Rheologically determined phase diagram and dynamically investigated phase separation kinetics of polyolefin blends
Rheologically determined phase diagram and dynamically investigated phase separation kinetics of polyolefin blends
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DOI：
10.1021/ma060103n
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发表时间：
2006-06-13
期刊：
影响因子：
5.5
通讯作者：
Wang, Zhi-Gang
中科院分区：
文献类型：
--
作者：
Niu, Yan-Hua;Wang, Zhi-Gang
乙烯/己烯（PEH）和乙烯/丁烯（PEB）统计共聚物的共混物表现出上临界溶解温度（UCST）的行为。本文采用流变学方法测定了PEH/PEB共混体系的相图，并从聚合物粘弹性的角度研究了共混体系的相分离动力学。基于时间-温度叠加原理和平均场理论，采用流变学方法确定了双结点和旋结点相分离温度。与光学技术相比，流变学可以在相当早期的阶段灵敏地检测相分离。结果发现，无论是在亚稳或不稳定的区域，相分离的共混物的储能模量下降时，相分离的进展。亚稳区G'下降幅度小于不稳定区，这是因为亚稳区的成核和生长过程以扩散为主，界面张力较弱，而不稳定区的成核和生长过程以调幅浓度波动为主，界面张力较强。在不稳定区G'的降低是由于浓度波动降低和界面张力降低的耦合作用，而在亚稳区G'的降低是由界面面积减小和变形能力增加的竞争作用决定的。
Blends of statistical copolymers ethylene/hexene (PEH) and ethylene/butene (PEB) show the behavior of an upper critical solution temperature (UCST). In this study, the phase diagram of PEH/PEB blends was determined by using rheological measurements, and the kinetics of phase separation was investigated from the viewpoints of polymer viscoelasticity. Based on time-temperature superposition (TTS) principle and mean field theory, rheology methods were used to determine the binodal and spinodal phase separation temperatures. Compared with optical techniques, rheology could sensitively detect phase separation in rather early stages. It was found that in either the metastable or unstable regions, storage moduli of the phase-separated blends decreased when phase separation progressed. The magnitude of G' decreasing was smaller in the metastable region than in the unstable region because the nucleation and growth process in the metastable region was dominated by diffusion and interfacial tension was much weaker, while in the unstable region, spinodal concentration fluctuations were dominant and interfacial tension was stronger. The decrease of G' in the unstable region was due to the coupling effects of reduced concentration fluctuations and decreased interfacial tension, whereas the decrease of G' in the metastable region was determined by competitive effects of the reduced interfacial area and increased deformability.