Directional motion of vibrated sessile drops: A quantitative study

Abstract

The directional motion of sessile drops can be induced by slanted mechanical vibrations of the substrate. As previously evidenced [13][14][15], the mechanical vibrations induce drop deformations which combine axisymmetric and antisymmetric modes. In this paper, we establish quantitative trends from experiments conducted within a large range of parameters, namely the amplitude A and frequency f of the forcing, the liquid viscosity η and the angle between the substrate and the forcing axis α. These experiments are carried out on weak-pinning substrates. For most parameters sets, the averaged velocity < v > grows linearly with A. We extract the mobility, defined as s = ∆<v> ∆A . It is found that s can show a sharp maximal value close to the resonance frequency of the first axisymmetric mode fp. The value of s tends to be almost independent on η below 50 cSt, while s decreases significantly for higher η. Also, it is found that for peculiar sets of parameters, particularly with f far enough from fp, the drop moves in the reverse direction. Finally, we draw a relationship between < v > and the averaged values of the dynamical contact angles at both sides of the drop over one period of oscillation.

Development of a Coating-Less Aluminum Superhydrophobic Gradient for Spontaneous Water Droplet Motion Using One-Step Laser-Ablation

“…Thus, the droplet has to overtake an increasing CAH during its trajectory, which also reduces the travel distance. Applying vibration, one could obtain slip mode motion of up to dozens of millimeters 49 with speeds up to 20 mm/s; 50,51 applying a temperature gradient one could observe the motion for a few millimeters; 52 and the combination of the mentioned methods allows motion for a few millimeters with a speed of a few millimeters per second. 53 The method described in the current study shows the motion distance at the same range or at least covers the lower end of that range.…”

Effects of gravity on natural oscillations of sessile drops

“…Ding et al. 2018; Costalonga & Brunet 2020). Recently, several relevant instabilities have been reported in some theoretical literature (Bostwick & Steen 2018; Steen, Chang & Bostwick 2019; Ding & Bostwick 2022 a , b ).…”

“…Note that this horizontal movement should be spontaneous and is different from the directional movement of the drop due to the parametric instability (see e.g. Ding et al 2018;Costalonga & Brunet 2020). Recently, several relevant instabilities have been reported in some theoretical literature (Bostwick & Steen 2018;Steen, Chang & Bostwick 2019;Ding & Bostwick 2022a,b).…”

Energetic study of ultrasonic wettability enhancement

“…If the foresaid thresholds are not exceeded, the vibration of the droplet will be stable and its behaviour can be predicted [15] with a dynamic contact angle. However, this prediction becomes more difficult when working at high frequency.…”