Description du sujet de thèse

The advent of the Internet of Things combined with the global energy transition requires taking into account the environmental impact of this new paradigm. Thus, ambient micro-energy harvesting (μW to mW range) has become an essential way to reduce the energy footprint of communicating sensors. In particular, the energy of low-frequency vibrations (<100 Hz) is usually recovered using piezoelectric oxides (PZT).
The objective of the project is to propose an alternative to piezoelectricity by developing eco-friendly flexoelectric polymer films, in accordance with the REACH regulation [1]. Flexoelectric effect, which corresponds to the appearance of an electric polarization induced by a strain gradient is a universal effect in all solid dielectrics. However, this coupling is relatively understudied and remains weak in comparison with piezoelectric effect in organic films. The goal is thus to elaborate and characterize highly polarizable all-organic soft films able to withstand large curvatures with sufficiently high flexoelectric coefficients to envisage their use as mechanical energy harvesters.
The two project partners (IETR, Nantes University and MOLTECH Anjou, University of Angers) have recently shown that giant flexoelectric coefficients could be achieved in specific semi-conducting polymers (1000 times larger than those of insulating polymers) under a curvature of 40 m-1 [2, 3].
These results are beyond the state of the art. The project will further improve the flexoelectric/mechanical properties of polymers conjugated by structural modifications allowing, for example, to increase the flexoelectric response at low frequency by flexoionic effect via the development of polyelectrolyte-conjugate systems. On the other hand, to obtain eco-responsible semiconductor polymers, syntheses with a limited environmental impact will be used to obtain conjugated systems, using solvents and green processes developed at MOLTECH-Anjou in recent years [4]. Finally, bioplastics based on plant raw materials will also be tested as a matrix charged by semiconductor molecules. All the materials developed will be used to manufacture and test energy harvesting prototypes subjected to different mechanical excitations in real conditions (air flow, seismic vibrations, sound pressure,...).
[1] https://www.ecologie.gouv.fr/reglementation-reach
[2] Saadeh, M, Frère, P, Guiffard, B. Revealing the flexoelectric‐like response of poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) thin films. Polym Adv Technol. 2020, 31, 2632– 2639
[3] Saadeh, M.; Aceta, Y.; Frère, P.; Guiffard, B. Enhancing flexoelectricity in PEDOT: PSS polymer films with soft treatments. J. App. Phys. 2021, 130 (1), 014103.
[4] Faurie, A. ; Grolleau J.; Gohier F.; Allain M.; Legoupy S.; Frère P. Toward sustainable organic semiconductors from a broad palette of green reactions. Eur. J. Org. Chem. 2017, 19, 2707-2714.

Contexte de travail

PhD will take place in the functional materials (FunMAT) team of the Institute of Electronics and Digital Technologies (CNRS affiliated research unit: IETR, Nantes University).
The ongoing activities of FunMAT cover wide aspects, from fundamental research on materials up to the characterization of their outstanding properties, and finally the electronic/microwave performance assessment of the related devices-demonstrators. More precisely, these actions are guided by the valorization and the control of the functional properties of the numerous materials developed within the FunMAT team, Nantes University. A particular emphasis is made on:
 the non-linear piezoelectric and ferroelectric properties of oxide bulk and thin film materials
 Flexoelectricity in polymeric films


The FunMAT's research is focused on the material elaboration and the improvement of their functional characteristics. The current studies deal with the description and interpretation of the observed phenomena, as well as the optimization of the targeted functional behaviors, even by developing specific characterization techniques.
Based on the electronic/microwave applications of the various studied material families, the research works are spread between 3 main topics:
 miniaturization and tunability
 sensor antennas
 energy harvesting and storage

The Materials/Devices co-design is a key advantage for the development of the future communicating & connected systems. In addition to the scientific progress in the field of electronic devices and antenna-based systems, the FunMAT activities open wide perspectives in other application areas, such as energy, healthcare, transport and Defense.
The PhD student will make some experiments in MOLTECH-Anjou (University of Angers)

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.

Informations complémentaires

Profil du candidat recherché :
Le (la) candidat(e) devra être titulaire d'un diplôme de Master en Science des matériaux, ou de chimie physique des polymères ou domaines connexes. Des connaissances en mécanique des milieux déformables et/ou en électronique seraient un plus. Le (la) candidate devra également présenter une affinité pour le travail expérimental et en équipe ainsi qu'une bonne maîtrise de l'anglais.
Eléments à fournir pour la candidature (par e-mail à benoit.guiffard@univ-nantes.fr et Pierre.Frere@univ-angers.fr) :
- CV
- lettre de motivation
- relevé de notes officiel de Master 1 (avec classement dans la promotion)
- si possible : relevé de notes officiel de Master 2 (avec classement dans la promotion, au moins de la partie écrite (sans le stage)
- lettre de recommandation du responsable de Master

Required qualifications
The successful candidate must hold a Master's degree in material science, polymer physics or a related field.
Experience in electromechanical characterization and electronics would be assets.
Good academic performance and a demonstrated knowledge of written and spoken English.
Strong interest in carrying out multidisciplinary and experimental research in team.


Document requirements
Curriculum Vitae - Your most recently updated C.V.
Grade transcripts and MSc diploma
Cover Letter
Letter of recommendation
To apply please send to benoit.guiffard@univ-nantes.fr and Pierre.Frere@univ-angers.fr