Open positions

The Gulliver lab regularly proposes PhD or post-doc felowshipsand internship opportunities for ESPCI students, Master 1 and 2 students and foreign students.

The following links redirect to each team’s proposition list:

NEW

Assistant engineer in instrumentation and experimental technics

As part of the ’Competitions external IT 2017, CNRS’, a position ’Assistant-e engineer in instrumentation and experimental technics’ was awarded to the UMR Gulliver by the INC.

The competition calendar is available on the website: http://www.cnrs.fr/fr/travailler/concours.htm
(Attention: closing of registrations at the end of June)

PhD Thesis: Complex Fluids at Interfaces

Soft matter is the field of study of highly-deformable and squishy objects, at the crossroads between biophysics, chemistry, hydrodynamics, and mechanics. There, interfaces and thermal fluctuations are crucial and the elementary components, such as colloids and polymers, belong to a mesoscopic size range - between ten nanometers and a hundred microns, typically. These features make soft matter so special in the sense that the local material properties can have a very large impact at the macroscopic scale, inducing the rich and complex zoology of behaviours that we observe in everyday’s life, involving: droplets, plastics and glasses, gels for food and cosmetics, liquid crystals in optical displays...
With the recent improvement of the observation techniques, such as atomic force microscopy or the surface forces apparatus, the nanoscale is now commonly accessible in experiments. There is thus a general trend towards the investigation of confinement properties of soft matter, complex fluids, and supercooled liquids, with obvious impact for fundamental science and nanotechnology. In fact, due to the mesoscopic sizes of the elementary constituents (e. g. macromolecules or colloids) one can reach quasi-2D situations where these constituents feel or become even larger than the system size, leading to anomalous flow properties, rheology, or interface-induced effects such as slip or elastohydrodynamic forces.
Within this context, the Soft Math group at Gulliver/ESPCI has developed a growing expertise in applied mathematics and physical modelling of those intriguing objects, together with a strong international collaborative network involving experimentalists and a large accessible data base. Using a combination of analytics, numerical resolutions of partial differential equations, and molecular dynamics, and organizing extended stays for our team members in our collaborators’ labs, as well as weekly communications with them, we address new experimental problems and model them. Importantly, fundamental thinking also leads us to propose pure theoretical models and designs of experiments on open problems, such as the glass transition for instance.
The PhD candidate, interested by all theses aspects of our activities, ranging from modelling of concrete experimental questions to developing of fundamental theories on complex fluids at interfaces, should not hesitate to visit our websites and contact us for more details.
Contacts:
Elie Raphaël (http://www.pct.espci.fr/~elie, elie.raphael (arobase) espci.fr) Thomas Salez (http://www.pct.espci.fr/~tsalez, thomas.salez (arobase) espci.fr)

PhD Thesis: Glass Transition at Interfaces

According to Philip Anderson, the deepest and most interesting unsolved problem in solid-state physics is probably the glass transition. Indeed, glassy materials are ubiquitous in nature, and discussions about glass transition involve many areas of physics, from molecular and spin glasses to hard-sphere jamming. In spite of the intense interest in the dynamical slowing that accompanies glass formation, a single microscopic theory has yet to emerge. Nevertheless, the phenomenological approach of free volume and the Doolittle ansatz have been used to support the Vogel-Fulcher-Tammann (VFT) relation, which describes many of the observed behaviors. Fundamental to glass formation are the suggestions that particles are increasingly crowded, and relaxation requires the cooperative participation of a growing number of particles. The hypothesis of a cooperatively rearranging region, as introduced by Adam and Gibbs [1], is appealing and has been observed in computational studies.
The suggested existence of a length scale ξ for cooperative rearrangement has led to tremendous interest in confined glass formers. Perhaps, the most active example of attempts to probe ξ is the study of glassy polymer films, where fascinating observations have been made. For the most studied case of polystyrene, reductions in the measured glass-transition temperature have been almost uniformly reported as the film thickness is reduced [2], both experimentally and numerically. It has been further suggested that this apparent anomaly is linked to the observed existence of a more mobile interfacial layer [3]. As a consequence, there have been many theoretical attempts to understand the glass transition in confinement, with varying degrees of complexity and success, but as of today the problem remains unsolved and the controversy holds.
Even more intriguing is perhaps the existence of a universal behaviour of those Tg-reductions for free-standing polystyrene films with large molecular weights [4], that is when the thickness of the sample is comparable to the typical size of one macromolecule – its radius of gyration. This other class of anomalies, most probably related with purely polymeric effects, is still an open question. One qualitative mechanism based on a reptation-like sliding motion has been proposed [5], but it could not describe quantitatively the observations.
The main topic of the thesis will thus be to address such theoretical questions, using a combination of analytical and numerical tools. The team belongs to an international network, including experimentalists that are experts of the field, and the graduate student will interact strongly with them and visit the corresponding laboratories. Finally, other questions related with soft condensed matter and nanofluidics, and emerging from the network, will be addressed in parallel.
References:
[1] G. Adam G., J. H. Gibbs, On the temperature dependence of cooperative relaxation properties in glass-forming liquids. J. Chem. Phys. 43 139 (1965).
[2] J. L. Keddie, R. A. L. Jones, R. A. Cory, Size-dependent depression of the glass transition temperature in polymer films, Europhys. Lett. 27 59 (1994).
[3] Z. Fakhraai, J. A. Forrest, Measuring the surface dynamics of glassy polymers, Science 319 600 (2008).
[4] K. Dalnoki-Veress, J. A. Forrest, P.-G. de Gennes, J. R. Dutcher, Glass Transition Reductions in Thin
Freely-standing Polymer Films: a Scaling Analysis of Chain Confinement Effects, J. de Phys. IV 10 221 (2000). [5] P.-G. de Gennes. Glass transitions in thin polymer films. Eur. Phys. J. E, 2 201, 2000.
Contacts:
Thomas Salez (http://www.pct.espci.fr/~tsalez, thomas.salez (arobase) espci.fr) Elie Raphaël (http://www.pct.espci.fr/~elie, elie.raphael (arobase) espci.fr)

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Practical information

ESPCI Administrator: Stéphanie Ledoux
Tél. : 01 40 79 47 39
stephanie.ledoux (arobase) espci.fr

CNRS Administrator: Solange Rogue
Tél. : 01 40 79 47 27
solange.rogue (arobase) espci.fr

Director: Elie Raphaël
Tél. : 01 40 79 46 00
elie.raphael (arobase) espci.fr

Assistant Director: Olivier Dauchot
Tél. : 01 40 79 58 42
olivier.dauchot (arobase) espci.fr

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