Fractal forming species and hierarchical growth in polymer electrolyte composites: Raman mapping and role of seed particles

Diffusion limited aggregation (DLA) is being reported in a polymer electrolyte composites PEO:NH4I + Al2O3 (acidic, basic and neutral). The aggregating specie is found to be I 3 - by using XRD and Raman spectroscopy. The involvement of NH 4 + ion in the fractal pattern formation has also been explained via ion pairing with I 3 - (i.e., M+ + I 3 - → M+ I 3 - ), by making ammonium tri-iodide specie. Raman mapping has been done to analyze the fractal forming species in detail. A qualitative model has been proposed to explain the observations. The aggregates that get frozen in the host polymer matrix by diffusive growth form different patterns and are found to have fractal dimension that varies from 1.6 to 1.8 which is consistent with diffusion limited aggregation. The steady state of ion diffusion in polymer electrolyte is analyzed in the framework of the Nernst–Planck equation. The ion transport mechanism in the polymer electrolyte composite (with and without fractal growth), has been studied with the help of ac conductivity (σ) and ionic/electronic transference number (ti/te).