Anke Lindner

PMMH/ESPCI

10, rue Vauquelin

75231 Paris Cedex 05

France

 

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Bâtiment P

+33 1 40 79 58 05

+33 1 40 79 45 23

anke.lindner@espci.fr

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Fluid-structure interactions

Deformation and transport of an elastic fibre in a viscous cellular flow

(Collaboration with Olivia du Roure and Mike Shelley)

The deformation of an elastic filament is studied in the vicinity of a stagnation point. Its deformation is shown to modify its transport properties in the cellular flow.  The picture shows a rigid centimetric filament (bottom left) and a flexible filament (upper right) in the same viscous flow of counter rotating vortices.

 

Flow of model suspensions in restrictions

(Collaboration with Olivia du Roure and Schlumberger)

The clogging of restrictions with fiber suspensions is studied as a function of the properties of the suspended fibers. The pictures show fiber suspensions approaching a restriction in a microfluidic channel. The fibers are directly fabricated inside the microfluidic device.

  

Mecanisms of adhesive failure

Debonding of a visco-elastic model adhesive

(collaboration with Julia Nase and Mike Shelley)


We investigate the link between the viscoelastic properties of model materials and the adhesive performance using a controlled debonding geoetrie (a TACK-test). The pictures show the complex fingering patterns observed during debonding of visco-elastic materials. They are function of the relative importance of viscous and elastic properties of the adhesive and determine the adhesive performance. 

Debonding from surfaces with controled roughness

(collaboration Al Crosby and Costantino Creton)

As a function of the surface topology and the visco-elasticity of the material, increased or reduced adhesion can be observed when debonding from rough surfaces.

Suspensions

Flow of dense non-Brownian suspensions

(collaboration with Eric Clement)

We study the flow of dense model suspension using selected flow geometries, as inclined plane flow or droplet detachment (see picture).

 

Active suspensions under flow

(collaboration with Eric Clement)

We study flow of e-coli suspensions (see picture) in microfluidic geometries to access properties as their effective viscosity or their interaction with boundaries.

Elastic flow instabilities

Elastic flow instabilities in a serpentine channel

(collaboration with Rob Poole, Manuel Alves and Sandra Lerouge)

The destabilization of flow of a viscoelastic liquid is studied in curved flow geometries. The instability onset is studied as a function of the viscoelastic properties of the fluid and the flow geometry.

The Saffman-Taylor instability in complex fluids

We study the Saffman-Taylor instability in complex fluids. More precisely, we study the relation between rheological properties and pattern formation in a Hele-Shaw cell. To do so, we use model fluids, having only one non-Newtonian property at a time. 
A rheological study shows that the dominant property of a solution of the rigid polymer Xanthane is the shear thinning viscosity, that a solution of the flexible polymer PEO exhibits normal stresses and that a polymer gel exhibits a yield stress. 
For classical fluids, the relative width of the Saffman-Taylor fingers is determined by the ratio of the viscous forces to the capillary forces. In the case of a shear thinning fluid, the viscous forces are altered, leading to a narrowing of the finger. A modification of the viscous stresses by the existence of a yield stress leads to very branched patterns with a characteristic finger width, that is a function of the yield stress. For an elastic fluid, the normal stresses exert an extra pressure on the finger, which is added to the capillary forces and leads to finger widening. The knowledge of the influence of each of this properties separately on the Saffman-Taylor instability, constitutes a basis for studying the instability in even more complex fluids. The studied properties are among the most frequently encountered non-Newtonian properties allowing for a better understanding of the instability in fluids that exhibit several non-Newtonian properties simultaneously. (PhD-theses: Pdf-files (in french))

Pattern formation in liquid crystals

The instabilities observed in electro-convection in liquid crystals are considered as an archetype of pattern formatting systems and have been intensively studied. So far the focus of the investigations has been mostly on the initial formation of convection rolls. Lately the interest was also drawn to more complex structures observed at even higher values of the control parameter. One of the patterns observed in this regime is for example the so called “chevron-structure”, where the convection rolls order to form a chevron like structure. This pattern has been known for a long time, but its origins have so far not yet been understood. Recent theoretical studies attempted to show that the formation of this kind of structures is always possible when certain symmetry conditions are fulfilled.
Here we study a specific system showing chevron formation. More precisely, we performe a linear and weakly non-linear analysis of the instability leading to the formation of convection rolls in the dielectric regime of nematic liquid crystals. We develope the form of the amplitude equations describing this system and performe an analytic calculation of the coefficients of the latter. The relative simplicity of the system under study allowes for an understanding of the basic contributions to the instability and it can be shown that the symmetry requirements for chevron formation predicted by the theoretical investigations are fulfilled in this specific system. This is a first step in the more general understanding of Chevron formation. The approach used here can in the future also be applied to other systems showing a second destabilisation at higher control parameters. This could help to understand other more complex patterns, not yet understood. (Master Theses: pdf-file (in german))