A molecular-level understanding of dynamics in imidazolium-based ionomers with different counterions and side chain lengths was investigated using X-ray scattering, oscillatory shear, and dielectric relaxation spectroscopy (DRS). Variations of the counterion size and side chain length lead to changes in glass transition temperature (T g ), extent of ionic aggregation, and dielectric constant, with consequences for ion transport. A physical model of electrode polarization is used to determine the number density of simultaneously conducting ions and their mobility. Imidazolium-based ionomers with larger counterion and longer side chain have lower T g , resulting in higher ionic conductivity and mobility. The ionic mobility is coupled to ion motions that are directly measured as a second segmental process in DRS, as these are observed to share the same Vogel temperature. Time−temperature superposition (tTS) was applied to create linear viscoelasticity master curves and to investigate the delay in chain motion related to ionic associations. tTS works well for these materials, and the terminal relaxation time increases with decreasing side chain length and smaller counterion size. X-ray scattering confirms the extent of ionic aggregation and helps to rationalize the observed dielectric constants. Larger counterions or longer side chains diminish ionic aggregation, and their ionomers have higher dielectric constants, which agree reasonably with the Onsager prediction at all temperatures studied. Smaller counterions or shorter side chains promote ionic aggregation, and their ionomers have lower dielectric constants, which are directly reflected in the lower content of simultaneously conducting ions.

In this paper, we report the high proton conductivity of a single high-purity Nafion nanofiber (1.5 S/cm), which is an order of magnitude higher than the bulk Nafion film ( approximately 0.1 S/cm). We also observe a nanosize effect, where proton conductivity increases sharply with decreasing fiber diameter. X-ray scattering provides a rationale for these findings, where an oriented ionic morphology was observed in the nanofiber in contrast to the isotropic morphology in the bulk film. This work also demonstrates the successful fabrication of high-purity Nafion nanofibers ( approximately 99.9 wt %) via electrospinning and higher humidity sensitivity for nanofibers compared to the bulk. These results should have a significant impact on fuel cells and sensors.

Ionic conductivity in new polymerized ionic liquids is of great interest as it applies to solidstate electrolytes for electrochemical and electromechanical applications. In this study, an ionic liquid monomer was synthesized and polymerized into random copolymers and their ionic conductivity and structure were investigated as a function of copolymer composition. Both nonionic-ionic and ionic-ionic copolymers were synthesized, where the nonionic and ionic monomers were hexyl methacrylate (HMA) and a methacrylate-based imidizolium neutralized with tetrafluoroborate (BF 4 ) or bis(trifluoromethane sulfonyl) imide (TFSI). In the nonionic-ionic copolymer, the ionic conductivity increased by over an order of magnitude with increasing HMA composition, even though the overall charge content decreased, because the addition of HMA significantly lowered the glass transition temperature. The ionic conductivity also increased by more than an order of magnitude in the ionic-ionic copolymer with increasing TFSI content, even though there was no change in the overall charge content, because substituting the larger anion TFSI for BF 4 resulted in weaker ionic interactions and also significantly lowered the glass transition temperature. In both types of copolymers, the temperature dependence of the ionic conductivity was well described by both Arrhenius and Vogel-Tamman-Fulcher models. An important difference between the two classes of random copolymers was that the nonionic-ionic copolymer exhibited microphase separation in X-ray scattering that correlated with a discontinuity in the increasing ionic conductivity with increasing HMA content suggesting that structure can also play a significant role in ion transport in polymerized ionic liquids.

Structure-property relationships for polymerized ionic liquids (PILs) relate chemical structure to ionic conductivity and reveal the importance of glass transition temperature ( T g ) and the energy associated with an ion-hopping mechanism for ion conduction for a series of alkyl-substituted vinylimidazolium PILs. The alkyl-substituted vinylimidazolium-based PILs with varying lengths of n -alkyl substituents provide diverse precursors with exchangeable anions to further enhance thermal stability and ionic conductivity. As the anion size increases, regardless of alkyl substituent length, T g decreases and the onset of weight loss, T D , increases. As the length of the alkyl substituent increases, T g decreases for PILs with Br − and BF 4 − counteranions. Ionic conductivity increases over an order of magnitude upon exchange of the counteranion from TfO − < Tf 2 N − . due to their unique combination of physical properties including high thermal stability, wide electrochemical window, negligible vapor pressure, and potentially high ionic conductivities. [3][4][5][6][7] Two particular classes of ILs are polymerizable ILs (PILs) that contain polymerizable functional groups and room temperature ILs (RTILs) with melting temperatures at or below room temperature. [ 8 ] Potential applications have included electrolytes in electromechanical transducers, artifi cial muscle fabrication, and non-volatile solvents for a myriad of chemical reactions. [ 9 ] Chen and Elabd investigated the solution properties and subsequent formation of electrospun fi bers of an imidazolium-containing methacrylate-based PIL. [ 10 ] This study revealed solution properties similar to polyelectrolyte solutions, and electrospun fi bers formed with intermediate fi ber diameters and onset of fi ber formation between polyelectrolyte and neutral polymers. The fi brous mats exhibited promising ionic conductivities at room temperature, and upon swelling with a RTIL, ionic conductivities were on the order of 10 mS cm − 1 . Long and co-workers also investigated the impact of counteranion on the solution and thermal properties of ammoniumbased polyelectrolytes. [ 11 ] Our study revealed the important infl uence of anion selection on the T g of the polyelectrolyte, and we observed polyelectrolyte electrospinning

New bis(ω‐hydroxyalkyl)imidazolium and 1,2‐bis[N‐(ω‐hydroxyalkyl)imidazolium]ethane salts are synthesized and characterized; most of the salts are room temperature ionic liquids. These hydroxyl end‐functionalized ionic liquids are polymerized with diacid chlorides, yielding polyesters containing imidazolium cations embedded in the main chain. By X‐ray scattering, four polyesters are found to be semicrystalline at room temperature: mono‐imidazolium‐C11‐sebacate‐C6 (4e), mono‐imidazolium‐C11‐sebacate‐C11 (4c), bis(imidazolium)ethane‐C6‐sebacate‐C6 (5a), and bis(imidazolium)ethane‐C11‐sebacate‐C11 (5c), all with hexafluorophosphate counterions. The other imidazolium polyesters, including all those with bis(trifluoromethanesulfonyl)imide (TFSI−) counterions, are amorphous at room temperature. Room temperature ionic conductivities of the mono‐imidazolium polyesters (4 × 10−6 to 3 × 10−5 S cm−1) are higher than those of the corresponding bis‐imidazolium polyesters (4 × 10−9 to 8 × 10−6 S cm−1), even though the bis‐imidazolium polyesters have higher ion concentrations. Counterions affect ionic conduction significantly; all polymers with TFSI− counterions have higher ionic conductivities than the hexafluorophosphate analogs. Interestingly, the hexafluorophosphate polyester, 1,2‐bis(imidazolium)ethane‐C11‐sebacate‐C11 (5c), displays almost 400‐fold higher room temperature ionic conductivity (1.6 × 10−6 S cm−1) than the 1,2‐bis(imidazolium)ethane‐C6‐sebacate‐C6 analog (5a, 4.3 × 10−9 S cm−1), attributable to the differences in the semicrystalline structure in 5c as compared to 5a. These results indicate that semicrystalline polymers may result in high ionic conductivity in a soft (low glass tranition temperature, Tg) amorphous phase and good mechanical properties of the crystalline phase.