Glass is one of the world’s oldest and most versatile of human creations. It is a combination of sand and other minerals. Found almost anywhere, glass is material which has properties which protect us, yet properties which allow it to shatter with ease. It is usually a completely transparent material and has multiple uses. There is no single chemical composition that characterises all glass. However, there is a typical process used in creating glass. The making of glass involves three basic types of ingredients: formers, fluxes, and stabilisers. In the past, glass was typically made with the former silica sand (SiO2). Being melted at 1700°C, it was not a practical and economically efficient method to create glass. This led to the addition of fluxes. With the addition of a flux called sodium oxide, the high melting point and viscosity of silica was reduced. To make glasses stronger and more durable, stabilisers are added. The most common stabiliser is lime (CaO), but others are magnesia (MgO), baria (BaO), and litharge (PbO). These stabilisers ensure that glass is more durable and less brittle. Glass is considered as an amorphous solid, being a solid material obtained from liquid that does not crystallise during cooling. Thus glass is often referred to as a supercooled liquid.
Glass is versatile as it has the ability to obtain different properties, making them more durable like ‘bullet proof glass’ or change colours, from opaque to transparent like ‘switchable glass’.
Recently, a new type of glass has been discovered. Labelled as ‘self healing glass’ and made from a low weight polymer – a polymer being a materials made of long, repeating chains of molecules – called polyether thioureas, the glass can heal breaks when pressed together by hand without the need for high heat to melt the material. All that is required for the glass to repair itself is applied pressure for at least 30 seconds, to be done at 21° (room temperature). Having only been discovered in December of 2017, this concept is not yet available to the public.
The properties of the polyether thioureas glass were discovered by accident by graduate school student Yu Yanagisawa, who was preparing the material as a glue. Yanagisawa found that when the surface of the polymer was cut the edges would adhere to each other, healing to form a strong sheet after being manually compressed for 30 seconds at 21°C. The research, published in Science, by researchers led by Professor Takuzo Aida from the University of Tokyo, promises healable glass that could potentially be used in phone screens and other fragile devices, which they say are an important challenge for sustainable societies.
Smartphone manufacturers have already used self-healing materials in devices. LG’s G Flex 2 shipped in 2015 with a coating on its back that was capable of healing minor scratches over time, although failed to completely repair heavier damage.
This new concept regarding the development of ‘self healing glass’ is important because this technology is more solely focused for the use on smartphones. With more than 2.2 billion smartphone users, and over $10 billion being spent on phone screen repairs, having ‘self healing glass’ would dramatically reduce the amount of money spent on repairs, benefitting the wider community. It could could also triple the lifespan of everyday products like car windows, construction materials, fish tanks and even toilet seats.
The new polymer glass is “highly robust mechanically yet can readily be repaired by compression at fractured surfaces”. The secret lies in the thiourea, which uses hydrogen bonding to make the edges of the shattered glass self-adhesive, according to Yanagisawa’s study.
Poly-ether-thiourea, on the other hand, is reported to exhibit an unusual hydrogen-bonding pattern that zig-zags through the material and promotes more even reparability without irregular crystallisation. Therefore, the polymer can regain its normal conformation and appearance after damage. Poly-ether-thiourea, like glass, has a markedly slow diffusion profile, but apparently heals itself much better than glass nonetheless.
The properties of poly-ether-thiourea, therefore, apparently allow it to “stick” back together at broken edges, and seal such a fracture together by itself in response to compression and room temperatures alone.