Stick-Slip Control in Nanoscale Boundary Lubrication by Surface Wettability

Abstract

We study the effect of atomic scale surface-lubricant interactions on nanoscale boundarylubricated friction, by considering two example surfaces -hydrophilic mica and hydrophobic graphene -confining thin layers of water in molecular dynamics simulations. We observe stickslip dynamics for thin water films confined by mica sheets, involving periodic breaking-reforming transitions of atomic scale capillary water bridges formed around the potassium ions of mica. However, only smooth sliding without stick-slip events is observed for water confined by graphene, as well as for thicker water layers confined by mica. Thus, our results illustrate how atomic scale details affect the wettability of the confining surfaces, and consequently control the presence or absence of stick-slip dynamics in nanoscale friction.

Atomic-Scale Sliding Friction on Graphene in Water

“…All the MD force curves shown in this work are time averages (over 25 ps) of the instantaneous forces obtained from single SMD runs. We have confirmed (see Supporting Information) that this procedure, commonly used to measure friction in vacuum, 19,[22][23][24]33 is also able to account for the entropic contribution of friction in liquid environments. In fact, the maximum force deviation obtained from a single SMD curve and the force calculated using multiple SMD runs and the Jarzysnki equation estimated is 0.0175 nN (see Supporting Information).…”

Surface dissimilarity affects critical distance of influence for confined water

“…Behaviour of water conned between surfaces of varying degrees of hydrophilicity has not been investigated until very recently. [1][2][3][4][5] Most of the mineral water interaction systems deal with only single surface 6,7 or similar surfaces 8,9 (homogenous) on either end of the conned volume. Water density, orientation and H-bond formation of such similar surface combinations have been studied extensively.…”

Organogel as durable anti-icing coatings

“…Besides, before ice detachment, force on the LP-OG surface increases rapidly, which means that lubricating domains on OG and effect of elastic deformation can be neglected. The absence of stick-slip dynamics in the sliding friction indicates that no capillary bridges are formed for thin LP lubricating layer, which can exert its bulk fluidity [36]. Temperature dependence of ice adhesion on LP-OG comes from dependence of viscosity on temperature.…”