The establishment of a sustainable society requires fuel-efficient vehicles in which lubricants play important roles. Blending optimum amounts of friction modifiers with lubricant is widely used to reduce fuel consumption caused by frictional loss. However, selection of the appropriate blending still strongly depends on experience. To develop a general selection role for the friction-reduction additives based on a quantitative standard, a number of C18-based fatty acids have been evaluated on the solid surfaces by different methods in the present study. In addition to the measurement of the friction coefficient (μ), the adsorption structures of the Langmuir–Blodgett monolayers of the fatty acids and their effects on the friction-reduction behaviors have been investigated using surface pressure–area (π–A) isotherms, sum-frequency generation vibrational spectroscopy and atomic force microscope. The present experimental results demonstrate a certain relationship between the adsorption structures of the fatty acids on the solid surface and their friction-reduction behaviors.
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