| Experts and researchers in various disciplines have always been in favor of the study of ionic liquids?ILs?.Known as“green solvents”and“designable solvents”,ILs have been studied by experts and scholars and their research results are widely distributed in various areas associated with human production and living For example,in the field of petrochemicals,ILs have been widely used in desulfurization,refining,separation and other processing steps as a chemical basic material;in the field of electrochemistry,ILs have opened up new paths in the fields of fuel cells,lithium-ion batteries for capacitors,organic electrosynthesis and sensors as a new type of electrolyte material.As we all know that the structure determines the property.Therefore,in order to understand the essence of these special physicochemical properties of ILs,we need to study the structural information of microscopic structures,interaction forces,and other microscopic properties in details.In this work,quantum chemical calculations have been used to study the microscopic nanostructures of dimer[Cnmim]2[BF4]2?n=16?.It was found that when the number of C in the imidazole cationic alkyl side chain is greater than 4,a T-T?tail-tail?stable geometry appears.The appearance of the special structure indicates that when the number of C in the imidazole cationic alkyl side chain is greater than 4,the tail of cation can be polymerized to form a micelle-like nanostructure.The results are consistent with analysis results of interaction energy analysis,NPA and interaction analysis.Previous studies have found that ILs mixed with a small amount of organic impurities and water will change their microstructure,physicochemical properties,and thermodynamic properties for ionic liquid mixing systems?ILMs?which affect its further application.Therefore,the study of ILMs laid the foundation for the further development of ILs.But the present study focuses on these changes and turns"harmful impurities"into"friendly partners".The study of ILMs laid the foundation for the further development of ILs.But the present study focuses on these changes and turns"harmful impurities"into"friendly partners".Therefore,the research of ILMs lays the foundation for the further development of ILs.As we all know,ethanol is a common organic solvent.The study of the binary mixed system of ILs and ethanol provides the new direction for the development of ILs.In this paper,quantum chemistry calculation?QM?and molecular dynamics?MD?simulation method were used to carry out in-depth research on[Cnmim][BF4]?n=2,4,6?,[Cnmim][PF6]?n=2,4,6?,ethanol,[Cnmim][BF4]/ethanol?n=2,4,6?and[Cnmim][PF6]/ethanol?n=2,4,6?.This paper is based on the density functional theory?DFT?of B3LYP/6-311+G?d,p?and we have optimized the microscopic geometric structure of[Cnmim][BF4]?n=2,4,6?,[Cnmim][PF6]?n=2,4,6?,ethanol,[Cnmim][BF4]/ethanol and[Cnmim][PF6]/ethanol.At the same time,we also studied the variation of microscopic geometric structure when ethanol was added to the system by microstructure analysis,interaction energy analysis and NPA.The interaction energy calculation shows that the stable sequence of types IIV is III>IV>I>II in[Cnmim][BF4]/ethanol?n=2,4,6?and IV>III>I>II in[Cnmim][PF6]/ethanol?n=2,4,6?.The analysis of the results and microscopic geometric structure analysis results show that ethanol,imidazole cation and anion constitute“W”hydrogen bond network for III and IV,indicate that the addition of ethanol increased the stability of ILMs.In this paper,the dynamic simulation study is carried out on the pure system of[Cnmim][BF4]?n=2,4,6?,[Cnmim][PF6]?n=4,6?,ethanol and the binary mixed system of[Cnmim][BF4]/ethanol[Cnmim][PF6]/ethanol by the Lammps software package and the force field of Amber.Through molecular dynamics simulation,the physical and chemical properties of the system and the radial distribution function are obtained.Using the calculation and analysis of the excess molar volume,we investigated the partial intersolubility system of[C2mim][BF4]/ethanol and[C4mim][PF6]/ethanol when the system is separated by phase separation The results show that ethanol is embedded the gap of ILs when the molar fraction of ethanol is less than 0.3 and 0.4 in[C2mim][BF4]/ethanol and[C4mim][PF6]/ethanol,respectively.can appear an extreme value when the molar fraction of ethanol is 0.30.5 and 0.40.6 in[C2mim][BF4]/ethanol and[C4mim][PF6]/ethanol,respectively.Phase separation occurs for partial intersolution system in this ranges.The in the partial intersolubility system of[C2mim][BF4]/ethanol and[C4mim][PF6]/ethanol appear the extremum when the molar fraction of ethanol is 0.30.5 and 0.40.6 respectively,this result shows that the transition process of microstructure near phase separation the critical point may be the fundamental reason for the increasing of nano area.The results of RDF analysis show that the length of the alkyl side chain influence the size of the first coordiation layer nano-microstructure to a certain extent,and there is an ILs polymer layer around ILs.In addition,we also analyzed the RDF in[C2mim][BF4]/ethanol and[C4mim][PF6]/ethanol.The results show that ethanol is embedded into the gap of ILs when the molar fraction of ethanol was less than 0.5.When the molar fraction of ethanol is about 0.5,ILs is present in ILMs with continuous phase.The critical point of phase separation for partial intersolubility system[C2mim][BF4]/ethanol and[C4mim][PF6]/ethanol occurrs when the molar fraction of ethanol is about 0.5. |
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