Institute of Physics, University of Silesia, 75 Pulku Piechoty 1a, 41-500 Chorzow, Poland.
Phys Chem Chem Phys. 2018 Nov 14;20(44):28211-28222. doi: 10.1039/c8cp05913f.
In this paper, we applied broadband dielectric spectroscopy (BDS) to investigate the molecular dynamics of three 4-methyl-1,3-dioxolane derivatives (MD) whose chemical structures differ in the length of non-polar alkyl side chains. We notice that small changes within their chemical structures have a pronounced impact on parameters characterizing the supercooled dynamics of the compounds selected for this study. Our detailed analysis of the dielectric response reveals that in the supercooled-liquid state besides the structural α-relaxation a sub-α Debye-like relaxation can be clearly distinguished. The observed two relaxation regimes mirror the structural complexity of the investigated MD derivatives. The amphiphilic nature of the investigated compounds and possible interactions between non-polar side chains can rationalize the observed behavior. To follow the molecular arrangement of MD derivatives at low temperatures, we also carried out Raman measurements. Additionally, we performed BDS measurements at elevated pressures which revealed that, as a result of compression, the sub-α contribution to the dielectric response disappeared. The paper concludes with a discussion of open questions about the possible molecular origin of the observed sub-α Debye-like process. These results provide fresh insight into the puzzling nature of the slow supramolecular relaxation modes in low-molecular glass forming liquids.
在本文中，我们应用宽带介电谱（BDS）研究了三种 4-甲基-1,3-二恶烷衍生物（MD）的分子动力学，它们的化学结构在非极性烷基侧链长度上有所不同。我们注意到，其化学结构中的微小变化对所选化合物的过冷动力学参数有显著影响。我们对介电响应的详细分析表明，在过冷液体状态下，除了结构 α-松弛之外，还可以清楚地区分出亚-α Debye 型松弛。观察到的两个弛豫区反映了所研究的 MD 衍生物的结构复杂性。所研究化合物的两亲性质和非极性侧链之间可能的相互作用可以解释观察到的行为。为了在低温下跟踪 MD 衍生物的分子排列，我们还进行了拉曼测量。此外，我们还在升高的压力下进行了 BDS 测量，结果表明，由于压缩，介电响应的亚-α贡献消失了。本文最后讨论了关于观察到的亚-α Debye 型过程的可能分子起源的一些悬而未决的问题。这些结果为低分子形成玻璃液体中缓慢的超分子弛豫模式的令人费解的性质提供了新的见解。
