Morphological Heterogeneity by Diffusional Kurtosis NMR Spectroscopy in Perfluorosulfonic Acid/SiO₂Composite Proton‐Exchange Membranes

Abstract

Diffusional kurtosis is introduced to characterize the heterogeneity of the channel architecture for ionic transport in proton exchange membranes. Measuring the apparent kurtosis by a pulsed-fi eld-gradient NMR spectroscopy technique may yield additional information about membrane morphology not available to the conventional water-diffusion method. Water diffusional kurtosis and the apparent diffusion coeffi cient are investigated for perfl uorinated sulfonic acid (PFSA)/SiO 2 nanocomposites. Diffusional kurtosis is anisotropic revealing higher channel heterogeneity in-plane of solution-cast fi lms compared with the transverse direction. Diffusional kurtosis is related to the nonGaussian character of the averaged diffusion propagator. A universal relationship is proposed for the root-mean-squared displacement.

Polymers Diffusivity Encoded by Stimuli‐Induced Phase Transition: Theory and Application to Poly(N‐Isopropylacrylamide) with Hydrophilic and Hydrophobic End Groups

“…The correlation between diffusion and chemical and biological phenomena is of particular importance. This molecular process not only reflects intrinsic properties of the diffusing species itself, but can also shed light on the surrounding environment . Stochastic mass transport measurements of water in polymers, microgels, gels, proteins, proton‐exchange membranes, porous materials, and brain by noninvasive nuclear magnetic resonance (NMR) methods proved to be an accurate technique for evaluation of diffusivity tensor D as well as its dependence of the surrounding morphology and architecture …”

Structure and Dynamics of Temperature‐Responsive Microgels and Hydrogels by NMR Spectroscopy, Relaxometry, and Diffusometry

“…[30,31] The diffusion of solvent molecules or solute particles not only reflects intrinsic properties of the diffusing species itself but can also give access to the environment morphology and allows for characterization of chemical and biological phenomena. [21,67,68] Furthermore, the diffusive properties of water might have important implications for the interpretation of hydrogel properties.…”

Diffusion of Gold Nanorods Functionalized with Thermoresponsive Polymer Brushes

“…Stochastic mass transport of macromolecules, nanoparticles, and composites in dispersions plays an important role in various fields of modern science. − This molecular process not only reflects intrinsic properties of the diffusing species itself but also can emphasize on the morphology and architecture of environment and allows characterization of chemical and biological phenomena. − …”