Clarification of the effects of adsorption films of ester-blended oil on friction by in situ reflectance spectroscopy

• Published in: Tribology international Vol. 187; p. 108718
• Main Authors: Hirata, Kodai, Murashima, Motoyuki, Umehara, Noritsugu, Tokoroyama, Takayuki, Hashizume, Naoya, Lee, Woo-Young, Takekawa, Daisuke, Narita, Keiichi
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.09.2023
• Subjects: Ester oil; In situ reflectance spectroscopy observation; Mixed lubrication condition; Oil adsorption; Ester oil; Mixed lubrication condition; In situ reflectance spectroscopy observation; Oil adsorption
• ISSN: 0301-679X
• DOI: 10.1016/j.triboint.2023.108718

In recent years, the demand for friction reduction in oil lubrication systems has become increasingly important due to the need to improve fuel economy and achieve carbon neutrality. Ester-based lubricants are known to show low friction and environmentally friendly, and they have high viscosity indexes. In the present paper, first, in situ reflectance spectroscopy was used to clarify the behavior of the oil-film thickness increase during sliding. The results showed that as the number of ester bonds increased from 1 to 4, the ester oil film thickened and the friction coefficient decreased from 0.10 to 0.06. In addition, oleic-acid-type lubricants were found to have superior ability to form a thicker oil film than the isostearic acid type. •Four esters exhibit different friction properties.•The larger the molecular size, the lower the coefficient of friction.•Esters functionalized with oleic acid have lower friction than isostearic acid types.•In situ reflectance spectroscopy shows the unique behavior of ester/PAO mixtures.•Ester molecules adhere to surfaces and form highly viscous adsorption layers.