Thermochimica Acta最新文献

Metal ion-nucleic acid interactions are important for their contribution in structure formation and their potential applications in nanotechnology. Hg²⁺ and Ag⁺ bind to T–T and CC mismatched base pairs, respectively, at the center of duplex DNA to form T–Hg–T and C–Ag–C. Although primer-extension by DNA polymerases with Hg²⁺ incorporated thymidine 5′-triphosphate to form T–Hg–T, the same reaction with Ag⁺ did not incorporate deoxycytidine 5′-triphosphate to form C–Ag–C. Here, isothermal titration calorimetric analyses to examine the effect of CC position in duplex DNA on Ag⁺ binding demonstrated that Ag⁺ did not bind to the terminal CC base pair in duplex, but it bound to the central CC base pair in duplex at 1:1 molar ratio with 9 × 10⁵ M^–1 binding constant. Ag⁺ did not bind to the terminal and central C–A, C–G, and C–T base pairs in duplex. These findings are useful for developing efficient metal-mediated base pair formation in nanotechnology.

N-ethyl-2,2-diisopropylbutylamide (WS-27) is a new cooling agent with a soothing, long-lasting cooling effect, widely used in personal care and cosmetic products. The dissolution behavior of WS-27 in fourteen mono solvents (methanol, ethanol, n-propanol, isopropanol, n-butanol, n-pentanol, methyl acetate, ethyl acetate, isopropyl acetate, propyl acetate, butyl acetate, dichloromethane, cyclohexanone, and acetone) was measured using a dynamic laser monitoring method from 263.15 K to 298.15 K under 101.6 ± 1.2 kPa. In these selected solvents, the solubility of WS-27 increased with increasing temperature. The van't Hoff equation, λh equation, modified Apelblat equation, Wilson model, and NRTL (non-random two-liquid) model were applied to correlate the experimental solubility data of WS-27, and the modified Apelblat equation showed the best-fitting results. In addition, the intermolecular interactions and solvent effect were analyzed using the Hirshfeld surface analysis, molecular electrostatic potential surface analysis, and KAT-LSER model analysis to understand the dissolution behavior of WS-27. The results indicate that the solubility of WS-27 is influenced by multiple factors, and there can be other factors as well. These fundamental data can provide essential information for the crystallization and purification process of WS-27.

The present paper proposes the isoconversional approach to a quantitative assessment of the reactivity in elementary and complex reactions studied by thermal methods under non-isothermal conditions. The focus is on the processes studied at a constant heating rate as the most common mode used in thermal analysis. The accuracy of the proposed approach is tested on simulated data for elementary reactions, whereas its practical application is demonstrated on few experimental examples. The effect of experimental uncertainties on the precision of the introduced reactivity factors is also considered.

Here we report on kinetic analysis of thermal degradation of polymer blends based on incremental isoconversional method coupled with mathematical deconvolution of thermogravimetric curves based on Fraser–Suzuki peak function. The measured kinetic envelope was decomposed into contributions approximately corresponding to degradation of each constituent of a polymer blend. Kinetic parameters from isoconversional analysis were further used for estimating the effect of blending on thermal stability of the constituents. Compared to routinely used parameters such as degradation onset temperature or DTG-peak temperature, the deconvolution analysis allows to determine stability of all components in a mixture regardless of their relative content. Here we also show that deconvolution analysis can be carried out directly on integral α(T) curves, thus bypassing the work with differential data dα/dt. Isoconversional analysis of deconvoluted α(T) curves allows to calculate various parameters for assessing the potentially accelerating or inhibiting effect on thermal degradation, for example, by means of decomposition half-time t_0.5. The results can be made more robust by utilizing relative criteria for stability such as t_0.5(blend)/t_0.5(neat polymer). Using this approach, detrimental effect of PHBV and PBAT on thermal stability of PLA above 300 °C was confirmed. On the other hand, stability of PHBV in both binary and ternary mixtures was improved compared to neat polymer.

This study provides insight into benefits of thermo-chemical conversion of coal slag as recovery process into value-added products. This research involves kinetic analysis of process conducted through non-isothermal thermal analysis measurements, with additional raw material characterization. Kinetic results showed that decomposition proceeds through two consecutive reactions steps (first one, including anorthite P1̅ → I1̅ phase transition, and then production of incongruent melting product (ternary system: CaO·Al₂O₃·2SiO₂ (CAS₂), where viscosity of slag changes), and second one including dehydration and formation of meta-muscovite, and subsequently, thermal disruption of muscovite de-hydroxylated phase, which proceeds with breaking of octahedral Al–O bonds), and one single-step reaction (attributed to CO-reduction of hematite to magnetite). Thermodynamic results showed an existence of physically meaningful isokinetic temperature (T_iso), which corresponds to active vibrational frequency of surroundings of SiO₂ reaction site, manifested through Si‒O bond weakening by catalytic reaction of freed hydroxide ion (OH⁻). It was concluded that at temperature T = T_iso, the course of process loses its dependence on temperature and pressure, regulating changes between thermodynamic parameters, through enthalpy-entropy compensation (EEC) effect.

To improve the combustion characteristics of micron-sized aluminum (Al) powder, a composite powder was prepared by doping a small amount (15 wt%) of magnesium fluoride (MgF₂), polytetrafluoroethylene (PTFE), and fluorinated graphite (FG) into the aluminum powder through solution dispersion method. The physical phase composition, micro morphology, thermal reactivity, and combustion performance of the composite powders were also characterized. The findings suggest that the promoting effect of the three fluorides on aluminum combustion can be ranked in the following descending order: FG > PTFE > MgF₂. The fluorides can to erode the Al₂O₃ shell layer directly, thus creating cracks and reaction pathways for the Al core enclosed within the shell. Moreover, the gasification of AlF₃ within the combustion products can escape from the surface of Al particles and promote the oxidation combustion of the exposed aluminum, which enhances the diffusion reaction on the active aluminum surface.

The experimental study of the kinetics and modes of the thermal degradation of polymethyl methacrylate (PMMA) in an argon flow was carried out. During thermogravimetric analysis the sample heating rates were 2, 5, 8, 20 and 35 K/min. Based on the integral isoconversional method the values of the kinetic rate constants of the PMMA thermal degradation were determined. When modeling the decomposition process of PMMA for low conversion degrees, it is advisable to use the reaction rate constant obtained for the conversion degree equal to 20 %, and for modeling the whole process – 50 %. Therefore, for evaluation calculations, it is possible to describe the process of PMMA decomposition with one gross reaction. Also, the investigation of the thermal degradation of PMMA particles under conductive heating conditions (680, 700, 720 K) in an argon and air was carried out. Based on the analysis of the data obtained, a scheme for the decomposition of PMMA, consisting of four stages, was established.

Ambient temperature fluctuations can affect the thermal noise and sensitivity of a large-volume Seebeck calorimeter. This paper proposes that a reference cell considerably smaller than the sample cell in the apparatus can effectively neutralize this noise. It is found that the thermal signals from both the reference and sample cells exhibit a convolution relationship. By deconvolving two distinct thermal pulses generated by abrupt changes in cooling fluid temperature, one from the reference cell and one from the sample cell, a corresponding response function is derived. And using this function, the noise is canceled out by subtracting the convoluted signal of the reference cell from that of the sample cell during isothermal calorimetry. Experimentally, utilizing this technique with two calorimeters, one with a 17.6-liter capacity and the other with a 27-liter capacity, has been shown to reduce noise by at least 5 % and 6 % from their initial values, respectively.

Herein we present a novel ‘polymerization strategy’ aimed at synthesizing flavor precursors, with a focus on enhancing their thermal stability and release properties. Three volatile flavors, menthol, methyl cyclopentenolone, and ethyl maltol, are reacted with acryloyl chloride to produce corresponding vinyl monomers. These monomers undergo radical polymerization to form homopolymers (P1−P3). To improve solubility in alcohol solvents, a hydrophilic oligoethylene glycol monomer is introduced, copolymerized with the flavor containing monomers, resulting in copolymers (P4−P6). An important advantage of these polymers lies in their significantly enhanced thermal stability, exhibiting an increase of approximately 100 to 200 °°C compared to small molecular flavors. Furthermore, our methodology enables efficient release of the target flavors upon heating, as evidenced by online analyses of volatiles from pyrolysis using fixed-bed reactor combined with single photoionization mass spectrometry (FBR-SPIMS) and pyrolysis-gas chromatography-mass spectrometry (Py-GC–MS). This work represents a practical and innovative approach to improving the thermal stability of volatile flavors and elevating their release temperature, offering promising applications in high-temperature food processing and tobacco industries.

In this study, the isothermal oxidation kinetics of magnetite (OM), high-Mg magnetite (MM), titanomagnetite (TM), and chromite (CM) were investigated by applying thermogravimetry (TG) analysis at temperatures ranging from 1073 K to 1223 K. The results show that different high-FeO spinels possess distinct oxidizability. The oxidation process of OM in the temperature range from 1073 K to 1223 K is faster than others, followed by MM and TM. While CM exhibits the poorest oxidizability, and generally undergoes complex phase transitions. In the initial stage of oxidation, high FeO spinels have a higher oxidation rate due to the surface oxidation of spinel particles. However, the oxidation rate gradually declines in the later stages of oxidation due to increased internal diffusion resistance. The results of oxidation kinetics indicate that the initial oxidation stage of four spinels can be described as random nucleation and subsequent growth mechanism. The average apparent activation energies of the initial oxidation stage of OM, MM, TM, and CM are 25.09 kJ/mol, 32.39 kJ/mol, 58.10 kJ/mol, and 82.42 kJ/mol, respectively.