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Reference : UMR8205-FLOROU-002
Workplace : CHAMPS SUR MARNE
Date of publication : Monday, May 11, 2020
Scientific Responsible name : Florence Rouyer
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2020
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Description of the thesis topic
Research in line with the pioneer work of Pickering succeeded recently to produce new objects which can be described as gas pockets in air and are named gas marbles. They are made of gas surrounded by a layer of grains constrained by thin liquid film in gas environment. The exceptional mechanical strength of their granular shell promise them to many applications  (for example: gas encapsulation, generation of materials with hierarchical porosity, acoustic insulation, vibration dampers).
At the microscale, three physical mechanisms inducing (possibly multicore) interactions between grains are at play: capillarity, grains contacts and viscous dissipation (in the liquid film and at the liquid/gas interfaces). The existence of gas marbles raises the following fundamental issues: How microstructure of the dispersed phases and microscale interactions are related and affect the macroscale behavior of the materials ? Are gas marbles and other ternary systems (unsaturated wet granular material, Pickering foams and granular foams) one class of material in a sense that they obey the same constitutive laws but with different state parameters defined by the physic at play at the microscale?
During this PhD, experiments will be performed in aim to understand the physical mechanism at the origin of these new objects and to characterize the mechanical properties of granular films and gas marbles. The studies of the two systems will allow correlating the physics at the two scales. On one hand, the static behavior of gas marble or gas marbles assemblies will be considered in regards to the elastic properties of the granular membrane/shell. On another hand, the dynamical properties of one gas marble or gas marbles assembly will be studied by acoustical waves propagation and interpreted considering the damping properties of granular films and assembly network. The multi-scale and ternary structure of the material might reveal different coupling modes of propagation (waves propagation in air and in the granular skeleton).
 Y. Timounay, O. Pitois, F. Rouyer, Gas Marbles: Much Stronger than Liquid Marbles, Phys. Rev. Lett. (2017). doi:10.1103/PhysRevLett.118.228001.
 “Gas Marbles” Store Air in Strong Spheres, June 2, 2017• Focus Physics 10, 62. 'Gas marbles' surprise with their strength, Kira Welter, Chemistry World, 14 June 2017. “Fortified gas marbles are 10 times stronger than regular bubbles”, Daily news, News Scientist, 8 June 2017. “Gas marbles are tough when squeezed”, Physics Today, 5 Jul 2017 in Research & Technology. “Robust marbles are made of air”, Physics World, 06 Jun 2017.
This PhD work is part of a ANR (French Agency of Research) project : PRC PhyGaMa starting January 2020 which concerns the PHysics of GAs MArbles. The project joins researchers from two laboraories : NAVIER (UMR CNRS, Ecole des Ponts et Université Gustave Eiffel) and FAST (UMR CNRS, Université Paris-Saclay).
This PhD will be conducted within the Rhéophysiqe team from NAVIER in Champs-sur-Marne. Few visits might be scheduled in FAST.
Constraints and risks
The candidate must have a degree Master degree (or engineer diploma) in Physics or Mechanics. The post requires knowledge of hydrodynamic, soft matter or granular matter as well as good level of communication skills, both oral and written (French and English required). Motivation, seriousness, ability to work independently and as part of a team will be taken into account during recruitment.
Applications must include a detailed CV; at least two references (people who may be contacted); a one page letter; a one-page summary of the master's thesis; grades
for the Masters 1 or 2 or the engineering degree).
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