Mastering molecular disorder | MIT News

Some materials, including metals, are made up of atoms tightly packed in a lattice or crystal. These structures are very good at conducting electricity and their behavior is often relatively easy to predict. Other materials such as plastics and other polymers show a strong disruption of their structures.

Adam Willard, Associate Professor of Chemistry at MIT, would like to shed light on these disordered structures. Using theoretical models and powerful supercomputers, he is developing ways to simulate the properties of these disordered materials and predict their behavior. This type of modeling could help researchers replace heavy and brittle silicon-based photovoltaic cells with lightweight and flexible alternatives made entirely of plastic.

"Our interest is genuinely to understand the role of molecular perturbations in physical processes that are important in both biology and energy sciences," said Willard, who recently received a tenure in MIT's Department of Chemistry. "We want to develop a deeper understanding of how molecular forces play a role in chemical processes that are fundamental to life and industry."

Fascinated by chemistry

Willard grew up in Bend, Oregon, wanted to be a doctor and entered the University of Puget Sound in Tacoma, Washington as a pre-med major. By the end of his sophomore year, however, he had lost his enthusiasm for medicine and decided to switch to a double degree in chemistry and mathematics.

Fortunately, the next course I had to take was a foundation course in quantum mechanics in the chemistry department, and I loved it, "Willard recalls. "I then decided it was going to be a pretty nice gig to be a chemistry professor because the material was so deep and fascinating."

After switching majors late on, Willard hadn't done much chemistry research as a student and decided to work in an experimental spectroscopy laboratory at the University of Puget Sound a year after graduation. “It was a great experience because I had to have a spectrometer to myself and spend long nights alone in the lab collecting data and thinking about things. I enjoyed it very much, ”he says.

He attended a graduate school at the University of California at Berkeley, which was shaped by his program in theoretical chemistry. There he used computer simulations to investigate how hydrophobic forces between large molecules influence their behavior and how water influences the interactions between such molecules.

After completing his PhD, Willard went to the University of Texas at Austin to do a postdoc studying quantum dynamics, particularly in organic photovoltaics - plastic solar cells. Such cells are lightweight, easy to manufacture, and relatively inexpensive. At the molecular level, however, these plastics are made up of many entangled strands that represent complex pathways for electron transport.

Much of Willard's work in the field, which has continued since joining MIT faculty in 2013, has focused on developing materials that allow electrons to move efficiently from where they are excited by light to can flow to the point where their energy is collected.

"For photovoltaic applications, we want to arrange photo-excitable molecules in a certain geometry. So when we excite a molecule, the excited electron is passed through the material from molecule to molecule, so that it is guided and transformed in a predictable manner." he says.

Aqueous environments

In his laboratory at MIT, Willard continued to study the interactions between water and other molecules. While he focused on hydrophobic interactions as a PhD student, he is now analyzing hydrophilic molecules and how they interact with each other in water.

“It is much more complicated to describe how hydrophilic objects interact with each other in water, as there are many different ways that surfaces can be hydrophilic while there is only one way to be hydrophobic. So if I solved the hydrophobic problem for one case, I solved it for all cases. However, the behavior of hydrophilic particles strongly depends on how hydrophilic they are. For example, positively and negatively charged surfaces have different influences on the surrounding water, ”says Willard.

Some important types of hydrophilic interactions include protein-protein interactions and protein-drug interactions. These molecules often form weak hydrogen bonds that hold them together. Water can affect these bonds and affect the strength of the bond between two proteins or a protein and a drug.

In recent years, Willard's research group has developed computational methods to analyze the hydration environment around a protein and how it depends on the conformation of a protein. They are now using machine learning techniques, similar to those used to teach computer models to recognize objects, to identify sites on a protein that certain drugs could target.

Another area of ​​research in his laboratory is interactions that occur on surfaces where electrochemical reactions take place, such as those found in batteries. These interactions are usually difficult to simulate because describing the electron path within the electrodes requires enormous computational resources. However, Willard's laboratory has developed methods to make this description more efficient. This type of modeling could help researchers develop better battery or electrocatalytic systems.

"We hope that our contributions will provide both a new fundamental theory that will help people better understand these systems and, in certain cases, provide molecular design principles that can be applied," says Willard.

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