Posts Categorized: Graduate Studies

Research on liquid film stability reveals mechanism behind destabilization on solid surfaces

Suraj Borkar

Suraj Borkar (ChemE PhD student)

For his research project titled “A New Perspective on the Stability of Liquid Films on Solid Surfaces”, Suraj Borkar (ChemE PhD student), under the guidance of Professor Arun Ramchandran, set out to better understand the cause of destabilization of films of hydrophobic liquids (for example oil) sandwiched between a liquid medium (like water) and a solid surface. Thin films of oil tend to break up into droplets under such conditions.

“For decades, researchers have accepted that for this thin film of oil to remain stable (i.e. it does not break up into droplets), the film thickness must be large, typically greater than 100 nm,” Borkar explains. “When films are thin (less than 100 nm), intermolecular forces can cause the oil film to become wavy, eventually causing the film to break up into oil droplets.”

While the mechanism behind the destabilization of thin layers was well understood, thicker layers were also observed to destabilize and this process was more mysterious. Classical theories explain that the destabilization occurs as a result of the presence of tiny and unavoidable dirt particles in the oil film. “However, even when researchers took extreme effort to avoid dirt particles, thick films still destabilized. Hence, the origin of instability for thick films has been a mystery until now” says Borkar.

The culmination of his research led to the discovery that the insolubility of the two liquids is not absolutely zero, and that this trace solubility was the cause of the destabilization, causing droplets to eventually form on the solid surface over time.

“We stumbled upon this observation back in 2015 and it took us seven years to thoroughly understand the mechanistic details” says Borkar. “I think the novelty of this research is that dissolved material spontaneously condenses on the solid surface in the form of droplets, without changing any thermodynamic property, such as temperature or pressure, that can lead to oversaturation conditions.”

Borkar says the utility of this discovery has applications in both industrial and commercial settings, for example the extraction of crude oil or the recycling of plastics. “A more niche area of research involves DNA transcription where transcription factors (typically water-soluble proteins) condense on a DNA molecule and commences the process of copying the genetic material in the DNA into a messenger RNA.”

Borkar’s research was published in the September 2021 issue of Nature Communications, a peer-reviewed, open access, scientific journal.


Good news from the Multidisciplinary Laboratory for Innovative Catalytic Science

William Broomhead

William Broomhead (ChemE PhD student)

Professor Cathy Chin and her team from the Multidisciplinary Laboratory for Innovative Catalytic Science have several reasons to celebrate!

On May 23, 2022, William Broomhead (ChemE PhD student) will deliver a lecture at the 27th North American Catalysis Society Meeting in New York City.

Broomhead’s talk will discuss the green-catalytic processes and systems for the selective partial oxidation of methanol, derived from the gasification of waste, to polyoxymethylene dimethyl ethers, which are sustainable fuel components suitable for direct blending into diesel.

The chemical conversion processes contain several catalytic reactions carried out in tandem. To achieve a one-step upgrading of methanol to larger ethers, a detailed understanding of the individual steps is necessary – particularly how the reactant molecules interact with the catalyst surface. Broomhead’s research focuses on discovering this chemistry on vanadium oxide-based catalysts, which contain multiple types of active sites and catalytic functions. This catalyst would enable the tandem chemistry, first activating methanol, and then connecting alcohol units together.

“Polyoxymethylene dimethyl ethers can have a huge impact as a sustainable fuel in todays society,” remarks Broomhead. “Blending these into existing diesel supplies can vastly reduce the emissions of harmful particulate matter. Plus, making these ethers from renewable methanol moves us closer to a carbon-neutral fuel economy.”

On April 14, 2022, a US Provisional Patent was filed for the project titled, Processes and systems for the selective partial oxidation of methanol to formaldehyde and for the production of polyoxymethylene dimethyl ether and catalysts used in the same. This project involved several members of the Multidisciplinary Laboratory for Innovative Catalytic Science including Broomhead and fellow PhD students Junfeng Guo, Guangming Cai, and Chengqian Wu. This collaborative effort could not have been achieved without the support of their supervisor Professor Chin and partners from Suncor and NSERC.


Innovative research on understanding stress relaxation behaviour

Short glass and carbon fibres are added to polymers, such as epoxy, to provide stiffness and strength. As the fibres are elastic, they behave like metal springs, but the polymers are viscoelastic, meaning that they undergo creep and stress relaxation. When elastic fibres are added to viscoelastic polymers, the fibres seem to strangely alter the behaviour of the polymer itself. Previous researchers have suggested that the polymer structure must be altered near the fibre surfaces.

To further understand the stress relaxation behaviour of short fibre composites, Numaira Obaid (ChemE PhD student) co-supervised by Professors Mark Kortschot (ChemE) and Mohini Sain (MIE), have taken a simple but innovative approach.

“We assumed the polymer structure was unchanged, but that the efficiency of the reinforcing fibres was changing over time because of the existing and well-understood polymer viscoelasticity,” says Kortschot. “With this in mind, we were able to design a model that predicts the behaviour of composites in a very simple way without needing to speculate about polymer structural changes. Using only independent measurements or properties of the polymer and fibres, we are able to determine how the composites will behave.”

This is significant as short fibre composites are widely used, including in many applications where there is long-term exposure to stress.

“The societal impact of the research is indirect since the main users are materials engineers. The semi-empirical models that were developed in this study can be used to predict the stress relaxation and creep of any short-fiber reinforced composite of any matrix/fiber combination. This is quite useful for the manufacturing sector, for example, it can help predict the rate at which residual stresses are released from manufactured composites to minimize component warpage. The application also extends to research in the biomedical field when designing and selecting synthetic composites to replace biological tissues where viscoelasticity may be a core functional characteristic, for example, in the design of artificial valves or arteries,” says Obaid.

This fundamental study, funded by NSERC and OGS, has been published in a series of three papers in the open-source journal Materials, and Composites Science and Technology.


Recovering a crucial and non-renewable resource from wastewater

Sara Abu-Obaid

Sara Abu-Obaid conducting research.

Phosphorous (P) is a critical component of biological processes. Yet, its over-enrichment in water bodies, known as eutrophication, can have detrimental effects on aquatic ecosystems. As a non-renewable resource with no known alternatives, it is important to recover P from wastewater. Sara Abu-Obaid (PhD candidate), supervised by Professor Ramin Farnood and Adjunct Professor Shahram Tabe, is looking to do just that.

“Eutrophication can lead to harmful algae blooms, which threaten the quality of drinking water and fish habitat. It also causes degradation of recreational opportunities and hypoxia, a state in which oxygen is so low in water that it kills fish, depletes valuable fisheries, disrupts the food chain, and the list goes on. However, phosphorous is essential for many industries, especially fertilizer production,” explains Abu-Obaid.

Her research project entitled, Fabricating Novel Mixed Matrix Membranes for Phosphorous Recovery from Domestic Wastewater, aims to contribute to a circular economy by recovering P. Unlike traditional P-removal methods normally employed in wastewater treatment plants, Abu-Obaid explains that membranes offer a chance to recover this valuable resource.

The use of membranes for P removal from water is normally avoided due to the high pressure and energy requirements of the process. This is because traditional membranes use size exclusion to ‘filter’ out the P. Since P is an ion, the membrane would have to be practically non-porous to achieve that, therefore requiring high pressure and energy. Abu-Obaid is fabricating low-pressure mixed matrix membranes to remove P from water and reducing its concentration to meet guidelines for environmental protection.

“The membranes I am using do not rely on size-exclusion, instead they utilize nanomaterials grown on the surface and inside the pores of the membrane to remove P from the water. This allows us to benefit from the use of nanomaterials without having to worry about separating them from the water after use. Using nanomaterials for water treatment remains a challenge due to fear of leaching and difficulties with separation after use. However, anchoring them on the surface of support materials, such as membranes, allows us to utilize their benefits without suffering from their possible drawbacks,” details Abu-Obaid.

The Fabricating Novel Mixed Matrix Membranes for Phosphorous Recovery from Domestic Wastewater project is funded by the University of Toronto, MITACS, and the Ontario Graduate Scholarship (OGS). Abu-Obaid hopes to publish her findings soon.


Improving the energy efficiency of pulp and paper mills

Michael Nwaeri and Manling Huang

From L-R: Michael Nwaeri and Manling Huang

Pulp and paper mills are often plagued with sodium salt scaling in their high solid evaporators. Research in the Department of Chemical Engineering & Applied Chemistry is looking to improve the energy efficiency of mills, and in the best case, reduce the potential downtime associated with the removal of scales through more intensive means.

A project led by Professor Niko DeMartini investigates the Effect of Various Resin and Fatty Acid Salts on Sodium Salt Scaling and their underlying mechanism. During several bench scale experiments, Michael Nwaeri (ChemE MASc 2T2), now a Junior Process Engineer at Bartek, identified important resin and fatty acids that were demonstrated to inhibit sodium salt scaling in a model solution.

Manling Huang (ChemE PhD student) using Nwaeri’s work as a foundation, is further studying the mechanism demonstrated to inhibit sodium salt scaling by completing a mass balance of the resin and fatty acids in the salt solution and crystals.

“The most interesting aspect of our project is that we are utilizing a by-product of the Kraft chemical recovery process. In industry, this by-product is known as tall oil soap, a mixture of different fatty and resin acid salts, which are typically separated and removed from the process. However, evidence in industry and in a few research labs, including ours, have begun to demonstrate that leaving a small amount of these fatty and resin acid mixture in the Kraft chemical recovery process can decrease sodium salt scaling,” says Huang.

Huang explained that by assisting pulp and paper mills alleviate this issue, it is possible to reduce the amount of steam required in high solid evaporators. Consequently, many mills would consume orders of magnitude less water leading to more energy-efficient mills and lessening our carbon footprint.

Huang will soon be moving to Gothenburg, Sweden for six months to learn from and operate the pilot-scale evaporator at Chalmers University of Technology. Her goal is to clarify the effect of fatty acid to resin acid ratio on sodium scaling rates, as well as the effects they may have mechanistically.

Professor DeMartini’s lab published their findings in Chemical Engineering Science in July 2021. The Effect of Various Resin and Fatty Acid Salts on Sodium Salt Scaling paper and was made possible through the backing of industrial partners from U of T’s Pulp and Paper Centre consortium and various research groups, including the lab of Professor Edgar Acosta.


Investigating the fate of phosphorus in the chemical recovery cycle of kraft pulp mills

Maryam MousaviMaryam Mousavi (ChemE PhD student) supervised by Professor Niko DeMartini is working on the fate of phosphorus in the chemical recovery cycle of kraft pulp mills. As mills tighten water cycles and look to replace fossil fuel with biomass fuels, the buildup of non-process elements (NPEs), especially phosphorus, is a significant concern for the industry.

“In a kraft pulp mill, a high concentration of NPEs in the recovery cycle can cause numerous operational problems such as scaling, corrosion and a high dead load in the lime cycle. The main NPEs are phosphorus, magnesium, manganese, aluminum and silica,” explains Mousavi.

“In the lime cycle, phosphorus can accumulate because it can react with lime particles and form calcium-phosphate compounds that are partially insoluble in the recausticizng process. Therefore, the unreactive lime needs to be purged (for land filling) and fresh lime/lime rock needs to be purchased to keep the amount of reactive calcium oxide (CaO) in the lime at a desirable level depending on the targeted causticizing efficiency,” Mousavi elaborates.

Mousavi’s work will broadly clarify the fate of phosphorous in the lime cycle and provide needed information for evaluating the impact of different technologies for replacing fossil fuels with biomass fuels on NPEs in the recovery cycle, with an emphasis on phosphorous. Her research will generate new ideas about how to recover phosphorus from lime in a form that is useable. Additionally, it will help both industry and society to reach their environmental related goals, as biomass is a renewable energy resource that produces less GHG emissions compared to fossil fuels.

Mousavi’s project could not have happened without the support of the 22 companies from around the world that form the U of T Pulp & Paper Centre consortium. This summer, Mousavi will be heading to Finland through funding provided by the Johan Gadolin Scholarship and Mitacs Globalink Award to investigate the fate of phosphorus in the gasification of bark. She will be conducting this research at Abo Akademi. The initial phases of her research have already been published in the Technical Association of the Pulp & Paper Industry (TAPPI) Journal. It is Mousavi’s hope that her international collaborations will strengthen her ability to have her research industrially applied.


ChemE student research published in ACS ES&T Water

Microplastics are common pollutants that can be found everywhere: in the food we eat, in the air we breath, in the Sahara Desert, and in deep oceans. A common way to study microplastics is to collect water/soil/sediment samples in the environment and analyze them in the lab, but this method comes with complications.

To quantify microplastic particles, specifically identifying the pieces of microplastic particles present, it is important to do so in a sample. However, this process is very slow as it requires manually counting particles one by one under a microscope. Automatic quantification methods do exist, but they are also slow and require expensive equipment and expertise to run them. In a project funded by CECSeed, PhD student Shuyao Tan (ChemE) studies Efficient Prediction of Microplastic Counts from Mass Measurements. Tan’s research aims to find an alternative microplastic quantification method that is overall fast, cheap and easy to use with minimal knowledge.

Tan’s collaborative research with fellow PhD student Kelsey Smyth (CivMin), Professors Elodie Passeport (ChemE, CivMin) and Joshua Taylor (ECE) was published in ACS ES&T Water in January 2020 focuses on developing an efficient, simple and affordable microplastic quantification method. Tan’s use of regression algorithms makes her research innovative. These algorithms are essential in predicting the number of microplastic particles in a sample solely based on simple measurable parameters such as the total weight of the sample. This method is accurate, fast and efficient as it only involves standard equipment, which includes balance, an oven and computer. Using standard equipment, this method can make hundreds of predictions within seconds and achieves lower levels of errors than one would see via manual sorting.

Tan is hoping to create more opportunities and encourage people to participate in microplastic studies. Simply attaching a metal filter to a tap and detaching it once a year can help predict the number of microplastics on the filter.

“By creating opportunities to involve more people in microplastic studies, we hope to provide valuable information for microplastic source identification and transportation studies, and contribute to reducing microplastics,” says Tan.

Read Shuyao’s published research.


Reducing water pollution through advances in microplastic research

Microplastic debris in major water systems has become a significant issue in recent years. Monitoring microplastic pollution and evaluating its health risks are largescale jobs. Bin Shi, a PhD student from the Department of Material Science & Engineering, strives to reduce these challenges through his project, Automatic quantification and classification of microplastics in scanning electron micrographs via deep learning.

Shi’s project, supervised by Professors Jane Howe (ChemE, MSE), Elodie Passeport (ChemE, CivMin) and Dwayne Miller (Chem, Physics), facilities microplastic quantification and classification with high accuracy, including instances when the microplastics are densely packed or imaged in complex environments with poor experimental settings.

“We have collected microplastics in various shapes and chemical compositions from daily supplies, such as washing and dryer machines, packing film, face and body wash, masks, cookware, and lunchboxes just to name a few examples. We have imaged these supplies by scanning electron microscopy (SEM). This offers greater depth of microplastics at a wider range of magnification than visible-light microscopy or a digital camera. Also, SEM has the potential to go down to the scale of nanoplastics. The smaller microplastics we can observe, the more microplastics we can take into account,” says Shi.

This approach has allowed Shi and his team to create the FIRST labelled open-source SEM dataset of microplastics for image segmentation. Additionally, Shi and his team applied deep-learning methods to automate and facilitate quantification and classification of microplastics in SEM images, which achieved a significantly improved performance than conventional methods.

“With the new data from our project, we have a way to further simplify microplastic quantification and classification. This helps us address the growing challenges that microplastics have posed to water systems, which affect human health, economic development, and political stability,” explains Shi.

Details of Shi’s project are available on the ScienceDirect website and will soon be published in the Science of the Total Environment Journal. Shi’s project was made possible through contributions from the Institute for Water Innovation Waterseed Program, Ontario Centre for the Characterisation of Advanced Materials research space, as well as students and professors from U of T Engineering. “Alone we can do so little, together we can do so much,” says Shi.


ChemE Student Discovery Award winners

Four graduate students have received Student Discovery Awards. Established in 2013, this award is presented to students who have successfully defended their MASc or PhD thesis at a Departmental Oral Examination within 2 or 5 years of program start date respectively, and have authored/co-authored at least one first-authored paper per year in the program at the time of the examination. Congratulations to:

John Anawati

Jihye Kim

Yijia (Erica) Wang

Kaushikraj Venkatesan

To be considered for this award, the student must submit a list of publications and a one-page impact statement to the Committee at the start of the examination.

 


Sheida Stephens receives Engineers Canada Manulife Scholarship

Sheida StephensSheida Stephens (PhD Candidate) supervised by Professor Grant Allen is one of three recipients of the 2021 Engineers Canada Manulife Scholarship, which provides $12,500 to each recipient to further their study/research in an engineering field. Click here to explore the various ways this year’s recipients are strengthening their knowledge in the field.


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