We’ve all experienced that moment of dread as a phone escapes your hand and tumbles to the floor. Will it be cracked when you pick it up? A cracked screen today could cost you hundreds of dollars to fix, but a new material accidentally developed by researchers in Tokyo might lead to phone screens that heal themselves after a crack.
Graduate student Yu Yanagisawa stumbled upon this new polymer while attempting to develop a type of glue. He found the material formed a hard glass-like surface, and small cuts or breaks would heal in a few seconds. Yanagisawa knew he was onto something here because that combination of properties is extremely elusive.
Most of the self-healing hard polymers created in the lab need to be exposed to high heat of at least 120 degrees Celsius (248 degrees Fahrenheit) to basically melt the tangled polymer chains and reset the covalent bonds. There are softer polymers that don’t need to be heated because they rely on hydrogen bonds to heal damage. However, a mechanically robust material with hydrogen bonds would end up with clustering and crystallization that interferes with healing. The new material, known as a polyether-thiourea, doesn’t do that because its hydrogen-bonded thiourea are non-linear and break up any crystalline structure.
The material is capable of healing fine cracks in as little as 30 seconds. All you need to do is press the edges together, and wait for them to stick. You don’t even need heat — room temperature will do just fine. After a few hours, the material should perform just as it did before the break. The key to this process is the hydrogen bonds between hydrogen and sulfur atoms. These are easier to re-associate than covalent bonds, but they’re also weaker. Still, with enough of them you can make the material quite robust. Hydrogen bonds are also what give water surface tension, but there it’s a bond between hydrogen and oxygen.
Clearly, everyone’s hoping this technology can be used in phone screens. There’s still a lot that could go wrong before that happens, though. The polymer needs to optically clear enough to have a display under it, and we don’t know anything about its resistance to scratches. The polymer may also prove too expensive to produce in large volumes for phone screens. That’s what doomed sapphire glass production for smartphone screens. Even if it costs a bit more, some people might prefer that to paying for a screen repair.
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