Influence of vanillic acid immobilization in Nafion membranes on intramembrane diffusion and structural properties

Abstract

Pulsed field gradient (PFG) NMR in combination with quasielastic neutron scattering (QENS) was used to investigate self-diffusion of water and acetone in Nafion membranes with and without immobilized vanillic acid...

Self‐Diffusion of a Chemical Warfare Agent Simulant and Water in Nafion by Pulsed Field Gradient NMR

“…This regime is defined by a coincidence of the water attenuation curves and an essentially monoexponential shape of these curves. In complete analogy with our previous data for acetone diffusion in Nafion loaded with water/acetone mixtures 17, 18, it is expected that such third regime occurs for all other DMMP concentrations in the limit of long diffusion times. However, the relatively short proton T 1 NMR relaxation times of water in the measured samples prevented an observation of the third regime for all other DMMP concentrations.…”

“…Our previous PFG NMR studies 17, 18 of water diffusion in Nafion have discussed the observed time dependence of the PFG NMR data for water, which were analogous to those reported in the current work, in the context of water diffusing along water channels that are not fully interconnected in Nafion membrane. The diffusion data were explained by the existence of micrometer‐sized domains inside Nafion in which these channels are interconnected for water to diffuse.…”

“…Our PFG NMR measurements were performed on the millisecond time scale, which is expected to be much longer than the time scale of these proton exchange processes 27, 28. Therefore, these exchange processes are not valid explanations for the observed time dependence of our PFG NMR data for water 17, 18.…”

“…The permeance of the domain boundary ( P ) was estimated under the assumption that diffusion of water in the limit of long diffusion times is hindered by two transport resistances in series. The first of these corresponds to diffusion within the interconnected water channel domains, and the second corresponds to the permeance of boundaries of such domains 17, 18, 23, 29, 30. …”

“…water channels. Our previous work has provided strong evidence of independent diffusion pathways for water and acetone within the Nafion polymer [17,18]. The presence of the interfacial PFE regions has been recognized as a key factor to understanding transport behavior in Nafion for advanced applications.…”