  We study the effect of atomic scale surface-lubricant interactions on
nanoscale boundary-lubricated friction, by considering two example surfaces -
hydrophilic mica and hydrophobic graphene - confining thin layers of water in
molecular dynamics simulations. We observe stick-slip 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.
