Polarization and Ion Transport in Poly(ionic liquid)-Grafted Nanoparticles

Poly(ionic liquid)-grafted nanoparticles (PILgNPs) are building units of PIL-based hybrid electrolytes where the nanoparticle structures and the connectivity of polyelectrolyte chains determine ion transport properties. This connectivity is enhanced by increasing the molecular weight of grafted PIL chains, which further enhances their molar conductivity. In this work, we integrate simulation and experimental results to explain the polarization response of PILgNPs under electric fields. We design dielectric measurements, where the conductivity of the samples is measured under large voltage gradient, to test whether PIL-grafted chains can be polarized by electric fields. PILgNPs with distinct graft lengths and graft densities are synthesized and characterized. Samples at low graft density exhibit negative and positive deviations in conductivity in reference to their unperturbed (no-field) state. Their response is observed to be irreversible as the conductivity continues increasing even in the absence of oscillating external fields during zero-field rest intervals. In contrast, the steady conductivity measured for the high graft density sample is attributed to the constraints where the re-arrangements of chains are entropically hindered. These results are explained by the polarization-induced chain reorientation under electric fields, corroborated through molecular dynamics simulations.