Insights on the study of nafion nanoscale morphology by transmission electron microscopy.
Insights on the study of nafion nanoscale morphology by transmission electron microscopy.
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DOI：
10.3390/membranes3040424
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发表时间：
2013-12-16
期刊：
影响因子：
4.2
通讯作者：
Downing KH
中科院分区：
文献类型：
--
作者：
Yakovlev S;Balsara NP;Downing KH
全氟磺酸是最常见的用于生物膜的材料之一，也是新材料比较的标准。尽管人们对Nafion的纳米结构很感兴趣，但它仍然是一个有争议的话题。虽然多项研究工作已经解决了Nafion的形态与透射电子显微镜，这些努力的结果往往是不一致的，不能令人满意地描述膜结构。在报告的结果中的差异的原因之一是缺乏足够的控制所造成的电子束照射的损害。在这项工作中，我们描述了一些方面的材料损伤，有很大的影响的结果。我们表明，辐射导致的质量损失和相分离的材料，并已观察到的形态，在许多情况下，造成的损害的文物。我们研究了样品温度对损伤的影响，结果表明，虽然在低温下工作并不能防止损伤和质量损失，但它会减缓损伤引起的伪影的形成，从而可以收集几乎未受损材料的信息性低剂量图像。我们发现样品的充电对损伤有很大影响，并且通过使用物镜孔径或导电支撑膜大大减少束流诱导的移动也可以看出照射下电荷中和的重要性。为了帮助解释低剂量图像，我们可以应用稍高的曝光，用电子束蚀刻掉疏水相，并显示由亲水相形成的网络。能量损失谱显示的证据表明，氟去除支配的光束损伤过程。
Nafion is one of the most common materials used for polyelectrolyte membranes and is the standard to which novel materials are compared. In spite of great interest in Nafion’s nanostructure, it is still a subject of controversy. While multiple research efforts have addressed Nafion’s morphology with Transmission Electron Microscopy, the results of these efforts have often been inconsistent and cannot satisfactorily describe the membrane structure. One of the reasons for differences in the reported results is the lack of sufficient control over the damage caused by electron beam irradiation. In this work, we describe some aspects of damage in the material that have a strong influence on the results. We show that irradiation causes mass loss and phase separation in the material and that the morphologies that have been observed are, in many cases, artifacts caused by damage. We study the effect of the sample temperature on damage and show that, while working at low temperature does not prevent damage and mass loss, it slows formation of damage-induced artifacts to the point where informative low-dose images of almost undamaged material may be collected. We find that charging of the sample has a substantial effect on the damage, and the importance of charge neutralization under irradiation is also seen by the large reduction of beam induced movement with the use of an objective aperture or a conductive support film. To help interpret the low-dose images, we can apply slightly higher exposures to etch away the hydrophobic phase with the electron beam and reveal the network formed by the hydrophilic phase. Energy loss spectroscopy shows evidence that fluorine removal governs the beam damage process.