  We introduce a model for zwitterionic monolayers and investigate its
tribological response to changes in applied load, sliding velocity, and
temperature by means of molecular-dynamics simulations. The proposed model
exhibits different regimes of motion depending on temperature and sliding
velocity. We find a remarkable increase of friction with temperature, which we
attribute to the formation and rupture of transient bonds between individual
molecules of opposite sliding layers, triggered by the out-of-plane thermal
fluctuations of the molecules' orientations. To highlight the effect of the
molecular charges, we compare these results with analogous simulations for the
charge-free system. These findings are expected to be relevant to nanoscale
rheology and tribology experiments of locally-charged lubricated systems such
as, e.g., experiments performed on zwitterionic monolayers, phospholipid
micelles, or confined polymeric brushes in a surface force apparatus.
