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PhD position - Dispersions of nanomagnets in ionic liquids for thermoelectric applications

par Emmanuelle Dubois, Guillaume Mériguet - 12 avril

The background of this PhD is a large European project called MAGENTA, MAGnetic nanoparticle based liquid ENergy materials for Thermoelectric device Applications, which began on the 1st of January 2017. Thermoelectric materials convert heat into electricity and are thus promising tools to produce electricity from waste heat, for example in automotive and microelectronic industries. The MAGENTA project proposes a disruptive technological pathway in thermoelectric material research, based on the use of ferrofluids in ionic liquids, which are colloidal dispersions of magnetic nanoparticles (nanomagnets) in ionic liquids.

In this project, the laboratory PHENIX focuses on the dispersion of magnetic nanoparticles in ionic liquids and on their thermodiffusive properties, in zero magnetic field and under field. Thermodiffusion indeed quantifies the gradient of concentration induced by a temperature gradient, through the Ludwig-Soret coefficient. Depending on several parameters, the nanoparticles move towards either cold or hot regions. This strongly influences the thermoelectric properties (Seebeck coefficient) and thus the voltage induced by a temperature gradient, measured by another partner of the project .

The controlled dispersion of maghemite γ-Fe2O3 nanoparticles (NPs) in ionic liquids is a key point of the project. Controlling the behaviour of these dispersions in a broad range of temperatures (up to 200°C) and under magnetic field is crucial for the considered use. The aim of the PhD is thus to find how to prepare such dispersions in the selected ionic liquids (provided by Solvionic, industrial partner of the project). This will be achieved by playing on the NPs/ionic liquid interface, as demonstrated in previous studies in Ethylammonium nitrate (EAN) [1]. In order to define the governing parameters for good thermoelectric properties, measurements need to be correlated to a deep knowledge of the details of the dispersions. This is the only way to understand the origin of the phenomena [2,3]. Therefore several physico-chemical quantities are necessary, as the refractive index, the charge of the nanoparticles, the interparticles interactions ... The latter quantities will be determined experimentally for example by Dynamic Light Scattering, Small Angle Scattering and/or electrophoresis. It needs to be explored in a broad range of temperature, which was never done before. In the course of the PhD, the candidate should also become involved in the thermodiffusion measurements.

[1] M. Mamusa et al, Concentrated assemblies of magnetic nanoparticles in ionic liquids , Faraday Discussions, 181, 193-209 (2015)
[2] C. Lopes Filomeno, et al, Ionic magnetic fluids in polar solvents with tuned counter-ions, Journal of Magnetism and Magnetic Materials, in press
[3] C. Lopes Filomeno, et al, Tuning the solid/liquid Interface in ionic colloidal dispersions : Influence on their structure and thermodiffusive Properties, J. Phys. Chem. C , in press

The applicant should be a good experimentalist interested in physical chemistry and able to work in an interdisciplinary team mixing physicists and chemists (7 permanent scientists at PHENIX covering all aspects of the subject). Around 30 PhDs are working at PHENIX, from many countries, part of them being involved in ionic liquids.

Contact : Dr. Emmanuelle Dubois
Net salary : 1430 €/month

Post-scriptum :

MAGENTA project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 731976.