环丁醇温致相变的原位拉曼光谱研究  

Study on the Temperature Dependent Phase Transformation of Raman Spectra for Cyclobutanol

作　　者：张焕君[1] 程学瑞[1] 任宇芬[1] 朱祥[1] 袁朝圣[1] 

机构地区：[1]郑州轻工业学院物理与电子工程学院,河南郑州450002

出　　处：《光谱学与光谱分析》2016年第2期408-412,共5页Spectroscopy and Spectral Analysis

基　　金：国家自然科学基金项目(11404292)资助

摘　　要：采用拉曼光谱和红外光谱解析了常温条件下环丁醇的各个振动模式及其与分子构象间的关联,结果表明液态环丁醇以赤道–反式构象为主,并含有少量的赤道间扭式构象。在此基础上结合差示扫描量热技术和变温拉曼光谱,原位研究了环丁醇的温致相变过程和分子构象随温度的变化。结果表明,冷却至140K的过程中,环丁醇并未结晶固化,而是保持亚稳定的无序液体状态,即出现过冷现象,继续降温至138K出现玻璃化转变。升温过程中,在170K时出现放热峰,同时有新的拉曼峰出现,并且拉曼峰的半高宽和强度发生明显的突变,表明环丁醇由无序结构转变为有序的结晶相。因此,我们获得了环丁醇的温致相变序列:液态→过冷液体→玻璃态→结晶态→液态。通过对环丁醇不同分子构象的拉曼特征峰的定量分析,证实环丁醇在降温过程中,反式构象和间扭式构象的比例未发生明显改变,即没有发生构象变化。然而升温时,伴随170K时结晶态的转变,反式构象特征峰的相对强度减小,表明部分分子由赤道–反式构象转变为赤道–间扭式构象。该研究结果对进一步理解和研究其他有机小分子的温致相变和构象变化具有指导意义。Cyclobutanol（C4H8O）is one of the four-membered ring type molecules,which usually adopts a non-planar equilibrium conformation,and the substituent group OH can adopt two positions relative to the puckered ring,the axial or the equatorial,giving rise to an additional degree of freedom and various molecular conformations.Additionally,temperature is one important thermodynamic parameter that greatly influents the structure and induces the possibility of conformational change or crystal change.As a consequence,there may be a number of phase transitions and molecular conformations for cyclobutanol under different temperature.In this paper,Raman and infrared spectroscopic technique were applied to investigate the vibration modes of cyclobutanol.The results indicate that the main component of the liquid cyclobutanol is equatorial-trans（Eq-t）conformer with a few Eq-g conformers at ambient condition.Then differential scanning calorimetry（DSC）and low temperature Raman spectroscopic were applied to study the phase transition of cyclobutanol during the cooling and heating process.It is observed that the Raman spectra and the intensities of these bands are not significantly changed during the cooling process.The results indicate that there is sill no presence of solidification especially cooling to 140 K,which indicates that the cyclobutanol still remains the liquid state and supercooled state is observed during the cooling process.And this supercooled liquid is one metastable state,not in thermodynamic equilibrium.Further cooling to 138 K,the super-cooling liquid cyclobutanol will transform into the glassy state,accompanied with a small change of entropy.During the heating process,as the temperature is raised to 180 K,the Raman peaks became sharper and some new characteristic peaks appeared abruptly and a discontinuous change was observed in bandwidths versus temperature.And these new signatures can be maintained upon to 220 K,and then will disappear as the temperature increasing continuously.This result indicates

关 键 词：环丁醇 拉曼光谱 相变 差示量热扫描 

分 类 号：O433.5[机械工程—光学工程]