Orientational Jumps in (Acetamide + Electrolyte) Deep Eutectics: Anion Dependence

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• 作者：Suman Das ; Ranjit Biswas ; Biswaroop Mukherjee
• 刊名：Journal of Physical Chemistry B
• 出版年：2015
• 出版时间：August 27, 2015
• 年：2015
• 卷：119
• 期：34
• 页码：11157-11168
• 全文大小：765K
• ISSN：1520-5207

文摘

All-atom molecular dynamics simulations have been carried out to investigate orientation jumps of acetamide molecules in three different ionic deep eutectics made of acetamide (CH₃CONH₂) and lithium salts of bromide (Br^{鈥?/sup>), nitrate (NO₃鈥?/sup>) and perchlorate (ClO₄鈥?/sup>) at approximately 80:20 mole ratio and 303 K. Orientational jumps have been dissected into acetamide鈥揳cetamide and acetamide鈥搃on catagories. Simulated jump characteristics register a considerable dependence on the anion identity. For example, large angle jumps are relatively less frequent in the presence of NO₃鈥?/sup> than in the presence of the other two anions. Distribution of jump angles for rotation of acetamide molecules hydrogen bonded (H-bonded) to anions has been found to be bimodal in the presence of Br鈥?/sup> and is qualitatively different from the other two cases. Estimated energy barrier for orientation jumps of these acetamide molecules (H-bonded to anions) differ by a factor of 鈭? between NO₃鈥?/sup> and ClO₄鈥?/sup>, the barrier height for the latter being lower and 鈭?.5k_BT. Relative radial and angular displacements during jumps describe the sequence ClO₄鈥?/sup> > NO₃鈥?/sup> > Br鈥?/sup> and follow a reverse viscosity trend. Jump barrier for acetamide鈥揳cetamide pairs reflects weak dependence on anion identity and remains closer to the magnitude (鈭?.7k_BT) found for orientation jumps in molten acetamide. Jump time distributions exhibit a power law dependence of the type, P(t_jump) 鈭?A(t_jump/蟿)鈭捨?/sup>, with both 尾 and 蟿 showing substantial anion dependence. The latter suggests the presence of dynamic heterogeneity in these systems and supports earlier conclusions from time-resolved fluorescence measurements.}