A Japanese research group prototyped what it claims is the world's first self-repairing glass that repairs itself after being broken.
The prototyped glass is made of a polymer material called "polyether thiourea." When the group evaluated the repair performance of the material, the mechanical strength of the material was restored to a level equivalent to the level before it was broken, after several hours of pressure bonding at a room temperature.
The group is led by Takuzo Aida, professor at the Department of Chemistry & Biotechnology, School of Engineering, the University of Tokyo. It developed the glass in cooperation with Yu Yanagisawa, graduate student at the department.
Polyether thiourea is hard and has a smooth surface. The research group found that, when two fracture surfaces of the material are pressed to each other, they fuse together. Considering the elastic modulus and mechanical strength of the material are 1GPa+ and 32MPa, respectively, it is an "astonishing characteristic," the group said.
Polyether thiourea was originally designed as an "intermediary body" for synthesizing polymer. It is called "molecular starch" and strongly adheres to the surface of biological molecule. The group found the characteristic in this process.
Multiple polymer materials having a structure similar to polyether thiourea were synthesized, and their mechanical strength and repair performance were evaluated. As a result, the group found that there are four conditions important for designing a self-repairing glass.
First, it is necessary to ensure local mobility by using a relatively short polymer chain. Second, for realizing a high mechanical strength by using a short polymer chain, it is necessary to form a high-density bridge by hydrogen bonding. Third, the high-density bridge formed by hydrogen bonding should not induce crystallization. Fouth, a structure that facilitates the exchange of hydrogen bonding is important.
The details of the research were published on the Dec 14, 2017, edition of the online version of Science magazine under the title of "Mechanically robust, readily repairable polymers via tailored noncovalent cross-linking."