Evaluation of molecular orientation in a polymeric monolayer at the air-water interface by polarization-modulated infrared spectroscopy
Evaluation of molecular orientation in a polymeric monolayer at the air-water interface by polarization-modulated infrared spectroscopy
复制标题
通过偏振调制红外光谱评估空气-水界面聚合物单层的分子取向
作者：
L. Mao;A. Ritcey;B. Desbat
采用偏振调制反射吸收光谱（PM-IRRAS）来记录在空气-水界面上铺展的单层（十二烷基）纤维素的红外光谱。烷基侧链的亚甲基对称和反对称延伸在单层光谱中清晰可见，在 2852 和 2922 cm -1 处有正峰。由此得出结论，侧链具有垂直于水面的净取向。在 1160-980 cm -1 区域中，还观察到纤维素主链的特征带为正 PM-IRRAS 峰。该结果表明刚性多糖链基本上平行于水面。作为分子面积函数记录的光谱显示，单层压缩过程中分子取向几乎没有变化。然而，通过压缩分散单层获得的致密薄膜与通过在低表面积直接铺展制备的薄膜之间存在明显的取向差异。
Polarization-modulated reflection-absorption spectroscopy (PM-IRRAS) is employed to record infrared spectra of a monolayer of(dodecyl)cellulose spread at the air-water interface. Methylene symmetric and antisymmetric stretches of the alkyl side chains are clearly visible in the monolayer spectra as positive peaks at 2852 and 2922 cm -1 . It is thus concluded that the side chains possess a net orientation perpendicular to the water surface. Bands characteristic of the cellulose backbone are also observed as positive PM-IRRAS peaks, in the region 1160-980 cm -1 . This result indicates that the rigid polysaccharide chain lies essentially parallel to the water surface. Spectra recorded as a function of molecular area reveal little change in molecular orientation during monolayer compression. Significant differences in orientation are however evident between dense films obtained by the compression of disperse monolayers and those prepared by direct spreading at low surface areas.