Thermochimica Acta最新文献

In this study, we investigate the melting behavior and crystallization of nanocomposites of poly(ε-caprolactone) (PCL), a biodegradable polymer, with pristine graphene, an economically feasible filler widely available from natural sources. Nanocomposites with pristine graphene loads between 0.01 and 5 wt% were prepared via solvent casting and primarily probed by Differential Scanning Calorimetry (DSC). Conventional DSC shows that the presence of graphene increases PCL crystallinity. Non-isothermal crystallization was studied using Mo's model, whereas other parameters as Activation Energy and Nucleation Activity were obtained. It is shown that graphene increases crystallization rates acting as nucleant, with no signatures of retardant effects. Compared with other classic nano-loads, like ad-hoc modified bentonite also analyzed for comparison, pristine graphene is more effective as nucleant, which indicates that it is better dispersed in PCL. Analysis by Self Successive Annealing (SSA), also carried out by DSC, reveals that graphene hinders the formation of crystals with lamellar thickness above 7.3 nm, as found in regular PCL. It may indicate that molecular interactions between PCL and pristine graphene disrupts the movement of polymeric chains, consequently limiting lamellar growth. Evidence of such interaction is found by Infrared and Raman spectroscopies that reveal broadening of the carbonyl peak of PCL and alteration of G and D' bands of graphene.

The solubility of 3, 4-O-isopropylidene clindamycin (OIC) was determined in twelve solvents at p = 101.3 kPa with the temperature from 273.15 K to 313.15 K. The solubility of OIC increases with the raise temperature. Among the selected solvents, 2-butanol showed the best dissolving ability for OIC, while acetonitrile showed the worst dissolving ability. The obtained data are neatly correlated with five models, including van't Hoff, Yaws, λh, Wilson, and nonrandom two-liquid interaction model (NRTL), with Yaws equation yielding the most accurate predicted results. Moreover, the Conductor-like Screening Model for Real solvents (COSMO-RS) provides better calculated results for the protic solvents than the aprotic ones except for acetonitrile. The dissolving mechanism of OIC was investigated with intermolecular interaction between OIC and solvents, and the analyses indicate that the dissolving process is affected by intermolecular interaction, molecular shape, and size of both solvents and the solute. The apparent thermodynamics analysis shows that the dissolving process of OIC before reaching equilibrium in the twelve solvents is spontaneous, endothermic, and enthalpy driven.

The thermal behavior of ultra-high molecular weight polyethylene (UHMWPE) with dioctyl adipate (DOA) was investigated by the differential scanning calorimetry (DSC) method. Capillary-porous bodies were obtained via thermally induced phase separation of DOA mixtures with polyethylenes of different molecular weight at different cooling rates. Analysis of the morphology of the prepared porous bodies together with DSC data and results of cloud point estimation revealed an unexpected effect of a cooling rate on the type of phase separation occurring in the mixture during its cooling from homogeneous state. Particularly it was shown that increase in the cooling rate reduces the probability of realization of liquid – liquid phase separation in the mixture. It was argued that such behavior, different from the standard semicrystalline polymers, is a result of kinetic hindrance of liquid – liquid phase separation in mixtures containing a polymer with such a high molecular weight.

Duplex RNA stabilization is important for the application in the artificial silencing of gene expression. Excess usage of cationic molecules with low binding affinity to duplex RNA may cause cytotoxicity due to nonspecific binding. Cationic molecules specifically binding to duplex RNA with high binding affinity are necessary for duplex RNA stabilization. Here, UV melting and isothermal titration calorimetric analyses revealed that our previously designed cationic oligodiaminogalactose 4 mer (ODAGal4) specifically stabilized duplex RNA by binding to it with approximately 10⁵ M⁻¹ binding constant, without binding to duplex DNA. Temperature dependence of thermodynamic parameters, including negative enthalpy and entropy changes, revealed that the magnitude of negative heat capacity change was quite large for small molecules binding to duplex RNA, suggesting the influence of the hydrophobic effect on the binding process. Our results suggest the therapeutic application of ODAGal4 as a key molecule for duplex RNA-binding specificity to prevent any nonspecific binding.

Nanofluids are considered as excellent coolants to optimize thermal management of electronic devices, where the nanoparticle morphology and the addition of surfactants can affect the thermal transport performance of nanofluids. Due to the limitations of high economic and computational cost in previous experimental and numerical simulation methods, the design of nanofluids urges for more efficient approaches. In this work, a novel machine learning framework coupled with molecular dynamics methods was proposed to model the multi-component mixing nanofluidic systems and explore the deep heat transfer mechanisms. Multi-input attribute point cloud dataset, dual channel sampling network and multi-nanoscale optimization scheme were used to improve the prediction performance of machine learning. The computational cost of the machine learning method is shortened by 36000 times compared with simulation methods. Moreover, our work can achieve up to 90 % prediction accuracy for surfactant adsorption properties. Furthermore, algorithm optimization strategy can improve the prediction accuracy of nanofluidic heat transfer performance by 40 %. The proposed framework has the potential to shorten the development cycle of nanofluidic design.

Research findings on the patterns of thermal decomposition and combustion are reported for widely used interior design materials. The experiments were conducted using a hardware and software system including a thermogravimetric analyzer (to record the characteristics of thermal decomposition), a gas analyzer (with H₂, CH₄, H₂S, SO₂, CO and CO₂ sensors) and a high-speed camera (to record the characteristics of ignition and combustion). The temperature of the oxidizing medium ranged from 500 to 900°C to investigate the conditions of thermal decomposition initiation and sustained combustion. It was established that the highest concentrations of toxic emissions were typical of the combustion of polypropylene at a maximum temperature of the oxidizing medium (900°C). Wood showed the shortest ignition delay time and the longest duration of combustion. The experimental data were used for a physical problem statement and mathematical model of heat and mass transfer to explore the thermal decomposition and combustion of interior design materials in different rooms. A comparison of the experimental findings with the mathematical modeling results validates the developed model. The growth rates of carbon monoxide and carbon dioxide concentrations were determined for construction (wooden) and interior design (polymer) materials. The maximum concentrations of CO and CO₂, and the minimum times taken to reach their threshold values corresponded to wood and polyvinyl chloride panels. This research provides a deeper insight into the thermal decomposition of a wide range of fuels and the formation of gaseous pyrolysis products of these fuels. The results obtained can be used to evaluate the toxicity of construction and interior design materials during compartment fires as well as to estimate the safe egress time and risks involved in the process. They can also serve as a database for the development and testing of mathematical models describing fire outbreaks and propagation in confined spaces.

A prototype of an innovative isothermal calorespirometer was developed to measure simultaneously heat production rate (calorimetry) and CO₂ evolution rate (respirometry) in real-time in a static batch vessel system. The relationship between these two variables forms the calorespirometric ratio, which serves as a crucial indicator for metabolic processes and allows for the differentiation of various metabolic pathways in simple (pure culture) and complex (e.g. soil) biological systems. The heat production rate is gauged by a thermoelectric generator situated at the bottom of the measuring channel (calorimetric unit), while the CO₂ evolution rate is monitored through a conductometric cell fixed on the lid of the channel (respirometric unit). The prototype is designed with a twin configuration, featuring both sample and reference channels. The spatial separation of the calorimetric and respirometric measuring units ensures the simultaneous measurement of the two rates from a single sample without the occurrence of crosstalk effects between the signals.

The electrical calibration of the calorimetric unit reveals heat losses (approx. 30 %) and response times (approx. 6 min) that are comparable to those of established isothermal calorimeters. In parallel, growth experiments conducted with baker`s yeast demonstrate the applicability of the calorespirometer prototype to biological systems.

There is a lack of research on the spontaneous combustion phenomenon and its main influencing factors in ultra-deep high-pressure shale oil reservoirs with additional fracturing. In this study, we examine the exothermic characteristics of shale oil oxidation using high-pressure differential scanning calorimetry (HP-DSC) and accelerating rate calorimetry (ARC). Subsequently, a reaction kinetics model is built by integrating the HP-DSC and ARC data. Furthermore, the main factors affecting spontaneous combustion are identified by combining the simulation results with range and variance analyses. The HP-DSC and ARC results indicate a positive potential for achieving spontaneous combustion in shale oil. The developed reaction kinetics model successfully captures the exothermic characteristics of shale oil oxidation. The simulation results demonstrate that spontaneous combustion occurs approximately 5 m away from the injection well, with a delay time of 10.74 days. The critical factors determining the occurrence of spontaneous combustion are O₂ concentration and oil saturation.

The research into using waste plastics as a substitute for coal powder and coke as a reducing agent has garnered significant attention, driven by various factors such as increased environmental concerns and growing interest in sustainable materials. This study investigates the process of carbothermal reduction using a mixture of waste polyvinyl chloride (PVC) and iron concentrate. Thermogravimetric analysis demonstrated that the heat-treated polyvinyl chloride products (PVC370) exhibited superior reaction properties compared to anthracite. Reduction tests indicated that PVC370-bearing pellets were less sensitive to temperature changes than anthracite-bearing pellets, highlighting a potential advantage of PVC370 in industrial applications. Moreover, the metallization ratio of PVC370-bearing pellets exceeded that of anthracite-bearing pellets before reaching 1150 °C. At a temperature of 1100 °C and a C/O of 0.8, the metallization ratio of PVC370-bearing pellets peaked at 83.17 %. During the reduction process of PVC370-bearing pellets, hydrogen (H₂), carbon monoxide (CO), and hydrogen chloride (HCl) were efficiently released at relatively low temperatures. The efficiency of gas release in the reduction process could be attributed to certain factors, such as the composition or structure of the PVC370-bearing pellets. Notably, the quality of gasses generated during the reduction process of PVC370-bearing pellets is superior to that of anthracite-bearing pellets, even when considering chlorine content.

In this paper, three aromatic bismaleimides (BMI-70, BMI-DE and BMI-80) and two aliphatic bismaleimides (BMI-DDA and BMI-C36) were synthesized. The structures were characterized using nuclear magnetic resonance (NMR) spectra and Fourier transform infrared (FT-IR) spectra. Their polymerization behaviors were discussed by non-isothermal differential scanning calorimetry (DSC). The thermal and dielectric properties of the poly(bismaleimide) were investigated using thermogravimetric analysis (TGA), dynamic thermo-mechanical analysis (DMA), and an impedance analyzer. The results indicate that the aliphatic bismaleimides exhibit lower apparent activation energies and dielectric properties, with BMI-DDA displaying an average activation energy of 105.5 kJ mol⁻¹ and the dielectric constant of P(BMI-C36) is 2.558 @ 10 MHz. The aromatic polybismaleimides possessed better thermal stability, among which, the 5 % thermal decomposition temperature (T_d,5) of P(BMI-70) was 513.5 °C, and the residual carbon rate at 800 °C was 44.6 %. In additional, water absorption was studied and their saturated water absorption was less than 4 %.