Microscopy
Confinement-induced refractive index change
Equipment
Materials
Plain strain moduli for the experimental interfaces
Surface cleaning
Roughness measurement
Friction
Contact area and load-bearing area size and average thickness of liquid layer calculation
Slope, root-mean-square roughness of the surfaces, and pressure
Average thickness measurement during sliding
Connection between theory and experiment
Viscosity as a function of specific film thickness
Plasticity in glass-on-glass contacts
Calculation of the average contact pressure
Fluorescent liquid adsorption
Change of dry friction coefficient with roughness and waiting time
The ratio between wet and dry friction coefficients was calculated on the basis of the assumption that the contribution of dry-on-dry contacts to the wet friction coefficient was negligible. Shear stress in the liquid is equal to shear stress in the material. Thus, τ=FA=μFNA=ηUh. This way, we found a relation for the friction coefficientμ=ηUAhFN(3)where η is the estimated viscosity, U is the sliding speed, A is the load-bearing area, h is the average thickness of the liquid, and FN is the normal force.
As the viscosity was estimated on the basis of ΛI and to compare data with the measurements in Fig. 3B, we plot the predicted ratio of dry and wet friction coefficients as a function of ΛI (see fig. S6).