Self-Healing polymers are a new type of composite material with the ability to repair damage autonomically (autonomic = start independently and finish automatically). The basic concept is that microcapsules of a healing agent is placed in the polymer along with particles of a chemical that cause the healing agent to solidify (usually called a catalyst). This concept is shown in the image below left (taken from White et al. Nature 2001). In step (i) a crack is moving through the polymers, in (ii) the crack has opened a microcapsule and in (iii) the healing agent has solidified and sealed up the crack. The image below right is an image of an actual self-healing polymer. The dark line running diagonally from top left to bottom right of the image is a crack. Along the crack the microspheres of healing agent have broken open and have turned dark.

If you break a self-healing polymer and place the two halves back together and wait a short while, the polymer will heal itself. After healing you can re-break the polymer and look at the broken surface (called the fracture plane, or the crack face). Depending on the amount of healing agent and catalyst, you may or may not cover the entire crack face. Below is a picture of the crack face of a healed self-healing polymer. The BLUE is the solidified healing agent.

The microcapsules and catalyst are very small. A typical microcapsule is only 180 micrometers (about .007 inches) in diameter (typical human hairs range from 90-180 micrometers in diameter). Depending on the fabrication method and chemicals used, a microcapsule can be very smooth or have a smooth inside and a very coarse outside. Below is a microcapsule with a very smooth inside and a coarse outside (which happens to look a bit like pac-man).

The uses for self-healing polymers are limitless. Initially self-healing polymers will be used in materials that are difficult or expensive to repair, but as the technology develops, self-healing technology will become more pervasive in all engineering materials.

There are research opportunities available in AML in self-healing polymers. Please contact Dr. Alan Jones for more information.