Isobaric and Isochoric Heat Capacities of Imidazolium-Based and Pyrrolidinium-Based Ionic Liquids as Function of Temperature: Modeling of Isobaric Heat Capacity

International audienceThe isobaric and isochoric heat capacities of seven 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imides, two 1-alkyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imides, and two bis(1-alkyl-3-methylimidazolium) tetrathiocyanatocobaltates were determined at atmospheric pressure in the temperature range from 293.15 to 323.15 K. The isobaric heat capacities were determined by means of differential scanning calorimetry, whereas isochoric heat capacities were determined along with isothermal compressibilities indirectly by means of the acoustic method from the speed of sound and density measurements. Based on the experimental data, as expected, the isobaric heat capacity increases linearly with increasing alkyl chain length in the cation of 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imides and no odd and even carbon number effect is observed. After critical comparison of the obtained data with the available literature data, the most reliable values are recommended. It has been also shown that, although the COSMOthermX calculations underestimated the isobaric heat capacity values whatever the temperature and the ionic liquid structure, the approach used during this work may be applied to estimate physical properties of non-single-charged ions as well. Additionally, based on the speeds of sound the thermal conductivities were calculated using a modified Bridgman relation

Acoustic and volumetric studies of binary mixtures of 1,3-butanediol + 1-pentanol

The results of acoustic and volumetric investigations of binary liquid mixtures of 1,3-butanediol with 1-pentanol at the temperatures (298.15, 308.15, and 318.15) K are presented. Basing on the phase speed of ultrasound values (measured by the pulse-echo-overlap method at 2.18 MHz) and densities, the excess values of the molar volume and isentropic compressibility (volume-specific and molar), were calculated. Their composition dependencies were expressed by Redlich-Kister polynomials. It turned out that mixing of 1,3-butanediol with 1-pentanol, results in an enhanced rigidity of the mixtures in comparison with that of the pure components. What is more, this rigidity increases with increasing temperature. At the same time the volume effects (expansion) upon mixing increase with increasing temperature too. The results are discussed in terms of the variations of the structure and molecular interactions

Ultrasonic absorption measurements by means of a megahertz – range measuring set

The aim of this work is a detailed description of measuring sets that were designed and constructed in our laboratory. These apparatus are based on the standard pulse technique where the amplitude of the first transmitted pulse is measured as a function of distance. The advantage of the method applied is achieving of a relative wide frequency range together with relatively high accuracy and precision of measurements. Moreover, this method enables absolute measurements of the attenuation coefficient. However, the quality of all measurements depends strictly on some elements that are not commercially available, such as the measuring cell with transmitting and receiving transducers, and the electronic parts of the measuring set. In order to illustrate the quality of our measuring sets, a few results for pure liquids as well as for some mixtures are presented

Speed of Ultrasound and Internal Pressure of Propanediol and Butanediol Isomers under Elevated Pressures

Speed of ultrasound and internal pressure of 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, and 1,3-butanediol at the temperatures ranging from 293.15 to 318.15 K and pressures up to 101 MPa are analyzed and discussed in terms of molecular structure and ability to form inter- and intramolecular hydrogen bonds