We directly monitor the absolute separation profiles that function as film thickness between a single glass disk and the charged polyelectrolyte brushes decorated steel slider in water using a home-made slider-on-disk apparatus

which reflects the structural conformation variations and interactions of polymer brushes under externally applied pressure

in addition to probing the relative variation of friction forces under different applied loads and sliding velocities. We find that the polyelectrolyte brushes modified surfaces can sustain high pressure and have extremely low friction coefficients (around 0.006 at pressures of 0.13 MPa; 0.5−0.6 without brushes). The water-lubrication characteristics are correlated to the structural conformation changes of the polyelectrolyte brushes that are mainly governed by electrostatic interactions and the osmotic pressure of counterions inside the polymer chains

which can be used to support and distribute the normal pressure. The apparent thickness of the brush decreases with the increase of loading forces

an increase in the ionic strength causes the polymer chains collapse

and the friction forces increase. This fundamental research is of great importance to understand the mechanical and structural properties of polyelectrolyte brushes and their influences on the tribological behaviors

and helps to design friction/lubrication-controlled surface/interface by taking advantage of polyelectrolyte brushes.