Orientation effects in the deuterium NMR spectroscopy of perfluorinated ionomer membranes

About the Interactions Controlling Nafion’s Viscoelastic Properties and Morphology

“…Measurements of the orientation dependence of 2 H NMR spectra have been successfully applied for the study of crystalline substances, − but are equally suitable for the measurement of residual anisotropies of the pseudonematic effect in polymers and ionomers. − ,− In such experiments, the sample is mounted in a goniometer, allowing for measurements of 2 H NMR spectra at different relative orientations to the magnetic field B 0 . These orientations are varied through rotating the sample by defined angles ϕ.…”

“…A rich source of additional information is 2 H NMR experiments on membranes containing heavy water. Deuterium ( 2 H, D) possesses a quadrupolar moment which makes deuterium-containing mobile molecules with internal quadrupolar interaction suitable for probing the anisotropy of their host through the so-called pseudonematic effect. − Historically, this effect was first exploited to reveal structural information on nematic liquid crystals and later also on elastomers stretched at temperatures above their α-transition. − For D 2 O-containing Nafion, the pseudonematic effect was first observed by Xu and Pak, , but it was the Madsen group recently studying this effect as a function of orientation and water (D 2 O) content. − Later, they stretched Nafion under hot and dry conditions (where this ionomer is very soft) before rehydrating with heavy water and recording 2 H NMR spectra at ambient temperature for different levels of hydration. , In contrast to the case of elastomers containing small amounts of weakly interacting deuterated molecules (e.g., benzene), the chemical activity of (heavy) water used for probing Nafion’s morphology strongly affects interactions controlling both morphology and viscoelastic properties. − From a PFG-NMR study, Klein et al clearly recognized that diffusional anisotropy induced through stretching strongly depends on stretching temperature.…”

14N NMR Spectroscopy of Nitrate Co-ions in Ionomer Membranes

“…The proton-decoupled 14 N NMR spectrum of Nafion after soaking in 3.0 M NH 4 NO 3 is shown in Figure . Since the commercial membrane is anisotropic, ,, with lines of strain clearly visible in the plane of the membrane, the NMR spectrum was measured in two orientations with respect to the magnetic field. A signal due to NO 3 - is readily detected at a chemical shift of −5.5 ppm in addition to the strong NH 4 + peak at −363 ppm.…”

“…The membrane was inserted into a 10 mm NMR tube and oriented so that the visible lines of strain were aligned either parallel or perpendicular to the magnetic field. This was achieved by rolling the membrane around a 5 mm NMR tube filled with D 2 O, which was then placed inside the 10 mm tube. , In all cases the magnetic field lies in the plane of the membrane. In this cylindrical geometry, bulk susceptibility effects on the chemical shifts should be reduced.…”

Spatial and temporal mapping of water content across Nafion membranes under wetting and drying conditions

“…However, an efficient measurement to directly characterize the spatial distribution of water and water flux across the PEM in an operational PEM fuel cell is still lacking. The Nafion microstructure is known to be anisotropic [9][10][11], which means that functional studies across the Nafion thin film are essential. Some model functional studies have examined Nafion alteration lengthwise.…”