Composite Polymer Electrolytes Based on Poly(ethylene glycol) and Hydrophobic Fumed Silica:  Dynamic Rheology and Microstructure

Abstract

Dynamic rheological techniques are used to probe the microstructures present in fumed silica-based composite polymer electrolytes. These electrolytes are obtained by dispersing hydrophobic fumed silica in a poly(ethylene glycol)−lithium salt solution and display high conductivities (σ298K > 10-3 S/cm), mechanical stability, and easy processability. The materials behave as soft solids (gels) under ambient conditions due to the presence of a three-dimensional network of silica entities. Network formation occurs as a result of van der Waals (dispersion) forces between the nonpolar surface layers on silica units. Factors which affect the van der Waals interaction, and hence the gel network density, include the nature of the PEG end group, the presence of ionic species, and the size of the hydrophobic surface group on the silica. The composites also exhibit shear-thinning behavior due to the shear-induced disruption of network bonds, and this behavior can be advantageously utilized in electrolyte processing.

Highly CO2‐Permeable and ‐Selective Membranes Derived from Crosslinked Poly(ethylene glycol) and Its Nanocomposites

“…Addition of inorganic nanoscale fillers such as FS can, at certain concentration and temperature conditions, result in the formation of physically crosslinked colloidal networks, as described in detail by Raghavan et al [23] and, more recently, Walls et al [24] in their rheological studies of polymer-based electrolyte gels. The requirements for a physical network in this regard are two-fold: [25] i) G¢ (the dynamic elastic shear modulus) must be consistently greater than G² (the dynamic viscous shear modulus), and ii) G¢ must be independent of the oscillatory frequency (x), especially in the terminal zone at low x (which corresponds to long relaxation times).…”

Nanocomposite polymer electrolytes containing silica nanoparticles: Comparison between poly(ethylene glycol) and poly(ethylene oxide) dimethyl ether

“…With these properties, fumed silica nanoparticles create a threedimensional network that prevents the viscous flow of low molecular weight polymer, and thus providing the required mechanical strength of polymer electrolytes. [25][26][27] In this study, the composite polymer electrolytes consisting of low molecular weight PEO, iodine salt MI (M 5 K 1 , imidazolium 1 ), and fumed silica nanoparticles have been prepared and characterized. Especially two kinds of electrolyte medium, i.e., poly (ethylene glycol) (PEG) and PEO dimethyl ether (PEODME), were compared to investigate the effect of terminal group in PEO, i.e., hydroxyl (À ÀOH) and methyl (CH 3 ).…”

Nanocomposite Electrolytes with Fumed Silica and Hectorite Clay Networks: Passive versus Active Fillers

“…[25±27] When a sufficient amount of fumed silica is dispersed in the liquid PEGdm±LiTFSI electrolyte, the fumed silica organizes into a three-dimensional network that provides the requisite mechanical strength through physical gelation [26,28] while retaining favorable ion transport with an ionic conductivity (r) in excess of 10 ±3 S cm ±1 at ambient temperature. [29] While the mechanical properties of such nanocomposites are primarily governed by the fumed silica, [26] ion transport is dictated by the PEGdm±LiTFSI matrix.…”

“…[29] While the mechanical properties of such nanocomposites are primarily governed by the fumed silica, [26] ion transport is dictated by the PEGdm±LiTFSI matrix. In contrast, nanocomposites derived from hectorite are formed by dispersing Li-exchanged synthetic hectorite in a mixture of EC and either PEGdm or propylene carbonate (PC).…”