Merkel Katarzyna, Loska Barbara, Welch Chris, Mehl Georg H, Kocot Antoni
Institute of Materials Engineering, University of Silesia, 75 Pułku Piechoty 1A, 41-500 Chorzów, Poland.
Department of Chemistry, University of Hull, Hull HU6 7RX, UK.
Phys Chem Chem Phys. 2021 Feb 25;23(7):4151-4160. doi: 10.1039/d1cp00187f.
Fourier-transform infrared polarized spectroscopy was employed, to obtain the three components of the infrared absorbance for a series of bent-shaped dimers containing double fluorinated terphenyl core (DTC5Cn, n = 5, 7, 9, 11). The data were used to calculate both uniaxial and biaxial order parameters, for various molecular groups of dimers. The molecule bend was estimated based on the observed differences between the uniaxial order parameters for the terphenyl core and central hydrocarbon linker. The orientational order, distinctly reverses its monotonic trend of increase to decrease at the transition temperature, from the uniaxial nematic to the twist-bend nematic phase as result of the director tilt in latter/(twist-bend) phase. The molecular biaxiality, which is negligible in the nematic phase, starts increasing on entering the twist-bend nematic phase, following a sin-square relationships with the tilt angle. The local director curvature is found to be controlled by the molecular biaxiality parameter.
采用傅里叶变换红外偏振光谱法，获取了一系列含有双氟化三联苯核心（DTC5Cn，n = 5、7、9、11）的弯曲形二聚体的红外吸光度的三个分量。这些数据用于计算二聚体各种分子基团的单轴和双轴序参量。基于三联苯核心和中心烃连接体的单轴序参量之间观察到的差异估计分子弯曲度。由于在后一个（扭曲弯曲）相中指向矢倾斜，取向序在转变温度下从单轴向列相到扭曲弯曲向列相明显地将其单调增加趋势反转成减小趋势。在向列相中可忽略不计的分子双轴性，在进入扭曲弯曲向列相时开始增加，与倾斜角呈正弦平方关系。发现局部指向矢曲率由分子双轴性参数控制。
