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  1. Free, publicly-accessible full text available July 10, 2024
  2. Dusastre, Vincent (Ed.)
    A critical challenge for next-generation lithium-based batteries lies in development of electrolytes that enable thermal safety along with use of high-energy-density electrodes. We describe molecular ionic composite (MIC) electrolytes based on an aligned liquid crystalline polymer combined with ionic liquids and concentrated Li salt. This high strength (200 MPa) and non-flammable solid electrolyte possesses outstanding Li+ conductivity (1 mS·cm-1 at 25 °C) and electrochemical stability (5.6 V vs Li|Li+) while suppressing dendrite growth and exhibiting low interfacial resistance (32 Ω·cm2) and overpotentials (≤ 120 mV @ 1 mA·cm-2) during Li symmetric cell cycling. A heterogeneous salt doping process modifies a locally ordered polymer-ion assembly to incorporate an inter-grain network filled with defective LiFSI & LiBF4 nanocrystals, strongly enhancing Li+ conduction. This modular material fabrication platform shows promise for safe and high-energy-density energy storage and conversion applications, incorporating the fast transport of ceramic-like conductors with the superior flexibility of polymer electrolytes. 
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    We report on the shear rheology of liquid crystalline solutions composed of charged, rodlike polymers that form supramolecular assemblies dispersed in water. Under steady shear, we observe shear thickening behavior, followed by a hesitation in the viscosity accompanied by an extremely narrow range of negative first normal stress difference. The Peclet number (Pe, shear rate normalized by rod rotational diffusivity) for the onset of shear thickening is in agreement with previous, high-resolution numerical simulations of the Doi–Edwards–Hess kinetic theory. We interrogate these dynamic responses through shear step-down experiments, revealing a complex evolution of transient responses. Detailed analysis of the stress transients provides compelling evidence that the principal axis of the rod orientational distribution, the nematic director, undergoes a cascade of transitions and coexistence of periodic states known as kayaking, tumbling, and wagging, before transitioning to steady flow alignment above a critical shear rate. 
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  5. null (Ed.)
  6. Abstract

    In order to better understand the design rules of epoxy–phenol thermosets we will report on the chemistry and (thermo)mechanical properties of cured epoxy–phenol thermoset films.Ortho‐,meta‐andpara‐isomers of dihydroxybenzene (DHB) were reacted with the diglycidyl ether of bisphenol A (DGEBA) in the presence of an acid catalyst or triphenylphosphine (PPh3). The glass transition temperatures (Tg) of the cross‐linked films decreases in the order ofmeta‐ (Tg = 115°C) > ortho‐(Tg = 102°C) > para‐DHB (Tg = 96°C) as measured by differential scanning calorimetry. Uniaxial tensile testing of cross‐linked films showed excellent stress–strain behavior. The average ultimate strength values ranged from 65 to 82 MPa and the average values of the strain‐at‐break ranged from 4.8% to 6.9% at 25°C for all cross‐linked films. When a PPh3was used, the network properties were profoundly different. The base catalyzed thermoset of DGEBA andmeta‐DHB shows aTgof 85°C, which is 30°C lower than theTgof the acid‐catalyzed analog. Tensile films appear to be more ductile, as they exhibit a strain‐at‐break of 20%. The results of this study confirm that simple dihydroxybenzene hardeners can be used to prepare cross‐linked films with excellent thermomechanical properties.

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