The
primary challenge regarding solid polymer electrolytes (SPEs)
is the development of materials with enhanced mechanical modulus without
sacrificing ionic conductivity. Here, we demonstrate that when stiff/rigid
polymer nanoparticles that are thermodynamically miscible with a polymer
are utilized in a blend with a liquid electrolyte, the elastic modulus
and the ionic conductivity of the resulting SPEs increase compared
to the linear polymer blend analogues. In particular, when poly(methyl
methacrylate), PMMA, nanoparticles, composed of high functionality
star-shaped PMMA, were added to low molecular weight poly(ethylene
oxide), PEO, doped with bis(trifluoromethane)sulfonamide (LiTFSI),
the resulting SPEs exhibit 2 orders of magnitude higher conductivity
and 1 order of magnitude higher mechanical strength compared to their
linear PMMA blend analogues. In addition, the former remain solidlike
over an extended temperature range. Key to their performance is the
morphology that stems from the ability of the PMMA nanoparticles to
disperse within the liquid electrolyte host, allowing for the formation
of a highly interconnected network of pure liquid electrolyte that
leads to high ionic conductivity (comparable to that of the neat PEO
electrolyte). The present strategy offers tremendous potential for
the design of all-polymer electrolytes with optimized mechanical properties
and ionic conductivity over a wide temperature window for advanced
electrochemical devices.
We investigated the linear viscoelasticity of bottlebrush polystyrenes (PSs) with total molar masses ranging from 132 to 769 kg/mol, bearing short side chains (with molar masses of 5 and 7 kg/mol, well below the entanglement limit of PS). Their estimated length to diameter ratio was smaller than 1, corresponding to a globular conformation and conforming to the molar mass dependence of the radii and to recent computer simulation results. The master curves were constructed by means of time− temperature superposition and featured a hierarchical relaxation (glassy, side-chain, intermediate, and terminal regimes) along with the absence of a rubbery plateau, indicating that the entire macromolecules behaved as unentangled polymers, though with some distinct features. The analysis of the dependence of storage and loss moduli on oscillatory frequency revealed cooperative side-chain dynamics at intermediate frequencies because of their mutual repulsion and Rouse-like dynamics at low frequencies. The zero-shear viscosity scaled with the total molar mass of the bottlebrush as η 0 ≈ M w,bottlebrush like Rouse chains; however, the respective dependence of the terminal flow time appeared to be stronger. The estimated values of the fragility index suggested that these unentangled bottlebrushes became stiffer with increasing length of the side chains but remained less stiff compared to linear PSs of the same total mass. These results are compared with and contrasted against bottlebrush data from the literature, suggesting universalities and distinct features likely attributed to chemical differences and calling for further investigations.
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