (iii) the degree of polymerization (iv) the control of the hard segment hydrogen bond density and distribution via the use of a chain extender and (v) different polymerization protocols. Solvent-resistant TPEUs with high molecular weight displaying polyethylene-like behavior and controlled polyester and urethane segment phase separation were obtained. Structure-property investigations revealed that the thermal transition temperatures and tensile properties increased and eventually plateaued with increasing molecular weight. Novel segmented TPEUs possessed high phase separation and showed elastomeric properties such as low modulus and high elongation analogous to rubber. The response of the structurally optimized TPEUs to environmental degradation was also established by subjecting the TPEUs to hydrothermal ageing. TPEUs exhibited thermal and mechanical properties that were comparable to commercially available entirely petroleum-based counterparts, and that could be tuned in order to achieve enhanced physical properties and controlled degradability. Author Keywords: Hydrothermal degradation, Molecular weight control, Polyester diols, Renewable resources, Structure-property relationships, Thermoplastic poly(ester urethane)s
Model for the Differential Susceptibility of Strontium Titanate
The appearance of a two-dimensional electron gas (2DEG) in oxide interfaces between strontium titanate (STO) and other materials has become a major area of study. The behaviour of the 2DEG in STO is not well understood in part because the dielectric properties of STO are not well characterized. The differential susceptibility has a major impact on the electric fields within strontium titanate, and therefore to understand the 2DEG a better understanding of the susceptibility is needed. An expression for the soft mode phonon frequency of bulk strontium titanate is derived and used to model the susceptibility as a function of spatially homogeneous electric field, temperature and wavevector. This model is used to discuss the effect of spatially inhomogeneous electric fields and the local vs. nonlocal nature of the susceptibility. The critical exponents and the free energy are determined and discussed. Author Keywords: critical exponents, differential susceptibility, quantum paraelectric, strontium titanate
Synthesis of Lipid Based Polyols from 1-butene Metathesized Palm Oil for Use in Polyurethane Foam Applications
This thesis explores the use of 1-butene cross metathesized palm oil (PMTAG) as a feedstock for preparation of polyols which can be used to prepare rigid and flexible polyurethane foams. PMTAG is advantageous over its precursor feedstock, palm oil, for synthesizing polyols, especially for the preparation of rigid foams, because of the reduction of dangling chain effects associated with the omega unsaturated fatty acids. 1-butene cross metathesis results in shortening of the unsaturated fatty acid moieties, with approximately half of the unsaturated fatty acids assuming terminal double bonds. It was shown that the associated terminal OH groups introduced through epoxidation and hydroxylation result in rigid foams with a compressive strength approximately 2.5 times higher than that of rigid foams from palm and soybean oil polyols. Up to 1.5 times improvement in the compressive strength value of the rigid foams from the PMTAG polyol was further obtained following dry and/or solvent assisted fractionation of PMTAG in order to reduce the dangling chain effects associated with the saturated components of the PMTAG. Flexible foams with excellent recovery was achieved from the polyols of PMTAG and the high olein fraction of PMTAG indicating that these bio-derived polyurethane foams may be suitable for flexible foam applications. PMTAG polyols with controlled OH values prepared via an optimized green solvent free synthetic strategy provided flexible foams with lower compressive strength and higher recovery; i.e., better flexible foam potential compared to the PMTAG derived foams with non-controlled OH values. Overall, this study has revealed that the dangling chain issues of vegetable oils can be addressed in part using appropriate chemical and physical modification techniques such as cross metathesis and fractionation, respectively. In fact, the rigidity and the compressive strength of the polyurethane foams were in very close agreement with the percentage of terminal hydroxyl and OH value of the polyol. The results obtained from the study can be used to convert PMTAG like materials into industrially valuable materials. Author Keywords: Compressive Strength, Cross Metathesis, Fractionation, Polyols, Polyurethane Foams, Vegetable Oils
Novel Aliphatic Lipid-Based Diesters for use in Lubricant Formulations
Structure-property relationships are increasingly valued for the identification of specifically engineered materials with properties optimized for targeted application(s). In this work, linear and branched diesters for use in lubricant formulations are prepared from lipid-based oleochemicals and their structure-property relationships reported. It is shown that the branched diesters possess exceptional physical property profiles, including suppression of crystallization, and are superior alternatives for use in lubricant formulations. For the linear aliphatic diesters, both high and low temperature properties were predictable functions of total chain length, and both were differently influenced by the fatty acid versus diol chain length. Symmetry did not influence either, although thermal stability decreased and thermal transition temperatures increased with increasing saturation. All of the linear diesters demonstrated Newtonian flow behaviour. Viscosity was also predictable as a function of total chain length; any microstructural features due to structural effects were superseded by mass effects. Author Keywords: Crystallization, Phase behaviour, Rheology, Structure-Function, Thermogravimetric analysis, Vegetable Oils
Mitigating Cold Flow Problems of Biodiesel
The present thesis explores the cold flow properties of biodiesel and the effect of vegetable oil derived compounds on the crystallization path as well as the mechanisms at play at different stages and length scales. Model systems including triacylglycerol (TAG) oils and their derivatives, and a polymer were tested with biodiesel. The goal was to acquire the fundamental knowledge that would help design cold flow improver (CFI) additives that would address effectively and simultaneously the flow problems of biodiesel, particularly the cloud point (CP) and pour point (PP). The compounds were revealed to be fundamentally vegetable oil crystallization modifiers (VOCM) and the polymer was confirmed to be a pour point depressant (PPD). The results obtained with the VOCMs indicate that two cis-unsaturated moieties combined with a trans-/saturated fatty acid is a critical structural architecture for depressing the crystallization onset by a mechanism wherein while the straight chain promotes a first packing with the linear saturated FAMEs, the kinked moieties prevent further crystallization. The study of model binary systems made of a VOCM and a saturated FAME with DSC, XRD and PLM provided a complete phase diagram including the thermal transformation lines, crystal structure and microstructure that impact the phase composition along the different crystallization stages, and elicited the competing effects of molecular mass, chain length mismatch and isomerism. The liquid-solid boundary is discussed in light of a simple thermodynamic model based on the Hildebrand equation and pair interactions. In order to test for synergies, the PP and CP of a biodiesel (Soy1500) supplemented with several VOCM and PLMA binary cocktails were measured using a specially designed method inspired by ASTM standards. The results were impressive, the combination of additives depressed CP and PP better than any single additive. The PLM and DSC results suggest that the cocktail additives are most effective when the right molecular structure and optimal concentration are provided. The cocktail mixture achieves then tiny crystals that are prevented from aggregating for an extended temperature range. The results of the study can be directly used for the design of functional and economical CFI from vegetable oils and their derivatives. Author Keywords: Biodiesel, Microstructure, Polymorphism, Pour point depressants, Triacylglycerol, Vegetable Oil Based Crystal Modifier

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