Matthieu Varagnat's homepage

(with Trushant Majmudar, in Gareth McKinley's Non-Newtonian Fluids laboratory at the Massachusetts Institute of Technology (MIT))

We study the problem of a liquid poured out of an orifice at a given height and speed that hits a solid surface. Everybody has experienced such a situation, for example by dropping honey onto a bread slice, or pouring shower gel onto one's hand. Honey is a purely viscous, newtonian fluid: the jet thins continuously and coils regularly. Newtonian fluids in this situation (a) have been well studied [1], but we add another level of complexity by studying viscoelastic jets.

Our main non-Newtonian fluid is a concentration cetylpyridinium chloride (CPyCl) wormlike micellar solutions. Jets of this fluid show novel behaviors: the jet widens at its base (reverse swell phenomenon) and folds back and forth on itself (b). Both are a result of the interplay of non-Newtonian properties (viscoelasticity, shear-thinning) with gravitational, viscous, and inertial effects in the jets.

We have mapped the jetting behaviors in the parameter space, composed of the height of fall, the flow rate, the viscosity and elasticity of the fluid - or the dimensionless numbers made out of their combinations. In addition, we have provided rationales for the transitions between the regimes, as well as predictions for the dependencies with the various parameters of folding amplitude and frequency and the amount of reverse swell.

Jets of some shampoos show another behavior, the leaping shampoo or Kaye effect (c). The jet bends and slides on the top of a mound of liquid, jumping as high as 5cm for a jet radius of 1mm!

Proc. Math. Phys. Eng. Sc.

460

(with Philippe Cordier, in Ludwik Leibler's Soft Matter and Chemistry laboratory of the Ecole Superieur de Physique et Chimie Industrielles de Paris (ESPCI))

Supramolecular polymers are assemblies of small molecules, bound together by non-covalent interactions, that behave like polymers. The properties of the material developped in Ludwik Leibler's lab has some properties with huge potential.

At low temperature, the molecules are bound by hydrogen links, and it has the mechanical advantages of a crosslinked rubber - low modulus, very high maximum strain, very low residual strain.

At higher temperatures, the non-covalent bonds break apart, resulting in a low-viscosity, newtonian fluid.

When the bonds are mechanically broken, they can reform if the two parts are put in contact.

It is, therefore, an easy-to-process, "green", self-healing rubber. This research has been published in Nature [2]

These properties have been found in the material when dodecane was added as a plasticizer. When water was used instead of dodecane, the rubber color changed from transparent yellow to opaque white. My work was to investigate the mechanical behaviour and the microstructure of that supramolecular rubber in this water-swollen version. These results have been presented in a report to the Ecole Polytechnique and may be published in the future.

[2] Cordier, P., Tournilhac, T., Souli-Ziakovic, C. & Leibler, L. Nature 451, 977980 (2008)

	Matthieu Varagnat Master of Science student in the Program in Polymer Science and Technology MIT - Departement of Materials Science and Engineering Graduated from the Ecole Polytechnique of Paris email : varagnat[at]mit[dot]edu
Research interests : Rheology of complex fluids, physics and mechanics of polymers.
Viscoelastic jets (with Trushant Majmudar, in Gareth McKinley's Non-Newtonian Fluids laboratory at the Massachusetts Institute of Technology (MIT)) We study the problem of a liquid poured out of an orifice at a given height and speed that hits a solid surface. Everybody has experienced such a situation, for example by dropping honey onto a bread slice, or pouring shower gel onto one's hand. Honey is a purely viscous, newtonian fluid: the jet thins continuously and coils regularly. Newtonian fluids in this situation (a) have been well studied [1], but we add another level of complexity by studying viscoelastic jets. Our main non-Newtonian fluid is a concentration cetylpyridinium chloride (CPyCl) wormlike micellar solutions. Jets of this fluid show novel behaviors: the jet widens at its base (reverse swell phenomenon) and folds back and forth on itself (b). Both are a result of the interplay of non-Newtonian properties (viscoelasticity, shear-thinning) with gravitational, viscous, and inertial effects in the jets. We have mapped the jetting behaviors in the parameter space, composed of the height of fall, the flow rate, the viscosity and elasticity of the fluid - or the dimensionless numbers made out of their combinations. In addition, we have provided rationales for the transitions between the regimes, as well as predictions for the dependencies with the various parameters of folding amplitude and frequency and the amount of reverse swell. Jets of some shampoos show another behavior, the leaping shampoo or Kaye effect (c). The jet bends and slides on the top of a mound of liquid, jumping as high as 5cm for a jet radius of 1mm! (a) Coiling of a Newtonian silicone oil 2.7 Mo (b) Folding of a CPyCl jet, with very noticeable reverse swell 3.1 Mo (c) Leaping shampoo (speed 1/100) 16.7 Mo [1] N.M. Ribe, Coiling of viscous jets, Proc. Math. Phys. Eng. Sc., 460, 2051, 3223-3239 (2004)	(a) (b) (c)
Supramolecular rubber (with Philippe Cordier, in Ludwik Leibler's Soft Matter and Chemistry laboratory of the Ecole Superieur de Physique et Chimie Industrielles de Paris (ESPCI)) Supramolecular polymers are assemblies of small molecules, bound together by non-covalent interactions, that behave like polymers. The properties of the material developped in Ludwik Leibler's lab has some properties with huge potential. At low temperature, the molecules are bound by hydrogen links, and it has the mechanical advantages of a crosslinked rubber - low modulus, very high maximum strain, very low residual strain. At higher temperatures, the non-covalent bonds break apart, resulting in a low-viscosity, newtonian fluid. When the bonds are mechanically broken, they can reform if the two parts are put in contact. It is, therefore, an easy-to-process, "green", self-healing rubber. This research has been published in Nature [2] These properties have been found in the material when dodecane was added as a plasticizer. When water was used instead of dodecane, the rubber color changed from transparent yellow to opaque white. My work was to investigate the mechanical behaviour and the microstructure of that supramolecular rubber in this water-swollen version. These results have been presented in a report to the Ecole Polytechnique and may be published in the future. [2] Cordier, P., Tournilhac, T., Souli-Ziakovic, C. & Leibler, L. Nature 451, 977980 (2008)	From http://www.sciam.com/article.cfm?id=self-healing-rubber-keeps-stretching-after-rip

Viscoelastic jets

(with Trushant Majmudar, in Gareth McKinley's Non-Newtonian Fluids laboratory at the Massachusetts Institute of Technology (MIT))

Supramolecular rubber

(with Philippe Cordier, in Ludwik Leibler's Soft Matter and Chemistry laboratory of the Ecole Superieur de Physique et Chimie Industrielles de Paris (ESPCI))