Self-healing material

Introduction

A self healing material is a material that has the built-in ability to partially repair damage occurring during its service life time. Usually, a material's properties degrade over time due to damage (such as microcracks) on a microscopic scale. These cracks can grow and ultimately lead to failure. Self-healing materials address this slow failure through the inclusion of an "active" phase that responds the the micro-damage by initiating a repair mechanism 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.] .

Self-Healing Approaches

The first report of a man-made self healing material was by the group of prof Scott White of the University of Illinois at Urbana-Champaign . 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, cemetitious, elastomeric, and fibre-reinforced composite [R.S. Trask, H.R. Williams, I.P. Bond: "Self-healing polymer composites:mimicking nature to enhance performance", Bioinspiration and Biomimetics. 2007. 2. 1-9.] materials).

In addition to the sequestered healing agent strategies described above, research into "intrinsically" self-healing materials is also being performed. For example, supramolecular polymers are materials formed by reversibly connected non-covalent bonds (i.e. hydrogen bond), which will disassociate at elevated temperatures. Healing of these supramolecullary based materials is accomplished by heating them and allowing the non-covalent bonds to break. Upon cooling new bonds will be formed and the material will potentially heal any damage. An advantage of this method is that no reactive chemicals or (toxic) catalysts are needed. However, these materials are not "autonomic" as they require the intervention of an outside agent to initiate a healing response.

Commercialization

Currently, there are no commercially available products that incorporate self-healing as defined by White and coworkers . There is at least one company attempting to bring these new materials to market, Autonomic Materials Inc [http://www.autonomicmaterials.com/] .

References

External links

* [http://www.autonomic.uiuc.edu/summary.html University of Illinois at Urbana-Champaign self healing research]
* [http://www.tudelft.nl/live/pagina.jsp?id=1cb5c99a-1a97-4ef6-b6e7-563a391bd413&lang=en TUDelft self healing material program]
* [http://www.mse.iastate.edu/polycomp/self-healing.html Iowa State self-healing composites research]
* [http://www.aer.bris.ac.uk/research/fibres/ University of Bristol self-healing composites research]
* [http://www.personal.utulsa.edu/~michael-keller/research.html University of Tulsa self-healing research]
* [http://www.selfhealingmaterials.nl Self healing material conference]
* [http://www.pubs.royalsoc.ac.uk/index.cfm?page=1340 Self-healing polymers and composites] themed issue of [http://www.pubs.royalsoc.ac.uk/index.cfm?page=1058 Journal of the Royal Society Interface]