Ubiquity of soft glassy dynamics in polypropylene–clay nanocomposites
Ubiquity of soft glassy dynamics in polypropylene–clay nanocomposites
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DOI：
10.1016/j.polymer.2006.12.029
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发表时间：
2007-02
期刊：
影响因子：
4.6
通讯作者：
Mark A. Treece;J. Oberhauser
中科院分区：
文献类型：
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作者：
Mark A. Treece;J. Oberhauser
研究了聚丙烯-粘土纳米复合材料的流变性与有机粘土负载、剥离程度和马来酸酐功能化聚丙烯增容剂的关系。样品在小振幅振荡剪切（SAOS）的末端状态下表现出不同程度的固体样响应，证明在固定的有机粘土加载下实现了粘土硅酸盐分层的差异。先前的研究还表明，机械渗透纳米复合材料在低频下表现出随时间对数增长的存储模量，这一行为归因于中尺度有机粘土网络的持续发展，类似于胶体凝胶。连续的低频SAOS实验不仅证实了这种行为，而且还揭示了聚丙烯-粘土纳米复合材料普遍存在这种行为，包括有机粘土负载和剥离程度使其低于表面机械渗透阈值的样品。在非相容样品上进行的类似实验支持与软玻璃动力学的类比，即范德华引力驱动异质凝胶状有机粘土网络的形成。相容剂上的悬垂基团官能团之间的分子间关联导致纯马来化样品的存储模量随时间呈对数增长，但本文报道的材料中马来化聚丙烯浓度的降低表明，随着时间的推移，通过网络的形成，不会影响固体样流变性。因此，我们证明了只有有机粘土网络的形成才是聚烯烃纳米复合材料中随时间变化的流变性的原因。
The rheology of polypropylene–clay nanocomposites was studied as a function of organoclay loading, degree of exfoliation, and presence of maleic anhydride functionalized polypropylene compatibilizer. Samples exhibit varying degrees of solid-like response in the terminal regime of small-amplitude oscillatory shear (SAOS), certifying that differences in clay silicate delamination were achieved for fixed organoclay loading. Previous work has also demonstrated that mechanically percolated nanocomposites exhibit logarithmically increasing storage modulus with time at low frequency, behavior attributed to the continuous development of a mesoscale organoclay network akin to that observed for colloidal gels. Continuous low frequency SAOS experiments not only affirm such behavior but also reveal that it is ubiquitous to polypropylene–clay nanocomposites, including samples whose organoclay loading and extent of exfoliation place them below the ostensible mechanical percolation threshold. Similar experiments conducted on uncompatibilized samples support the analogy to soft glassy dynamics, whereby van der Waals attractions drive the formation of a heterogeneous, gel-like organoclay network. Intermolecular associations between pendant group functionalities on the compatibilizer have contributed to logarithmic increases in the storage modulus with time for pure maleated samples, but the reduced concentrations of maleated polypropylene present in the materials reported here are shown to not influence the solid-like rheology over time through network formation. Thus, we demonstrate that only organoclay network formation is responsible for the time-dependent rheology in polyolefin nanocomposites.