振荡剪切场中聚合物熔体的有序与结晶

The mechanism of shear-induced crystallization and modification of the structure and properties of polymeric materials has generated much interest internationally for its potential to answer both fundamental problems in polymer physics and technological problems in polymer processing. Formation, relaxation and static crystallization behavior of ordered structures in steady sheared polymer melts has been widely studied for decades. However, the mechanism of oscillatory shear-induced crystallization is different from steady shear-induced crystallization and was so far not extensively studied. It is known that polymer melts, under the influence of the oscillatory shear field during the whole crystallization process, exhibit rich ordered structures, different growth processes of crystals and morphology, when compared with the steady sheared melts. In this project, we focus on the effect of oscillatory shear flow on the formation of ordered structures in polymer melts and crystallization from the structured melt. A comparison of our results with the formation and crystallization of ordered structures induced by a steady shear flow allows us to highlight the differences in growth mechanism. This project introduces ordered structures of polymer melts into oscillatory shear flow, and provides a novel new idea in understanding the relationship between the morphology, structure and final properties.

流动对聚合物结晶的影响机制及利用流动调控聚合物的结晶形态结构和性能一直是高分子物理和聚合物加工研究的热点。现有工作大都是研究稳态剪切流场作用下熔体中不同尺度有序结构的形成机制及剪切流动停止后有序结构的松弛和有序熔体的静态结晶，关于振荡剪切诱导结晶机制及与稳态剪切流动诱导结晶的差异方面的研究尚未见到。与稳态剪切场相比，振荡剪切场能够诱导复杂流体形成更丰富的结构，且可以施加于熔体结晶全过程，有助于研究流动对晶体生长过程的影响，并调控晶体生长过程。本项目拟开展振荡剪切场中聚合物熔体有序及结晶的研究，以探明振荡剪切场中聚合物熔体的有序及结晶机制，揭示振荡剪切与稳态剪切流动诱导结晶的差异及流动对晶体生长的影响，可以丰富和发展流动诱导结晶研究，同时为通过成型加工调控聚合物制品的结晶形态结构和性能提供新思路和新方法。

流动对聚合物结晶的影响机制及利用流动调控聚合物的结晶形态结构和性能一直是高分子物理和聚合物加工研究的热点。现有工作大都是研究稳态剪切流场作用下熔体中不同尺度有序结构的形成机制及剪切流动停止后有序结构的松弛和有序熔体的静态结晶，关于振荡剪切诱导结晶机制及与稳态剪切流动诱导结晶的差异方面的研究较少。本项目搭建了纤维往复拖曳熔体流动装置，研究了振荡剪切对剪切后等规聚丙烯结晶形态结构。结果表明：与单向拖曳流动得到以纤维表面排核为中心的单个柱状晶相比，往复拖曳流动可以在纤维附近诱导生成柱晶带（柱晶带包含着数条沿流动方向生长的柱晶）；拖曳幅度、拖曳周期、剪切时间对柱晶带内柱晶的数量、长度和柱状晶中β相含量均有影响；利用示踪粒子法研究了振荡过程中熔体速度分布的变化，发现垂直于纤维方向剪切速率分布不连续，且在纤维表面附近速度随剪切时间变化较大，这种剪切速率分布不连续流动（流场）诱导的取向有序结构可能是产生柱晶带的原因。本项目通过研究振荡剪切场中聚合物熔体有序及结晶行为，丰富和发展了聚合物流动诱导结晶研究，同时为通过成型加工调控聚合物制品的结晶形态结构和性能提供新思路。