Figure 5. Rationalizing friction between oppositely charged surfaces.

(a) Charge densities in cation (red)- and anion (blue)-rich layers normalized by the surfaces charge density, q_s. (b) Charge dependence of the mean distances between the wall and the forth layer, d_4-S (red curve), between the fourth and third layers d_3–4 (blue curve) and between the third and second layers, d_3-2 (black curve). (c) Velocity profiles inside the IL film for the indicated values of q_s. (d) Charge dependencies of the friction force shown at load F_L = 188 MPa.