[freebeard]

Let's fool around and see what we can find out.

phys.org: Solid state lubricant uses atomically thin sheets to achieve extremely low friction

The team has now presented a new type of material with special properties: The lubricant COK-47 is not liquid like lubricating oil, but a powdery solid substance. On a nanoscale, it consists of stacks of atomically thin sheets, like a tiny stack of cards.

When the material comes into contact with water molecules, these platelets can slide past each other very easily—a so-called tribofilm is created, which ensures extremely low friction. This makes COK-47 a highly interesting lubricant in humid conditions.

The research is published in the journal Advanced Science.

Organic and inorganic: The best of both worlds

The research team has been working with metal-organic frameworks (MOFs) for years. These are a new class of materials that consist of inorganic building blocks connected by organic molecules. There are many possibilities of adapting these materials at an atomic level for a specific purpose—for example, Dominik Eder's group has used them in recent years as photocatalysts for hydrogen production or for water purification.

In most cases, metal-organic framework compounds are nanoparticles that contain clusters of metal atoms, linked by organic compounds. "However, the material COK-47 has an important special feature," explains chemist Pablo Ayala, co-author of the current study. "The inorganic components of this material are two-dimensional sheets of titanium oxide—and this dramatically influences its behavior."

Detailed investigations have now shown that in a humid environment, water molecules separate the bonds between the titanium oxide sheets, allowing the flat structures to slide past each other and thus form a so-called "tribofilm." Such a sliding film can be extremely effective in reducing friction, for example between two moving parts in a machine.