Coacervates, Collaboration and Community Building

A boring class as an undergraduate started Charles Sing on the path to finding his true passion: polymer science and a career in academia.

Written by Molly Fried

Associate Professor and Director of Graduate Studies Charles E. Sing joined the Chemical and Biomolecular Engineering department in 2014 after “taking the long route” to chemical engineering.

“My original intention as an undergraduate was to pursue a degree in chemical engineering but then I got sidetracked a little bit, and ended up doing a degree in polymer science,” said Sing. “The funny story is I found the first class that I had in chemical engineering to be really boring. But the first class I had in polymer science was really fascinating, so I decided that was really the direction I wanted to go. Of course, while I am glad I made that decision, I am happy that I found my way back to chemical engineering – which is anything but boring!”

Sing attended Case Western Reserve University for his bachelor's and master's degrees. He then received his doctorate from the Massachusetts Institute of Technology (MIT) in materials science with a focus on polymers under the mentorship of professor Alfredo Alexander-Katz. From there, he did his postdoctoral research at Northwestern University, working with professor Monica Olvera de la Cruz.

“I wanted to work for the foremost expert in the area of polyelectrolytes, which was a topic I was interested in learning more about, and has since become a major component of my group’s research,” Sing said.

During his graduate work, Sing decided to pursue a career in academia because the goal of understanding something at its deepest levels really resonated with him. The privilege of being able to do fundamental scientific work stuck with Sing, and he happily accepted a faculty position offer from the department.

“I was fortunate to end up in a place that is really a great fit for me,” Sing said. “I benefit from the very interdisciplinary and very collaborative environment here. There are a lot of very deep thinkers on campus that I can interact with and work with.”

Collaboration in Research

Collaboration has long been and continues to be a core part of Sing’s research at the University of Illinois, which focuses on studying the fundamental physics of polymers and how their molecular properties affect material level observations.

“The fundamental feature of these molecules is that they’re long and wiggly,” Sing explained with a grin. “The physics of this is really fascinating because there’s a lot of disorder in these systems. There are a lot of complicated phenomena that emerge at the larger length scales characteristic of polymers.”

Sing also said the realization that so many biomolecules like DNA, proteins and polysaccharides are polymers was eye-opening. He has been inspired by the variety of materials that can be made using polymers.

“Life has decided to use these molecules as its building blocks,” he said.  

In one ongoing project that explores this theme, Sing is working with fellow Chemical and Biomolecular Engineering professors Ying Diao, Damien S. Guironnet and Simon A. Rogers to look at bottlebrush polymers.  These polymers move quickly to form relatively large structures at length scales similar to the wavelength of light. Using molecular simulation and statistical mechanics, Sing studies how these kinds of polymers assemble and give rise to ‘structural colors’ similar to those that occur in butterfly wings. He then uses his models to provide theoretical insight and molecular context for the experimental research of his colleagues.

“My group’s models have made predictions that match very well with what my experimental colleagues have been finding,” he said.

Sing is also part of a newer collaboration with professors Ken Schweizer, Chris Evans and Paul Braun in the Department of Material Science & Engineering at Illinois. This project studies how molecular penetrants move through dense polymer networks to separate small molecules. At relatively low temperatures, this material can reach a glass transition temperature where the molecules move slowly, and the segmental motion of the network affects the motion of the particles significantly. The long-term goal is to apply this knowledge to making separation processes cheaper and cleaner for the environment. 

Another project that Sing has worked on throughout his entire time at Illinois stems from a conversation he had at a conference with Illinois alumna Sarah Perry (PhD 10). They talked about a system called ‘complex coacervates’, which are phase-separating solutions of oppositely charged macromolecules. The attractions between these drive the phase separation process for anything from biological processes to shampoo. Although this phenomenon is important to both industry and fundamental science, the physics of these systems remains poorly understood. Sing is part of a concerted effort in his scientific community to study the physics of the systems further. 

“One of the things I’ve been most proud of is that we’ve been able to show how precise monomer sequences affect electrostatic interactions,” Sing said. “In protein molecules, you’ve got this long molecule and it’s got these little elements that are in a very specific sequence, and we can show how this affects phase separation.” 

Sing has been able to demonstrate how the strength of charged interactions in these systems can be tuned at a fundamental level, which is a notable development in this area.