Silica nanoparticles densely grafted with PEO for ionomer plasticization

Abstract

A method for densely grafting poly(ethylene oxide) chains to the surface of silica is presented. The PEO-grafted nanoparticles (PEONPs) are dispersed in a PEO single-ion conductor to accelerate ion transport with an additive that is not molecular, oligomeric, or ionic. Grafting high molecular weight brushes to nanoparticles suppresses PEO crystallinity and lowers the glass transition temperature of the nanocomposite ionomers. Ionic conductivity can be improved by up to an order of magnitude at room temperature with increasing PEONP content while viscosity is reduced. Dielectric spectra corroborate the enhanced ionic conductivity as ion relaxation times decrease with PEONP content. The PEONPs are compared with bare silica nanoparticles (SNPs), which demonstrate more homogenous dispersion in the PEO ionomer than PEONPs. Good dispersion in the SNP nanocomposite ionomers results in viscosity improvements by up to 3 orders of magnitude, but reduces ionic conductivity by one order magnitude. PEONPs show potential as additives to other solid electrolytes, while SNPs enable a more robust electrolyte with modest conductivity penalty.