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Electrolytes in super-hydrophobic confinement

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Hydrophobic nanoporous materials behave as anti-sponges when immersed within aqueous solutions. The liquid, that can be forced to enter the nanopores at high pressure, is spontaneously expelled out of the pores when the pressure is released. This process, that converts mechanical energy into interfacial energy, in a reversible manner, is appealing for a quick storage/restitution of energy with high efficiency and power density one order larger than the one of current energy storage solutions in particular supercapacitors based on nano structured materials [1].

The fundamental research developed at the Liphy on nanoporous anti-sponges is driven with the applicative prospect of kinetic energy recovery in urban transportation (ANR LyStEn). From a physical point of view, the process involves nano-capillarity phenomena such as the wetting and the drying of solid surfaces by a liquid in a confined environnement [2]. We have recently demonstrated that electrolyte solutions can be particularly attractive to significantly increase the amount of stored energy via an osmotic contribution based on the selectivity properties of sub-nanometer pore size materials [3]. This osmotic contribution arises in particular because steric repulsion of ions out of small pores.
Now if the pores are slightly larger than the ions what is the behavior of the electrolytes ? How ions organize inside the pores ? What is the the contributions of electrostatic interactions ? What is the impact on intrusion and extrusion ? The goal of the PhD is to address these questions considering electrolyte solutions confined in ordered supra-nanometer pore size material in the range 1-10 nm.

This will be done combining dynamical high pressure experiments on a unique instrument developed at the LiPhy and neutron scattering experiments devoted to the characterization of hydrophobic nanoporous material and liquid confined within the nanopores. The overall objective is to understand the physical mechanisms governing the intrusion and extrusion of solutions in hydrophobic confinements in various conditions, and elaborate a quantitative modelisation of coupled phenomena.

The thesis, funded by the LyStEn project, will be directed by Elisabeth Charlaix and Cyril Picard. The work will be done in interactions with several members of the LiPhy and will rely on collaborations in France and abroad.

The candidate should have a strong background in physics, soft matter and material science, as well as good interests in physico-chemistry. More generally the candidate should feel at ease with transdisciplinarity.

Contacts :

[1Q. ZHANG et al. Nanomaterials for energy conversion and storage, Chem. Soc. Rev. 42.7 (2013)

[2L. GUILLEMOT et al. Activated drying in hydrophobic nanopores and the line tension of water, Proc. Natl. Acad. Sci. 109.48 (2012)

[3M. MICHELIN-JAMOIS et al. Giant osmotic pressure in the forced wetting of hydrophobic nanopores, Phys.Rev.Lett. 115 (2015)