Choosing a hard question in soft matter

“Mike, you could change your life!” said Michael Solomon’s graduate school labmate, pointing to an advertisement for a postdoc in Australia. Their supervisor had taped it to a wall.

Solomon was just wrapping up a PhD in chemical engineering, focusing on fluid dynamics and polymers, at the University of California, Berkeley. It had been interesting, but he didn’t see a puzzle that he could spend a career solving.

When he put that application in the mail to the University of Melbourne, Solomon took the first step into a field in which he would distinguish himself – he was named a fellow of the American Association for the Advancement of Science (AAAS) in 2016.

While this postdoc was for polymers, the professor, David Boger, also worked with colloids – fluids composed of liquid and particles. Solomon learned the polymers position was filled, so he asked Boger to consider him for a colloids project.

“I owe him a ton because he knew about the work I’d done in polymers and was willing to take a risk on some guy who didn’t even really know what a colloid was,” said Solomon.

To hear Solomon talk about it, you might think that Boger – now a Fellow of the Royal Society and a member of the National Academy of Engineering – had taken Solomon on as an act of charity. Boger remembers things differently.

Over a period of 18 years, Boger said, “We had many postdocs from around the world in the Particulate Fluids Research Centre. Mike was the best of a strong group.” He added, “I have the highest possible regard for Mike as a scientist and a person.”

We had many postdocs from around the world in the Particulate Fluids Research Centre. Mike was the best of a strong group. I have the highest possible regard for Mike as a scientist and a person.

At the time, Solomon came with the recommendation of his PhD advisor Susan Muller, a professor of chemical and biomolecular engineering at Berkeley. And Boger had a soft spot for students interested in broadening their knowledge, having worked in heat transfer and non-Newtonian fluid dynamics before exploring colloids and particulates.

Solomon recalls the research as practically motivated and blue sky at the same time. Boger wanted to thicken mine tailings – the fluid contaminated with toxic chemicals leftover from the first steps in isolating valuable ores. Tailings are stored behind dams, but when these dams break, such as occurred in Brazil in 2015, they can cause environmental disasters.

The goal was to make the fluid ten times thicker – into a mud that couldn’t travel quickly into the surrounding water. How to manage it was up to Solomon.

At the time, he could measure how a material behaved. “And we could try to control it by say changing the pH, or adding additives in, but it was pretty trial and error,” said Solomon.

He tried to look at what was going on inside materials by shining a laser through them. The patterns in the light on the other side reveal details of the particle structure. But it wasn’t enough.

“You do scattering; you get the average structure. But it turns out, it’s only a tiny fraction of the particles that set a lot of those properties that we care about. And if you just get an average measurement, it’s not really sensitive to those few percent,” said Solomon.

He needed a way to see the particles structure directly. This was the challenge he began chasing in Boger’s lab, eventually bringing it with him to the University of Michigan as an assistant professor of chemical engineering in 1997.

“You can harness a whole other piece of your imagination or visual processing circuitry to understand better what is going on in these materials,” said Solomon.

There was already a device that could look directly at these particles: a 3D confocal microscope. The University of Michigan had one. Unfortunately, it was in the medical school, and he wasn’t likely to get much access. Buying one cost about $250,000.

So, Solomon began collecting names for a National Science Foundation (NSF) major instrumentation grant – finding engineers who also wanted to look at tiny things, whether particles, nanostructures or cells. Strong demand among biomedical engineers, plus a few results from Michigan Medicine’s microscope, convinced the NSF panel.

In hindsight, Solomon looks at that proposal as a long shot, maybe even “a little crazy.” But at the time, it seemed like the only way forward.

“I try to think about that when I hire or make funding decisions. I think about just how important these risks can be for people who are trying to do something really different,” said Solomon.

The gamble by the NSF panel arguably paid off. Using the microscope, Solomon was able to show for the first time how particle shape affects the behavior of colloids such as gels. Colloid studies moved from “stacking bowling balls” to considering other shapes, such as ellipsoids and rods. These investigations earned him his place as an AAAS fellow.

“Our work tries to take the trial and error out of material development in this space,” said Solomon. “If you want this kind of mechanical property, or if you want this kind of optical property, this is the particle you’ll need, and this is how you’ll need it to self-assemble.”

In addition to his strength as a researcher, Solomon is recognized for his excellence in education, developing new courses at the undergraduate and graduate levels related to polymers, colloids and nanoengineering. His awards include the U-M Henry Russel Award in 2003, the Rackham Faculty Recognition award in 2008 and the College of Engineering’s Education Excellence Award in 2010.

He’s served on committees and held leadership positions at the Society of Rheology, the American Institute of Chemical Engineers and the Journal Rheological Acta. At U-M, he has been the Associate Dean for Academic Programs and Initiatives at the Horace H. Rackham School of Graduate Studies and is the current dean of Rackham.

Solomon is passionate about graduate education because it enables students to dig into a problem over the course of years. “This kind of long view – the ability to work with an idea for a long time – is really a competitive advantage that not many other kinds of training offer,” he said.

In his own field, a future in which we can design materials at the nanoscale to have exactly the properties we need is indeed a long way off, but his work moves us further down the road.

Solomon is also Vice Provost for Academic Affairs-Graduate Studies and a professor of macromolecular science and engineering.