The dependence of properties on the structure and morphology of semicrystalline polymers offers an effective way to tailor the properties of these materials through structure control. To this end, establishing the str...The dependence of properties on the structure and morphology of semicrystalline polymers offers an effective way to tailor the properties of these materials through structure control. To this end, establishing the structure and property relationship is of great importance. For a right characterization of the crystal structure, several techniques can be used. Among these techniques, electron diffraction has its advantage for determining the crystal structure related to specific formation condition since it can combine with bright and dark fields observation of the sample. This feature article describes the application of electron diffraction in determining the crystal structure of semicrystalline polymers with elaborately selected examples. We focus on how the electron diffraction can be used to disclose the crystal structure, mutual orientation of different crystals, as well as the disorders included in the polymer crystals.展开更多
The large size of the crystallites in poly（L-lactide） and the low growth rate enable detailed time- and temperaturedependent X-ray scattering studies of the ordering processes to be carded out. A layer located inter...The large size of the crystallites in poly（L-lactide） and the low growth rate enable detailed time- and temperaturedependent X-ray scattering studies of the ordering processes to be carded out. A layer located intermediate between crystals and melt-like regions is observed which finally takes on crystalline order. Recrystallization processes during heating change the complete stack structure rather than the crystallites individually and produce voids in the stacks, Establishment of a new stable structure after a temperature jump in the melting range can be followed in time. DSC experiments indicate times of melting of the order of minutes.展开更多
Dielectric relaxation spectroscopy（DRS） of poly（ε-caprolactone） with different draw ratios showed that the mobility of polymer chains in the amorphous part decreases as the draw ratio increases. The activation en...Dielectric relaxation spectroscopy（DRS） of poly（ε-caprolactone） with different draw ratios showed that the mobility of polymer chains in the amorphous part decreases as the draw ratio increases. The activation energy of the α process, which corresponds to the dynamic glass transition, increases upon drawing. The enlarged gap between the activation energies of the α process and the β process results in a change of continuity at the crossover between the high temperature a process and the α and β processes. At low drawing ratios the a process connects with the β process, while at the highest drawing ratio in our measurements, the a process is continuous with the αprocess. This is consistent with X-ray diffraction results that indicate that upon drawing the polymer chains in the amorphous part align and densify upon drawing. As the draw ratio increases, the α relaxation broadens and decreases its intensity, indicating an increasing heterogeneity. We observed slope changes in the α traces, when the temperature decreases below that at which τα≈ 1 s. This may indicate the glass transition from the ‘rubbery＇ state to the non-equilibrium glassy state.展开更多
基金supported by the National Natural Science Foundation of China (Nos. 50833006, 21274009,51221002 and 50973008)
文摘The dependence of properties on the structure and morphology of semicrystalline polymers offers an effective way to tailor the properties of these materials through structure control. To this end, establishing the structure and property relationship is of great importance. For a right characterization of the crystal structure, several techniques can be used. Among these techniques, electron diffraction has its advantage for determining the crystal structure related to specific formation condition since it can combine with bright and dark fields observation of the sample. This feature article describes the application of electron diffraction in determining the crystal structure of semicrystalline polymers with elaborately selected examples. We focus on how the electron diffraction can be used to disclose the crystal structure, mutual orientation of different crystals, as well as the disorders included in the polymer crystals.
基金This work was supported by the Deutsche Forschungsgemeinschaft. Thanks are also due to the Fonds der Chemischen Industrie for financial help.
文摘The large size of the crystallites in poly（L-lactide） and the low growth rate enable detailed time- and temperaturedependent X-ray scattering studies of the ordering processes to be carded out. A layer located intermediate between crystals and melt-like regions is observed which finally takes on crystalline order. Recrystallization processes during heating change the complete stack structure rather than the crystallites individually and produce voids in the stacks, Establishment of a new stable structure after a temperature jump in the melting range can be followed in time. DSC experiments indicate times of melting of the order of minutes.
基金the research programme of the Dutch Polymer Institute (DPI),project#623
文摘Dielectric relaxation spectroscopy（DRS） of poly（ε-caprolactone） with different draw ratios showed that the mobility of polymer chains in the amorphous part decreases as the draw ratio increases. The activation energy of the α process, which corresponds to the dynamic glass transition, increases upon drawing. The enlarged gap between the activation energies of the α process and the β process results in a change of continuity at the crossover between the high temperature a process and the α and β processes. At low drawing ratios the a process connects with the β process, while at the highest drawing ratio in our measurements, the a process is continuous with the αprocess. This is consistent with X-ray diffraction results that indicate that upon drawing the polymer chains in the amorphous part align and densify upon drawing. As the draw ratio increases, the α relaxation broadens and decreases its intensity, indicating an increasing heterogeneity. We observed slope changes in the α traces, when the temperature decreases below that at which τα≈ 1 s. This may indicate the glass transition from the ‘rubbery＇ state to the non-equilibrium glassy state.
