Self-healing glass found by accident
A tough, clear plastic that can be fixed with a squeeze of the hand when it cracks has been accidentally discovered by scientists in Japan.
The glass-like substance, which was originally being investigated as a new kind of biomolecular glue, can be fixed with mild pressure applied for 30 seconds at room temperature.
While researchers have discovered plenty of self-healing materials over recent years it is the first to combine this property with the robustness of a rubber or a thermoplastic. Its uses might include durable glassware and shatterproof windscreens.
Yu Yanagisawa, a graduate student at the University of Tokyo, inadvertently solved a problem that had dogged his peers for decades when he was preparing a binding agent from a polymer known as TUEG3.
He found that a 2mm-thick sheet of the stuff the size of a Sim card could comfortably support a load of 300g. When the surface was broken, all he had to do was compress it at an ambient temperature of 21C for half a minute and it was as good as new.
Writing in the journal Science, Mr Yanagisawa and his colleagues explained that polymers tended either to be strong but reparable only at high temperatures, or healable but brittle because of their tendency to form crystals as the gaps were closed over. ‘‘So far, rubber-like soft materials and thermoplastic elastomers with H [hydrogen] bonding motifs have been designed to heal upon gentle compression,’’ they wrote.
‘‘However, the presence of a large number of H-bonds often leads to crystallisation or clustering of polymer materials, thereby making them brittle. In other words, high mechanical robustness and healing ability tend to be mutually exclusive.’’
The advantage of TUEG3, which comes from a family of molecules known as polyetherthioureas, is that its structure – and in particular the fairly chaotic arrangement of its hydrogen bond arrays – allows it to resume its old shape with relative ease and without crystallising.
Mr Yanagisawa said that he had been stunned by his discovery. ‘‘I only half believed it when I found it, so I repeated the experiment many times,’’ he told NHK, the largest Japanese broadcaster. ‘‘I hope the repairable glass becomes a new environmentally friendly material that eliminates the need to be thrown away if it is broken.’’
Whether the finding could be adapted for touchscreens remains to be seen.
In April a group at the University of California announced that it had developed the first self-healing polymer that could conduct electricity, while Motorola was this year awarded a patent for a smartphone display that could repair itself by generating its own heat.