Direct Imaging of Nanoscale Morphology of Perfluorosulfonic Acid Ionomers
Notice bibliographique
Résumé
Understanding the nanostructure and morphology of perfluorosulfonic acid (PFSA) ionomer and its correlation to functional properties are extremely important for designing new ionomer materials. A number of structural models of ionomer (mainly Nafion ® ) have been proposed based on x-ray scattering data to explain the impact of morphology on its water swelling and transport properties. One of the earliest models is cluster network model where spherical ionic clusters, connected by a narrow channel are embedded by amorphous fluorocarbon matrix. 1 Alternatively, Gebel and coworkers have proposed fibrillar model, which consists of fluorocarbon crystallites surrounded by ionic groups. 2 Most recently, parallel water channel model is proposed by Schmidt-Rohr et al. where large fluorocarbon crystallites consists the parallel channel that are decorated with the sulfonate group inside. 3 The common element to these models is a phase separated morphology – fluorocarbon phase and ionic cluster phase. However, disagreement regarding the shape, size and behaviour of the phases remain. To resolve the controversy, direct imaging technique such as electron microscope have been employed but never been successful to resolve the real nanostructure and morphology. In our approach, we have employed transmittance electron microscope (TEM) to directly image the well-defined crystalline phase (fluorocarbon matrix) and amorphous phase (ionic cluster). The ionomer film was prepared on the spongy carbon film supported by Cu grid adopting self-assembly method 4,5 . Both free-standing and carbon-supported films ranging in thickness of around 4 to 50 nm were generated and investigated by the instrument Tecnai TF20 G2 FEG-TEM (FEI, Hillsboro, Oregon, USA) at 200kV acceleration voltage. The image was captured by Gatan UltraScan 4000 CCD (Gatan, Pleasanton, California, USA) at 2048x2048 pixels. Although a number of research papers have discussed the crystalline phase in ionomer structure but found it challenging to image because of the high degree of disorderdness of the ionomer materials. Therefore, researchers mostly relied on SAXS/SANS data to depict the structural morphology. Hence, it is very exciting to present images where the crystalline phase is clearly evident by direct TEM imaging of Nafion ® ionomer Nanofilm without any chemical modification and treatment (Figure 1). The highly ordered crystalline phase consists of a number of lamellae that are surrounded by the amorphous phase. The crystalline phase varies from 4 to 6 nm in size. The d spacing of those lamellae was calculated to be 0.37 nm. This particular structure of ionomer is consistent with the Fibrillar model proposed by Gebel et al . 2 where the majority of hydrophobic, Teflon-like phase stay in the high density crystalline region and amorphous phase consist of ionic domains (Figure 2). These results may help resolve the debate around ionomer structure model. It is also interesting to see that the crystalline phase is evident regardless of equivalent weight of ionomers whereas the size, shape and extent of the crystalline phase depends on the equivalent weight. We plan to discuss the thermal annealing and dispersion effect on the morphological change of the ionomer in the nanofilms. The morphology of supported film comparing with freestanding nanofilm also will be discussed. Acknowledgements Financial Early Researcher Awards (Ontario Ministry of Research and Innovation) and Natural Sciences and Engineering Research Council of Canada (NSERC), MITACS Elevate PDF Fellowship (Devproshad K. Paul), Automotive Fuel Cell Cooperation (AFCC). References 1. W. Y. Hsu and T. D. Gierke, Macromolecules, 1982 , 15, 101. 2. L. Rubatat, G. Gebel, and O. Diat, Macromolecules , 2004 , 37,7772-7783 3. K. Schmidt-Roh and Q. Chen, Nat. Mater, 2008 , 7, 75-83. 4 . D. K. Paul, K. Karan, J. Giorgi, A. Docoslis and J. Pearce, Macromolecules 2013 , 46 (9), 3461–3475 5. D. K. Paul, A. Fraser, J. Pearce and K. Karan, ECS Trans . 2011 , 41 (1), 1393-1406.
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Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».