Nancy Sottos

Education Nancy Sottos studied mechanical engineering at the University of Delaware, receiving her B.S. in 1986 and her Ph.D. in 1991. She was named the Donald B. Willet Professor of Engineering of the Department of Materials Science and Engineering She was appointed co-chair of the Molecular and Electronic Nanostructures Research Theme at the Beckman Institute for Advanced Science and Technology in 2004, succeeding Jeffrey Moore. and Fellow of the Society for Experimental Mechanics (2012). She was the president of the Society for Experimental Mechanics for 2014–2015. She was elected a member of the National Academy of Engineering in 2020 for contributions to the design and applications of self-healing and multifunctional materials.

Research

Self-healing polymers Sottos helped develop the first polymeric self-healing material with colleagues including Jeffrey Moore and Scott White. Their approach was to develop a polymeric matrix which involved both a reactive liquid healing agent and a catalyst. While undamaged, these were kept structurally separate. The liquid agent was contained inside non-reactive reservoirs within the material, while the catalyst was dispersed throughout the polymer. Once the material was damaged and a crack occurred, the reservoirs broke open, and capillary action caused the liquid agent to disperse into the damaged area, where it reacted with the catalyst and solidified to seal the crack. They have studied both the use of a contained healing agent and a dispersed catalyst, and the use of a dispersed healing agent and a contained catalyst. Using dicyclopentadiene (DCPD) and Grubbs' catalyst in an epoxy matrix, polycyclopendiene was formed to seal cracks, recovering up to 75% of the original fracture toughness.

They have since developed a catalyst-free self-healing system

Microvascular networks Sottos has also focused on the design of microvascular networks for the distribution of active fluids in autonomous materials systems. Such designs offer possibilities for "self-healing, regeneration, self-sensing, self-protection and self-cooling" properties, similar to those of biological systems.

To create such a material, a three-dimensional pattern of organic inks is laid down, and the interstitial pores in the pattern are filled with epoxy resin. The polymer is left to cure, and then the ink is removed. The spaces it leaves form well-defined, three-dimensional microchannel networks, which can be filled with healing agents. With this design, a greater supply of self-healing agent can be incorporated into the created material. The process of constructing such a material is very complex. It is reported that microvascular networks can support healing of larger-scale damage, up to 11.2 mm.

Self reporting materials A team led by Sottos and Wenle Li has developed polymeric structural materials that can indicate the presence of damage by changing color. Such self-reporting materials can act as a color changing warning system. The researchers created a polymer that contained microcapsules of epoxy resin and PH-sensitive dye. Damage to the polymer causes the capsules to break open and the epoxy and dye to mix. The resulting reaction causes the color of the material to change from yellow to red. The deeper the damage, the more intense the color change. This autonomous visual indicator can enable engineers to detect mechanical damage and intervene before a structure is compromised.

Smart materials Sottos is involved in the development of self-sensing, mechano- and thermo- chemically active polymeric materials. These smart inorganic polymers belong to the class of smart materials, exhibiting stimuli-responsive functions. A specific input stimulus such as a change in force or temperature can trigger a desired change in one or more properties of the polymer. In one set of experiments, researchers used spiropyran molecules to detect mechanical stress. The spiropyran (SP) mechanophore was covalently bonded into a stretchy barbell-shaped polymer called polymethyl acrylate (PMA) and a small, glasslike bead-shaped polymer called polymethyl methacrylate (PMMA). The researchers have also demonstrated that mechanical force can power a chemical response in the polymer, changing the covalent bonding.

Thermal sensitivity Another area of research focuses on the prevention of thermal runaway in batteries. The researchers coated the anode or separator layer of the battery with microspheres sensitive to heat. An increase in temperature causes the microspheres to melt, blocking transmission of the lithium ions and causing the battery to shut down. Microspheres of both polyethylene and paraffin wax were tested with CR2032 Li-ion batteries and demonstrated both successful operation of the battery at normal temperatures and shutdown of the battery at temperatures below those at which the battery's separator would become damaged.

Thin films Sottos has also been involved in research on thin films, and the measurement techniques for dynamic interfacial energy measurements of adhesion in multilayer thin films.

Awards Sottos has received numerous awards for her teaching and research. These include: The Hetényi Award from the Society for Experimental Mechanics (2004) for J. Wang, R. L. Weaver, N. R. Sottos "A parametric study of laser induced thin film spallation" Experimental Mechanics 42, no. 1 (2002): 74–83. Scientific American's SciAm 50 Award (2008) The M.M. Frocht and B.J. Lazan awards from the Society for Experimental Mechanics (2011) Tau Beta Pi Daniel C. Drucker Eminent Faculty Award (2014) The C.E. Taylor award from the Society for Experimental Mechanics (2020) National Academy of Engineering (2020) The W.M. Murray award and lecture from the Society for Experimental Mechanics (2021) American Academy of Arts and Sciences (2022) National Academy of Sciences (2022)

Culture Self-healing materials created by Sottos and others at the Beckman Institute were included in the exhibit Science Storms at the Museum of Science and Industry in Chicago in 2010.