Schemes of the sin strain input wave (─) and shear stress output response (red ─) (the dotted line represents the π/4 phase shift output wave (- - -)), and corresponding low frequency dynamic spectra (logarithmic representation). a) Solid-like behavior: input and output waves are close in phase: G′ > G″ with G′ and G″ weakly dependent on the frequency. b) Viscous behavior: input and output waves are out of phase with Δϕ > π/4 (here Δϕ = π/2) with G′ negligible and G″ vanishing with the frequency. c) Improving liquid/surface interactions reduces the dissipation, suppresses the low frequency noise and makes appear an elastic response (Fig. 5a).