Structure, Mechanical Properties, and Dynamics of Polyethylenoxide/Nanoclay Nacre-Mimetic Nanocomposites
Structure, Mechanical Properties, and Dynamics of Polyethylenoxide/Nanoclay Nacre-Mimetic Nanocomposites
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DOI：
10.1021/acs.macromol.9b01931
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发表时间：
2020-03-10
期刊：
影响因子：
5.5
通讯作者：
Walther, Andreas
中科院分区：
文献类型：
--
作者：
Eckert, Alexander;Abbasi, Mozhdeh;Walther, Andreas
基于高比例合成高纵横比纳米粘土与聚合物相结合的仿珍珠质纳米复合材料不断突破先进材料性能的界限，例如高阻氧性、非凡的机械性能、防火性和玻璃般的透明度。此外，由于明确的层状纳米复合材料排列，他们提供了有趣的模型系统来研究纳米限制下的聚合物。尽管使用蒸发自组装形成此类层状纳米复合材料并通过纳米粘土/聚合物比例控制纳米粘土通道间距的一般行为是已知的，但聚合物基质和纳米粘土增强材料的一些组合不符合已建立的模型。在这里，我们展示了对这种不寻常的聚合物/纳米粘土对的彻底表征和分析，这种聚合物/纳米粘土对不符合一般行为。聚环氧乙烷（PEO）和氟锂蒙脱石钠形成仿珍珠母的层状纳米复合材料，该复合材料完全透明，具有高机械刚度和高气体阻隔性，但当添加越来越多的聚合物时，纳米粘土通道间距的扩张有限。当 PEO 的分子量变化超过四个数量级时，这种行为仍然存在，并且可以追溯到耗尽力。通过 X 射线衍射和质子低分辨率固态 NMR 的仔细研究，我们能够量化纳米粘土通道之间以及嵌入 PEO 基质中的类晶团簇周围的移动和固定聚合物种类的数量。我们进一步阐明了不寻常的受限聚合物动力学，表明特定表面相互作用的相关作用。
Nacre-mimetic nanocomposites based on high fractions of synthetic high-aspect-ratio nanoclays in combination with polymers are continuously pushing boundaries for advanced material properties, such as high barrier against oxygen, extraordinary mechanical behavior, fire shielding, and glass-like transparency. Additionally, they provide interesting model systems to study polymers under nanoconfinement due to the well-defined layered nanocomposite arrangement. Although the general behavior in terms of forming such layered nanocomposite materials using evaporative self-assembly and controlling the nanoclay gallery spacing by the nanoclay/polymer ratio is understood, some combinations of polymer matrices and nanoclay reinforcement do not comply with the established models. Here, we demonstrate a thorough characterization and analysis of such an unusual polymer/nanoclay pair that falls outside of the general behavior. Poly(ethylene oxide) (PEO) and sodium fluorohectorite form nacre-mimetic, lamellar nanocomposites that are completely transparent and show high mechanical stiffness and high gas barrier, but there is only limited expansion of the nanoclay gallery spacing when adding increasing amounts of polymer. This behavior is maintained for molecular weights of PEO varied over four orders of magnitude and can be traced back to depletion forces. By careful investigation via X-ray diffraction and proton low-resolution solid-state NMR, we are able to quantify the amount of mobile and immobilized polymer species in between the nanoclay galleries and around proposed tactoid stacks embedded in a PEO matrix. We further elucidate the unusual confined polymer dynamics, indicating a relevant role of specific surface interactions.