Showing papers on "Differential scanning calorimetry published in 1986"
TL;DR: In this article, a study has been made of the crystallization behavior of poly(ether-ether-ketone), PEEK, under isothermal and non-isothermal conditions.
635 citations
TL;DR: In this article, a low-temperature differential scanning calorimetry technique was used to measure the characteristic sub-zero glass transition temperature, T′ g, of a maximally freeze-concentrated aqueous solution.
427 citations
TL;DR: The combined DSC and IR results suggest that thermal transitions occurring near 65 degrees and 85 degrees C involve increased acyl chain motion of stratum corneum lipids.
285 citations
TL;DR: Differential scanning calorimetry (DSC) and density gradient technique (DGT) were used to determine, both isothermally and dynamically, the crystallization kinetics of polyetheretherketone (PEEK) as mentioned in this paper.
Abstract: Differential scanning calorimetry (DSC) and the density gradient technique (DGT) were used to determine, both isothermally and dynamically, the crystallization kinetics of polyetheretherketone (PEEK). The data were analyzed by a model utilizing, for the first time, two crystal nucleation and growth processes which were observed experimentally in a typical Avrami plot of the isothermal data. Thus, by modeling the data as two separate Avrami type crystallization processes occurring in parallel, both isothermal and dynamic data could be predicted with the same model constants. The first process provided an Avrami exponent of 2.5 and an onset temperature of 320°C. The second process displayed an Avrami exponent of 1.5 and an onset temperature of 342°C. The validity of this dual mechanism crystallization model was proven in practice by predicting with best fit model constants, a wide range of crystallinities of both neat and carbon fiber-reinforced PEEK samples that had been made at different cooling rates from the melt.
272 citations
TL;DR: Amorphous alloy powders of the types NiZr, Cozr, FeZr and CuZr are produced by mechanical alloying from crystalline elemental powders as discussed by the authors, which is monitored by microstructural investigations, x-ray diffraction, and, where applicable, by magnetization measurements.
Abstract: Amorphous alloy powders of the types NiZr, CoZr, FeZr, and CuZr are produced by mechanical alloying from crystalline elemental powders. The alloying and amorphization process is monitored by microstructural investigations, x‐ray diffraction, and, where applicable, by magnetization measurements. The crystallization temperatures, determined by differential scanning calorimetry, are comparable to those measured for rapidly quenched and solid state reacted amorphous metals of the same compositions.
226 citations
TL;DR: Comparison of hydrated 1:1 fatty acid/soap systems with hydrated soap systems suggests that the reduced degree of charge repulsion between polar groups causes half-ionized fatty acids in excess water to form bilayers rather than micelles.
Abstract: The physical properties in water of a series of 1:1 acid-soap compounds formed from fatty acids and potassium soaps with saturated (10-18 carbons) and omega-9 monounsaturated (18 carbons) hydrocarbon chains have been studied by using differential scanning calorimetry (DSC), X-ray diffraction, and direct and polarized light microscopy. DSC showed three phase transitions corresponding to the melting of crystalline water, the melting of crystalline lipid hydrocarbon chains, and the decomposition of the 1:1 acid-soap compound into its parent fatty acid and soap. Low- and wide-angle X-ray diffraction patterns revealed spacings that corresponded (with increasing hydration) to acid-soap crystals, hexagonal type II liquid crystals, and lamellar liquid crystals. The lamellar phase swelled from bilayer repeat distances of 68 (at 45% H2O) to 303 A (at 90% H2O). Direct and polarized light micrographs demonstrated the formation of myelin figures as well as birefringent optical textures corresponding to hexagonal and lamellar mesophases. Assuming that 1:1 potassium hydrogen dioleate and water were two components, we constructed a temperature-composition phase diagram. Interpretation of the data using the Gibbs phase rule showed that, at greater than 30% water, hydrocarbon chain melting was accompanied by decomposition of the 1:1 acid-soap compound and the system changed from a two-component to a three-component system. Comparison of hydrated 1:1 fatty acid/soap systems with hydrated soap systems suggests that the reduced degree of charge repulsion between polar groups causes half-ionized fatty acids in excess water to form bilayers rather than micelles.(ABSTRACT TRUNCATED AT 250 WORDS)
193 citations
TL;DR: In this article, a new equation was derived from Johnson-Mehl-Avrami equation to calculate the activation energy of crystallization for metallic glass E, d [ ln (d x d t ) p ]/d (1/T p ) = − E R, where x is the volume fraction of transformation, t the effective time, Tp the peak temperature of crystallisation at d2x/dt2=0, R the gas constant.
Abstract: A new equation is derived from Johnson-Mehl-Avrami equation to calculate the activation energy of crystallization for metallic glass E, d [ ln ( d x d t ) p ]/ d (1/T p ) = − E R , where x is the volume fraction of transformation, t the effective time, Tp the peak temperature of crystallization at d2x/dt2=0, R the gas constant. It demonstrates that (dx/dt)p can be used instead of the cooling rate B in a Kissinger plot. This new equation has successfully predicted the activation energy of crystallization for Pd76Y9Si15 during non-isothermal annealing; and indicated, as expected, that the maximum rate of crystallization in DSC increases by the same factor as the heating rate does.
183 citations
TL;DR: In this paper, the thermal decomposition of citric acid is studied by thermogravimetry (TG) and differential scanning calorimetry(DSC) techniques under various conditions.
176 citations
TL;DR: In this paper, differential scanning calorimetry (d.s.c.) and gel permeation chromatography (g.p.c) were used to study the thermal degradation of 4,4′-diphenylmethane/1,4-butanediol based monodisperse urethane model compounds.
148 citations
TL;DR: The structure and properties of the as-quenched and subsequently crystallized isotactic propylene (PP) films were characterized by various techniques in this article, including X-ray diffraction, differential scanning calorimetry (DSC), and torsion pendulum measurements.
Abstract: Glassy isotactic propylene (PP) films of thickness up to 0.3 mm were obtained by an ultraquenching technique. The structure and properties of the as-quenched and subsequently crystallized samples were characterized by various techniques. Electron microscopy indicates the glass has no structure larger than 25 A. X-ray diffraction shows PP crystallizes from the glass into a smectic structure at ca. −20°C and then transforms to monoclinic microcrystals at ca. 40°C; a nodular structure (80 to 100 A in diameter) was observed on the surface. The transformation temperature increases with the film thickness. Annealing above the α-relaxation temperature results in an increase in the nodule size. A correspondence was found between the diameter of the nodules observed on the surface and long spacings obtained by small-angle X-ray scattering from the bulk. Dynamic mechanical spectra show the presence of two relaxation-like peaks at ca. −10°C and 10°C for the as-ultraquenched samples. X-ray scattering, differential scanning calorimetry (DSC), and torsion pendulum measurements show PP crystallizes from the glass at a temperature, depending on the rate of heating, that corresponds to the lower relaxation peak temperature.
136 citations
TL;DR: Differential scanning calorimetry is utilized to monitor the solid-state reaction of crystalline metals to form an amorphous alloy in multilayered thin-film diffusion couples of elemental Ni and Zr in order to study the kinetics of these reactions.
Abstract: We have utilized differential scanning calorimetry to monitor the solid-state reaction of crystalline metals to form an amorphous alloy in multilayered thin-film diffusion couples of elemental Ni and Zr. The heat of formation of amorphous Ni68Zr32 alloy from the elemental metals is measured directly and found to be 35 ± 5 kJ/mole. The kinetics of these reactions has been examined. The activation energy for interdiffusion in the amorphous phase is determined to be E=1.05±0.05 eV.
TL;DR: The thermodynamic properties and mechanisms of solid state phase transformations in some hydrocarbon molecular crystals reversibly absorb large amounts of heat as discussed by the authors have been studied for polyhydric alcohols related to pentaerythritol.
TL;DR: In this paper, the effect of variations in the amine-to-epoxy ratio r on the glass transition temperature Tg is examined and a method is developed to determine the activation energy.
Abstract: Differential Scanning Calorimetry (DSC) is used to study the curing behavior of epoxy systems. For non-catalyzed diamine-epoxy systems, the reaction enthalpy ΔH and the glass transition temperature Tg are evaluated and related to the structure of the hardener. A method is developed to determine the activation energy. The effect of variations in the amine-to-epoxy ratio r on Tg is also examined. A maximum value is observed for r = 1. Then, the influence of benzyldimethylamine as catalyst in an anhydride/DGEBA system and in three diamine/DGEBA systems is reported. In the cases of DDS and DDA curing agent the maximum value of Tg is shifted, to r = 0, 6. The results are explained by different reaction mechanisms.
TL;DR: Although indomethacin remained as a glass for 2 years at room temperature, pulverized glassy indometHacin was found to crystallize, and the rate of crystallization was determined by the X-ray diffraction method and followed first-order kinetics.
Abstract: Glassy indomethacin was prepared by cooling the melt, and the glassy state was confirmed by the jump of heat capacity and the anomalous endothermic park (heat capacity maximum) in the differential scanning calorimetry (DSC) curve. The influences of the cooling rate of the melt and the heating rate of the glass formed on the glass transition temperature (Tg) were examined, and the apparent activation energy of glass transition was calculated to be 212.5kJ/mol. The relaxation process below Tg was traced in terms of the area under the anomalous endothermic park of the DSC curve and the rate of relaxation during annealing was found to reach the maximum at about 303 K. The rate of dissolution of glassy indomethacin was far greater than that of crystalline indomethacin. Although indomethacin remained as a glass for 2 years at room temperature, pulverized glassy indomethacin was found to crystallize, and the rate of crystallization was determined by the X-ray diffraction method. The degree of crystallization was determined by Hermans' method, and was found to reach a maximum of 60% after 2 months. The process of crystallization followed first-order kinetics.
TL;DR: In this article, a model butanediol-MDI-polypropylene oxide polymers have been synthesized to explore the structure-property relationships in urethane/polyether polymers.
Abstract: Model butanediol–MDI–polypropylene oxide polymers have been synthesized to explore the structure–property relationships in urethane/polyether polymers. The results of mechanical, thermal, and spectroscopic analyses agree remarkably well. The phase mixing in these polymers decreases with increasing hard-segment length, while the hard-segment stability increases with increasing hard-segment length. This is demonstrated clearly by dynamic mechanical, differential scanning calorimetry, infrared, and NMR studies. The importance of hydrogen bonding to the stability of the hard segment is strongly supported by the variable-temperature infrared experiments. The critical hard-segment size for phase segregation was shown to be two butanediols per hard segment. The temperature limit of the flatness of the storage modulus was tied to the thermal stability of the hard-segment hydrogen bonding which is controlled largely by the length of the hard segment and the extent of the hydrogen bonding.
TL;DR: Examples demonstrating the use of these methods for the development of the dosage form are given: choice of the salt form, phase-diagrams, drug substance-excipient interactions, physical changes on processing or during storage, and even analysis of the pharmaceutical form.
TL;DR: In this paper, an analysis of the cure kinetics of several different formulations composed of bifunctional epoxy resins and aromatic diamines was performed, including the reaction rate order, activation energy, and frequency factor.
Abstract: Synopsis An analysis of the cure kinetics of several different formulations composed of bifunctional epoxy resins and aromatic diamines was performed. A series of isothermal differential scanning calorimetry (DSC) runs (at higher temperature) and Fourier transform infrared spectroscopy (FT-IR) runs (at lower temperature) provided information about the kinetics of cure in the temperature range 18-160°C. All kinetic parameters of the curing reaction, including the reaction rate order, activation energy, and frequency factor were calculated and reported. Dynamic and isothermal DSC yielded different results. An explanation was offered in terms of different curing mechanisms which prevail under different curing conditions. A mechanism scheme was proposed to account for various possible reactions during cure.
TL;DR: Analytical expressions applied to ice crystallization for applications in cryobiology and could also probably be used in other fields of research such as crystallization from silicates or other mineral or organic glasses.
TL;DR: In this article, a thermal analysis of rice starch/1-monoglyceride mixtures at intermediate water content (50%) was carried out using Differential Scanning Calorimetry (DSC) and Thermo-Mechanical Analysis (TMA).
TL;DR: In this article, the authors determined the free-volume hole sizes in amine-cured epoxy polymers by comparing the observed ortho-positronium lifetimes with the known lifetime-free volume correlation for low-molecular-weight systems.
Abstract: Positronium annihilation spectroscopy (PAS) has been used to study the microstructural properties of amine-cured epoxy polymers. We have determined the free-volume “hole” sizes in these polymers by comparing the observed ortho-positronium lifetimes with the known lifetime–free volume correlation for low-molecular-weight systems. The free volumes for four epoxies with different crosslink densities are found to vary significantly over the temperature range between −78° and 250°C. The free-volume holes for these polymers are found to range from 0.025 to 0.220 nm3. Two important transition temperatures were found: one corresponds to the glass transition temperature Tg determined by differential scanning calorimetry (DSC), and the other occurs about 80–130°C below Tg. The sub-Tg transition temperature is interpreted tentatively as being where hole size reaches dimensions adequate for positronium trapping or else the onset temperature for local mode or side-chain motions. These two transition temperatures plus two additional onset temperatures are found to be correlated with crosslink densities calculated from stoichiometry.
TL;DR: In this article, the melting behavior of poly(aryl-ether-etherketone) was investigated using Fourier transform infra-red (FTir) spectroscopy and differential scanning calorimetry (d.s.c.) as part of a study of a carbon fibre reinforced PEEK composite.
TL;DR: Moment analysis of the 2H NMR spectra demonstrate that the main gel to liquid-crystalline phase transition is progressively broadened and its onset temperature lowered by increasing concentrations of alpha-tocopherol.
Abstract: The effects of 5, 10, and 20 mol % incorporation of alpha-tocopherol (vitamin E) on 50 wt % aqueous multilamellar dispersions of sn-2-substituted [2H31]palmitoylphosphatidylcholine (PC-d31), a saturated, deuterated phospholipid prepared from egg lysophosphatidylcholine, have been studied by deuterium nuclear magnetic resonance (2H NMR) and differential scanning calorimetry (DSC). Moment analysis of the 2H NMR spectra as a function of temperature and DSC heating curves demonstrate that the main gel to liquid-crystalline phase transition is progressively broadened and its onset temperature lowered by increasing concentrations of alpha-tocopherol. Below the transition temperature (40 degrees C) for PC-d31 bilayers, the 2H NMR spectra indicate that acyl chain motion is increased by addition of alpha-tocopherol and that this effect extends to lower temperatures with higher alpha-tocopherol content. Above the transition, average carbon-deuterium bond order parameters calculated from the first spectral moment establish that alpha-tocopherol increases acyl chain ordering within the PC-d31 bilayer by as much as 17% at 20 mol % incorporation. Profiles of order parameter vs. chain position, constructed from 2H NMR spectra following application of the depaking technique, show that despite higher order the general form of the profile is not significantly altered by alpha-tocopherol.
ARCO1
TL;DR: In this article, the properties of poly(ethylene oxide) and poly(methyl methacrylate) blends were investigated as a function of composition using optical and scanning electron microscopy, differential scanning calorimetry and dilatometry.
Abstract: Morphology, crystallinity, and melting behaviour of solution-cast films of poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) blends were investigated as a function of composition, using optical and scanning electron microscopy, differential scanning calorimetry, and dilatometry. Up to a content of about 40 wt.-% of PMMA the blend films are completely filled with PEO spherulites, no separated domains of PMMA being observed. This observation suggests, in agreement with small angle X-ray scattering analysis, that for such compositions the PMMA molecules are incorporated in interlamellar regions of PEO spherulites. Blends with higher content of PMMA show islands of crystalline PEO within a matrix of PMMA; large amorphous regions coexist with not well developed PEO spherulites. Addition of PMMA strongly increases the nucleation density for PEO crystals. The solubility parameters δ of PEO and PMMA were calculated from specific volume values as a function of temperature. It was found that at temperatures higher than that of PEO melting the difference δ(PEO) - δ(PMMA) is very low suggesting that the two polymers are compatible in the melt. Compatibility of PEO and PMMA was also predicted by using a theoretical approach which allows to calculate the free energy of mixing as a function of composition and temperature.
TL;DR: In this article, a relationship between the maximum crystallization rate (d x d t ) p, the Avrami exponent n and the rate constant Kp at the peak temperature of crystallization was established: (dx/dt)p = 0.37 nKp.
Abstract: The investigation of the crystallization kinetics of Pd80B4Si16 glass by differential scanning calorimeter (DSC) indicated a two-stage crystallization process during phase change. A relationship between the maximum crystallization rate ( d x d t ) p , the Avrami exponent n and the rate constant Kp at the peak temperature of crystallization was established: (dx/dt)p = 0.37 nKp. By means of this equation defined as the maximum reaction rate equation we were able to calculate the parameters of crystallization kinetics of Pd80B4Si16 glass for both crystallization stages. The activation energy increase from E = 98.2 kcal/mol. at the MSI stage to E= 109.1 kcal/mol. at the MSII stage. The Avrami exponent has essentially doubled its value from n = 1.1−1.2 at the MSI stage to n = 1.9−2.1 at the MSII stage.
TL;DR: Investigation of the influence of cholesterol (CHOL) on the main phase transition in single shell dipalmytoylphosphatidylcholine (DPPC) vesicles found interesting differences for three probes sensing different parts in the hydrophobic region of the phospholipid bilayer.
TL;DR: A detailed study using d.c. as mentioned in this paper of the melting behavior of isotactic polypropylene isothermally crystallized from the melt has been carried out, where the origin of multiple fusion endotherms was sought.
TL;DR: In this article, the kinetics of polycyclotrimerization of 2,2-bis(4-cyanatophenyl)propane were analyzed by differential scanning calorimetry and IR spectroscopy.
Abstract: The kinetics of polycyclotrimerization of 2,2-bis(4-cyanatophenyl)propane was analyzed by differential scanning calorimetry and IR spectroscopy. The autocatalytic character of the reaction was elucidated by modelling the conversion-time curves of systems with definite admixtures of the found intermediate products. Furthermore, quantitative relations between the purity of the dicyanate, the rate of the brutto reaction, the temperature of the DSC maximum, and the B-time of the resin were found.
Die Kinetik der thermischen Polycyclotrimerisierung von 2,2-Bis(4-cyanatophenyl)propan wurde mit Hilfe von DSC und IR-Spektroskopie untersucht. Der autokatalytische Charakter der Reaktion wurde durch Modellierung der Umsatz-Zeit-Kurven bei Zusatz difinierter Mengen der nachgewiesenen Zwischenprodukte aufgeklart. Weiterhin wurden quantitative Beziehungen zwischen Reinheitsgrad des Dicyanats, Geschwindigkeit der Bruttoreaktion, Lage des DSC-Maximums und B-Zeit gefunden.
TL;DR: In this article, the influence of morphological transitions on the hydrogen-bonding behavior of polyurethanes is investigated by simultaneous measurements of Fourier-transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC).
Abstract: The influence of morphological transitions on the hydrogen-bonding behavior of polyurethanes is investigated by simultaneous measurements of Fourier-transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The materials examined are a noncrystalline polyurethane hard segment, a crystallizable polyurethane hard segment, and a segmented polyurethane block copolymer containing crystallizable hard segments. Integrated absorbance data show that the hydrogen-bonding behavior is insensitive to crystalline transitions within the hard segment microdomains, but that it does reflect morphological transitions in the block copolymer that are associated with intersegmental mixing. In addition, the spectral data show conclusive evidence for reversal of the urethane reaction at high temperatures.
TL;DR: Amorphous Fe•Zr powders have been prepared by mechanical alloying in a powder mill as discussed by the authors, and the results are characterized by x-ray diffraction, differential scanning calorimetry, and saturation magnetization measurements.
Abstract: Amorphous Fe‐Zr powders have been prepared by mechanical alloying in a powder mill. The samples are characterized by x‐ray diffraction, differential scanning calorimetry, and saturation magnetization measurements. The glass forming range reaches from 30 to 78 at. % Fe being much wider than for melt‐spun samples. Eutectic concentrations do not play any role. The results are compared with the glass forming ability predicted by free‐enthalpy diagram calculations based on the Miedema model [A. R. Miedema, Philips Tech. Rev. 36, 217 (1976)]. Amorphization by mechanical alloying seems to be a metastable equilibrium process neglecting intermetallic phases. Rather high crystallization temperatures are found in the concentration range which is not accessible by melt spinning.
TL;DR: Differential scanning calorimetry (d.s.c.) has been used to determine the amount of crystallized paraffins and the temperature at which crystals appear in a diesel fuel containing no additive and submitted to slow cooling as mentioned in this paper.