Ionic Conductivity and Self-Assembly in Poly(isoprene‑<i>b</i>‑ethylene oxide) Electrolytes Doped with LiTf and EMITf

Diblock copolymers of poly­(isoprene-<i>b</i>-ethylene oxide), PI-<i>b</i>-PEO (IEO), are employed as templates for the development of nanostructured polymer electrolytes by salt-doping. For this purpose, lithium triflate (CF₃SO₃Li, LiTf) and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (CF₃SO₃–C₆H₁₁N₂, EMITf) salts were separately introduced at various [EO]:[salt] ratios. The local structure, nanodomain morphology and ion dynamics of the resulted block copolymer electrolytes were investigated by infrared spectroscopy, X-ray scattering, differential scanning calorimetry and dielectric spectroscopy. The structural investigation revealed strong effects of both LiTf and EMITf salt addition to the copolymer nanodomain morphology. These include transitions between different ordered nanophases and an increased domain spacing. The latter was independent of the kind of salt providing the possibility of studying ion transport under identical nanodomain sizes but in the presence of different interactions. Ionic conductivity in the two systems was fundamentally different. In IEO/EMITf ionic conductivity was much higher and comparable to the PEO/EMITf case. However, in IEO/LiTf, ion conductivity was reduced by a factor of a 100 relative to the PEO/LiTf case. This reflects combined effects of increased interaction parameter and of preferential wetting of electrodes. These results suggest ways for manipulating ion transport in polymer electrolytes

Kinetics of Light-Induced Concentration Patterns in Transparent Polymer Solutions

When exposed to weak visible laser light, solutions of common polymers like poly­(isoprene) and poly­(butadiene) respond by local concentration variations, which in turn lead to refractive index changes. Various micropatterns have been recently reported, depending mostly on the solvent environment and the irradiation conditions. Here, we focused on the simpler case of single polymer-rich filaments and we employed phase contrast microscopy to systematically investigate the influence of laser illumination and material parameters on the kinetics of the optically induced local concentration increase in the polydiene solutions. The refractive index contrast of the formed filaments increased exponentially with the laser illumination time. The growth rate exhibited linear dependence on the laser power and increased with polymer chain length in semidilute solutions in good solvents. On the contrary, the kinetics of the formed filaments appeared to be rather insensitive to the polymer concentration. Albeit the origin of the peculiar light field-polymer concentration coupling remains yet elusive, the new phenomenology is considered necessary for the elucidation of its mechanism