John Tomko is a Senior Scientist in the Department of Mechanical and Aerospace Engineering at the University of Virginia. During his Ph.D., he was a Virginia Space Grant Consortium Fellow and Hertz Foundation Fellowship finalist, where his research used ultrafast laser spectroscopy methods to measure nanoscale heat transport between different phases of matter; his research has been published in over 30 peer-reviewed journals and presented at over fifteen international conferences. John’s current research is focused on further understanding and manipulating energy at the nanoscale to better design next-generation power devices, thermal energy storage materials, and materials optimized for extreme environments.
1. How does Materials Science and Engineering relate to sustainability?
Materials Science and Engineering (MSE) is an extremely interdisciplinary field, as it encompasses the study of any and all materials. For example, I can walk down the hall and find someone who has spent their entire life studying and improving only stainless steel or, say, Aluminum-based materials. However, the next office down might have a professor that is developing materials for quantum computing. The shared focus in MSE is simply the fact that we are trying to solve problems in society from a material perspective. Even then, each application might require different material properties to be optimized (or “engineered”) — how can I make steel stronger to increase the height of skyscrapers? How can I make steel lighter for aircraft efficiencies?
With this in mind, I think it might be less surprising to hear that sustainability has only very recently become a focal point in MSE research. In the past, we have been trying to figure out how to make materials stronger, faster, more resistant to damage, etc., without much consideration of their life cycle or environmental impact.
In recent years, this mentality has started to shift from the above statements — researchers are now beginning to ask themselves “What is the carbon-cost of this material from the day I make it until the end of its use?” And we can start coming up with ways to reduce the environmental impact, while maintaining performance, through leveraging different aspects of materials engineering, including looking at new ways to manufacture pre-existing materials using processes that rely on less energy or water, the development of entirely new materials that are either biodegradable or can be recycled/reused, as well as trying to introduce materials that can increase the efficiency of systems and devices to reduce energy usage.
2. What is Heat Transfer and how do you define Thermal Conductivity?
My research is primarily focused on improving heat transfer and thermal transport in different material systems. Rather than looking at a single class of materials or application, we actively try to improve this important property across a wide-range of material systems.
Heat transfer is simply the field of understanding how heat, or thermal energy, moves between materials — if something gets hot, what happens?
You deal with heat transfer every day: When you cook your food, how long does it take to reach the correct temperature? Why do I overheat with a sweater on a warm day? Why is my laptop getting so hot?
All of these are answered based on how well different materials move heat across them. It seems to take an eternity for water to heat up to cook pasta because water is a poor heat conductor; you can’t wear a jacket during the summer because they’re designed to insulate and store heat to keep you warm; and your laptop is overheating, which is not-so-good for performance, because electronic devices have been designed for good electrical conduction, but usually ‘trap’ a lot of heat, which accumulates over time.
Our usual metric of how ‘good’ a material is at moving this heat is called it’s “Thermal Conductivity.” Going back to our pasta example: You probably use a wooden spoon for stirring hot water. This is because wood has a low thermal conductivity, so the heat from the water takes a long time to travel through the wood and thus the opposite end remains cool enough to hold. Try stirring hot water with a metal spoon and you’ll find that it quickly becomes way too hot to hold — this is because metals typically have a high thermal conductivity and move heat very efficiently.
3. How does Thermal Conductivity and Thermal Transfer relate to sustainability?
I think an excellent case example is the following: Every year, Lawrence Livermore National Laboratory determines the total energy usage in the United States. In 2019, for example, less than 15% of all energy came from renewable resources — so it’s immediately evident that we still have a lot of work to do in moving away from resources such as natural gas, coal, and petroleum. Perhaps more surprisingly is how much of our nation’s total energy production is wasted in the form of heat: Nearly 68% of all energy is simply lost in the form of rejected heat. Recall the example of your laptop heating up? That’s electricity that simply is not being used for anything; the electricity has been lost in the form of thermal energy.
The problem with this waste heat is that it is independent of how we made that energy. In other words, even if all energy was produced from fully renewable resources, we would still be losing 68% of all produced energy in the form of heat!
One active area of research in MSE is investigating materials that can convert this waste heat back into useful energy, like electricity. These ‘thermoelectric’ devices require materials engineering strategies to minimize the thermal conductivity in order to maximize their efficiency.
While this might help grid-scale energy problems, it is unlikely you would ever use a thermoelectric in your personal laptop. Rather, another active research has been trying to develop entirely new electronic devices that are designed to maximize the heat transfer rates, including thermal conductivity, to minimize how much heat is built up and thus decrease the amount of energy that is needed to function.
Another huge area of research is focused on increasing efficiency of material systems, or reducing how much energy input is required to power a device. For example, there is a significant amount of work that is aiming to improve how much heating and cooling is required for buildings by making materials that can ‘switch’ their thermal conductivity so that the building matches the temperature of the environment as necessary.
4. What trends are you seeing in Materials Science and Engineering related to the energy sector?
There is a ton of work being done, both in the academic community and industrial sector, on developing new materials for both energy generation and conversion (e.g., devices that produce energy), as well as storage and transport (e.g., devices that hold energy).
In terms of production, a great example is solar cells: We have seen a massive in solar cell usage in both residential and commercial settings, over the last few decades — this increase is due to increased production capabilities, not new technologies. While MSE certainly contributed heavily toward new manufacturing routes that enabled this increase, these Silicon-based solar cells that we use are mostly the same design developed by Bell Labs in the 1950’s! Unsurprisingly, these commercial solar cells are < 20% efficient. So there is a ton of work looking at new materials to replace these silicon-based cells, such as perovskites, that can achieve significantly higher efficiencies at an even lower cost than current technologies.
Again, as mentioned above, thermoelectric materials that can convert heat into electricity are a hot-topic in MSE — we are constantly trying to find materials that can be used at large scales rather than just a lab setting.
I think a large percent of the general population tends to overlook the fact that we not only need to produce electricity, but this electricity has to be moved over massive distances, and is typically generated at a faster rate than it can be spent, so that we need to store it for large amounts of time. But recall: electricity tends to be wasted in the form of heat, especially when we try holding it for too long of a time or move it over too large of a distance. So, you can imagine, we are constantly trying to develop and engineer materials to reduce this effect from occurring. For example, there is just an unbelievable amount of research devoted to developing new batteries. It is easy to forget that only a few years ago, the battery life of a standard iPhone was nearly half of what it is today — this is due to the fact we are constantly trying to improve the efficiency of batteries through materials engineering research.
5. How does technology enable your research?
My research is looking at how heat moves on the nanoscale — so we are looking at heat at length scales that are one-billionth of a meter. It turns out that this length-scale dictates the majority of what we see happening even in large systems. In other words, consider heating water on your stovetop: heat is able to move by single water atoms colliding with each other, and the rate of their collisions determines how efficiently, or how quickly, you can heat up the pot of water.
To make better materials and devices, we need to understand these collision-like processes that are occurring on these ultra-small length scales. So in the same way that you may use a thermometer to measure the temperature, or how much heat there is, in your pot of water, we need a nanoscale thermometer to measure heat transfer at this molecular level.
It turns out that it isn’t so easy to make a physical thermometer that is one-billionth of a meter long. Instead, we use lasers as our nanoscale thermometers; in the same way that the light from a microscope can see extremely small objects, we can use the light from lasers to measure the temperature of these nanoscale objects!
However, every laser isn’t the same, and so the limits of our nanoscale laser-thermometers are dictated by the limits of the laser system itself. Consider that the time of heat transfer scales closely with the length of the system — larger pots of water will take longer to boil than small ones. So while it may take five minutes for the pot of water to boil, it only takes a nanoscale material picoseconds to heat up (one-trillionth of a second). Because of this, we not only need an ultra-small thermometer, we also need an ultra-fast laser that can respond quickly enough to these changes in temperature. Given this, it might not be surprising that we don’t rely on standard laser pointers for our measurements, but instead we are constantly moving to state-of-the-art laser systems that push the limits of resolution, both in terms of time and length scales.
6. In 2018, you were part of the UVA team that won the Patagonia Business Case Competition. Your team was commended for reframing Patagonia’s Challenge question. What was your approach to this competition?
I want to start off with mentioning that this experience was one of the highlights of my time in graduate school; it was just an amazing combination of scientific advances approached from a business perspective, while trying to redefine the way the textile industry could approach sustainability.
Quick background to those unfamiliar: Each year, Patagonia (the apparel company, not the country), pairs with UC Berkeley’s Center for Responsible Business to release a ‘case competition’ where graduate students submit solutions to problems that the company is facing with regards to sustainability or environmental issues. In this competition, a team of graduate students from schools across the nation first submit a proposal of how they can address the given problem. Then the top 10 teams are selected and invited to UC Berkeley to present their solutions to a board of judges from the company. Based on these presentations, they select winners who are then invited to travel to Patagonia’s HQ in Ventura, CA and discuss implementation of their proposed solution (as well as go surfing with them!).
In 2018, the case topic was “How Patagonia can best achieve carbon neutrality by 2025 not only for itself, but to provide a model for industry to follow suit.” Our team at UVA consisted of myself, another Ph.D. student in MSE, a Ph.D. student in Environmental Science, and two MBA students, and we developed an extremely interdisciplinary strategy to address the problem, where we identified science-based targets for emissions, a transition to ‘novel’ material systems that could be have a ‘closed’ life-cycle, and the adoption of renewable energies and strategic land sink offsets.
I think this highly-interdisciplinary approach to the problem was our key to success. The materials we proposed for next-generation clothing are almost revolutionary, especially with regards to sustainability, but it would be impossible to implement them without considering the other aspects that a company would need to make such a switch from the current clothing materials. Without the expertise of the students coming from a business perspective, as well as someone who truly understood the ins-and-outs of carbon impact, we would not have had nearly as much success.
7. How can advances in Materials Science and Engineering enable our society’s pursuit of sustainability? What is on the horizon in the realm of Materials Science and Engineering related to sustainability?
Materials are the basis of everything we use as a society; your Starbucks coffee cup is now biodegradable, your iPhone’s battery life lasts longer, and airplanes stay in the sky much longer all because of advances in materials engineering. It (usually) isn’t dumb-luck that we find materials that can replace old technology — it’s through many years of trial-and-error and development that these types of changes can occur.
I think in the near-future, at least in commercial technologies, it’s unlikely that we will see new, revolutionary materials that completely change the way we currently operate. Short-term, we’ll likely see a focus on continuing to improve what already works fairly well.
For example, when we think of ‘sustainable’ materials, lifetime and longevity usually aren’t the first words that come to mind — we are usually focusing on reducing CO2 emissions while driving a car or how many forests were devastated to build a new housing development. But what if your electric vehicle’s (EV) battery needed to be replaced every year? It turns out that simply making the battery produces so much CO2 that EVs are actually worse for the environment than petrol- or diesel-powered cars until they both drive ~50,000 miles. In other words, if you needed to replace the battery every year in an EV due to material failure, then EVs would actually produce over 63% more CO2 than conventional vehicles.
By no means am I suggesting that EVs shouldn’t be implemented, if not mandated, for the sake of the environment — it just takes a few years to see the payoff. And this only works if we are modifying materials in ways such that they can last for many years without replacement, which is no small feat. The exact same statements can be made for almost every single ‘green’ technology — the carbon cost of making materials is always a massive component of their total foot-print that we simply need to develop ways to reduce the amount we are producing.
In the long-term, though, I’m sure that we will see some very cool material systems that can start changing the way we are thinking about sustainability at a societal level. At the academic level, for example, there is a ton of work on bio-inspired materials, like squid-ring-teeth proteins, that have unique properties that simply don’t exist in materials that we use today (e.g., tunable thermal conductivity and self-healing properties). These new properties are what ultimately enable the formation of new technologies that we can use as a society. However, the road-map from academic, lab-scale demonstrations to commercial product is typically on the order of 5–10 years at a minimum. So, while we’re extremely excited at the university level for these fascinating properties, it may be a few years before we are wearing bio-inspired clothing in our athletic gear.
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