Institute of Physics, University of Silesia in Katowice, ul. Uniwersytecka 4, 40-007 Katowice, Poland.
Silesian Center for Education and Interdisciplinary Research, ul. 75 Pułku Piechoty 1a, 41-500 Chorzów, Poland.
Sci Rep. 2017 Feb 9;7:42174. doi: 10.1038/srep42174.
In this paper, we demonstrate and thoroughly analyze the activation volumetric properties of selected liquid crystals in the nematic and crystalline E phases in comparison with those reported for glass-forming liquids. In the analysis, we have employed and evaluated two entropic models (based on either total or configurational entropies) to describe the longitudinal relaxation times of the liquid crystals in the density scaling regime. In this study, we have also exploited two equations of state: volumetric and activation volumetric ones. As a result, we have established that the activation volumetric properties of the selected liquid crystals are quite opposite to such typical properties of glass-forming materials, i.e., the activation volume decreases and the isothermal bulk modulus increases when a liquid crystal is isothermally compressed. Using the model based on the configurational entropy, we suggest that the increasing pressure dependences of the activation volume in isothermal conditions and the negative curvature of the pressure dependences of isothermal longitudinal relaxation times can be related to the formation of antiparallel doublets in the examined liquid crystals. A similar pressure effect on relaxation dynamics may be also observed for other material groups in case of systems, the molecules of which form some supramolecular structures.
本文展示并深入分析了所选向列相和晶相液晶的激活体积特性，并与报道的玻璃形成液体进行了比较。在分析中，我们采用并评估了两种熵模型（基于总熵或构象熵）来描述液晶在密度标度范围内的纵向弛豫时间。在本研究中，我们还利用了两种状态方程：体积和激活体积方程。结果表明，所选液晶的激活体积特性与玻璃形成材料的典型特性完全相反，即当液晶等温压缩时，激活体积减小，等温体弹性模量增加。使用基于构象熵的模型，我们提出在等温条件下激活体积的压力依赖性增加以及等温纵向弛豫时间的压力依赖性的负曲率可以与所研究的液晶中反平行二联体的形成有关。在分子形成某些超分子结构的情况下，对于其他材料组，在系统中也可能观察到类似的压力对弛豫动力学的影响。
