Dual Nature of Large and Anisotropic Glass-Forming Molecules in Terms of Debye-Stokes-Einstein Relation Revealed.

IF 2.8 2区 化学 Q3 CHEMISTRY, PHYSICAL
The Journal of Physical Chemistry B Pub Date : 2024-12-12 Epub Date: 2024-12-03 DOI:10.1021/acs.jpcb.4c04757
Abin Raj, Marzena Rams-Baron, Kajetan Koperwas, Żaneta Wojnarowska, Marian Paluch
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引用次数: 0

Abstract

The fundamental Debye-Stokes-Einstein (DSE) relation between rotational relaxation times and shear viscosity attracts longstanding research interest as one of the most important characteristics of many glass-forming liquids. Here, we provide strong evidence, missing so far, for the relevance of anisotropy for DSE-related behavior. Dielectric spectroscopy and shear viscosity measurements were employed to get insight into the decoupling between reorientation relaxation times and viscosity for anisotropic glass-formers with dipole moments oriented parallel or perpendicular to the long molecular axis. We found that in the case of large and anisotropic molecules, the breakdown of DSE relation depends on the component of anisotropic rotation contributing to the dielectric response. Specifically, for glass-formers with dipole moment perpendicular to the long molecular axis, the DSE relation was found to be valid throughout the supercooled regime. Contrary, a departure from the DSE predictions in the intermediate supercooled regime, was observed for glass-formers where only short-axes contributions were relevant in dielectric response. MD simulations revealed differences in the mechanism of short and long axes reorientations suggesting that for anisotropic objects, not the reorientation mechanism itself, but the aspect of anisotropic motion, is the key to understanding the behavior of these systems in the context of DSE relation.

从Debye-Stokes-Einstein关系揭示大的各向异性玻璃形成分子的双重性质。
旋转松弛时间和剪切粘度之间的基本德拜-斯托克斯-爱因斯坦(DSE)关系作为许多玻璃形成液体的最重要特征之一,引起了长期的研究兴趣。在这里,我们为各向异性与dse相关行为的相关性提供了强有力的证据,迄今为止还没有。采用介电光谱和剪切粘度测量来深入了解偶极矩取向平行或垂直于长分子轴的各向异性玻璃的重定向弛豫时间和粘度之间的解耦关系。我们发现在大分子和各向异性分子的情况下,DSE关系的击穿取决于各向异性旋转对介电响应的贡献。具体来说,对于偶极矩垂直于长分子轴的成玻璃,发现DSE关系在整个过冷状态下都是有效的。相反,在中间过冷状态下,在只有短轴贡献与介电响应相关的玻璃形成中,观察到与DSE预测的偏离。MD模拟揭示了短轴和长轴重定向机制的差异,这表明对于各向异性物体,不是重定向机制本身,而是各向异性运动方面,是理解这些系统在DSE关系背景下行为的关键。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
CiteScore
5.80
自引率
9.10%
发文量
965
审稿时长
1.6 months
期刊介绍: An essential criterion for acceptance of research articles in the journal is that they provide new physical insight. Please refer to the New Physical Insights virtual issue on what constitutes new physical insight. Manuscripts that are essentially reporting data or applications of data are, in general, not suitable for publication in JPC B.
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