90 research outputs found
Stability of Big Surface Bubbles: Impact of Evaporation and Bubbles Size
Surface bubbles have attracted much interest in the past decades. In this
article, we propose to explore the lifetime and thinning dynamics of
centimetric surface bubbles. We study the impact of the bubbles size as well as
that of the atmospheric humidity through a careful control and systematic
variation of the relative humidity in the measuring chamber. We first adress
the question of the drainage under saturated water vapor conditions and show
that a model including both capillary and gravity driven drainage provides the
best prediction for this process. Additionally, unprecedented statistics on the
bubbles lifetimes confirm experimentally that this parameter is set by
evaporation to leading order. We make use of a model based on the overall
thinning dynamics of the thin film and assume a rupture thickness of the order
10-100 nm to obtain a good representation of these data. For experiments
conducted far from saturation, the convective evaporation of the bath is shown
to dominate the overall mass loss in the cap film due to evaporation
The Life of a Surface Bubble
Surface bubbles are present in many industrial processes and in nature, as
well as in CO beverage. They have motivated many theoretical, numerical and
experimental works. This paper presents the current knowledge on the physics of
surface bubbles lifetime and shows the diversity of mechanisms at play that
depend on the properties of the bath, the interfaces and the ambient air.
In particular, we explore the role of drainage and evaporation on film
thinning.
We highlight the existence of two different scenarios depending on whether
the film cap ruptures at large or small thickness compared to the thickness at
which van der Waals interaction come in to play
Measurement of the temperature decrease in evaporating soap films
Recent advances have demonstrated that evaporation can play a significant
role on soap film stability, which is a key concern in many industrial areas
but also for children playing with bubbles. Thus, evaporation leads to a film
thinning but also to a film cooling, which has been overlooked for soapy
objects. Here, we study the temperature variation of an evaporating soap film
for different values of relative humidity and glycerol concentrations. We
evidence that the temperature of soap films can decrease after their creation
up to 8C. We propose a model describing the temperature drop of
soap films after their formation that is in quantitative agreement with our
experiments. We emphasize that this cooling effect is significant and must be
carefully considered in future studies on the dynamics of soap films.Comment: 6 page
Effective water/water contact angle at the base of an impinging jet
The base of a jet impinging on an ultrapure water bath is studied
experimentally. At the impact point, a train of capillary waves develops along
the jet. By performing Particle Tracking Velocity measurements, we show that
there is a boundary layer separation between the jet and the meniscus. We thus
describe the shape of this meniscus with a hydrostatic model. A striking
observation is the existence of an effective non-zero water/water contact angle
between the jet and the meniscus. The rationalization of this finite contact
angle requires a full description of the shape of the interface. By doing an
analytical matching between the meniscus and the jet, we show that the
capillary waves can be considered as reflected waves present to ensure pressure
continuity. It is finally shown that the value of the apparent contact angle is
fixed by energy minimization, with an excellent agreement between prediction
and experiment for small jets
Dynamics of bubbles spontaneously entering in a tube
When an open tube of small diameter touches a bubble of a larger diameter,
the bubble spontaneously shrinks and pushes a soap film in the tube. We
characterize the dynamics for different bubble sizes and number of soap films
in the tube. We rationalize this observation from a mechanical force balance
involving the Laplace pressure of the bubble and the viscous force from the
advancing soap lamellae in the tube. We propose a numerical resolution of this
model, and an analytical solution in an asymptotic regime. These predictions
are then compared to the experiments. The emptying duration is primarily
affected by the initial bubble to tube diameter ratio and by the number of soap
films in the tube
Generation of Giant Soap Films
Artists regularly make soap bubbles several meters long. In this article we
make soap films up to two meters high by pulling a horizontal fishing line
driven by belts out of a soapy solution at velocities ranging from 20 cm/s to
250 cm/s. We characterize the thickness profile of the central part of the film
that behaves like a rubber band under tension. We show that its thickness
profile is well described by a static model in which a homogeneous elastic film
is stretched by its own weight. This leads to an exponential thickness profile
with a characteristic length given by a competition between gravity and surface
elasticity. The prefactor is fixed by the shape and area of the film, governed
by the fishing line motion but also by a continuous extraction of foam film
from the lateral menisci, thicker than the central part, and that progressively
invades the film from its lateral boundaries. The model we propose captures the
subtle interplay between gravity, film elasticity and film extraction and leads
to predictions in good agreement with our experimental data
Study of charge-charge coupling effects on dipole emitter relaxation within a classical electron-ion plasma description
Studies of charge-charge (ion-ion, ion-electron, and electron-electron)
coupling properties for ion impurities in an electron gas and for a two
component plasma are carried out on the basis of a regularized electron-ion
potential without short-range Coulomb divergence. This work is motivated in
part by questions arising from recent spectroscopic measurements revealing
discrepancies with present theoretical descriptions. Many of the current
radiative property models for plasmas include only single electron-emitter
collisions and neglect some or all charge-charge interactions. A molecular
dynamics simulation of dipole relaxation is proposed here to allow proper
account of many electron-emitter interactions and all charge-charge couplings.
As illustrations, molecular dynamics simulations are reported for the cases of
a single ion imbedded in an electron plasma and for a two-component
ion-electron plasma. Ion-ion, electron-ion, and electron-electron coupling
effects are discussed for hydrogen-like Balmer alpha lines.Comment: 13 figures, submitted to Phys. Rev.
Soft Matter Drainage in a rising foam
International audienceRising foams created by continuously blowing gas into a surfactant solution are widely used in many technical processes, such as flotation. The prediction of the liquid fraction profile in such flowing foams is of particular importance since this parameter controls the stability and the rheol-ogy of the final product. Using drift flux analysis and recently developed semi-empirical expressions for foam permeability and osmotic pressure, we build a model predicting the liquid fraction profile as a function of height. The theoretical profiles are very different if the interfaces are considered as mobile or rigid, but all of our experimental profiles are described by the model with mobile interfaces. Even the systems with dodecanol, which are well known to behave as rigid in forced drainage experiments. This is because in rising foams the liquid fraction profile is fixed by the flux at the bottom of the foam. Here the foam is wet with higher permeability and the interfaces are not in equilibrium. These results demonstrate once again that it is not only the surfactant system that controls the mobility of the interface, but also the hydrodynamic problem under consideration. For example liquid flow through the foam during generation or in forced drainage is intrinsically different
A new setup for giant soap films characterization
Artists, using an empirical knowledge, manage to generate and play with giant
soap films and bubbles. Until now, scientific studies of soap films generated
at a controlled velocity and without any feeding from the top, studied films of
a few square centimeters. The present work aims to present a new setup to
generate and characterize giant soap films (2~m 0.7~m). Our setup is
enclosed in a humidity-controlled box of 2.2~m high, 1~m long and 0.75~m large.
Soap films are entrained by a fishing line withdrawn out of a bubbling solution
at various velocities. We measure the maximum height of the generated soap
films, as well as their lifetime, thanks to an automatic detection. This is
allowed by light-sensitive resistors collecting the light reflected on the soap
films and ensures robust statistical measurements. In the meantime, thickness
measurements are performed with a UV-VIS-spectrometer, allowing us to map the
soap films thickness over time
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