A Collaboration of Opportunity and Necessity

The partnership began when Sottos arrived at Illinois in 1991 just a few months after White, occupying an office at Talbot Lab that turned out to be right next to White's office.

Sottos: It also turned that out that after I met Scott I found out that we had been running in the same circles for years but had never met each other. We had gone to some of the same meetings as graduate students. We both have backgrounds in composite materials but with a subtly different focus. Scott's focus when he first got here was on how to make a composite and how to integrate many things into a composite material, and my focus was on small-scale experimental methods, how the different components in a composite interact at almost a molecular level. Throughout our first couple of years we used to go to lunch and discuss sort of blue sky type research projects and how we might collaborate, because as assistant professors you are kind of in a track doing your own thing. At some point the idea of selfhealing came up, which ties in with some of the things that both Scott and I were working on about adding extra functionality, sort of unusual multi-functionality, into composites, into polymers, giving them functions that they don't normally have. … Self-healing became one of those functions and we got a very small research grant from the Army Corps of Engineers to look at concepts for self-healing. That was just an engineering study, though. What came out of that study was that we thought that microcapsules were a good idea, and that microencapsulation was the way to go if you wanted to bring in this self-healing functionality. We quickly tried a couple of chemistries that we knew but they were somewhat limited. Then Scott went to visit Jeff.

White: Nancy and I and Philippe Geubelle worked together for a while thinking about concept development for self-healing systems. We had a small grant around 1995. We started hatching out ideas and the microcapsule concept was one we were looking at. With the concepts that we wanted to pursue, it became very clear very quickly that we were in over our heads in terms of the chemistry involved. Then I looked on the U of I Web site and did some searching for stellar, outstanding, wonderful chemist with knowledge of polymers and it came up empty (drawing laughs). But then I found Jeff's name and went over to his office with a student of mine at the time. … I took it at face value that he was actually going to think about it and get back and we left. But he didn't get back, so I said we need to go talk to Jeff again. So we went back.

Sottos: As Jeff will tell it, Scott was persistent. Once Jeff got involved, he suggested the chemistry that we eventually used in the Nature paper. It was something that Scott and I would never have dreamed of using on our own. It was very new, very different, and we just would not have had the experience to work with the catalyst.

White: We put together a proposal, all of us, and the thing that really got us going forward was the Campus Critical Research Initiative award. They gave us some money to actually have students working on it and we collaborated and started having joint group meetings that started evolving the research.

Patience Pays Off with Nature Paper

The Nature paper in February 2001 turned out to be huge news in the scientific and popular press. It reported on using microcapsules for autonomic, or self-repair, of cracks in polymer materials. The process works, according to the Autonomic Healing Research group's Web site by "incorporating a microencapsulated healing agent and a catalytic chemical trigger within an epoxy matrix. An approaching crack ruptures embedded microcapsules, releasing healing agent into the crack plane through capillary action. Polymerization of the healing agent is triggered by contact with the embedded catalyst, bonding the crack faces." The discovery was carried in newspapers and Web sites worldwide and earned a front page story in the Washington Post. The work has since expanded to self-healing microvascular composites and recently produced a paper demonstrating a practical application of the microencapsulated system.

Sottos: This project just sort of percolated from the bottom up, which is not always how projects go. And it wasn't like there was this whole community of people and this whole gigantic literature on self-healing; there were just indications that this is a good idea. Some polymers like asphalt tend to self-heal, that is a word that was used in literature, and there were people who did polymer welding but the notion of building this into any material was brand new.

Sottos: I have to say that Scott has been our cheerleader. It was a difficult problem and it took a lot of things to come together correctly. I would say that I was pessimistic more than once along the way. Scott's a good leader in that respect; just keeping everybody moving forward even when it seems like the research isn't going the direction you want it to.

White: I don't give up. That's the problem (laughing).

White: The one thing that gets to the heart of that is that the publication of the Nature paper was February of 2001 and we had started in 1995 on these simple tests. The first positive test we got was late 2000. That's five years of failure after failure after failure.

Moore: The key was the 'bullet' test. It's simply an object in the shape of a bullet. Sottos: It was a little cylinder of polymer that had the microcapsules and the catalyst. It had the healing components in it. So it was easy to make a whole bunch of these and you would just tap a razor blade into them and bring them back together. Then we would have students that would try to pull them apart and we would measure how hard it was to pull them apart on a scale of one to five.

Moore: Not scientific. (laughs)

Sottos: There were no forces measured, it wasn't quantitative. Then it became that the strongest student in the group was supposed to pull them apart and if it was a five on his scale then we knew we had healing. We didn't publish that (laughing). It was just a good example of how those initial meetings were actually pretty fun. We've been having fun for quite a long time. We actually got to know each other very well as we were writing the Nature paper."