Origin of the melt memory effect in polymer crystallization
Origin of the melt memory effect in polymer crystallization
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DOI：
10.1016/j.polymer.2010.07.010
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发表时间：
2010-08-19
期刊：
影响因子：
4.6
通讯作者：
Brito, Antonio M.
中科院分区：
文献类型：
--
作者：
Martins, Jose A.;Zhang, Weidong;Brito, Antonio M.
熔体在足够高的温度下短时间退火或在较低的温度下长时间退火后，可获得熔体重复结晶实验的再现性。这种退火工艺消除了聚合物熔体记忆。它的物理起源仍然难以捉摸，但它与结晶的前体结构有关。什么是前驱体结构，以及它们如何受到剪切流和熔体温度的影响也不清楚。在这项工作中，我们确定了两种明确的熔体状态：完全松弛的熔体和剪切到稳定状态的熔体。完全松弛熔体的结晶速度最慢，而熔体剪切至稳定状态的结晶速度最快。我们证明了在相同温度下从两种不同熔体状态结晶的聚合物具有相似的平均球晶尺寸，但剪切到稳定状态的熔体具有较低的粘度和较少的缠结数，这是这些熔体中结晶动力学加速的原因。将熔体剪切至稳定状态的退火减慢了结晶动力学，直到它与完全松弛的熔体相当。(C) 2010 Elsevier Ltd.版权所有。
Reproducibility of repeated crystallization experiments from melts is obtained after annealing the melt at a sufficiently high temperature for short time, or at lower temperatures for longer time. This annealing process erases the polymer melt memory. Its physical origin remains elusive, but it is linked to precursor structures for crystallization. What precursor structures are, and how they are affected by shear flow and melt temperature is also unclear. We identify in this work two well-defined melt states: the fully relaxed melt and the melt sheared up to a steady state. Crystallization from fully relaxed melts is slowest while from melts sheared up to the steady state is fastest. We demonstrate that polymers crystallized at the same temperature from the two different melt states have similar average spherulite size, but melts sheared up to steady state have lower viscosity and low number of entanglements, this being the reason for the acceleration of crystallization kinetics in these melts. Annealing of the melts sheared up to the steady state slows down the crystallization kinetics until it becomes comparable with that of fully relaxed melts. (C) 2010 Elsevier Ltd. All rights reserved.