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Identifying the Transient Cooperative Processes behind the Dynamic Behavior of Sheared Polymer Melts

识别剪切聚合物熔体动态行为背后的瞬态协同过程

基本信息

批准号：
329695734
负责人：
Dr. Sivasurender Chandran
金额：
--
依托单位：
Institut Charles Sadron
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2016
资助国家：
德国
起止时间：
2015-12-31 至 2018-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/329695734?language=en
关键词：
Identifying Transient Cooperative Processes behind

项目摘要

Polymer melts exhibit a rich dynamic behavior when exposed to intense shear fields. For example, amorphous polymers display a shear thinning behavior, while crystallizable polymers form correlated segments within the flow-oriented structures. However, the role of such correlations on the dynamic behavior of crystallizable polymer melts is highly unexplored. In this context, we have recently shown the manifestations of such correlated segments on the visco-elastic behavior of sheared polymer melts through the dewetting technique. We have compared the dynamics of atactic polystyrene (aPS, amorphous) and isotactic polystyrene (iPS, crystallizable) films above the melting point (Tm). For aPS films, the apparent viscosity (hf) deduced from the dewetting experiments was expectedly smaller than the zero shear bulk viscosity (hbulk). Surprisingly, for iPS films hf was always greater than hbulk, even at about 50K above the melting temperature, with hf/hbulk following an Arrhenius behavior. The corresponding activation energy of 160±10 kJ/mol suggested a cooperative motion of segments, which were aligned and agglomerated by the fast dewetting process. Since the temperatures are above Tm, the observed cooperativity can only be transient. It is the aim of the current proposal to build on this premise by performing systematic dewetting, oscillatory rheometry (measure of the macroscopic viscosity) and time resolved in-situ X-ray scattering experiments (local structure and dynamics) for identifying the origin of transient cooperative processes in crystallizable polymers and examining their influence on the viscoelastic properties of polymer melts. To this end, polymers with different chemical structures and molecular weights will be sheared and probed in-situ using the complimentary techniques to provide a connection between the local dynamics (heterogeneities) and its macroscopic consequences. Support from the theoretical front is assured with the help of our external collaborator Dr. Semenov, Strasbourg. In addition, we expect that our studies will indicate novel strategies and pathways for tuning the properties of polymer melts.

当暴露于强剪切场时，聚合物熔体表现出丰富的动态行为。例如，非晶聚合物表现出剪切变薄的行为，而可结晶聚合物在流动取向结构中形成相关的片段。然而，这种相关性在可结晶聚合物熔体动力学行为中的作用尚未得到充分研究。在这种情况下，我们最近通过脱湿技术展示了这些相关片段在剪切聚合物熔体粘弹性行为上的表现。我们比较了熔点（Tm）以上的无规聚苯乙烯（aPS，无定形）和等规聚苯乙烯（iPS，可结晶）薄膜的动力学。对于aPS膜，从脱湿实验推导出的表观粘度（hf）预期小于零剪切体粘度（hbulk）。令人惊讶的是，对于iPS膜，即使在熔融温度以上约50K时，hf始终大于hbulk， hf/hbulk遵循Arrhenius行为。对应的活化能为160±10 kJ/mol，表明在快速脱湿过程中，段之间存在协同运动，并发生了排列和团聚。由于温度高于Tm，观察到的协同性只能是短暂的。在此前提下，本课题的目标是通过进行系统的脱湿、振荡流变学（测量宏观粘度）和时间分辨原位x射线散射实验（局部结构和动力学）来确定可结晶聚合物中瞬态协同过程的起源，并研究它们对聚合物熔体粘弹性性能的影响。为此，具有不同化学结构和分子量的聚合物将被剪切并使用互补技术进行原位探测，以提供局部动力学（异质性）与其宏观后果之间的联系。在斯特拉斯堡的外部合作者谢苗诺夫博士的帮助下，理论方面的支持得到了保证。此外，我们期望我们的研究将为调整聚合物熔体的性质提供新的策略和途径。