Thermodynamics and Transport Behavior of 1-Ethyl-3-methylimidazolium Dimethyl Phosphate + Protic Solvents

We employ a suite of experimental techniques to determine the densities, viscosities, conductivities, and excess enthalpies of four binary ionic liquid (IL) + solvent systems composed of 1-ethyl-3-methylimidazolium dimethyl phosphate ([emim][DMP]) with water, ethylene glycol (EG), triethanolamine (TEA), and glycerol (Gly). These measurements reveal interesting viscosity vs composition relationships for the [emim][DMP] + TEA and [emim][DMP] + Gly systems, in which there are local viscosity maxima at intermediate solvent + IL compositions. We attribute this behavior to evolution of IL–solvent hydrogen bonding networks with a changing electrolyte composition. Analysis of the excess enthalpies reveals exothermic mixing for all four systems, suggesting that ion–solvent interactions (particularly hydrogen bonding) are energetically favorable compared to IL–IL and solvent–solvent interactions.