Today’s relentless tech advances can often feel like something from a sci-fi film. But perhaps one development in particular feels distinctly like the conjuring of a Hollywood special effects department: the rise of self-healing materials.
Both Motorola and Samsung, for instance, have filed patents for mobile phone screens that can repair their own cracks. While the technology may be some way off being released to market, the idea of self-healing products has nonetheless captured the public imagination. After all, healing properties and molecular self-repair mechanisms feel more biological than technological.
Scientists hope that self-healing materials will improve the durability of everything from cars and electronics to bridges and aeroplane fuselages. The White Research Group at the Beckman Institute for Advanced Science and Technology is currently working on several types of self-healing materials – including batteries and electronic circuit components. If their research makes it out of the lab and into our handheld devices, it could alter how we think about everyday objects and products.
Already it is already possible to buy self-healing products that can prolong the lifespan of dams, bridges, water basins and other vital structures. This is thanks to a self-healing concrete developed by the Dutch company Green Basilisk, a spin-off from Delft University of Technology. “Concrete will always crack,” says Bart van der Woerd, managing director of Green Basilisk, “and it’s not watertight. When a crack occurs water will come in and the [steel] reinforcement can corrode.”
The company’s solution relies on bacteria that convert their food source (calcium lactate) into limestone when a crack allows oxygen and water in. This process can heal cracks of up to 0.8mm, reducing the risk of serious damage to the structure.
“When the crack is healed, the bacteria will die because there’s no oxygen anymore,” says Van der Woerd. “But just before dying they produce another spore, so when another crack occurs in the same place in the concrete the whole process will begin again.”
Green Basilisk’s products can be added to the concrete mixture or used as a repair system for existing concrete structures, and in 2017 were included in the concrete walls of a water basin for the Port of Rotterdam.
It is just one of a number of approaches to developing self-healing products, the most common of which involves embedding microcapsules filled with liquid adhesive into certain materials – a technique pioneered by scientists at the Beckman Institute in 2000. When the material breaks, the microcapsules crack open, releasing the liquid and healing the damage. But this method only works once.
Researchers at the Beckman Institute have since produced composite materials similar to those used in aeroplanes and cars that can self-heal multiple times, thanks to a 3D vascular network that consists of hollow fibres filled with healing agents. These are threaded throughout the material, much like a biological circulatory system.
Scientists are also developing polymers with molecular self-healing systems, says Sybrand van der Zwaag, professor of Novel Aerospace Materials at Delft University of Technology and chairman of the Netherlands’ Innovation Oriented Research Programme on self-healing materials. “The polymer consists of strong molecular bonds, which give the material its [physical] properties, and weaker bonds, which can break without breaking the strong bonds – so when the two [damaged] surfaces are brought together they reheal,” he says.
“It’s like if you have two magnetic pieces connected to a piece of string: you can apply a load, but at a certain load it [the bond between the pieces] will break. All you need to do is reconnect the two – in this case, magnetic pieces – and then you restore the bond. That is called reversible chemistry, and modern self-healing polymers are based on this concept.”
In some cases, the healing process is activated by heat, but there are also self-healing elastomers (a natural or synthetic polymer with elastic properties, such as rubber), which don’t require it. “They heal at room temperature in a period of, say, minutes to hours,” says Van der Zwaag.
The commercialisation of self-healing materials has been somewhat slow, but Van der Swaag says that self-healing coatings for cars are becoming more commonplace. US-based company Feynlab, for instance, has developed a self-healing memory polymer woven into a ceramic coating, which heals small scratches and light swirl marks and keeps paintwork in top-notch condition.
Splashing the affected area with hot liquid or treating it with a heat gun will return the polymer to its original state. In fact, even leaving the car in the sunshine will slowly cause any swirls and scratches to vanish. “Once the surface reaches roughly 140F (60C) it essentially snaps back into its memory state,” says Nolan Robinett, marketing manager for Feynlab.
Feynlab’s coating is currently applied to most vehicles after sale, but Robinett says the company wants to “work with the automotive manufacturers directly and get this technology applied at a production level”.
Autonomic Materials Inc, which was founded in 2007 by the Beckman Institute scientists that pioneered self-healing polymers, also sells self-healing coatings, adhesives and sealants. Its microcapsule-based self-healing products are added to paint and can be applied to everything from wind turbines to oil-rigs, warding off rust and extending the lifespan of valuable equipment. They also make water-based coatings last as long as solvent-based ones, which are harder on the environment.
Increasing the time between repainting something like an oil rig from five years to 15 or more can save the owners “millions and millions of dollars”, says Grant Jones, director of business development for AMI.
Self-healing coatings are particularly well-suited to hard-to-reach equipment, such as offshore wind turbines. “We’ve also been able to encapsulate different things within our self-healing additive,” adds Jones. This means the owner of the turbine could, for instance, add a UV tracer to microcapsules to help them identify where micro-cracks are occurring on the turbine.
In future, more materials with self-healing properties could also find real-world applications – including those long-promised self-healing touchscreens. But for now, at least, a decent case is still the best way to keep your phone free of cracks.
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