Fig. 1: AFM slippage measurement.
a Schematics of the tuning fork AFM system, with a typical resonance curve on (b). In (c), we sketch the drainage flow between the micrometric tungsten tip and the mica surface. If we extrapolate linearly the velocity profile in the solid. It vanishes at a non-zero distance from the wall: the slip length. The no-slip boundary condition (b = 0) thus corresponds to a zero velocity at the surface. On the other hand, a perfect slip boundary condition (zero friction) is equivalent to a vanishing of the stress at the interface. The AFM system allows to extract the complex mechanical impedance of the contact at 30 kHz \(Z={Z}^{\prime}+Z{''}\) for a given sphere-plane distance D. d Elastic response \({Z}^{{\prime} }\) of the confined liquid. The inset shows a zoom on the mechanical contact where the phase regulation is suddenly lost and the frequency shift saturates at −1 kHz. This discontinuity allows us to determine the position of the mechanical contact (D = 0) with nanometric resolution. e Typical approach curve at room temperature (blue) showing the dissipation increasing as more energy is lost to the confined viscous flow. In orange, we show the inverse dissipative impedance 1/Z″ versus sphere-plane distance D.
