The behaviour of long molecules diffusing in solid polyethylene
The behaviour of long molecules diffusing in solid polyethylene
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DOI：
10.1038/266043a0
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发表时间：
1977-03
期刊：
影响因子：
64.8
通讯作者：
J. Klein;B. Briscoe
中科院分区：
文献类型：
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作者：
J. Klein;B. Briscoe
根据目前的两相模型，半结晶聚合物由不透、较致密的晶相(片层)和可渗透、较不致密的非晶相(片层间区域)1组成。所有渗透和传输特性主要发生在后者中，并且是整体中非晶相的总的无定形分数和嵌入非晶相中的微晶的几何形状的函数。对于从熔体以不同速度冷却的线性聚乙烯，气体扩散剂的扩散系数D根据x是相应的结晶体积分数而变化2，3，以及(1−x)无定形度。然而，长链扩散剂的扩散行为可能会非常不同。例如，有人认为，长链分子通过聚乙烯层间无序区域的传输将受到层间束缚分子和纠缠的存在的很大影响。这些是无序区域中相对不能移动的特征，可以阻止长链分子的运动，但如果它们的大小小于这些特征之间的间隔，则不会阻碍较小(例如气体)扩散剂的运动。De Gennes关于爬行的扩展5给出了长分子在聚乙烯中的扩散系数的半定量关系：长分子在缓慢冷却的聚乙烯中的扩散速度应该比在淬火的聚乙烯中快，尽管后者中的无序分数较高，并且与气体或轻蒸汽扩散的行为形成鲜明对比，因为快速冷却会导致更多的固定连接分子6，这限制了长扩散，但对小分子几乎没有影响。我们在此报告支持这一模型的结果。
SEMI-CRYSTALLINE polymers, according to the current twophase model, consist of an impermeable, denser crystalline phase (the lamellae) and a permeable, less dense amorphous phase (the interlamellar regions) 1. All permeation and transport properties occur predominantly in the latter, and are a function of the overall amorphous fraction within the bulk and the geometry of the crystallites embedded in the amorphous phase. For linear polyethylene cooled at various rates from the melt, the diffusion coefficient D of gaseous diffusants varies2, 3 according to where x is the corresponding crystalline volume fraction, and (1− x) the amorphicity. The diffusional behaviour of long chain diffusants, however, may be very different. For example, it has been suggested4 that the transport of long chain molecules through the disordered interlamellar regions of polythene will be greatly influenced by the presence of interlamellar tie-molecules and entanglements. These are relatively immobile features in the disordered region which can obstruct the movement of long chain molecules, but not that of smaller (for example, gaseous) diffusants if their size is less than the separation between these features. An extension of de Gennes ideas on reptation5 gives a semiquantitative relation for the diffusion coefficient of long molecules in polyethylene: long molecules should diffuse faster in slowly cooled than in quenched polyethylene, in spite of the higher disordered fraction in the latter and in marked contrast to the behaviour of gaseous or light vapour diffusants, because rapid cooling results in a greater profusion of fixed tie-molecules6, which constrain long diffusants but have little effect on small ones. We report here results which support this model.