DoD Awards Propel Research in Chemistry and Materials Science
This apparatus, designed by Prof. Suits and graduate student Chandika Amarasinghe and fabricated in the Department of Physics & Astronomy Machine Shop, allows his team to study collisions in molecular beams in vacuum. The beams are going almost the same direction so that the relative velocity between them can approach zero, like two cars moving the same direction on the highway. Reseachers can then take “pictures” of the scattering patterns when the collision happens. The team's current experiment uses four different powerful lasers to prepare the molecules in a single quantum state and then detect them after the collision.
The University of Missouri recently was awarded two highly coveted Multidisciplinary University Research Initiative (MURI) awards from the Department of Defense (DoD), making MU one of only three higher education institutions in the nation to receive more than one award. The University of Washington and Massachusetts Institute of Technology also received two of the 24 MURI grants awarded this year from a pool of 295 proposals. Even more unusual is the fact that both MU awards went to the same department, chemistry, albeit for completely different projects. Both projects involve interdisciplinary teams from multiple institutions, and both are expected to last five years.
Quantum State Control of Molecular Collision Dynamics
Professor Arthur Suits, BA ’86 chemistry, says manipulating and controlling the outcome of chemical reactions has been a long-term goal that is now within reach. Currently, scientists can put two chemical reactants into a beaker and know that the molecules will combine in certain ways to make a certain product.
“Controlling chemistry is saying we want the reaction to go this way or that way, or we want to make the less stable product,” Suits says. “We don’t have the ability to do that now, but that is the dream.”
Suits says he and his colleagues will be working in the realm of quantum mechanics. In classical mechanics, objects exist in a specific place at a specific time. However, in quantum mechanics, objects instead exist in a haze of probability; they have a certain chance of being at point A, another chance of being at point B and so on.* This is called quantum superposition. A “quantum state” refers to the various states of a physical system (such as an electron) that are specified by particular values of attributes of the system (such as electron charge and spin) and are characterized by a particular energy.**
“Everything has quantum states, and if we are studying a reaction in a beaker at room temperature, it has countless quantum states, and you can’t just pick one and ask what it does,” he says. “But with techniques that have been developed recently with molecular beams that can cool molecules close to absolute zero and lasers that can pick out particular states, we can create molecules in precise quantum states and direct their interaction in precise ways. Then we can do things like scattering (molecular collisions) and see what happens when we have one quantum state of a particular molecule or another. If you want to understand the structure of a particle, you collide something against it, and the scattering pattern tells you about the forces that are involved.”
Suits says at its heart, all chemistry is scattering—an encounter between one molecule and another molecule. “The molecules scatter off of an atom, and then they make a pattern, and that pattern is very sensitive to the forces between atoms, and that pattern from the scattering is what we measure,” he explains.
Understanding Chemical Behavior
Suits’ team includes physicists and chemists from Stanford University, Harvard University, the University of Colorado Boulder, the University of New Mexico, and the University of Nevada, Las Vegas. The team will receive $1.25 million per year for up to five years. He says most of the DoD award money will pay the salaries of students and postdocs involved in the project. Suits says quantum computing is one of the driving forces behind the research.
“For that you need cold molecules and control over the quantum states—that is the heart of quantum computing, so there are many aspects of how our research can play in quantum computing,” he says. “Quantum computing relies on having entangled superposition states of molecules, which means you have to know the quantum states, and you want to be able to interact with them, so this contributes directly to that.”
This illustration shows a single state of a highly vibrationally excited nitrogen oxide molecule scattering off an argon atom into a different single quantum state (it actually shows hundreds of such events).
Suits, the principal investigator for the project, says the overarching goal is to create a toolkit to help scientists understand all aspects of chemical behavior, and ultimately, to have the ability to control that behavior.
“It’s pushing the scientific frontier and training the next generation of scientists,” he says.
Integrating Multiscale Modeling & Experiments to Develop a Meso-Informed Predictive Capability for Explosives Safety & Performance
Professor Tommy Sewell says his team is building a capability to allow scientists to predict the behavior of energetic materials, which cover a wide range of applications including military munitions, propellants, pyrotechnics, and industrial explosives.
“The way explosives are typically initiated is you impart a shock wave into the material, but because these materials are very heterogeneous—somewhat like concrete where you have gravel in a cement matrix—when that shock wave encounters interfaces between components or microscopic pores in the material, energy becomes localized,” Sewell says. “If the temperature in those localized regions gets sufficiently high, it can cause chemistry to begin—a process we call ignition. And if there is a sufficient number of ignition sites activated in the sample, they’ll spread and grow into a cooperative phenomenon called initiation, and that leads to detonation.”
Sewell says there is an incredible amount of physics, materials science, and chemistry occurring during this process, all of which are interacting with each other.
“If we are to have a predictive capability for this sort of thing, it is imperative we understand the fundamental underlying phenomena—the detailed processes by which energy becomes localized upon the initial passage of the shockwave, and the resulting processes that occur on longer space and time scales,” he says. “We’ve got to get this exactly right, but it is extremely complex…there’s a lot going on under the hood.”
Enter the HAL 9000
In order to better understand these processes, Sewell says his team will use artificial intelligence or machine learning to sift through mountains of experimental and simulated data and to identify correlations in the data that scientists might miss. But he says machine learning will only take his team so far.
“If all that you seek is knowledge, maybe that is good enough for some purposes, but it’s not good enough for us,” he says. “What we seek is understanding, and that comes from ‘carbon-based’ computing (human thought and physical models), not silicon-based. A long-term goal is to minimize the amount of experimentation and the assorted costs and do most of the work in computer simulations, and then use experimentation to validate the results. If we’re successful, we will end up with a framework that can be adapted to treating the initiation phenomenon for a wide variety of explosives.”
Sewell says another goal is to reduce accidents involving energetic materials. When pushing a payload into space, NASA or SpaceX can lose millions of dollars, and potentially human life, if that rocket propellant transitions from a stable burn over to a detonation, turning the payload into dust.
“What we are trying to do, based on highly interdisciplinary research that involves physical chemists such as myself, material scientists, and mechanical engineers doing both experimental and theoretical research across a wide range of spatial scales, is to develop a theoretical framework that will allow us to derive the next generation of reactive burn models that are far more predictive than models currently in use,” Sewell says. “The goal is to reduce accidents, to improve safety, and to be able to design energetic formulations that would have much more tightly tailored performance.”
Training Future Scientists
Sewell, the principal investigator on the project, says he and co-principal investigator H.S. Udaykumar, of the University of Iowa, will be collaborating with researchers from the University of Illinois at Urbana–Champaign, the University of Illinois at Chicago, Columbia University, Purdue University, and the Rensselaer Polytechnic Institute in New York. The team was awarded $1.5 million per year for up to five years.
“The final product is not just the model at the end of the day—there is going to be a lot of student and postdoctoral training, cross-fertilization of ideas, lots of papers, and likely spin-off collaborations from the research,” Sewell says. “A major piece of this is training the future workforce in integrated, interdisciplinary science and engineering, so these students and postdocs who come from our effort over the next five years will be ready to show up on deck and take some serious swings as they move into their careers.”