Synthesis of surface-grafted conjugated polyelectrolyte multilayers as well as conjugated polymer hydrogels and a systematic study of interdependence of mixed conduction and degree of swelling

• Applicant: Professor Dr. Mukundan Thelakkat
• Subject Area: Polymer Materials ; Synthesis and Properties of Functional Materials
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 459614649

Organic mixed ion-electron conductors (OMIEC)act as active materials in organic electrochemical transistors (OECTs). These materials should show high ionic and electronic charge transport in swollen state under bias. The mixed conduction fully depends on the degree of swelling in aqueous media under bias and therefore, a control over the degree of swelling of the OMIEC is required to study and understand the interplay of diverse properties such as electronic transport, ionic transport, swelling and stability in aqueous media.In this project, we plan the synthesis of novel OMIECs with a control of swellability as well as high mixed ion-electron conduction properties towards highly efficient systems with operational stability in OECT devices without the requirement of external cross-linkers. Our hypothesis is that, a desired tuning and control of the degree of swelling of OMIECs is feasible by the use of a) conjugated polyelectrolyte multilayers and b) conjugated polymer hydrogels. Both systems will be surface grafted to ensure durability of the films in electrolyte. The conjugated polyelectrolyte multilayers will be realized by sequentially depositing anionic and cationic conjugated polyelectrolytes via LbL assembly. The conjugated polymer hydrogels will be prepared by C-H insertion cross-linking (CHic) of conjugated polyelectrolytes using polymerizable diazomalonic ester (MAz). Both concepts offer unique tissue-like soft mechanical properties combined with the electronic properties of organic semiconductors. The main aim is to control the degree of swelling to elucidate the influence of swelling on electronic and ionic properties of OMIECs in both types of systems. In the former, the degree of swelling will be tuned by the number of double layers, whereas in the latter it will be controlled by the degree of cross-linking. Another parameter to tune the swelling of the conjugated polyelectrolyte multilayers is by varying the salt concentration and ionic strength of the electrolyte. We specifically focus on: 1. How does the LbL assembly of multilayers vary from CHic approach in terms of degree of swelling, its control, on response time, cycling and thin film stability of an OECT? 2. How does mixed conduction depend on the degree of swelling ?The elucidation of mixed conduction as a function of swelling as envisaged in this proposal, facilitates the understanding of complex interplay of swelling and mixed-ionic electronic transport properties for the first time in a systematic way. This proposal offers a fundamental step towards establishing guidelines in designing efficient OMIECs which fulfil all the desired prerequisites of optimum swelling, high ion and electron transport as well as stability in aqueous medium.

• DFG Programme: Research Grants