Cation size-dependent modulation of dielectric and electrical features in PMMA/PEO/MoS _<b>2</b> nanocomposites functionalized with quaternary ammonium iodides

This research examines PMMA/PEO/MoS₂ ternary nanocomposites functionalized with tetrabutylammonium (TBAI), tetrahexylammonium (THAI), and tetramethylammonium (TMAI) iodides. XRD reveals reduced PEO crystallinity, with TMAI showing the strongest polymer–filler interactions. Cation size dictates distinct mechanisms: TBAI's bulky butyl groups enable MoS₂ interlayer intercalation, THAI provides optimal steric balance for uniform dispersion, while TMAI's small methyl groups favor surface adsorption, limiting polarization. Dielectric properties follow Maxwell–Wagner–Sillars polarization; TBAI achieves the highest permittivity (ε′≈51.2) and loss (ε″≈32.3) at 353 K, whereas TMAI exhibits minimal loss akin to the pure blend. Energy density shows no net gain due to the permittivity–loss trade-off. AC conductivity confirms order-of-magnitude enhancement for TBAI (σac≈1.79×10−6 S/cm), with impedance and modulus analyses validating enhanced ionic mobility for THAI and TBAI. THAI provides the optimal dielectric–transport balance. However, breakdown strength, cycling stability, thermal stability, and mechanical flexibility remain unevaluated, rendering practical application claims speculative. These findings offer fundamental guidance for future energy-storage material design.