Conductivity of ionic liquid-derived polymers with internal gold nanoparticle conduits

The transport properties of self-supporting Au nanoparticle-ionic liquid-derived polymer composites were characterized. Topographic AFM images confirm the perforated lamellar composite architecture determined by small-angle X-ray scattering (SAXS) and further show that the in situ synthesized Au nanoparticles are localized within the hydrophilic (water) domains of the structure. At low Au nanoparticle content, the images reveal incomplete packing of spherical particles (i.e., voids) within these columns. The confinement and organization of the Au nanoparticles within the hydrophilic columns give rise to a large manifold of optical resonances in the near-IR region. The bulk composite conductivity, R_b, was determined by ac electrochemical impedance spectroscopy (EIS) for samples prepared with increasing Au ³⁺ content over a frequency range of 10 Hz to 1 MHz. A 100-fold increase was observed in the bulk conductivity at room temperature for composites prepared with the highest amount of Au³⁺ (1.58 ± 0.065 mol) versus the no Au composite, with the former reaching a value of 1.3 × 10^-4 S cm^-1 at 25 °C. The temperature dependence of the conductivity recorded over this range was well-modeled by the Arrhenius equation. EIS studies on samples containing the highest Au nanoparticle content over a broader range of frequencies (2 × 10 ^-2 Hz to 5 × 10⁵ Hz) identified a low frequency component ascribed to electronic conduction. Electronic conduction due to aggregated Au nanoparticles was further confirmed by dc conductivity measurements. This work identifies a nanostructured composite that exhibits both ionic transport through the polymeric ionic liquid and electronic conduction from the organized encapsulated columns of Au nanoparticles.