Ionic liquid-air interface probed by sum frequency generation spectroscopy and molecular dynamics simulation: influence of alkyl chain length and anion volume

Understand the structure of ILs/air interface on a molecular level is significant. In this work, liquid-air class ILs containing 1-alkyl-3-methylimidazolium cations ([Cnmim]+, n = 4, 6 and 8) was investigated by sum-frequency generation vibrational spectroscopy experiment. The length alkyl chain anion type (tetrafluoroborate ([BF4]−), thiocyanate ([SCN]−), dicyanamide ([DCA]−), hexafluorophosphate ([PF6]−)) were varied to determine their intrinsic effects micro-structure interface. Meanwhile, combining with experiment, orientation angle surface density for anions at air analyzed dynamics simulation. It found that butyl side protrudes out into as well between 30°–50°. volume has almost no influence methyl chains tend planar increased length. This research highly significant theoretical quantitative understanding chemistry imidazole-based ILs.