Superlubricity is a state of low friction, broadly defined as the state with the coefficient of friction lower than 0.01. This level is not achievable with classical lubrication mechanisms and currently other methods are being searched for. Existing methods of superlubricity require specific conditions, material combinations or limited to the nano- or micro scales.
A group of the researchers from Tsinghua University, Beijing work on the topics of macro-scale superlubricity based on the principles of formation of the hydrogen layer between the surfaces in contact. The layer, is capable of withstanding high pressures and at the same time is easy to shear, which results in super low friction coefficients. They showed that the mixture of glycerol and water is capable of producing such a layer and superlubricity can be achieved and controlled with widely used steel materials and applied conditions.
Recently, they explored unique tribological properties of biological liquid obtained from mucilage of Brasenia schreberi – an aquatic floating plant, which is abundant in China. They used this liquid as lubricant to decrease the friction between quartz glass surfaces and achieved superlubric state of friction – 0.004-0.006. They found, that superlubricity occurs when a stable mucilage adsorption layer is formed on the quartz surfaces (8 nm thick) due to hydrogen bonding. This layer can withstand a high load and also easy to shear, so that the resultant friction coefficient is low.
The research revealed the mechanisms of the superlubricity in the particular case, but also can help to develop new lubricants to achieve and control the superlubricity state.
Further details can be found in the original article by Liu P, Liu Y, Yang Y, Chen Z, Li J, Luo J., Mechanism of biological liquid superlubricity of Brasenia schreberi mucilage.
Credit for image: Dacrycarpus~commonswiki.