Molecular Simulations Of The Microstructures And Interactions Of Imidazolium-Based Ionic Liquids At The Interface Of Carbon Nanotubes

Electric double layer capacitors（EDLCs）have received widespread attention because of their high power density,long cycle life,and other advantages.In recent years,EDLCs composed of carbon nanotubes（CNTs）electrodes and imidazolium–based ionic liquid electrolytes have become a hot research topic.Exploring the microstructures of the ionic liquids around the CNT electrodes and analyzing the underlying interaction mechanisms are meaningful for designing high performance EDLCs.In this thesis,molecular dynamics（MD）simulations were used to study the interactions between different ionic liquids and neutral CNTs,as well as their effects on the solvation structures.On this basis,we continue to explore the microstructures of ionic liquid at the interface of charged CNTs and the interactions behind them.In Chapter 2,we have performed MD simulations to explore the solvation structures of two imidazolium–based ionic liquids（[EMIM][BF₄]and[BMIM][BF₄]）around the single–walled CNTs with various diameters,and our attentions mainly focus on how the alkyl chain length of the cations and the diameter of the CNTs influence the interface properties and interaction mechanism.The MD simulations results show that increasing the nanotube diameter will enhance the interactions between the ions and the CNTs,which cause more anions and cations to gather around the larger CNT.However,the alkyl chains of cations have little effect on the solvation structures.In addition,theπ–πstacking effect between the cations and the CNTs is beneficial for the imidazolilum rings of cations to be parallel to the CNTs.However,increasing the length of the alkyl chain has a greater effect on the dynamic properties and thereby significantly slows down the rotational motion of the cations,which is different from the effect on the structural properties.In addition,the dependence of the rotation of the anions around the CNTs on the length of the alkyl chains is the same as that of the cations.The simulation analysis further reveals that the alkyl chains of the cations can affect the hydrogen bonds between the cations and the anions,which has an indirect influence on the rotation of the anions,resulting in the same dependence of the rotational motion of anions on the length of the alkyl chain.In Chapter 3,we further studied the microstructures and interactions of imidazolium–based ionic liquids at the interface of charged CNTs.The simulation mainly determined by the electrostatic attraction with the electrode,while the accumulation near the positive electrode is mainly determined by the electrostatic attraction with other ions,which is independent on the charge density.Meanwhile,for the CNT electrodes with higher negative surface charge density and larger diameter,cations can form crowding phenomenon near the surface of the CNT electrodes.In addition,it is notable that the imidazolium rings of cations exhibit more orderly arrangements at the interface of both positive and negative CNT electrodes with a lower charge density.This is mainly due to the strongerπ–πstacking interactions between interfacial cations and the CNT electrodes,as well as the stronger hydrogen bonds between the interfacial cations and anions.