Soap bubbles can be easily generated by varies methods, while their formation process is complicated and still worth study. A model about the bubble formation process was proposed in Phys. Rev. Lett. 116, 077801 recently, and it was reported that the bubbles were formed when the gas blowing velocity was above one threshold. However, after repeating these experiments, we found the bubbles could be generated in two velocities ranges which corresponded to laminar and turbulent gas jet respectively, and the predicted threshold was only effective for turbulent gas flow. The study revealed that the bubble formation was mainly influenced by the aerodynamics of the gas jet blowing to the film, and these results will help to further understand the formation mechanism of the soap bubble as well as the interaction between gas jet and thin liquid film.
In this paper, we study the formation process of a soap bubble by blowing soap film. Both bubble diameter and formation position were investigated in experiments. We found that the ratio between bubble size and soap film column is constant, and that the formation position increases linearly within a critical length-range. We used the theory of Rayleigh-Plateau instability to explain these findings. The theoretical explanations are consistent with the experimental data.
Interdisciplinary Centre of Energy Sciences, Indian Institute of Science（印度科学学院交叉能源科学中心）；Department of Mechanical Engineering, Indian Institute of Science（印度科学学院机械工程系）
A proof-of-concept demonstration of the electrowetting-on-dielectric of a sessile soap bubble is reported here. The bubbles are generated using a commercial soap bubble mixture - the surfaces are composed of highly doped, commercial silicon wafers covered with nanometre thick films of Teflon. Voltages less than 40V are sufficient to observe the modification of the bubble shape and the apparent bubble contact angle. Such observations open the way to inter alia the possibility of bubble-transport, as opposed to droplet-transport, in fluidic microsystems (e.g. laboratory-on-a-chip) - the potentia…
Wetting of sessile bubbles on solid and liquid surfaces has been studied. A model is presented for the contact angle of a sessile bubble based on a modified Young equation - the experimental results agree with the model. A hydrophilic surface results in a bubble contact angle of 90 deg whereas on a superhydrophobic surface one observes 134 deg. For hydrophilic surfaces, the bubble angle diminishes with bubble radius - whereas on a superhydrophobic surface, the bubble angle increases. The size of the Plateau borders governs the bubble contact angle - depending on the wetting of the surface.
The merging of two soap bubbles is a fundamental fluid mechanical process in foam formation. In the present experimental study the liquid films from two soap bubbles are brought together. Once the liquid layers initially separated by a gas sheet are bridged on a single spot the rapid merging of the two liquid films proceed. Thereby the connecting rim is rapidly accelerated into the separating gas layer. We show that due to the dimple formation the velocity is not uniform and the high acceleration causes initially a Rayleigh-Taylor instability of the liquid rim. At later times, the rim takes he…
We use Direct Numerical Simulations to study the two-dimensional flow of a rotating, half soap bubble that is heated at its equator. The heating produces buoyancy and rotation generates a Coriolis forces in the fluid. However, due to the curved surface of the bubble, the buoyancy and Coriolis forces vary with latitude on the bubble, giving rise to rich flow behavior. We first explore the single-point properties of the flow, including the Reynolds and Nusselt numbers, mean fields, and Reynolds stresses, all as a function of latitude. For a given Rayleigh number, we observe a non-monotonic depen…
A soap bubble is a metastable object that eventually breaks. Indeed, the soapy water film thins until rupture, due to drainage and evaporation. In our experimental investigations, floating bubbles at the surface of a liquid bath have been considered. Their lifetime has been measured and reported with respect to their radius. Large bubbles last longer than small ones. Moreover, small bubbles have more predictable lifetimes than large ones. We propose a general equation for that lifetime, based on the lubrication theory. The evaporation is shown to be an essential process which determines the bu…
We use direct numerical simulation (DNS) to explore the effect of tilt on two-dimensional turbulent thermal convection on a half-soap bubble that is heated at its equator.In the DNS, the bubble is tilted by an angle $δ\in[0^{\circ},90^{\circ}]$, the Rayleigh number is varied between $Ra\in[3\times10^6, 3\times10^9]$, and the Prandlt number is fixed at $Pr=7$.The DNS reveals two qualitatively different flow regimes: the dynamic plume regime (DPR) and the stable plume regime (SPR).In the DPR, small dynamic plumes constantly emerge from random locations on the equator and dissipate on the bubble.…
All children enjoy blowing soap bubbles that also show up in our bath and when we wash dishes. We analyze the thinning and breaking of soap bubble neck when it is stretched. To contrast with the more widely studied film whose boundaries are open, we concentrate on the bubble with a conserved air volume V. Like film (F), non-equilibrium state can be divided into four regimes for bubble (B): (1) roll-off, (2) cusp approach, (3) pinch-off and (4) breakup. We establish the existence of self-similarity in F-1, B-1 and B-3, and universal property in F-1 and B-1 for the profile of soap membrane. The …
Soap bubbles occupy the rare position of delighting and fascinating both young children and scientific minds alike. Sir Isaac Newton, Joseph Plateau, Carlo Marangoni, and Pierre-Gilles de Gennes, not to mention countless others, have discovered remarkable results in optics, molecular forces and fluid dynamics from investigating this seemingly simple system. We present here a compilation of curiosity-driven experiments that systematically investigate the surface flows on a rising soap bubble. From childhood experience, we are familiar with the vibrant colors and mesmerizing display of chaotic f…
We experimentally investigate the impact of a liquid jet on a soap film. We observe that the jet never breaks the film and that two qualitatively different steady regimes may occur. The first one is a refraction-like behavior obtained at small incidence angles when the jet crosses the film and is deflected by the film-jet interaction. For larger incidence angles, the jet is absorbed by the film, giving rise to a new class of flow in which the jet undulates along the film with a characteristic wavelength. Besides its fundamental interest, this study presents a new way to guide a micro-metric fl…
Using mixtures of soap, water, and long chain polymers, free-floating soap bubbles can be formed with volumes approaching 100 m$^3$. Here we investigate how such thin films are created and maintained over time. We show how the extensional rheology is the most important factor in creating the bubble, and how polydispersity in molecular weight of the solvated polymers leads to better performance at lower concentrations. Additionally, using IR absorption, we measure soap film thickness profiles and film lifetimes. Although the initial thickness mostly depends on the choice of detergent, polymers …
Bubbles and droplets are ubiquitous in many areas of engineering, including microfluidics where they can serve as microreactors for screening of chemical reactions. They are often formed out of a constriction (a microfluidic channel or a cylindrical tube) by blowing a given volume of gas into a liquid phase. It is obviously crucial to be able to control their size, which is not always easy due to the coupling between the volume of the bubble and the gas pressure induced by the Laplace law. In this paper, we examine the size and formation dynamics of soap bubbles blown from a cylindrical tube, …
As a bubble bursts at a liquid-air interface, a tiny liquid jet rises and can release the so-called \textit{jet drops}. In this paper, the size of the top jet drop produced by a bubble bursting is investigated experimentally. We determine, and discuss, the first scaling law enabling the determination of the top jet drop size as a function of the corresponding mother bubble radius and the liquid properties (viscosity, surface tension, density), along with its regime of existence. Furthermore, in the aim of decoupling experimentally the effects of bubble collapse and jet dynamics on the drop det…
Fast liquid jets, called micro-jets, are produced within cavitation bubbles experiencing an aspherical collapse. Here we review micro-jets of different origins, scales and appearances, and propose a unified framework to describe their dynamics by using an anisotropy parameter $ζ$, representing a dimensionless measure of the liquid momentum at the collapse point (Kelvin impulse). This parameter is rigorously defined for various jet drivers, including gravity and nearby boundaries. Combining theoretical considerations with hundreds of high-speed visualisations of bubbles collapsing near a rigid …
When an asymmetric bubble collapses it generally produces a well defined high velocity jet. This is remarkable because one might expect such a collapse to produce a complex or chaotic flow rather than an ordered one. I present a dimensional argument for the ubiquity of jets from collapsing bubbles, and model the aspherical collapse of a bubble with pieces of Rayleigh's solution for spherical collapse and its cylindrical analogue. This model explains the ubiquity of jet formation in aspherical collapse, and predicts the shape and velocity profile of the resulting jet. These predictions may be t…
This Letter presents the novel experimental observation of long and narrow jets shooting out in disconnecting large elongated bubbles. We investigate this phenomenon by carrying out experiments with various viscosities, surface tensions, densities and nozzle radii. We propose a universal scaling law for the jet velocity, which unexpectedly involves the bubble height to the power 3/2. This anomalous exponent suggests an energy focusing phenomenon. We demonstrate experimentally that this focusing is purely gravity-driven and independent of the pinch-off singularity.
The collapse of a vapor bubble near a flat solid boundary results in the formation of a jet that is directed towards the boundary. In more complex geometries such as corners, predictions of the collapse cannot be made in a straightforward manner due to the loss of axial symmetry. We experimentally investigate the bubble collapse and jet formation in corners formed of two flat solid boundaries with different opening angles. Using potential flow analysis, we accurately predict the direction of the jet and bubble displacement. We further show that for a corner with an opening angle $α$, there exi…
Over the last two decades, since explosive boiling has been widely used in industry, research on it has been increased. Thermal bubble jet printer, micro injectors and using in micro medicine for injection are some possible applications. The operation of thermal bubble jets consist of three stages: 1- Heat transfer process, 2- Bubble formation and growth in the microchannel, and 3-Drop ejection. The effect of fluid properties on the operation of thermal bubble jet is investigated in this paper. Thus the effect of fluid properties is investigated in each above mentioned processes. Eventually, c…
A vapor bubble collapsing near a solid boundary in a liquid produces a liquid jet that points toward the boundary. The direction of this jet has been studied for boundaries such as flat planes and parallel walls enclosing a channel. Extending these investigations to enclosed polygonal boundaries, we experimentally measure jet direction for collapsing bubbles inside a square and an equilateral triangular channel. Following the method of Tagawa and Peters (Phys. Rev. Fluids 3, 081601, 2018) for predicting the jet direction in corners, we model the bubble as a sink in a potential flow and demonst…
The analysis of numerical simulations describing the collapse of capillary cavities reveals that the jets originated from the bursting of bubbles are driven by the condition that the dimensionless liquid flow rate per unit length directed towards the axis of symmetry, $q_\infty$, remains nearly constant in time. This observation, which is justified in physical terms because liquid inertia prevents appreciable changes in $q_\infty$ during the short time scale characterizing the jet ejection process, together with the fact that bubble bursting jets are produced from the bottom of a conical cavit…
Bubbles dispersed in liquids are widely present in many natural and industrial processes, and play a key role in mediating mass transfer during their lifetime from formation to rising to bursting. In particular, nano/micro-sized particulates and organisms, present in the bulk water can be highly enriched in the jet drops ejected during bubble bursting, impacting global climate and public health. However, the detailed mechanism of this enrichment remains obscure, with the enrichment factor being difficult to predict. Here, we experimentally investigate the enrichment of nano/micro-sized particl…
A small, spherical bubble of high internal pressure is inserted into water at constant ambient pressure as a model of a laser-induced bubble. Its subsequent dynamics near a flat solid boundary is studied in dependence on the distance of the bubble to the boundary by numerically solving the Navier-Stokes equations with the help of the open source software environment OpenFOAM. Implemented is the finite volume method for discretization of the equations of motion and the volume of fluid method for capturing the interface between the bubble interior and exterior. The bubble contains a small amount…
Soap bubbles are by essence fragile and ephemeral. Depending on their composition and environment, bubble bursting can be triggered by gravity-induced drainage and/or the evaporation of the liquid and/or the presence of nuclei. They can also shrink due to the diffusion of the inner gas in the outside atmosphere induced by Laplace overpressure. In this paper, we design bubbles made of a composite liquid film able to neutralize all these effects and keep their integrity for more than one year in a standard atmosphere. The unique properties of this composite film are rationalized with a nonlinear…
Jet droplets from bubble bursting are determined by a limited parametrical space: the liquid properties (surface tension, viscosity, and density), mother bubble size and acceleration of gravity. Thus, the two resulting parameters from dimensional analysis (usually, the Ohnesorge and Bond numbers, Oh and Bo) completely define this phenomenon when both the trapped gas in the bubble and the environment gas have negligible density. A detailed physical description of the ejection process to model both the ejected droplet radius and its initial launch speed is provided, leading to a scaling law incl…
Bubbles generated with lasers under confinement have been investigated for their potential use as the driving mechanism for liquid micro-jets in various microfluidic devices, such as needle free jet injectors. Here, we report on the study of bubble formation by a continuous-wave (CW) and a pulsed laser inside an open-ended microfluidic capillary. This results in a direct comparison between bubbles generated by laser sources emitting light in different time scales (ms and ns). The bubble kinetics represents an important parameter because it determines the available kinetic energy for a subseque…
As the liquid jet plunges into a free surface, significant air is entrained into the water and forms air pockets. These air pockets eventually break up into small bubbles, which travel downstream to form a bubbly wake. To better understand the underlying flow physics involved in the bubble entrainment, in the linked videos, air entrainment due to a water jet plunging onto a pool of stationary water was numerically studied by using the 3DYNAFS software suit. The flow field is simulated by directly solving the Navier-Stokes equations through the viscous module, 3DYNAFS-VIS, using a level set met…
Bubbles at a free surface surface usually burst in ejecting myriads of droplets. Focusing on the bubble bursting jet, prelude for these aerosols, we propose a simple scaling for the jet velocity and we unravel experimentally the intricate roles of bubble shape, capillary waves, gravity and liquid properties. We demonstrate that droplets ejection unexpectedly changes with liquid properties. In particular, using damping action of viscosity, self-similar collapse can be sheltered from capillary ripples and continue closer to the singular limit, therefore producing faster and smaller droplets.Thes…
In the minutes immediately preceeding the rupture of a soap bubble, distinctive and repeatable patterns can be observed. These quasi-stable transient structures are associated with the instabilities of the complex Marangoni flows on the curved thin film in the presence of a surfactant solution. Here, we report a generalised Cahn-Hilliard-Swift-Hohenberg model derived using asymptotic theory which describes the quasi-elastic wrinkling pattern formation and the consequent coarsening dynamics in a curved surfactant-laden thin film. By testing the theory against experiments on soap bubbles, we fin…
In this paper, the size of bubbles formed through the breakup of a gaseous jet in a co-axial microfluidic device is derived. The gaseous jet surrounded by a co-flowing liquid stream breaks up into monodisperse microbubbles and the size of the bubbles is determined by the radius of the inner gas jet and the bubble formation frequency. We obtain the radius of the gas jet by solving the Navier-Stokes equations for low Reynolds number flows and by minimization of the dissipation energy. The prediction of the bubble size is based on the system's control parameters only, i.e. the inner gas flow rate…
We report a detailed experimental characterization of the periodic bubbling regimes that take place in an axisymmetric air-water jet when the inner air stream is forced by periodic modulations of the pressure at the upstream air feeding chamber. When the forcing pressure amplitude is larger than a certain critical value, the bubble formation process is effectively driven by the selected frequency, leading to the formation of nearly monodisperse bubbles whose volume is reduced by increasing the forcing frequency. We reveal the existence of two different breakup modes, M1 and M2, under effective…
A jet of water entering into a pool of the same liquid can generate air entrainment and form bubbles that rapidly raise to the surface and disintegrate. Here we report the equivalent phenomenon produced by a plunging dry granular jet, so far unexplored. For grains smaller than a critical size, the granular jet entering into the pool produces air entrainment that leads to bubbles formation. The bubbles formed are covered by a shell of grains attached to the bubble air-water interface due to capillary-induced cohesion. In contrast to classical air bubbles, these "granular bubbles" are stable ove…
Cavitation bubbles collapsing and rebounding in a pressure gradient grad(p) form a "micro-jet" enveloped by a "vapor jet". This letter presents unprecedented observations of the vapor jets formed in a uniform gravity-induced grad(p), modulated aboard parabolic flights. The data uncovers that the normalized jet volume is independent of the liquid density and viscosity and proportional to zeta=grad(p)*R0/p, where R0 is the maximal bubble radius and p is the driving pressure. A derivation inspired by "Kelvin-Blake" considerations confirms this law and reveals its negligible dependence of surface …
