Dielectric spectroscopy and rheology of polymeric and small-molecule electrolytes in the linear and nonlinear response regimes

• Applicant: Professor Dr. Roland Böhmer, since 8/2021
• Subject Area: Polymer Materials ; Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 461147152

An increasing number of electronic- and energy storage applications require materials which are not only electrically highly conducting, but are also featuring a mechanical behavior suitable for both industrial processing and safe usage. Volume miniaturization and mechanical flexibility, both technologically highly desirable, impose additional requirements on such electrolytes. To be able to optimize them, it is of utmost importance to understand the physical parameters that govern their charge and mass transport when they are experiencing such large electrical and/or mechanical fields. Polymer electrolytes and ionic liquids rigidified with suitable gelation agents (leading to so called ionogels) are particularly suitable model systems to address these issues. This is because via preparations including suitable charge concentrations, chain morphologies (in polymer electrolytes), and gelation agents (in ionogels), the electrical conductivity and mechanical stiffness of the resulting electrolytes can be fine-tuned. For such materials in which the local charge transport takes place on time scales much shorter than those corresponding to the structural rearrangements of the embedding matrix, a combination of nonlinear electrical and mechanical spectroscopies must be employed in order to elucidate, in a complementary fashion, the motional processes occurring beyond the linear-response regime. Adopting this approach, an important goal of this project is to clarify, on the one hand, how the electrical and mechanical degrees of freedom of soft ionic conductors are affected under increasingly stronger external fields and, on the other hand, to unravel how these degrees of freedom mutually impact on each other. The latter issue can be addressed, for instance, by monitoring the electrical conductivity of electrolytes that are subjected to strong oscillatory mechanical loads in so-called rheo-dielectric experiments. To monitor possible structural changes induced by large shearing, accompanying X-ray scattering investigations will be carried out in the framework of an existing collaboration. A direct comparability of the different measuring techniques requires the experimental and theoretical determination of analogous quantities, e.g., when the shear fluidity is to be compared with the electric conductivity or when the shear modulus is to be compared with the electric modulus in the nonlinear response regimes. Therefore, apart from performing the corresponding experimental investigations, another important goal of this project is to further develop existing models and constitutive equations and to further test and refine them on the basis of the experimental results. In this way, also an improved theoretical understanding of the charge and mass transport of the soft electrolytes under study can be expected.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Dr. Catalin Gainaru, until 8/2021