Description du sujet de thèse

The PhD student will develop new electroactive polymers, including bio-based materials, with high electrocaloric (EC) cooling performance. These cooling performances will be optimized by adjusting key structural features and process parameters, all of which influence dielectric and EC properties. Various approaches will be explored. In-depth physical-chemical structural analysis will be conducted by the PhD student, thus allowing for the elucidation of the impact of these modifications on the polymers' architecture, crystallization, and electrocaloric properties. This analysis will contribute to the creation of a comprehensive 3D phase diagram (composition, temperature, electric field) for each newly developed material. Special attention will be given to reliably characterizing the electrocaloric effect. With this in mind, the PhD student will contribute to the development of a standardized approach to measure the performance of electrocaloric polymers. The polymers with the best performance will then be integrated into in flat, light, flexible, scalable, and energy efficient cooling devices in collaboration with research groups at Université Paris-Saclay.

Contexte de travail

After two years of record-breaking heat, cities all around the world have been threatened by temperatures soaring up to 50°C, straining inhabitants health, and bringing power grids on the verge of collapse. The need for a major leap forward in our strategies to tackle heatwaves in densely inhabited areas hence stands out. Cooling efficiency of traditional air conditioning systems is a major and central issue, as globally, up to 20 % of the electricity used in buildings is consumed by air conditioners and electric fans, according to the International Energy Agency. Nonetheless, the harshness of heat-waves, even in currently temperate areas, imposes a dire need for elaborating new approaches where standard air conditioners used in large indoor spaces, will work side by side with small, light, and easily deployable cooling devices able to keep vehicles, drug, and food containers, and human bodies (i.e. personal heat management) at a sustainable temperature, even when outdoor temperature peaks around 50 °C. This project proposes an innovative approach to cooling where electrocaloric (EC) P(VDF-TrFE-CFE) polymers films will be used as refrigerant in flat, light, flexible, scalable, energy efficient, cooling/heat-pump tiles. These will be working over a temperature difference of the order of 20-30 °C at 20 % of the Carnot COP with a cooling power of the order of 100 mW/cm2. An integrated approach to heat management, bringing the EC refrigerant into contact with the reservoirs shall allow reaching higher efficiencies and better compactness. This project will open the way to new, efficient, easily deployable, portable, and scalable cooling technologies that can drastically change how we tackle severe heatwaves.
In collaboration with University of Paris-Saclay and CentraleSupélec, the LCPO aims at developing new electroactive polymers to tackle the aforementioned challenges. The LCPO has a vast experience in electroactive polymers. This work includes the precise engineering of the microstructure of these semi-crystalline polymers, alongside in-depth characterization to elucidate their structure-property relationships and enhance their performance in various energy-related applications. These applications include ferroelectric capacitors, piezoelectric energy harvesters, pyroelectric temperature sensors and significant contributions to the development of electrocaloric coolers. The latter involves a patented approach that introduces unsaturation in the backbone of fluorinated polymers, resulting in some of the best electrocaloric performance recorded to date. Additionally, the LCPO has focused on formulating inks from these materials for industrially scalable printing techniques, such as screen printing, and has studied the influence of various solution processing parameters on the resulting device properties.