Ionic liquid mixed with poly(methyl methacrylate)-grafted nanoparticle aggregates at low particle concentrations was shown to exhibit different dynamics and ionic conductivity than that of pure ionic liquid in our previous studies. In this work, we report on the quasi-elastic neutron scattering results on ionic liquid containing polymer-grafted nanoparticles at the higher particle concentration. The diffusivity of imidazolium (HMIM + ) cations of 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (HMIM-TFSI) in the presence of poly(methyl methacrylate)-grafted iron oxide nanoparticles and the ionic conductivity of solutions were discussed through the confinement. Analysis of the elastic incoherent structure factor suggested the confinement radius decreased with the addition of grafted particles in HMIM-TFSI/solvent mixture, indicating the confinement that is induced by the high concentration of grafted particles, shrinks the HMIM-TFSI restricted volume. We further conjecture that this enhanced diffusivity occurs as a result of the local ordering of cations within aggregates of poly(methyl methacrylate)-grafted particles.
This content will become publicly available on June 28, 2023
Ion Channels in Sulfonated Copolymer-Grafted Nanoparticles in Ionic Liquid
The use of ionic liquids as solvent for polymers or polymer-grafted nanoparticles provides an exciting feature to explore electrolyte-polymer interaction. 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (HMIm-TFSI) holds specific interactions with the polymer through ion-dipole or hydrogen bonding. For this work, poly(methyl methacrylate)-b-poly(styrene sulfonate) (PMMA-b-PSS) copolymer-grafted Fe3O4 nanoparticles with different sulfonation levels (~4.9-10.9 mol% SS) were synthesized and their concentration dependent ionic conductivities were reported in acetonitrile and HMIm-TFSI/acetonitrile mixture. We found that conductivity enhancement with the particle concentration in acetonitrile was due to the aggregation of grafted particles, hence sulfonic domain connectivity. The ionic conductivity was found to be related to the effective hopping transfer within ionic channels. To the contrary, the conductivity decreased or remained constant with increasing particle concentration in HMIm-TFSI/acetonitrile. This result was attributed to the ion coupling between ionic liquid and copolymer domains.
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- Soft Matter
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- National Science Foundation
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