Study reveals that solidified lubricants do not change back to liquid form

Oct 18, 2011

A new study by GW Professor Yongsheng Leng, assistant professor of engineering and applied science, and postdoctoral scientist Yajie Lei, reveals that solidified lubricants in tight pores do not change back to a liquid form. The new discovery will help in understanding and designing new lubricant to improve our fuel economy.

This study was published today by the American Physical Society (APS) and can be viewed at this link

Stick-slip between solids, which produces squeaks heard in our daily lives, can also happen in lubricated contact. For example, engine oil lubricates our car engine, but if the gap in the lubricant is too tight, the lubricant will get stuck or solidified, leading to stick-slip motion and high friction.

Many physicists believe that this stick-slip friction is associated with the alternate changes in the physical property of the lubricant, for example, during the stick the lubricant changes to a solid and during the slip, the solidified lubricant changes back to a liquid.

However,  this new study by molecular dynamics computer simulations shows that during the slip the solidified lubricant in very tight pore does not change back to a liquid. Instead, it simply undergoes molecular slips inside the film. Through the time variations of the frictional force and energy changes during the stick-slip cycle, this study further reveals how the friction energy is lost during the different stages of the stick and slip.

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not rated yet Oct 18, 2011
Interesting. Little tiny rapid phase changes o,O ?

*wearing dunce cap*
not rated yet Oct 18, 2011
It's the well known effect of surface tension. The melting/boiling point of materials is increased/decreased significantly, when their surface gets high negative/positive curvature.

not rated yet Oct 19, 2011
I just read about interesting experiments, where tiny bubbles containing the mixture of oxygen and hydrogen are burning spontaneously, whereas the large bubbles or the mixture of gases inside of bottle remains stable.


One of the high level explanation of this interesting phenomena could be, inside of tiny bubbles of positive space curvature the pressure is elevated in such a way, the combustion of gases proceeds spontaneously there. Such finding could have many practical applications: we could burn the flammable gases safely, if we would pass their mixture with oxygen through tiny porous membrane submersed in water.

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