We investigate in this paper, via molecular dynamics simulations, the composition dependent solution structures in the binary mixtures composed of the ionic liquid (IL), 1-butyl-3methyl-imidazolium hexafluorophosphate, ([BMIM] [PF₆]), and three different co-solvents of comparable sizes but with differing polarities. These cosolvents are acetonitrile (dipolar), 1,4-dioxane (quadrupolar) and hexane (non-polar). Five different IL mole fractions for the binary mixtures (F_IL = 0.90, 0.75, 0.50, 0.25, 0.10) along with the neat solvents have been studied. The cosolvent polarity and concentration dependencies have been assessed through the examination of the composition dependent spatial and radial distribution functions, coordination numbers and the Voronoi polyhedra analyses. The solution structure is found to be dominated by the cosolvent clustering at high IL concentrations, and segregation of the IL into polar and non-polar domains in dilute IL solutions, their extent being strongly dependent upon cosolvent polarity. The aggregation behavior of the IL in the non-polar and dipolar binary mixtures is explained in terms of the Debye screening length (DSL). Such an explanation, however, fails to explain the comparable solubility of 1,4-dioxane in this IL. Isodensity surfaces constructed from the simulated spatial distribution functions show a dramatic cosolvent polarity dependence for the binary solution structure and reflects that microscopic phase segregation is the most pronounced for IL + hexane binary mixtures. The Voronoi polyhedra (VP) analyses indicate broader void and neck distributions upon dilution of the IL by cosolvents, suggesting increased heterogeneity in the solution structure of the binary mixtures. The severe phase segregation observed for [BMIM] [PF₆] + hexane mixtures at the low IL concentrations did not allow similar VP analyses for this binary mixture for all the mixture compositions considered.

我们在本文中通过分子动力学模拟研究了离子液体（IL），1-丁基-3甲基-咪唑六氟磷酸盐（[BMIM] [PF ₆ ]）和三种可比较尺寸但极性不同的不同助溶剂。这些助溶剂是乙腈（双极性），1，4-二恶烷（四极性）和己烷（非极性）。二元混合物的五个不同的IL摩尔分数（F _IL = 0.90，0.75，0.50，0.25，0.10）和纯溶剂一起进行了研究。助溶剂的极性和浓度依赖性已经通过检查与组成有关的空间和径向分布函数，配位数和Voronoi多面体分析进行了评估。发现溶液结构主要由高IL浓度的助溶剂簇集和稀释的IL溶液中IL分离成极性和非极性域组成，它们的程度强烈取决于助溶剂的极性。IL在非极性和偶极二元混合物中的聚集行为用Debye筛选长度（DSL）来解释。然而，这种解释不能解释1，4-二恶烷在该IL中的可比溶解度。由模拟的空间分布函数构造的等渗表面显示出二元溶液结构对助溶剂极性的显着依赖性，并反映出微观相偏析对于IL +己烷二元混合物最为明显。Voronoi多面体（VP）分析表明，用助溶剂稀释IL后，空隙和颈部分布更宽，表明二元混合物溶液结构中的异质性增加。[BMIM] [PF]的严重相分离 提示二元混合物溶液结构中的异质性增加。[BMIM] [PF]的严重相分离 提示二元混合物溶液结构中的异质性增加。[BMIM] [PF]的严重相分离对于所有考虑的混合物组成，在低IL浓度下的₆ ] +己烷混合物均不允许对该二元混合物进行类似的VP分析。