Temperature dependent densities of mixtures of 1-butyl-3-methylimidazolium hexafluorophosphate + poly(ethylene glycol)

Abstract

Densities of 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) + poly(ethylene glycol) (average molar mass 200 g mol^–1) [PEG200] mixtures have been measured over the entire composition regime in the temperature range of 283.15–363.15 K at 10 degree intervals, using a density meter based on electromagnetically induced oscillations of a U-shaped glass tube and an inbuilt Peltier thermostat. The density versus temperature data of [bmim][PF₆] + PEG200 mixtures at each composition have been fitted to a simple linear equation : <img src='/image/spc_char/po.gif'>. The fits are observed to be satisfactory at each composition. The excess molar volumes of [bmim][PF₆] + PEG200 mixtures are observed to be negative and significant over the entire composition range. Irrespective of the temperature, the maximum absolute excess molar volumes are observed in PEG-rich region at <i>X</i>_[bmim][PF6]~ 0.3. Importantly, the absolute values of excess molar volumes for [bmim][PF₆] + PEG200 mixtures appear to increase slightly with increasing temperature. These observations are attributed to the presence of strong interactions within the [bmim][PF₆] + PEG200 mixtures. Specifically, they are proposed to be due to the presence of extensive intermolecular H-bonding involving C2 hydrogen of [bmim⁺] and termini –OH as well as ethoxy –O– of PEG200 within [bmim][PF₆] + PEG200 mixtures.