The effect of molecular structure on the traction properties of polyglycol oils was investigated using a traction tester, and in-situ observation of the oil film was performed with a micro-Fourier transform infrared spectrometer under elastohydrodynamic lubrication conditions. The sample oils used were polypropylene glycol (PPG) diol, PPG triol, PPG dimethyl ether, PPG diester, PPG diamine, PPG triamine, and poly-α-olefin. The traction coefficient and oil film thickness of the sample oils were sensitive to the functional group at the terminal of the molecule. The sample oil containing polar functional group is larger in oil film thickness and traction coefficient than non-polar hydrocarbon oil, poly-α-olefin. These results suggest that the hydrogen bonding of functional groups was strengthened by high pressure in the Hertzian contact region. Moreover, the effect of water in the sample oils on the traction behavior was discussed. Water was dissolved into the sample oils from the atmosphere during the lubrication test, and it is implied that water in PPG diamine affect the traction coefficient.
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