Small‐angle neutron scattering investigation of structural changes in nafion membranes induced by swelling with various solvents

Abstract

The structure of Nafion-117 perfluorosulfonate ionomer membranes was investigated with small-angle neutron scattering techniques. Structural changes induced by the swelling of the membranes with water, alcohols, and dipolar, aprotic solvents were monitored at solvent-swelling levels ranging from approximately 2 vol % to greater than 50 vol %. Membranes swollen up to approximately 50 vol % solvent exhibited two scattering maxima, one known to be associated with ionic regions of the membrane structure and one known to be associated with correlation distances between crystalline regions in the membrane structure. The positions of both maxima shifted toward lower scattering vector values as the solvent content in the membrane increased. The shift in the position of both maxima was linearly related to the solvent volume fraction in the membrane. The Bragg spacings corresponding to both the ionic-feature scattering maximum and the crystalline-feature scattering maximum were plotted versus the solvent volume fraction in the membranes, and the data fit with linear regression. The slopes associated with the curves of the spacing versus the solvent volume fraction were greater for the crystalline-feature spacing than for the ionic-feature spacing for all solvents other than water; this was indicative of preferential segregation of nonaqueous solvents into regions of the structure not directly associated with the ionic scattering maximum.

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

“…Previous studies have reported that the ionic peak shifts to lower q values (higher d spacing) as the volume fraction of solvent in the membrane increases due to expansion of the distance between the ionic domains. 52 Because the broad peak at q ≈ 0.04 Å -1 represents correlation between crystalline regions within the membrane, its position yields information about the nature of swelling within the ionic regions of Nafion separating the crystalline regions. Figure 9b shows the SANS profiles of the different hybrid systems prepared from Nafion.…”

“…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.…”

Hot-Pressing Effects on Polymer Electrolyte Membrane Investigated by2H NMR Spectroscopy

“…3 The structure and alignment of PEM hydrophilic channels tends to be strongly influenced by membrane-electrode-assembly (MEA) preparation methods such as hot-pressing, 8,[11][12][13][14] polymer processing for membrane production, 5,6,[13][14][15] and swelling degree. [4][5][6][15][16][17] Thus, it is desirable to study the PEM in wet states in order to probe the proton conduction within and the hydrophilic channel structures of the functioning PEM. PEM hydrophilic channels have been primarily investigated by scattering techniques using neutrons and X-rays, [3][4][5][12][13][14][16][17][18] however, these techniques detect both systematic ordering of the hydrophobic polymer backbone and hydrophilic clusters.…”

“…[4][5][6][15][16][17] Thus, it is desirable to study the PEM in wet states in order to probe the proton conduction within and the hydrophilic channel structures of the functioning PEM. PEM hydrophilic channels have been primarily investigated by scattering techniques using neutrons and X-rays, [3][4][5][12][13][14][16][17][18] however, these techniques detect both systematic ordering of the hydrophobic polymer backbone and hydrophilic clusters. In contrast, various nuclear magnetic resonance (NMR) methods have been used to probe water dynamics in the hydrophilic clusters as well as the cluster structures.…”

Relação morfologia-propriedades elétricas de eletrólitos compósitos de Nafion para célula a combustível de alta temperatura

“…O isopropanol, além de ser um bom solvente para as cadeias do Nafion, possui baixa constante dielétrica [111]. Ambos os fatores reduzem a intensidade do pico do ionômero 76 que pode auxiliar na determinação do espalhamento das partículas dispersas no polímero [37,159]. Adicionalmente, como mostrado na Tabela O pico do ionômero foi atribuído ao espalhamento devido à separação de fases hidrofóbicas e hidrofílicas no Nafion na escala nanométrica; a microestrutura do Nafion consiste de um conjunto de micelas invertidas cilíndricas fortemente unidas por interações eletrostáticas entre os pares iônicos.…”