Chemical Thermodynamics and Thermal Analysis最新文献

Poly(vinyl alcohol) PVA is a synthetic polymer used in a variety of applications and exhibits unusual thermal behavior. In this work, differential scanning calorimetry (DSC), isothermal and non-isothermal thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), optical microscopy, viscometry and kinetic modeling were used to study the thermal behavior of PVA for providing further insights about the thermochemical transition. It is shown that the value of specific heat of thermochemical transition is comparable to theoretical values derived from chemical bond dissociation energy values. Activation energy's contribution to the specific heat of thermochemical transition seems to be low. Contradictions among the conclusions from various analytical techniques, regarding the glass transition of PVA, are discussed and interpreted. Settlement of these contradictions leads to the conclusion that like PVA's melting point, its glass transition is also a thermochemical transition but with no detectable mass loss.

Recent advances in nanotechnology have led researchers to investigate various approaches to the development of nanofluids with enhanced thermal conductivities that can replace conventional industrial coolants. Of particular interest have been MXene based nanofluids. The current investigation focuses on MXene/water and MXene/ethylene-glycol/water nanofluids with particle concentrations ranging from 0.1 to 0.5 wt% of MXene. The results of this investigation found as much as a 30.6% improvement in the effective thermal conductivity of the 0.5 wt% MXene/water nanofluid compared to the pure water base fluid. In addition, an improvement of 27.3% in the effective thermal conductivity was observed in MXene/ethylene-glycol/water nanofluid. MXene was found to provide superior enhancement in the effective thermal conductivity when compared with other particles, such as metal, metal oxide, and graphene, both in DI water and in ethylene glycol. In addition, MXene did not significantly increase the viscosity as is typically the case for other nanosuspensions containing carbon nano materials, e.g. nanotubes, graphene. The physical properties indicated that MXene based nanofluids present a number of very attractive thermophysical properties for application as industrial coolants.

Through dielectric measurements of aqueous n-hexyltrimethylammonium bromide solutions, the structure and dynamics of ion-pairs, micelles, and water are investigated as functions of concentration and temperature. The frequency range of the study was ∼ 0.2 ≤ν/GHz ≤ 89, and the concentrations were changed from 0.0448 to 0.8476 mol.dm⁻³ at 298.15 K. The effects of temperature (278.15 ≤ T/K ≤ 338.15) on two selected solutions with concentrations above and below the critical micelle concentration were examined. A summation of three Debye processes fits the complex permittivity data of solutions with concentrations below the critical micelle concentration. To fit the spectra above the critical micelle concentration, a summation of five Debye processes is needed. Below the critical micelle concentration, solutes relax due to the tumbling motion of solvent-shared ion pairs. The two micelle relaxation processes that have been seen are the result of free and bound counter ions tangentially and radially diffusing around the charged micelles. Maxwell-Wagner relaxation is equivalent to the high frequency micelle relaxation process. Both the solvent and micelle dispersion provide acceptable volume fractions. Hexyltrimethylammonium behaves like higher n-alkyltrimethylammonium micelles in the context of micelle relaxation. Before critical micelle concentration, the cations, anions, and ion pairs strongly hydrate a total of ∼18 ± 4 non-rotational water molecules. Beyond the critical micelle concentration, there are an additional ∼ 5 ± 2 non-rotational water molecules in addition to ∼ 15 ± 3 slower-moving water molecules in the hydrophobic hydration shell.

The influence of two important parameters in the synthesis of TATP (the type of catalyst and the presence or absence of stirring during the precipitation process) on its sublimation was studied by thermal gravimetric analysis. TATP synthesised with H₂SO₄ as catalyst and without stirring during the precipitation process sublimates faster than the other types, due to its transformation in DADP under influence of the presence of residual acid. Between the other types of TATP, where no transformation to DADP was observed, only small differences in sublimation rate were measured. These differences are related to their different sublimation temperatures as observed during DSC experiments.

The influence of the same synthesis parameters on the sublimation of HMTD was also investigated. Unlike TATP, HMTD decomposes during sublimation. This decomposition depends on the synthesis parameters. AKTS simulations show that the HMTD synthesis parameters have an influence on the temperature dependency of the kinetic parameters of the HMTD decomposition.

This study investigated the liquid-phase volume expansion to optimize the gas antisolvent (GAS) process condition. During the GAS process, particle precipitation does not take place in any operational conditions. Therefore, thermodynamic models are required to select the appropriate conditions and understand the precipitation mechanism. The Peng–Robinson equation of state with van-der-Waals (vdW2) mixing rules was used for the evaluation of the proper operational conditions at the temperature ranges of 308–338 K. The volume expansion of the system was studied at different process conditions for the binary (carbon dioxide-solvent) and ternary (carbon dioxide-solvent-rosuvastatin) systems. For this purpose, rosuvastatin (ROS) and carbon dioxides were solute and antisolvent, respectively. Dimethyl sulfoxide, ethanol, propanol, butanol, and pentanol were chosen as organic solvents. The minimum pressure for the ternary (carbon dioxide-dimethyl sulfoxide-rosuvastatin) system at 308, 318, 328, and 338 K was 7.80, 8.58, 9.79, and 11.1 MPa, respectively. The effect of solvent on volume expansion and minimum pressure was investigated. The calculated P_min was 80, 82.4, 85.4, and 89.4 bar for ethanol, butanol propanol, and pentanol at 318 K respectively. According to modeling results, there was a direct relationship between the molecular weight of solvent with the same structure and minimum pressure.

The density (ρ) and speed of sound (u) of binary solutions containing protic ionic liquids such as N‑butyl ethanolammonium acetate [NBEA][Ace] and N‑butyl ethanolammonium propionate [NBEA][Pro] with Dimethyl Sulfoxide (DMSO) were determined over a temperature range of (293.15 to 318.15) K at intervals of 5 K at 0.1 MPa pressure. The apparent molar volume (V_φ), isentropic compressibility (k_s) and apparent molar isentropic compressibility (k_s,φ) were estimated using the measured data. The apparent molar volume (V_φ^∞) and apparent molar isentropic compressibility (k_φ^∞) at infinite dilution, as well as the related empirical parameters (S_v, B_v, S_k and B_k), were calculated using the Redlich-Mayer type equation. The solute-solute and solute-solvent interactions are indicated by the obtained limiting apparent molar volume and limiting apparent molar isentropic compressibility. Furthermore, the apparent molar expansibility at infinite dilution was calculated using temperature dependent apparent molar volume at infinite dilution (E_φ^∞).

As a rare sugar, D-Tagatose is regarded as an excellent low-energy food sweetener. It is especially beneficial for physical health, such as inhibiting hyperglycemia, improving intestinal flora, and avoiding caries. It is broadly employed in food, medicine, cosmetics, and other fields. Acquiring D-Tagatose solubility is vital to develop D-Tagatose crystallization process to obtain high-quality D-Tagatose production. In this study, the solubility of D-Tagatose in seven pure solvents (methanol, ethanol, n-propanol, water, N, N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone), three binary solvents (ethanol-water mixtures, ethanol-methanol mixtures, and n-propanol-water mixtures) was determined by HPLC method at temperatures from 293.15 K to 323.15 K. Then, the Van't Hoff equation, Apelblat equation, λh equation, NRTL equation, CNIBS/Redlich-Kister model and modified Jouyban-Acree-van't Hoff model were used to correlate the solubility. The correlated solubility accounted for suitable compatibility with the experimental results (ARD <10%). Furthermore, we investigated the intermolecular interactions in the crystal structure through Hirshfeld surface analysis and estimated the overall charge distribution of molecules by molecular electrostatic potential surface (MEPs). Then, we analyzed the solvent effects and solvation free energy to explain the solubility behaviors. The results indicated that hydrogen bonds play a decisive role in determining the solubility of D-Tagatose.

Quinolinium surfactants possessing pyridinium rings have a wide range of biological applications due to its antimicrobial activity. In this study, we have used quinolinium based surfactant series i.e.1-alkylquinolinium bromide and 6-hydroxy-1-alkylquinolinium-bromide. The physicochemical behavior of quinolinium based surfactant have been carried out by various techniques viz. conductivity, surface tension and fluorescence measurements in aqueous and 10% (v/v) methanol at 300K.The critical micelle concentration (CMC) values found from conductivity, surface tension and fluorescence are in good agreement of a surfactant in aqueous and 10% (v/v) methanol. The CMC value of 1-alkyquinolinium-bromide series is higher than its derivative series (6-hydroxy-1-alkyquinolinium-bromide). The values of Г_max increases with increases chain length of the both the quinolinium surfactants, as well as A_min values increases with increasing chain length of surfactants.