Showing papers on "Differential scanning calorimetry published in 1999"
TL;DR: In this paper, Branch chain-length distributions of amylopectins were analyzed quantitatively using a high-performance anion-exchange chromatography system equipped with a postcolumn enzyme reactor and a pulsed amperometric detector.
Abstract: Structures and properties of starches isolated from different botanical sources were investigated. Apparent and absolute amylose contents of starches were determined by measuring the iodine affinity of defatted whole starch and of fractionated and purified amylopectin. Branch chain-length distributions of amylopectins were analyzed quantitatively using a high-performance anion-exchange chromatography system equipped with a postcolumn enzyme reactor and a pulsed amperometric detector. Thermal and pasting properties were measured using differential scanning calorimetry and a rapid viscoanalyzer, respectively. Absolute amylose contents of most of the starches studied were lower than their apparent amylose contents. This difference correlated with the number of very long branch chains of amylopectin. Studies of amylopectin structures showed that each starch had a distinct branch chain-length distribution profile. Average degrees of polymerization (dp) of amylopectin branch chain length ranged from 18...
1,381 citations
TL;DR: In this article, 1-alkyl-3-methylimidazolium tetrafluoroborate (TFLB) is described as an isotropic ionic liquid with an enantiotropic smectic A mesophase.
Abstract: Air- and water-stable 1-alkyl-3-methylimidazolium tetrafluoroborate salts with the general formula [Cn-mim][BF4] (n = 0–18) have been prepared by metathesis from the corresponding chloride or bromide salts. The salts have been characterised by 1H NMR and IR spectroscopy, microanalysis, polarising optical microscopy and differential scanning calorimetry. Those with short alkyl chains (n = 2–10) are isotropic ionic liquids at room temperature and exhibit a wide liquid range, whereas the longer chain analogues are low melting mesomorphic crystalline solids which display an enantiotropic smectic A mesophase. The thermal range of the mesophase increases with increasing chain length and in the case of the longest chain salt prepared, [C18-mim][BF4], the mesophase range is ca. 150 °C.
1,169 citations
TL;DR: Although ITC is particularly suitable to follow the energetics of an association reaction between biomolecules, the combination of ITC and DSC provides a more comprehensive description of the thermodynamics of an associating system.
Abstract: The principles of isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC) are reviewed together with the basic thermodynamic formalism on which the two techniques are based. Although ITC is particularly suitable to follow the energetics of an association reaction between biomolecules, the combination of ITC and DSC provides a more comprehensive description of the thermodynamics of an associating system. The reason is that the parameters DeltaG, DeltaH, DeltaS, and DeltaCp obtained from ITC are global properties of the system under study. They may be composed to varying degrees of contributions from the binding reaction proper, from conformational changes of the component molecules during association, and from changes in molecule/solvent interactions and in the state of protonation.
739 citations
TL;DR: In this article, the authors present a systematic study of structural modifications and hydrogen absorption-desorption kinetics of ball-milled magnesium hydride, and they show that after only 2 h of milling, a metastable orthorhombic (γ)-morphological phase is formed.
683 citations
TL;DR: The drying and oxidative degradation of linseed oil have been investigated through exposition of samples in form of thin films to indoor laboratory conditions, or treated at a constant temperature of 80°C, or with irradiation at wavelengths >295 mm as discussed by the authors.
395 citations
TL;DR: In this article, the authors investigated the thermal stability of prismatic Li-ion cells and their components and concluded that the heat generation from the decomposition of PE material and reaction of that with electrolyte initiates thermal runaway in a Li−ion cell, under thermally or abusive conditions.
Abstract: Thermal stability of fully charged 550 mAh prismatic Li‐ion cells (Sn‐doped carbon) and their components are investigated. Accelerating rate calorimetry (ARC) is used to determine the onset temperature of exothermic chemical reactions that force the cell into thermal runaway. Differential scanning calorimetry (DSC) and thermogravimetry analysis are used to determine the thermal stability of the cell's positive electrode (PE) and negative electrode (NE) materials from 35 to 400°C. The cell self‐heating exothermic reactions start at 123°C, and thermal runaway occurs near 167°C. The total exothermic heat generation of the NE and PE materials are 697 and 407 J/g, respectively. Heat generations of the NE and PE materials, washed in diethyl carbonate (DEC) and dried at ≈65°C under vacuum, are significantly lower than unwashed samples. Lithium plating increases the heat generation of the NE material at temperatures near the lithium melting point. Comparison of the heat generation profiles from DSC and ARC tests indicates that thermal runaway of this cell is close to the decomposition temperature range of the unwashed PE material. We conclude that the heat generation from the decomposition of PE material and reaction of that with electrolyte initiates thermal runaway in a Li‐ion cell, under thermally or abusive conditions. © 1999 The Electrochemical Society. All rights reserved.
374 citations
TL;DR: In this paper, the Zr57Nb5Al10Cu15.4Ni12.6 bulk metallic glass forming liquid is reinforced with WC, SiC, W, or Ta particles.
367 citations
TL;DR: In this article, three epoxy systems (DGEBA+mPDA, TGDDM+DDS, and Fiberite 934TM) were used to investigate glass transition temperature variation of epoxy under hygrothermal environment exposure.
352 citations
TL;DR: In this paper, the thermally induced phase separation of aqueous poly(N,N-diethylacrylamide) (PDEA) was studied by means of differential scanning calorimetry and UV−visible spectrophotometry.
Abstract: The thermally induced phase separation of aqueous poly(N,N-diethylacrylamide) (PDEA) was studied by means of differential scanning calorimetry and UV−visible spectrophotometry. The polymer was show...
315 citations
TL;DR: In this paper, a detailed study of the Nafion-water system has been performed using water sorption isotherm, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and FT-IR with the aim of investigating the state of water in the nafion membrane.
Abstract: A detailed study of the Nafion–water system has been performed using water sorption isotherm, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and FT-IR with the aim of investigating the state of water in the Nafion membrane. The last technique in particular can yield valuable information on molecular interactions, especially those involving water molecules. The first water molecules interact with sulfonic groups, forming hydronium H3O+ and –SO3- ions, while the following water molecules aggregate with H3O+ to form counter-ion clusters with five or six water molecules. Increasing the water content promotes cluster growth and cluster aggregation with the formation of a continuous water phase, where for every four molecules of water one has two hydrogen bonds, and each of the other three only one. All the sorption, calorimetric and infrared data agree with the proposed model of two non-interacting phase systems: the water-phase and the perfluoro-phase with sulfonic groups at the interphase. The only observed effects of water on Nafion polymer are sulfonic group dissociation and partial destruction of crystallinity associated in polymer swelling.
307 citations
TL;DR: In this paper, the solubilities of block copolymers were determined at 35°C and pressures up to 27 atmospheres in a systematic series of phase separated polyether-polyamide segmented block Copolymers containing either poly(ethylene oxide) [PEO] or poly(tetramethylene dioxide) [PTMEO] as the rubbery polyether phase and nylon 6 [PA6] or nylon 12 [PA12] as hard polyamide phase.
Abstract: The solubilities of He, H2, N2, O2, CO2, CH4, C2H6, C3H8, and n-C4H10 were determined at 35°C and pressures up to 27 atmospheres in a systematic series of phase separated polyether–polyamide segmented block copolymers containing either poly(ethylene oxide) [PEO] or poly(tetramethylene oxide) [PTMEO] as the rubbery polyether phase and nylon 6 [PA6] or nylon 12 [PA12] as the hard polyamide phase. Sorption isotherms are linear for the least soluble gases (He, H2, N2, O2, and CH4), convex to the pressure axis for more soluble penetrants (CO2, C3H8, and n-C4H10) and slightly concave to the pressure axis for ethane. These polymers exhibit high CO2/N2 and CO2/H2 solubility selectivity. This property appears to derive mainly from high carbon dioxide solubility, which is ascribed to the strong affinity of the polar ether linkages for CO2. As the amount of the polyether phase in the copolymers increases, gas solubility increases. The solubility of all gases is higher in polymers with less polar constituents, PTMEO and PA12, than in polymers with more polar PEO and PA6 units. CO2/N2 and CO2/H2 solubility selectivity, however, are higher in polymers with higher concentrations of polar repeat units. The sorption data are complemented with physical characterization (differential scanning calorimetry, elemental analysis, and wide angle X-ray diffraction) of the various block copolymers. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2463–2475, 1999
TL;DR: In this article, the X-ray diffraction and infrared spectroscopy (IR) analysis confirm that polystyrene macromolecules can be inserted between lamella layers and whose layer separation is consequently higher than in the polymer-free clay.
Abstract: Polystyrene-Na+-montmorillonite(PS-Na+-MMT) nanocomposites are prepared by a simple emulsion polymerization. The X-ray diffraction(XRD) and infrared spectroscopy (IR) analysis confirm that polystyrene(PS) macromolecules can be inserted between lamella layers and whose layer separation is consequently higher than in the polymer-free clay. The enhanced thermal properties of composites are measured by differential scanning calorimetry(DSC) and thermogravimetric analysis(TGA) thermogram and indicate that the glass transition and the decomposition onset temperature of obtained nanocomposites are found to be moved to the higher temperature region. The increased Young's modulus of the obtained nanocomposites is ascribed to the intercalation of PS in clay galleries as well as the fine dispersion of clay particles into the polymer matrix.
TL;DR: In this paper, a new class of materials has been synthesized, which showed a reversible capacity of and stable cycling, and differential scanning calorimetry studies showed much improved thermal stability of these materials in their totally charged states in contact with electrolyte.
Abstract: A new class of materials has been synthesized. The compound showed a reversible capacity of and stable cycling was demonstrated. Differential scanning calorimetry studies showed much improved thermal stability of these materials in their totally charged states in contact with electrolyte. The exothermic peak at in a charged electrode containing was drastically reduced asx increases in . No exotherm was observed below for in its totally charged state. We believe that the use of these materials will improve the overall safety of batteries. ©1998 The Electrochemical Society
TL;DR: In this article, the thermal behavior of variably separated flax and hemp fibres was characterized by means of thermogravimetric and differential scanning calorimetric analyses.
TL;DR: In this paper, the melting behavior of isothermally crystallized poly(butylene succinate) (PBS) has been investigated using differential scanning calorimetry (DSC) and wide-angle X-ray analysis.
Abstract: The melting behavior of isothermally crystallized poly(butylene succinate) (PBS) has been investigated using differential scanning calorimetry (DSC) and wide-angle X-ray analysis. The samples crystallized between 80°C to 100°C show middle endotherm at the position just before the high exotherm, while the others under 80°C show two endotherms (low and high). From the results of the melting peak vs. crystallization temperature plot, it was suggested that the middle endotherm corresponds to the melting process of the original crystallites and the high endotherms to the melting process of the recrystallized ones. As the DSC heating rate was increased, the peak temperature of the low and middle endotherms increased and that of the high endotherm decreased, indicating that the low endotherm was due to the original crystallites as well as the middle endotherm. Consequently, in the heating scan of PBS, the existence of two kinds of morphologically different crystallites as well as the process of melting and recrystallization becomes evident. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1357–1366, 1999
TL;DR: In this paper, a combination of differential scanning calorimetry and atomic force microscopy was used to study the crystallization, melting, and morphology of random ethylene/1-octene copolymers.
Abstract: Studies of the crystallization, melting, and morphology of random ethylene/1-octene copolymers by a combination of differential scanning calorimetry and atomic force microscopy are presented. Two d...
TL;DR: The thermal behavior of Nafion-117 membranes was investigated by thermogravimetric analysis (TG) and differential scanning calorimetry (DSC).
Abstract: The thermal behavior of Nafion-117 membranes was investigated by thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). TG measurements revealed that the mechanism of thermal degradation of a Nafion membrane in the acid form is different from that of Nafion in the sodium form. The DSC curves for the first heating, for both acid and salt forms, display two endothermic peaks, near 120 and 230°C. The high-temperature peak was assigned to the crystalline domains melting in Nafion, and the low-temperature peak was attributed to a transition into ionic clusters, since this transition exhibits significant changes depending on the nature of the counterion and the degree of hydration.
TL;DR: The high thermal stability of polybenzoxazines is a combined result of polymerization of acetylene terminal functional group and oxazine ring-opening polymerization as mentioned in this paper, and the high char yield achieved for this class of materials is in the range of 71-81% by weight at 800°C in a nitrogen atmosphere and 30% at 700°c in air as it is determined by thermogravimetric analysis.
TL;DR: In this paper, a series of copolymers were prepared from N-substituted acrylamides by free radical polymerization in solution, and the chemical composition of the final copolymer was found to be very close to the original monomer composition in the feed prior to polymerization.
TL;DR: In this paper, a new computational technique (advanced isoconversional method) has been used to determine the dependence of the effective activation energy (Eα) on α for isothermal and nonisothermal TGA data.
Abstract: The methods of thermogravimetric analysis (TGA) and differential scanning calorimettry (DSC) have been used to study the thermal decomposition of ammonium perchlorate (AP). TGA curves obtained under both isothermal and nonisothermal conditions show a characteristic slowdown at the extents of conversion, α = 0.30−0.35. DSC demonstrates that in this region the process changes from an exothermic to an endothermic regime. The latter is ascribed to dissociative sublimation of AP. A new computational technique (advanced isoconversional method) has been used to determine the dependence of the effective activation energy (Eα) on α for isothermal and nonisothermal TGA data. At α > 0.1, the Eα dependencies obtained from isothermal and nonisothermal data are similar. By the completion of decomposition (α → 1) the activation energy for the isothermal and nonisothermal decomposition respectively rises to ∼110 and ∼130 kJ mol-1, which are assigned to the activation energy of sublimation. The initial decomposition (α → ...
TL;DR: Solid dispersion particles of itraconazole were prepared with various pH-independent and -dependent hydrophilic polymers and were characterized by differential scanning calorimetry, powder X-ray diffraction and scanning electron microscopy to improve the solubility and dissolution rate of a poorly water-soluble drug.
TL;DR: The benefits of Modulated Temperature DSC over conventional differential scanning calorimetry (DSC) for studying thermal transitions in materials are reviewed by means of examples and examples are presented demonstrating the ability of MTDSC to detect subtle transitions more readily and without loss of resolution.
TL;DR: This review provides an up-to-date overview of the applications of DSC in the drug development process and should serve as a broad introduction to those starting work in this area, and also as a valuable reference for those already practising in this field.
TL;DR: In this article, the thermal behavior of hydration products in ordinary Portland cement as a function of age was investigated using differential scanning calorimeter (DSC) and X-ray diffraction analysis.
TL;DR: In this article, the formation and concentration of α and γ polymorphs in metallocene-catalyzed isotactic poly(propylenes) have been studied with a set of polymers that have a wide range in molecular weight and defect contents.
Abstract: The molecular, thermodynamic, and kinetic factors that govern the formation and concentration of the α and γ polymorphs in metallocene-catalyzed isotactic poly(propylenes) have been studied with a set of polymers that have a wide range in molecular weight and defect contents. With these polymers it was possible to investigate the influence of molecular weight on γ formation at a fixed defect concentration, as well as the role of the defect concentration at constant molecular weight. The major experimental techniques used were wide-angle X-ray scattering and differential scanning calorimetry complemented by microscopy. From these studies the role of chain microstructure, the crystallization temperature, and the thermodynamic and kinetic requirement for the formation of the γ form could be established in more quantitative detail than heretofore. A particular important finding was the fact that at fixed defect concentration the fractional content of the γ polymorph goes through a maximum with crystallization...
TL;DR: 31P-NMR indicates the coexistence, within a certain range of temperatures, of lamellar and hexagonal phases, or hexagonal phase precursors, relevant in the interpretation of certain forms of interfacial enzyme activation and in the regulation and dynamics of the bilayer structure of cell membranes.
TL;DR: Although the theoretical percentage of CPM on aging remained fairly constant over the processing temperature ranges in this study, the HC levels remaining in the extruded films during storage were a function of time and temperature.
Abstract: Hydroxypropylcellulose (HPC) films containing drugs or hydrophilic or hydrophobic plasticizers were prepared by a hot melt extrusion process. Polyethylene glycol 8000 (PEG 8000) 2%, triethyl citrate (TEC) 2%, acetyltributyl citrate (ATBC) 2%, and polyethylene glycol 400 (PEG 400) 1% were the plasticizing agents studied. In addition, either hydrocortisone (HC) 1% or chlorpheniramine maleate (CPM) 1% was incorporated into the films as a model drug. The physical-mechanical properties of the films that were investigated included tensile strength (TS), percentage elongation (%E), and Young's modulus (YM). Differential scanning calorimetry (DSC) was utilized to determine glass transition temperatures (Tg' s). These parameters were studied as a function of time and temperature. The glass transition temperatures initially decreased with the inclusion of the drugs and plasticizers. However, after 6 months aging, films containing PEG 400 and HC showed a marked increase in Tg. The films containing PEG 400 showed phy...
TL;DR: In this paper, a correlation function analysis of the SAXS data was performed on poly(ethylene terephthalate) (PET) isothermal crystallization and subsequent melting by time-resolved synchrotron small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), and temperature modulated DSC (MDSC) techniques.
TL;DR: In this paper, the authors investigated the thermal and viscoelastic property enhancement on crosslinked epoxy using two types of nanoreinforcement, namely, organoion exchange clay and polymerizable polyhedral oligomeric silsesquioxane (POSS) macromers.
Abstract: The properties of nanostructured plastics are determined by complex relationships between the type and size of the nanoreinforcement, the interface and chemical interaction between the nanoreinforcement and the polymeric chain, along with macroscopic processing and microstructural effects. In this article, we investigated the thermal and viscoelastic property enhancement on crosslinked epoxy using two types of nanoreinforcement, namely, organoion exchange clay and polymerizable polyhedral oligomeric silsesquioxane (POSS) macromers. Glass transitions of these nanocomposites were studied using differential scanning calorimetry (DSC). Small-strain stress relaxation under uniaxial deformation was examined to provide insights into the time-dependent viscoelastic behavior of these nanocomposites. Since the size of the POSS macromer is comparable to the distance between molecular junctions, as we increase the amount of POSS macromers, the glass transition temperature Tg as observed by DSC, increases. However, for an epoxy network reinforced with clay, we did not observe any effect on the Tg due to the presence of clay reinforcements. In small-strain stress relaxation experiments, both types of reinforcement provided some enhancement in creep resistance, namely, the characteristic relaxation time, as determined using a stretched exponential relaxation function increased with the addition of reinforcements. However, due to different reinforcement mechanisms, enhancement in the instantaneous modulus was observed for clay-reinforced epoxies, while the instantaneous modulus was not effected in POSS–epoxy nanocomposites. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1993–2001, 1999
TL;DR: In this article, two glass transitions (T g ), ∼70°C and ∼250°C, were observed for the first time using MDSC during the process of heat treatment.