Microstructure of ionic liquids mixed with water on the charged graphene surface: A coarse-grained molecular dynamics simulation study

Abstract

Ionic liquids (ILs) inevitably absorb a certain amount of moisture from the air during the synthesis and utilization processes. The presence of water can have a significant impact on the interfacial property of ILs on charged graphene surfaces. This study employs molecular dynamic (MD) simulation to explore the microstructure of ILs [BMIM + ][BF4-] (1-butyl-3-methylimidazolium tetrafluoroborate) mixed with water on charged surfaces and examine the existence of water and surface charge density on interfacial behaviors. The result shows that coarse particles accumulate on the charged surface as the charge density of the surface increases. More anionic particles A (anions [BF4-]) are absorbed to the positively charged surface, resulting in a more obvious layered structure between anionic and cationic particles. However, coarse particles C3 (Butyl chain in cationic group) rotate due to the repulsion from co-ions and move slightly away from the upper negatively charged surface. Besides, due to the strong interaction from the anionic particles, water molecules distribute asymmetrically on the upper and lower surfaces with different charges, and as the charge density increases, the peak location of number density moves closer to the surface. The results provide a molecular-level understanding of the effect of surface water and charge density on the interfacial microstructure of ILs on charged surfaces.