Molecular Design And Demulsification Mechanism Of Temperature-Sensitive Ionic Liquid Microemulsion

As the formation and demulsification of temperature-responsive ionic liquid（IL）microemulsion can be controlled by simply changing the temperature,it has many important applications in extraction and separation,enzymatic catalysis and drug delivery.Up to date,there are rarely reports about the temperature-sensitive IL microemulsions.Therefore,the formation and demulsification mechanism are not clear,which limited the rational design of temperature-responsive IL microemulsion.As part of the national natural science foundation of China（NO.21773058）,the formation and demulsification mechanism of temperature-sensitive IL microemulsion were investigated and some new temperature-sensitive microemulsion systems consisting of mixed ILs was established in this work.The main research contents included:1.The tetrabutylphosphonium trifluoroacetate([P₄₄₄₄][CF₃COO])/1-dodecyl-3-methylimidazolium bromide([C₁₂mim]Br)/H₂O temperature-sensitive IL microemulsion was synthesized and characterized by phase diagram and dynamic light scattering.By analyzing the changes of interaction energies,radial distribution functions and coordination numbers of microemulsion system,it was found that the interaction change of[CF₃COO]^-and H₂O with temperature is the main driving force for the formation and demulsification of microemulsion.Then,a series of simulation systems with different contents of[P₄₄₄₄][CF₃COO]and[C₁₂mim]Br were investigated.It was noted that the trend of interaction energy change of per unit volume of[CF₃COO]^-and H₂O for microemulsion systems with different contents could well describe the trend of the experimental demulsification temperature.2.The temperature-sensitive IL microemulsion systems which is composed of[P_444,n]Br（n=8,10,12,14,16,18）,[C₁₂mim]Br and H₂O were constructed.The phase diagram and dynamic light scattering technique were used to study the influence of alkyl chain length of cations on the phase behavior.The IL microemulsion systems with different alkyl chain length were simulated by the molecular dynamics simulation.By analysing the trajectory files,interaction energies,the radial distribution functions,and the coordination numbers,it was found that the microemulsion system composed by phosphonium IL with longer alkyl chain has the lower demulsification temperature.3.The mixed temperature-sensitive ILs of tetrabutylphosphonium nitrate([P₄₄₄₄][NO₃])and tributyl-n-octylphosphonium trifluoroacetate([P₄₄₄₈][CF₃COO])was selected as non-polar phase,water as polar phase and[C₁₂mim]Br as surfactant.The system was studied by dynamic light scattering and phase diagram.Molecular dynamics simulation was also used to study the formation and demulsification mechanism of the microemulsion system.Through the analysis of the trajectory files,the change value of interaction energies at 278K and 358K,and the radial distribution functions,it was found that with the increase of temperature,the interaction between[P₄₄₄₈]⁺,[P₄₄₄₄]⁺,[CF₃COO]^-,[NO₃]^-and water molecules were decreased,the[P₄₄₄₈]⁺-[CF₃COO]^-interaction and the interaction of[P₄₄₄₄]⁺,[P₄₄₄₈]⁺with surfactant were increased,resulting of phase separation of the microemulsion system.