What does unbreakable glass mean?

Materials researchBreak-proof glass for smartphones and co.

Transparent, hard, durable - glass has many advantages. But also a disadvantage:

"The problem is its fragility. If glass falls to the floor, it shatters all too easily. So: a terrible material in terms of fragility."

Even laminated glass is not ideal, says Francois Barthelat of McGill University in Montreal. It is true that an intermediate layer made of plastic ensures that the windshield of a car, for example, does not break into pieces if a stone falls. But more or less long cracks form, because of which the entire pane has to be replaced often enough. So the Canadians looked for an alternative - and found it with Mother Nature:

"Our model is mother-of-pearl, the inner shell of certain mussels. For the most part, mother-of-pearl consists of calcium carbonate, which is actually a very fragile mineral. But it is also criss-crossed with thin layers of protein entire clamshell. "

The protein content in mother-of-pearl is low, just five percent. But it is enough to act as a kind of crack stopper: the protein layers pick up a crack and absorb it so that it cannot spread any further - the mussel shell remains intact. But how can this natural trick be transferred to technology?

Effective shock absorber made of glass and polymer

Barthelat and his people tried the laser:

"With the laser, we engrave millimeter-sized contours in thin panes of glass, they have the shape of honeycombs. And then we glue several of these panes of glass together with a polymer."

The result is similar to a brick wall with tiny pieces of glass as bricks and the polymer as mortar. If this material receives an impact, the glass bricks can give way, being held together by the polymer mortar. A highly effective shock absorber, that is what the load tests showed:

"We made panes from our material and deliberately maltreated with a rod. It turned out that the material is two to three times more stable than laminated glass. When we saw that, we were pretty satisfied."

Indeed: the slow motion shots are impressive. When hit by a metal rod, an ordinary pane of glass shatters into a thousand pieces, and laminated glass gets innumerable cracks. The disc made of artificial mother-of-pearl, on the other hand, only dents a little at the joint, but otherwise remains intact.

Diverse uses

A material that should be versatile, says Francois Barthelat:

"We are thinking of more stable windows and glass facades for architecture. But that could also be useful for cars and airplanes, or as better hail protection for solar cells. It would also be interesting to use them in smartphones and tablets. Then they would not break so quickly if they did that fall down. "

But before that, the experts still have to tinker a little. Because so far they have only succeeded in manufacturing panes several millimeters thick. For smartphones, on the other hand, you need layers of glass that are no thicker than a third of a millimeter. And there are more questions to be answered. For example: How durable is the polymer mortar, especially in a harsh environment, and how long does it remain as transparent as glass? At least one thing is not a problem, says Barthelat - inexpensive mass production:

"With our technology, the material can be produced quite cheaply in large quantities. This is different from many other research approaches, in which you can often only produce tiny samples from break-proof glass. As far as commercialization is concerned, this is a plus point for our method. "