Self-healing material
A self healing material is a material which has the build-in ability to - partially - repair damage occuring during its service life time. Usually materials properties degrade over time due to the initiation of damage (like micro cracks) on a microscopic scale that tend to grow and will ultimately lead to failure of the material. From the biological world we know about mechanisms that continuously sense damage and repair it. In the field of materials science researchers are now trying to engineer this type of behaviour into man-made materials, so called self healing materials.
The first report of a man-made self healing material was by the group of prof Scott White of the University of Illinois [1]. They reported an epoxy system containing microcapsules. These microcapsules were filled with a (liquid) monomer. If a microcrack occurs in this system, the microcapsule will rupture and the monomer will fill the crack. Subsequently it will polymerise, initiated by catalyst particles (Grubbs catalyst)that are also dispersed through the system. This model system of a self healing particle proved to work very well: the service life time of a structure made of such material will be significantly higher.
Currently a number of research groups world wide is developing self healing mechanisms for essentially all materials classes (metals, polymers, ceramics and cemetitious materials). Besides the mechanism of micro encapsulation from White and co-workers, many other 'healing strategies' are being explored (e.g. reversible chemistries, dynamic precipitation etc).
references
- ^ 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. 2001 409, 794-797.