Behaviour of n-alkanes confined between iron oxide surfaces at high pressure and shear rate: A nonequilibrium molecular dynamics study

• Published in: Tribology international 2019-09, Vol.137, p.420-432
• Main Authors: Echeverri Restrepo, Sebastián, van Eijk, Marcel C.P., Ewen, James P.
• Format: Article
• Language: English
• Subjects: Alkanes; Coefficient of friction; Couette flow; Dynamic structural analysis; Elastohydrodynamic lubrication; Iron oxides; Long range order; Lubrication; Molecular dynamics; Molecular structure; Shear rate
• ISSN: 0301-679X; 1879-2464
• DOI: 10.1016/j.triboint.2019.05.008

The behaviour of n-alkanes confined and sheared between iron oxide surfaces has been studied using nonequilibrium molecular dynamics simulations. The molecular extension, orientation, film structure, flow, and friction have been investigated for a range of n-alkane chain lengths under conditions representative of the elastohydrodynamic lubrication regime. At high pressure, the molecules show strong layering and long-range order, suggesting solid-like films. Conversely, high shear rates result in less elongated, layered, and ordered molecules; indicating more liquid-like films. Although Couette flow is usually observed for short n-alkanes, the flow is often non-linear for long n-alkanes. The friction coefficient increases logarithmically with shear rate, but the slope decreases with increasing pressure such that it becomes insensitive to shear rate for long n-alkanes.