Effects of Silica Surfaces on the Structure and Dynamics of Room-Temperature Ionic Liquids: A Molecular Dynamics Simulation Study

Abstract

Room-temperature ionic liquids (ILs) at solid surfaces have been recognized for their significant interfacial properties in electrochemical and electronic devices. To ascertain the interface effects, we investigate the dynamical and structural properties of two ILs in nanoscale confinement at various temperatures. Specifically, we perform all-atom molecular dynamics simulations for ILs composed of 1-butyl-3-methylimidazolium cations and hexafluorophosphate ([Bmim][PF6]) or tetrafluoroborate ([Bmim][BF4]) anions sandwiched between amorphous silica slabs. Analyses of the structure indicate a bilayered arrangement in the interfacial region and preferred cation orientation at the surface with the methyl groups pointing toward the wall and the butyl tails projected inward. Mean square displacements and incoherent scattering functions reveal slowed and heterogeneous dynamics of all ionic species in the slit pore. In particular, spatially resolved analyses show that the structural relaxation times increase by ab...