New use for liquid crystal

Researchers have developed an entirely new class of substance that can be used as a lubricant: liquid crystalline fluid. Although it is a liquid, its molecules display directional properties like crystals do.

A consortium that includes the Fraunhofer Institute for Mechanics of Materials IWM says that when two surfaces move in opposite directions, the liquid crystal molecules between two surfaces align themselves so that the frictional resistance is extremely low. This enables nearly frictionless sliding.

While liquid crystals are known for their use in liquid crystal displays (LCDs) in TV screens and mobile phones, Nematel GmbH suggested that they could be used as lubricants. The company turned to Fraunhofer IWM to see if the idea would work.

Dr Tobias Amann applied the lubricant made from liquid crystal between two metal workpieces. “Even in the first test, we measured extremely low friction coefficients,” Dr Amann said.

The Fraunhofer researchers discovered that liquid crystal is suitable as a lubricant because its molecules are long and thin.

“When used as a lubricant between two surfaces that slide past each other, the molecules become aligned in parallel to each other in ordered boundary layers,” explained Dr Andreas Kailer, acting director for the Tribology business unit at Fraunhofer IWM. These layers are very stable but slide easily over each other, keeping friction and wear to a minimum.

Still, much was missing before a liquid crystal lubricant suitable for practical applications could be developed. Fraunhofer IWM launched a project along with Nematel and the lubricant experts at Dr Tillwich GmbH in 2010, sponsored by the German Federal Ministry of Education and Research (BMBF).

Susanne Beyer-Faiss, a chemist at Tillwich, improved the liquid crystal’s stability with help from additives. At the same time, her colleague Werner Stehr built a special test unit that uses laser technology to enable contact-free measurement of the extremely low friction coefficients.

At Fraunhofer IWM, Dr Amann tested different liquid crystals manufactured by Dr Holger Kretzschmann at Nematel; among other things, Dr Amann conducted friction experiments with various materials, including iron, copper and ceramic. He also examined the chemical mechanisms displayed during friction and the effects of mixing different liquid crystal molecules.

Dr Amann deciphered the mechanisms that are responsible for these ultra-low frictional coefficients and discovered how to further optimise the new lubricants in specific ways. He also examined the chemical mechanisms displayed during friction and the effects of mixing different liquid crystal molecules. When the project came to an end, the partners had produced a liquid crystalline lubricant prototype that performed best in sliding bearings made of iron.

For this pioneering work, Dr Amann, Dr Kailer, Beyer-Faiss, Stehr and Dr Kretzschmann received the Stifterverband Science Prize, which is awarded every two years for scientific excellence in applied research projects.

Currently, the award winners are developing innovative sliding bearings lubricated with liquid crystal for small electric motors for use in the automobile industry, for instance in alternators or windshield wiper motors.