PhD subjects

Thermoelectric (TE) materials that are capable of converting heat into electricity have been considered as one possible solution to recover the low-grade waste-heat (from industrial waste-stream, motor engines, household electronic appliances or body-heat).



At SPHYNX, we explore thermoelectric effects in an entirely different class of materials, namely, complex fluids containing electrically charged nanoparticles that serve as both heat and electricity carriers. Unlike in solid materials, there are several inter-dependent TE effects taking place in liquids, resulting in Se values that are generally an order of magnitude larger that the semiconductor counterparts. Furthermore, these fluids are composed of Earth-abundant raw materials, making them attractive for future TE-materials that are low-cost and environmentally friendly. While the precise origins of high Seebeck coefficients in these fluids are still debated, our recent results indicate the decisive role played by the physico-chemical nature of particle-liquid interface.



The goal of the PhD project is two-fold. First, we will investigate the underlying laws of physics behind the thermoelectric potential and power generation and other associated phenomena in a special type of complex fluids, namely, ferrofluids (magnetic nanofluids). The results will be compared to their thermos-diffusive properties to be obtained through research collaboration actions. Second, the project aims to develop proof-of-concept hybrid solar-collector devices that are capable of co-generating heat and electricity.



The proposed research project is primarily experimental, involving thermos-electrical, thermal and electrochemical measurements; implementation of automated data acquisition system and analysis of the resulting data obtained. The notions of thermodynamics, fluid physics and engineering (device) physics, as well as hands-on knowledge of experimental device manipulation are needed. Basic knowledge of optics and electrochemistry is a plus. For motivated students, numerical simulations using commercial CFD software can also be envisaged.

The project is experimental and focuses on the study of new families of polyelectrolytes (PE) by determining their phase diagrams as a function of variations in temperature, added salt or pH. This will be done optically (microscopy, diffusion) at CEA Saclay. Once the diagrams have been established, the phase separation (PS) of the PE solutions will be studied by confocal fluorescence microscopy to determine the growth laws and the scaling behavior of the separation. Phase separation is a dynamic process that will be initiated by temperature or concentration quenches, followed by the acquisition of time series images or correlation functions. It will lead to the formation of spatial structures that will be used to achieve an interconnected porous geometry. The results will be translated into guidelines for membrane manufacturing procedures that will be applied in Montpellier (European Institute of Membranes) to manufacture porous polyimide membranes of high mechanical and thermal resistance. Another side of the project will be to reproduce the experimental finding by a theoretical model able 1/ to explain the measured phase diagrams, 2/ to complete existing phase field theories for phase separation of neutral polymers to describe PE phase separation.

To fight against infectious diseases, the design of antimicrobial materials and surfaces is gaining momentum. Beside the current COVID-19 pandemic and its direct consequences on other infectious diseases, the World Health Organization (WHO) is worried about another major health disaster that could arise because of the difficulties to fight against infections due to multidrug-resistant (MDR) bacteria and fungi. In this context, efficient antimicrobial materials and surfaces could play a key role to prevent the spread of such pathogens.



The objective of this thesis project is to develop antibacterial surfaces based on polyionene, a type of polymers that trap pathogens. These grafted surfaces developed at IRAMIS (3 patents) have been characterized by physico-chemical and biological studies. We have shown their effectiveness both as a bacterial trap (pro-adhesive effect) and antibacterial. The "bacterial trap" effect could be advantageously exploited to clean contaminated surfaces or to probe places that are difficult to access. This project will bring together chemists of IRAMIS (DRF) and in microbiologists of JOLIOT (DRF) to identify the best formulations of polymers and graftings, and to document the antibacterial effects on pathogenic agents (spores of Bacillus, vegetative forms of Gram + and Gram - bacteria).

Giving a general view of the colloidal stability of nanoparticles in a biological environment remains difficult. This comes mainly from the complexity of biological environments and the diversity of nanoparticles in terms of size distribution, shape, nature of external surface and nanostructure. In particular, the number of physico-chemical studies on “soft” organic particles obtained by self-assembly of bioconjugates remains low. To understand how the physico-chemical characteristics of "soft" nanoparticles direct their interactions with blood proteins, we propose, in collaboration with the Institut Galien, to study a concrete case where the nanostructure and the surface charge of the nanoparticles give different pharmacologically efficiency (analgesic). The objective is to study in detail how nanoparticles formed by self-assembly of bioconjugates interact with a model biological medium, taking into account both the main components (albumin, hemoglobin and lipoproteins) and the hydrodynamic flow from the circulation blood.