Determination of Physicochemical Parameters of Ionic Liquids and Their Mixtures with Solvents Using Laser-Induced Gratings

The laser-induced gratings (LIGs) technique has been applied for the simultaneous determination of sound speed and thermal diffusivity in the room temperature ionic liquid (RTEL) 1-ethyl-3-methylimidazolium ethylsulfate, [EMIm][EtSO4], its mixture with 85.68 mol % acetone, C3H6O, and pure acetone. The measurements have been performed in a quartz glass cuvette at ambient pressure and temperature. Radiation of a pulse-repetitive Q-switched Nd:YAG pump laser (1064 nm) effected quasi-resonant excitation of overtone-combinational vibrational states of the RTIL molecules followed by the appearance of laser-induced gratings. The temporal evolution of the transient gratings (oscillation and damping) was recorded using Bragg-diffraction of a continuous-wave probe laser radiation. From the LIG signals' temporal profiles, values of the sound speed and thermal diffusivity were determined and, in addition, the isentropic compressibility and thermal conductivity were derived. The results are in a reasonable agreement with those reported in the literature. Furthermore, since the data for the determination of the physicochemical properties can be obtained with a single laser pulse, the LIG technique has potential for applications where data acquisition at high repetition rates is desirable for example to monitor processes.