Differential Scanning Calorimetry Peak Research Articles

A novel process for making alkaline iron oxide nanoparticles by a solvo thermal approach

In the present work alkaline iron oxide nanoparticles are synthesized by a novel solvo thermal approach and characterized exhaustively by various complementary techniques. Field emission scanning electron microscopy (FESEM) studies reveal that the size of nanoparticles is in the range of 31.5 nm to 96.9 nm. Energy-dispersive X-ray spectroscopy spectral analysis reveals the presence of oxygen, carbon, iron, and sodium. The X-ray diffraction studies confirm the formation of tetragonal NaFeO2 as the major phase along with orthorhombic NaFeO2·H2O and rhombohedral FeCO3 (siderite) as the minor phases. Fourier transform infrared spectroscopy exhibits peaks due to the stretching and bending vibrations of O-H, C=O, CH3-N, CH3, C-H, C-N, and Fe-O groups. Differential scanning calorimetry (DSC) results display an endothermic peak at 100.85°C and a very small endothermic peak at 791.56°C with 819.73 mJ and 349.28 mJ energies respectively. These DSC peaks can be correlated with thermal gravimetric analysis (TGA) peaks representing 31.04% weight loss and 7.70% weight loss respectively in the sample at around 160°C and 980°C respectively.

Detection of magnesium compounds in dietary supplements and medicinal products by DSC, Infrared and Raman techniques

The aim of this study was to learn to what extent the selected instrumental techniques, differential scanning calorimetry (DSC), as well as Fourier-transform infrared (FTIR) and Raman spectroscopies, can be used to detect both organic or inorganic magnesium compounds in the dietary supplements and medicinal products. Besides magnesium compounds as the active pharmaceutical ingredients (APIs), the preparations contain also other organic and inorganic APIs and several excipients. The study will be extended over the analysis of the products manufactured by various firms but containing the same API at different levels. In this way, it will be possible to assess the impact of excipients on the DSC scans and the FTIR and Raman spectra of a dominant constituent present in a studied preparation. The study on thirty commercially available dietary supplements and medicinal products has shown that in the majority of cases the DSC, FTIR and Raman techniques could be used for the detection of APIs in these commercial products. This was possible with the aid of the endothermic DSC peaks and the so-called matching factors of the FTIR and Raman spectra to those of substances used as standards. Both the complex composition and low levels of API in the studied preparations have been identified as the factors which have a strong impact on the usefulness of the three techniques for the detection of APIs in the dietary and medicinal products.

DMA and DSC studies of accelerated aged parchment and vegetable-tanned leather samples

The aim and the novelty of this work was the use of both dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC), in water and in dry state, for the investigation of the effects of temperature and relative humidity on degradation of recently manufactured parchments and vegetable-tanned leathers. The materials were subjected to accelerated ageing under action of heat and moisture for progressively increasing time lengths. The studies have proved that accelerated ageing causes a progressive decrease of the temperature of denaturation in water excess, but has no or minor effect on that in dry state. Also, under same ageing conditions parchments undergo a greater degree of deterioration than leathers, as evidenced by a more dramatic change in the DSC peaks (in water) and in the shrinkage curves (DMA). The results can be interpreted as a partial gelatinization occurring in the thermal conditions used for accelerated ageing. The paper presents the advantage of using both techniques, namely that DSC results can assist in interpretation of the DMA curves and that the good correlation of denaturation temperatures obtained by DSC and DMA ascertain these values. Such studies can be useful for understanding the processes that take place on natural ageing of historical parchments and leathers, as well as for establishing proper conditions of their storage.

Synthesis and Crystal Structure of Anhydrous Analog of 1,25-Dihydroxyvitamin D3

As predicted by single crystal X-ray crystallography, and contrary to the reported suggestions, the anhydrous form of calcipotriol, a therapeutically important vitamin D analog, was found stable enough to be used as an active pharmaceutical ingredient. The crystal and molecular structure of calcipotriol anhydrate was solved and refined using single crystal X-ray diffraction. The analog was obtained by a novel convergent synthesis from the vitamin D C-22 sulfone, as an advanced intermediate and a side-chain fragment. The homo-chiral side-chain aldehyde was obtained from cyclopropanecarboxyaldehyde by the chromatographic separation of the intermediate diastereomeric salts with (S)-naproxen. Calcipotriol anhydrate showed a single peak in differential scanning calorimetry and the absence of a peak from a water molecule, typical for the monohydrate. Calcipotriol anhydrate, as the only 1,25-dihydroxylated analog of vitamin D3 , exists as a mixture of both α- and β-forms of the A-ring, present in the asymmetric part of the unit cell of the crystal lattice. The intermolecular hydrogen bonding between both conformers in the crystal lattice indicated that the stability of calcipotriol anhydrate might be at least the same as for the known monohydrate. The usefulness of calcipotriol anhydrate as an active pharmaceutical ingredient was confirmed by the stability study in the standard conditions used for the storage of vitamin D analogs.

Mechanism and kinetics of crystallization of amorphous Fe81B13Si4C2 alloy

Crystallization process of amorphous Fe81B13Si4C2 alloy manifested as a slightly asymmetrical exothermic peak in temperature range 770–820K of differential scanning calorimetry (DSC) curves. Complex crystallization DSC peak was deconvoluted into three steps corresponding to formation of α-Fe(Si), Fe3B and Fe2B crystalline phases. Fe2B phase is formed from the amorphous matrix, while metastable Fe3B decomposes, providing constituents for subsequent formation of Fe2B phase. Examination of mechanism and kinetics of each individual step of crystallization yielded similar values of kinetic triplets, indicating similar crystallization mechanism for all individual phases, which was subsequently discussed using the values of Avrami exponents of individual crystallization steps. Both the range of and changes in values of the local Avrami exponent suggested the appearance of impingement, which precluded full applicability of JMA equation, and mixed nucleation type with accelerating nucleation for crystallization of all phases. Position of the transformation-rate maxima of individual crystallization steps indicates that anisotropic growth is the prevailing type of impingement. Estimation of lifetime showed very high stability of the alloy against crystallization at room temperature, with exponential decline in lifetime with temperature increase.

Curing behavior of dicyandiamide/epoxy resin system using different accelerators

Various amounts of dicyandiamide (Dicy), two grades of epoxy resins, i.e. Epiran 06 and Epikote 828, and three different accelerators including benzyl dimethyl amine (BDMA), 3-(4-chlorophenyl)-1,1-dimethyl urea (Monuron) and 2-methyl imidazole (Im) were used in curing of Dicy/epoxy resin system. Both of the used epoxy resins were based on diglycidyl ether of bisphenol A (DGEBA). The effects of type and concentration of accelerators on curing behavior were studied by differential scanning calorimetry (DSC) method in dynamic or non-isothermal mode. The optimum concentration of Dicy for curing of epoxy resins was obtained based on the glass transition temperature of the cured epoxy/Dicy formulations. The maximum glass transition temperature of 139 °C was obtained at the stoichiometric ratio of Dicy to epoxy of 0.65. The results showed that BDMA has a broader curing peak in DSC and starts the cure reaction earlier than the others. However, Monuron has a narrow curing reaction peak with good cure latency. The tensile properties of Dicy-cured Epiran 06 and Epikote 828 epoxy resins reinforced with chopped strand mat showed that these two epoxy resins have similar mechanical properties. For composites based on the Epiran 06 and Epikote 828 reinforced with 40 wt % glass chopped strand mat, tensile strength and modulus were 156 and 153.4 MPa and 11.6 and 12.4 GPa, respectively.

Phase transitions in smectogenic liquid crystal 4-butoxybenzylidene-4′-butylaniline (BBBA) doped by multiwalled carbon nanotubes

The phase transitions in smectogenic liquid crystal BBBA (4-butoxybenzylidene-4′-butylaniline) doped by multi-walled carbon nanotubes (NTs) were studied by methods of optical transmission, differential scanning calorimetry (DSC), measurement of electrical conductivity and analysis of microscopic images. The concentration of NTs was varied within 0–1% wt. Non-monotonous (extremal) changes in temperature, enthalpies and half-width of the DSC peaks of transitions between different phases (smectics, nematic, isotropic) were observed for NT concentrations between 0.05 and 0.1% wt. A noticeable increase of electrical conductivity σ in the same concentration interval evidenced the presence of percolation transition and formation of conductive NT networks. The detailed analysis of σ behavior in the whole concentration interval 0–1% wt revealed the presence of a fuzzy type percolation with multiple thresholds in the studied BBBA + NT suspensions. The percolation behavior was strongly dependent on the temperature, and a noticeable step-like drop of σ in the vicinity of isotropic-nematic transition was observed after the multiple heating–cooling cycles.

Age splitting of the La(Fe1−xSix)13Hy first order magnetocaloric transition and its thermal restoration

The La(Fe1−xSix)13Hy system has a first order ferromagnetic phase transition with a large magnetocaloric effect for 0.11 < x < 0.13. Such materials produced the highest currently published cooling power of a magnetic refrigerator. Adjusting the H content, y allows selection of any Curie point Tc from ∼200 K to 330 K, but hydrogen-unsaturated material (y < 1.6) with a first order transition exhibits an unusual instability. If La(Fe1−xSix)13Hy is held within a few K of its initial Tc, an initially single magnetic transition, with a sharp differential scanning calorimetry peak, gradually splits into two transitions separated by a large temperature interval. The ultimate splitting interval depends almost linearly on (1.6-y) and Tc. If the material is held more than 10 K above or below Tc, an initially sharp transition is retained, and a split transition is restored to its original sharp single transition. The recovery rate increases with temperature. For temperatures above 320 K, the recovery rate is rapid enough to allow overnight recovery of magnetocaloric material that is in a split state. This method was employed to maintain high performance of La(Fe1−xSix)13Hy in a magnetic refrigerator. In order to verify that the recovery process involves the macroscopic movement of hydrogen within the solid, a portion of 0.2 mm diameter particle material with a split transition was ground into particles of 0.05 mm diameter. The unground 0.2 mm particles and the ground 0.05 mm particles were held at 13 K above Tc. The 0.3 mm particles recovered their initial single transition, but the 0.05 mm particles, when examined as a group, retained their split line, presumably because they had been separated into particles with differing total hydrogen fraction y.

New Approach To Study Starch Gelatinization Applying a Combination of Hot-Stage Light Microscopy and Differential Scanning Calorimetry

To overcome the difficulty of the original polarizing microscope-based method in monitoring the gelatinization of starch, a new method for dynamically monitoring the gelatinization process, integral optical density (IOD), which was based on the digital image analysis technique, was proposed. Hot-stage light microscopy and differential scanning calorimetry (DSC) techniques were coupled to study the dynamic changes of three types of starches: type A (corn starch), type B (potato starch), and type C (pea starch), during the gelatinization process in an excess water system. A model of response difference change of crystallite could represent the responding intensity of crystallization changes in the process of starch gelatinization. Results demonstrated that three crystalline types of starch underwent a process of swelling, accompanied with gradual disappearing of the crystallite. This difference was mainly associated with the diversity and composition of the starch structure. The IOD method was of advantage compared to the previous traditional methods that are based on a polarization microscope, such as counting the particle number and calculating polarization area methods, because it was the product of two parameters: optical density and area, which would be a response of both light intensity and area of birefringence light. The single peak in DSC corresponded to the combination of crystalline helix-helix dissociation and the reduction of the molecule helix-coil transition, while the gelatinization degree measured by the IOD method mainly corresponded to the helix-helix dissociation. The gelatinization mechanism could be revealed clearer in this study.

English

  Collagen is a major structural protein of connective tissues. It can be used as a prosthetic biomaterial applicable to artificial skin, tendon ligaments and development collagen implants. In the present study, an attempt was made to isolate and characterize collagen from the marine sponge, Spirastrella inconstans. The total protein content of sponge collagen was relatively high (32%). While determining the molecular weight of crude and purified collagen through sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), the crude showed three bands (80, 60 and 59 kDa molecular weight) and purified showed only a single band (58 kDa). The structural properties were analyzed by using fourier transform infra red (FT-IR) spectrum and the stability of collagen was also given the single transition peak in differential scanning calorimetry (DSC). The microstructure of sponge collagen showed highly porous and interconnected scaffolds in scanning electron microscopic (SEM) analysis.   Key words: Collagen, Spirastrella inconstans, SDS-PAGE, Fourier transform infrared (FT-IR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM)

Disulfide bond-stabilized physical gels of an asymmetric collagen-inspired telechelic protein polymer

We designed and produced an asymmetric collagen-inspired telechelic protein polymer with end blocks that can form triple helices of different thermal stabilities. Both end blocks consist of a motif that can form triple helices at low temperature, but one of these blocks carries an additional cysteine residue at the end. The cysteine residues can form disulfide bridges under oxidizing conditions, leading to dimer formation. This effectively stabilizes the triple helices, resulting in a double melting peak in differential scanning calorimetry: one corresponding to helices without disulfide bridges and one at significantly higher temperature, corresponding to stabilized helices. Under reducing conditions, the disulfide bridges are broken and the molecule behaves similarly to the symmetric variant. We find that these disulfide bridges also lead to an increase of the elastic modulus of the helical polymer network, probably because the number of helices in the system increases and also the disulfide bridges can crosslink different triple helical nodes.

Cononsolvency Revisited: Solvent Entrapment by N-Isopropylacrylamide and N,N-Diethylacrylamide Microgels in Different Water/Methanol Mixtures

Aqueous dispersions of homo- and copolymer microgels of N-isopropylacrylamide (NiPAm) and N,N-diethylacrylamide (DEAm) with different compositions are temperature-dependently studied by means of proton nuclear magnetic resonance spectroscopy (1H NMR) and differential scanning calorimetry (DSC). Furthermore, the effect of varying the solvent composition by adding methanol is investigated. Methanol addition leads to a broadening of the thermally induced volume phase transition in case of NiPAm-containing samples, as confirmed by DSC. At the same time, the width of transition approaches the one of neat PDEAm. Two different solvent species, namely bulk-like and restricted solvent, are observed as separate lines in 1H NMR experiments when the gels deswell. The restricted nature of the second species is affirmed by pulsed field gradient (PFG) NMR self-diffusion experiments. The temperature Tsplit from which on the restricted species is found cannot be directly related to the volume phase transition temperature determined by DSC. The difference between Tsplit and the DSC peak temperature changes depending on the NiPAm-content of the microgel. An increase in the shift difference between the two solvent signals with temperature indicates a continuous change of the restricted solvent environment. At even higher temperature, the shift difference of restricted and bulk solvent approaches asymptotically a constant value. In general, the observed effects of methanol addition are consistent with an increasing complexation of the amide protons of the microgel (originating from the NiPAm units) with methanol. In contrast, poly(DEAm) does not show any anomaly concerning transition width and Tsplit upon methanol addition. This is attributed to the lack of amide protons. The results indicate that the presence of cononsolvency can be explained by the presence of the amide proton.

CALORIMETRIC DETERMINATION OF PHOSPHOLIPID-MELITTIN INTERACTIONS

The effect of melittin incorporated into the phospholipid bilayer DPPC at mole fractions up to 3.75 mol% have been investigated. The study reveals a considerable influence of melittin on the phase transition profile and volumetric properties of the DPPC bilayer. The temperature dependence of the coefficient of expansion, a , and the volume fluctuations of DPPC – melittin bilayer membranes in their different transition phases were determined by using pressure perturbation calorimetry (PPC), a relatively new and efficient technique, and differential scanning calorimetry (DSC). The experiments were carried out in the temperature range from 10 to 85 °C. Incorporating melittin up to 1.25 mol% into the lipid bilayer abolishes the pretransition. Remarkably, there is no shift in the transition temperature up to 2.5 mol% melittin, while more than one shoulder is observed at the low-temperature side of the DSC peak for 3.75 mol%, and a slight shift in melting temperature, T m to 32 o C. This could be linked to the lytic property of melittin at these high peptide concentrations.

High temperature thermal stability of ultrafine-grained silver processed by equal-channel angular pressing

The high temperature thermal stability of the ultrafine-grained (UFG) microstructures in low stacking-fault-energy silver was studied by differential scanning calorimetry (DSC). The UFG microstructures in two samples having purity levels of 99.995 and 99.99 at.% were achieved by four passes of equal-channel angular pressing at room temperature. The defect structure was studied by electron microscopy, X-ray line profile analysis, and positron annihilation spectroscopy before and after the exothermic DSC peak related to recovery and recrystallization. The heat released in the DSC peak was correlated to the change of defect structure during annealing. It was found for both compositions that a considerable fraction of stored energy (~15–20 %) was retained in the samples even after the DSC peak due to the remaining UFG regions and a large density of small dislocation loops in the recrystallized volumes. The larger impurity level in Ag yielded a higher temperature of recrystallization and a lower released heat. The latter observation is explained by the much lower vacancy concentration before the DSC peak which is attributed to the segregation of dopants at grain boundaries resulting in a smaller free volume in the interfaces.

Fast-scan vs conventional differential scanning calorimetry (DSC) techniques in detection of crystallization events of tolbutamide–polyethylene glycol composite

This study investigated the capacity of fast-scan (400 °C min−1) against conventional (10 °C min−1) differential scanning calorimetry (DSC) techniques to track crystallization phenomenon in tolbutamide–polyethylene glycol 3000 composites prepared by hot melt method (mass ratios 1:1, 1:5, and 1:9) and stored at 25 and 75 % relative humidities. Drug crystallization in composites was indicated by X-ray diffractometry (XRD) and scanning electron microscopy characterization over 40 days storage. With reference to XRD as gold measurement standard, fast-scan DSC could not map the crystallization events of composites (Pearson correlation: fast-scan DSC peak temperature and enthalpy versus XRD peak intensity and area, p > 0.05). Conventional DSC was able to indicate marked drug crystallization through an increase in endothermic enthalpy value of peaks at high temperature regimes between 250 and 360 °C due to formation of high melting point crystal form.

Ferroelectric Transition of Sr5SmTi3Nb7O30 Tungsten Bronze Ceramics Investigated Using Differential Scanning Calorimetry and Raman Scattering

Ferroelectric transition of Sr5SmTi3Nb7O30 tetragonal tungsten bronze ceramics was investigated using dielectric characterization, differential scanning calorimetry (DSC), and the in situ Raman scattering. The first‐order ferroelectric transition was indicated around 200°C by the dielectric peak and the endothermic DSC peak on heating. The ferroelectric transition exhibited large thermal hysteresis and severe depression of the Curie–Weiss temperature (T0), where the transition peak did not show up on cooling in both the permittivity and DSC curves. The thermal hysteresis was attributed to the complex nature of the tungsten bronze structure. According to the DSC results, gradual recovery of the endothermic peak occurred after aging at 20°C, indicating the gradual stability of the ferroelectric phase after cooling from the high temperature paraelectric phase. Meanwhile, anomalies in the Raman spectra were also observed around 200°C, corresponding to the ferroelectric transition. Mechanism of the ferroelectric transition in Sr5SmTi3Nb7O30 ceramics was discussed according to the variation of the external and internal Raman modes with increasing temperature.

Thermoanalytical study of linkage isomerism in coordination compounds

The non-isothermal differential scanning calorimetry (DSC) experiments revealed that linkage isomerization of both pure trans-[Co(en)2(ONO)2]PF6 (dinitrito isomer) and trans-[Co(en)2(NO2)2]PF6 (dinitro isomer) occurs in the solid state at elevated temperatures. The process was found to be exothermic for the dinitrito isomer and endothermic for dinitro isomer. The pure isomers could be considered to be in metastable states at ambient temperatures which would be converted to an equilibrium mixture of both isomers (stable state) upon heating. Since the isomerization of both isomers may be described as a two stages process, the corresponding DSC peaks have been resolved into two peaks by means of nonlinear curve fitting tools of PeakFit® software. The resolution of the peaks helped us to determine enthalpy changes of stepwise isomerization of both isomers. A first-order initial rate and Kissinger methods have been employed to estimate kinetic parameters of the stepwise isomerization reactions. The Kissinger method provided more reliable kinetic results. The high activation energy and positive entropy changes of isomerization of both isomers are considered as indication of a dissociative mechanism in solid state.

Thermal Stability of the R Phase of a Rapidly Solidified Ti-47.3Ni (at%) Alloy

Transformation behavior of rapidly solidified Ti-47.3Ni (at%) alloy ribbons and thermal stability of the R phase in the ribbons were investigated by means of differential scanning calorimetry (DSC), X-ray diffraction, and transmission electron microscopy. Rapidly solidified Ti-47.3Ni alloy ribbons showed the two-stage B2-R-B19' martensitic transformation behavior. The B2-R transformation in the ribbons was observed even after annealing at 1,223 K, which was attributed to the fact that a specific orientation relationship between Ti 2Ni and matrix in the ribbons is maintained after annealing at 1,223 K. The DSC peak temperature of the B2-R transformation (TR*) decreased with raising annealing temperature, which was attributed to the increased volume fraction of Ti2Ni, thus causing an increased Ni content in the matrix.

Kinetic evaluation of non-isothermal crystallization of oxidized extra virgin olive oil

Abstract In this study, accelerated storage tests were carried out at 60 °C up to 20 weeks on three extra virgin olive oils (Evoos) with different total phenol contents and fatty acid compositions (named as EvooA, EvooB, and EvooC). Their oxidative statuses, evaluated by means of primary oxidation value and total phenolic content, were related to both the shapes of differential scanning calorimetry (DSC) cooling curves and thermal properties. DSC cooling curves were all deconvoluted as crystallization occurs in a quite narrow range, and the single steps are not well separated. The first deconvoluted DSC peak for the three samples tested, which occurs in the temperature interval between −45 °C and −30 °C, can probably be ascribable to the crystallization of tri-unsaturated triacylglycerols. A non-isothermal crystallization kinetic procedure, derived by the well-known isothermal Avrami equation, combined with the method of Ozawa, was applied to the first deconvoluted DSC peak only by processing the data rel...

Liquid crystalline properties of new unsymmetrical compounds with benzothiazole core detected by TG/DSC-POM-XRD

Thermal properties of two azomethine liquid crystals with a benzothiazole core were synthesized and investigated by applied Mettler-Toledo AG equipment (TG/DSC). Azomethines with benzothiazole core was obtained by nucleophilic addition of benzothiazole-2-car- boxaldehyde in N,N-dimethylacetamide (DMA) solution with 4-(heptadecafluoroctyl)aniline (BTA1) or 4-hexa- decylaniline (BTA2). The differential scanning calorimetry (DSC) was employed to evaluate their phase transitional behavior. Variable heating and cooling rates were used to study liquid crystalline properties of azomethines with benzothiazole core. Compound BTA1 exhibited liquid crystalline properties, while BTA2 is non-mesogenic. Three or four endothermic DSC peaks were observed for both compounds during heating process with the rate 0.5 C/min. The mesophase was identified and confirmed by XRD study and polarized optical microscopy (POM) too. The thermal stability was determined by thermo- gravimetric analysis (TG). The temperatures of 5% mass loss (T5%) of BTA1 and BTA2 range from 212 to 317 Ci n nitrogen.