Ionic Aggregates in Partially Zn-Neutralized Poly(ethylene-<i>r</i><i>an</i>-methacrylic acid) Ionomers:  Shape, Size, and Size Distribution

Winey, Karen I.; Laurer, Jonathan H.; Kirkmeyer, Brian P.

doi:10.1021/ma991374j

Cited by 66 publications

(78 citation statements)

References 11 publications

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“…As mentioned above, the combined SAXS profile of pristine SPEEK membrane showed a broad hump, similar to the so-called "ionomer peak" identified in a wide range of ionomer materials, including Nafion, 49 poly(ethylene-ran-methacrylic acid)-based 50 and poly(ethylene-co-acrylic acid) 51 based ionomers. Despite a large library of related work, a universally accepted morphological model for the solid-state structure of these ionomers has yet to emerge.…”

Section: Resultssupporting

confidence: 57%

Microstructure-Property Relationships in Sulfonated Polyether Ether Ketone/Silsesquioxane Composite Membranes for Direct Methanol Fuel Cells

Yun

Parrondo

Zhang

et al. 2014

J. Electrochem. Soc.

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The synthesis, structural characterization, and performance evaluation of silsesquioxane -based sulfonated polyether ether ketone (SPEEK) composite membranes for direct methanol fuel cell (DMFC) applications are presented. 3-(trihydroxysilyl)-1-propanesulfonic acid (TPS) was used as a silsesquioxane (SQO) precursor. Two batches of SPEEK membranes with ion exchange capacities (IEC) of 1.06 ± 0.02 meq/g (denoted by SPEEK11) and 1.34 ± 0.05 meq/g (denoted by SPEEK13) were prepared. The SQO loadings in the composite membranes ranged from 5 wt% to 30 wt%. The ionic conductivity of the SPEEK13 membrane (at 60 • C) increased by up to 15 mS/cm (27%) upon incorporation of 15 wt% TPS-derived SQO, while the methanol permeability was at best slightly lowered (5-10%). The morphological changes in the composite membranes resulting from the introduction of SQO was studied by small angle X-ray scattering. The sharp decrease in conductivity with TPS loading was attributed to these changes in the membrane ionic domains. The performance of DMFCs with these SPEEK/SQO composite membranes was governed more by the proton conductivity than the methanol crossover. Compared to pristine SPEEK, the improved DMFC performance (at 60 • C using air and 3M methanol) of SPEEK11+5 wt% TPS and SPEEK13+5 wt% TPS composite membranes (187 mA cm −2 and 240 mA cm −2 at 0.4 V, respectively) was observed. The crossover of methanol from the anode to cathode through the ionic membrane remains one of the challenging obstacles in direct methanol fuel cells (DMFC). Methanol crossover to the cathode leads to a reduction in the operating voltage due to depolarization and mixed potential, and concurrent contamination of the Pt catalyst.1 Perfluorinated membranes such as Nafion have traditionally been used for DMFC systems. However, even though Nafion provides high conductivity and chemical stability, it exhibits large methanol permeability, resulting in relatively poor DMFC performance.2-6 Composite membranes, prepared by adding inorganic materials to an ion conducting polymer matrix, have been proposed and studied in an attempt to reduce methanol crossover.7 Sulfonated polyether ether ketone (SPEEK) is a good choice as a matrix for DMFC applications because it is relatively inexpensive and has lower methanol permeability compared to Nafion. It also exhibits good thermal stability, good mechanical strength and reasonable ionic conductivity.

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Section: Resultssupporting

confidence: 57%

Microstructure-Property Relationships in Sulfonated Polyether Ether Ketone/Silsesquioxane Composite Membranes for Direct Methanol Fuel Cells

Yun

Parrondo

Zhang

et al. 2014

J. Electrochem. Soc.

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“…No lines have been seen in any ionomer micrograph to this reviewer's knowledge. Further, in two studies, [120,121] samples were tilted slightly to determine if the diameter or aspect ratio changed with tilt angle, and no changes were seen. With likely diameter/thickness ratio between 3 and 5 for a reasonable planar circular structure, it is not clear whether tilting experiments definitely rule out circular planar aggregates; but certainly, the lack of change with tilting does make circular aggregates unlikely.…”

Section: Ionic Aggregates: Nanometer Length Scalementioning

confidence: 99%

“…ZnEMAA [121] Spheres, $2.1 nm Extrusion. Size almost independent of neutralization level, polydispersity index less than 1.5.…”

Section: Compression Moldingmentioning

confidence: 99%

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Review and critical analysis of the morphology of random ionomers across many length scales

Grady

2008

Polymer Engineering & Sci

101

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This review presents a description of what is known about ionomer morphology. All papers on ionomer morphology are not included in this review; but all relevant questions about ionomer morphology are posed and answered as completely as possible. The review is critical; that is, reasons are given for morphologies that are deemed to be more or less likely. The review is organized along three length scales: sub-nanometer, nanometer to 10 nm, and greater than 10 nm. Within each length scale, all three phases are considered: crystalline, amorphous, and ionic aggregate. The purity of the three phases, the arrangement of atoms in the three phases, the size and shape of the three phases, and their arrangements in space relative to each other are explored in this review. A model for the shape of aggregates in ionomers that have well-ordered internal environments is presented. This model proposes that aggregates are fundamentally planar, but will ''roll up'' into tubes or other related structures in order to reduce the number of atoms at aggregate edges. This model was developed primarily based on the varied morphologies ionomers have shown in electron micrographs, but is consistent with other indirect measurements of ionomer morphology.

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“…A previous high-voltage transmission electron microscopy (TEM) study of solution-cast thin films of Zn-SPS 21 showed promise in this regard, although the effect of solution casting on ionomer morphology has since been shown to depend on solution composition. 22 Recently, Winey and colleagues 23,24 imaged the ionic aggregates of semicrystalline poly(ethylene-comethacrylic acid) random ionomers using STEM equipped with a field emission electron gun (FEG). The bulk morphologies of these ionomers were maintained using cryo-ultramicrotomy for sample preparation.…”

Section: Introductionmentioning

confidence: 99%

Spherical and vesicular ionic aggregates in Zn-neutralized sulfonated polystyrene ionomers

Kirkmeyer¹,

Weiß²,

Winey³

2001

J. Polym. Sci. B Polym. Phys.

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Ionic Aggregates in Partially Zn-Neutralized Poly(ethylene-ran-methacrylic acid) Ionomers: Shape, Size, and Size Distribution

Cited by 66 publications

References 11 publications

Microstructure-Property Relationships in Sulfonated Polyether Ether Ketone/Silsesquioxane Composite Membranes for Direct Methanol Fuel Cells

Microstructure-Property Relationships in Sulfonated Polyether Ether Ketone/Silsesquioxane Composite Membranes for Direct Methanol Fuel Cells

Review and critical analysis of the morphology of random ionomers across many length scales

Spherical and vesicular ionic aggregates in Zn-neutralized sulfonated polystyrene ionomers

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