Materials Science

The generation of polymer brushes by surface-initiated polymerization techniques has become a powerful tool for the creation of hybrid materials. Governed by the type and amount of polymer used in the modification, the chemical and physical properties of a surface can be tailored by polymer grafting. In this study, a commonly used polymer flocculant, polyacrylamide (PAM), was grafted onto the surface of activated carbon (AC). This hybrid material was designed with the intent of combining the functionalities of both the activated carbon and the polymer flocculant, potentially acting in a synergistic manner. The PAM grafted AC (AC-PAM) was examined as a flocculant in the treatment of mature fine tailings (MFT). AC-PAM was synthesized by surface-initiated activators generated by electron transfer atom transfer radical polymerization (SI-AGET ATRP). This was accomplished by pre-functionalizing the surface of activated carbon by oxidation, followed by the attachment of an ATRP initiator. From this surface, SI-AGET ATRP of acrylamide monomers was performed. The resulting AC-PAM was characterized by FTIR, XPS, TGA, SEC, and BET analysis. Characterization results indicated the successful grafting of polyacrylamide from the surface of activated carbon. The AC-PAM was measured to contain approximately 10.6% PAM by weight, and the average-number molecular weight of the grafted polymer was 176,100 g/mol. The flocculation performance of AC-PAM and PAM were compared by performing settling tests with 5 wt% MFT. The optimal polymer dosage for PAM was found to be 10,000 ppm, producing an initial settling rate of 3.51 m/hr and a supernatant turbidity of 430 NTU. Comparatively, the optimal dosage for AC-PAM was found to be 20,000 ppm, producing a supernatant turbidity of 114 NTU and a fast initial settling rate of 27.54 m/hr. The improved flocculation performance is hypothesized to occur due to the effective increase in the molecular weight of PAM when grafted from the surface of activated carbon. In all, our work demonstrates the successful grafting of PAM from AC, as well as potential wastewater treatment applications for these types of hybrid materials.

Author Keywords: Activated carbon, Atom transfer radical polymerization, Flocculation, Grafting, Polyacrylamide, Surface-initiated polymerization

Coherent anti-Stokes Raman scattering (CARS) microscopy is a label-free chemical imaging modality that uses CARS as a contrast mechanism to spatially resolve materials based on their molecular vibrational spectra. Due to the presence of a non resonant background that obfuscates the chemical information contained in CARS spectra, CARS images suffer from poor contrast and cannot be readily used for quantitative chemical analysis. Over the past two decades, spectral retrieval methods have been developed to obtain Raman-like spectra from CARS spectra. These methods promise to improve image contrast and enable reliable quantitative analysis. In this work I systematically evaluate a selection of the forefront spectral retrieval methods, including both analytical and machine learning approaches, to determine how well they perform at the task of non resonant background removal. The more recent machine learning methods demonstrate remarkable performance on spectra resembling the training dataset but are not as suitable as the analytical methods in general. The analytical methods based on the discrete Hilbert transform thus remain preferable due to their ease-of-use and general applicability.

Author Keywords: chemical imaging, coherent anti-stokes raman scattering, kramers-kronig analysis, machine learning, non-resonant background, spectral phase retrieval

Naphthenic acids are a major contaminant of concern and a focus of much research around remediation of oil sand process affected waters, OSPW. Using activated carbon adsorbents are an attractive option given their low cost of fabrication and implementation. A deeper evaluation of the effect naphthenic acid structural differences have on uptake affinity is warranted. In this thesis an in-depth exploration of naphthenic acid adsorption onto activated carbon is provided including many more model naphthenic acid species than what have been assessed previously in adsorption studies. Both adsorption kinetics and isotherms at the relevant alkaline pH of OSPW using several different carbon adsorbents with pH buffering to simulate the behaviour of real OSPW were evaluated. Given the time sensitive application of most adsorbents towards treating contaminated waters such as OSPW, achieving fast adsorption rates for model naphthenic acids is an important goal worth considering. Textural properties of activated carbon most conducive for fast adsorption kinetics were assessed using several candidate model species. Clear evidence is presented, demonstrating the influence of both the pore size distribution and particle size of porous adsorbents on uptake rates of naphthenic acids, demonstrating that careful optimization of these adsorbent properties can result in adequate uptake rates. Adsorption isotherms were used to assess model naphthenic acid affinity towards activated carbon. Uptake for the model naphthenic acids varied considerably regardless of the activated carbon used, ranging from 350 mg g-1 to near zero highlighting recalcitrant species. The equilibrium data was explored to identify important structural features of these species and key physiochemical properties that influence adsorption. It was demonstrated that certain naphthenic acids are resistant to adsorption when hydrophobic adsorbents are used. Adsorption isotherm modelling helped explore interactions occurring at the interface between naphthenic acids and adsorbent surfaces. Naphthenic acid hydrophobicity was identified as an importance physiochemical property for achieving high adsorption capacities onto activated carbon. Evidence is also presented that indicates favorable hydrogen bonding between naphthenic acids and surface site hydroxyl groups, demonstrating the importance of adsorbent surface functionality for naphthenic acid uptake. The adsorption mechanism was further explored through use of a thermodynamic analysis of the model naphthenic acid system using activated carbon. Standard state enthalpy and isosteric enthalpy of adsorption values were used to further support the proposed mechanisms occurring between model species and activated carbons. This research highlights the challenges associated with removing naphthenic acids from OSPW through adsorption and identifies how adsorbent surface chemistry modification will need to be used to increase the removal efficiency of recalcitrant naphthenic acid species when using activated carbon.

Author Keywords: Activated Carbon, Isotherms, Kinetics, Modelling, Naphthenic Acids, Thermodynamics

Access to human blood for forensic research and training in bloodstain pattern analysis (BPA) can be difficult due to many ethical, safety and cost concerns. Mammalian blood alternatives can be sourced, especially from local and willing abattoirs, but some concerns remain, and the added difficulties of high variation and species-specific differences in cellular components pose other issues. Therefore, synthetic alternatives to human blood provide practical options for the BPA community. This thesis explores the use of alginate hydrogels as a base material for forensic blood substitute (FBS) development. Hydrogels are first explored as a suitable environment for DNA stability and functionality and compared to other polymer systems. The ability of DNA to remain intact while undergoing electrospray ionization (ESI) is also investigated. The FBS design focuses on mimicking the fluid properties and genetic capabilities of whole human blood – a material not developed in FBSs previously. ESI was used to develop microparticles (MPs) that serve as cellular components of human blood (the red blood cells – RBCs, and white blood cells – WBCs). The microparticles were ionically crosslinked using calcium to provide small MPs (RBCs) or covalently crosslinked with functional DNA to provide larger WBC-like functional particles. The integration of these novel MPs into alginate-based materials is optimized and their use in BPA scenarios is explored. The FBS is tested in BPA scenarios of dripping experiments, impact patterns, and the ability to extract and amplify the contained DNA. In addition, the stability (or shelf-life) of the FBS was also assessed. The FBS exhibited similar spreading ratios to blood and demonstrated feasibility in use for impact angle (a) determination and impact pattern creation. Importantly, the DNA contained within the FBS could be processed with analogous protocols used in DNA evidence processing, enhancing its applicability to BPA research and training.

Author Keywords: Alginate hydrogels, Bloodstain pattern analysis, Electrospray ionization, Forensic blood substitutes, Forensic materials, Synthetic DNA design

Microwave resonances in isolated water-based spheres, dimers, and trimers are explored using simulations conducted with COMSOL Multiphysics. The study centers on morphology-dependent resonances (MDRs) and hotspot characteristics in cm-sized objects at microwave frequencies. Monomers subjected to microwave radiation exhibit four distinct resonant modes at specific sizes characterized by electric and magnetic field distributions which correspond to magnetic-dipolar, electric-dipolar, magnetic quadrupolar, and electric quadrupolar resonances, respectively. Dimer configurations reveal intriguing hotspot features, with axial hotspots emerging as a key resonant characteristic. The three fundamental dimer orientations dictate unique resonant behaviors, highlighting the sensitivity of hotspot intensity to orientation changes, but smooth and consistent trends during transitions between them. Investigations into trimer structures, as a more intricate geometry formed by interconnected dimers, reveal the subtle interactions of spheres in a trimer structure. Trimer hotspots largely reflect the sum of isolated dimer hotspot contributions, showcasing the energy conservation with no evidence of a newly formed hotpot. Our results, while arising as a consequence of the particularly high index of refraction of water at GHz frequencies, are generalizable to other length scales (such as nano-photonics), were materials with sufficiently high refractive index and transparency to be found.

Author Keywords: COMSOL simulations, Electromagnetic physics, Microwave frequencies, Morphology-dependent resonance, water-based objects

There is a `universal' picture of a charged domain wall (CDW) in theoretical work, often depicted as residing in an infinite thickness film, charge neutral, and with no bias voltage applied. However, in experiment CDWs are shown with none of these assumptions. CDWs are produced in thin or ultra-thin films, the CDW is not charge neutral, and a bias voltage is being applied. We look to go beyond these assumptions. It was shown that a positively charged domain wall (DW) moves against an external electric field which is not expected. The free electron density was also shown to determine the DW displacement amount. When the film thickness is lowered (ultra-thin film) we get a negatively charged DW which still moves against an external electric field, which agrees with experiment of a CDW in a ultra-thin film. This suggests the charge on the DW does not determine displacement direction.

Author Keywords: charged domain wall, displacement

In this work, a deep learning approach proposed by Valensise et al. [3] for extracting Raman resonant spectra from measured broadband CARS spectra was explored to see how effective it is at removing NRB from our experimentally measured "spectral-focusing"-based approach to CARS. A large dataset of realistic simulated CARS spectra was used to train a model capable of performing this spectral retrieval task. The non-resonant background shape used in creating the simulated CARS spectra was altered, to mimic our experimentally measured NRB response. Two models were trained: one using the original approach (Specnet) and one using the updated NRB "Specnet Plus", and then tested their ability to retrieve the vibrationally resonant spectrum from simulated and measured CARS spectra. An error analysis was performed to compare the model's retrieval performance on two simulated CARS spectra. The modified model's mean squared error value was five and two times lower for the first and second simulated CARS spectra, respectively. Specnet Plus was found to be more effective at extracting the resonant signals. Finally, the NRB extraction abilities of both models are tested on two experimentally measured CARS hyperspectroscopy samples (starch and chitin), with the updated NRB model (Specnet Plus) outperforming the original Specnet model. These results suggest that tailoring the approach to reflect what we observe experimentally will improve our spectral analysis workflow and increase our imaging potential.

Amino acids make up proteins, which are the building blocks of life. A balance of amino acids is needed to maintain a healthy state. Tyrosine (Tyr) is synthesized from the metabolism of phenylalanine, which is an essential amino acid, meaning it can only be obtained from the diet. It is related to many metabolic and neurodegenerative diseases. Tyr can undergo post-translational modifications such as phosphorylation and nitration, which are implicated in cancer and nitrative stress, respectively. Although there are many methods to detect Tyr and its analogues, phosphotyrosine (pTyr) and nitrotyrosine (nTyr), these methods are time-consuming, involve expensive instruments and involve tedious process. This research proposes a new type of nanomaterials, carbon dots (CDs), to detect these amnio acids. Data indicate that CDs can be used to detect nTyr with a limit of detection of 34 μM in the linear range of 20 - 105 μM. The amenability of CD-nTyr assay was also tested in various biological matrices and biological molecules and was shown to be sensitive to nTyr. Nitration of Tyr was carried out in the presence of sodium nitrite and hydrogen peroxide catalyzed by either Cu(II) or Fe(III) to mimic biological reactions and CDs were tested as both inhibitors and indicators of Tyr nitration. Although CDs did not inhibit the nitration reaction of Tyr, they did not serve as indicators of Tyr nitration due to the quenching of CDs by the nitrating agents. This shows the importance of using CDs to detect nTyr and further use it for biological applications to detect diseased states.

Author Keywords: amino acids, carbon dots, nanomaterials, sensor, spectroscopy, tyrosine

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

Vegetable oils represent an ideal and renewable feedstock for the synthesis of a variety of functional materials. However, without financial incentive or unique applications motivating a switch, commercial products continue to be manufactured from petrochemical resources. Two different families of high value, functional materials synthesized from vegetable oils were studied. These materials demonstrate superior and unique performance to comparable petrochemical analogues currently on the market.

In the first approach, 3 amphiphilic thermoplastic polytriazoles with differing lipophilic segment lengths were synthesized in a polymerization process without solvents or catalysts. Investigation of monomer structure influence on the resultant functional behaviour of these polymers found distinctive odd/even behaviour reliant on the number of carbon atoms in the monomers. Higher concentrations of triazole groups, due to shorter CH2 chains in the monomeric dialkynes, resulted in more brittle polymers, displaying higher tensile strengths but reduced elongation to break characteristics. These polymers had similar properties to commercial petroleum derived thermoplastics. One polymer demonstrated self-assembled surface microstructuring, and displayed hydrophobic properties. Antimicrobial efficacy of the polymers were tested by applying concentrated bacterial solutions to the surfaces, and near complete inhibition was demonstrated after 4 hours. Scanning electron microscope images of killed bacteria showed extensive membrane damage, consistent with the observed impact of other amphiphilic compounds in literature. These polytriazoles are suited for applications in medical devices and implants, where major concerns over antibiotic resistance are prevalent.

In the second approach, a series of symmetric, saturated diester phase change materials (PCMs) were also synthesized with superior latent heat values compared to commercial petrochemical analogues. These diesters exhibit melting temperatures between 39 °C and 77 °C, with latent heats greater than 220 J/g; much greater than paraffin waxes, which are currently the industry standard. Assessment of the trends between differing monomer lengths, in terms of number of CH2 groups of the 24 diesters synthesized exhibited structure/function dependencies in latent heat values and phase change temperatures, providing an understanding of the influence of each monomer on PCM thermal properties. A synthetic procedure was developed to produce these PCMs from a low value biodiesel feedstock. Application of these PCMs in the thermoregulation of hot beverages was demonstrated using a representative diester. This PCM cooled a freshly brewed hot beverage to a desired temperature within 1 minute, compared to 18 minutes required for the control. Furthermore, the PCM kept the beverage within the desired temperature range for 235 minutes, 40 % longer than the control.

Author Keywords: Antimicrobial Surface, Click Chemistry, Green Chemistry, Phase Change Material, Polytriazole, Renewable