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Molecular Alignment and Ion Transport in Rigid Rod Polyelectrolyte Solutions
journal contribution
posted on 2014-05-13, 00:00 authored by Ying Wang, Jianwei Gao, Theo J. Dingemans, Louis A. MadsenCombining molecular alignment with
selective ion transport can
increase the freedom to design ion-conducting polymeric materials
and thus enhance applications such as battery electrolytes, fuel cells,
and water purification. Here we employ pulsed-field-gradient (PFG)
NMR diffusometry, 2H NMR spectroscopy, polarized optical
microscopy, and small-angle X-ray scattering to determine relations
between counterion transport, dynamic coupling of water, and molecular
alignment in aqueous solutions of a rigid rod sulfonated-aramid polyelectrolyte:
poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide)
(PBDT). 23Na PFG NMR on PBDT solutions and simple sodium
salt solutions shows significantly slower Na+ counterion
diffusion in PBDT, providing agreement between counterion condensation
theory and quantitative transport information. Strikingly, from 2H NMR spectroscopy we observe that the orientational order
parameter of partially aligned solvent D2O molecules increases
linearly with polymer weight percentage over a large concentration
range (1.4 to 20 wt %), while the polymer chains possess essentially
a large and fixed order parameter Smatrix = 0.76 as observed using both SAXS and 2H NMR on labeled
polymers. Finally, we apply a two-state model of water dynamics and
a physical lattice model to quantitatively relate D2O spectral
splittings and nematic rod–rod distance. These studies promise
to open new pathways to understand a range of anisotropic polymer
systems including aligned polymer electrolyte membranes, wood composites,
aligned hydrogels, liquid crystals, and stretched elastomers.
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Keywords
counterion transporttransport informationfuel cellsalignmentD 2Ocounterion diffusionanisotropic polymer systems2 H NMR spectroscopybattery electrolyteslattice model23 Na PFG NMRNMR diffusometrywood composites2 H NMRSAXSorder parameter Smatrixorientational order parameterPBDT solutionspolymer electrolyte membranesstudies promiseion transportcounterion condensation theorypolymer weight percentagewater purificationD 2O molecules increasesIon TransportMolecular AlignmentRigid Rod Polyelectrolyte SolutionsCombiningwater dynamicssodium salt solutionspolymer chains
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