PRISM :: Browsing by Author "Trifkovic, Milana"

Browsing by Author "Trifkovic, Milana"

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Open Access
A Confocal Rheology Study of Network Stabilized Bicontinuous Emulsion Gels
(2018-08-24) Malone, Rachel Alexis; Trifkovic, Milana; Karan, Kunal; Bryant, Steven L.
In this thesis, a new bicontinuous soft material was discovered. Bicontinuous intraphase jammed emulsion gels (bipjels) were formed from critical mixtures of water and 2,6-lutidine and were stabilized with commercially produced alumina coated silica nanoparticles. Using a novel confocal rheology platform, the microstructure and rheological properties of the bipjels were simultaneously studied and provided key insights into the morphology and stability of the new materials during their formation, aging, and cooling. Through varying the concentration of the nanoparticles and the initial mixing energy delivered to the bipjel mixtures, the final morphologies could be tuned. A curvature analysis was performed over the aging of the different biPjel samples showing traits of optimal hyperbolic surfaces. The bipjels did not lose their strength upon cooling and liquids remixing which bodes well for their future development as an advanced material. Bipjels represent a new gateway for understanding the role non-interfacially localized particles play in stabilizing non-equilibrium morphologies.
Open Access
Advanced Control and Optimization for the SAGD Process and Bitumen Upgrading
(2018-09-07) Purkayastha, Sagar Neel; Trifkovic, Milana; Gates, Ian Donald; Plaksina, Tatyana; Shor, Roman J.
Thermal recovery techniques, like Steam-Assisted Gravity Drainage (SAGD), are used to produce the majority of the crude bitumen, in Canada. However, suboptimal production techniques have led to the use of automatic control techniques for production, in recent times. Concurrently, while Proportional Integral Derivative and single variable Model Predictive Control (MPC) strategies have proven to be superior to manual control, they have resulted in comparable performance. Consequently, for improved performance, a novel Multi Input Multi Output (MIMO) MPC is presented in this thesis and compared with a Multi Input Single Output (MISO) MPC. The results indicated a 171% improvement in oil recovery for the novel MIMO MPC over the MISO MPC. This thesis also presents an optimization strategy for integrated design and schedule of a partial bitumen upgrader. The key consideration is in identifying that the design and operation problems are not mutually exclusive, but instead, synergistic in nature. Consequently, the research documented in this thesis, elucidates two formulations; maximizing proﬁt and minimizing energy usage to highlight this concept. The results highlighted that both the design and scheduling decision variables change as per the medium term forecasts of the volatile commodity and energy pricing markets. Therefore, a design independent of the scheduling constraints or a schedule based on a ﬁxed design may lead to suboptimal results in the design and/or schedule decision space(s). Finally, the last part of the thesis focuses on the optimal power management of a microgrid on a depleted SAGD facility, comprising of an Organic Rankine Cycle based turbine to convert the geothermal SAGD waste heat into electricity, a Gas Turbine, a Battery Storage System, the central grid, and the facility itself. Furthermore, this work also introduces a Kelly Criterion (KC) based microgrid scheduling technique, which is based on maximizing information gain and is independent of supply-demand relationships. Moreover, for this study, a wavelet network based forecasting technique is used to capture the electricity market volatility. The case study presented corroborated the hypothesis that the KC approach is independent of demand and supply forecasts, and is able to perform optimally in a highly volatile energy market.
Open Access
Aerodynamic Performance and Starting Behavior of Multi-Bladed Waterpumping Windmills
(2021-05-07) John, Itoje Harrison; Wood, David; Morton, Chris; Korobenko, Artem; Trifkovic, Milana; Visser, Kenneth Dale
Windmills for waterpumping typically operate at low speed and high torque owing to their multi-bladed nature. This low Reynolds number, Re, operation, however, complicates the rotor aerodynamic behavior due to the mutual interaction between adjacent blades. While studies on aerodynamic and starting performance of windmills indicate that increasing blade number and airfoil type are critical analysis and design parameters, the low Re behavior of the commonly used cambered blades is still poorly understood. Accordingly, the rotor performance and starting behavior of a cambered, multi-bladed, waterpumping windmill were experimentally and analytically investigated at low tip speed ratios using three-, six-, twelve-, and twenty-four-bladed rotor configurations based on Wegereef’s 1984 blade profile. Comprehensive wind tunnel testings were performed to provide accurate airfoil data at flow conditions typical of the low Re and high angles of attack experienced by windmills during starting. Implementation of the blade element momentum (BEM) with a generally more accurate, helical vortex theory-based tip loss function or otherwise “finite blade function” for very low speed wind turbines other than the commonly used Prandtl tip loss factor provided insights on the blade elements performance and subsequently, the global performance parameters. Wind tunnel and theoretical studies showed that design parameters not limited to solidity impact the rotor performance and starting behavior. Increasing the blade number improves the rotor performance coefficients and starting performance by reducing idling time. Generally, there is good agreement between the wind tunnel measurement results and BEM prediction for the range of tip speed ratio considered, except below the optimal tip speed ratio region. In that region, discrepancies due to solidity effects unaccounted for in the BEM prediction were observed and shown to increase with blade number. The impact of blockage was examined with both low and high blockage wind tunnels and found to be significant. For a given rotor model and varying wind tunnel areas, the blockage effects increase with solidity. Overall, the experiment provided better performance, highlighting the importance of accounting for high solidity in low wind speed aerodynamic performance prediction. Useful preliminary guides are proposed to optimize the windmill rotor design.
Embargo
Application of 3D Printing in Calcium Looping for Carbon Capture
(2024-08-19) Ince, Cameron James; Mahinpey, Nader; Trifkovic, Milana; Jinguang, Hu
Calcium looping was first proposed in 1999 as an alternative CO2 removal process that functions using two interconnected fluidized bed reactors filled with limestone sorbent. Since that time research has been focused on increasing the stability of the limestone sorbent and discovering the optimal operating conditions. This material is available both from naturally occurring mineral formations, and from industrial sources such as steel slag. With the advent of additive manufacturing and 3D printing there has been some nascent research conducted on 3D printed sorbents for use in carbon capture and catalysis. Fluidized bed processes like calcium looping are an area where monolith sorbents may lead to lower costs of capture, by reducing the pressure drop across the column, as well as sorbent attrition. In this work a novel limestone mixture was created and then extruded through a commercially available 3D printer, in order to create limestone monoliths which can be used for carbon capture in a calcium looping system. Limestone was commercially sourced, then pulverized, milled, and sieved to form a fine powder with a particle diameter less than 63µm. This was then mixed into a paste and extruded into a variety of geometries. These monoliths were tested inside of a 1” ID 316 SS reactor. Four monoliths were tested in total, and their adsorptive capacities, as well as pressure drops were compared with a random packing and pure limestone powder. Reaction conditions inside of the reactor consisted of a mild calcination and carbonation. Calcination was done at 850°C, under pure N2, whereas carbonation was conducted at 650°C with 15% CO2, balance N2. The monolith demonstrated a slightly lower adsorption capacity than a powder, but showed higher stability over ten cycles, and less sintering. The adsorptive performance of these monoliths was slightly lower than the traditional powder, but the pressure drop across the column was reduced by ~58% on average. This provides a proof of concept that limestone based calcium oxide (CaO) could be used in a fixed-bed reactor system, as opposed to the traditional fluidized bed system.
Open Access
Assessment of Amount of Emulsion Stabilizers in Oil Sands Bitumen
(2023-07) Tamayo Duran, Leidy Carolina; Yarranton, Harvey; Bryant, Steven; Trifkovic, Milana
In current commercial oilsands bitumen extraction processes, ores of different quality are blended to utilize poorer quality ores and maintain a consistent processibility. The choice and proportion of ores in the blend is guided by the fines content of the ores. However, the processibility does not correlate consistently with the fines content, leading to poorer than predicted performance. It was hypothesized that the deviations in processibility were caused by differences in emulsion stability which could be attributed to different amounts of emulsion stabilizers in the bitumens from different ores. These stabilizers are believed to be concentrated in the asphaltenes, the least soluble fraction of the bitumen. To test the hypothesis, the amount of strong emulsifiers was assessed for asphaltenes from different mines in Alberta. Bitumen was extracted with cyclohexane using a multistage method equivalent to a counter current process with a solvent/ore ratio of 0.67 w/w. Asphaltenes were separated and the toluene insoluble components were removed. The asphaltenes were fractionated by solubility and interfacial adsorption methods. The strong stabilizer content was determined by comparing the stability of water-in-oil emulsions prepared from the different fractions dissolved in a solution of heptane and toluene. Finally, the stability of water-in-oil emulsions prepared from bitumen in the same solution was measured to determine if the there was a correlation between the strong stabilizer content and water-in-bitumen emulsion stability. No correlation was found and therefore the hypothesis was disproven and variations in strong stabilizer content are not likely to impact ore processibility. The extraction data collected in this study also allowed testing the claim that bitumen recovery in non-aqueous extraction (NAE) is unaffected by ore quality. Bitumen recovery and product quality were measured for each ore. It was observed that bitumen recovery correlated negatively with the clay content of the ore. This loss of recovery was attributed to bitumen adsorption on clays, where higher clay content led to greater mass adsorption and lower recovery. The product quality was found to be insensitive to the ore quality.
Open Access
Biodegradable Cryogels for Adsorption and Electrochemical Oxidation of Organic Dyes
(2022-01-03) Abuhatab, Saqr S; Trifkovic, Milana; Hu, Jinguang; Kibria, MD G
The supply of clean water is becoming one of the greatest challenges of the 21st century. Therefore, sustainable and cost-effective measures must be developed and implemented to reduce water scarcity and prevent contamination of our water systems. This work aims to develop novel, environmentally-friendly 3D structured adsorbents for the removal of dissolved organic pollutants from wastewater. This was achieved by developing hydrophobic cryogels composed of TEMPO-oxidized cellulose nanofibers (TOCN) and electrochemically exfoliated graphene (EEG). TOCN/EEG cryogels were hydrophobized by incorporating oleic acid (OA) into the precursor gels. The cryogels were synthesized by mixing the components at 50 °C and 300 rpm for one hour, followed by freeze-drying the gels. The effect of OA loading, TOCN/EEG weight ratios (1:1 and 1:2), and initial solids content were systematically investigated through microstructural and rheological characterization of the precursor gels, and the morphology and adsorption capacity of the derived cryogels. The optimum OA loading for the hydrophobization of TOCN (HTOCN) was found to be 5 wt.%, at which the strongest gel was obtained. The initial solids content and EEG loadings in the precursor gel alter the morphology and adsorption capacity of the derived cryogels. The maximum adsorption uptake was increased by 180% for the 1:1 HTOCN/EEG weight ratio when the initial solids content in the precursor gels was increased from 1 wt.% to 4 wt.% compared to only 70% rise when the solids content was increased from 1.5 wt.% to 6 wt.% for the 1:2 HTOCN/EEG cryogels. The drop in the adsorption capacity enhancement of the 1:2 HTOOCN/EEG cryogels was attributed to the higher extent of EEG sheets aggregation at higher EEG contents. The electrochemical regeneration studies confirmed the ability to oxidize the methylene blue adsorbed onto the cryogels with minimal changes in the cryogels’ adsorption capacities after multiple regeneration cycles. The cryogel made of 1:1 HTOCN/EEG with 1 wt.% solids content gel was tested for 18 adsorption-electrochemical regeneration cycles with no observable mass loss and retained adsorption capacity confirming the feasibility of the proposed approach for developing adsorbents with long-term stability.
Open Access
Coarsening Dynamics in Co-Continuous Polymer Blends and Composites
(2023-04-18) Shah, Rajas Sudhir; Trifkovic, Milana; Bryant, Steven; Karan, Kunal; Natale, Giovanniantonio; Wong, Joanna; Mohraz, Ali
Co-continuous polymer blends find extensive use across multiple industries. However, the morphology of these blends is thermodynamically unstable, which causes coarsening during processing. As a result, it is essential to understand the coarsening mechanism to improve their performance. Unfortunately, the current literature lacks a comprehensive explanation of the microstructural changes that occur during coarsening. To address this issue, the study employs 4D laser scanning confocal microscopy coupled with rotational rheometry to observe the coarsening dynamics in real-time. The aim is to understand the interplay between viscoelasticity and morphology during coarsening. The results show that when the ratio of interfacial tension to viscosity of blends exceeds a critical value, they tend to break down into droplet-matrix structures. The study also focuses on improving the stability and functionality of blends by incorporating solid particles. In literature, particle surfaces are often chemically modified, requiring complex and costly treatments. Therefore, this study examines the stability of co-continuous blends with pristine particles and how particle size and size distribution affect the stability. The study investigates the coarsening dynamics of blends filled with five different silica particles of diameters ranging from 5 nm to 490 nm. The results show that particle size does not play a role in blend stability when particles are thermodynamically driven to their preferred polymer phase. However, a striking effect is achieved when particles are kinetically trapped at the interface. The interparticle interaction governs their extent of agglomeration and, consequently, their ability to stabilize the morphology. The most effective, 140 nm and 250 nm particles are then added into blends under different loading ratios to simulate polydispersity in four different blends. The study demonstrates that polydispersity in particle size does not negatively affect blend stability. The efficacy of particles to suppress coarsening is dependent on their initial localization in the blend, which is determined by polymer characteristics. Overall, the study's findings provide a better understanding of the coarsening mechanism and stabilization of co-continuous morphology in polymer blends using particles. The results contribute to the fundamental knowledge of these materials and can aid in improving their design in various industries.
Open Access
Conductive Nanocomposites of Polystyrene/Polyamide 6/Carbon Nanotube: The role of Polymer/Filler Interaction on Blend Morphology and Electrical Properties Evolution
(2016) Ahmadian Hoseini, Amir Hosein; Trifkovic, Milana; Sundararaj, Uttandaraman; Roberts, Edward; Jeje, Ayodeji Aderopo
This thesis advances the field of conductive filler/polymer composites (CPCs) by providing insight to this critical question: what is the significance of polymer/filler interaction on morphology and electrical properties of CPCs? Carbon nanotubes (CNTs) as conductive filler and two immiscible polymers, i.e. polystyrene (PS) and polyamide 6 (PA6), as matrix were melt blended with different compositions. The generated blends were investigated morphologically via light transmission, scanning electron, and transmission electron microscopy techniques; and electrically including DC conductivity, EMI shielding, imaginary permittivity and current-voltage characteristic. It was found that high interaction between PA6 and CNT led to excellent dispersion state, but hindered conductive network formation; while in more agglomerated PS/CNT composites, CNTs percolated much more readily. In PS/PA6/CNT blends, CNTs were selectively localized in PA6 phase. Though CNT-rich phase was not co-continuous, percolation still occurred, and higher electrical conduction was obtained.
Open Access
Correlating macroscopic rheological behaviour to microstructure of polymer flocculated Mature Fine Tailings (MFT)
(2021-01-28) Nagial, Rahul; Trifkovic, Milana; Hu, Jinguang; Yarranton, Harvey W
Northern Alberta holds over 178 million barrels of proven oil reserves in the form of oil sands. However, these deposits require extensive processing to extract the bitumen and result in generation of vast amount of tailings waste. The growing inventory of tailings represents a huge oil sands industry liability and an enormous environmental issue due to the associated GHG emissions and potential pollution of water bodies in their vicinity. Treatment of tailings with polymers (combined with other processes such as thin-lift drying, atmospheric fines drying) is one of the preferred methods for capturing the suspended solids and releasing the trapped water. However, the fundamental understanding of microstructure of the sludge formed after polymer treatment (i.e. flocculation) is still lacking. The microstructural information is vital for designing enhanced flocculation procedures. In this study, the microstructural and rheological parameters were utilized to understand the effect of processing conditions on the polymer flocculation of mature fine tailings (MFT). Laser scanning confocal microscope (LSCM) was used to capture 3-D images of sludge fabric and microstructural parameters (i.e. porosity and fractal dimension). Oscillatory amplitude sweep tests were performed to acquire rheological signature of the flocculated samples. The effect of overshearing as well as ionic strength of the polymer solution was investigated. It was shown that as the over-shearing time increased from 30 sec to 210 sec, the porosity of flocculated MFT increased from 18.77% to 31.26% and the fractal dimension decreased from ~2.903 to ~2.869. An explicit link between microstructural and rheological parameters was established, wherein bond breakage was quantified both at micro and macro scales. This information can be used to optimize energy input, increase water release and improve sediment strength in MFT flocculation procedures. Flocculation experiments done with process water showed that ionic strength of the process water utilized for polymer dissolution by itself does not change polymer configuration significantly (as compared to model process water) to change the strength of sludge appreciably. However, dilution of MFT resulted in lower sludge strength post flocculation, but these differences became negligible after aging the samples for 30 days due to consolidation effects.
Embargo
Design of graphene-chitosan-based aerogels for CO2 capture
(2023-08) Pal, Sucharita; Natale, Giovanniantonio; Trifkovic, Milana; Natale, Giovanniantonio; Trifkovic, Milana; Sundararaj, Uttandaraman; Manhinpey, Nader
The significant effects of global CO2 emissions on our environment and climate highlight the importance of finding feasible solutions for capturing CO2, to tackle the consequences of anthropogenic greenhouse gases. This study introduces two novel approaches for producing highly effective CO2 adsorbents using graphene and chitosan precursors. The first approach involves combining glycated chitosan (GC) with electrochemically exfoliated graphene (EEG) nanoplatelets, through a physical crosslinking mechanism. Glycation of chitosan improves its dispersion in water by introducing more hydroxyl functional groups and reduces its amorphous parts, resulting in a bimodal particle size distribution. The unique and specific interactions between amine and phosphate groups proposed here trap hydrogen ion-water crystals within its network, which on freeze drying generates mesoporous microstructures. By inducing mesoporosity through the physical crosslinks of amine groups on GC and phosphate groups on EEG, the CO2 adsorption capacity of the EEG-GC aerogels is significantly enhanced. The extent of glycation and the weight ratio of EEG to GC is demonstrated to impact the microstructure and mesoporosity of the precursor gel and derived aerogels. The optimized EEG-GC18 aerogels exhibit a high BET surface area of 136.29 m2 g-1 and exceptional CO2 adsorption capacity (2.88 mmol g-1) and selectivity (43.8) at 298 K and 1 bar. In the second approach, the hierarchically structured aerogels are synthesized by generating covalent amide crosslinks between chitosan (CS) and manganese dioxide (MnO2) functionalized electrochemically exfoliated graphene (MEEG). An innovative approach was undertaken to achieve a two-fold enhancement in surface area where MnO2 functionalization prevents graphene aggregation by acting as a steric barrier between consecutive graphene sheets, while the strong amide bond formation between MEEG and CS inhibits preferred ice-crystal growth during aerogel synthesis. The resulting MEEG-CS aerogels exhibit a high surface area of 374.2 m2 g-1 and exceptional CO2 adsorption capacity (3.94 mmol g-1) and selectivity (65.2) at 298 K and 1 bar, surpassing previously reported hierarchically structured CO2 adsorbents. Although, in order to incorporate hierarchical structuring, for both EEG-GC and MEEG-CS, primary amine adsorption sites have been sacrificed, however, the enhanced surface area improved the accessibility to the available adsorption sites, thus increasing overall CO2 uptake. The electrical conductivity of the aerogels from both routes enables direct electrical heating, leading to quicker regeneration times and lower energy costs. The utilization of EEG-GC and MEEG-CS aerogels offers new avenues for designing innovative porous materials that act as hybrid adsorbents combining both physisorption and chemisorption mechanisms to address climate change concerns.
Open Access
Developing Rapid Screening Tools for Predicting Nanomedicine Transport Limitations
(2016) Sarsons, Christopher; Rinker, Kristina; Grainger, David; Kallos, Michael; Cramb, David; Trifkovic, Milana; Murari, Kartikeya
Nanomedicines represent the future of medicine. Targeted therapies promise to increase treatment efficacy while simultaneously reducing side effects. However, despite two decades of dedicated research, this paradigm shift has found little clinical traction. Partly to blame is the multitude of off-target sinks and degrading factors that limit delivery efficiency. Rapid, cost effective, in vitro models may be able to screen novel nanomedicines for their susceptibility to these transport limitations. This thesis focuses on studying nanoparticle transport in two specific domains: endothelium interactions and extracellular matrix diffusion, utilizing in vitro platforms. Laser-scanning confocal microscopy and associated image analysis techniques allow fluorescently-labelled, cell-associated nanoparticles to be quantified. However, image analysis procedures lack standardization. Endothelial cells were exposed to fluorescent nanoparticles to investigate whether different image analysis techniques could impact particle quantification. Significant differences were found when fluorescence quantification and image normalization methods were varied, as well as when image projections were analysed. Fluid flow forces impact nanoparticle interactions with the endothelium. The association of quantum dots with human endothelial cells was studied after flow preconditioning in a parallel plate flow chamber at various flow magnitudes. The results were compared with distribution patterns of quantum dots in zebrafish embryo vasculature. It was found that quantum dots preferentially accumulate in lower flow vessels, and associate more with cells that have undergone lower flow preconditioning. A novel platform was developed to study the transport of gold nanoparticles in extracellular matrix. It was found that matrix density and particle diameter impact the matrix diffusion of particles. These results were supported by a tumour-bearing murine model and in silico predictions of particle behaviour. Characterization of these three models lead to a decision matrix to select nanoparticle properties based on patient-specific pathophysiology. The novel platform was further applied to understanding the effect of polyethylene glycol surface functionalization on liposome diffusion in extracellular matrix. It was found that polymer conformation is an important driver of particle-matrix interactions. Together this work provides new insights into nanoparticle transport limitations, showcases the predicative value of in vitro modelling of particle transport and offers new tools towards increasing the clinical translation of nanomedicines.
Open Access
Development of High-Strength Composites with Sustainable Fibers for Structural Applications
(2024-09-18) Sarker, Rahul; Kibria, Md Golam; Hu, Jinguang; Sumon, Kazi Z; Trifkovic, Milana
Despite Canada's abundant biomass resources, a significant portion remains underutilized due to a lack of large-scale industrial applications. This research explores the utilization of low-value biomass, specifically aspen fiber, in fused filament fabrication (FFF) to develop biocomposites. Various chemical treatments (NaOH, silane, and maleic anhydride (MA)) were applied to improve fiber compatibility with polylactic acid (PLA). Both untreated and treated fibers at 10% loading were blended with PLA and extruded into 3D printable filaments. Results showed that MA-treated fiber-based composites had around 15% higher tensile strength and modulus, along with a 30% enhancement in storage modulus than untreated ones. Additionally, a 25% reduction in water uptake was witnessed in MA-treated aspen-derived composites. Successfully 3D-printed biocomposites with up to 30% fiber loading were achieved without nozzle clogging, though higher fiber loading negatively impacted mechanical properties. This study also investigates the potential of CNT incorporation in asphaltene-derived carbon fibers and the impact of carbon fiber reinforcement to enhance the mechanical properties of biocomposites. This research contributes to the development of sustainable and high-performance composite materials by exploring the potential of underutilized resources and advanced manufacturing techniques.
Open Access
Diffusiophoresis of Active Colloids: From Synthesis to Dynamics in Complex Media
(2020-04-28) Saad, Shabab; Natale, Giovanniantonio; Trifkovic, Milana; Benneker, Anne M.
Active particles are examples of non-equilibrium systems that have gained a lot of momentum over the past few decades due to their ability to generate enhanced diffusive motion in fluid media. This work focuses on the synthesis and dynamics of active Janus colloids from single particle (dilute concentration regime) to cluster formations (concentrated regime). Two types of active colloids are explored: a) pH-responsive calcium carbonate (CaCO3) Janus colloids that are biocompatible in nature and b) silica particles half-coated with platinum Janus microspheres that are able to self-propel in presence of hydrogen peroxide. First, a methodology to half-coat the CaCO3 particles with a silica layer via Pickering emulsion is developed. Then the self-diffusiophoretic motion of the carbonate Janus colloids at different acid concentrations is investigated in simple Newtonian media. It is found that with increasing hydrogen ion concentrations, the pH-responsive colloids experience higher mean-square displacements due to self-propulsion velocities and longer particle trajectories. Synthetic Si/Pt active colloids were dispersed in two different viscoelastic fluids (Polyvinylpyrrolidone and Polyacrylamide) of different molecular weights and concentration regimes. These two systems were chosen to probe different relaxation times from relatively short (~5ms) for PVP to large (~14.5s) for PAM but always smaller than the rotary Brownian motion time scale (~20s). Within this regime, the coupling between the self-propulsion velocity and the medium rheology is investigated. The Janus colloids are found to get physically confined by polymeric entanglements but surprisingly they are able to escape the physical cage in a time scale much shorter than the relaxation time of the polymer solution. Finally we demonstrate how the collective motion of active colloids (cluster organization) can be autonomously controlled by tuning the fluid rheology. Such studies are highly relevant for applications of self-propelling colloids in targeted drug delivery, water and soil remediation where complex environments are naturally present.
Open Access
Effect of Graft Density of Partially Hydrophobic Copolymers on the Treatment of Oil Sands Mature Fine Tailings
(2021-12-07) Kalyanaraman, Gayathri; Trifkovic, Milana; Lu, Qingye Gemma; Achari, Gopal; Trifkovic, Milana; Nassar, Nashaat
Alberta is well renowned for its oil sands mining that has led to enormous deposits of waste called tailings (alkaline slurry of residual bitumen, clay, and water). The presence of clays and fine silts in the tailings successively reduce their ability to settle naturally and dewater under the effects of gravity. The continuous accumulation of the tailings and the inability to treat them pose a risk to its surroundings. To resolve these issues, industries utilize several techniques, among which flocculation methodology is commonly employed to enhance the dewatering performance, capture the suspended solids, and improve the strength of the tailings using polymers (flocculants). The flocculation effectiveness depends on the polymer design with respect to the tailings system it is acting on, and this comes from understanding the microstructure of the polymer-flocculated sediment. Traditionally there are two broad groups of polymers: hydrophilic (water-liking) and hydrophobic (water-hating) for MFT (Mature fine tailings) flocculation. Researchers have shifted the focus to partially hydrophobic flocculants due to the long-term consolidation issues with conventional hydrophilic flocculants. This study employs partially hydrophobic copolymers with three different graft densities (30%, 40%, 50%). A combination of mechanical (Rheology, Dean-stark) and imaging (Laser Scanning Confocal Microscopy (LSCM)) experiments were conducted to understand and correlate the microstructure of polymer with that of the resulting MFT aggregates. Rheological experiments were performed to assess the strength of the treated MFT sediment. The LSCM was employed to image the microstructure of the polymer dispersion and the flocculated MFT aggregates. The obtained MFT images were further quantified in volume fraction and fractal dimension to evaluate the amount of inter-floc water (present between the flocs). Similarly, Dean-Stark experiments were performed to evaluate the amount of intra-floc water (enclosed within the individual flocs). It was shown that as the graft density of the polymers increased, the “initial” flocculation performance considerably improved. In contrast, there was no significant change in the “long-term" rheological signature among the three samples. The information on the inter-floc and intra-floc water obtained from LSCM and Dean-Stark studies have contributed to a better understanding of the spatial distribution of water within the flocculated sediment and their response to the polymer behaviour at varying graft densities. The effect of increasing the polymer graft density has led to a decrease in the dewatering rate with an increase in the amount of intra-floc water in the MFT sediment post flocculation. This approach clarifies that the flocculant's design, as understood from the spatial distribution of the water, plays a significant part in influencing the water release and water-retention ability of the flocs.
Open Access
Engineering Integrity: Using text-matching software in a graduate level engineering course
(2019-04-18) Crossman, Katie; Paul, Robyn; Behjat, Laleh; Trifkovic, Milana; Fear, Elise C.; Eaton, Sarah Elaine; Yates, Robin Michael
Academic misconduct is an unfortunate reality for many post-secondary level educators across disciplines; however, there is currently a paucity of Canadian research on Academic Integrity (Eaton, 2018). This study describes an inter-disciplinary project to investigate the potential for text-matching software to prevent and avoid plagiarism by graduate level engineering students. Conceptual/Theoretical Framework: Our study was informed by the potential for text-matching software to help students understand and avoid plagiarism (Zaza & McKenzie, 2018) and faculty identify instances of plagiarism in an engineering course (Cooper & Bullard, 2014). Although text-matching software has been commercially available since the 1990s, its acceptance within academic contexts is uneven. Reasons for this are manifold, but the most commonly expressed concerns are about a) the punitive nature of the software use; b) the potential for it to be used as a tool for cheating students to “beat the system”, and c) privacy concerns (Savage, 2004). Methodology / Approach: In this project, approved by the institutional REB, assignments submitted in a graduate-level engineering communication course were analyzed using text-matching software, Ithenticate. The first phase of the study involved collecting baseline data from students enrolled in a graduate-level Engineering course (N=132). As per REB protocol, individual results were not shared with the professor or teaching assistants and sharing of aggregated results is not permitted until after February 15, 2019. In our presentation, we share baseline results, as well as outcomes of the second phase of the research, in which the research associate revealed the deception, explained the study, and solicited consent from students to have their next assignment harvested and analyzed. The research associate also introduced the software and provided a workshop on academic integrity including strategies for avoiding plagiarism, such as paraphrasing. Subsequent to these workshops, assignments written by consenting participants were analyzed with Ithenticate to determine whether a reduction in textual similarity occurred. Results / Findings: The results of this study indicate that text-matching software can be useful to students and educators to prevent and identify academic misconduct. This study will add to the growing body of empirical research about academic integrity in Canada and in particular, in engineering contexts.
Open Access
Exploiting Maximum Capillary Pressure and Detachment Energy Synergy for 3D-Printable High Internal Phase Emulsions with Ultra-low Loadings of Water-Wetting Carbon Dots
(2024-04-02) Karhana, Gaurav; Trifkovic, Milana; Bryant, Steven; Kantzas, Apostolos; Natale, Giovanniantonio
High Internal Phase Emulsions (HIPEs), with internal phase volume fractions exceeding 0.74, hold potential for diverse applications. Nonetheless, their broader adoption is constrained by limitations, including the need for high concentrations of stabilizers and the ability to fine-tune their morphology. This thesis evaluates the capability of two fully water-wetting sub-10 nm asphaltene-derived carbon dots — asphaltene-derived carbon dots 1 (ACD1) and asphaltene-derived carbon dots 2 (ACD2) — for stabilizing oil-in-water (o/w) HIPE. A universal route is introduced to generate o/w HIPEs with ultra-low loading of water-wetting solid stabilizers by exploiting the synergy of high maximum capillary pressure to resist the thinning of liquid films and particle detachment energy. The HIPE formation involves a 2-minute single-step homogenization of ACDs, water, and dodecane. HIPE was generated with a minimal particle loading of 0.025wt% ACD1, capable of emulsifying 0.82 of oil volume fraction. To probe the link between the evolving microstructure and rheological properties, laser scanning confocal microscopy (LSCM), rheometer, and confocal-rheology (LSCM in conjunction with dynamic oscillatory amplitude sweep) were utilized, testing HIPE thixotropy and creep recovery. A correlation between the HIPE microstructure and rheological properties with the emulsion stabilization mechanisms has been established. The result is a HIPE with spherical dispersed droplets, superior thixotropy, shear-thinning behavior, excellent creep recovery, complete structural recovery, and storage stability of more than 6 months, achieved with just 0.075wt% ACD1 loading. Taking advantage of these properties, finely detailed 3D structures have been successfully printed using an ultra-low loading of 0.075wt% ACD1-stabilized HIPE in an extrusion-based 3D printing method at a low extrusion pressure of 4kPa with a nozzle diameter of just 0.400 mm. This addresses the challenges in HIPE 3D printing, like high extrusion pressures and the need for large nozzle sizes or additional chemicals, thereby broadening the potential applications of HIPEs in 3D printing technologies.
Open Access
An Exploration of Numerical Methods for Thermally-Induced Convection in Storage Tanks and Films
(2021-07-19) Pletnyov, Fedir; Jeje, Ayodeji; Azaiez, Jalel; Trifkovic, Milana; Chen, Zhangxing; Mohamad, Abdulmajeed; Upreti, Simant Ranjan
The study is on conditions for onset of convection, the transient and steady states velocity and temperature patterns in 2D and 3D coordinates for fluids in vertical cylindrical storage tanks. The Navier-Stokes and energy equations are formulated using vorticity, stream function (2D) / vector potential (3D) and temperature as the dependent variables, with and without dynamic free surfaces. Solving the transport equations and exploring conditions for multiple solutions, of which only certain patterns may be realizable, is time-consuming. The development of computationally efficient algorithms is crucial to reduce computation overheads. In this work, software package for the simulation of 2D and 3D problems with parallel implementation was developed. For 2D simulation, the numerical methods in package include Gauss-Seidel with Red-Black (GS-RB) ordering, Alternating Direction Implicit with Fast Fourier Transform (ADI + FFT) and with Evolutionary Factorization with Logarithmic time step (ADI+EFL), Geometric Multigrid (GMG), Jacobian Free Newton-Krylov (JFNK). For 3D simulation, GS-RB (parallel) and ADI-EF (Samarskii-Andreev) with FFT for the vector potential equations were developed. The non-linear systems of PDE were approximated using central (CFD) and monotonic - conservative (MCFD) finite differences schemes. The boundary conditions for vorticity in 3D were derived using the one grid step methods for a second order accuracy. For 2D simulations, the Polezhaev - Gryaznov method was extended for the axisymmetric domain. These approaches significantly improved CPU performance. The investigation was restricted to one component liquids, and cylindrical tanks with evaporation at the free surfaces were of primary interest. Specification of appropriate boundary conditions for the free surface is difficult as the interface may be deformed due to the inertia of ascending and descending streams and gradients of the interfacial tension. The contour is unknown a priori. In lien of detailed calculations, evaporation was incorporated through the application of Hashemi-Wesson’s empirical correlation between vaporization rates and the local surface temperature. To understand the interfacial dynamics and to develop the numerical scheme for modeling evolving surface contours, deformation of thin liquid layers locally heated along strips was explored.
Open Access
Fluorescent polycatecholamine nanostructures as a versatile probe for multiphase systems
(RSC Advances, 2018-09-13) Ozhukil Kollath, Vinayaraj; Derakhshandeh, Maziar; Mudigonda, Thanmayee; Islam, Muhammad Naoshad; Trifkovic, Milana; Karan, Kunal; Mayer, Francis D.
Shape and size controlled nanostructures are critical for nanotechnology and have versatile applications in understanding interfacial phenomena of various multi-phase systems. Facile synthesis of fluorescent nanostructures remains a challenge from conventional precursors. In this study, bio-inspired catecholamines, dopamine (DA), epinephrine (EP) and levodopa (LDA), were used as precursors and fluorescent nanostructures were synthesized via a simple one pot method in a water–alcohol mixture under alkaline conditions. DA and EP formed fluorescent spheres and petal shaped structures respectively over a broad spectrum excitation wavelength, whereas LDA did not form any particular structure. However, the polyepinephrine (PEP) micropetals were formed by weaker interactions as compared to covalently linked polydopamine (PDA) nanospheres, as revealed by NMR studies. Application of these fluorescent structures was illustrated by their adsorption behavior at the oil/water interface using laser scanning confocal microscopy. Interestingly, PDA nanospheres showed complete coverage of the oil/water interface despite its hydrophilic nature, as compared to hydrophobic PEP micropetals which showed a transient coverage of the oil/water interface but mainly self-aggregated in the water phase. The reported unique fluorescent organic structures will play a key role in understanding various multi-phase systems used in aerospace, biomedical, electronics and energy applications.
Open Access
Greener on the Other Side: Assessing the Economic and Emissions Impacts of Demand-Side Technologies in Electricity Grids
(2020-01) Tierney, Matthew W.; Bergerson, Joule A.; Wood, David H.; Zareipour, Hamidreza; Trifkovic, Milana
The long-term goals of energy transitions are clear: to provide a secure, consistent, and cost-effective power supply that is sustainable with low Greenhouse Gas emissions. However, energy transitions around the world focus more simply on an increase in renewable energy and decrease in fossil fuel use. This focus on the generation side alone misses a key opportunity in the electricity system, demand-side technologies. Demand-side technologies are those capable of making controlled and deliberate changes to demand within the system. This thesis provides two case studies investigating demand-side technologies, firstly from the grid perspective and secondly from the perspective of a demand operator. Grid scale impacts were explored in terms of marginal changes in the merit order, where fluctuation in supply and demand are accounted for by dispatching generators. Generators in the merit order were found to be far less organized by fuel-type than previously suggested in the literature. As a result, calculating emissions based on the marginal generator provided unreliable numbers. The economic case for demand side technologies in current grids shows potential, as a small reduction in demand across key hours had a major impact on the yearly cost of the grid. On the operator side, demand-shifting technologies, solar PV, and a combination of solar with storage were compared based on their ability to achieve operational cost savings in different electricity grids. Grid price trends had a major impact on which technologies are most beneficial, with certain pricing patterns benefitting each technology differently. Allowing consumers access to grid wholesale prices, as well as providing pricing signals, would allow users to make informed decisions on what technology is best to invest in. Together, the two studies show a clear case for the benefits of adopting demand-shifting technologies. Significant savings are available to the grid at large, as well as to the individual operator. During the energy transition, balancing the adoption of renewables with demand-shifting measures will be valuable in ensuring price and grid stability.
Open Access
Insights into the Interplay between Nanoparticle Interfacial Interactions and Bulk Properties of Complex Systems via Colloidal Probe AFM
(2021-01-13) Ganjeh Anzabi, Pejman; Trifkovic, Milana; Lu, Qingye G; Ponnurangam, Sathish; Sundararaj, Uttandaraman; Kim, Seonghwan; Zeng, Hongbo
The addition of a nanosized particle to materials is now a well-established method for engineering their properties. Despite the significant progress in the realm of nanoscience and nanotechnology, commercially available so-called “nanofilled”materials have a relatively small share of the market. This is the result of the challenging and tedious task of designing, processing, and mass-producing these materials for a specific application of interest. A tremendous amount of research hasconfirmed that quantifying nanoparticle (NP) interfacial interactions and correlating them to the macroscopic properties facilitate the design of nanofilled materials. Therefore, this dissertation is evolved around the fundamental task of quantifying interactions and correlating it to the dispersion of NP in a host matrix. To address the former, colloidal probe atomic force microscopy (CP-AFM) is utilized to develop a method for measuring the surface free energy (SFE) of NPs. The effect of roughness on the measurements is included by employing Persson’s model. The method is validated on several systems including polystyrene, glass, hydrophobicglass, graphene oxide (GO), and reduced graphene oxide (rGO). Interfacial energy values of GO with selected organic solvents are later calculated to predict GO’s solubility in different solvents using a proposed mean-field lattice model. The modelcan successfully predict the experimentally observed solubility trend and be deployed as a decision-making tool for choosing solvents for rGO. As the final contribution, a model based on the concept of Boltzmann distribution is proposed to predict the uneven distribution of NPs in immiscible biphasic systems such as emulsions and polymer blends. This model demonstrates that factors such as NP’s size and shape, temperature, the possibility of it forming a chemical bond with the molecules of host matrix, and finally entropic contributions can be as important as the wetting coefficient in determining NP's localization. As there has been no systematic investigation of the factors mentioned above on the selective localization of NP, the model paves the road for implementing new strategies to control the localization of NPs in biphasic systems.