Motion of Newtonian drops deposited on liquid-impregnated surfaces induced by vertical vibrations

We have studied the motion of drops on inclined liquid-impregnated surfaces (LISs) subject to vertical vibrations. The liquid drops comprise distilled water and different aqueous solutions of glycerol of increasing viscosity. The use of weak pinning LISs strongly affects the dynamical phase diagram. First of all, there is no trace of the dominant static region at low oscillating amplitudes reported for oscillating solid surfaces characterized by contact angle hysteresis. On the contrary, at sufficiently low oscillating amplitudes, the drops always move downwards with a velocity that depends only on the drop viscosity. Further increasing the oscillating amplitude may drive the drop upwards against gravity, as reported for dry surfaces. The use of more viscous drops widens this climbing region. Arguably, the main novelty of this work concerns the observation of two distinct descending regimes where the downhill speed differs by a factor of five or more. Fast-rate videos show that the evolution of the drop profile is diverse in the two regimes, likely because the vertical oscillations reduce the effect of the oil meniscus surrounding the drop at high accelerations.