The wetting behavior of aqueous imidazolium based ionic liquids: a molecular dynamics study

S Bhattacharjee and S Khan, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, 8595-8605 (2020).

DOI: 10.1039/d0cp00143k

Aqueous ionic liquids are of particular interest due to their tunability of physical and chemical properties and a deeper understanding of their structure-property relationship is desired. Molecular dynamics (MD) simulations were conducted to study the wetting behavior of aqueous imidazolium-based ionic liquids (ILs), consisting of a 1-ethyl-3-methylimidazolium EMIM(+) cation and either a hydrophilic boron tetrafluoride BF4(-) or a hydrophobic bis(trifluoromethylsulfonyl)imide NTF2(-) anion mixed in water. To understand the effect of anion and concentration of ILs at the graphite solid-liquid interface, wettability studies were performed with IL concentrations from 0-50 wt%. The contact angle of aqueous IL droplets decreases with increasing IL concentration. Droplet characteristics near the surface were investigated by profiling the density perpendicular (z-direction) and horizontal (r-direction) to the graphite sheet; this was further quantified by an orientation order parameter. Due to the preferred adsorption of ILs, water depletes near the surface as IL concentration increases. The hydrophobic NTF2(-) anion forces the IL toward the interface from the bulk, whereas the hydrophilic BF4(-) anion causes the IL to remain in the bulk of the droplet. Differences in water-anion hydrogen bonding, the nature of the anions, and their interfacial tensions are crucial factors in the wetting behavior of aqueous ionic liquids.

Return to Publications page