Giant ELEctrostriction of soft NAnomaterials for energy harvesting – ELENA

The demand for new technologies of energy conversion is dramatically increasing with various needs in wireless micro-systems, robotics, portable electronics, medical applications, autonomous sensor networks, etc. Harvesting energy from mechanical ambient vibrations is one of the most promising approaches to power wireless MEMS and autonomous sensor networks. Variable capacitors made with electrostrictive materials, i.e. which exhibit changes of dielectric properties when they are deformed, present several advantages over other mechanical energy harvesters, such as piezoelectric or electromagnetic systems. Electrostrictive materials can be easily integrated in MEMS and operate at a low bias voltage. Mechanical vibrations induce changes of capacitance which are converted with the suitable electronics into electrical energy. The major challenge in the field consists in achieving large changes of capacitance under mechanical deformations. An exciting approach, which is based on the use of polymers filled with conductive nano-inclusions, is the topic of a fast and worldwide growing interest. The presence of the nanoparticles leads to an increase of the dielectric constant of the material. Non-percolated nanocomposites can exhibit large changes of capacitance in response to a mechanical deformation. Nevertheless, the potential of this technology is far from being optimized because the permittivity of materials that have been investigated is not yet sufficiently large and the sensitivity to stress of the materials (electrostriction coefficient) remains limited. Electrostrictive composites are generally made of random dispersions of particles without any structural optimization. In the ELENA project, we propose to fabricate and formulate self-assembled near-percolated networks of conductive carbon nanotubes (CNT) in elastic soft polymer matrices (poly-dimethyl siloxane). The stiffness, level of connectedness and morphology of the networks will be finely controlled via the interactions between the CNT, their segregation in emulsion templates or micro-fabrication processes including high resolution ink-jet printing. It has been experimentally shown in the frame of other studies (composites, dispersions of CNT, etc.) that such materials can exhibit giant dielectric constants in near percolated conditions. In addition, self-assembled or microfabricated near percolated networks are expected to exhibit a giant stress-sensitivity such as materials near a critical point. This opens a unique opportunity for novel electrostrictive materials with unprecedented performances. The key challenge of the ELENA project will consist in validating this exceptional potential. On the basis of actual measurements of the dielectric properties of CNT materials, we target improvements beyond the state of the art by more than one order of magnitude in terms of dielectric constant and electrostriction coefficients. This significant step forward will be validated by the integration of electrostrictive nanocomposites into organic or hybrid MEMS which will allow large strain deformations. Full validation will be achieved with the development of the suitable electronics to quantify the electrical energy produced by an actual demonstrator in device operation at completion of the project. Considering their unprecedented performances and the fact that they will be produced via low-cost and scalable technologies, devices developed in ELENA will offer new practical and effective solutions in the field of energy harvesting. The project will be developed by a multidisciplinary consortium that includes three academic laboratories with expertise in chemistry, physics, MEMS design and fabrication and electronics and one industrial partner actively working in the field of organic electronics.