Founder of TriboNet, Editor, PhD (Tribology), Tribology Scientist at ASML, The Netherlands. Expertise in lubrication, friction, wear and contact mechanics with emphasis on modeling. Creator of Tribology Simulator.
Brasenia schreberi mucilage – superlubric biological liquid
21.03.2016
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.
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This is an amazing discovery, especially the ability of the researchers to achieve 0.004-0.006 CoF superlubric states. But, I was struck by an interesting fact…
The stable mucilage adsorption (hydrogen bonding) layer formed on the ultra-smooth quartz substrate was measured at 8nm thickness, that being more than twice the Ra height of the remaining surface asperities on a car engine part measured after ISN by Phantaslube® technology!
Once you ponder that scale for a moment, the magnitude of the ISN technology becomes fully evident.
What I was interested in here is that a liquid from a mucilage of Brasenia schreberi can be so good. 🙂
Of course, but the superlubricity seen was in the lab, on ultra-smooth silicon substrate. This is related to an earlier point regarding “real world” application versus that which is seen only in the lab and incapable of commercial use. If machined metal parts normally range between 100 nm – 200 nm Ra, an 8 nm mucilage layer isn’t going to do much. That’s the point with ISN technology and trying to rescue tribologists out of the prison of their HDL thought processes. HDL is over. If the lubrication technology leaves asperities on the frictional contact surfaces, it is doomed to failure – no matter how good the lubricant is.
Yes, I agree, the limit of the classical lubrication is reached. But we will still probably having it around for sometime due to reliability issues and things like that. And actually, in some applications, there is a need in high friction, or a balance between high and low friction. Since lubrication is a well known area, it may be attractive to use then.