Nafion neutron studies

Roche and co-workers used SAXS and small-angle neutron scattering (SANS) to study the morphology of 1200 EW Nafion membranes in the acid and neutralized forms with a range of water contents. ... 

Previous studies about dynamics of water near interfaces by quasi-elastic neutron scattering involved measurements of the mobility of water on the surface of Nafion membranes [63,64], the diffusive motions and the density of states of water in silica gels [65], and the interfacial melting of ice in graphite and talc pow-... 

As in other ionomers, the ion exchange sites in "Nafion" membranes are observed to aggregate and form clusters. Ionic clustering in "Nafion" membranes has been indicated by a variety of physical studies including dielectric relaxation (1), small angle x-ray scattering (1-4), neutron scattering (4), electron micro-... 

A model of structure has been developped from electron microscopy and X-ray studies in Nafions (6). No basic difference exists between X-ray and neutron techniques. Nuclear interactions of neutrons with matter are characterized by the coherent scattering length and the corresponding values for H and D are very different Because of the different origins of the contrast, X-ray and neutron small angle scattering techniques are complementary. 

A more thorough investigation at intermediate humidity levels is needed. In addition, it is clear that a number of other studies including scattering at larger Q, quantitative investigations of intensities, and a comparison of small-angle neutron and x-ray results are needed to understand the complex structure present in hydrated Nafions. 

Furthermore, in 2001, Ballard entered an alliance with Victrex to produce two new membrane alternatives. One membrane is based on sulfonated poly(arylether) ketone (a variant of s-PEEK) supplied by Victrex, which may be better suited to PEM fuel cell fabrication applications. In March 2002, U.S. Patent 6359019 was issued to Ballard Power for a graft-polymeric membrane in which one or more trifluoro-vinylaromatic monomers are radiation graft polymerized to a preformed polymeric base. The structures of BAM membranes have been studied by way of small-angle neutron scattering or SANS. ° The study of the ionomer peak position suggests the existence of relatively small ionic domains compared to Nafion, despite large water content. Phase separation in the polymer matrix is possibly crucial for the manbrane s mechanical and transport properties. 

The structure of PEMs, in particular their phase-separated morphology at nm-scale, has been studied with a number of experimental techniques, including small- and wide-angle X-ray and neutron scattering, infrared and Raman spectra, time-dependent FTIR, NMR, electron microscopy, positron annihilation spectroscopy, scanning probe microscopy, and scanning electrochemical microscopy (SECM) (for a review of this literature see [31]). Structural studies of PEMs have mainly focused on Nafion. A thorough recent review on this particular membrane is provided in [32]. 

The state of water in Nafion was examined by several authors, employing a multitude of techniques. Dielectric relaxation studies [46], neutron scattering data [47], and infrared data [48] showed that 20-24% of the water is in the organic phase. The rest is in the ion clusters, where its physical properties differ from those of bulk water. 

Perrin, J. C., Lyonnard, S., and Volino, F. 2007. Quasielastic neutron scattering study of water dynamics in hydrated Nafion membranes., 111(8),... 

Nafion has been the subject of extensive characterization studies [1]. Its microstructure has been exhaustively studied by scattering methods, especially small angle X-ray scattering (SAXS) and small angle neutron scattering (SANS) [19-23]. Mechanical properties of Nafion as functions of temperature have been used to identify temperature-induced transitions [2,24—27]. Transport of protons and water has also been the subject of numerous studies over the past 25 years [28-34]. However, there has been limited progress in coimecting the chemical structure of Nafion to mechanical and transport properties, especially how these properties are altered due to environmental conditions. In this chapter, we will review recent studies of mechanical and transport properties of Nafion done under controlled conditions of water activity and temperature. 

Volino, F., Pineri, M., Dianoux, A.J., De Geyer, A. (1982) Water mobility in a water-soaked Nafion membrane a high-resolution neutron quasielastic study. Journal of Polymer Science Polymer Physics Edition, 20, 481-496. 

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