Structure of Quaternary Ammonium Ionic Liquids at Interfaces: Effects of Cation Tail Modification with Isoelectronic Groups

Abstract

Herein we use molecular dynamics simulations to investigate the effects of cation tail modification with isoelectronic groups on interfacial structure of room-temperature ionic liquids (RTILs) when confined between two oppositely charged or two neutral graphene sheets. The RTILs chosen in this regard are triethyloctylammonium bis(trifluoromethylsulfonyl)imide (N2228+/NTf2–) and (2-ethoxyethoxy)ethyltriethylammonium bis(trifluoromethylsulfonyl)imide (N222(2O2O2)+/NTf2–). For all the systems studied, we determined number density, free energy, electric field and electrostatic potential profiles along the axis normal to graphene sheet plane. Our results predict that in both the systems, the positively charged graphene sheets are screened predominantly by anionic atoms and cationic tail groups that are embedded in the cavities formed by the anions in the interfacial region, and the extent of screening for the RTIL containing alkyl-substituted cations is slightly higher than that in the diether-substituted anal...