During crystallization, conformational changes are often accompanied by the formation of interactions. Terahertz (THz) spectroscopy exhibits strong responses to the crystalline poly(lactic acid) (PLA). Therefore, we estimate the relative crystallinity and investigate the effect of conformational transition on the vibration of PLA by THz spectroscopy. By comparing with the results of X-ray diffraction (XRD) and differential scanning calorimetry (DSC), the validity of THz spectroscopy to calculate crystallinity is verified. Furthermore, the peak intensity of PLA at 2.01 THz increases with crystallinity. Combined with Fourier transform infrared spectroscopy (FTIR), the vibrational intensity of PLA at 2.01 THz is highly correlated with the contribution of gt conformation, showing a linear relationship. In addition, the vibrational peak of PLA also reflects the interchain interactions. We believe that the increase in peak intensity with increasing crystallinity originates from the effect of the dipole–dipole interactions between the carbonyl groups. Our study demonstrates the ability of THz spectroscopy to estimate the crystallinity of PLA, and the peak at 2.01 THz shows conformational and interaction sensitivities.

中文翻译：

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用太赫兹光谱研究聚乳酸的结晶度和构象

在结晶过程中，构象变化往往伴随着相互作用的形成。太赫兹 (THz) 光谱对结晶聚乳酸 (PLA) 表现出强烈的响应。因此，我们估计了相对结晶度，并通过太赫兹光​​谱研究了构象转变对 PLA 振动的影响。通过与X射线衍射（XRD）和差示扫描量热法（DSC）的结果对比，验证了太赫兹光谱计算结晶度的有效性。此外，PLA 在 2.01 THz 处的峰值强度随着结晶度的增加而增加。结合傅里叶变换红外光谱（FTIR），PLA在2.01 THz处的振动强度与gt的贡献高度相关构象，呈线性关系。此外，PLA的振动峰也反映了链间相互作用。我们认为随着结晶度的增加峰强度的增加源于羰基之间偶极 - 偶极相互作用的影响。我们的研究证明了太赫兹光谱能够估计 PLA 的结晶度，并且在 2.01 太赫兹处的峰值显示了构象和相互作用的敏感性。