Densities of 1-Butyl-3-methylimidazolium Hexafluorophosphate plus Poly(ethylene glycol) in the Temperature Range (283.15 to 363.15) K

Densities of 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) + poly(ethylene glycol) [PEG] mixtures prepared with PEGs of average molecular weight 400 (PEG400), number-average molecular weight M-n 570 to 630 (PEG600), and number-average molecular weight M-n 950 to 1050 (PEG1000), respectively, have been measured over the entire composition regime in the temperature range (283.15 to 363.15) K at 10 K intervals using a density meter based on electromagnetically induced oscillations of a U-shaped glass tube and an in-built Peltier thermostat. The density of ([bmim][PF6] + [PEG]) mixtures at each composition for all three PEGs is found to decrease linearly with increasing temperature. The excess molar volumes (V-E) of all the three ([bmim][PF6] + PEG) mixtures were observed to be negative at all temperatures and were correlated to the mole fraction of [bmim][PF6], X-[bmim][PF6], in the mixture by Redlich-Kister-type equations. Importantly, the absolute values of V-E for ([bmim][PF6] + PEG) mixtures appear to increase slightly with increasing temperature. These observations are attributed to the presence of complex interactions within the ([bmim][PF6] + PEG) mixtures. Specifically, they are proposed to have their origin in extensive intermolecular H-bonding involving the C2 hydrogen of [bmim(+)] and termini -OH as well as the ethoxy -O- of PEG within ([bmim][PF6] + PEG) mixtures.