Study Of Characteristics At Air/Liquid Interface Of Imidazolium-Based Ionic Liquids Using Molecular Dynamics Simulation And Sum Frequency Generation Spectroscopy

Ionic liquids are a new generation of green media and functional materials,and have extensive research and application in chemical,chemical,biological,and materials fields.Most of their functions are related to the interface.Imidazolium-based ionic liquids are the most common and widely used class of ionic liquids,and their gas-liquid interface has also attracted the people's attention.At present,many experiments have been carried out to study the gas-liquid interface of imidazole ionic liquids,and many microscopic mechanism explanations have been obtained.However,there are still problems such as difficulty in verification and inability to quantitatively study.In this paper,the gas-liquid interface of imidazolium-based ionic liquids was studied in detail by means of sum frequency generation spectroscopy and molecular dynamics simulation.The quantitative information of interface structure and molecular orientation was obtained and compared.The main conclusions of the paper are as follows:The gas-liquid interface structure of 1-butyl-3-methylimidazolium salt of different anions was studied by vibrational sum frequency generation spectroscopy and molecular dynamics simulation.The results show that the anion structure has little effect on the side chain structure of the cation.In the experiment,the side chain orientation of the cation is about 42?,and the orientation angle in the simulation is about 55?,the reason for the difference is the experimental conditions,such as the vapor pressure of water etc.The effect of side chain length on the ionic liquid interface was studied,and the research was extended on the simulation.First,the results show that the side chain length has little effect on the orientation angle of the methyl interface at the tail end of the side chain.Then,the proportion of methylene groups at the interface increases with the length of the side chain.Last,the orientation of the long side chain ionic liquid at low temperature occurs.The change,from the vertical tendency to the horizontal tendency,and the main influence on the orientation change is the middle portion of the side chain.According to the experimental and simulation results of this paper,the micro-kinetic structure of ionic liquid gas-liquid interface is described,and the mechanism is speculated.It provides a theoretical basis for the application of imidazole ionic liquid in the future.