Charles Schroeder: Advancing a Molecular Understanding of Nature

This profile originally appeared in the Fall/Winter 2017 issue of Mass Transfer, the magazine for alumni and friends of Chemical and Biomolecular Engineering at Illinois. For a listing of all our faculty members, please visit our directory or explore the department’s research pages for overviews of our groundbreaking research programs.

A faculty member since 2008, Charles M. Schroeder characterizes soft materials at the single molecule level. A major focus of his research is to understand how molecular scale properties give rise to emergent behavior, including mechanical, structural, electronic, or fluorescence properties. In recent years, he has established himself as an innovator in the field of single polymer dynamics, extending the field to molecular studies of new materials, complex molecular architectures, branched polymers, and much more.

Schroeder has been the Ray and Beverly Mentzer Faculty Scholar since 2015 and in August, he was promoted to full Professor. He holds affiliations with several departments on campus, including Chemistry, Materials Science & Engineering, and Bioengineering. He is an affiliate at the Frederick Seitz Materials Research Laboratory, a member of the Biosystems design group at the Carl R. Woese Institute for Genomic Biology, and this fall he joined a new collaborative research group at the Beckman Institute that will lead large-scale research efforts in computational molecular science.

Schroeder’s research also extends into the areas of colloids and `squishy’ particles. In 2016, Schroeder’s group developed the Stokes Trap, which is a fundamentally new way to trap and manipulate multiple particles in a free solution using just fluid flow. His group is using this new method to understand the process of vesicle adhesion and fusion, which will provide fundamentally new insights into a broad class of materials used in personal care products. In a different area of research, his group works at the frontiers of developing new insights into new electronically active materials and polymers. Recently, his group studied the sol-gel transition and optoelectronic properties of synthetic pi-conjugated oligopeptides, which directly informs how these materials can be processed. In addition, Schroeder is part of a multi-institutional, multi-disciplinary team creating a new class of synthetic sequence-defined polymers that can be used in batteries, energy storage, and sophisticated lightweight electronics.

With his research, he aims to achieve a molecular understanding of advanced materials or functional materials and how to understand their non-equilibrium behavior, with an eye toward how to process those materials.

“A materials scientist or a materials chemist will try to come up with a new material. But then, how do we understand how to take the material and process it and make something useful out of it? We strive to understand the molecular properties of these materials, and how they can be used to inform macroscopic behavior during processing and ultimate end applications,” Schroeder said.

Experimental and Simulation Foundations
A native of New Jersey, Schroeder gravitated to engineering and the sciences at an early age. His father was an electrical engineer who worked at Bell Labs and during the company’s open houses, he would visit the lab where his father drew fiber optic cables from a three-story-high furnace. In high school, he excelled in chemistry, and as a freshman at Carnegie Mellon University, he decided to major in chemical engineering.

At Carnegie Mellon, Schroeder received a rigorous undergraduate education, which he credits for establishing a strong fundamental basis that has helped move him forward in his career. As an undergraduate researcher, he worked on experimental projects and computational modeling with mentors Bob Tilton and Myung Jhon. In the Tilton group, he investigated colloidal suspensions and stability or instability issues that occurred when the suspensions were mixed with polymers, so called depletion flocculation. In the Jhon group, he conducted Monte Carlo simulations of polymer spreading dynamics on solid surfaces, specifically related to data storage and hard drive computer discs. The latter project got him thinking more about complex fluids and soft materials, and ultimately Schroeder decided to pursue a graduate degree and focus on those areas. He spent two summers of his undergraduate years at an internship at Intel in Portland, Oregon, working in a microchip fabrication facility (Fab 15). The experience helped solidify his decision to pursue fundamental research in the engineering sciences, instead of process engineering.

For his graduate education, he enrolled at Stanford University. As a graduate student, Schroeder knew he wanted to work in complex fluids, soft materials, and polymer dynamics, and several faculty members at Stanford were active in those areas. He joined up with Eric Shaqfeh, an expert in theory and computation of complex materials and soft materials. At the time, Shaqfeh had recently begun collaborating with physicist Steve Chu, who was conducting some of the first single molecule studies of polymer dynamics and biophysics.

“I couldn’t have asked for a better set of mentors. They were demanding and had high expectations. They were a superb set of mentors, both scientifically and in supporting my development as a young scientist,” he said.

At Stanford, Schroeder built his experience in conducting simulations and experiments. Back then, and still today, he was drawn slightly more to the experimental side of things, in imaging and microscopy. As his years as a graduate student wrapped up, Schroeder knew he wanted to expand his knowledge in biochemistry and biomolecular materials and, at the same time continue working in fluorescence microscopy and imaging. For his postdoctoral position, he chose the lab of chemist Sunney Xie at Harvard University. Xie ran a single molecule lab focused on biophysics and advanced imaging methods.

“That experience expanded the horizons of what my skill set would enable me to do. It was more than thinking about the physical aspects of materials. I started to learn about chemical and biological aspects of how to make materials, how to synthesize them, how to study them as well,” he said.

As a postdoc, Schroeder worked in DNA replication, but he gravitated back toward more advanced materials, ones inspired by biology. That’s where his research program is situated today.

“All the biochemistry and experimental methods that I learned (as a postdoc) help us to study the problems that we do today,” he said.

Characterizing, Understanding New Materials
After three years as a postdoctoral scholar at Harvard, followed by a six-month fellowship at the University of California, Berkeley, Schroeder joined the faculty of the University of Illinois Department of Chemical and Biomolecular Engineering.

“There’s an appreciation for pursuing fundamental work in this department, and I knew my research program would fit in well. Having the strength of all the science and engineering departments on campus is a huge benefit. You can find top-notch collaborators, expertise, equipment—it’s all here. The combination of scientific excellence and the capacity and desire for collaboration really makes this place a great place to be,” Schroeder said.

In recent years, through collaboration and interest, Schroeder’s research has gone in the direction of optoelectronic materials and single molecule studies of complex polymers. (Optoelectronic materials are optically active, meaning if you shine light in certain wavelengths, they respond. Their applications are in OLEDs, energy storage, and energy capture applications.)

Schroeder is interested in combining elements from biology, chemistry, and materials science to understand how to not only make new materials, but also how to characterize them in unique ways.

For example, his lab has worked on synthetic pi-conjugated peptide-based polymers, which are conjugates between natural peptides and synthetic polymers that are good at transporting charge. Schroeder is studying the self-assembly properties of these materials into supramolecular structures and their functions and how they conduct charge. In recent work, his lab is extending these ideas to nucleic acid conjugated materials.

“At the same time, we’ve also been taking one of our main tools, which is direct imaging or single molecule imaging, and applying that to more complex systems, trying to understand molecular scale dynamics and more complex materials systems like branched polymers or concentrated or entangled solutions.” Entangled polymer solutions generally exhibit complex topological chain crossings, not too different than a bowl of cooked spaghetti. Understanding dynamics in these systems at the molecular level is a grand challenge in the field.

One of the newer developments to come out of his lab is the Stokes Trap, a fundamentally new way to trap and “micromanipulate” multiple particles in a free solution using just fluid flow.

“Unlike optical trapping or electrical trapping, our method doesn’t require perturbative force fields such as a strong electric field. It only uses gentle fluid flow to confine and manipulate particles. We’re using it now to look at interactions between soft materials like vesicles or cells, such as how does the process of vesicle collision or adhesion happen? Our work tends to be focused on these fundamental questions, but these are materials that are used in foods, personal care products, detergents, and liquid fabric softeners,” he said.

Looking ahead to new projects, Schroeder is excited about combining elements of biopolymers with synthetic polymers to look at the additive or new properties that arise. Specifically, they’re using elements from nucleic acid hybridization or base pairing to guide the structure of optoelectronic materials.

For the project in collaboration with Northwestern University’s Michael Jewett and funded by the Department of Defense’s Multidisciplinary University Research Initiatives (MURI), Schroeder built a new experimental apparatus in Roger Adams Laboratory called a scanning tunneling microscope-break junction (STM-BJ) instrument. With this new scanning tunneling microscope, they are able to measure charge transport through a single small molecule or oligomer. The MURI team also includes chemists such as Jeffrey Moore from Illinois, and the overall goal is to synthesize sequence-defined polymers that are conductive.

“This is a long polymer chain where we control at every site the chemical identity of each monomer. If this is possible, then we can directly determine how the charge transport properties depend on the primary monomer sequence. It’s the combined advantage of having sequence control and then how does this level of control affect functional properties.”

“It’s cool to think about charge transport or conductance in a single molecule to begin with, but then to also think about how you can control that by changing sequences is pretty fascinating. This is an example of applying molecular scale tools or single molecule tools to characterize advanced materials,” Schroeder said.

Another newer collaboration of Schroeder’s is centered at the Beckman Institute for Advanced Science and Technology. Led by Yang Zhang, a professor of nuclear, plasma, and radiological engineering, the Computational Molecular Science Group is a new research theme that consolidates campus-wide expertise on computational molecular science. It aims to facilitate interdisciplinary research in several strategic areas and push the frontiers of theory-driven computational molecular science. For example, members of the group will attempt to understand various chemical reactions and transport phenomena from the molecular and electronic level; design new synthetic pathways for radical forms of materials and medicines; and characterize and rationalize the behavior of matter far away from equilibrium. The group also includes fellow ChBE faculty member Charles Sing.

“This will be a great opportunity for computational scientists and experimentalists to work together in the field of materials, which will synergize our work,” Schroeder said.

Since establishing his research program at Illinois, Schroeder has trained graduate students from the Department of Chemical and Biomolecular Engineering and other departments, including Biophysics, Mechanical Engineering, and Materials Science. His graduate students have obtained positions in academia (going on to postdoctoral positions and faculty) and industry (such as Intel and Google). One of his first Ph.D. students (Dr. Arnab Mukherjee, PhD ‘14) is now an Assistant Professor at the University of California-Santa Barbara in the Department of Chemical Engineering. Like most ChBE faculty, Schroeder has had numerous undergraduates work in his lab—close to 30 undergraduates, including several who have gone on to top-ranked PhD programs.

Recently he took a sabbatical and was a visiting associate at the California Institute of Technology, where he interacted with many researchers, including John Brady, Julia Kornfield, Dave Tirrell, and Mikhail Shapiro.

“It was nice to get away to have some space to think about new directions and see a different program of research, to come up with new ideas. It was also great to come back.”

In his free time, Schroeder enjoys running and relaxing with his two dogs—a Pointer-Beagle and a Pointer-Greyhound.