Researchers in the Schroeder and Moore groups at the University of Illinois at Urbana-Champaign have published a new study that illustrates how changes in the polymer sequence affect charge transport properties. This work required the ability to build and study chain molecules with high levels of precision.
The paper, “Charge Transport in Sequence-Defined Conjugated Oligomers,” was published in the Journal of the American Chemical Society.
Chain molecules or polymers are ubiquitous in modern society, with organic electronic materials increasingly used in solar cells, flat panel displays, and sensors. However, conventional materials are generally made by statistical polymerization, where the order of the subunits or monomers — the monomer sequence — is random.
“Traditional polymerization methods do not give us a perfect level of control of sequence,” said Charles Schroeder, the associate head and Ray and Beverly Mentzer Professor in Chemical and Biomolecular Engineering and a full-time faculty member at the Beckman Institute for Advanced Science and Technology. “As a result, it has been challenging to ask how the monomer sequence affects its properties.”
The researchers developed a method called iterative synthesis to deal with the problem. “Protein synthesis in our cells occurs by adding the amino acids one by one. We use the same method for making synthetic polymers where we add distinct monomers in a one-by-one fashion. This allows us to precisely control the sequence in a linear arrangement,” said Hao Yu, a graduate student in the Schroeder Group, and the Moore Group led by Jeff Moore, the Stanley O. Ikenberry Endowed Chair and professor of chemistry.
After making the materials, the researchers studied their charge transport properties using single molecule techniques. In this way, they were able to measure the conductance through single chains, much like a ‘molecular wire.’
“Molecular wires are generally good at transporting charge,” Schroeder said. “We wanted to know how the charge transport properties change if the overall sequence changes.”
Yu added molecular anchors at both ends of the chain molecule to enable the characterization. “We used a technique called the scanning tunneling microscope-break junction method, where the anchors link to two gold electrodes and form a molecular junction,” said Songsong Li, a graduate student in the Schroeder Group. “Then we impose an applied bias or voltage across the molecule, and this allows us to measure the charge transport properties of these polymers.”
“Currently the synthesis method is labor intensive,” Schroeder said. “Moving forward, we are developing automated synthesis methods in the Beckman Institute to generate large libraries of sequence-defined molecules.”
“The implications of this work are significant,” said Dawanne Poree, program manager at the Army Research Office that supports the work. “It’s often been wondered if the sequence-dependent properties observed in biological polymers could translate to synthetic polymeric materials. This work represents a step toward answering this question. Additionally, this work provides key insights into how molecular structure can be rationally designed and manipulated to render materials with designer properties of interest to the Army such as nanoelectronics, energy transport, molecular encoding, and data storage, self-healing, and more.”
The work was supported by the U.S. Department of Defense by a multidisciplinary university research initiative through the Army Research Office, an element of the U.S. Army Combat Capabilities Development Command’s Army Research Laboratory.
Editor’s note: The paper “Charge Transport in Sequence-Defined Conjugated Oligomers” can be found at https://doi.org/10.1021/jacs.0c00043.
Handling very soft, delicate items without damaging them is hard enough with human hands, let alone doing it at the microscopic scale with laboratory instruments. Three new studies show how scientists have honed a technique for handling tiny, soft particles using precisely controlled fluid flows that act as gentle microscopic hands. The technique allows researchers to test the physical limits of these soft particles and the things made from them – ranging from biological tissues to fabric softeners.
The three studies, led by the University of Illinois’ Charles Schroeder, the Ray and Beverly Mentzer Faculty Scholar of chemical and biomolecular engineering, detail the technology and application of the Stokes trap – a method for manipulating small particles using only fluid flow. In the newest study, published in the journal Soft Matter, the team used the Stokes trap to study the dynamics of vesicles – squishy fluid-filled particles that are stripped-down versions of cells and have direct relevance to biological systems, the researchers said. This follows up on two recent studies in the journals Physical Review Fluids and Physical Review Applied that expanded the power of the trapping method.
“There are several other techniques available for manipulating small particles, such as the widely used and Nobel Prize-winning optical trap method that uses carefully aligned lasers to capture particles, ” said Dinesh Kumar, a chemical and biomolecular engineering graduate student and lead author of two of the studies. “The Stokes trap offers several advantages over other methods, including the ease of scaling up to study multiple particles and the ability to control the orientation and trajectories of different shape particles such as rods or spheres.”
Armed with the improved Stokes trap technology, the team set out to understand the dynamics of lipid vesicles when they are far from their normal equilibrium state.
“We wanted to understand what happens to these particles when they are pulled on in a strong flow,” Schroeder said. “In real-world applications, these materials are stretched when they interact with each other; they are processed, injected and constantly undergoing stresses that lead to deformation. How they act when they deform has important implications on their use, long-term stability and processability.”
“We found that when vesicles are deformed in a strong flow, they stretch into one of three distinct shapes – symmetric dumbbell, asymmetric dumbbell or ellipsoid shape,” Kumar said. “We observed that these shape transitions are independent of the viscosity difference of the fluids between vesicle interior and exterior. This demonstrates that the Stokes trap is an effective way to measure stretching dynamics of soft materials in solution and far from equilibrium.”
With their new data, the team was able to produce a phase diagram that can be used by researchers to determine how certain types of fluid flow will influence deformation and, ultimately, the physical properties of soft particles when pulled on from different flow directions.
“For example, products like fabric softeners – which are composed of vesicle suspensions – do not work correctly when they clump together,” Kumar said. “Using the Stokes trap, we can figure out what types of particle interactions cause the vesicles to aggregate and then design a better-performing material.”
The technique is currently limited by the size of particles that the Stokes trap can catch and handle, the researchers said. They are working with particles that generally are larger than 100 nanometers in diameter, but in order for this technology to apply more directly to biological systems, they will need to be able to grab particles that are 10 to 20 nanometers in diameter – or even down to a single protein.
The team is currently working to capture smaller particles and collaborating with colleagues at Stanford University to apply the Stokes trap to study membrane proteins.
Schroeder also is affiliated with the Beckman Institute for Advanced Science and Technology, the department of chemistry and the department of materials science and engineering at the U. of I.
Former U. of I. graduate student Anish Shenoy is a co-author of the Physical Review Applied and the Physical Review Fluids studies, and U. of I. undergraduate student Channing Richter is a co-author of the publication in Soft Matter.
The National Science Foundation supported this work under the CBET Particulate and Multiphase Processes Program, Award 1704668.
The paper “Conformational dynamics and phase behavior of lipid vesicles in a precisely controlled extensional flow” is available online and from the U. of I. News Bureau. DOI: 10.1039/C9SM02048A
Recyclable plastics that contain ring-shaped polymers may be a key to developing sustainable synthetic materials. Despite some promising advances, researchers said, a full understanding of how to processes ring polymers into practical materials remains elusive. In a new study, researchers identified a mechanism called “threading” that takes place when a polymer is stretched – a behavior not witnessed before. This new insight may lead to new processing methods for sustainable polymer materials.
Most consumer plastics are blends of linear polymers. The concept of plastics made purely from ring polymers – molecules that form a closed ring – presents an enticing opportunity for sustainability, as shown by the Autonomous Materials Systems group at the Beckman Institute for Advanced Science and Technology. Once a single bond holding ring polymers together breaks, the entire molecule falls apart, leading to disintegration on demand. However, processing such polymers into practical materials remains a challenge, the researchers said.
A 2013 University of Illinois-led study showed that ring polymers could be broken with heat, but this comes at a price – the resulting plastics would likely become unstable and begin to break down prematurely.
In the new study, U. of I. researchers Charles Schroeder and Yuecheng (Peter) Zhou examine the flow dynamics of DNA-based ring and linear polymer solutions to tease out clues about how synthetic polymers interact during processing. Their findings are published in the journal Nature Communications.
“We lack a fundamental understanding of how ring polymers stretch and move in flow while navigating around other neighbor polymer chains. This work allowed us to probe these questions at a molecular level,” said Schroeder, a chemical and biomolecular engineering professor, Beckman Institute researcher and study co-author.
In Schroeder’s lab, the researchers stretch and squeeze polymers, causing them to flow and allowing direct observation of the behavior of individual molecules using single-molecule fluorescence microscopy.
“There is a fluctuation in the shape of the ring polymers and this depends on the concentration of linear polymers in the solution,” said Zhou, a graduate student, Beckman Institute researcher and lead author of the study. “We do not see this behavior in pure solutions of ring or linear polymers, so this tells us that something unique is happening in mixed solutions.”
Using a combination of direct single-molecule observations and physical measurements, the team concluded that the changes in shape of the ring polymers occur because linear molecules thread themselves through the ring molecules when stressed, causing the ring shape to fluctuate under fluid flow.
“We observed this behavior even when there is a very low concentration of linear polymers in the mix,” Zhou said. “This suggests that it only takes a very minute level of contamination to cause this phenomenon.”
This threading of linear polymers through ring polymers during stress is something that had been theorized before, using bulk-scale studies of the physical properties, but now it has been observed at the molecular scale, the researchers said.
“Bulk studies typically mask the importance of what is going on at the smaller scale,” Schroeder said.
How these observations will translate into further development of sustainable consumer plastics remains unclear, the researchers said. However, any insight into the fundamental molecular properties of mixed-polymer solutions is a step in the right direction.
“To make pure ring polymer plastics a reality, we need to understand both mixed and pure solutions at a fundamental level,” Schroeder said. “Once we can figure out how they work, then we can move on to synthesizing them and ultimately how to use them in sustainable consumer plastics.”
Former U. of I. graduate student Kai-Wen Hsiao, Kathryn E. Regan and Rae M. Robertson-Anderson, of the University of San Diego, and Dejie Kong and Gregory B. McKenna, of Texas Tech University, contributed to this study.
The National Science Foundation supported this research.
By Lois Yoksoulian, U of I News Bureau
To reach Charles Schroeder, email email@example.com.
To reach Peter Zhou, email firstname.lastname@example.org.
Congratulations to Professor Charles Schroeder, who has been selected to receive the 2019 Journal of Rheology Publication Award from the Society of Rheology.
The award recognizes the best paper published in the Journal of Rheology during the preceding two years. Schroeder will be recognized at the annual meeting of the Society of Rheology in October. Previous winners of this award include University of Illinois Elio Tarika Chair Emeritus Charles “Chip” Zukoski; Ronald G. Larson, the George Granger Brown Professor at the University of Michigan; and John F. Brady, Chevron Professor of Engineering at the California Institute of Technology; and other leaders in the field.
Schroeder is the Ray and Beverly Mentzer Faculty Scholar in Chemical and Biomolecular Engineering. His research group studies the dynamics of polymers, proteins, and soft materials using single molecule techniques. A major goal of his research is to understand how microscopic phenomena give rise to the emergent, macroscopic properties of soft materials.
As the global datasphere expands, so does the need for more data storage. Enter DNA, the carrier of life’s genetic information, which offers a potential storage media of unprecedented density, durability, and efficiency.
However, using DNA as storage is currently costly and there is a lack of processing systems suited for this technology.
The University of Illinois at Urbana-Champaign is undertaking a $1.5 million effort to produce new DNA-based storage nanoscale devices using chimeric DNA, a hybrid molecule made from two different sources. Chemical and Biomolecular Engineering Professor Charles Schroeder is one of the Illinois researchers collaborating on the project. As part of the three-year project, “SemiSynBio: An on-chip nanoscale storage system using chimeric DNA,” the team will design a method to read, write, and store data in a more cost-effective way than current DNA storage techniques.
“We’re going to take cheap, native DNA and combine it with chemically modified nucleotides,” said Olgica Milenkovic, Illinois professor of electrical and computer engineering and researcher in the Coordinated Science Lab. “It will be stored and accessed using a novel implementation of a state-of-the-art semiconductor system.”
By 2025, the world will generate 163 zettabytes (one trillion gigabytes) of data a year, in part due to emerging technologies such as the Internet of Things, predicts research group IDC. While not all of that data will be stored, the demand for storage may outpace traditional storage capabilities.
DNA is an attractive solution because it can store up to 455 exabytes (1 exabyte is 1 billion gigabytes) in one gram, according to a 2015 report in the New Scientist. In addition, it is remarkably durable.
“We are still finding bones from over 100,000 years ago from which we can extract DNA,” said Milenkovic. “We don’t know of another storage medium that has such durability.”
During the course of the project, the research team will design and synthesize hybrid DNA molecules that contain non-natural chemical modifications. The goal is to expand the storage capacity enabled by DNA coding methods, essentially increasing the number of equivalent bits.
To accomplish this task, the team will employ concepts from molecular design and engineering and chemical synthesis.
The goal is to create a device that mimics the capabilities of a computer’s hard drive.
“Synthesis of chemically modified DNA essentially constitutes the ‘write’ step, and development of new methods for processing and de-encoding the chemical information stored in the DNA will constitute the ‘read’ step,” said Charles Schroeder, Professor and the Ray and Beverly Mentzer Faculty Scholar in Chemical and Biomolecular Engineering at Illinois. “I envision that the ‘reading’ and ‘storage’ steps could be built into an integrated device.”
The grant is funded through SemiSynBio, a partnership between the National Science Foundation (NSF) and the Semiconductor Research Corporation (SRC), which seeks to lay the groundwork for future information storage systems at the intersection of biology, physics, chemistry, computer science, materials science and engineering. Altogether, SemiSynBio is funding eight projects for a total of $12 million.
In addition to Milenkovic and Schroeder, Illinois collaborators include Jean-Pierre Leburton, the Gregory E. Stillman Professor of Electrical and Computer Engineering and professor of Physics, and Xiuling Li, Professor of Electrical and Computer Engineering. Leburton is also a researcher in the Beckman Institute and the Coordinated Science Lab, while Li is part of the Micro and Nanotechnology Lab.
Milenkovic also recently received a three-year, $2.5 million grant from DARPA to combine synthetic DNA with computing. Her co-PIs include Huimin Zhao and Alvaro Hernandez of Illinois, David Soloveichik of the University of Texas at Austin, and Marc Riedel of the University of Minnesota.
Written by Kim Gudeman, Coordinated Science Lab
For more information about the SemiSynBio program, please see the NSF news release.
The polymers that make up synthetic materials need time to de-stress after processing, researchers said. A new study has found that entangled, long-chain polymers in solutions relax at two different rates, marking an advancement in fundamental polymer physics. The findings will provide a better understanding of the physical properties of polymeric materials and critical new insight to how individual polymer molecules respond to high-stress processing conditions.
The study, published in the journal Physical Review Letters, could help improve synthetic materials manufacturing and has applications in biology, mechanical and materials sciences as well as condensed matter physics.
“Our single-molecule experiments show that polymers like to show off their individualistic behavior, which has revealed unexpected and striking heterogeneous dynamics in entangled polymer solutions,” said co-author Charles Schroeder, a professor of chemical and biomolecular engineering and faculty member of the Beckman Institute for Advanced Science and Technology at the University of Illinois at Urbana-Champaign. “A main goal of our research is to understand how single polymers – acting as individuals – work together to give materials macroscopic properties such as viscosity and toughness.”
Using a technique called single-molecule fluorescence microscopy, researchers can watch – in real time – as individual polymer molecules relax after the stretching, pulling and squeezing of the manufacturing process. “Imagine looking into a bowl of cooked spaghetti and watching the motion of a single noodle as the bowl is mixed,” Schroeder said.
“We found that the polymers exhibit one of two distinct relaxation modes,” said co-author and graduate student Yuecheng (Peter) Zhou. “One group of polymers relaxed via a single decaying exponential rate and the other group showed a two-phase process. That second population undergoes a very quick initial retraction followed by a slow relaxation. The existence of two different molecular populations was unexpected and not predicted by classic theory.”
This study worked with high molecular-weight DNA because it serves as an ideal model of other types of synthetic organic polymers, the researchers said.
“We chose DNA as our model polymer because it is a very large molecule and the chains are big enough to image in our microscope,” Schroeder said. “They are also all the same weight, which provided us with a very clean, well-defined system for data analysis.”
The researchers found that the percentage of the molecular subpopulation that exhibits the two-phase relaxation behavior increases as the overall polymer concentration increases in the entangled solutions.
“We are not certain why the single-mode relaxation or fast-retraction mode seems to be concentration-dependent, but it may have to do with enhanced interpolymer friction – the more polymers, the higher the chance they will interact, especially out of equilibrium,” Zhou said. “We are working with theorists here at the University of Illinois to better explain the single-mode and two-mode relaxation phenomena.”
The team is excited to bring new insight to the understanding of how complex fluids flow and how they are processed and manufactured, especially with polymers that are subjected to intense stress, such as the fluids that are used for 3D printing.
The National Science Foundation supported this research.
Written by Lois Yoksoulian, University of Illinois News Bureau
To reach Charles Schroeder, email email@example.com.
Congratulations to Chemical and Biomolecular Engineering graduate student Prapti Kafle and the Diao Group for winning the Science Image Challenge award!
The annual research image competition is organized by the School of Chemical Sciences’ Viz Lab. Winners were honored at the SCS VizLab Open House on Dec. 14.
Kafle’s image is called, “Colors of Nature.” Here’s the description: Cross-polarized microscopy image of multilayered film consisting of alternate layers of an anti-cancer drug ellipticine and an edible polysaccharide polymer, pullulan. The nanothin film, produced by successive shearing of the drug and polymer solutions on silicon, embraces a magnificent morphology with needles and spherulites, that evokes colorful elements of nature unique to spectator’s imagination.”
The Diao Lab pursues fundamental understanding and control of molecular assembly processes to advance innovations in printed electronics for energy and healthcare.
Congratulations also to graduate student Bo Li with the Schroeder Group. His image “Supramolecular Fibers” was a finalist.
“AFM image of self-assembled supramolecular fibers consisting of pi-conjugated oligopeptide. Upon fast evaporation of polar solvent, synthetic pi-conjugated oligopeptides spontaneously self-assembled into supramolecular fibers due to directional hydrogen bonding and pi-pi stacking interactions.”
Understanding various chemical reactions and transport phenomena from the molecular and electronic level; designing new synthetic pathways for radical forms of materials and medicines; characterizing and rationalizing the behavior of matter far away from equilibrium—these are just a few of the grand scientific and engineering challenges that the newest research group in the Beckman Institute aims to tackle.
By bringing together various research efforts across campus and leveraging outstanding resources at Illinois, such as the Computational Science and Engineering (CSE) program and the National Center for Supercomputing Applications (NCSA), the group plans to lead large-scale research efforts in the area of computational molecular science that would be beyond the capability of an individual research group.
The Computational Molecular Science (CMS) Group has been established within the Molecular and Electronic Nanostructures research theme at the Beckman. Yang Zhang, a professor of nuclear, plasma, and radiological engineering, is named the founding group leader.
Along with Zhang, the other nine faculty members of the group include Charles Schroeder and Charles Sing of the Department of Chemical and Biomolecular Engineering; Narayana Aluru, of the Department of Mechanical Science and Engineering; Paul Braun, Andrew Ferguson, and Kenneth Schweizer, of the Department of Materials Science and Engineering; and Martin Gruebele, So Hirata, Nancy Makri, of the Department of Chemistry.
“Our goal is to consolidate campus-wide expertise on computational molecular science to facilitate interdisciplinary research in several strategic areas at the Beckman Institute and Illinois, and eventually establish a world-leading thrust in the frontier of theory-driven computational molecular science,” Zhang said.
CMS is profoundly interdisciplinary. It embodies physics, which underpins the underlying fundamental principles; chemistry, which both explores higher-level emergent principles and creates novel synthetic routes of remarkable organic, inorganic, bio-molecular building blocks that can self-assemble to structures with unique properties; and molecular biology and medical science, which are imperative to improve our health and quality of life.
“This group is an intellectual powerhouse with ambitious aspirations to advance important problems in molecular design thinking. Their activities cut across a number of experimental projects in the institute and so, wisely, the new CMS group integrated key experimentalists into its faculty roster,” said Jeff Moore, director of the Beckman Institute.
“The unique aspect of the CMS group is the emphasis of statistical and quantum mechanical theories-driven method development and applications,” said Zhang. “Through these computations, our ambition is to significantly extend our understanding of the equilibrium and non-equilibrium properties of matter from the molecular and electronic level, along with the creation of simulation, visualization, and analysis software packages that would become the golden standards in the field of CMS.”
The research topics of the CMS group include first-principle and semi-empirical methods, large-scale molecular dynamics simulations, advanced rare event sampling techniques, intelligent coarse graining and dimensionality reduction, and big data analysis – all targeted to advance molecular science. The impact of the work is amplified through close collaborations with experimentalists, synthetic chemists, materials scientists, and engineers.
The CMS group will synergistically collaborate with other groups, such as the Theoretical and Computational Biophysics and the Autonomous Materials Systems groups, at Beckman Institute.
New research from Chemical and Biomolecular Engineering at the University of Illinois offers new insight into the self-assembly of electrically-active biohybrid materials, which consist of natural peptides linked to synthetic conductive polymers. The results, published recently in ACS Central Science, promise to aid solution-based processing of next-generation optoelectronic materials such as flexible organic semiconductors.
Thanks to recent advances in materials chemistry, researchers have been able to design and create new materials for advanced energy storage and capture applications. Supramolecular assembly of molecular-scale building blocks is a powerful method that can be used to generate materials with exceptional structural and functional diversity for these applications. However, there’s still a need to understand the mechanisms underlying the assembly of biohybrid/synthetic molecular building blocks, which ultimately control the emergent properties of hierarchical assemblies, according to Charles Schroeder, Professor and Ray and Beverly Mentzer Faculty Scholar.
Using cutting-edge techniques in microrheology, optical spectroscopy, and electron microscopy, Schroeder and his research team studied the concentration-driven self-assembly and sol-gel transition of synthetic pi-conjugated oligopeptides with different chemistries.
“Using this combined approach based on optical and mechanical analysis, we monitored the self-assembly process of synthetic oligopeptides in situ through the sol-gel transition, which reveals fundamentally new insight for how these materials form gels and how they can be processed,” Schroeder said.
Yuecheng (Peter) Zhou, a graduate student in Schroeder’s group, was first author on the study. “For the first time, we measured the critical fiber concentration, critical gel concentration, and diffusive exponent for pi-conjugated oligopeptides. Our results show that the assembled gel microstructures remain homogeneous throughout the sol-gel transition by concentration-driven assembly under neutral pH. These findings will effectively guide the bottom-up design in solution processing for next-generation functional materials,” Zhou said.
The article, “Concentration-Driven Assembly and Sol-Gel Transition of π-Conjugated Oligopeptides” is available online. In addition to Schroeder and Zhou, the authors are University of Illinois postdoc Dr. Bo Li and graduate student Songsong Li; along with Herdeline Ann Ardoa, graduate student at Johns Hopkins University, John Tovar, Professor at Johns Hopkins University; and William Wilson, Professor at Harvard University and Adjunct Research Professor at the Frederick Seitz Materials Research Laboratory at the U of I.
Congratulations to Yuecheng Peter Zhou, a graduate student in Chemical and Biomolecular Engineering Professor Charles Schroeder’s research group, for winning second place in the student presentation competition at the 2017 Great Lakes Chinese American Chemical Society (GLCACS) conference.
Zhou’s presentation was entitled, “Single polymer relaxation dynamics in entangled solutions.” For his Ph.D. thesis research, Zhou uses single molecule techniques to study linear and circular polymer dynamics in different concentration regimes under various flow fields such as extensional flow and oscillatory extensional flow. He is a graduate student in Materials Science and Engineering at the University of Illinois.
GLCACS is the local chapter of Chinese American Chemical Society in the Great Lakes area, which includes Illinois, Indiana, Wisconsin, Michigan, Minnesota, and Ohio. The chapter promotes professional development and networking for GLCACS members and non-members. Members are comprised of professionals from industry as well as professors, research fellows, and students.
The annual conference was held in Evanston on June 10.