Physicochemical properties of 1-alkyl-3-methylimidazolium chloride–urea melts

Physicochemical data of the novel low-melting-point melt systems combining urea with the 1-alkyl-3-methylimidazolium chloride ([R1MeIm]Cl) were examined in order to produce an alternative to room-temperature ionic liquid that is very expensive to prepare and purify compared to the conventional molecular solvents. [HexMeIm]Cl- and [MeOctIm]Cl-rich urea melts, which have almost the same pyrolysis temperature as neat [HexMeIm]Cl and [MeOctIm]Cl organic salts, showed a stable liquid phase at room temperature. The various physicochemical properties of the [MeOctIm]Cl-rich urea room-temperature melts were measured as a function of temperature. The VTF equation was fitted to the conductivity and viscosity data, and a simple polynomial was fitted to the density data. Interestingly, although the 75.0–25.0 mol% [BuMeIm]Cl–urea melt did not give a stable liquid phase at room temperature, the melt showed favorable conductivity that exceeds that for the [MeOctIm]Cl-rich urea melts at the temperature exceeding 323 K. Further investigation on the applications, e.g., Cu electroplating, SEM observation technique, and Au nanoparticle preparation, using the [R1MeIm]Cl–urea melt system revealed that the melt system has a great possibility as an alternative to the RTIL.