Aggregation in Ionic Liquids: Molecular Dynamics Simulation

The spatial microheterogeneity in ionic liquids (ILs) is one of the the key features and has been proved useful in understanding the special behavior and interpreting many Physical phenomena of ILs , including the heterogeneous self diffusion , surface layering , as well as their surfactant-like micelles formed in IL/water mixtures.1 ,2 As a result , much attention has been paid to the related researches , including both experiment and simulation. 3 ,4The self-aggregation or segregation exists both in IL solution and neat IL composed entirely of ions. In this work , the self-aggregation in ILs composed by [Cnmim]+ (n=2 , 4 , 6 , 8 , and 10) and Br- were investigated by molecular dynamics simulation at the molecular level based on the all-atom force field. Both the neat ILs and the mixture of [C12mim]Br with water were studied. In order to reduce the computational time , united atom force field was utilized for the mixture of [C12mim]Br with water. Center of mass and site-to-site radial distribution functions (RDFs) were employed to study the ionic pair interactions. To depicture more visual structures of these ILs , the spatial distribution functions (SDFs) that stand for the three-dimensional probability distributions of ions and molecule were studied. A way based on the atomicity density was developed for estimating and understanding the inhomogeneous structure at nanometer scale. Dynamics behaviour and diffusion of ions , molecules and clusters were characterize through the mean-square displacement and self diffusion fuctions. References:(1)   Wang , Y.; Jiang , W.; Yan , T.; Voth , G. A. Acc. Chem. Res. 2007 , 40 , 1193-1199. (2)   Dupont , J. Acc. Chem. Res. 2011 , 44 , 1223-1231. (3)   Chen , S. M.; Kobayashi , K.; Kitaura , R.; Miyata , Y.; Shinohara. , H. ACS Nano 2011 , 5 , 4902-4908. (4)   Liu , X.; Zhou , G.; Zhang , S.; Wu , G. Mol. Sim. 2010 , 36 , 1123-1130.