Calorimetric Techniques Research Articles

Critical Cooling Rate of Fast-Crystallizing Polyesters: The Example of Poly(alkylene trans-1,4-cyclohexanedicarboxylate)

Controlling the cooling rate experienced by a material during a manufacturing process is a challenge and a major issue. Industrial processing techniques are very diverse and may involve a whole range of cooling rates, which are sometimes extremely high for small and/or thin manufactured parts. For polymers, the cooling rate has consequences on both the microstructure and the time-dependent properties. The common cooling rates associated with conventional calorimetric measurements are generally limited to a few tens of degrees per minute. This work combines several calorimetric techniques (DSC, modulated-temperature DSC, stochastically-modulated DSC and Fast Scanning Calorimetry) to estimate the critical cooling rate required to melt-quench fast-crystallizing polyesters to their fully amorphous state, based on the example of a series of poly(alkylene trans-1,4-cyclohexanedicarboxylate) (PCHs) with a number of methylene groups in the main structure of the repeating unit nCH2 varying from 3 to 6. The even-numbered ones require faster cooling rates (about 3000 K s−1 for nCH2 = 4, between 500 and 1000 K s−1 for nCH2 = 6) compared to the odd-numbered ones (between 50 K min−1 and 100 K s−1 for nCH2 = 3, between 10 and 30 K min−1 for nCH2 = 5).

Monitoring in-situ dissolution of polystyrene-acrylonitrile (SAN) via calorimetry and spectroscopy

Dissolution/precipitation recycling is an environmentally friendly solution that could be potentially implemented for ABS recycling. In this paper, a set of useful calorimetric, spectroscopic, and rheological techniques and methods are presented to monitor in-situ the dissolution of the ABS matrix: poly(styrene-acrylonitrile) (SAN). In line with the Hansen solubility parameters, methyl ethyl ketone (MEK) has been selected to be a suitable solvent for SAN dissolution. Thermodynamic and kinetic aspects of the dissolution process were investigated by using calorimetry and in-situ ATR-FTIR spectroscopy. Through an isoconversional method, the effective activation energy and the main steps involved in the dissolution process were determined. A rheological characterization of the solution SAN-MEK was also performed to provide further information on the rheological behavior.

Elucidating the Binding Interaction of a Highly Efficient Phytochemical-Sinapic Acid with Human Serum Albumin: A Spectroscopic and Calorimetric Approach

Polyphenolic compounds have received much attention due to their major function as antioxidants. Sinapic acid (SA) is an orally bioavailable phytochemical with excellent free radical scavenging property transported in the blood by human serum albumin (HSA) which is the chief carrier protein found abundantly in human plasma. SA contains a single phenolic group. This study investigates the binding and interaction mechanism between SA and HSA by multiple spectroscopic and calorimetric techniques, such as UV/visible absorption spectroscopy, intrinsic fluorescence studies, Fourier transform infrared (FTIR) spectroscopy and isothermal titration calorimetry (ITC). UV/visible absorption spectroscopy showed hyperchromicity in the absorption spectra, suggestive of structural change due to complex formation between HSA and SA. Intrinsic fluorescence measurements, performed at three different temperatures, showed quenching of the fluorescence spectra and the mechanism of quenching was static in nature which occurred due to ground state complex formation. The FTIR results demonstrated a 16% decrease in α-helical content of the secondary structure of HSA in the presence of SA. Hydrogen bonds and hydrophobic forces were the main forces of interaction, according to the thermodynamic characteristics found through ITC. Moreover, the data obtained through ITC indicated strong binding affinity between HSA and SA and supported the exothermic and spontaneous nature of the interaction.

Interdigitated orthogonal smectic and cybotactic nematic mesomorphism in three-ring hockey-stick-shaped 1,2,4-oxadiazole mesogens

Although hockey-stick-shaped liquid crystals with three-ring molecular architecture show remarkable thermal behavior, work on such systems is rarely reported. In particular, the investigations incorporating the novel oxadiazole core, which provides thermal and hydrolytic stability as well as polarity, have been scarcely presented. Given these observations, we intended to investigate such LCs derived from 3,5-diphenyl-1,2,4-oxadiazole. In this study, we report on the synthesis and elaborative characterization of a novel series of hockey-stick-shaped mesogens namely, methyl 4-(5-(4-n-alkoxyphenyl)-1,2,4-oxadiazol-3-yl)benzoate. To reveal the structure-property correlations, the substitution on the C-3 core in the form of methyl ester group has been held constant, while the substituent on the C-5 core has been varied with different n-alkoxy tails. While the thermal gravimetric analysis confirms the thermal stability, the methodical studies on the mesomorphism using optical, calorimetric, and X-ray diffraction techniques confirmed the occurrence of smectic A and nematic phases having interdigitated and cybotactic orders respectively. The lower and middle/higher members, respectively, show the N phase, and N and SmA phases, which follow the general trend reported hitherto for the homologues series of LC compounds. The quantum mechanical calculations using density functional theory revealed the bending angles, dipole moments, and HUMO/LUMO band gaps.

Evaluation of hydrogen storage performance of Ti0.25Zr0.25V0.15Nb0.15Ta0.2 high-entropy alloy using calorimetric technique

The features of phase transformations during interaction of BCC-type Ti0.25Zr0.25V0.15Nb0.15Ta0.2 high-entropy alloy (HEA) with hydrogen and the accompanying thermal effects have been examined using the Tian-Calvet calorimetric technique. The alloy was produced by the pendent drop melt extraction method in the form of microfibers and then coated with a thin layer of palladium to eliminate the preliminary high-temperature activation and enable first hydrogenation at room temperature. Two reaction stages were distinguished on the measured heat emission curves. Using XRD data, these stages were attributed to the formation of a BCC-type hydrogen solid solution and a phase transition to FCC-type dihydride phase. Recorded values of the reaction enthalpy decrease in absolute terms from 145 kJ/mol H2 (dilute solid solution) to 73–77 kJ/mol H2 (BCC→FCC) and to 20 kJ/mol H2 (H solution in FCC dihydride). The overall heat emission of the entire process as a whole is 110 kJ/ mol H2. The course of the dehydrogenation process depends strongly on the applied temperature and at 493 K results in the formation of a BCT-type monohydride, which was not detected during hydrogenation. The detailed calorimetric data obtained here significantly change the previously existing ideas about thermal effects during this type HEAs hydrogenation, based on calculations using the Van't-Hoff equation. The reported findings are of special importance for various hydrogen related applications of HEAs

Understanding the NaxMnO2 System: A Thermodynamics and XPS Approach.

The NaxMnO2 system is an important class of materials with potential applications in rechargeable batteries, supercapacitors, catalysts, and gas sensors. This work reports the synthesis of NaxMnO2 (x = 0.39, 0.44, 0.48, 0.66, and 0.70) compounds and their characterization by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and impedance spectroscopy (IS) techniques. The compounds in this series exhibit a significant variation in their structures with the extent of Na-content. The change in the nature of bonding with increasing Na content was investigated, and its effect on material stability as well as electrotransport properties was investigated. A detailed thermodynamic evaluation of these materials was carried out employing calorimetric techniques, and the data were correlated with changes in the chemical environment around the Na ion. This analysis is crucial for predicting the thermodynamic stability of NaxMnO2 compounds under different environments for their applications in Na-ion batteries.

Binding and displacement study of gentamicin, 5-fluorouracil, oxytetracycline and rolitetracycline with (BSA: Drug2) complex using spectroscopic and calorimetric techniques: Biophysical approach

Understanding of energetics of interactions between drug and protein is essential in pharmacokinetics and pharmacodynamics study. The binding affinity (K) helps in investigating how tightly or loosely drug is bound to protein. The binding, displacement, conformational change and stability study of drugs- gentamicin (GM), 5-fluorouracil (5FU), oxytetracycline (OTC) and rolitetracycline (RTC) with bovine serum albumin (BSA) has been carried out in presence of each other drug by fluorescence, UV–visible spectroscopy, molecular docking, circular dichroism techniques and thermal denaturation method. The site marker study and docking methods have confirmed that 5FU and GM are able to bind at site 1 and OTC and RTC at site II of BSA. The order of their binding affinities with BSA for the binary system were as GM <5FU < OTC < RTC with the order of 102 < 103 < 105 < 105–6 M−1. The displacement study has shown that higher affinity drug decreases the equilibrium constant of another drug already in bound state with BSA if both these drugs are having the same binding site. Therefore 5FU, GM (binding site 1) drugs were not able to displace OTC and RTC (binding site 2) and vice-versa as they are binding at two different sites. The binding constant values were found to be decreasing with increasing temperature for all the systems involved which suggests static or mixed type of quenching, however can only confirmed with the help of TCSPC technique. The ΔG0 (binding energy) obtained from docking method were in accordance with the ITC method. From molecular docking we have determined the amino acid residues involved in binding process for binary and ternary systems by considering first rank minimum binding energy confirmation. From CD it has been observed that RTC causes most conformational change in secondary and tertiary structure of BSA due to the presence of pyrrole ring. OTC-RTC with higher affinity showed highest melting temperature Tm values while low affinity drugs in (5FU-GM) combination showed lowest Tm value. 5FU showed large endothermic denaturation enthalpy ΔHd0 due to the presence of highly electronegative fluorine atom in the pyridine analogue.

Measurements of Enthalpies of Mixing of Sn–Ga–In Ternary Alloy System by Calorimetric Technique

Measurements of Enthalpies of Mixing of Sn–Ga–In Ternary Alloy System by Calorimetric Technique

Insulin amyloid fibril formation reduction by tripeptide stereoisomers.

Insulin fibrillation is a problem for diabetic patients that can occur during storage and transport, as well as at the subcutaneous injection site, with loss of bioactivity, inflammation, and various adverse effects. Tripeptides are ideal additives to stabilise insulin formulations, thanks to their low cost of production and inherent cytocompatibility. In this work, we analysed the ability of eight tripeptide stereoisomers to inhibit the fibrillation of human insulin in vitro. The sequences contain proline as β-breaker and Phe-Phe as binding motif for the amyloid-prone aromatic triplet found in insulin. Experimental data based on spectroscopy, fluorescence, microscopy, and calorimetric techniques reveal that one stereoisomer is a more effective inhibitor than the others, and cell live/dead assays confirmed its high cytocompatibility. Importantly, in silico data revealed the key regions of insulin engaged in the interaction with this tripeptide, rationalising the molecular mechanism behind insulin fibril formation reduction.

Experimental and theoretical study on the interaction of an ionic resorcin[4]arene and some pollutants in aqueous solution

The complexation process between an ionic resorcinarene, C-ethyl-tetraminomethylated-resorcin[4]arene hydrochloride, with resorcinol, phenol and potassium cyanide has been studied in aqueous solution using spectroscopic, calorimetric, and computational techniques. The results show the formation of resorcinarene-phenol and resorcinarene-resorcinol inclusion complexes stabilized by means of π-π interactions. On the other hand, the interaction between the macrocycle and the cyanide ions is principally mediated by ion pairing and electrostatic interactions. A turn-on effect on the fluorescence intensity is found when resorcinol or phenol is added to the macrocycle. The quantification and detection limits have been calculated and the obtained values are comparable to other sensors reported in the literature. These results extend the use of this type of macrocycles as chemosensors.

Effects of twelve organic solvents on process hazards and reaction selectivity of m-xylene nitration: Combined calorimetric technique and DFT calculations

Selection of appropriate solvents is of great significance for achieving efficient and safe m-xylene nitration. In this study, the exothermic behavior of m-xylene nitration under twelve organic solvents were studied by reaction calorimetry. The process hazards were assessed by calculation of thermal safety parameters. The reaction selectivity was quantified. The anhydrides exhibited the prominent promotion as water absorbent and active reagent in nitration, followed by selected aliphatic hydrocarbons, chlorinated hydrocarbons. While acetic acid, propionic acid and ethyl acetate had negative effects. The maximum yield of 95.6 % was achieved in nitric acid-acetic anhydride (HNO3-Ac2O) system. The thermal weight loss of the products appeared at around 150−230 °C by thermogravimetry experiments. The activation energy was determined to be 192.9 kJ/mol through adiabatic kinetic calculations. Furthermore, the solvent effects were analyzed by calculating the solvent polarity and its interaction energy with HNO3. The different action mechanisms of Ac2O and Pc2O on NO2+ generation were revealed. The density functional theory calculations were in agreement with the experimental results. These findings can provide guidance for understanding of the solvent effect on the reaction hazards and selectivity of m-xylene nitration, and provide experimental and theoretical basis for solvent screening for the nitration of similar aromatic compounds.

A device for rapid calorimetric measurements on small biological tissue samples

A new calorimetric technique is described that allows high-throughput heat production rate measurements on small biological tissue samples. The technique is based on the widely used thermopile chip technology combined with an innovative method for precise transport and positioning of samples of different biological materials at the thermal power detector inside the calorimeter. The new transport and positioning technique is a combination of fluidic and mechanical transport, where the latter is realized by a magneto-motor drive. The transport facility ensures good diffusive oxygen penetration into the sample, which is essential for highly metabolically active materials. The proper functioning of the device is demonstrated by measuring the heat production of metabolically active brown adipose tissue, biopsied tegu lizard muscle, and live Drosophila larvae at different stages and temperatures.

التنبؤ المبكر بالاعتلال الكلوي لمرضى عراقين مصابين بالسكري النوع الثاني بدلالة تقييم بعض العوامل البيوكيمائية ذات الصلة

داء السكري من النوع 2 (T2DM) هو مرض معقد يصيب العديد من الأعضاء إلى جانب البنكرياس مثل الكلى والكبد والدماغ والعين. بسبب ارتفاع السكر في الدم لفترات طويلة وعدم السيطرة على مرض السكري مع وجود عوامل خطر أخرى ، يمكن أن تحدث مضاعفات مرض السكري. تشمل مضاعفات مرض السكري مضاعفات الأوعية الدموية الدقيقة والأوعية الدموية الكبيرة التي تستهدف الكلى. تهدف الدراسة الحالية إلى التحقق من مستوى الانجوتينسن المحول للانزيم ACE-2)) ، عامل نمو النسيج الضام (CTGF) جنبًا إلى جنب مع بعض العوامل البيوكيميائية ذات الصلة في النساء المصابات بداء السكري واعتلال الكلية السكري مقارنة بالضوابط الصحية. اشتملت الدراسة على 90 مريض تتراوح أعمارهم بين 30-65 سنة. يعانون من مرض السكري من النوع 2 مقسمون إلى ثلاث مجاميع على أساس معايير ACR تشمل البيلة الألبومينية الطبيعية ، البيلة الألبومينية الدقيقة ، البيلة الألبومينية الكبيرة 30 مريضًا لكل مجموعة و 30 شخصًا يتمتعون بصحة جيدة كانوا بمثابة المجموعة الضابطة ، منمن زاروا مستشفى بغداد التعليمي / المدينة الطبية و مستشفى اليرموك التعليمي ، في الفترة ما بين ديسمبر 2021 ومايو 2022. تم تحديد مستوياتACE-2 و CTGF باستخدام تقنية ELISA. أظهرت النتائج وجود فروق ذات دلالة إحصائية بين مجموعات المرضى والمجموعة الضابطة لعامل CTGF ، ووجد أن مستويات ACE-2 تزيد بشكل كبير في مجموعات المرضى عن مجموعة التحكم الصحية. كما أظهرت النتائج أن كلا من سكر الدم الصائم FBS و هيموكلوبينA1C (HbA1C)قد زاد بشكل ملحوظ في مجموعات المرضى مقارنة بالمجموعة الصحية. علاوة على ذلك ، كشفت قيم معدل الترشيح الكبيبي المقدر( ( eGFR عن فروق ذات دلالة إحصائية بين جميع المجموعات المدروسة ، وكذلك اظهرت نتائج ACR وجود فروقات ذات دلالة إحصائية بين مجموعات المرضى الثلاثة ، والتي تمثل المعايير الأساسية لتصنيف مجموعات المرضى. على أساس النتائج التي تم الحصول عليها في هذه الدراسة ، يمكن استنتاج ان عاملي ACE-2 و CTGF يمكن تطبيقهما كواسمات تنبؤية مبكرة موثوقة للكشف عن المرض.

Kinetics of the plastic crystal transition in neopentyl glycol

The thermal hysteresis exhibited in plastic crystal compounds greatly reduces their cyclic efficiency, limiting their potential for replacing current environmentally harmful refrigerants. A mechanistic understanding of the origins of this hysteresis has yet to be established. Here, we systematically investigate the transformation kinetics of the model plastic crystal, neopentyl glycol (NPG), through microscopic and calorimetric techniques. We reveal an asymmetry between the forward (heating) and reverse (cooling) transitions. We also demonstrate that the forward transformation is rate-limited by the rate of growth of rotationally disordered domains. In contrast, the reverse transformation is rate-limited by the nucleation of the ordered crystal domain, demonstrated by the sharp exothermic peaks in calorimetry and rapid self-nucleation phenomena observed optically. This nucleation limitation is largely responsible for the large thermal hysteresis in NPG, which we observe to be as large as 16.7 °C for an approximately 10 mg sample cooled at 0.5 °C min−1. These findings demonstrate the underlying origin of the thermal hysteresis and introduce a direction to mitigate hysteresis in plastic crystal transformations.

Accelerated aging procedure of epoxy structural adhesive for marine offshore applications

Knowledge of the long-term performance of adhesive connections is undoubtedly of paramount importance to enable their deployment in civil, mechanical, and other engineering applications. Over time, adverse environmental conditions can strongly influence the performance of adhesive joints leading to a progressive deterioration of their initial mechanical properties. The use of adhesive connections for secondary structures in offshore applications is a technology that allows for the rapid creation of structural members that, however, cannot ignore the influence of hydrothermal effects on mechanical performance due to environmental conditions. In this context, the investigation of the hygrothermal durability of adhesive connections was undertaken through an extensive experimental programme. More specifically, 130 cylindrical steel joints bonded with a commercially epoxy resin for structural applications were tested in Mode I using an Arcan-modified device. Prior to test, the specimens were placed in climatic ovens capable of combining the effects of temperature and humidity for approximately 320 days. In addition, the glass transition temperature, Tg, was assessed by employing the differential scanning calorimeter (DSC) technique to correctly define the experimental ageing conditions. The experimental results show how ageing conditions influence the mechanical properties of the epoxy resin investigated. Finally, some predictive formulations are proposed to calculate the loss of strength of adhesive joints over time.

Investigation of soybean oil epoxidation process with phase transfer catalyst: Risk of thermal runaway

This paper explores an efficient and eco-friendly epoxidation process using the phase transfer catalyst ([(C18H37)2(CH3)2N]3{PO4[W(O)(O2)2]4}), which offers more advantages over the use of carboxylic and inorganic acids as catalysts in the Prileschajew epoxidation process. Consequently, a study of the process's thermal hazards is imperative. The paper conducts a comprehensive analysis of the process, employing a combination of calorimetric techniques. The critical runaway temperature, stabilization temperature, and required heat dissipation rate to prevent thermal runaway reactions were calculated using the Semenov model. On-line Fourier transform infrared spectroscopy and reaction calorimetry were used to relate the reaction mechanism and exothermic behavior of the actual production process, and a reliable model was developed for the calculation of reaction enthalpy. The findings indicate that the thermal risk depends on the rate of double bond epoxidation, which provides offering valuable insights for safe industrial-scale ESO production.

Characterization methods to predict extrusion performance in thermoplastic polyurethane batches

Thermoplastic polyurethanes (TPUs) are a class of urethane elastomers which flow at elevated temperatures, enabling a diverse set of processing techniques including industrial-scale extrusion and injection molding. Due to variations in the relative content of hard and soft segments within the polymer chains, as well as block lengths and chemistries, this material exhibits a wide range of viscoelastic properties depending on the synthetic process and thermal history. Numerous manufacturers produce their own proprietary brands of TPU, thus creating a diverse market for a product whose processability varies depending on the supplier. Lot dependent undesirable characteristics may be observed during melt extrusion, including degradation at process-relevant temperatures, increases in viscosity over time, and buildup of solid-like particulates during extrusion. This manuscript implements a combination of chemorheological, spectroscopic, solubility, light scattering, and calorimetric techniques to understand the formation of this solid particulate phase during extrusion. The presence of endothermic transitions, large degrees of branching, rapidly changing viscoelastic properties, and poor dissolution capabilities were correlated with the worst performing lots of TPU in terms of extrudability. These findings suggest that solidification is caused by physical crosslinking through hard phase aggregation, which is attributed to differences in polymer branching architecture, high chain mobility, and strain under extrusion conditions. The strong association between polymer branching and solidification during extrusion highlights the capability for these characterization techniques to rapidly screen for extrusion-related performance of TPUs prior to processing.

Physical aging of a biodegradable alicyclic polymer: poly (pentamethylene trans-1,4-cyclohexanedicarboxylate)

Physical aging of poly (pentamethylene trans-1,4-cyclohexanedicarboxylate) (PPeCE), a biodegradable alicyclic polyester, was investigated using Fast Scanning Calorimetry (FSC), a recent calorimetric technique allowing to accelerate physical aging and study the associated relaxation processes at different aging temperatures in an experimentally-reasonable time scale. Different mechanisms were highlighted by varying the aging temperature on a temperature range of more than 60 °C. At aging temperatures well below the glass transition temperature, several relaxation mechanisms were evidenced, probably related to secondary relaxation processes (β relaxations). When the aging temperature approaches the glass transition temperature, the primary relaxation process (α relaxation) becomes predominant.

Phase diagram study of Na2O–ThO2–P2O5 system and investigation of thermo physical properties of quaternary compounds

The subsolidus phase relations in Na2O–ThO2–P2O5 pseudo ternary system were determined at 1223 K. Synthesis of all the phases, used for drawing phase diagram, was carried out by solid state route. Formation of ternary and quaternary compounds in Na2O–ThO2, Na2O–P2O5, ThO2–P2O5 and Na2O–ThO2–P2O5 systems was confirmed at 1223 K. With the help of these compounds and phase analysis of number of synthetic mixtures, prepared by reacting different mol fractions of Na2O, ThO2 and P2O5 at 1223 K, phase diagram was drawn and phase boundaries were established. No ternary compound was identified in Na2O–ThO2 system. Formation of three quaternary phosphates, Na2Th(PO4)2, NaTh2(PO4)3 and Na5Th(PO4)3 was confirmed at 1223 K. XRD pattern of monoclinic Na5Th(PO4)3, synthesized for the first time and found iso structural with Na5Th(AsO4)3 and its lattice parameters were obtained by Le Bail method. Thermogravimetric studies of quaternary phosphates were carried out in air to investigate their thermal stability. All the three compounds decompose to ThO2 at 1673 K. Two step weight loss in TG curve of Na2Th(PO4)2 confirmed its decomposition to ThO2 via NaTh2(PO4)3 as an intermediate. To calculate thermal expansion coefficients, high temperature XRD (HT-XRD) data of Na2Th(PO4)2, NaTh2(PO4)3 and Na5Th(PO4)3 was collected in air between the temperature range of 298–1173 K. All these compounds exhibit positive thermal expansion with the average volume expansion coefficient values ranging between 30 and 60 × 10−6 K−1. Heat capacities of these compounds were measured in the temperature range of 308–873 K using Differential Scanning Calorimetry (DSC) technique.

Investigation on the molecular interaction between dietary flavone luteolin and alpha-2-macroglobulin using multi-spectroscopic, calorimetric and molecular dynamics simulation techniques

The current study examined the mechanism of interaction between luteolin and human αlpha-2-macroglobulin (α2M) to determine the binding mode and the interaction of the ligand using biophysical and molecular modelling methods. The UV-absorbance confirmed the formation of a complex between α2M and luteolin. Luteolin considerably reduced the intrinsic fluorescence of α2M via dynamic quenching determined by fluorescence quenching. The binding process was spontaneous and moderate (Kb = 0.70 × 104 M−1, 300 K), and the hydrophobic interaction was a significant factor in their interaction. With increasing luteolin concentration, the anti-proteolytic activity of α2M declines by approximately 35 % of its native functional activity. Förster energy was used to determine the energy transfer and the binding distance between the ligand and the protein which was found to be 2.77 nm for the α2M-luteolin complex in accordance with fluorescence resonance energy transfer (FRET). Synchronous fluorescence and red-edge excitation shift (REES) data were used to determine the changes in the microenvironment around Tyr and Trp residues in the presence of luteolin. The circular dichroism (CD) showed changes in conformation upon binding of luteolin to α2M. The Fourier transform infrared spectroscopy (FTIR) spectra provided additional evidence that the secondary structure of α2M was considerably altered by the addition of luteolin. The molecular docking simulation revealed that, in addition to hydrophobic interactions, the hydrogen bonds were involved in the interaction of α2M-luteolin complex.