The kinetic friction coefficient of neutral and charged polymer brushes

The compression-dependence of the friction coefficients of neutral and charged polymer brushes at the same surface coverage is studied using dissipative particle dynamics (DPD) at two different shear rates. The chemical potential of the solvent particles is kept constant along the compression curve in order to mimic the experimental conditions. We conclude that the kinetic friction coefficient between charged brushes is higher than that of neutral brushes at low compressions and smaller at high compressions. These differences are small. We also show that it is possible to simulate ultra-low friction coefficients comparable with experiments using the smallest shear rate accessible in a mesoscale simulation. The unexpected behavior of the shear deformation-induced structural heterogeneities in charged polymer brushes calls for further experiments to elucidate this local reorganization of the ions in adsorbed charged polymers.