Figure 4.

Thin-film rheology and tribology for dry [C₂C₁Im][EtSO₄] at 0 and 35% RH. (a) Surface forces. (b, f) Friction as a function of sliding velocity at selected film thicknesses: (b) D₀= 2 nm, D_+Δ = 3 nm at loads of 1.3 and 0.4 mN, respectively, for the dry IL, and (f) D₀ = 0.8, D_+Δ = 3 nm and D_+2Δ = 5 nm at the applied loads of 0.026, 0.26, and 1.8 mN, respectively, for the IL equilibrated at 35%RH. (d, e) Lateral force as a function of time while sliding at 300 nm/s for a film thickness D₀ at 0 and 35% RH. The noise is of the same order of magnitude as the variation of the lateral force. (c, g) Effective viscosity η_eff as a function of strain rate for IL films with two different thicknesses (D₀ and D_+Δ) at (c), 0% RH and (g), 35% RH. G′ and G″ are shown in Figure S1d. Bulk viscosity = 0.115 Pa·s.⁴⁰ The water content in the bulk IL at 35% RH is 1.51 water-to-IL mole ratio (12.56 vol %). (a, c) Reprinted (adapted) with permission from ref (34). Copyright 2022 American Chemical Society.