Drop motion induced by vertical vibrations

Abstract

We have studied the motion of liquid drops on an inclined plate subject to vertical vibrations. The liquids comprised distilled water and different aqueous solutions of glycerol, ethanol and isopropanol spanning the range 1-39 mm 2 s −1 in kinematic viscosities and 40-72 mN m −1 in surface tension. At sufficiently low oscillating amplitudes, the drops are always pinned to the surface. Vibrating the plate above a certain amplitude yields sliding of the drop. Further increasing the oscillating amplitude drives the drop upward against gravity. In the case of the most hydrophilic aqueous solutions, this motion is not observed and the drop only slides downward. Images taken with a fast camera show that the drop profile evolves in a different way during sliding and climbing. In particular, the climbing drop experiences a much bigger variation in its profile during an oscillating period. Complementary numerical simulations of 2D drops based on a diffuse interface approach confirm the experimental findings. The overall qualitative behavior is reproduced suggesting that the contact line pinning due to contact angle hysteresis is not necessary to explain the drop climbing.

Directional motion of vibrated sessile drops: A quantitative study

“…These limitations can be tackled with various means, like the use of superhydrophobic surfaces [5,6], electrowetting [7], a combination of both [8] or Leidenfrost drops on ratcheted surfaces [9,10]. Several studies have evidenced that mechanical vibrations of the substrate can induce drop motion [11][12][13][14][15][16][17][18][19], as well as particle resuspension [20]. These phenomena have generic features, in common with other related situations : the generation of surface waves on thin films by external vibrations [21], the non-harmonic response of drop subjected to MHz ultrasonic surface waves inducing both their motion and low-frequency oscillations [22], or the crawling motion of sessile droplets on solid surfaces via acoustic radiation pressure [23].…”

“…Also recently, Borcia et al [17], Sartori et al [18] addressed the vibration-induced motion of two-dimensional sessile drops with phase-field numerical methods, with comparisons to experiments. Although CAH could not be included within these models, they could capture realistic behavior, especially in the influence of viscosity, wetting-conditions [17], or even the occurrence of parametric forcing with a drop responding at half the forcing frequency [18].…”

Controlling the distance of highly confined droplets in a capillary by interfacial tension for merging on-demand

“…The liquids solutions are chosen to investigate the dependence of the droplet speed for variable surface tensions γ, while keeping λ constant and, vice versa, to study the effect of the viscosity ratio for a fixed interfacial tension. 50 As a matter of fact, as shown in Table 1, the presence of glycerol in water does not strongly affect the value of γ, while it causes a variation of one order of magnitude in λ (from λ ≃ 0.24 to λ ≃ 3.40). Differently, adding ethanol or Tween20 to the aqueous phase does not induce significant variations in λ, while γ drastically changes.…”

Climbing a slippery slope

“…As shown in figure 1(c), the vertical oscillations alternately make the drop tall or flat, depending on the direction of the acceleration; superimposed horizontal vibrations will rock the drop more when the drop is tall, and thus more compliant, compared to when the drop is flattened and less compliant. Various models with differing assumptions and approximations have been proposed to explain the cause of climbing drops (Benilov 2010;John & Thiele 2010;Benilov 2011;Benilov & Billingham 2011;Benilov & Cummins 2013;Borcia, Borcia & Bestehorn 2014;Sartori et al 2015;Ding et al 2018). A recent overview of these is given in Bradshaw & Billingham (2018).…”

“…www.cambridge.org/core/terms. https://doi.org/10.1017/jfm.2019Phase diagram for a water drop (a) on a PMMA surface from(Sartori et al 2015) and (b) on a LIS from…”