Japanese scientists have designed a new type of mud from a mixture of water and clay that can also act as an alternative to plastic.
According to a report in New Scientist, Takuzo Aida and his team at the University of Tokyo, Japan, mixed a few grams of clay with 100 grams of water in the presence of tiny quantities of a thickening agent called sodium polyacrylate and an organic “molecular glue”. The thickening agent teases apart the clay into thin sheets, increasing its surface area and allowing the glue to get a better hold on it.
This means that, while the mixture is almost 98 per cent water, it forms a transparent and elastic hydrogel with sufficient mechanical strength to make a 3.5 centimetre-wide self-standing bridge.
“The strength of the material depends on the sum of the forces acting between the molecules in the clay nanosheets and the glue,” said Aida. These so-called supramolecular forces, such as hydrogen bonds, also help to trap water molecules between the clay sheets.
Some other hydrogels rely on covalent chemical bonds rather than supramolecular forces for their strength. “One disadvantage of this is that when the covalent bonds break, the material irreversibly loses its strength,” said Aida. Supramolecular forces, on the other hand, can easily reform, so if the material fails under stress it can quickly regain its strength.
According to Aida, the gel takes just 3 minutes to form, and making it requires no understanding of the chemical process involved. “One of the primary breakthroughs is the overall simplicity of the procedure coupled with the exceptional physical properties of the final assemblies,” said Craig Hawker at the University of California in Santa Barbara.
“Toughness, self-healing and robustness are just some of the initial physical properties that will be found for this new class of materials,” he said. “I predict that this approach will lead to the design of even more impressive materials in the near future,” he added.