A differential scanning calorimetric study of cysteine hydrochloride monohydrate

An irreversible phase change, ΔH (transition) = 5.44 ± 0.11 kcal mol^?1 at 337.1 ± 0.3 K has been confirmed in L-(+)-cysteine hydrochloride monohydrate. Phase transitions resulting from thermal pretreatment are also reported and discussed.     

Origins of endothermic peaks in differential scanning calorimetry

The origins of multiple peaks observed by differential scanning calorimetry have been examined in detail for a linear polyethylene fraction crystallized from dilute solution and for bulk-crystallized copolymers of ethylene. At least two major bases are demonstrated. One is melting–recrystallization; the other a consequence of the distribution of crystallite sizes. The melting–recrystallization process, however, often only yields one endothermic peak. This peak is therefore not characteristic of the original crystallites present. In these situations complementary methods need to be used to determine the melting temperature. We have complemented the calorimetric studies with measurement of the crystallite size distribution as determined from the Raman low frequency acoustical mode spectra. A major increase occurs cooperatively in the crystallite size distribution during the initial melting. Most importantly, we have also been able to make a direct comparison between the interfacial free energies of thin crystallites formed from dilute solution and from bulk-crystallized linear polyethylene.     

The calorimetric calibration of differential scanning calorimetry cells

In this paper it is shown that in many cases enthalpy determinations can be carried out with a precision <1%. The influences of various sample and instrumental properties are described. The enthalpies of 24 compounds with 30 phase changes (polymorphic transitions or melting points) were redetermined. Twelve of the compounds with 15 transitions in the temperature range 0?670°C are selected and recommended for calorimetric DSC calibration. The linearization of the calibration curve as stated by the manufacturer of the instrument employed was fully confirmed.     

A differential scanning calorimetric study of some phenol derivatives

Differential scanning calorimetry has been applied to derive the fusion enthalpies and entropies of series of mono and dimethylphenols, mono and dichlorophenols, and mono and dinitrophenols.

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Zusammenfassung DSC wurde verwendet zur Ermittlung der Schmelzenthalpie und Entropie der Reihen von Mono- und Dimethylphenolen, Mono- und Dichlorphenolen, Mono- und Dinitrophenolen.

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A differential scanning calorimetric study on phase transformations of HgI2

A quantitative study of the different factors that influence the- transformation of mercuric iodide was carried out with differential scanning calorimetry. The transformation temperature and the peak width during the heating of the material were followed. An attempt was made to explain the experimental results.

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Zusammenfassung Mittels Differential-Scanning-Kalorimetrie wurde der Einfluss verschiedener Faktoren auf die- Umwandlung von Quecksilberjodid quantitativ untersucht. Dabei wurde die Umwandlungstemperatur und die Signalbreite beim Erhitzen der Substanz beobachtet. Es wurde ein Versuch unternommen, die experimentellen Ergebnisse zu erklären.

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A differential scanning calorimetric study on phase transformations of HgI2

The influence of stoichiometry on the mercuric iodide to transformation temperature was studied in a limited region around the exact stoichiometry. It is concluded that although this influence is small, the transformation temperature has its highest value at the exact stoichiometry composition.

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Zusammenfassung In einem begrenzten Intervall in der Nähe der exakten Stöchiometrie von Quecksilberjodid wurde der Einfluß der Stöchiometrie auf die/ß Umwandlungstemperatur untersucht. Es konnte festgestellt werden, daß dieser Einfluß zwar gering ist, die Umwandlungstemperatur ihren größten Wert jedoch bei der exakten Stöchiometrie erreicht.

     

A differential scanning calorimetric study on the irreversible thermal unfolding of concanavalin A

A differential scanning calorimetry study on the thermal denaturation of concanavalin A at pH 5.2 where it exists in the dimeric form was carried out. The calorimetric transitions were observed to be irreversible and the transition temperature of the protein increased with increasing scan rate, indicating that the thermal denaturation process is under kinetic control. The thermal unfolding, and its scan rate dependence could be explained according to the kinetic scheme with k as first-order kinetic constant whose change with temperature is given by the Arrhenius equation. Using this model, rate constant as a function of temperature and activation energy of the process have been calculated. The average activation energy of the kinetic process using different approaches is 129±10 kJ mol⁻¹. The differential scanning calorimetric results on transition temperatures and calorimetric enthalpies supported by intrinsic fluorescence indicate that the irreversibility in the calorimetric transitions of concanavalin A includes a combination of post-transition aggregation, chain separation and loss of cofactor.     

A differential scanning calorimetric study of phase transitions in polysubstitutedn-alkylammonium halides

A DSC investigation of severaln-alkylammonium salts is reported. The results of this investigation can be used to help decide which of several crystalline forms should be studied by X-ray diffraction for the best correlation between the liquid and solid states.

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Zusammenfassung Es wird über eine DSC-Untersuchung verschiedenern-Alkylammoniumsalze berichtet. Die Ergebnisse dieser Untersuchung können zur Entscheidung beitragen, welche von mehreren Kristallformen durch Röntgendiffraktion untersucht werden sollten um die beste Korrelation zwischen den flüssigen und festen Zuständen zu erzielen.

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Résumé On communique les résultats d'une étude par analyse calorimétrique différentielle (DSC) de divers sels den-alkylammonium. Les résultats de cette étude donnent des indications pour le choix des formes cristallines qui nécessitent d'être étudiées par diffraction des rayons X afin d'obtenir la meilleure corrélation entre les états liquides et solides.

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N- . .

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Visiting Professor of Chemistry, 1973–1974, Hebrew University, Jerusalem, Israel.

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This investigation was partially supported by the National Science Foundation. The hospitality of the Department of Inorganic and Analytical Chemistry of the Hebrew University is gratefully acknowledged. The authors thank Prof. I. Mayer and A. S. Kertes of the Hebrew University for suggesting this problem and for kindly furnishing samples of then-alkylammonium halides.     

A differential scanning calorimetric study of the radical polymerization of N-vinylpyrrolidone in dimethylformamide

Polymerization of N-vinylpyrrolidone (NVP) in dimethylformamide was studied by differential scanning calorimetry (DSC). The concentration of NVP was 0.75 M, that of the radical initiator (azobisisobutyronitrile) 0.01 or 0.02 M. For proper evaluation of scanning thermograms, it was necessary to correct for incomplete monomer conversion due to premature initiator exhaustion and to consider the instantaneous initiator concentration. If these points were allowed for in the computations, activation parameters agree well with those obtained from isothermal thermograms. The values for the overall activation energy were E_a = 82 and 84 kJ/mol, and those for the pre-exponential factor $\text{Z = 6 × 10}{}^{\mathrm{?9}}\text{and}\text{13 × 10}{}^{\mathrm{?9}}\text{(}\text{mol/l}\text{)}{}^{\mathrm{<mtext>?1</mtext><mtext>2</mtext>}}\text{.}\text{sec}{}^{\mathrm{?1}}$, obtained from the scanning (dynamic) and the isothermal method, respectively.     

Thermogravimetric analysis and differential scanning calorimetric studies on nanoclay-filled TPU/PP blends

Thermal stability of ester-thermoplastic polyurethane (TPU)/polypropylene (PP) and ether-TPU/PP blends was evaluated by thermogravimetric studies. Thermal studies were made as a function of blend ratio. Effects of compatibilization using MA-g-PP and nanoclay addition on thermal stability were evaluated. Mass loss at 400 °C was found to decrease with increasing PP content were determined. Finally the compatibility and crystallization behavior of the blends were studied by differential scanning calorimetry. Compared to the ether-TPU blend nanocomposites, the ester-TPU blends showed better compatibility and thermal stability.     

A differential scanning calorimetric study of phase transitions in Na2SO4

The results of a differential scanning calorimetric study of the transitions involving the various polymorphs of Na₂SO₄ are described. They are discussed in the light of their crystal structures and also in conjunction with more recently published data regarding these transitions.

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Zusammenfassung Die Ergebnisse einer mit Differentialabtastkalorimetrie durchgeführten Untersuchung der Übergänge verschiedener Polymorphe von Na₂SO₄ werden beschrieben. Sie werden im Hinblick ihrer Kristallstrukturen und im Zusammenhang mit verschiedenen unlängst veröffentlichten Daten bezüglich dieser Übergänge diskutiert.

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Résumé On décrit les résultats de l'étude, effectuée par analyse calorimétrique différentielle, des transitions mettant en jeu les diverses formes polymorphes de Na₂SO₄. Les résultats sont discutés en tenant compte des données récemment publiées sur ces transitions.

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Effects of exposure of chloroquine picrate to the sun: A differential scanning calorimetric study

In a continuing study of the effect of exposure of chloroquine and its salt derivatives to the sun, the picrate was investigated. The picrate gives a sharp endothermic effect of melting at 209.2 °C, before it decomposes, to give an exothermic peak at 255.6 °C. The endothermic peak of melting at 209.2 °C was found suitable for the quantitative determination of chloroquine picrate in sun-exposed samples.

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Zusammenfassung In Fortführung einer Untersuchung über Veränderungen von Chloroquin und dessen Derivaten, wenn diese der Sonne ausgesetzt werden, wurden die Pikrate untersucht. Bei den Pikraten werden ein scharfer, dem Schmelzvorgang zuzuschreibender Effekt bei 209.2 °C und ein mit der Zersetzung einhergehender exothermer Peak bei 255.6 °C beobachtet. Der endotherme Peak bei 209.2 °C erwies sich als geeignet zur quantitativen Bestimmung von Chloroquinpikrat in der Sonne ausgesetzten Proben.

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, . 209,2 ° 255,6 ° . , 209,2 ° , .

     

Differential scanning calorimetric examination of the tracheal cartilage after primary reconstruction with differential suturing techniques

Summary Resection and subsequent end-to-end anastomosis of the windpipe is a tried-and-tested acceptable method for the surgical treatment of segmental defects. There are a variety of different techniques for tracheal end-to-end anastomosis, but controversial reports highlight the fact that the suturing technique of the anastomosis is still subject of debate. We aimed to show the postoperative effects of the continuous and simple interrupted suturing technique respectively on the tracheal cartilage using differential scanning calorimetry. Transsection and subsequent reanastomosis of the cervical trachea was performed in 14 adult beagle dogs. The trachea was anastomized with continuous or simple interrupted sutures respectively depict no change in microcirculation after the resection of the trachea, but significant decrease following the completion the anastomosis with continuous sutures. Conventional histological analysis did not show any marked postoperative change in the tracheal cartilage but our DSC scans clearly demonstrated the differences between the intact cartilages and the ones involved in the anastomosis.     

Differential scanning calorimetric examination of the tracheal cartilage after primary reconstruction with differential suturing techniques

Objective

Long segmental tracheal defects often lead to life threatening clinical conditions. Treatment of these lesions still represents an unsolved surgical challenge. The aim of the study was to test the effect of continuous and simple interrupted suturing in the replacement of long segment tracheal defects using polytetrafluoroethylene (PTFE) vascular prosthesis in a rabbit model.

Methods

2 cm long segment of the cervical trachea was resected in 20 New Zealand rabbits. The trachea was replaced with reinforced polytetrafluoroethylene vascular graft. The anastomoses were performed telescopically using continuous (group I, n = 10) or simple interrupted sutures (group II, n = 10). Laser Doppler measurements were taken before the resection and following the anastomoses. Length of survivals were noted, the patency and microscopical pattern of the anastomoses were evaluated. Calorimetric examinations were performed to detect possible structural changes in the tracheal cartilage.

Results

Following the resection local microcirculation decreased by 9 ± 4%. The anastomoses caused a significant decrease of 29% in group I (p = 0.02) and 13% in group II. The mean survival was 58 ± 17 and 135 ± 25 days, respectively. Calorimetric results showed no change after the resection, but significant shift in melting temperature and calorimetric enthalpy proved the presence of structural changes of the cartilage in group II.

Conclusions

We saw significant lowering of microcirculation following continuous sutures, while simple interrupted stitches produced only moderate decrease. We found that interrupted suture technique is superior to the continuous technique causing only moderate damage to the tracheal anastomosis.     

Positron annihilation lifetime and differential scanning calorimetric study of immiscible NBR/PE blends

The temperature dependence of the mean size of nanoscale free‐volume holes, 〈V_h〉, in polymer blend system consisting of polar and nonpolar polymers has been investigated. The positron lifetime spectra were measured for a series of polymer blends between polyethylene (PE) and nitrile butadiene rubber (NBR) as a function of temperature from 100 to 300 K. The glass transition temperatures (T_g) for blends were determined from the ortho‐positronium (o‐Ps) lifetime τ₃ and the mean size of free‐volume holes 〈V_h〉 versus temperature as a function of wt % of NBR. The T_gs estimated from the PALS data agree very well with those estimated from DSC in view of different time scales involved in the two measurements. Both DSC and PALS results for the blends showed two clear T_gs of a two‐phase system. Furthermore, from the variation of thermal expansivity of the nanoscale free‐volume holes, the thermal expansion coefficients of glass and amorphous phases were estimated. Variations of the o‐Ps formation probability I₃ versus temperature for pure PE and blends with low wt % of NBR were interpreted on the basis of the spur reaction model of Ps formation with reference to the effects of localized electrons and trapping centers produced by positron irradiation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 227–238, 2009     

Gas chromatographic and differential scanning calorimetric studies of new bonded silicas in connection with transition phenomena

Summary In order to give a molecular interpretation to the phase transition observed with densely bonded octadecyl-silicas in reversed phase liquid chromatography (RPLC) as well as in gas chromatography (GC), nine new bonded silicas were prepared including grafts with polar groups at the extremities of long spacers (18 carbon atoms). The interpretation is simplified by using large-pore macroporous substrates and inverse GC in conjunction with differential scanning calorimetry (DSC) as the test method. A phase transition is observed in almost all cases, but the temperature range is lower and more extended in comparison to the dimethyloctadecyl reference silica. An interpretation of the phase transition is given, based on the folding of the chains and the resulting autodensification of the layer.     

A novel differential scanning calorimetric method to study the complexation of β-cyclodextrin with steroid in solid state

This communication demonstrates that, by simply minotiring the evaporation of water molecules included in β-cyclodextrin cavity, complexation of β-cyclodextrin with steroid in solid state can be studied. The reported method is simple, rapid and novel.     

Thermogravimetric, differential scanning calorimetric and experimental thermal transport study of MWCNT/NBR nanocomposites

Pristine multiwalled carbon nanotubes (MWCNTs) were impregnated in acrylonitrile butadiene rubber (NBR) using internal dispersion kneader and two roller mixing mill to investigate the effects of various nanotubes concentrations on the thermal transport/stability of rubber nanocomposites. Thermal conductivity (λ _N) and thermal impedance (R) measurement experimental setups were established according to ASTM E1225-99 and D5470-03. The 1 mass % addition of MWCNTs in the polymer matrix has enhanced R up to 44 % and reduced λ _N of the rubber nanocomposite up to 40 % compare to the base composite formulation. Thermal decomposition and differential thermal analyses of the fabricated composite specimens simulate that the thermal stability and endothermic capability are augmented with increasing the nanotubes contents in the host matrix. The progressive incorporations of carbon nanotubes into the rubber matrix have efficiently influenced the composite specimens regarding glass transition, crystallization, and melting temperatures including their specific enthalpies. Scanning electron microscopy along with the energy dispersive spectroscopy was used to analyze MWCNTs dispersion in NBR matrix, compositional analysis of the nanocomposite, and impregnated nanotubes.