Origin of Carbon Nanotubes Induced Poly(L-Lactide) Crystallization: Surface Induced Conformational Order
Origin of Carbon Nanotubes Induced Poly(L-Lactide) Crystallization: Surface Induced Conformational Order
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DOI：
10.1021/ma802758k
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发表时间：
2009-04-28
期刊：
影响因子：
5.5
通讯作者：
Yang, Chuanlu
中科院分区：
文献类型：
--
作者：
Hu, Xiao;An, Haining;Yang, Chuanlu
碳纳米管（CNTs）是一种有效的成核剂，可以提高聚合物的结晶动力学，诱导独特的结晶形态。最初的研究集中在碳纳米管的高成核效率上。1,2例如，Agarwal等人发现，在低至0.03 wt%的浓度下，CNTs可以使聚对苯二甲酸乙酯成核结晶。最近的实验表明，除了成核效应外，即使在静态条件下，碳纳米管也可以非常有效地模板聚合物片，使其以羊肉串的方式垂直于碳纳米管表面生长。4-6由于碳纳米管作为成核剂的作用，剪切对结晶动力学的影响很小。有趣的是，Li等人在单个碳纳米管上周期性地对聚合物材料进行了图案化处理，从而产生了纳米杂交羊肉串（NHSK）结构，其中单个碳纳米管被视为羊肉串。7,8这些报告表明，即使不施加流动（剪切、拉伸或混合流动），单独使用碳纳米管也能诱导聚合物链的取向，而流动通常用于定向晶体的形成。9-11取向薄片的标志是在结晶早期形成纤维状成核前体（或中间相），这些前体是超过临界尺寸的取向链簇或束。不幸的是，在碳纳米管诱导的聚合物结晶的早期阶段发生了什么还远不清楚，尽管它是结晶过程中所采取的路线的关键指南。到目前为止，越来越多的报道表明，在聚合物结晶之前或结晶初期存在一种预序结构。聚合物的预定顺序包括分子间的位置和取向顺序以及分子内的构象顺序。在结晶形成之前，聚合物链经历了有利于结晶形成的构象调整和取向转变。在本研究中，我们试图借助原位傅里叶变换红外光谱（FTIR）在早期阶段揭示碳纳米管诱导聚合物结晶的起源。
Carbon nanotubes (CNTs) have been recognized as an effective nucleating agent to enhance the crystallization kinetics of polymers and induce unique crystalline morphology. The initial investigations have focused on the high nucleation efficiency of CNTs. 1, 2 For example, Agarwal et al. found that CNTs can nucleate crystallization of poly (ethylene terephthalate) at concentrations as low as 0.03 wt%. 3 Recent experiments have shown that, in additional to the nucleating effect, CNTs are very efficient in templating polymer lamellae to grow perpendicular to the CNT surface in a shish-kebab fashion even under quiescent conditions. 4-6 Because of the power of CNTs as nucleating agents, shear has a minor effect on the crystallization kinetics. 4 Interestingly, Li, et al. have patterned polymeric materials periodically on individual carbon nanotubes, resulting in nanohybrid shish-kebab (NHSK) structures, where a single CNT is regarded as the shish. 7, 8 These reports imply that CNTs alone can induce orientation of polymer chains even without imposition of flow (shear, elongational, or mixed flow) which is generally applied to incur formation of oriented crystals. 9-11 The indicator of oriented lamellae is the formation of fiber-like nucleation precursors (or mesophase) at an early stage of crystallization, which are oriented chain clusters or bundles above a critical size.Unfortunately, what happens in the early stage of CNT-induced polymer crystallization is far from clear, even though it is a crucial guide to the route taken in crystallization. Up to now, more and more reports have shown that a preordering structure exists before or at the early stage of polymer crystallization. Polymer preordering comprises intermolecular positional and orientational order as well as intramolecular conformational order. Before the crystallite appears, polymer chains go through conformation adjustment and orientation transformation in a way which favors the formation of crystallites. 12-14 In this study, we attempt to reveal the origin of CNT-induced polymer crystallization at an early stage with the help of in situ Fourier transform infrared spectroscopy (FTIR).