Ionic liquids are viewed as green media for many engineering applications and exhibit exceptional properties, including negligible vapor pressure, null flammability, wide liquid range, and high thermal and chemical stabilities. We present new thermophysical properties of 1-alkyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imides ([C n C 1 pyr][NTf 2 ] with n = 3, 4) for future application them as heat-transfer media. The speed of sound was measured at pressures up to 100 MPa and at temperatures from 293 K to 318 K. The pρT, pC p T data, and derived thermophysical properties were determined using the acoustic method. TGA of [C n C 1 pyr][NTf 2 ] and cytotoxicity of [C n C 1 pyr][NTf 2 ] and their imidazolium counterparts ([C n C 1 im][NTf 2 ]) are investigated. The physicochemical properties of [C n C 1 pyr][NTf 2 ] are compared with those of [C n C 1 im][NTf 2 ] and commercial heat-transfer fluids (Therminol VP-1, Therminol 66, Marlotherm SH). [C 3 C 1 pyr][NTf 2 ] and [C 4 C 1 pyr][NTf 2 ] have a wide liquid range of ∼480 K and high decomposition onset temperatures of 771 and 776 K, respectively. [C n C 1 pyr][NTf 2 ] exhibit high energy storage density of ∼1.98 MJ m −3 K −1 , which is slightly dependent on temperature and pressure. The thermal conductivity of [C n C 1 pyr][NTf 2 ] is comparable to that of commercial heat-transfer fluids. [C n C 1 pyr][NTf 2 ] have lower toxicity for normal human dermal fibroblast cells than [C n C 1 im][NTf 2 ]. Thus, [C n C 1 pyr][NTf 2 ] are promising heat-transfer fluid candidates.
The isobaric and isochoric heat capacities of six disubstituted imidazolium-based ionic liquids with different anions and two trisubstituted imidazolium-based bis-(trifluoromethylsulfonyl)imides were determined at atmospheric pressure in the temperature range from 293.15 to 323.15 K. The isobaric heat capacities were determined using differential scanning calorimetry. The isochoric heat capacities were determined indirectly by means of the acoustic method from the speed of sound and density measurements. Also, other connected with the speed of sound quantities such as isentropic and isothermal compressibilities as well as internal pressures were determined. The highest compressibilities show both trisubstituted imidazolium-based bis(trifluoromethylsulfonyl)imides whereas 1-ethyl-3-methylimidazolium thiocyanate shows the lowest compressibility. The critical comparison of the isobaric heat capacity data with the available literature data makes possible a recommendation of the most reliable heat capacity values. Analyzed predictive capability of two heat capacity models based on the group contribution method is poor in the case of the [C(CN) 3 ] − anion. Additionally, based on the speeds of sound, the thermal conductivities were calculated using a modified Bridgman relation and compared with values estimated by a group contribution method. Here, the worst results are obtained in the case of [SCN] − anion.
One of the possible research directions for developing the modern energy sector is searching for innovative working fluids with exceptional properties, which leads to reducing energy consumption and the costs of the operation of the system. As a continuation of our investigations of ionic liquids (ILs) for their use as heat transfer fluids (HTFs), we present new thermophysical properties of 1). Speeds of sound were conducted in the temperature range 298−323 K and in the pressure range 0.1−76 MPa. The temperature and pressure dependence of densities, isobaric heat capacities, and related quantities were obtained by acoustic method. The viscosities, the TGA, and the cytotoxicities were also conducted. The thermal conductivities, energy storage densities, Prandtl numbers, isobaric heat capacities, viscosities, densities, isobaric thermal expansibilities, and isothermal and isentropic compressibilities of [C n MMIm][TFSI] are compared with those of 1-alkyl-3-methyl-1H-imidazol-3-ium bis[(trifluoromethyl)sulfonyl]azanides [C n MIm][TFSI], n = 2, 4) and 1-alkyl-1-methylpyrrolidinium bis[(trifluoromethyl)sulfonyl]azanides ([C n MPyr][TFSI], n = 3, 4), considered as good candidates as HTFs and commercial HTFs. The wide liquidity range (∼450 K), high decomposition onset temperature (∼763 K), significant energy storage density (∼1.95 × 10 6 J m −3 K −1 ) of [C 2 MMIm][TFSI] and [C 4 MMIm][TFSI] predestine them as heat transfer media in sustainable energy systems.
A series of five alcohols (3-methyl-2-butanol, 1-cyclopropylethanol,
1-cyclopentylethanol, 1-cyclohexylethanol, and 1-phenylethanol) was
used to study the impact of the size of steric hindrance and its aromaticity
on self-assembling phenomena in the liquid phase. In this Letter,
we have explicitly shown that the phenyl ring exerts a much stronger
effect on the self-organization of molecules via the O–H···O scheme than any other
type of steric hindrance, leading to a significant decline in the
size and concentration of the H-bonded clusters. Given the combination
of calorimetric, dielectric, infrared, and diffraction studies, this
phenomenon was ascribed to its additional proton-acceptor function
for the competitive intermolecular O–H···π
interactions. The consequence of this is a different packing of molecules
on the short- and medium-range scale.
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