Non-ideal behaviour of. 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF6] in ethylene glycol monomethyl ether; CH3OCH2CH2OH (EGMME), ethylene glycol dimethyl ether; CH3OCH2CH2OCH3 (EGDME) and diethylene glycol dimethyl ether; CH3(OCH2CH2)(2)OCH3 (DEGDME) have been investigated over the whole composition range at T= (298.15 to 318.15) K. To gain insight into the mixing behaviour, results of density measurements were used to estimate excess molar volumes, V-m(E), apparent molar volumes, V-phi,V-i, partial molar volumes, (V) over bar (m,i), excess partial molar volumes, (V) over bar (E)(m,i), and their limiting values at infinite dilution, (V) over bar (infinity)(phi,i), (V) over bar (infinity)(m,i) and (V) over bar (E,infinity)(m,i), respectively. Volumetric results have been analyzed in the light of Prigogine-Flory-Patterson (PFP) statistical mechanical theory. Measurements of refractive indices n were also performed for all the binary mixtures over whole composition range at T= 298.15 K. Deviations in refractive indices Delta(phi)n and the deviation of molar refraction Delta(xR) have been calculated from experimental data. Refractive indices results have been correlated with volumetric results and have been interpreted in terms of molecular interactions. Excess properties are fitted to the Redlich-Kister polynomial equation to obtain the binary coefficients and the standard errors. (C) 2007 Elsevier Ltd. All rights reserved.