Imagine a car that would never experience a tyre puncture, a plane that can remain structurally intact over thousands of flights, or a ship that’s insusceptible to corrosion. These may sound like far-fetched ideas, but that hasn’t stopped materials scientists from developing advanced self-healing materials that could one day achieve this.
It’s inevitable that vehicles frequently used as transport will experience scratches, micro-cracks or dents during their lifecycles – whether due to collisions or environmental conditions. For most private car owners, the consequences range from aesthetic imperfections to personal expense for repairs.
Self-Healing Materials Promising For The Transport Industry
One class of materials that has held a lot of promise for design engineers in recent years, especially those in the transport industries, is self-healing materials. As the name suggests, self-healing materials are designed with the capability to repair themselves if they are damaged – without needing manual repair. Here, the goal is to extend the lifespan of materials and their applications and, in some cases, the healed material boasts greater properties than it did in its pre-damaged state.
What Are Self-Healing Materials?
Before examining how self-healing materials might benefit transport applications, we must first define what a self-healing material is. As outlined in the Matmatch A–Z of smart materials whitepaper, self-healing materials include mainly polymers and elastomers. There is a growing focus on other materials, such as ceramics and metals. But it has, understandably, proven more difficult to imbue these materials with self-healing properties – particularly within metals with less atomic mobility.
Encapsulated Healing
Encapsulated healing is arguably the most common technique for incorporating self-healing properties into materials such as polymers and polymer composites. This mechanism incorporates micro- or nano-capsules of healing agent into the material’s structure, during the manufacturing stage.
Materials that use this mechanism will feature catalysts dispersed throughout the material matrix, alongside the microcapsules of healing agent. When a crack occurs, it will lead the microcapsule to rupture and release the healing agent into the crack. The released agent reacts with the catalyst and undergoes a process that causes it to harden and fill the crack.
Microvascular Healing Systems
To overcome the single-use limitations of the embedded capsules approach, materials scientists took a leaf out of Mother Nature’s book. As Dr Kathleen Toohey noted in a seminal 2007 study in the field of self-healing materials, Healing in biological systems is accomplished by a pervasive vascular network that supplies the necessary biochemical components. Toohey led a study that incorporated a similar vascular network into the substrate of an epoxy resin.
Such a material contains a network of microtubes that allow the healing agent to flow to the location of damage by leveraging capillarity, or the ability of liquids in capillary tubes to flow independently of external forces. When a crack occurs, the change in surface tension in the vascular network causes the healing agent to pump to the point of damage, at which point it reacts to embedded catalyst particles and then hardens and seals the crack.
Intrinsic Healing
Both encapsulation mechanisms and microvascular structures offer promise for the field of self-healing materials. However, each of these techniques involves the development of extrinsic healing polymers, which require the use of a separate healing agent.
For some materials scientists and researchers, the goal is to develop intrinsic self-healing polymers that regenerate using dynamic chemical bonds within the material itself. Whereas the lifespan of extrinsic healing polymers is limited by the quantity of dormant healing agent present in the material, intrinsic healing materials could theoretically offer a near-endless capacity for reparation.
Applications Of Self-Healing Materials In The Automotive Industry
These materials might promise an exciting prospect for design engineers, but most have not yet been scaled-up to a commercial stage. Although brands such as Lamborghini and Goodyear have teased self-healing cars and tyres, respectively, in recent years, these applications remain largely conceptual.
However, that doesn’t stop us from imagining where self-healing materials might lead or conceiving of how they will fit into future designs. Decades from now, it’s possible that cars constructed of lightweight, self-healing CFRP chassis will travel on concrete roads that autonomically repair potholes using embedded limestone-producing bacteria. Any minor punctures or cracks in the tyres could also be healed by hybrid rubber tyres.
