Influence Of Zwitterions on Properties and Morphology of Ionomers: Implications for Electro-Active Applications

Abstract : The influence of tailored electrostatic interactions on the physical properties and morphology of high performance polymeric membranes remains as a critical concern for emerging technologies. We demonstrated earlier the synthesis of acrylic-based sulfobetaine-containing copolymers in non-fluorinated solvents, and the electrospinning of such copolymers below the expected entanglement concentration. Swelling of the zwitterionomer membranes in EMIm ES ionic liquid at 10 wt% IL concentration resulted in composites with similar mechanical performance, but significantly higher ionic conductivities. In this work, we designed cationic ionomers bearing methanesulfonate anions for a direct comparison to the sulfobetaine-containing copolymers. We determined, employing DMA, SAXS and AFM, that the zwitterionomer films have superior mechanical performance to their cationic analogs and are more microphase separated. We propose that the stronger electrostatic interactions with zwitterions are ionic in nature, different from the dipole-dipole interactions in typical ionomers. In an effort to prepare zwitterionomer-based electro-active devices, we prepared zwitterionomer/EMIm ES composites using both the "swelling" and the "cast with" methods. A correlation of DMA, SAXS, and impedance spectroscopy results revealed that the sample preparation methods had a profound influence of the mechanical and electrical performance of the composite membranes.