The thermodynamic properties of flow-induced precursor of polyethylene  

作　　者：Dong Liu Kunpeng Cui Ningdong Huang Zhen Wang Liangbin Li 

机构地区：[1]National Synchrotron Radiation Laboratory and College of Nuclear Science and Technology [2]CAS Key Laboratory of Soft Matter Chemistry [3]University of Science and Technology of China

出　　处：《Science China Chemistry》2015年第10期1570-1578,共9页中国科学（化学英文版）

基　　金：supported by the National Natural Science Foundation of China(51325301,51033004,51120135002,51227801);the Joint Fund of the National Natural Science Foundation of China and the China Academy of Engineering Physics(U1330202);Project 2013BB05 supported by the Key Laboratory of Neutron Physics,China Academy of Engineering Physics;in part supported by"Ludo Frevel Crystallography Scholarships"from the International Centre for Diffraction Data

摘　　要：Flow-induced preordering or precursor(FIP) has been studied in a series of lightly cross-linked high-density polyethylene with a combination of extensional rheology and in situ synchrotron radiation small-angle X-ray scattering(SAXS) and wide-angle X-ray diffraction(WAXD) measurements. Based on the incipient strains of SAXS and WAXD signals during extension in a large temperature range, strain-temperature diagrams for flow-induced preordering and nucleation were constructed and revealed that flow-induced crystallization(FIC) undergoes two stages: melt-precursor transition(MPT) and precursor-nuclei transition(PNT). At different temperatures, FIP with different inner structures and morphologies can be induced by strain; these embryos have shape and structure that are related to those of the corresponding critical nuclei. With the strain-temperature diagrams, the thermodynamic properties of FIP are deduced, which shows that compared with the relative nuclei the FIP always has a lower bulk free energy(?H) and a much lower surface free energy(?e). In extreme cases(high temperature), the ?e of FIP can be negligible. The quantitative estimation of the thermodynamic parameters suggests the existence of variant FIPs, which plays a vital role for the subsequent progress of PNT and the whole process of FIC.Flow-induced preordering or precursor（FIP） has been studied in a series of lightly cross-linked high-density polyethylene with a combination of extensional rheology and in situ synchrotron radiation small-angle X-ray scattering（SAXS） and wide-angle X-ray diffraction（WAXD） measurements. Based on the incipient strains of SAXS and WAXD signals during extension in a large temperature range, strain-temperature diagrams for flow-induced preordering and nucleation were constructed and revealed that flow-induced crystallization（FIC） undergoes two stages： melt-precursor transition（MPT） and precursor-nuclei transition（PNT）. At different temperatures, FIP with different inner structures and morphologies can be induced by strain; these embryos have shape and structure that are related to those of the corresponding critical nuclei. With the strain-temperature diagrams, the thermodynamic properties of FIP are deduced, which shows that compared with the relative nuclei the FIP always has a lower bulk free energy（？H） and a much lower surface free energy（？e）. In extreme cases（high temperature）, the ？e of FIP can be negligible. The quantitative estimation of the thermodynamic parameters suggests the existence of variant FIPs, which plays a vital role for the subsequent progress of PNT and the whole process of FIC.

关 键 词：flow-induced precursor（FIP） SHISH-KEBAB thermodynamic parameters SAXS WAXD POLYETHYLENE 

分 类 号：O632.12[理学—高分子化学]