1990s
“The AFOSR has been the single most important factor in my scientific career. Without their support the entire field of autonomous (self-healing) materials would probably not exist. AFOSR was the only agency to step forward and fund our work at a point when it was extremely high risk. Ultimately their investment yielded a successful launch of a worldwide research effort, several start-up companies, commercial products, and the realization of other material functionalities deriving from our original effort. I believe what defines AFOSR as a scientific organization is their willingness to support high-risk, high-reward efforts as part of the AFOSR research portfolio. My team has been extremely fortunate to work with some of the best Program Managers in the world over the years, including Dr. Ozden Ochoa, Dr. Tom Hahn, and Dr. Les Lee. Each has supported our philosophy of pushing the boundaries of science and engineering, and their research horizon extends far beyond the current funding cycle. I’m also extremely grateful that AFOSR and the Program Managers I’ve worked with see the incredible value of funding interdisciplinary work. Our team consists of an aerospace engineer (Scott White), a materials scientist (Nancy Sottos) and a chemist (Jeff Moore) all working side-by-side on a common research theme. Together, these disciplines allow us to tackle important and long-standing problems while greatly increasing our likelihood of success. On behalf of our entire research team, we wish the AFOSR a very happy 60th birthday and look forward to their next 60 years of exploration and discovery.”
Dr. Scott White, University of Illinois at Urbana-Champaign Self-Healing Materials: Can Air and Space Vehicles Live Forever? (1998-present) In 1998, Dr. Ozden Ochoa, an AFOSR materials Program Manager, attended a workshop where Dr. Scott White from the University of Illinois at Urbana-Champaign presented a paper on “selfhealing plastic.” Ochoa and follow-on AFOSR Program Managers Dr. H. Thomas Hahn and Dr. Les Lee enthusiastically followed up with White’s proposal for a process whereby microscopic cracks in aircraft structures could “heal” themselves. Initially supported by seed money from the University of Illinois in the mid-1990s, and rejected by other funding agencies because they thought the work was “too high risk,” AFOSR funding resulted in a seminal 2001 paper in the journal Nature, “Autonomic Healing of Polymer Composites,” which gained worldwide attention. White’s initial concept consisted of placing microcapsules of a healing agent and a special catalyst into a structural compositematrix material. When damage occurs, the microcapsules rupture and release the healing agent and catalyst into the damaged area, filling and bonding the void. Further research has discovered a simpler and economical catalyst-free system, and demonstrated a technique for fabricating 3-D microvascular networks within various materials that can continuously transport the healing agent to damaged sites via a circulatory-like system. White noted that these miniscule networks could work as compact fluidic factories in sensors, chemical reactors, and computers, and could also cool in response to a heat load or, conversely, heat when too cold. They can also be configured to be self-diagnosing, and be able to sense biological agents. Self-healing micro-electronic structures are also being investigated to obviate dielectric breakdowns because of thermal or mechanical cycling. With new catalysts and healing agents, material integrity can be assured up to approximately 180 degrees Celsius. This basic research program has progressed from a capsule-based system to a vascular system, to an intrinsic approach to self-healing, wherein with the use of dynamic polymers and inert scaffolds one can synthesize two types of dynamic covalent bond-based polymer systems, which can be forever changed from liquid to solid and vice versa when renewed bonding is necessary. What began in 1998 as a high-risk technology endeavor has resulted in the possibility of a highly sophisticated approach to the autonomous healing of aircraft structures. This program is an unparalleled testament to the high-risk, high-payoff philosophy of AFOSR Program Managers in support of the Air Force mission.81
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