Rinesh T, Srinivasan H, Sharma V K, Mitra S
Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India.
Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, India.
J Chem Phys. 2024 Jul 14;161(2). doi: 10.1063/5.0213402.
Aqueous mixtures of deep eutectic solvents (DESs) have emerged as a subject of interest in recent years for their tailored physicochemical properties. However, a comprehensive understanding of water's multifaceted influence on the microscopic dynamics, including its impact on improved transport properties of the DES, remains elusive. Additionally, the diffusion mechanisms within DESs manifest heterogeneous behavior, intricately tied to the formation and dissociation kinetics of complexes and hydrogen bonds. Therefore, it is imperative to explore the intricate interplay between bond kinetics, diffusion mechanism, and dynamical heterogeneity. This work employs water as an agent to explore their relationships by studying various relaxation phenomena in a DES based on acetamide and lithium perchlorate over a wide range of water concentrations. Notably, acetamide exhibits Fickian yet non-Gaussian diffusion across all water concentrations with Fickian (τf) and Gaussian (τg) timescales following a power-law relationship, τg∝τfγ, γ ∼ 1.4. The strength of coupling between bond kinetics and different diffusion timescales is estimated through various power-law relationships. Notably, acetamide-water hydrogen bond lifetime is linked to diffusive timescales through a single power-law over the entire water concentration studied. However, the relationship between diffusive timescales and the lifetime of acetamide-lithium complexes shows a sharp transition in behavior at 20 wt. % water, reflecting a change from vehicular diffusion below this concentration to structural diffusion above it. Our findings emphasize the critical importance of understanding bond dynamics within DESs, as they closely correlate with and regulate the molecular diffusion processes within these systems.
近年来，深共熔溶剂（DESs）的水性混合物因其可定制的物理化学性质而成为一个备受关注的课题。然而，对于水对微观动力学的多方面影响，包括其对DESs改善的传输性质的影响，仍缺乏全面的理解。此外，DESs中的扩散机制表现出异质性行为，与配合物和氢键的形成和解离动力学密切相关。因此，探索键动力学、扩散机制和动力学非均匀性之间的复杂相互作用势在必行。这项工作以水为媒介，通过研究基于乙酰胺和高氯酸锂的DES在广泛水浓度范围内的各种弛豫现象来探索它们之间的关系。值得注意的是，在所有水浓度下，乙酰胺都表现出菲克型但非高斯型扩散，菲克（τf）和高斯（τg）时间尺度遵循幂律关系，τg∝τfγ，γ ∼ 1.4。通过各种幂律关系估计键动力学与不同扩散时间尺度之间的耦合强度。值得注意的是，在所研究的整个水浓度范围内，乙酰胺 - 水氢键寿命通过单一幂律与扩散时间尺度相关联。然而，扩散时间尺度与乙酰胺 - 锂配合物寿命之间的关系在水含量为20 wt.%时表现出行为上的急剧转变，这反映了在此浓度以下从载体扩散到在此浓度以上结构扩散的变化。我们的研究结果强调了理解DESs内键动力学的至关重要性，因为它们与这些系统内的分子扩散过程密切相关并对其进行调节。
