Wang, YT (reprint author), Chinese Acad Sci, Inst Theoret Phys, CAS Key Lab Theoret Phys, 55 East Zhongguancun Rd,POB 2735, Beijing 100190, Peoples R China.
In this work, we have performed molecular dynamics (MD) simulations to compare the structural and dynamical properties of three ionic liquids (ILs), 1-ethyl-3-methyl-imidazolium tetrafluorborate ([EMI+][BF4-]), 1,1'-dimethy1-4,4'-bipyridinium bis(tetrafluorborate) ([VIO2+][BF4-](2)), and 1,1'-dimethy1-4,4'-bipyridinium bis(trifluoromethylsulfonyl)imide (bistriflimide in short) ([VIO2+][Tf2N-](2)), aiming to discover the influence of ion rigidity on the physical properties of ILs. [VIO2+] is more rigid than [EMI+], and [BF4-] is more rigid than [Tf2N-]. [VIO2+][BF4-](2) has an anion distribution different from the other two by the higher and sharper peaks in the cation-anion radial distribution functions, reflecting a close-packed local structure of anions around cations. [VIO2+][BF4-](2) and [VIO2+][Tf2N-](2) have similar dynamics much slower than [EMI+][BF4-], and [VIO2+][Tf2N-](2) shows a more isotropic molecular distribution than [VIO2+][BF4-](2) and [EMI+][BF4-]. Additionally, we have simulated two modified viologen-based ILs to reinforce our interpretations. We conclude from the above simulation results that the rigidity of anions influences the alignment of cations and that the rigidity of cations shows a large obstacle to their rotational capacity. Moreover, we have observed a slower diffusion of [VIO2+][BF4-](2) due to the electrostatic correlations, which stabilizes the ion-cage effect.
Ramirez-Gonzalez, PE,Ren, G,Saielli, G,et al. Effect of Ion Rigidity on Physical Properties of Ionic Liquids Studied by Molecular Dynamics Simulation[J]. JOURNAL OF PHYSICAL CHEMISTRY B,2016,120(25):5678-5690.