Crystallization and dissolution of flow-induced precursors
Crystallization and dissolution of flow-induced precursors
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DOI：
10.1103/physrevlett.100.048302
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发表时间：
2008-02-01
影响因子：
8.6
通讯作者：
Chadwick, John C.
中科院分区：
文献类型：
--
作者：
Balzano, Luigi;Kukalyekar, Nileshkumar;Chadwick, John C.
我们利用一种特殊合成的具有双峰分子量分布(MWD)的线性高密度聚乙烯来证明只有可能产生扩链(SHISH)晶体的悬浮液。这种悬浮液可以在高于但接近不受约束的延长链晶体的平衡熔化温度(T-m(0)=141.2℃)的高温下产生，并且需要拉伸MWD的最长链。在142℃作用120个S(-1)对1个S的剪切流后，X射线散射表明存在大量有限结晶度或没有结晶度的亚稳态针状前驱体。太小的前体在一个时间尺度上溶解，这个时间尺度与最长聚合物分子的旋转时间完全相关。然而，超过临界尺寸的前体结晶形成延伸链。
We make use of a specially synthesized linear high density polyethylene with a bimodal molecular weight distribution (MWD) to demonstrate that it is possible to produce a suspension of extended-chain (shish) crystals only. Such a suspension can be generated at high temperatures, above but close to the equilibrium melting temperature of the unconstrained extended-chain crystals (T-m(0)=141.2 degrees C) and requires stretch of the longest chains of the MWD. After the application of a shear flow of 120 s(-1) for 1 s at 142 degrees C, x-ray scattering suggests the presence of a large number of metastable needlelike precursors with limited or no crystallinity. Precursors that are too small dissolve on a timescale that correlates perfectly with the reptation time of the longest polymer molecules. Whereas, precursors that exceed a critical size crystallize forming extended-chain shishes.