February 24, 2014
Shaping materials for practical use goes back to the dawn of humanity, the earliest materials being stone, metals and clay, said Ronald Larson, the A. H. White Distinguished University Professor of Chemical Engineering.
While these materials remain important to this day, modern shapeable materials are often long molecular chains called polymers, which offer many new applications. "They appear everywhere. You wear them; they're in cars; they're in electronic equipment, and they're in biology," he said.
Larson will offer a Distinguished University Professor lecture celebrating this distinction, and will cover his wide-ranging expertise in the area of complex fluids — materials that, like clay, exhibit a mix of liquid and solid properties.
The talk, titled "Shape-Shifting Molecules in Technology and Biology," will be given at 4 p.m. March 10 in the Rackham Amphitheatre. A reception will follow in Rackham Assembly Hall. Distinguished University Professorships are the highest honor offered by the university.
The key to many complex fluid applications is controlling how they deform. One of Larson's major accomplishments was the discovery of a new kind of instability, leading to turbulence in the flow of polymers. Unlike the turbulence of river rapids, caused by momentum, flowing polymers can develop turbulence due to their own stretchiness or elasticity.
Understanding such phenomena helps manufacturers avoid rough "shark skin" textures in thin plastic sheets, such as kitchen cling film, which would use up excessive material. Now, as microfluidic devices gain applications in biology and medicine, elastic turbulence can mix fluids in narrow channels that are too small for conventional strategies.
Larson will also discuss the cause of polymer elasticity: the constant jitter of atoms and molecules at the molecular level. Responding to bombardment on all sides, the polymer wants to coil up — it pulls back when stretched. He will go on to explain how biology harnesses this jitter for reading DNA.
Looking to the future, Larson holds that nature still has much to teach us about making the most of polymers.
"Most ultra-strong polymers that we make have to be spun out of toxic solvents at high temperatures," he said. "Nothing invented is tougher on a per-weight basis than dragline spider silk, and it's spun in water at room temperature."
In addition to his excellence as a researcher, Larson is recognized by students and faculty alike as an outstanding teacher and mentor. His title names Alfred H. White, who founded the Department of Chemical Engineering in 1898. He also is the George Granger Brown Professor of Chemical Engineering, professor of mechanical engineering, and professor of macromolecular science and engineering.