结晶
材料科学
吸收(声学)
光谱学
太赫兹辐射
结晶学
吸收光谱法
红外光谱学
分析化学(期刊)
化学
光学
有机化学
光电子学
物理
量子力学
复合材料
作者
Zhenqi Zhu,Yujing Bian,Xun Zhang,Ruonan Zeng,Bin Yang
摘要
The observed properties of crystalline polymers are determined by their internal structure, which in turn is the result of their different crystallization behaviors. Here, we investigate the crystallization behavior of poly(lactic acid) (PLA) by terahertz time-domain spectroscopy (THz-TDS) at varied temperatures. We find that the changes in the chain packing and conformation of PLA are characterized by THz spectroscopy. Combining X-ray diffraction (XRD) and infrared spectroscopy (IR), we attributed the blue-shift of the THz peak to the tightness of the chain packing, while its absorption enhancement is caused by the conformation transition. The effects of chain packing and chain conformation on the characteristic peak are phased. Furthermore, absorption discontinuities of the characteristic peaks of PLA crystallized at different temperatures are observed, which originated from differences in the degree of conformational transition caused by different thermal energies. We find that the crystallization temperature at which the absorption mutation of PLA occurs corresponds to the temperature at which the motion of the segment and molecular chain is excited, respectively. At these two temperatures, PLA exhibits different scales of conformational transitions leading to stronger absorption and larger absorption changes at higher crystallization temperatures. The results demonstrate that the driving force of PLA crystallization is indeed from changes in chain packing and chain conformation, and the molecular motion scale can also be characterized by THz spectroscopy.
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