Modelling the behaviour of elastomers doped with ionic liquids for displacement sensor & energy harvesting applications

For the past ten years, laboratories at INSA Lyon (LGEF, ElyTMaX^a, IMP and MateIS) have been collaborating with laboratories at Tohoku University (based in Sendai, Japan) on the study of electro-active polymers. In this context, we are interested in elastomers lightly doped with ionic liquids (low melting point salts). These electrode-coated materials can deform under the action of an external electric field in flexion. The origin of this deformation is the diffusion and accumulation of ions in the vicinity of the electrodes. Interestingly, after removal of the electric field, a residual anion-rich layer is observed in a stable manner. We also observed that after such a treatment, imposing a deformation on these materials generates an electrical potential difference on their electrodes, which corresponds to the conversion of mechanical energy into electrical energy.

The aim of this thesis is to improve our understanding of the behaviour of this type of material and, ideally, to predict the performance of other, untested materials in order to suggest ways of improving it. It will take the form of a Franco-Japanese collaboration (18 months in France and 18 months in Japan) to: 1) experimentally study the electro-mechanical behaviour and the evolution of the structure under stress of these new materials 2) model and simulate the effect of stress/strain fields on the local concentration of ionic charges, which modifies the electric field gradients and therefore the potential. More specifically, mechanically activated diffusion of ions will be modelled and simulated via a finite element code using experimentally determined material parameters (diffusion coefficients and dielectric permittivity). The role of the anionic layer and its structure will need to be explained, and its stability as a function of the imposed deformation is probably one of the key points in this behaviour. The results obtained could be used to propose new types of sensors or materials for energy harvesting.

The thesis will initially take place on the Doua campus in Villeurbanne, mainly at the LGEF and ElytMaX^a, with the possibility of working with the project's partner laboratories (IMP and MateIS). The candidate will then go to Sendai in Japan to the University of Tohoku. If the candidate is selected by a jury from the INSA Lyon doctoral school, he/she will receive a grant from the Ministry of Higher Education of around €1,700 per month (net). Travel costs between France and Japan will be covered. He/she may also be able to do some additional teaching. (^a The ElyTMaX laboratory is an IRL (International Research Laboratory), part of which is based in Lyon and the other in Sendai.)

We are looking for a candidate with a Master's degree or an engineering degree specialising in physics and/or materials science. The candidate should have been introduced to the use of finite element methods. Given the particular context of the thesis, the candidate will also need to be mobile and adaptable. The main language of the thesis will be English. (Knowledge of French and Japanese is not required)