Flexoelectricity in soft conjugated polymer films – Flex-SCO

The project deals with experimental and theroretical study of ambient mechanical energy harvesting with flexoelectric-like polymer films. The considered transduction mechanism is the flexoelectric effect which corresponds to an electrical polarization induced by a strain gradient. This effect is expected to be exalted in the case of flexible compounds like soft polymers, which are able to withstand very large curvature. However, this presently understudied coupling remains weak in comparison with piezoelectric effect in organic films. The objective of Flex-SCO is to develop all organic films, with flexoelectric coefficients up to 1000 times larger than those actually measured, allowing to propose an alternative to piezoelectric materials. The methodology consists in using semi-conducting conjugated molecules/polymers exhibiting high polarizability. Hence, the objective is to enhance both the interfacial and ionic polarizations in polymer films to induce dipolar motion and free charges transport (i.e. large polarization changes) under strain gradient. The combination of the two functionalities- flexibility and enhanced flexoelectricity- would enable integration of these films in task-oriented devices for ambient low frequency (<100 Hz) micro-energy harvesting in the µW-mW range and from different sources (wind flow, pressure,..). Thus, flexoelectric polymer-based energy harvesters could contribute to power distributed and isolated low consumption sensors for the Internet of Things (IoT) applications.
The work program consists of 4 work packages (WPs).
The first WP deals with the project coordination and dissemination.
The second WP aims to bring out the structures which will allow to reach the highest flexoelectric coefficients, while maintaining good flexibility of the films and easy processing by conventional methods such as electrodeposition, spin coating or doctor blade. Mainly, based on the partners’ preliminary results and works recently published about flexoelectric effect in polyelectrolyte materials (PEM), three different axes of work around the conjugated materials have been identified: (1) structural modifications of conjugated systems; (2) conjugated polyelectrolyte systems and (3) dielectric polymers with conjugated side chains.
The third WP aims at gaining detailed information on structure and properties of the flexoelectric films in both pristine and blend forms, and the development of devices based on this knowledge. Structural, dielectric and flexoelectric properties of polymer thin films will be studied in purpose to selecting the compositions with the largest flexoelectric coefficients but also the ability for mechanical energy harvesting. A comprehensive study of the relationships between morphological and electrical, dielectric parameters and the flexoelectric response in polymer compositions will be realized as a function of the film thickness (range : 0.5 – 100 µm) in order to assess the size scaling effect. The influence of electrode configuration will also be studied. Based on this knowledge, energy harvesters will be developed and optimized in WP4.
WP4 is devoted to the realization and evaluation of flexoelectric polymer-based vibrational energy harvesters. Different types of harvesting devices will be studied depending on the mechanical excitation (forced vibrations, air flow, acoustic pressure,…). Design and assembly of specific test benches (like wind tunnel experiments) will be carried out to verify the electro-mechanical models and identify the optimal energy harvester configuration.