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

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.