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Experiments involving Interfacial Hydrodynamics,
Wetting and Non-wetting, Complex fluids and general "Soft Matter". |
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Spreading flowers, with Angelina Aessopos, Vladimir Entov, Anette (Peko) Hosoi , Marc Fermigier and Gareth McKinley |
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The spreading of a droplet
of food dye on a layer of semi-dilute polymer solution leads to a fingering
pattern. Although Carlo Marangoni identified the motor of these phenomena
as the contrast between the surface trensions of the diferent interfaces in
the 1880's, the origin of these dendrites remains an open question.
Click on the picture to watch the video (6.5Mo) |
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Gobbling droplets,
with Christian Clasen , Gareth McKinley & Vladimir Entov |
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A jet of liquid is unstable because of surface tension and usually breaks into small droplets. The addition of minute quantities of polymeric molecules provides an additive elastic stress which stabilizes the liquid column. In this situation the terminal droplet has the time to gobble many of its incoming neighbors before its detachment. Click on the picture to watch the video (5.9Mo). |
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Dripping of a jelly liquid,
with Christian Clasen , Gareth McKinley & Vladimir Entov |
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Concentrated surfactant
solutions eventually exhibit particular molecular structures
(“worm like micelles”) which lead to a jelly liquid. The material
behaves as a soft elastic solid when a light stress is applied but
flows as a liquid under higher stresses.
When a droplet of such a liquid drips from a pipette, a long thread connects the droplet to the pipette and progressively necks and breaks down when the thread reaches a certain diameter. Click on any picture to watch the video (2.2Mo).
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| Rolling Stones, |
Once deposited on a tilted planar surface
coated with some viscous liquid, a sphere rolls down and slides at
the same time. Tire prints like patterns are formed behind the ball. Click on the pictures to
watch "stones" racing inside a rotating drum (2.7Mo)
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Fingering instabilities in viscoelastic liquids,
with Ryan Welsh & Gareth McKinley |
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The separation of two plates
bridged by a thin layer of a viscoelastic liquid leads to complex
instabilities. The experiment shown was done using a polystyrene Boger fluid characterized by a relaxation time of 3 min. The larger fingering structure corresponds to a Saffman Taylor instability: a fluid of low viscosity (air) penetrate into a viscous liquid which generates viscous fingering. Elastic stresses in the solution are also induced when the polymeric molecules get stretched enough. They are responsible for the secondary structure which develops at larger strains. The endplate diameter is 5mm, the initial gap between the endplate is 0.1 mm and the Deborah number (relaxation time/experiment time) is 43. Click on the picture to watch a video of this experiment (1.2Mo).
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Wrinkling of elastic membranes,
with Christophe Riera , Gareth McKinley & L.Mahadevan |
Wrinkles can grow when an elastic membranes
is stretched between two clamps. This pattern results from a competition
between tensile and bending stresses and mainly depend on the geometry
of the sample. This experiment provides a simple analogy with the elastic
oinstabilitybserved with visco-elastic fluids. |
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Ganesha instability,
with Gareth
McKinley
&
L.Mahadevan |
Multi-walled nanotubes exhibits
periodic ripples when they are bent. This instability essentially depends
on the tubes geometry but not on the material properties. The same popliteal
ripples are also observed with macroscopic rubber sheet scrolls or even
on elephant trunks!
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Ex-vivo rheology of spider silk, with Nikola Kojić, Christian Clasen & Gareth McKinley |
Nephila clavipes
spider (female) and one of her major ampulate glands
Although spider silk has been revered during last decade for its unmatched mechanical properties, very little is known about the rheological properties of the spinning dope. Determining the shear and extensionnal rheology of the spinning dope should give some guidance to understand the complex spinning process occurring along the spider spinning canal. |
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Super Hydrophobic Surfaces,
initially with David Quéré
& Denis Richard, |
The combination of an hydrophobic material and and rough surface can lead to super hydrophobic surfaces. A water droplet deposited on such a substrate remains at rest on the tops of the roughness which widely reduces the contact area of the liquid with the solid. The drop is mainly in contact with air and keeps the shape it would have in the air. Click on the picture to watch a video (2Mo) of the dynamics of water on such a surface. |
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The shape of Tektites,
with Tim Kreider, John Bush , Linda Elkins Tanton , Pascale Aussillous and David Quéré |
Tektites are believed to be the "splashes"
from the impact of big meteorites on the Earth. The molten silica
material (mainly from terrestrial origin) would be ejected with some
spinning motion which deforms the liquid drops. These rotating shapes
are often frozen by the cooling down of the liquid during its flight. |
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Liquid trains in a tube,
with David Quéré |
If two adjacent liquids are introduced in
a capillary tube, a spontaneous motion of this bislug
is generally observed when the tube is hold horizontally. This
flow relies on the asymmetry of the system: capillary forces
on the three menisci do not necessarily balance and their contrast
drives the bislug. Click on the picture to watch a video of a bislug experiment (3.3Mo). |
