Rubber-Like Glass Stretches at Transition Point

A ‘rubber-like’ glass has been developed by researchers in Japan. Scientists from the Tokyo Institute of Technology and Asahi Glass have discovered a type of oxide glass that behaves differently when it is stretched from a supercooled, liquid state.

The ‘mixed alkali metaphosphate glass’ possesses a molecular structure similar to that of organic rubber: long, soft, straight chain molecules. It was found to expand and contract like rubber at a temperature close to the ‘glass transition temperature’ (Tg) (when the glass changes from a supercooled liquid to a solid).

Lithium, sodium, potassium, cesium and phosphorus oxide were used to form the metaphosphate glass. It was stretched when supercooled. Upon heating and elongation, the straight chain molecules in the glass became highly orientated and the glass itself became rubber-like. Further heating the glass made it shrink by around 35% before returning to its original unordered molecular state. The process is known as ‘entropic elasticity’, and this is the first time that a type of glass has been shown to display it.

At room temperature, the glass is as brittle as normal glass. It is only when it is heated to the vicinity of Tg that it exhibits its stretchablitity.

The glass may have applications in high temperature or strongly oxidative environments.