Research interests 

Experiments involving Interfacial Hydrodynamics, Wetting and Non-wetting, Complex fluids and general "Soft Matter".

Recent experiments 
(You may want to download a free Quick Time movie player to visualize the movie links .

Spreading flowers,

with Angelina Aessopos, Vladimir Entov, Anette (Peko) Hosoi , Marc Fermigier and Gareth McKinley

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)


Gobbling droplets,

with Christian Clasen , Gareth McKinley & Vladimir Entov


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).

Dripping of a jelly liquid,

with Christian Clasen , Gareth McKinley & Vladimir Entov

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).

Rolling Stones, 

with Jacqueline Ashmore , Howard Stone   & Gareth McKinley

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. 
An overhang situation is also possible: an heavy ball rolls down eventually without falling off, only hold by a liquid bridge!
This project has been inspired from nice experiments from A.Samadani and A.Kudrolli on granular media.

Click on the pictures to watch "stones" racing inside a rotating drum (2.7Mo)

Fingering instabilities in viscoelastic liquids, 

with Ryan Welsh & Gareth McKinley

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).


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. 

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!


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.

Super Hydrophobic Surfaces,

initially with David Quéré & Denis Richard,
currently with G. McKinley, K.Lau, K.B.K. Teo, M. Chhowalla, G.A.J. Amaratunga and W.I. Milne

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.

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.

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.
This motion is not perpetual since a trail of the liquids is left behind the bislug which is consumed during its displacement.

Click on the picture to watch a video of a bislug experiment (3.3Mo).