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采用低温溶解法制备了再生纤维素膜,运用扫描电子显微镜、傅里叶红外光谱仪和X射线衍射仪对所制薄膜进行形貌和晶型表征。在此基础上,结合太赫兹时域光谱和傅里叶变换红外光谱技术,测量了再生纤维素膜的太赫兹光谱。据此,详细指认了再生纤维素在太赫兹波段的特征峰,指出再生纤维素的太赫兹透过率随波数的减少而增大的现象是由其无定形部分所导致。通过比较再生纤维素和脱脂棉在100～700cm～(-1)的光谱特性,发现两者具有相似的峰形,但再生纤维素在此波段的特征峰相对于脱脂棉特征峰发生了不同程度的蓝移。据此,提出了鉴别纤维素Ⅱ和纤维素Ⅰ_β同质异晶体的一种新方法。重要的是,还采用CASTEP对纤维素Ⅱ晶体进行结构优化及光谱的理论研究,并对再生纤维素的太赫兹特征峰进行了系统的归属。理论计算结果表明,再生纤维素在42和54 cm～(-1)处的太赫兹特征峰分别是由平移振动和转动的晶格振动模式引起,而位于68～238 cm～(-1)间的太赫兹特征峰则与—CH_2OH基团的扭绞振动以及C—H及O—H的变形振动相关。此外,351～583 cm～(-1)范围内的吸收峰与C—O—C及吡喃环的骨架振动相关,而611和670 cm～(-1)两处的吸收峰则主要源于O—H的面外弯曲振动。结果不仅揭示了再生纤维素的物质结构与太赫兹光谱间的联系,也为理论上研究部分结晶的聚合物及生物有机大分子等的太赫兹响应的物理原理提供了参考。
The regenerated cellulose membrane was prepared by low temperature dissolution method. The morphology and crystal structure of the membrane were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. On this basis, the terahertz spectrum of regenerated cellulose membrane was measured by the combination of terahertz time-domain spectroscopy and Fourier transform infrared spectroscopy. Accordingly, the characteristic peaks of regenerated cellulose in the terahertz band are specified, and the phenomenon that the terahertz transmittance of regenerated cellulose increases with the decrease of the wavenumber is caused by the amorphous portion thereof. By comparing the spectral characteristics of regenerated cellulose and absorbent cotton at 100 ~ 700cm ~ (-1), it was found that both of them had similar peak shape, but the characteristic peak of regenerated cellulose relative to the characteristic peak of absorbent cotton had different degrees of blue shift. Accordingly, a new method to identify the cellulose and fiber Ⅰ_β isomorphous crystal was proposed. Importantly, CASTEP was also used to optimize the structure of cellulose II crystals and theoretical studies of the spectra. The terahertz peaks of regenerated cellulose were systematically assigned. The theoretical calculation results show that the terahertz characteristic peaks of regenerated cellulose at 42 and 54 cm -1 are caused by translational vibration and rotating lattice vibrational modes, respectively, while those located at 68 ~ 238 cm -1 The terahertz characteristic peak is related to the twisting vibration of -CH 2 OH group and the deformation vibration of C-H and O-H. In addition, the absorption peaks in the range of 351-583 cm -1 correlated with the skeleton vibration of C-O-C and pyran ring, while the absorption peaks at 611 and 670 cm -1 mainly originated from O-H out of plane bending vibration. The results not only revealed the relationship between the structure of the regenerated cellulose and the terahertz spectrum, but also provided a reference for the theoretical study of the terahertz response of partially crystalline polymers and bioorganic macromolecules.