With the aim of studying the behaviour of binary mixtures, ionic liquid + molecular solvent, we have combined experimental measurements of density and viscosity at different temperatures and ionic liquid concentrations with atomistic simulations. 1,3-Dimethyl imidazolium dimethyl phosphate was chosen due to its ability to dissolve cellulose from different sources. Three solvents, dimethyl sulfoxide, ethanol and trifluoroethanol were chosen to cover a wide range of solvatochromic parameters. Experimental data were successfully fitted to correlating equations. Volumetric and dynamic properties were calculated by means of atomistic simulations. The effect of coulombic interactions on physical properties was addressed by scaling the partial charges of ionic species. Besides, the influence of hydrogen bond over the measured properties was analysed. Finally, the role of each solvent during the cellulose dissolution in ionic liquids was discussed.