Nanostructure and Local Dynamic Effects on Ionic Conductivity of Polymer-Grafted Nanoparticles in Ionic Liquids

In this talk, I will present our recent results about structures and dynamics of poly(methyl methacrylate) (PMMA)-grafted iron oxide nanoparticles in (1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) (HMIM-TFSI) / solvent mixtures. The dynamics of HMIM⁺ cation is measured with QENS experiments and conductivity of grafted particles in HMIM-TFSI is obtained from impedance spectroscopy. Higher diffusivity and conductivity were achieved when grafted particles are dispersed in HMIM-TFSI/acetonitrile mixture than in methanol. These results reveal that acetonitrile solvates HMIM-TFSI and better dispersion of grafted particles leads to better mixing between PMMA and TFSI^- anions. The ion-dipole interactions between TFSI^- and PMMA self-dissociate HMIM-TFSI, thereby increase the number of free cation carriers. The dynamic measurements combined with conductivity results suggest that grafted particles dispersion and conductivity increases with the solvation and with the interactions between high graft density PMMA and TFSI^-. Particles form strings in methanol and yield lower conductivity. In conclusion, both solvation and solubility of grafted particles in ionic liquid/solvent mixtures determine the mobility of ions in well-defined particle dispersions.