变温红外光谱研究表面双稳态液晶分子的相变过程

运用变温红外和样本-样本相关光谱对40～150 ℃温度区间内的表面双稳态液晶分子MHOCPOOB的相变过程中的分子构象、排布及相互作用的变化进行研究。结果表明：室温时，分子烷基链中同时存在Zigzag和Gauche两种构象。随温度升高，其中有序的Zigzag构象转化为无序的Gauche 构象，链的扭曲程度增加。刚性核部分，羰基与相邻的苯环形成共轭体系，苯环之间相互倾斜排列，在相变过程中羰基与苯环的共平面作用逐渐被打破，且在相变点苯环间的二面角明显增大。由于表面稳定化的作用，使得在液晶盒表面上的一层膜，其结构并不随温度、相结构的变化而变化，因而在液晶盒的光谱中观察到的相变点较少。通过二维光谱作者发现，在122 ℃时分子出现细微结构调整。

Phase Transitions of Surface-Stabilized Liquid Crystal Studied by Temperature-Dependent FTIR Spectroscopy

The FTIR spectra were measured for liquid crystal molecules in CaF2 cell over a temperature range of 40-150 degrees C. The alkyl chain transformed from ordered zigzag-dominated conformation to disordered gaucheness-dominated conformation with increasing temperature. Meanwhile, the degree of freedom of the rotation of the carbonyl group increased, the co-plane interaction between the carbonyl group and the phenyl ring broke, and the conjugation between the C=O bond and the phenyl ring was reduced at the S(CA)* --> S(A) phase transition point, followed by the increase of the plane angle between the two phenyl rings. Due to the surface stability effect of the LC cell, there existed on the cell surface a layer whose structure was independent of the temperature and LC phase. Therefore, the molecules still retained its originally phase property even at temperatures near and above the transition point.