Differential scanning calorimetry study of reactions of phenyl glycidyl ether with phosphoric acid

The reactions of phenyl glycidyl ether (PGE) with phosphoric acid in three molar ratios have been studied by means of DSC alone. The results obtained from isothermal measurements are as follows:H=–91.0 kJ/mole PGE(1:1 molar ratio);H=–100.5 kj/mole PGE (1:2/3 molar ratio).The DSC curves obtained from dynamic experiments are multipeaked and giveHvalues higher than those obtained from isothermal measurements. These results can be explained by taking into account the acid concentration, the different reactivities of the hydrogens of the phosphoric acid and the possibility that secondary reactions occur.

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Zusammenfassung Die Reaktion von Phenylglycidyläther (PGE) mit Phosphorsäure wurde bei drei verschiedenen molaren Verhältnissen allein mittels DSC untersucht. Isotherme Messungen ergaben folgende Werte:H=–91.0kJ/mol PGE (molares Verhältnis 1:1);H=–100.5 kJ/mol PGE (molares Verhältnis 3:2). Die bei dynamischen Experimenten erhaltenen DSC-Kurven weisen viele Peaks auf und ergebenH-Werte, die größer als die durch isotherme Messungen erhaltenen sind. Diese Ergebnisse können erklärt werden, wenn die Säurekonzentration, die unterschiedliche Reaktivität der Wasserstoffatome der Phosphorsäure und die Möglichkeit des Verlaufs sekundärer Reaktionen in Rechnung gestellt werden.

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Differential scanning calorimetry

This study was aimed to investigate the physicochemical changes induced in 200 nm extruded oligolamellar DPPC:DPPG (10:1) liposomes by freezing, followed by γ-irradiation, in the absence and presence of 5 mM stable cyclic nitroxide radicals, 2,2,6,6-tetramethylpiperidine-1-oxyl (Tempo) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (Tempol). The characterization is based on the use of differential scanning calorimetry (DSC) and was aimed to differentiate the contribution of freezing and γ-irradiation in the presence and absence of nitroxides. Liposomal preparations of DPPC/DPPG which have sub-, pre- and main-phase transitions in the temperature range (0°C<T _m<50°C) were used. Our results show that: (1) freezing modified and induced fusion to MLV as well as fission to SUV, (2) freezing did not fully prevent the radiation-induced changes in the thermotropic characteristics of the liposomes, and (3) Tempo and Tempol did not prevent the changes in thermotropic behavior caused as a result of freezing of the liposomal dispersion. These results demonstrate that DSC is a powerful and sensitive tool in both physical and chemical studies of lipid assemblies. This work was supported in part by the Szold Foundation, Jerusalem, Israel and United State-Israel Binational Science Foundation (grant 95/318 to Y.B.).     

Differential scanning calorimetry study of haemin thermal stability

A differential scanning calorimetry study of the thermal behaviour of haemin in N,N-dimethylformamide solution was carried out. The samples were scanned with different scan rates in the temperature range 25-130°C. The UV VIS spectrophotometry was used as assistant measurement method. The scan rate dependent and irreversible exothermic peaks were found. The activation energies of observed transitions were calculated assuming kinetically controlled process. The nature of thermal behaviour of haemin in DMF solutions is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Differential scanning calorimetry of irradiated polymers

DSC was used to study the influence of fast electron irradiation on the molecular mobility and melting of semicrystalline polymers and copolymers of ethylene and of fluorocopolymer. The heat capacity-temperature dependences obtained in the range from 100 K to 500 K revealed the specific features of the irradiation effect on four relaxational transitions associated with the appearance of segmental motion in different molecular elements of the disordered regions in the polymer. The pronounced dependence of the radiation stability of crystallites on the thermal prehistory of the object under study was found. The results were interpreted on the basis of the decisive role of the molecular mobility and free volume for the predominance of the radiation cross-linking of the molecules. Correlations were established between the characteristics of the thermal transitions and the mechanical properties of the irradiated polymers.     

Differential scanning calorimetry of chlorinated polyethylenes

The heats of fusion of low-density polyethylene and chlorinated polyethylenes of varying chlorine content have been investigated by differential scanning colorimetry (DSC). Linear correlations are found between the chlorine content and the apparent heat of fusion, crystallinity, and the maximum specific heat measured in the temperature range 90–120°C. The effect of heat treatment on crystallinity is shown to be strongly dependent on the chlorine content of the polymers.     

Differential scanning calorimetry and fibre analysis

Differential scanning calorimetry is a technique capable of providing much useful information on the physicochemical properties of polymeric fibres. While it is currently used primarily in research, it is ideally suited for the routine analysis and quality control of fibres.     

Differential scanning calorimetry of spin-oriented polyester yarn

Polyester yarn spun over a range of wind-up speeds has been characterized using differential scanning calorimetry. Samples prohibited from shrinking during the thermal analysis show slightly smaller heats of fusion and crystallization and reduced cold crystallization temperatures than samples that are free-to-shrink, particularly in the intermediate wind-up speed region. One critical observation made is that the cold crystallization temperature reaches a minimum at some relatively low overall molecular orientation (n 0.020) and fails to decrease further. A likely explanation is that crystallization continuously removes polymer from the melt in the spinline in regions where the local orientation reaches some critically high value.

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Zusammenfassung Mit verschiedenen Aufspulgeschwindigkeiten gesponnenes Polyestergarn wurde durch DSC charackterisiert. Die während der tyermischen Analyse am Schrumpfen gehinderten Proben zeigen, besonders bei mittleren Aufspulgeschwindigkeiten, eine etwas geringere Schmelz- und Kristallisationswärme und niedrigere kalte Kristallisationstemperaturen als Proben, die ungehindert schrumpfen konnten. Die kalte Kristallisationstemperatur erreicht bei enier relativ niedrigen Gesamtmolekularorientierung (n 0.020) ein Minimum und nimmt nicht weiter ab. Wahrscheinlich ist, dass durch die Kristallisation das Polymer in den Bereichen, in denen die lokale Orientierung einen kritischen Wert erreicht, kontinuierlich aus der Schmelze entfernt wird.

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The author appreciates the input provided by Dr. R. M. Mininni and the help of Dr. W. E. Bessey in fiber spinning and Ms. E. Fernekess in thermal analysis. The author is grateful to Celanese Corporation for allowing publication of this work.     

Differential scanning calorimetry study of Ge1−xSnxSe2.5 glasses

The glass-forming tendency and specific heat in ice cold water-quenched Ge_1?xSn_xSe_2.5 glassy alloys with 0H _f, the heat ΔH _c associated with the crystallization of an amorphous phase and the glass transition temperatureT _g were deduced from the DSC curves. The composition dependence of glass forming ability,T _g and crystallization behavior has been discussed.     

Differential scanning calorimetry study of the solidification sequence of austenitic stainless steel

The solidification sequence of austenitic stainless steels can be predicted with thermodynamic calculations. Another way is to use models where the value of the Cr_eq./Ni_eq. ratio determines the relationship between the solidification mode and the composition factor. In this study the solidification of AISI 304LN stainless steel at different cooling rates was studied using differential scanning calorimetry (DSC). The samples were linearly heated above the liquidus temperature to 1550 °C at heating rates of 5, 10, and 25 K/min. The solidification (cooling) scans from 1550 °C involved the same selected ramps. After the DSC measurements the samples were metallographically analyzed to reveal the variations in the solidification microstructures. The microhardness of the solidified samples was also measured. It was found that the cooling rate critically influenced the solidification. The solidification behavior, which depends on the cooling rate, determines the evolution of the microstructure. At the slowest cooling rates a relief-cell morphology was observed, and at the fastest cooling rate the formation of dendrites was evident. With an increasing cooling rate the liquidus temperature decreased and the reaction enthalpy increased.     

Differential scanning calorimetry study of blood serum in chronic obstructive pulmonary disease

Differential scanning calorimetry (DSC) has been applied for studies of blood serum from patients sick with chronic obstructive pulmonary disease (COPD). The denaturation of serum proceeds as endothermic process over the temperature range 45–85 °C. Distinct changes in the shape of DSC curves have been observed for serum from patients with severe stage of COPD (treated with inhaled corticosteroids) relative to serum from healthy individuals. The first moment of the thermal transition with respect to the temperature axis shifts from the normal value of 63.9 ± 0.3 to 65.3 ± 0.7 °C and to 67.6 ± 1.6 °C for early and advanced stages of disease, respectively. The results of our studies suggest age dependence of blood serum denaturation transition.     

Differential scanning calorimetry study of complex fluorides of titanium,niobium and tantalum

The enthalpy and temperature of the sublimation of nitrosyl fluoride or nitryl fluoride—titanium, niobium and tantalum fluoride adducts were determined from DSC measurements. A closed-cell DSC technique was employed to determine the enthalpies and temperatures and to study the dissociation reactions of some of these adducts.     

Differential scanning calorimetry as an analytical tool in the study of drug-cyclodextrin interactions

The interactions of trimethoprim, sulphadiazine and sulphamethoxazole with natural (a- b-, g- ) and amorphous (RAMEB) or crystalline (DIMEB) methylated b-cyclodextrins were investigated both in aqueous solution (using phase-solubility analysis) and in the solid state (using DSC supported by X-ray analysis). In particular, DSC studies enabled determination of the relative degree of crystallinity of each drug in its physical and ground mixtures with the different cyclodextrins on the basis of the variation of its heat of fusion in comparison with that of the pure drug. In all cases, the host cavity size was a prevalent factor for the inclusion complexation in liquid state. On the contrary, it had a negligible effect on solid-state interactions in terms of drug amorphization. DIMEB and RAMEB exhibited similar performances in aqueous solution, showing that the presence of methyl-groups improved the complexing and solubilizing properties of b-cyclodextrin. However, DSC studies revealed that RAMEB was clearly more active in performing solid-state interactions, i.e. drug amorphization, and as stabilizing agent for the amorphous state brought forth. This revised version was published online in July 2006 with corrections to the Cover Date.     

Differential scanning calorimetry of univalent dihydrogen phosphates and arsenates

The high temperature phase relations (20°C) of LiH₂PO₄, NaH₂PO₄, KH₂PO₄, RbH₂PO₄, CsH₂PO₄, NH₄H₂PO₄, KH₂AsO₄, RbH₂AsO₄, CsH₂AsO₄ and NH₄H₂AsO₄ have been studied. All materials decompose at higher temperatures. Solid—solid transitions are studied when present and transition temperatures, transition enthalpies, decomposition temperatures, decomposition enthalpies and decomposition products are discussed.     

Differential scanning calorimetry of semiconducting As-Se glasses containing Sb

The compositional dependence of the glass transition temperature (T _g), and the temperature of the maximum rate of crystallization (T _p) of As-Se glasses containing Sb has been measured using non-isothermal DSC. The variation of these characteristic temperatures is found useful in interpreting the structural changes in As-Sb-Se glasses. The role of Sb in these glasses and its effect on the crystallization characteristics is analyzed.     

Differential scanning calorimetry of spun and drawn polyester yarn

Polyester yarn spun over a range of wind-up speeds and subsequently drawn at 373 K has been characterized by differential scanning calorimetry. Samples that are constrained from shrinking during the thermal scan respond differently than samples that are free-to-shrink. In the region of intermediate orientation, the constrained samples typically show a lower cold crystallization temperature: In the region of high orientation, the constrained samples typically show a higher melting temperature. The results are quantitatively similar to those based on fibers in which the orientation is imparted directly by high speed spinning.     

Differential scanning calorimetry (DSC) of semicrystalline polymers

Differential scanning calorimetry (DSC) is an effective analytical tool to characterize the physical properties of a polymer. DSC enables determination of melting, crystallization, and mesomorphic transition temperatures, and the corresponding enthalpy and entropy changes, and characterization of glass transition and other effects that show either changes in heat capacity or a latent heat. Calorimetry takes a special place among other methods. In addition to its simplicity and universality, the energy characteristics (heat capacity C _P and its integral over temperature T—enthalpy H), measured via calorimetry, have a clear physical meaning even though sometimes interpretation may be difficult. With introduction of differential scanning calorimeters (DSC) in the early 1960s calorimetry became a standard tool in polymer science. The advantage of DSC compared with other calorimetric techniques lies in the broad dynamic range regarding heating and cooling rates, including isothermal and temperature-modulated operation. Today 12 orders of magnitude in scanning rate can be covered by combining different types of DSCs. Rates as low as 1 μK s⁻¹ are possible and at the other extreme heating and cooling at 1 MK s⁻¹ and higher is possible. The broad dynamic range is especially of interest for semicrystalline polymers because they are commonly far from equilibrium and phase transitions are strongly time (rate) dependent. Nevertheless, there are still several unsolved problems regarding calorimetry of polymers. I try to address a few of these, for example determination of baseline heat capacity, which is related to the problem of crystallinity determination by DSC, or the occurrence of multiple melting peaks. Possible solutions by using advanced calorimetric techniques, for example fast scanning and high frequency AC (temperature-modulated) calorimetry are discussed.     

Differential scanning calorimetry of sodium and potassium nitrates and nitrites

Differential scanning calorimetry (DSC) experiments were performed with NaNO₃, KNO₃, (Na,K)NO₃, NaNO₂ and KNO₂ over the temperature range 350–990 K. Endothermic peaks, indicative of decomposition reactions, were observed to occur in the single salts above their melting points. The equimolar mixture of sodium and potassium nitrate did not decompose in the temperature range specified. The nitrites began to decompose at 800±10 K. Sodium nitrate began to decompose at 840±10 K and potassium nitrate began to decompose at 820±20 K. These results were compared with previously reported differential thermal analysis investigations of NaNO₃ and KNO₃.