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首页> 外文期刊>RSC Advances >Nanostructure domains, voids, and low-frequency spectra in binary mixtures of N,N-dimethylacetamide and ionic liquids with varying cationic size
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Nanostructure domains, voids, and low-frequency spectra in binary mixtures of N,N-dimethylacetamide and ionic liquids with varying cationic size

机译：N，N-二甲基乙酰胺与阳离子尺寸不同的离子液体的二元混合物的纳米结构域，空隙和低频光谱

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Classical molecular dynamics (MD) simulations were carried out on binary mixtures of N , N -dimethylacetamide (DMA) with hydroxide based ammonium ionic liquids (ILs), tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), tetrabutylammonium hydroxide (TBAH), at three different mole fractions of IL ( X _(IL) ). The solvation of DMA molecules by ions of ILs was studied by the combined distribution function (CDF). CDFs show that anions have strong correlations with the DMA due to the hydrogen bonding. Increasing the DMA disrupts the nanosegregated domains and causes changes in correlations of cation–DMA and anion–DMA. Also, increased translational motion of ions, as well as the fluidity of IL and a significant improvement in self-diffusion coefficients, are observed with the presence of more DMA. The structural microheterogeneity was investigated using the Voronoi tessellation method. Domain analysis confirms the formation of discreet domains by anions at all the mole fractions. The results also complement the experimental observations, which suggest that two types of aggregations are possible in given mixtures: below and above 0.5 X _(IL) . When the alkyl chain length on the cation increases, a notable decrease in ion translational motion was observed in the IL rich region. In the concentrated IL mixture, the self-diffusion coefficient of the cation is higher than that of the corresponding anion; further addition of IL ( X _(IL) < 0.5) results in weaker interactions between DMA and anion when compared to DMA–cation. The mean collision time of each species is found to have an inverse relation with X _(IL) . The analysis of the vibrational density of states provides the low-frequency spectral feature of the mixtures.
机译：经典的分子动力学（MD）模拟是在N，N-二甲基乙酰胺（DMA）与基于氢氧化物的铵离子液体（ILs），氢氧化四乙铵（TEAH），氢氧化四丙铵（TPAH），氢氧化四丁铵（TBAH）的二元混合物上进行的，在三个不同的摩尔分数IL（X _（IL））。通过组合分布函数（CDF）研究了离子液体离子对DMA分子的溶剂化作用。 CDFs显示，由于氢键，阴离子与DMA具有很强的相关性。 DMA的增加会破坏纳米分离域，并导致阳离子DMA和阴离子DMA的相关性发生变化。同样，在存在更多DMA的情况下，观察到离子的平移运动增加，IL的流动性和自扩散系数的显着提高。使用Voronoi镶嵌方法研究了结构的微观异质性。结构域分析证实了阴离子在所有摩尔分数下都形成了离散的结构域。该结果还补充了实验观察结果，这表明在给定的混合物中两种类型的聚集是可能的：低于和高于0.5 X _（IL）。当阳离子上的烷基链长度增加时，在富含IL的区域中观察到离子平移运动显着下降。在浓缩的IL混合物中，阳离子的自扩散系数高于相应阴离子的自扩散系数。与DMA-阳离子相比，进一步添加IL（X _（IL）<0.5）会导致DMA与阴离子之间的相互作用减弱。发现每种物质的平均碰撞时间与X _（IL）成反比关系。状态振动密度的分析提供了混合物的低频频谱特征。

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