Materials Today Lab Profile: Nancy Sottos
Imagine polymer materials that can heal themselves when damaged or change color when under stress. Or polymer gels that can mimic blood clotting to protect and regenerate damaged vascular networks. Nancy Sottos of the University of Illinois Urbana Champaign (UIUC) did just that and has devoted her career to the development of materials systems inspired by nature’s ability to design self-healing, self-regenerating, self-reporting, and self-protecting materials.
Nancy Sottos is currently Swanlund Endowed Chair in the Department of Materials Science and Engineering and the Beckman Institute, where she has been since 1991, after receiving a Ph.D. from the University of Delaware. She has been the recipient of many awards including, most recently, the Society of Engineering Science Medal, IChemE Global Research Award, and the Hetényi Award from the Society for Experimental Mechanics. She is a Fellow of the Society of Engineering Science and the Society for Experimental Mechanics.
Nancy Sottos talked to Materials Today about her current research and future plans.
How long has your group been running?
I have been at the University of Illinois my entire career. My group, which is based in the Department of Materials Science at the University of Illinois Urbana Champaign (UIUC), has been running for 28 years. My group is also part of a larger interdisciplinary group that I lead called the Autonomous Materials Systems Group (AMS) in the Beckman Institute for Advanced Science and Technology at UIUC, which was officially formed in 2001, approximately 18 years ago.
How many staff currently makes up your group?
The Sottos group consists of two postdoctoral researchers, 14 graduate students and 10 undergraduate researchers, with a research program coordinator. The larger AMS group involves six other faculty from different departments and over 60 researchers total.
What are the major themes of research in your group?
Our research is focused on the creation of materials systems with unprecedented functions through a unique combination of bioinspired design, novel manufacture, and multiscale characterization at the intersection of chemistry, materials science, and mechanics. Inspired by autonomous function in biological systems, our group develops polymers and composites capable of self-healing and regeneration, self-reporting, and self-protection to improve reliability and extend material lifetime. A key goal is to understand the mechanical behavior of these complex, heterogeneous materials through meso- and microscale characterization of deformation and failure mechanisms. My group has developed new experimental tools to characterize material response in self-healing materials, mechanochemically active polymers and well as other coupled systems such as composite electrodes used in electrochemical energy storage and thin film interfaces.
How and why did you come to work in these areas?
Self-healing polymers – The development of self-healing polymers with the ability to autonomously repair crack damage without human intervention has led to safer and longer-lasting materials. Our team introduced the first self-healing polymers that incorporate microencapsulated monomeric healing agents coupled with matrix-embedded catalysts . Crack damage triggers the release and subsequent polymerization of the encapsulated healing agent after exposure to the embedded catalyst, effectively rebonding the cracked faces closed. Through a synergistic combination of polymer chemistry, fabrication, and mechanical testing, we demonstrated that up to 90% of the original fracture toughness can be recovered in catastrophically damaged materials. This seminal advancement established a new paradigm for recovery of structural performance to pre-damage levels under ambient conditions and without external intervention. Following this landmark publication – now cited more than 3000 times – the field of self-healing polymers has grown explosively.
Microvascular Materials – Our group developed microvascular materials to address the problem of multiple repair events in polymers  and fiber-reinforced composites . The introduction of vascular networks addressed three significant technological challenges for self-healing, including the delivery of a large volume of healing agents to the site of excessive damage, the repetitive healing of damage (compared to depletion of microcapsules once the first damage event occurs), and the use of a wider range of healing chemistries beyond those that can be microencapsulated. A remarkable demonstration of large-volume damage repair utilized vascular delivery and employed a novel, two-stage polymer chemistry that mimicked blood clotting with a fast liquid gelation reaction followed by polymerization .
Mechanochemically Active Materials – My group has also made significant contributions in the design of polymeric materials where mechanical stress initiates a chemical reaction that provides assessment of the stress state prior to failure. This creative leap forward in polymer mechanochemistry is accomplished by incorporating force-sensitive molecules, known as mechanophores, into a polymer . Specifically, mechanochromic spiropyran mechanophores linked directly into a polymer backbone are triggered by mechanical force to induce an intense color change in regions of high stress concentration. These and subsequent advances have opened new ways of thinking about mechanochemical activation of chemical reactions and the productive use of mechanoresponsive materials.
Bioinspired Manufacturing – A relatively new focus area for my group involves the development of low energy methods for manufacturing polymers and composites with complex functions. Manufacture of high-performance thermoset components requires the monomer to be cured at elevated temperatures (ca. 180 °C) for several hours under combined external pressure and internal vacuum. Curing is generally accomplished using large autoclaves or ovens that scale in size with the component. This traditional curing approach is slow, requires a large amount of energy, and involves significant capital investment. Recent work by AMS  reports the frontal polymerization (FP) of a high-performance thermoset polymer that allows the rapid fabrication of parts with microscale features, 3D printed structures, and continuous carbon fiber-reinforced polymer composites using minimal external energy. This polymerization process uses 10 orders of magnitude less energy and can cut two orders of magnitudes of time over the current manufacturing process. The resulting polymer and composite parts possess similar mechanical properties to those cured conventionally.
Societal Impact – In a recently published Insight article, we forecast the coming age of resilient infrastructure based on self-healing materials . Remarkably, this bold prediction is coming to fruition already. Modifications of the original microcapsule-based system have resulted in self-healing materials that are efficiently prepared, safe, and economical. Several members of AMS co-founded Autonomic Materials Inc. (AMI), which in December 2016 produced a commercially available, self-healing epoxy primer named metaPrime™ marketed by the Illinois-based company Rust-Oleum®. In addition to commercial coatings, self-healing materials have potential to impact the reliability of products in many industrial sectors from high performance aerospace composites to microelectronics to soft robotics. Worldwide interest in self-healing materials continues to grow as evidenced by increasing archival research papers, patents and conference activity.
What facilities and equipment does your lab have?
The AMS Lab at the Beckman Institute consists of five contiguous rooms of shared laboratory space totaling 2500 sq. ft. with ten 6 ft. fume hoods for the fabrication and characterization of multifunctional materials. Equipment ranges from materials processing (3D printers, composite prepregger, hot press, ovens), polymer characterization (rheometer, dynamic mechanical analyzer (DMA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) mass spec), imaging (high resolution, high speed cameras, infrared cameras), and traditional optical and digital microscopes. The group also has access to amazing shared user facilities for materials characterization at the Institute where we utilize environmental SEM, microCT and confocal Raman microscopes and the Fredrick Seitz Materials Research Lab (MRL) where we use an array of SEM, TEM, FIB, XPS, and x-ray characterization equipment.
Do you have a favorite piece of kit or equipment?
Our system for Digital Image Correlation (DIC) based strain measurements or our custom 3D printer.
What do you think has been your most influential work to date?
The initial work on microcapsule-based self-healing materials and its application to coatings is probably the most impactful.
What is the key to running a successful group?
Running a successful interdisciplinary group relies on several key factors: (1) engaging with faculty with exciting ideas from a range of disciplines who are interested in collaboration; (2) having high quality lab and office space where students from different disciplines can co-locate and interact; (3) holding stimulating group meetings where students are required to communicate effectively across disciplines; (4) stimulating creativity and interaction between group members; (5) knowing when to take the lead and when to compromise on research ideas; and (6) fostering mutual respect between all group members.
How do you plan to develop your group in the future?
We hope to bring our unique interdisciplinary focus to more manufacturing-related research problems.
- S. R. White, N. R. Sottos, P. H. Geubelle, J. S. Moore, M. R. Kessler, S.R. Sriram, E.N. Brown, S. Viswanathan. Autonomic Healing of Polymer Composites. Nature 409 (2001) 794-797.
- K. S. Toohey, N. R. Sottos, J. A. Lewis, J. S. Moore, S. R. White. Self-healing materials with microvascular networks. Nature Materials 6 (2007) 581-585.
- D. A. Davis, A. Hamilton, Y. Yang, L. D. Cremar, D. V. Gough, S. L. Potisek, M. T. Ong, P. V. Braun, T. J. Martínez, S. R. White, J. S. Moore, N. R. Sottos. Force-Induced Activation of Covalent Bonds in Mechanoresponsive Polymeric Materials. Nature 459 (2009) 68-72.
- J. F. Patrick, K. R. Hart, B. P. Krull, C. E. Diesendruck, J. S. Moore, S. R. White, N. R. Sottos. Continuous Self-Healing Life Cycle in Vascularized Structural Composites. Advanced Materials 26 (2014) 4302-4308.
- S. R. White, J. S. Moore, N.R. Sottos, B. P. Krull, W. A. Santa Cruz, R. C. R. Gergely. Restoration of Large Damage Volumes in Polymers. Science 344 (2014) 620-623.
- J. F. Patrick, M. J. Robb, N. R. Sottos, J. S. Moore, S. R. White. Polymers with autonomous life-cycle control. Nature 540 (2016) 363-370.
- H. Tavassol, E.M.C. Jones, N.R. Sottos, A. A. Gewirth. Electrochemical stiffness in lithium-ion batteries. Nature Materials 15 (2016) 1182-1187.
- S. Kang, K. Yang, S. R. White, N. R. Sottos. Silicon Composite Electrodes with Dynamic Ionic Bonding. Advanced Energy Materials 7 (2017) 1740045.
- J. Sung, M. J. Robb, S. R. White, J. S. Moore, N. R. Sottos. Interfacial Mechanophore Activation Using Laser-Induced Stress Waves. J. Am. Chem. Soc., 140 (2018) 5000–5003.
- I. D. Roberston, M. Yourdkhani, P. J. Centellas, J. E. Aw, D. G. Ivanoff, E. Goli, E. M. Lloyd, L. M. Dean, N. R. Sottos, P. H. Geubelle, J. S. Moore, S. R. White. Rapid energy-efficient manufacturing of polymers and composites via frontal polymerization. Nature 557 (2018) 223-227.
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