Structure, Microheterogeneity, and Transport Properties of Ethaline Decoded by X-ray/Neutron Scattering and MD Simulation

作者：Keke Chai, Toshio Yamaguchi, Taisen Zuo, Jochi Tseng, Kazutaka Ikeda, Yongquan Zhou · 发表于：The Journal of Physical Chemistry B · 年份：2024 · DOI：10.1021/acs.jpcb.4c02826 · 被引用次数：8 · 研究领域：Phase Equilibria and Thermodynamics、Crystallography and molecular interactions、Ionic liquids properties and applications

Ethaline, a deep eutectic solvent (DES) composed of choline chloride (ChCl)–ethylene glycol (EG) in a 1:2 molar ratio, is garnering significant interest for its wide potential applications. The nature of liquid formation and the structure of H-bonds within ethaline were investigated by X-ray scattering (XRS), neutron scattering (NS), and MD simulations. The sum of the dissociation energy barriers of Ch-EG (3.31 kJ·mol –1 ) and EG-Cl (4.28 kJ·mol –1 ) exceeds that of Ch-Cl (5.97 kJ·mol –1 ). This results in a more pronounced solvation of ChCl by EG compared to ChCl association, facilitating the solubilization of ChCl crystals by EG to form a DES. A partial radial distribution function (PDF) reveals that Cl – solvation is dominated by the hydroxyl group of EG, while the methylene group dominates Ch + solvation. The spatial distribution function (SDF) shows that the distribution of EG and Cl – around Ch + partially overlaps with that of the quaternary ammonium group. However, the center of mass distance of Ch-Cl (4.95 Å) is significantly lower than that of Ch-EG (5.65 Å), suggesting a favorable advantage for Cl – in this competition. Chain and ring structure distributions provide direct evidence of the microheterogeneity of ethaline. Hydroxyl groups on the EG promote the formation of a chain structure in ethaline, while methylene groups favor a ring structure. H-bond, carbon H-bond, and Cl – bridge bond restrict Cl – diffusion. This new understanding is crucial for a deeper comp...