Viscoelastic and dielectric signatures in PMMA blends with ionic liquids

Poly(methyl methacrylate) (PMMA) was blended with two ionic liquids (ILs), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMIM-TFSI) and N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr₁₄-TFSI), to clarify how the IL amount and structure govern the viscoelastic and dielectric responses of the composite material. Samples were prepared by solution casting, followed by thermal, mechanical, and dielectric characterization. Differential scanning calorimetry revealed a monotonic decrease in glass transition temperature as a function of IL weight fraction, consistent with plasticization. Rheological measurements showed a pronounced reduction in the rubbery-plateau value and a decrease in segmental relaxation time, reflecting the plasticizing effect of ILs. Dielectric spectroscopy revealed a pronounced shift of the dominant loss peak to higher frequencies, consistent with accelerated IL-related dipolar/ionic dynamics in the blends, while the β-relaxation remained essentially unchanged and DC conductivity emerged. Fragility analysis further demonstrated suppressed cooperativity in segmental dynamics. Overall, ILs modify both segmental dynamics and charge transport. By combining rheology and dielectric spectroscopy, we obtain molecular-level insight into these changes and derive design guidelines for transparent antistatic polymer films.