(307d) Understanding the Extent of Ionic Dissociation and Ionic Conductivity in Model Thin Film Polymer Electrolytes As a Function of Different Side Chain Configurations

Numerous electrochemical systems depend upon ion-conducting polymer electrolyte materials used as membrane separators and electrode binders. In many instances, the rate of ion transport within these materials governs ohmic resistances and energy efficiency. A key challenge in ion-conducting polymer electrolyte materials for fuel cells, electrolysis, and electrochemical separations is robust and stable performance under a wide range of hydration values. Central to the rationale design of ion-conducting polymers is a fundamental understanding as to how chemical composition and macromolecular architecture influence thermodynamic and transport behavior of ions and water. In this presentation, I will present our work on studying the ionic activity coefficients and ionic conductivity of model thin film block copolymer electrolytes prepared via directed self-assembly and characterized via advanced metrology and molecular dynamics simulations. The preparation of model thin films commences with perpendicular alignment of self-assembled poly(styrene-block-2-vinyl pyridine) (PSbP2VP) lamellae to the substrate surface. The conversion of the non-ionic block copolymer into a block copolymer electrolyte occurred by alkylating the nitrogen in the P2VP domain with various halogenated reagents via a Menshutkin reaction. Alkoxy crosslinks and alkyl side-chain to pyridinium were prepared and compared against existing data sets on n-methyl pyridinium. New processing schemes were devised to introduce alkoxy and alkyl side chains post self-assembly without disrupting the nanostructure morphology. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) confirmed retention of the structure after successful alkylation. The differences in activity coefficients with the various side chain configurations were determined via ion sorption experiments and swelling-deswelling behavior using a quartz crystal microbalance. Ionic conductivity was probed at different relative humidity percentages on interdigitated electrode substrates. Finally, molecular dynamics (MD) simulations were also performed to assess ionic dissociation and ionic conductivity on the BCEs with the various hydrophilic, alkoxy side chains and hydrophobic, alkyl side chains.