When Ron Larson was a student at the University of Minnesota, one of his physics professors had a cartoon illustration of a roughed-up boxer taped to his office door. The caption read: “Problems worthy of attack prove their worth by hitting back.”
“I often tell students, ‘If you’re struggling it could well be because you’ve got problem really worth struggling against,’” said Larson, the George Granger Brown and A.H. White Distinguished University Professor of Chemical Engineering. “If it’s a worthy problem, don’t expect it to be an easy problem.”
But for Larson, who studies the not-quite-liquid, not-quite-solid class of substances known as complex fluids, there’s nothing quite like the moment when one of those pugilant problems begins to reveal hints to its solution.
At Bell Laboratories, where Larson worked before coming to Michigan in 1996, one such problem involved the struggle to explain why polymers, which flow relatively slowly, developed the kinds of patterns usually associated with fast-flowing streams like water or smoke.
Larson and his colleagues developed a set of equations, and every day for six or seven months, Larson would devote some time to trying to solve them. When the first set of equations didn’t pan out, he set them aside and started on a more complicated set, but nothing worked. Every day when he got home, his wife would ask if he’d found a solution, and after months of answering, “No,” he was getting discouraged. One day, she told him she’d pray that he would find the answer.
“I had no idea you could pray for such things,” Larson said.
That night he had a vivid dream in which he returned to the first set of equations. There was one value in the equation that had been a guess, and Larson had filled the space with a 1. In the dream he changed the 1 to a 10, and the answer was right there.
The next day he went to the lab and did the same thing, solving equations that went a long way toward explaining how polymers flow.
“The most rewarding part is understanding – getting insights and discovery,” he said. “That’s the thing that’s the most fun.”
His current research, supported by a National Science Foundation grant, involves a problem that the polymer physics community has been working on for 30 years. Polymers are made up of long, tangled strands, similar to a knot of fishing line. The tangles give the polymer its elasticity, and the constant, subtle motion of the strands causes them to gradually untangle themselves. He and his students are trying to better understand what controls the rate of disentanglement, but what they’ve found so far hints that a lot of existing theories about polymer disentanglement may be wrong. Or, as he sometimes tells students when their problems get more complex rather than less, this problem is getting worthier all the time.
Larson, who also has appointments in biomedical engineering, mechanical engineering and macromolecular science and engineering, works to better understand, predict and change the behavior of complex fluids in order to develop better medicines, paints and consumer products.
Complex fluids turn up in our foods, paints, shampoos and medicines. They include polymers, molten metals, suspensions and solutions, even DNA – all of which have structure, like solids, but also the liquid-like ability to flow under the right circumstances.
Larson’s lab has helped Dow Chemical better understand how to convert paints from oil-based to latex and produce polymer coatings that control the speed at which drugs release into the body.
Using multi-scale computer models, he and his students can manipulate virtual atoms and look at structures in nanoscale. That’s led to software that helps companies test formulations in the virtual world before anyone touches a flask in the lab.
Larson began working with polymers as a chemical engineer at Bell Labs in 1980. His work there included a collaboration with Nobel Prize winner Steve Chu that helped establish the now-common practice of using DNA to model polymer dynamics.
Chu discovered that DNA, which is bigger and easier to work with than polymer molecules, makes a great stand-in for polymers, thanks to its coiled, stretchy structure.
Larson helped him confirm this and was one of the first engineers to start using DNA to better understand how polymers behave. Their method has become a bridge between polymer chemists and biophysicists.
“It’s become the standard method of trying to understand polymer dynamics, and now that people know how to do it, they’re also also going back into biology and using these kinds of imaging methods for other biopolymers,” he said. “It was an early step toward merging the polymer community and the biophysical community.”