Braun Group People
Aaron Jackson
Graduate Student in Materials Science and Engineering
B.S. in Materials Science and Engineering from Cornell University (2006)
Self-Healing Materials: Improved encapsulation chemistries for self-healing materials.
Self healing materials are inspired by the biological processes of healing. In order to bring this concept to synthetic applications, a compartmentalized self-healing system has been developed here at the University of Illinois (Figure 1). The original system utilized encapsulated dicyclopentadiene (DCPD) which could be polymerized by a solid catalyst, Grubbs catalyst, through ring opening metathesis polymerization. Capsules on the order of 10’s to 100’s of microns in diameter where incorporated into an epoxy matrix to heal cracks 10’s of microns in size.
Figure 1:Depiction the encapsulation approach to a self-healing composite material. With crack propagation (a), capsules are punctured releasing healing agent (b). After the healing agent comes in contact with the catalyst, it polymerizes (c).1
One area where improvement is necessary is when flaws in the material approach nanometer sizes or the material features are simply smaller than the 100 micron capsules normally employed. In this case, encapsulation techniques have been developed to achieve healing for smaller size-scales. 2 DCPD, for instance, has recently been encapsulated in polymer capsules less than 1 micron in diameter. These capsules, however, are not easily dispersed in bulk polymer materials and, as a result, additional steps must be taken to further protect and functionalize the capsules.
My current research is to improve upon the encapsulation of DCPD in polymer capsules by adding an inorganic coating, such as silica. Both Stöber3 and non-Stöber processes can be employed to coat capsules with silica. When smaller capsules are coated with silica, they can be dispersed more readily in a bulk polymer. In addition, this coating shows promise where high temperature applications are concerned since it is expected that the inorganic layer with smaller pore sizes will provide a better barrier to diffusion of species into or out of the capsules.
Future work will focus on improving the coating procedures for more generalized use and to develop testing techniques that can quantify the healing produced by the capsules. This research is funded by a grant from the Air Force Research Labs.
[1] White et al. Nature. 409, 794-797(2001)
[2] Blaiszik et al. Composites Sci Tech. 68, 978-986 (2008)
[3] Stober et al. J Colloid Interface Sci. 26, 62-69 (1968)
Professor Paul Braun • Phone: +1.217.244.7293 • Fax: +1.217.333.2736 • Email: pbraun@illinois.edu
Department of Materials Science and Engineering • University of Illinois at Urbana-Champaign