An axisymmetric film bridge collapses under its own surface tension, disconnecting at a pair of pinchoff points that straddle satellite bubble. The free-boundary problem for the motion and adjacent inviscid fluid has finite-time blowup (pinchoff). This is solved numerically using vortex method in boundary-integral formulation dipole strength distribution on surface. Simulation good agreement with available experiments. trajectory up to carried out. self-similar behaviour observed near shows...

Drawing inspiration from the adhesion abilities of a leaf beetle found in nature, we have engineered switchable device. The device combines two concepts: surface tension force large number small liquid bridges can be significant (capillarity-based adhesion) and these contacts quickly made or broken with electronic control (switchable). grabs releases substrate fraction second via low-voltage pulse that drives electroosmotic flow. Energy consumption is minimal because both grabbed released...

A capillary surface is an interface between two fluids whose shape determined primarily by tension. Sessile drops, liquid bridges, rivulets, and drops on fibers are all examples of shapes influenced contact with a solid. Capillary can reconfigure spontaneously or exhibit natural oscillations, reflecting static dynamic instabilities, respectively. Both instabilities related, review stability precedes the case. The focus case here hydrodynamic surfaces subject to constraints (a) volume...

An inviscid spherical liquid drop held by surface tension exhibits linear oscillations of a characteristic frequency and mode shape (Rayleigh oscillations). If the is pinned on circle contact shapes change frequencies are shifted. The problem inviscid, axisymmetric, volume-preserving constrained pinning along latitude solved here. formulation gives rise to an integrodifferential boundary value problem, similar that for Rayleigh oscillations, in with bowl [M. Strani F. Sabetta, J. Fluid Mech....

Abstract A sessile droplet partially wets a planar solid support. We study the linear stability of this spherical-cap base state to disturbances whose three-phase contact line is (i) pinned, (ii) moves with fixed angle and (iii) that smooth function contact-line speed. The governing hydrodynamic equations for inviscid motions are reduced functional eigenvalue problem on operators, which parameterized by base-state volume through static mobility via spreading parameter. solution facilitated...

During dropwise condensation from vapor onto a cooled surface, distributions of drops evolve by nucleation, growth, and coalescence. Drop surface coverage dictates the heat transfer characteristics depends on both drop size number present at any given time. Thus, manipulating is crucial to maximizing transfer. On earth, manipulation achieved with gravity. However, in applications small length scales or low gravity environments, other methods removal, such as energy gradient, are required....

Abstract A vortex ring is a torus-shaped fluidic vortex. During its formation, the fluid experiences rich variety of intriguing geometrical intermediates from spherical to toroidal. Here we show that these constantly changing can be ‘frozen’ at controlled time points into particles with various unusual and unprecedented shapes. These novel ring-derived particles, are mass-produced by employing simple inexpensive electrospraying technique, their sizes well hundreds microns millimetres. Guided...

A method for determining the stability of general static capillary surfaces is illustrated by application to liquid bridge. Axisymmetric bridges with fixed contact lines under gravity are parametrized three quantities: bridge length L , volume V and Bond number B . The delivers: (i) envelopes in { L, V, } parameter space constant-pressure constant-volume disturbances (generating new recovering classical results), (ii) unstable modes any equilibrium (state instability) once one state known...

In this work, we study the resonance behavior of mechanically oscillated, sessile water drops. By oscillating drops vertically and within prescribed ranges frequencies amplitudes, a rich collection modes are observed their dynamics subsequently investigated. We first present our method identifying each mode uniquely, through association with spherical harmonics according to geometric patterns. Next, compare measured theoretical predictions using both classical theory Lord Rayleigh Lamb for...

High-speed images of driven sessile water drops recorded under frequency scans are analysed for resonance peaks, bands and hysteresis characteristic modes. Visual mode recognition using back-lit surface distortion enables modes to be associated with frequencies, aided by the identifications in Part 1 (Bostwick & Steen, J. Fluid Mech. , vol. 760, 2014, pp. 5–38). is a linear stability analysis that predicts how inviscid drop spectra depend on base state geometry. Theoretically, states...

Drawing parallels to the symmetry breaking of atomic orbitals used explain periodic table chemical elements; here we introduce a droplet motions, also based on but guided by recent spectral theory. By this theory, higher mode shapes are discovered and wettability spectrometer is invented. Motions partially wetting liquid support have natural shapes, motions ordered kinetic energy into table, each characteristic spherical-cap drop volume material parameters. For water having contact angle...

Contact-line mobility characterizes how fast a liquid can wet or unwet solid support by relating the contact angle $\unicode[STIX]{x0394}\unicode[STIX]{x1D6FC}$ to contact-line speed $U_{CL}$ . The changes dynamically with speeds during rapid movement of across solid. Speeds beyond region stick–slip are focus this experimental paper. For these speeds, inertia and surface tension compete while damping is weak. parameter $M$ defined empirically as proportionality, when it exists, between ,...

The classical boundary-layer scaling laws proposed by Howard for Rayleigh–Bénard convection at high Rayleigh number extend to the analogous case of in saturated porous media. We computationally study two-dimensional porous-media near onset this behaviour. main result paper is observation and instabilities that lead deviations from relations. At numbers below regime, fluctuations born a Hopf bifurcation strengthen eventually develop into thermal plumes. appearance plumes corresponds behaviour...

Dynamic wetting phenomena are typically described by a constitutive law relating the dynamic contact angle θ to contact-line velocity UCL. The so-called Davis-Hocking model is noteworthy for its simplicity and relates UCL through mobility parameter M, which has historically been used as fitting particular solid-liquid-gas system. recent experimental discovery of Xia & Steen (2018) led first direct measurement M inertial-capillary motions. This opens up exciting possibilities anticipating...

We analyze shape oscillations of sessile water drops with fully mobile contact lines (CL) aboard the International Space Station. The unique microgravity environment enables study centimeter-sized droplets associated inertial-capillary motions. Plane-normal substrate vibrations induce resonance behaviors quantified by frequency scans from which natural frequencies and mode shapes are identified for nine different hydrophobic surfaces. Experimental observations agree well with, validate, a...

Electroosmosis, originating in the double-layer of a small liquid-filled pore (size R ) and driven by voltage V , is shown to be effective pumping against capillary pressure larger liquid droplet B provided dimensionless parameter σ 2 /ε|ζ| VB enough. Here surface tension liquid/gas interface, ε dielectric constant, ζ zeta potential solid/liquid pair. As size diminishes, required pump eletroosmotically scales as ∼ / . Accordingly, needed smaller higher-pressure droplets can actually decrease...

Centre-of-mass motions of two coupled spherical-cap droplets are considered. A model with surface tension and inertia that accounts for finite-amplitude deformations is derived in closed form. Total droplet volume λ half-length L the tube connects control parameters. The dynamics reside phase-plane. For lens-like < 1, any there a single steady state about which vibrate limit-cycle behaviour. λ>1, symmetric loses stability (saddle point) new antisymmetric states arise oscillations...

This paper presents a new method to determine the zeta potential of porous substrates in contact with liquid. Electroosmosis, arising near solid/liquid boundaries within fully saturated substrate, pumps against capillary pressure from surface tension droplet placed series pump. The is based on measuring liquid/gas interface deflection due imposed electric difference. distinguishing features our technique are accuracy, speed, and reliability, accomplished straightforward cost-effective setup....

Abstract A spherical drop is constrained by a solid support arranged as latitudinal belt. This belt splits the into two deformable caps. The edges of are given lower and upper latitudes yielding ‘spherical belt’ prescribed extent position: two-parameter family constraints. belt-constrained Rayleigh drop. In this paper we study linear oscillations coupled spherical-cap surfaces in inviscid case, viscous case studied Part 2 (Bostwick & Steen, J. Fluid Mech. , vol. 714, 2013, pp. 336–360),...

A static rivulet is subject to disturbances in shape, velocity and pressure fields. Disturbances interfacial shape accommodate a contact line that either (i) fixed (pinned) or (ii) fully mobile (free) preserves the angle. The governing hydrodynamic equations for this inviscid, incompressible fluid are derived then reduced functional eigenvalue problem on linear operators, which parametrized by axial wavenumber base-state volume. Solutions decomposed according their symmetry (varicose)...

Condensation proceeds as dropwise or filmwise depending on the wettability of condensing surface. These two modes condensation have disparate heat transfer coefficients, with often exceeding filmwise. This work reports a surface switchable superhydrophilic to hydrophobic wetting behavior that can exhibit both condensation. Relative highly state, which yields condensation, nonwetting state exhibits and twice coefficient. Relevance thermal management is additionally discussed.

Observations of the collapse a soap-film bridge from connected to disconnected state are recorded. The equilibrium framework for this nonequilibrium event is classical. Experiments confirm predictions stable and unstable equilibria. A quasistatic description introduced dynamic states extend static theory. It found adequately describe trajectory while still connected.

The transition from steady to time-periodic motion in the analog of Benard convection a two-dimensional region fluid-saturated porous media is studied by means an eigenfunction expansion and branch-tracing technique. This method leads location at Rayleigh number 9.9 times that onset. small-amplitude has period 0.012 shorter than thermal diffusion time comes into existence through Hopf bifurcation. structure progression destabilizing disturbance indicates dominant effect instability convected...