Rui Wang: From theoretical models to real world solutions

By Michael Barnes

It was in early 2003 when Rui Wang, a third-year undergraduate from Zhejiang University in Hangzhou, China, first came to the College of Chemistry. Wang was spending two months as a visiting chemical engineering student at UC Davis. Intrigued by the College’s reputation and its unique structure, he made an appointment with chemical engineering professor Jeff Reimer, and stopped by to talk.

Wang didn’t know it then, but his career would become intertwined with that of the college’s Chemical and Biomolecular Engineering department, and 16 years later, he would return to Berkeley as the department’s newest faculty member. Just like the polymer networks that he studies, Wang’s life has had many interconnected strands that led him here to an office in Gilman Hall and a joint appointment with fellow theorists in the Pitzer Center for Theoretical Chemistry.

Wang was born in 1981 in Chengdu, the capital of Sichuan province, a growing regional commercial center with a thriving electronics industry. His father was a factory manager and his mother a nurse. He attended high school there, and when it was time to pick a university, he chose the prestigious Zhejiang University in Hangzhou, about 100 miles southwest of Shanghai. “Zhejiang University is one of China’s best, and Zhejiang Province is near my mother’s hometown, which also appealed to me,” says Wang.

Wang earned his ChemE B.S. in 2005, electing to stay on at Zhejiang University for his master’s degree. He was an outstanding student who studied techniques for producing polymers, winning awards for his research papers (and later his thesis). However, he didn’t discover his scientific passion until he ventured to McMaster University in Ontario, Canada, for a six-month visitor’s position in 2007. There he studied with An-Chang Shi, a theorist in polymer physics.

Wang comments, “It was at McMaster that I first read the writings of Pierre-Gilles de Gennes (1932-2007), who won the Nobel Prize in Physics in 1991. I was so impressed with the breadth of his thinking that I decided to switch from polymer chemistry to working on soft-matter physics.”

De Gennes, who has been called “the Isaac Newton of our time,” was a postdoc at Berkeley with physicist Charles Kittel in 1959. Wang states, “De Gennes had an amazing ability to spot common features in patterns of order, or lack of it, in a variety of physical systems, from magnets, liquid crystals to polymers, and to describe general rules for how these systems move from order to disorder and back.”

Wang went on to complete his M.S. in 2008 and traveled to Pasadena to begin work on his chemical engineering Ph.D. at Caltech. He wrote several theoretical studies of polymers, membranes and charged interfaces with his Ph.D. adviser, Zhen-Gang Wang.

While at Caltech, he met then postdoc, Bradley Olsen, who had received his Berkeley ChemE Ph.D. in the lab of Rachel Segalman in 2007. Olsen moved on to MIT to start his own research group, and Wang became one of his postdocs in 2015. He was the first theorist in Olsen’s group. During his time at MIT, Wang began to study polymer networks and devise theoretical models of how defects in these networks affect their characteristics. He then worked with several experimentalists to verify the predictions of his models.

Wang states, “Theory and experiments are not opposites or substitutes. Theoreticians and experimentalists need to work together to explore the boundaries of scientific knowledge. At MIT, I often worked on theoretical problems as the only theoretician in a research group of experimentalists.”

Wang’s research involves refining theoretical models of polymer networks to accurately predict their characteristics based on the number and type of defects in the network. Unlike crystals or metal-organic frameworks, polymer networks are connected in random patterns without any spatial order. Different defects in the network are inevitable and can cause tremendous changes in the nature of the polymer.

In his research Wang has rigorously quantified the number of the varieties of defects and their impacts on the topology, mechanical response and percolation of polymer networks. For example, a polymer link, instead of connecting to a nearby junction, might loop back to its original junction. Or two or more links might join in an irregular way as a “double bridge” that disrupts the regular pattern of the network. (See Figure one for examples of these cyclic defects.)

Like his role model, Nobel Laureate De Gennes, Wang was looking for fundamental principles that spanned more than one type of system. Says Wang, “Beyond polymer networks, cyclic defects that suppress the spread of information also exist in many other networks. Good examples are routing loops in computer networks and acquaintance clusters in social networks. Understanding and controlling cyclic defects is critical to many forms of network science and engineering.”

In January 2019, Wang joined the faculty of the Department of Chemical and Biomolecular Engineering (CBE). He is also a member of the Pitzer Center for Theoretical Chemistry, the world’s leading group of theoretical chemists. For the first time in his career, Wang will be surrounded by like-minded theorists.

The concept of a theoretical chemical engineer may seem like a contradiction, but it is actually part of the tradition of the College. An early practitioner of this approach was CBE professor John Prausnitz, who came to Berkeley in 1955 and began working with physical chemists. He laid the theoretical foundation for the use of molecular thermodynamics in gas separation techniques. Emeritus professor Prausnitz has characterized this work as seeking the “future practical.” His success earned him the 2003 National Medal of Science.

Both the problems that chemical engineers must help solve, and the tools available to them, have evolved dramatically during the last few decades. The classical problems of unit operations and process engineering have become more tractable. Meanwhile, emerging problems in energy storage and biomaterials, just to name a few, are now at the forefront of the tasks that engage chemical engineers.

Asks Wang, “How can we realize the social benefits of energy storage and biomedical materials? These are fundamental challenges, and we need to apply new scientific principles to serve engineering problems. Modern chemical engineering has become an increasingly molecular-based discipline, and the number of unknowns is too large to explore in an ad hoc fashion with experiments alone. Theory can help suggest which experiments, out of the hundreds that could be conducted, will lead to the right path.

“It’s my hope that we’ll make the discoveries necessary to allow us to rationally design new materials from the molecular level. Major improvements in materials—electrolytes for safer batteries and electric vehicles, synthetic tissues to repair damaged organs, membranes for purifying drinking water, intelligent soft particles for sensors and actuators—will require molecular-level theory. Without new approaches we can’t design new materials. And without new materials we can’t touch society’s important problems.

“For me,” concludes Wang, “Berkeley is the best place for this work for four reasons. First is the department’s tradition of theoretically sophisticated chemical engineering. Second is the Pitzer Center with its strong group of theorists interested in a variety of research areas in physical chemistry. Third is that I can collaborate with the world-leading experimentalists in polymer and soft materials. Fourth is that at Berkeley I will be able to work with the best students.”

The College of Chemistry welcomes Wang and wishes him the best in his pursuit of the future practical.R