利用拉曼光谱对短链烷烃的相变过程及旋转相的研究

Study of Rotator Phase and Phase Transition of Short-Chain Alkane by Means of Raman Spectroscopy

利用激光拉曼光谱研究了二十六烷的凝结相变过程。在冷却过程中,二十六烷经历了从液相→旋转相→固态单斜晶相的相变过程。主要研究了烷烃分子碳链上CH2弯曲振动、CH2剪式振动、C—C伸展振动和CH3平面摇摆等振动模式的变化过程,包括这些模的频率、半宽和强度变化等,研究在相变过程中不同振动模式的的演变顺序和过程,反映各种振动模式与分子结构的相关性,并了解反式构象和歪曲构象在相变过程中的变化,从而更深入的理解烷烃等非晶体物质的相变过程。此外,通过分析800～1500cm-1波段各个拉曼波峰在降温过程中的变化过程,得到了二十六烷的旋转相的温度区间,证明可以利用拉曼光谱来观察烷烃相变过程中出现的旋转相。

Raman spectroscopy was used to investigate the phase transition of n-hexacosane for real-time cooling run. In the cooling process, the n-hexacosane experienced the melt phase→rotator phase→monoclinic crystal phase transition. The changes in band intensity and frequency in the CH2 bending, CH2 twisting, skeletal C—C stretching, and CH3 rocking regions were mainly analyzed in order to know the changing sequence and process of these vibrational modes, and to reflect the relationship between these vibrational modes and molecular structure. Besides, the changes in band intensity and frequency revealed both transitions, particularly when using band components related to gauche bonds. Our research shows that Raman spectroscopy is an effective tool to monitor the phase transition of n-alkanes or even long-chain polymers. In addition, by analyzing the Raman peaks in 800-1 500 cm^-1 in the cooling process of n-hexacosane, the temperature range of rotator phase was obtained, proving that Raman spectroscopy can be used to observe the rotator phase occurring during the phase transition of paraffin.