Charge Transport of Polyester Ether Ionomers in Unidirectional Silica Nanopores

Dielectric relaxation spectroscopy is employed to investigate charge transport properties of two polyester ether ionomers in the bulk state and when confined in unidirectional nanoporous membranes (average pore diameter = 7.5 nm). Under nanometric confinement in nonsilanized pores, the macroscopic transport quantities (dc conductivity and characteristic frequency rate) are lower by about 1.4 decades compared to the bulk. The remarkable decrease of transport quantities in nonsilanized nanoporous membranes can be quantitatively explained by considering the temperature dependence of the interfacial layer between the ionomer and the silica membrane surfaces. On the other hand, an enhancement of dc conductivity is observed when the surfaces of the pores are treated with a nonpolar organosilane. This effect becomes more pronounced at lower temperatures and is attributed to slight changes in molecular packing density caused by the two-dimensional geometrical constraint

Introducing Large Counteranions Enhances the Elastic Modulus of Imidazolium-Based Polymerized Ionic Liquids

Polymerized ionic liquids (PILs) are believed to be ideal solid-state polymer electrolytes, and hence experimental and computational studies have been widely undertaken to understand the relationship between the chemical structure and mechanical/dielectric properties and the ionic conductivity of PILs. However, it is still a challenge to understand the effect of counterion ionic volume on the material properties of PILs. Herein, we demonstrate the effect of the ionic volume ratio of counteranions to side-chain cations on linear viscoelastic response using three imidazolium-based PILs with different counteranions. We show that the elastic modulus is significantly enhanced at temperatures higher than glass transition temperature once the ionic volume of the counteranion exceeds that of the side-chain cation. Our results provide an additional strategy to improve mechanical properties of PILs, while maintaining relatively high ionic conductivity

Polymerized Ionic Liquids: Correlation of Ionic Conductivity with Nanoscale Morphology and Counterion Volume

The impact of the chemical structure on ion transport, nanoscale morphology, and dynamics in polymerized imidazolium-based ionic liquids is investigated by broadband dielectric spectroscopy and X-ray scattering, complemented with atomistic molecular dynamics simulations. Anion volume is found to correlate strongly with <i>T</i>_g-independent ionic conductivities spanning more than 3 orders of magnitude. In addition, a systematic increase in alkyl side chain length results in about one decade decrease in <i>T</i>_g-independent ionic conductivity correlating with an increase in the characteristic backbone-to-backbone distances found from scattering and simulations. The quantitative comparison between ion sizes, morphology, and ionic conductivity underscores the need for polymerized ionic liquids with small counterions and short alkyl side chain length in order to obtain polymer electrolytes with higher ionic conductivity