Materials are mundane, extraordinary, ubiquitous and — perhaps most importantly for the engineering profession — pliable.
They are natural and manmade. Their stealth structural powers are often overlooked in our lives today, but certainly not in hindsight.
Human history is demarcated by the in-vogue material of the age: stone, bronze, iron, steel and so on. No revolutions of any sort without these. No nonstick pans, either. And forget the moon landing. Nix heart valves and hip implants, too.
What we now call “materials science” really is a continuum that connects us with our ancestors, our “smiths” and metallurgy tradespeople at least as far back as 25,000 BCE. Over time, we have undone material limitations and also conjured new materials altogether, our formulas spanning from crude application of heat to intricate nanostructuring, all in service of improving our overall quality of life.
Materials science is a profoundly transformative, pioneering research area in the Cockrell School of Engineering at The University of Texas at Austin. To walk in these halls is to walk among modern-day explorers — award-winning engineers — unlocking the highest material properties and bending the world to their will using no sorcery but the natural laws of physics and chemistry.
Let’s take a glimpse through the laboratory doors to discover a few of the world-changing materials and processing techniques our engineers are conquering.
Electronic Tattoos: A Skin-Tight Sensation of Meandering Ribbons
Nanshu Lu, an assistant professor in the Department of Aerospace Engineering and Engineering Mechanics, looked to silicon and metal as central elements for her materials science breakthrough: wearable electronic tattoos that gather and communicate data, simultaneously harvesting energy.
These wearable electronic devices have the ability to pick up and transmit the human body’s vital signals, tracking heart rate, hydration level, muscle movement, temperature and brain activity.
Lu’s wearables are surely on the path to change the way we monitor our health. But she almost never got there.
As a graduate student, she realized she wanted to pivot from a theoretical focus, for which she needed only a pencil and paper to write about materials, to a more experimental approach. Once she started on that path, she faced new obstacles in asking for help.
Lucky for all of us, she didn’t give up. “I just learned from everyone who was willing to teach me, whether it was an undergraduate student or a first-year Ph.D. student. It didn’t matter. I literally learned from everyone,” Lu recalls.
And as soon as she started her post-doc at the University of Illinois, she hit the ground running to expand the field of flexible electronics.
Lu describes solving the problem of stretchable metal with the humility of one deciphering a simple math equation: “By creating serpentine shapes, or ‘meandering ribbons,’” she explains, “I can stretch brittle materials [such as silicon] quite long without actually changing the material, atoms or composition. So I’m basically playing the geometry game to change something from being as stiff as steel to being as soft as tofu without losing any functionality.”
These serpentine ribbons are so thin, Lu can place them inside the stamp-sized tattoo patches. The tattoo material clings to the tiniest wrinkles on human skin. And Lu’s wearable patches are so sensitive that she and her team can envision humans wearing the patches to more easily maneuver a prosthetic hand or limb using muscle signals. For now, Lu says, “we are trying to add more types of sensors including blood pressure and oxygen saturation monitors to the low-cost patch.”
Had Lu not shifted away from theories to experiments — where formulas are physically proven, disproven and sometimes confounded — these wonders might never have been. And she certainly doesn’t regret her conversion. “I love that seeing is believing; I really love that. Reality — nature — is the best teacher for us.”
Silicene: The Swiss Army Knife of Materials
“There’s nothing in my childhood that says I should be in this area,” says electrical and computer engineering associate professor Deji Akinwande, “except that I was just generally consumed with questions.” He actually describes himself as an intellectual “late bloomer.”
But in fact, Akinwande’s revolutionary research would illustrate quite the opposite. The transistors he’s developed out of silicene — the world’s thinnest silicon material, at one atom-layer thick — hold the promise of transforming computers and other electronics. These silicene transistors could be crucial in building dramatically faster, smaller and more efficient computer chips. However, while silicene has shown outstanding electrical properties, it has, until now, proved difficult to work with because of its instability when exposed to air.
“The challenge is, silicene is like both a dragon and a ghost,” Akinwande says. “It’s just so difficult to chain it, to understand it, to bring it under control … and it’s also incredibly difficult to measure it. You look at it and all of a sudden it’s gone.”
Until a few years ago, manmade silicene was a purely theoretical material. Looking at carbon-based graphene, another atom-thick material with promise for computer chip development, researchers began to speculate that silicon atoms could be structured in a broadly similar way.
Akinwande and his team developed a new method for fabricating silicene between two protective films — alumina on top and silver below — that are peeled away later in the process, at which point the silicene sheet is transferred to an insulating substrate.
There wasn’t much precedent to build on, but Akinwande attests that such is the nature of pioneering research. “There’s not a lot there telling you ‘do this’ or ‘do that,’” he says. “It’s like an investigation in which you’re just searching for the truth, like a child playing with his toys.”
Akinwande and his team are currently working on a way to enable stable, long-term silicene production and operation. “Silicene and related atomic films are considered the Swiss army knife of all materials,” Akinwande says. “It can potentially do anything you want it to do; you just need to turn the right knob.”
Supergel: A Self-Powered, Self-Healing Marvel
Mechanical engineering assistant professor Guihua Yu is quick to credit nature as the inspiration for his latest discovery.
“Very recently, I brought my daughter and son to an aquarium and we were looking at an octopus,” Yu explains. “It’s actually a very smart creature — how it can manipulate things and really adapt to its environment. Octopi can change their shape and become strong or weak depending on their environment, so they’re very responsive.”
Just like the octopus, Yu’s supergel is a responsive adapter. A hybrid of a conductive polymer gel and a self-assembling supramolecular gel, the gel is truly “super” in that it needs no external force — such as the application of light, temperature or acidity — to trigger its self-repairing properties. As a result, the supergel can be used to construct circuits in flexible and self-repairable electronics.
Furthermore, its porous structure makes it amenable to nanochemical modifications for many exciting applications in solar energy, energy storage, electronics and even bio-applications such as artificial skin and self-healing paste for surgical use.
Like his father, who worked in a Chinese government-owned sugar factory during his childhood, Yu took an interest in chemistry and chemical engineering as a young man. He was especially motivated by his high-school chemistry lecturer’s vivid classroom experiments. “It’s all like magic to me,” Yu says.
Yu’s research group is pursuing further mechanistic understanding and optimization of its supergel, as well as working on other organic nanomaterials and their hybrids for advanced applications in energy and environmental technologies.
“The materials scientist’s most important job is not to make materials for high-profile publication only,” Yu says, “but to make materials that are useful in daily life — and that is far more challenging.”
Smart Window Coating: The Case of Light and Heat, Unbound
“The idea of creating materials to meet certain targeted needs for an application really caught my attention, even in high school,” recalls chemical engineering associate professor Delia Milliron.
And she’s certainly met a need — she and her team have designed energy-efficient smart-window composite materials capable of achieving something that seems impossible: separating visible light from near-infrared (or heat-causing) light.
“The first moment that we saw an optical effect that we were able to switch the transmittance, it was the happiest moment,” Milliron says. It was about a year-and-a-half into the project when they had their game-changing breakthrough.
“We didn’t really know why our material worked and other materials hadn’t worked,” Milliron says. “There’s a lot you don’t know at that point, but we knew it was working and built on it from there.”
Milliron’s goal always had been to find a material that could control both heat and light, separately, and she had an idea for how to build a composite material to do that. “When I told my post-doc about it, I remember standing in my office and drawing on the whiteboard and said, ‘So here’s the idea — it won’t work. There are 10 reasons I can tell you, immediately, why this shouldn’t work, but we should try it anyway.’ She got it to work and we got these beautiful results, and we didn’t understand why. Then it stopped working, and in the process of trying to make it work again, we really figured out what was going on and how this was actually possible.”
Ultimately, Milliron’s team became the first to develop dual-band electrochromic materials by blending two materials with distinct optical properties for selective control of visible and heat-producing near-infrared light. Using a small jolt of electricity, a nanocrystal material could be switched back and forth, enabling independent control of light and energy.
By allowing indoor occupants to more precisely control the energy and sunlight passing through a window, Milliron’s new nanocrystal-based materials could significantly reduce costs for heating, cooling and lighting buildings. It all started with the identification of a need: “People said, ‘Hey, this is a problem, if you could solve it, that would be great,’” Milliron says. “So we did.”
— Ashley Lindstrom | Illustrations by Chris Gash