DÉFORMATION ET TRANSPORT D’UN FILAMENT ÉLASTIQUE DANS UN ÉCOULEMENT CELLULAIRE VISQUEUX

We study the deformation and transport of an elastic filament in a viscous cellular flow. We used a simple experimental model system consisting of a one centimeter long elastic filament with controlled geometry and elasticity and a viscous flow formed by a lattice of stagnation points.First, we characterized the buckling instability of the filament approaching a stagnation point. We have shown that this instability is controlled by the elasto-viscous number Sp which compares the relative intensity of the viscous forces deforming the filament and the elastic forces resisting the deformation.Then, we showed that the parameters related to the dynamics of the fiber transported are crucial in the prediction of the buckling probability. In parallel to the experimental analysis, numerical simulations were performed in collaboration with Michael Shelley. The characterization of the dynamical parameters and their influence on the buckling instability allows the prediction of a buckling event as a function of the elasto-viscous number Sp and the dynamical parameters linked to the transport of filament accros the lattice.Finally, we investigated how the deformation and the size of the filament affect its transport properties.Ce travail porte sur l’étude de la déformation et le transport d’un filament élastique dans un écoulement cellulaire visqueux. Pour cette étude nous avons utilisé un système expérimental modèle simple constitué d’un filament élastique centimétrique de géométrie et d’élasticité contrôlées et d’un écoulement constitué d’un réseau de points de stagnation.Dans un premier temps, nous avons caractérisé l’instabilité de flambage du filament à l’approche d’un point de stagnation. Nous avons ainsi montré que cette instabilité est contrôlée par le nombre élasto-visqueux Sp qui compare l’intensité relative des forces visqueuses qui tendent à déformer le filament et des forces élastiques qui cherchent à le maintenir droit.Nous avons ensuite mis en évidence que les paramètres liés à la dynamique de la fibre évoluant librement à la surface de l’écoulement sont des paramètres cruciaux déterminant si le filament flambe ou pas à l’approche d’un point de stagnation. Cette analyse s’est aussi appuyée sur des simulations numériques modélisant le même système en collaboration avec Michael Shelley. La caractérisation de ces différents paramètres et de leur influence sur l’instabilité de flambage permet ainsi la prédiction de l’existence ou non d’un évènement de flambage à partir du nombre élasto-visqueux Sp et des paramètres dynamiques du filament.Enfin nous nous sommes intéressés à la manière dont la déformation du filament et sa taille influent sur ses propriétés de transport

Microfluidic Study of Foams Flow for Enhanced Oil Recovery (EOR)

In this paper, we report an experimental study of foam flow in different channel geometries using microfluidic devices in the framework of Enhanced Oil Recovery (EOR). Two different processes of foam formation are studied. The first corresponds to co-injection of gas and water through a cross junction which gives rise to a monodisperse foam. The second one corresponds to the fragmentation of large bubbles by a porous media, a foam formation process simulating multiphase flows in rocks. The foam formation is completely controlled and characterized varying both the water and gas pressure applied. We also use a microdevice with two permeabilities that permits to highlight the diversion of the continuous phase in the low permeability channels. The observations are important for a better understanding of the implied phenomena in EOR as well as to determine pertinent data to feed flow simulators

Microfluidic Study of Foams Flow for Enhanced Oil Recovery (EOR)

In this paper, we report an experimental study of foam flow in different channel geometries using microfluidic devices in the framework of Enhanced Oil Recovery (EOR). Two different processes of foam formation are studied. The first corresponds to co-injection of gas and water through a cross junction which gives rise to a monodisperse foam. The second one corresponds to the fragmentation of large bubbles by a porous media, a foam formation process simulating multiphase flows in rocks. The foam formation is completely controlled and characterized varying both the water and gas pressure applied. We also use a microdevice with two permeabilities that permits to highlight the diversion of the continuous phase in the low permeability channels. The observations are important for a better understanding of the implied phenomena in EOR as well as to determine pertinent data to feed flow simulators

Bending of elastic fibres in viscous flows: the influence of confinement

We present a mathematical model and corresponding series of microfluidic experiments examining the flow of a viscous fluid past an elastic fibre in a three-dimensional channel. The fibre’s axis lies perpendicular to the direction of flow and its base is clamped to one wall of the channel; the sidewalls of the channel are close to the fibre, confining the flow. Experiments show that there is a linear relationship between deflection and flow rate for highly confined fibres at low flow rates, which inspires an asymptotic treatment of the problem in this regime. The three-dimensional problem is reduced to a two-dimensional model, consisting of Hele-Shaw flow past a barrier, with boundary conditions at the barrier that allow for the effects of flexibility and three-dimensional leakage. The analysis yields insight into the competing effects of flexion and leakage, and an analytical solution is derived for the leading-order pressure field corresponding to a slit that partially blocks a two-dimensional channel. The predictions of our model show favourable agreement with experimental results, allowing measurement of the fibre’s elasticity and the flow rate in the channel

Rheology of cellulose nanofibrils and silver nanowires for the development of screen-printed antibacterial surfaces

TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl)-oxidized cellulose nanofibrils (T-CNF) and silver nanowires (Ag NWs) were formulated as active inks. Their rheological properties were investigated to design optimal conditions for processing by the screen-printing process, with the aim of preparing antibacterial patterns. Rheological experiments mimicking the screen-printing process were applied to different ink formulations to investigate their thixotropic and viscosity properties. The experiments conducted at 1wt% total mass content and different ratios of T-CNF/Ag NWs showed that the recovery (%), the recovery time and the viscosity are formulation dependent. A ratio 2:1 (T-CNF/Ag NWs) and total mass content of 2.5wt% were then selected to prepare an ink suitable for screen printing. Printing defects were corrected by addition of water-soluble polymer hydroxypropyl methylcellulose (HPMC). The selected formulation printed on flexible polyethylene terephthalate (PET) substrate displayed a 67.4% antibacterial activity against E. coli in a standard contact active test, with a transparency superior to 70%, proving the promising features of the developed solution for active packaging applications