Small‐angle scattering studies of nafion membranes

Abstract

SynopsisThe physical structure of Nafion membranes has been investigated by small-angle neutron scattering (SANS) and small-angle x-ray scattering (SAXS). Samples in the acid form may exhibit two scattering peaks. The first, observed by SANS at an angle corresponding to a Bragg spacing of 180 A, is shown to arise from structures in crystalline regions. A second peak at larger scattering angles is shown to arise from ion-containing regions which may be swollen with water. Salt-form samples made by soaking the acid form in an aqueous salt solution can also exhibit the same two scattering signals. But in amorphous salt-form samples produced by quenching from the melt the first peak is absent. This permits a more accurate study of the second peak by SAXS, which shows that the second scattering component is present as a maximum over a wide range of water contents but is absent in a sample dried at 200OC. The position of the peak shifts to lower scattering angles (or larger spacings) at higher water contents. Possible structural models that might give rise to the maximum are discussed. A calculation of the SAX invariant is made and results are consistent with a phase separation of a large fraction of the water.

Mechanics-based model for non-affine swelling in perfluorosulfonic acid (PFSA) membranes

“…Experimental data from Roche et al [49], Laporta et al [24] and Kim et al [34] for the sorption of non-predried PFSA from water vapor are plotted in Fig. 8.…”

“…This relationship is referred to as non-affine deformation and has been shown to occur for PFSA membranes by a number of studies in literature [11,[18][19][20][21][22]29,[33][34][35]. Despite the growing body of literature on the sorption behavior [7,8,10,24,34,35,38,40,[44][45][46][47][48][49][50] and nano-structural modeling and characterization [11,13,[17][18][19][20][21][22]28,29,31,[33][34][35][36]39,49,51,52] of PFSA ionomers, the relationship between the water uptake and nanostructure, temperature, mechanical properties and membrane pretreatment is not well established. Understanding of these issues requires a general, yet fundamental model, which is the subject of this study.…”

Novel Organic−Inorganic Hybrids with Increased Water Retention for Elevated Temperature Proton Exchange Membrane Application

“…nique to identify structural organization within polymer systems and has been used extensively to study the nanostructure of Nafion membranes. [49][50][51][52] The random ionic clusters in Nafion act as a local cross-link and give rise to a local variation in cross-link density. Such network, on swelling in a low molecular weight solvent, exhibits competition between the osmotic pressure and the local elastic junction, resulting in local variation in polymer concentration.…”

Hydrocarbon proton conducting polymers for fuel cell catalyst layers

“…[29][30][31] While PFSA ionomers exhibit excellent chemical and mechanical stability, they are expensive, highly permeable to methanol (and largely unsuitable for DMFCs), 32 and their glass transition temperature occurs at 90-110 C, 22 which is below the operational temperature preferred by the automotive industry. Durability studies have shown that PFSI degrades in the presence of radicals, and moreover, reaction products exacerbate the dissolution and transport of Pt from the CL into the membrane.…”