National Synchrotron Radiation Lab, CAS Key Laboratory of Soft Matter Chemistry, University of Science and Technology of China, Hefei, China.
MOE Key Laboratory of Space Applied Physics and Chemistry, Shaanxi Key Laboratory of Macromolecular Science and Technology, School of Science, Northwestern Polytechnical University, Xi'an, 710072, P. R. China.
Soft Matter. 2017 May 21;13(19):3639-3648. doi: 10.1039/c7sm00107j. Epub 2017 Apr 27.
Structural and morphological transitions of flow-induced crystallization (FIC) in poly(1-butene) (PB-1) melt have been studied by combining extensional rheology and in situ synchrotron radiation ultrafast wide- and small-angle X-ray scattering (WAXD/SAXS) measurements. Unexpectedly, metastable Form III is crystallized directly from the PB-1 melt by high-speed extension, which has a short lifetime of several tens of milliseconds and manifests the thermodynamic and kinetic competition among Form III, Form II and melt under flow. Relative crystallinity evolution of Form II after extension reveals a crystal melting dominated process within the observation time of 120 s even under high supercooling. This is opposite to the common case of FIC but supports the idea that flow alters the obtained crystal size and its thermodynamic stability. Additionally, a morphological transition from a flow-induced network to shish is observed by SAXS with increasing extension temperature from below to above the melting point of Form II. With above observations, we construct nonequilibrium structural and morphological diagrams of FIC in strain rate-temperature space, which may guide the industrial processing of the PB-1 material.
通过结合拉伸流变学和原位同步辐射超快广角和小角 X 射线散射（WAXD/SAXS）测量，研究了聚 1-丁烯（PB-1）熔体中流动诱导结晶（FIC）的结构和形态转变。出乎意料的是，亚稳态 III 型通过高速拉伸直接从 PB-1 熔体中结晶，其寿命只有几十毫秒，表现出 III 型、II 型和熔体在流动下的热力学和动力学竞争。拉伸后 II 型的相对结晶度演变表明，即使在高过冷度下，在 120 秒的观察时间内，结晶仍主要以熔融为主。这与常见的 FIC 情况相反，但支持了流动改变获得的晶体尺寸及其热力学稳定性的观点。此外，随着拉伸温度从低于到高于 II 型的熔点升高，通过 SAXS 观察到从流致网络到 shish 的形态转变。通过以上观察，我们在应变速率-温度空间中构建了 FIC 的非平衡结构和形态图，这可能指导 PB-1 材料的工业加工。
