Capillary descent

Abstract

A superhydrophobic capillary tube immersed in water and brought in contact with the bath surface will be invaded by air, owing to its aerophilicity. We discuss this phenomenon where the ingredients of classical capillary rise are inverted, which leads to noticeable dynamical features. (1) The main regime of air invasion is linear in time, due to the viscous resistance of water. (2) Menisci in tubes with millimetre-size radii strongly oscillate before reaching their equilibrium depth, a consequence of inertia. On the whole, capillary descent provides a broad variety of dynamics where capillary effects, viscous friction and liquid inertia all play a role.

Experimental and theoretical studies on the dynamic landing of water striders on water

“…By employing the best fitting (dashed line) of the experimental data, we obtain e max E 0.91 mJ m À1 E 4.55 sl c . In fact, the scaling relation v max 2 B m p À1 we have obtained in eqn ( 7) is consistent with the result of Vella and Li (see eqn (32) in ref. 21), who assumed that there exists a certain value of h max during the occurrence of sinking (Section S6, ESI †).…”

“…When the kinetic energy of the strider completely dissipates, it stands quietly on water (Fig. 3a), reminiscent of the vibration behavior of springs, 23,27,[30][31][32]35 which is attributed to the competition among inertia, capillarity and drag force. Therefore, the oscillation can be described by combining the concept of a damped harmonic oscillator with scaling analysis.…”

“…Therefore, there must exist other mechanisms that account for the dissipation of energy, which makes the present model different from the previous analysis which mainly considered the dissipation induced by liquid viscosity. [30][31][32][33] To figure out the source of dissipation responsible for the degradation of oscillation, we examine the details of the landing process by employing a micro lens (Nikon AF-S 24-120 mm) mounted on a high-speed camera. As shown in Fig.…”

“…In this regard, we are particularly interested in the oscillation of the water surface triggered by the water strider landing. In fact, the capillarity-related oscillation is a fundamental issue in a wide range of systems, such as the bounce and coalescence of drops and bubbles, [22][23][24][25][26][27][28][29] capillary rising in tubes, [30][31][32][33][34] and drop drainage. 35 An investigation of the oscillating dynamics may provide design guidelines to the attitude control of waterwalking bionic robots.…”

How to Compute the Contact Angle inside an Opaque Capillary Tube: A Universal Equation

“…Figure a,b illustrates the geometric configuration of the liquid column inside a capillary tube with an inner diameter of D 0 , assuming a spherical‐crown‐shaped liquid surface with a sphere diameter of D (when D 0 /2 is smaller than the capillary length $$\sqrt {\gamma /\rho {\rm{g}}} $$). [ 17 ] The additional pressure (Δ p , or Laplace pressure), induced by the liquid surface tension ( γ ), leads to the rising or descending height ( h ). As such, the following relationship can be formulated $$\begin{equation} \Delta p = 4\gamma /D = \rho gh \end{equation}$$…”