Florence Rouyer

Gustave Eiffel University · Laboratoire NAVIER

Controlling the stability of a granular film is essential in a wide range of industrial applications, from aerated building materials to recovering ore by flotation and treating wastewater. We therefore carry out experiments of granular film opening where particles of hundred of micrometers above random close packing zip the two interfaces of a soa...

The prediction of the lifetime of surface bubbles necessitates a better understanding of the thinning dynamics of the bubble cap. In 1959, Mysels et al. [Soap Films: Studies of Their Thinning and a Bibliography (Pergamon, New York, 1959)], proposed that marginal regeneration, i.e., the rise of patches thinner than the film should be taken into acco...

The prediction of the lifetime of surface bubbles necessitates a better understanding of the thinning dynamics of the bubble cap. In 1959, Mysel \textit{et al.} \cite{mysels1959soap}, proposed that \textit{marginal regeneration} i.e. the rise of patches, thinner than the film should be taken into account to describe the film drainage. Nevertheless,...

Surface bubbles are present in many industrial processes and in nature, as well as in carbonated beverages. 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 ba...

Surface bubbles are present in many industrial processes and in nature, as well as in CO$_2$ 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, t...

Massive foam formation in aquatic environments is a seasonal event that has a significant impact on the stability of marine ecosystems. Liquid foams are known to filter passive solid particles, with large particles remaining trapped by confinement in the network of liquid channels and small particles being freely advected by the gravity-driven flow...

The lifetime of a single bubble on the surface of an alcohol-water liquid bath is measured at intermediate humidity rates. Thanks to an automatic bubble generation device associated with a lifetime measuring device, we carry out a statistical study of the bubble lifetime, which extends over three decades, from 0.1 to 100 s. Up to alcohol concentrat...

The addition of sweeteners in fizzy beverages not only affects the sugar content but also the bubbles stability. In this article, we propose a model experiment, in which the lifetime of hundreds of single bubbles is measured, to assess the stability of bubbles in solutions containing either sucrose or sweeteners. We show that the bubbles are indeed...

The addition of sweeteners in fizzy beverages not only affects the sugar content but also the bubbles stability. In this article, we propose a model experiment, in which the lifetime of hundreds of single bubbles is measured, to assess the stability of bubbles in solutions containing either sucrose or sweeteners. We show that the bubbles are indeed...

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 c...

At the end of their life, surface bubbles burst and emit aerosols, which drastically impact exchanges in liquid as well as in pathogens or flavors with the surrounding atmosphere. This exchange depends on the thickness of the liquid film and is thus linked to the bubble drainage dynamics and to their lifetime. In this article, we propose to explore...

We carry out a series of experiments with the aim of completing our knowledge of wall slip characteristics, through a deductive approach based on macroscopic behavior observations. More precisely, we use model materials (direct and inverse emulsions) and determine the variations of wall slip properties depending on the material parameters (droplet...

From well-controlled long creep tests, we show that the residual apparent yield stress observed with soft-jammed systems along smooth surfaces is an artifact due to edge effects. By removing these effects, we can determine the stress solely associated with steady-state wall slip below the material yield stress. This stress is found to vary linearly...

Including solid particles in liquid films drastically change their properties: "gas marbles" can resist overpressure and underpressure without deforming contrary to their pure liquid counterparts, also known as soap bubbles. Such gas marbles can therefore prove useful as gas containers able to support stresses. Yet, as their liquid counterparts, th...

This movie shows how gas marbles are made.

Enwrapping liquid droplets with hydrophobic particles allows the manufacture of so-called “liquid marbles” [Aussillous and Quéré Nature (London) 411, 924 (2001); Mahadevan Nature (London)411, 895 (2001)]. The recent intensive research devoted to liquid marbles is justified by their very unusual physical and chemical properties and by their potentia...

We compute the effective viscosity of particulate soap films thanks to local velocity fields obtained by Particle Image Velocimetry (PIV) during film retraction experiments. We identify the jamming of these 2D capillary suspensions at a critical particle surface fraction (≃ 0.84) where effective viscosity diverges. Pair correlation function and num...

Since the pioneering works of Taylor and Bretherton, the thickness (Formula presented.) of the film deposited behind a long bubble invading a Newtonian fluid is known to increase with the capillary number power (Formula presented.) ((Formula presented.)), where (Formula presented.) is the radius of the circular tube and (Formula presented.) is the...

We perform retraction experiments on soap films where large particles bridge the two interfaces. Local velocities are measured by PIV during the unstationnary regime. The velocity variation in time and space can be described by a continuous fluid model from which effective viscosity (shear and dilatational) of particulate films is measured. The 2D...

We study the formation of yield-stress fluid foams in millifluidic flow-focusing and T-junction devices. First, we provide a phase diagram for the unsteady operating regimes of bubble production when the gas pressure and the yield-stress fluid flow rate are imposed. Three regimes are identified: a co-flow of gas and yield-stress fluid, a transient...

We investigate experimentally the stability of bubble production in yield-stress fluids (YSF) and highly viscous silicone oil, using flow-focusing and T-junction devices. When the exit channel is initially pre-filled with the fluid and the gas is pressure-driven, the production is highly unstable, despite a regular frequency of bubble production in...

Rising 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 rheology of the final product. Using drift flux analysis and r...

We study for the first time the bursting dynamics of thin liquid films laden with hy-drophobic micronic particles either with free or constrained edges. We highlight that the particles can arrange in bilayer or monolayer configurations and explore a range of particles coverage from zero to random close packing. When the particles bridge the two int...

We study the production of bubbles inside yield stress fluids (YSFs) in axisymmetric T-junction and flow-focusing devices. Taking advantage of yield stress over capillary stress, we exhibit a robust break-up mechanism reminiscent of the geometrical operating regime in 2D flow-focusing devices for Newtonian fluids. We report that when the gas is pre...

Rising 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...

To what extent are aqueous foams prone to clogging? Foam permeability is measured as a function of particulate loading (trapped hydrophilic particles) under conditions where the particle to bubble size ratio is allowed to increase when the number of particles per bubble is fixed. In addition to experiments performed on the foam scale, we investigat...

Aqueous foams are studied both as materials with many applications, and as model systems for fields ranging from metallurgy to mathematics to biology. They are complex fluids with unique and unusual properties, exemplified as much by their multiscale structure as by the dynamical processes through which they evolve and even their dual liquid-like a...

There is no clear statement on the role of particles in the drying of liquid marbles, which are liquid drops coated with hydrophobic solid particles. While some works report a similar drying time for liquid marbles and bare water drops others observe a faster evaporation of either liquid marbles or of bare water drops. To provide insight into the s...

We present experimental results of film drainage on top of gas bubbles pushed by gravity towards the free surface of highly viscous Newtonian liquid with a uniform interface tension. The temporal evolution of the thickness of the film between a single bubble and the air/liquid interface is investigated via interference method. Experiments under var...

First, we report observations achieved on a gravitationally driven film drainage with molten glass pointing out a stabilizing effect when temperature is larger than 1250 °C. A model to describe the change of surface tension with the film thickness due to the evaporation of oxide species is proposed. A lubrication model is derived taking into accoun...

Ce manuscript d'Habilitation à Diriger des Recherches présente mes travaux de recherche pour la période 2000-2011, pendant laquelle je me suis intéressée à la description et à la compréhension de la dynamique d'écoulement des mousses aqueuses ainsi qu' à l'écoulement de liquide et de particules dans un tel milieu. Une brève introduction aux mousses...

We investigate the behavior of coarse particles confined in foam channels during drainage. Results are reported for particle velocities measured at both microscopic (single foam channel) and macroscopic (foam) scales, as a function of the average velocity of the liquid flow and of the confinement parameter that is the ratio of particle diameter to...

We investigate the sedimentation of fine particles in liquid channels of foams. The study combines numerical simulations with experiments performed in foams and in isolated vertical foam channels. Results show that particulate motion is controlled by the confinement parameter (λ) and the mobility of the channel surfaces modelled by interfacial shea...

We measure the permeability of a fluidized bed of monodispersed bubbles with soap solution characteristic of mobile and non-mobile interfaces. These experimental data extend the permeability curves previously published for foam in the dry limit. In the wet limit, these data join the permeability curves of a hard sphere suspension at porosity equal...

We measure the permeability of a fluidized bed of monodispersed bubbles with soap solution characteristic of mobile and non-mobile interfaces. These experimental data extend the permeability curves previously published for foam in the dry limit. In the wet limit, these data join the permeability curves of a hard sphere suspension at porosity equal...

Although extensively studied in the past, drainage of aqueous foams still offers major unaddressed issues. Among them, the behaviour of foam films during drainage has great significance as the thickness of the films is known to control the Ostwald ripening in foams, which in turn impacts liquid drainage. We propose a model relating the films' behav...

A forced Ostwald ripening experiment is performed on a single foam bubble. The bubble size is followed as the system is wetted with a constant liquid flow rate delivered from one of the bubble Plateau borders. Obtained ripening velocities cannot be described with a model based on a constant film thickness assumption. Within these well-controlled ex...

We perform forced-drainage experiments in aqueous foams and compare the results with data available in the literature. We show that all the data can be accurately compared together if the dimensionless permeability of the foam is plotted as a function of liquid fraction. Using this set of coordinates highlights the fact that a large part of the pub...

We study the low frequency stress response of aqueous foams, subjected to oscillatory strain. As the strain amplitude is progressively increased starting from zero, the initially linear viscoelastic response becomes nonlinear as yielding sets in. To characterize this crossover from solid-like to liquid-like behaviour quantitatively, the full harmon...

Liquid foams were recognized early to be porous materials, as liquid flowed between the gas bubbles. Drainage theories have been established, and foam permeability has been modeled from the microscopic description of the equivalent pores geometry, emphasizing similarities with their solid counterparts. But to what extent can the theoretical work de...

We show that the model of permeability proposed by Kozeny and Carman and originally validated on packed beds of spheres -- with porosity around 0.4 -- is a particular case and can be extented to liquid fraction from 0.001 up to 0.85 for systems made of monodisperse entities. The knowledge of the specific surface area is essential. This modeling all...

Foam drainage is modelled by the flow of liquid through Plateau borders (PBs) that are the liquid channels resulting from the merging of three liquid films separating the gas bubbles. Available models generally neglect the influence of these films. Yet, within drainage conditions, experimental observations indicate a strong coupling of these films...

This paper deals with the drainage of liquid foams. The liquid velocity is known to be related to viscous dissipation occurring within the elements of the liquid network, i.e. the channels and the nodes. When compared together, available values for the hydrodynamic resistance of a foam node appear to span over more than one order of magnitude. To c...

In many foam applications, particles flow through the liquid network of aqueous foam made of channels and nodes. These channels named Plateau border are the junctions between three soap films and have fluid interfaces (non zero velocity). To understand the complex behaviour of this transport, we focus our experiments on a single particle flowing wi...

Foams and foaming pose important questions and problems to the chemical industry. As a material, foam is unusual in being a desired product while also being an unwanted byproduct within industry. Liquid foams are an essential part of gas/liquid contacting processes such as distillation and absorption, but over-production of foam in these processes...

Dimensional arguments suggest that the yield stress of aqueous foams and emulsions, for a given volume fraction of the dispersed phase, should scale as the ratio of surface tension and a length scale, such as the mean bubble radius. We show that yield stress data from the literature and from our experiments follow this scaling only in a very rough...

We study the onset of yielding in stable three-dimensional dry foams following the start up of steady shear flow. By means of a charge-coupled device camera equipped with a small depth-of-field objective, we visualize the Plateau border network in the bulk of the foam. The onset of yielding is identified with the deformation gamma(c) for which shea...

The final stages of a coin spinning on a flat surface have recently been proposed [H.K. Moffatt, Nature (London) 404, 833 (2000)] as an example of a finite-time singularity, wherein the precession rate of the symmetry axis of the coin diverges as it comes to a stop. We report measurements by high-speed video imaging of the rolling motion of disks a...

We have measured the spectrum of velocity fluctuations in a granular system confined to a vertical plane and driven into a homogeneous, steady state by strong vertical vibration. The distribution of horizontal velocities is not Maxwell-Boltzmann and is given by P(v) = Cexp[-beta(|v|/sigma)(alpha)] where alpha = 1.55+/-0.1 at all frequencies and amp...

We measure experimentally the density (rho) and temperature (Tg = 1/2 ) profiles in a 2D vertical plane, of macroscopic grains fluidized by oscillation in the vertical (z) direction. Far enough from the energy source, we verify that the condition of mechanical equilibrium is dP/dz = -rho(z)g, where the pressure is calculated from the equation of st...

Non-brownian sedimenting suspensions exhibit density and velocity fluctuations. We have performed experiments on a quasi-2D counter-flow stabilized suspension of 2000 spherical particles, namely a liquid-solid fluidized bed in a Hele-Shaw cell. This 2D suspension displays a uniform concentration but the particle radial distribution function and the...

We perfom an experiment on a vertical layer of spherical steel beads that we shake vertically, with the goal of creating a 2D granular gas. If the vertical shake is strong enough, gravity effects and phase-coherent motion become negligible: the motion of grains is then predominantly governed by inelastic grain-grain collisions. We find the position...

We quantitatively analyze the correlation between the dynamic of one sphere and its neighborhood in a 2D fluidized suspension of macroscopic spheres. It appears that both the radial and the orientational distribution of spheres around a referenced one clearly depend on wether this particle flows upwards or downwards. We then look at the dynamics of...

We study experimentally the hydrodynamic-interaction-controlled random walk (RW) of noncolloidal spheres in a quasi-2D fluidized suspension. This macroscopic ``molecular'' system is anisotropic. Particle trajectories are Brownian-like and, from time to time, fast upward correlated. The vertical RW is hyperdiffusive, but the horizontal one is Gaussi...

We follow the dynamics of a 2D non-colloidal counter-flow stabilized suspension of a few thousands of spherical particles quenched between two parallell plates: a liquid-solid-fluidized bed in a Hele-shaw cell. The particles execute a random walk controlled by long-range hydrodynamic interactions. We follow the trajectories and measure the velociti...

We model liquid transport in a foam (i.e. drainage) by unidirectional flow transverse to a triangular planar area that represents channels (i.e. Plateau borders) cross-section. Partial mobility of the interfaces is obtained balancing the bulk viscous stress with the surface viscous stress and velocity equal to zero is imposed at the vertices. In li...

Nous nous intéressons à l'écoulement de liquide au sein d'un milieu poreux constitué d'un empilement de sphères molles. Du fait de leurs grandes déformabilités, une compression de l'empilement permet à la géométrie de la phase interstitielle d'évoluer et de s'approcher de celle d'une mousse (ou d'une émulsion) où les bulles (ou gouttes) sont rempla...