Numerous electrochemical systems depend upon ion-conducting polymer electrolyte materials used as membrane separators and electrode binders. In this project, the ionic conductivity of model thin film, self-assembled block copolymer electrolytes (BCEs) were investigated using advanced metrology and molecular dynamics simulations. Ionic conductivity dictates ohmic overpotentials across polymer ion-exchange separators and the energy efficiency in deionization platforms. The preparation of model thin films commences with perpendicular alignment of self-assembled poly(styrene-<i>block</i>-2-vinyl pyridine) (PS<i>b</i>P2VP) 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. BCEs with systematically varied side-chains, such as alkoxy crosslinks, alkyl, and zwitterionic, to pyridinium were prepared post self-assembly using newly developed processing schemes. The side-chains were installed in the BCEs while retaining the microphase separated nanostructure from self-assembly. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) confirmed retention of the structure after successful alkylation and the presence of the side-chain chemistry. Ionic conductivity was measured on interdigitated electrode substrates with the various BCEs interfaced with DI water and under different relative humidity percentages. Molecular dynamics simulations were performed on three model BCE systems representing polymers with alkoxy, alkyl and zwitterionic side chains on the pyridinium group, complementing the experimental studies, to assist in obtaining molecular level insight into the solvation structures and the ion transport processes in the materials. The initial simulation results show that ion-charge pairs (i.e., counterion and positively charged pyridinium) in the BCEs are dissociated and the chloride ions are mainly solvated by water present in the system.

Understanding the extent of ionic dissociation and ionic conductivity in model thin film polymer electrolytes as a function of different side chain configurations

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