Meng Kun, Dong Xia, Hong Song, Wang Xin, Cheng He, Han Charles C
State Key Laboratory of Polymer Physics and Chemistry, Joint Laboratory of Polymer Science and Materials, Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, CAS, Beijing 100080, People's Republic of China.
J Chem Phys. 2008 Jan 14;128(2):024906. doi: 10.1063/1.2812927.
Isothermal crystallization after shear in a blend of isotactic polypropylene (iPP) and poly (ethylene-co-octene) (PEOc) was investigated by in situ optical microscopy and shear hot stage under various thermal and shear histories. Crystalline cylindrites during growth were observed in phase-separated iPPPEOc blends for the first time. According to our results, the very long cylindrites are formed which are much longer than the dimensions of the liquid-liquid phase-separated domains under shear, and the cylindrites appear to grow through noncrystallizable domains, as well as through crystallizable ones. Obviously, the nuclei ("shish") come from the oriented and entangled network strands instead of pulled-out long chains. The number of cylindrites and the distortion and breakup of the cylindrites are related to the shear rate and shear time. On the other hand, the number of spherulites increases not only with shear rate but also with liquid-liquid phase separation time. Spherulites always form with longer induction time than cylindrites due to the different nucleation mechanism. The shish is nucleated through the shear-induced mechanism, and most of the spherulites are nucleated through liquid-liquid spinodal decomposition and crossover after the cessation of shear. During the process of experiments, we also found three kinds of shish-kebab structures, which provide further physical insights into the mechanism of the shish formation in polymer blend after liquid-liquid phase separation under shear.
通过原位光学显微镜和剪切热台，在各种热历史和剪切历史条件下，研究了等规聚丙烯（iPP）与聚（乙烯 - 共 - 辛烯）（PEOc）共混物在剪切后的等温结晶过程。首次在相分离的iPP-PEOc共混物中观察到生长过程中的柱状晶。根据我们的结果，形成了非常长的柱状晶，其长度远大于剪切下液 - 液相分离区域的尺寸，并且柱状晶似乎穿过不可结晶区域以及可结晶区域生长。显然，晶核（“串晶”）来自取向和缠结的网络链，而不是拉出的长链。柱状晶的数量以及柱状晶的扭曲和破裂与剪切速率和剪切时间有关。另一方面，球晶的数量不仅随着剪切速率增加，而且随着液 - 液相分离时间增加。由于成核机制不同，球晶形成的诱导时间总是比柱状晶长。串晶通过剪切诱导机制成核，并且大多数球晶在剪切停止后通过液 - 液旋节线分解和转变而成核。在实验过程中，我们还发现了三种串晶 - 串晶束结构，这为剪切下液 - 液相分离后聚合物共混物中串晶形成机制提供了进一步的物理见解。
