In the final steps, the researchers deposit a brittle epoxy coating on top of the substrate, and fill the network with a liquid healing agent.
In the researchers’ tests, the coating and substrate are bent until a crack forms in the coating. The crack propagates through the coating until it encounters one of the fluid-filled “capillaries” at the interface of the coating and substrate. Healing agent moves from the capillary into the crack, where it interacts with catalyst particles. If the crack reopens under additional stress, the healing cycle is repeated.
“Ultimately, the ability to achieve further healing events is controlled by the availability of active catalyst,” said Kathleen S. Toohey, a U. of I. graduate student and lead author of the paper. “While we can pump more healing agent into the network, ‘scar tissue’ builds up in the coating and prevents the healing agent from reaching the catalyst.”
In the current system, the healing process stops after seven healing cycles. This limitation might be overcome by implementing a new microvascular design based on dual networks, the researchers suggest. The improved design would allow new healing chemistries – such as two-part epoxies – to be exploited, which could ultimately lead to unlimited healing capability.
“Currently, the material can heal cracks in the epoxy coating – analogous to small cuts in skin,” Sottos said. “The next step is to extend the design to where the network can heal ‘lacerations’ that extend into the material’s substrate.”
Source:University of Illinois at Urbana-Champaign