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Browsing by Author "Colby, Ralph H."

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    Imidazole-containing triblock copolymers with a synergy of ether and imidazolium sites
    Jangu, Chainika; Wang, Jing-Han Helen; Wang, Dong; Fahs, Gregory B.; Heflin, James R.; Moore, Robert Bowen; Colby, Ralph H.; Long, Timothy E. (The Royal Society of Chemistry, 2015-03-06)
    Reversible addition-fragmentation chain transfer (RAFT) polymerization enabled the synthesis of well-defined A-BC-A triblock copolymers containing a synergy of pendant ether and imidazolium sites. The soft central BC block comprises low Tg di(ethylene glycol) methyl ether methacrylate (DEGMEMA) and 1-(4-vinylbenzyl) methyl imidazolium units. External polystyrene blocks provide mechanical reinforcement within a nanoscale morphology. Dynamic mechanical analysis (DMA) of the A-BC-A triblock copolymers exhibited a plateau region, which suggested the formation of a microphase-separated morphology. Atomic force microscopy (AFM) and small angle X-ray scattering (SAXS) collectively probed the morphology of the A-BC-A triblock copolymers, revealing long-range order at the nanoscale dimensions. Dielectric relaxation spectroscopy (DRS) examined the ion-transport properties of ionomeric A-BC-A triblock copolymers and random copolymers with different compositions. The role of morphology was demonstrated with block copolymer nanoscale structures providing superior ionic conductivity and mechanical performance compared to random copolymers. Under a 4 V direct current (DC) applied voltage, electromechanical transducers derived from these triblock copolymer membranes with added ionic liquid showed superior actuation performance compared to a benchmark Nafion[registered sign] membrane, suggesting potential for ionic polymer device applications. This was attributed to optimum modulus, improved ionic conductivity, and microphase-separated morphology of triblock copolymers.
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    Uncorrelated Lithium-Ion Hopping in a Dynamic Solvent-Anion Network
    Yu, Deyang; Troya, Diego; Korovich, Andrew G.; Bostwick, Joshua E.; Colby, Ralph H.; Madsen, Louis A. (American Chemical Society, 2023-03)
    Lithium batteries rely crucially on fast charge and mass transport of Li+ in the electrolyte. For liquid and polymer electrolytes with added lithium salts, Li+ couples to the counter-anion to form ionic clusters that produce inefficient Li+ transport and lead to Li dendrite formation. Quantification of Li+ transport in glycerol-salt electrolytes via NMR experiments and MD simulations reveals a surprising Li+-hopping mechanism. The Li+ transference number, measured by ion-specific electrophoretic NMR, can reach 0.7, and Li+ diffusion does not correlate with nearby ion motions, even at high salt concentration. Glycerol's high density of hydroxyl groups increases ion dissociation and slows anion diffusion, while the close proximity of hydroxyls and anions lowers local energy barriers, facilitating Li+ hopping. This system represents a bridge between liquid and inorganic solid electrolytes, thus motivating new molecular designs for liquid and polymer electrolytes to enable the uncorrelated Li+-hopping transport needed for fast-charging and all-solid-state batteries.