Ion Association in 1-Butyl-3-methylimidazolium Hexafluorophosphate / Naphthalene Mixtures

MARIO G. DEL PÓPOLO AND , PIETRO BALLONE

Ionic Liquids: From Knowledge to Application

American Chemical Society

Año: 2009; p. 403 - 418

Mixtures of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6]) and naphthalene have been investigated by molecular dynamics simulations based on an empirical potential model, covering the full range of concentrations from the pure ionic liquid to pure naphthalene. The composition dependence of thermodynamic functions and of dynamical properties highlights a continuous but relatively sharp transition taking place at 20% ionic liquid concentration. The analysis of the electric conductivity and of simulation snapshots reveals that the transition marks the transformation of the [C4mim][PF6] bonding from molecular-dipolar at low concentration to ionic at high concentration. The probability distribution for the microscopic electric fields acting on the naphthalene atoms broadens significantly in going from the molecular to the ionic state, suggesting that optical spectroscopy and core level spectroscopy could be used to probe the transition at the atomistic scale.