Molecular Alignment-Mediated Stick-Slip Poiseuille Flow of Oil in Graphene Nanochannels

The flow behavior of oil in nanochannels has attractedextensiveattention for oil transport applications. In most, if not all, ofthe prior theoretical simulations, oil molecules were observed toflow steadily in nanochannels under pressure gradients. In this study,non-equilibrium molecular dynamics simulations are conducted to simulatethe Poiseuille flow of oil with three different hydrocarbon chainlengths in graphene nanochannels. Contrary to the conventional perceptionof steady flows of oil in nanochannels, we find that oil moleculeswith the longest hydrocarbon chain (i.e., n-dodecane)exhibit notable stick-slip flow behavior. An alternation betweenthe high average velocity of n-dodecane in the slipmotion and the low average velocity in the stick motion is observed,with a drastic, abrupt velocity jolt of up to 40 times occurring atthe transition in a stick-slip motion. Further statisticalanalyses show that the stick-slip flow behavior of n-dodecane molecules originates from the molecular alignmentchange of oil near the graphene wall. The molecular alignment of n-dodecane shows different statistical distributions understick and slip motion states, leading to significant changes of frictionforces and thus notable velocity fluctuations. This work providesnew insights into the Poiseuille flow behavior of oil in graphenenanochannels and may offer useful guidelines for other mass transportapplications.

Automated summary

The flow behavior of oil in nanochannels has been extensively studied for oil transport applications. In this study, non-equilibrium molecular dynamics simulations are used to investigate the Poiseuille flow of oil in graphene nanochannels. Contrary to prior observations of steady flows, it is found that oil molecules with long hydrocarbon chains exhibit notable stick-slip flow behavior. The stick-slip motion is attributed to changes in molecular alignment near the graphene wall, resulting in significant friction force variations and velocity fluctuations.