A new scaling number reveals droplet dynamics on vibratory surfaces

The Challenge of Superhydrophobicity: Environmentally Facilitated Cassie–Wenzel Transitions and Structural Design

“…These capillary waves alter the shape of the interface, prompting fluid movement and adjustments in the pressure distribution at the interface. [107,109] Concurrently, the viscous effects within the droplet and the dissipation of the TPCL are impeded. [110] It is crucial to grasp the mechanism and critical conditions of the C-W transition during droplet vibration.…”

“…In State 2, the droplet's CA decreases rapidly, the contact radius increases, and droplet diffusion occurs. Song et al [ 107 ] discovered that the diffusion diameter of the droplet is related to the vibration Web number ( $$We{b}^* = \ \rho U_{\mathrm{V}}^2{D}_0/\gamma $$, where, U v is the velocity amplitude of vibration) but not to the vibration frequency ( Figure a). The diffusion velocity is directly proportional to time ( x ≈ t ).…”

“…[ 103b ] The dynamic pressure value, which is positively correlated with the Web * value, promotes droplet expansion behavior. [ 107 ] The transition occurs when the input energy is above the threshold. For the vibration energy threshold provided by SAW, its size is: [ 108 ] $$$$\begin{equation}E \approx \frac{{{r}^*}}{x}{{\pi}}R_{\mathrm{c}}^2{\gamma }_{{\mathrm{SL}}} - {\gamma }_{{\mathrm{SG}}}\end{equation}$$$$Where, r * , x , and R c are the average surface roughness, particle radius, and contact line radius of the droplet, respectively.…”

“…Open symbols, semi-filled symbols, and solid symbols identify that f * = 10, 15, and 28 kHz, respectively. Reproduced with permission [107]. Copyright 2021, Elsevier Inc. b) Spreading dynamics and variation in the CA associated with the (left) leading (edge away from the interdigitated transducer) and (right) trailing (edge close to the interdigitated transducer) edges of the drop under SAW excitation.…”

Superhydrophobic Strategy for Nature-Inspired Rotating Microfliers: Enhancing Spreading, Reducing Contact Time, and Weakening Impact Force of Raindrops

“…It is generally believed that the spreading process of the impacting droplet is driven by inertia and mainly resisted by surface tension, so the maximum spreading coefficient β max is related to the Weber number ( We = ρ D 0 U 0 2 /σ, where ρ is the fluid density, D 0 is the droplet diameter, U 0 is the droplet impact velocity, and σ is the surface tension), which is a measure of the relative importance of the fluid’s inertia compared to its surface tension. Researchers have studied the spreading problem of impacting droplets on superhydrophobic surfaces and developed various scaling laws suitable for different conditions. ,− The contact time τ c is defined as the time from the droplet contacting the surface to its complete rebounding. Previous literature has proved that τ c on flat superhydrophobic surfaces is about 2.6τ 0 , where τ 0 is the inertial-capillary time, τ 0 = (ρ D 0 3 /8σ) 1/2 . , Bird et al first proposed to reduce the contact time by macrostructures, and they achieved a contact time reduction of about 37% on surfaces decorated with superhydrophobic macroscopic ridges .…”