Correlation between Morphology, Water Uptake, and Proton Conductivity in Radiation‐Grafted Proton‐Exchange Membranes

Abstract

An SANS investigation of hydrated proton exchange membranes is presented. Our membranes were synthesized by radiation‐induced grafting of ETFE with styrene in the presence of a crosslinker, followed by sulfonation of the styrene. The contrast variation method was used to understand the relationship between morphology, water uptake, and proton conductivity. The membranes are separated into two phases. The amorphous phase hosts the water and swells upon hydration, swelling being inversely proportional to the degree of crosslinking. Hydration and proton conductivity exhibit linear dependence on swelling. Proton conductivity and volumetric fraction of water are related by a power law, indicating a percolated network of finely dispersed aqueous pores in the hydrophilic domains.magnified image

Morphological Study of Poly(vinylbenzyl chloride)-Grafted Poly(ethylene-co-tetrafluoroethylene) [ETFE-g-PVBC] Films Using Small-Angle Neutron Scattering Analysis

“…4 It was found that the inter-crystalline distance was largely affected by the degree of grafting and degree of crosslinking. In our previous study, the morphology of crystalline for PS-grafted ETFE films prepared using a simultaneous irradiation method was investigated using DMA, DSC, XRD, and SAXS instruments.…”

“…1 The morphological studies of crystalline for polystyrene (PS)-grafted fluoropolymer films prepared using a preradiation grafting method have been mainly investigated using small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) instruments. [3][4][5] Mortensen et al reported small-angle neutron studies on the morphology of PS-grafted poly(tetrafluoroethyleneco-hexafluropropylene) (FEP) films prepared by a preirradiation method. 3 In their works, the styrene monomer was found to be mainly grafted to the amorphous domain of an FEP film during the pre-irradiation grafting process.…”

Grafting design: a strategy to increase the performance of radiation‐grafted membranes

“…Membranes of type A have been synthesized and thoroughly investigated at the Paul Scherrer Institute over the last decade . The optimized reaction conditions for styrene grafting were found to be a mixture of 70 vol% isopropanol, 10 vol% ultrapure water and 20 vol% styrene monomer at temperatures between 55 and 60 °C .…”

“…After stirring for 5 h at room temperature the sulfonated films were removed from the reaction mixture and repeatedly washed with ultrapure water (3 × 800 mL). Hydrolysis of the functionalized films to sulfonic acid groups was performed in ultrapure water (800 mL) at 80 °C for 15 h. More information can be found elsewhere …”

Investigations of crystallinity and chain entanglement on sorption and conductivity of proton exchange membranes

“…which afford high IEC membranes (42 mmol/g) that do not dissolve in water. Modifications to the graft copolymer architecture, including molecular weight, graft length, graft number density, and degree of sulfonation confer subtle but impactful changes on the membrane's transport properties [37][38][39][40][41][42]. For instance, shorter graft side chains yield larger, but fewer, ionic-rich domains -which reduces swelling and allows for even greater proton conductivity [37].…”