Showing papers on "Differential scanning calorimetry published in 1978"
TL;DR: The polymorphic phase behavior of aqueous dispersions of phosphatidylethanolamines isolated from human erythrocytes, hen egg yolk and Escherichia coli have been investigated employing 31P NMR techniques as mentioned in this paper.
387 citations
TL;DR: Purple membranes of Halobacterium halobium were studied by differential scanning calorimetry and a small endothermic transition was seen, believed to be reversible, involving a cooperative change in crystalline structure of the membrane.
Abstract: Purple membranes of Halobacterium halobium were studied by differential scanning calorimetry. No transition was detected at temperatures below 70 degrees C. A small endothermic transition was seen at about 80 degrees C and a larger one at 100 degrees C. The larger transition is the irreversible denaturation of bacteriorhodopsin. The smaller transition is accompanied by a change in the visible absorption spectrum and is believed to be reversible, involving a cooperative change in crystalline structure of the membrane.
152 citations
TL;DR: It is concluded from the calorimetric data that the purity of the sample is better than 99.94 mol % and that the transition closely approximates an isothermal first-order transition.
Abstract: High sensitivity differential scanning calorimetry is employed in the study of the gel to liquid crystal phase transition of a highly purified sample of dipalmitoylphosphatidylcholine in multilamellar bilayer suspension. It is concluded from the calorimetric data that the purity of the sample is better than 99.94 mol % and that the transition closely approximates an isothermal first-order transition.
141 citations
TL;DR: Differential scanning calorimetry is used in this article to study the crystallization kinetics of two commerical Fe-Ni metallic galsses near their glass transition point, and activation energies for the crystallisation process are estimated from the time to 50% transformation as close to 100 kcal mol−1 and are interpreted as arising from viscous flow.
Abstract: Differential scanning calorimetry is used to study the crystallization kinetics of two commerical Fe-Ni metallic galsses near their glass transition point. For 0.01
116 citations
113 citations
TL;DR: In this paper, a derivative thermogravimetric analysis (DTG) was used to determine the exothermicity of polybutadiene degradation in the temperature range of the first weight loss stage.
Abstract: Using derivative thermogravimetric analysis (DTG), polybutadiene is shown to degrade by two distinct weight loss events when heated dynamically. The volatile products of the first stage are almost exclusively depolymerization products (butadiene and vinylcyclohexene). The residue—cyclized and crosslinked polybutadiene—degrades in the second stage. Increasing the heating rate or sample size results in increased depolymerization; and at a 100°C/min heating rate, up to 50% of the initial sample weight is converted to depolymerization products. Differential scanning calorimetry (DSC) indicates that degradation is exothermic in the temperature range of the first weight loss stage. The determined exothermicity (0.95 kJ/g polybutadiene) is independent of heating rate. Infrared observations show cis—trans isomerization in the same temperature range. Kinetic analysis of the DTG data yields an apparent activation energy of 251 kJ/mole for depolymerization, while for the overall reactions is the first stage, DSC data yield 170 kJ/mole. Why the exothermicity of the degradation is independent of the depolymerization/cyclization ratio is not clear.
108 citations
TL;DR: The lipid phase transition of Escherichia coli was studied by high sensitivity differential scanning calorimetry and concluded that E. coli can grow nromally with as much as 20% of its membrane lipids in the ordered state but that if more than 55% of the lipids are ordered, growth ceases.
83 citations
TL;DR: In this paper, the activation energy, ΔE, and the pre-exponential constant, A, for both the inception of crystallization and the peak in the crystallization exotherm were determined by differential scanning calorimetry.
Abstract: Amorphous Fe‐B ribbons with 72‐88 a/o Fe were prepared by melt‐spinning. The inception of crystallization and the growth of crystals was determined by differential scanning calorimetry. The activation energy, ΔE, and the pre‐exponential constant, A, for both the inception of crystallization and the peak in the crystallization exotherm are independent of composition from 72‐82 a/o Fe. ΔE and A steadily decline as the Fe content is increased from 82 to 88 a/o Fe. The concurrence of the ΔE and A values for the inception of crystallization and for the peak in the crystallization exotherm suggests that the same diffusion mechanism is controlling the kinetics in both periods. This compositional dependence of constants in the Arrhenius relation is attributed to decreased filling of holes by B in the Bernal‐like structure as the Fe content increases.
78 citations
TL;DR: In this article, the structural changes have been studied with gel chromatography, viscometry, infrared spectroscopy, differential scanning calorimetry, and gravimetric measurements.
Abstract: Samples of low-density polyethylene (LDPE), high-density polyethylene (HDPE), and tetratetracontane (n-C44H90) free from additives were heated in air at temperatures between 120 and 180°C. As a comparison, “as received” HDPE containing unspecified additives has also been included.
The structural changes have been studied with gel chromatography, viscometry, infrared spectroscopy, differential scanning calorimetry, and gravimetric measurements.
LDPE, HDPE, and n-C44H90 follow the same course of thermooxidative degradation when they are free from additives and present in the molten state. Both molecular-diminishing and enlargement reactions occur. At temperatures below 150°C molecular enlargement is not observed until after rather long exposure times, whereas at higher temperatures enlargement occurs immediately. The difference is because “peroxide curing” becomes increasingly important above 150°C, whereas ester formation is operating at all temperature levels. Degradation below Tm is restricted to the amorphous phase that results in a different degradation pattern.
In accelerated testing work extrapolations of the Arrhenius type in the prediction of structural change are thus not justified, even within the actual narrow temperature range. Neither are changes in commonly used standards like carbonyl content justified as a measure of the changes; for example, in mechanical properties.
The stabilizer in the unpurified HDPE not only influences the induction period but also the course of the thermooxidative degradation.
77 citations
TL;DR: Gelation and melting of aqueous gelatin were investigated by differential scanning calorimetry in this paper, where the results were interpreted in terms of the fringed micelle model and the diameter of the rematured collagen fibril were found to be in excellent agreement with those determined previously by electron microscopy.
Abstract: Gelation and melting of aqueous gelatin were investigated by differential scanning calorimetry. This phenomenon can be analyzed as a conventional crystallization process assuming predetermined primary nucleation and unidirectional growth. The results were interpreted in terms of the fringed micelle model. Calculated values of the diameter of the rematured collagen fibril were found to be in excellent agreement with those determined previously by electron microscopy.
70 citations
TL;DR: The effects of the very long chain fatty acids, arachidic and behenic appears to be similar to those of cholesterol in that they cause a broadening of the phase Transition with a lowering of the transition enthalpy but have little effect on the temperature at which the phase transition occurs.
01 Jan 1978
TL;DR: In this paper, 13C NMR Spectroscopy of polymers has been used for high performance Gel Permeation Chromatography and Light Scattering in Synthetic Polymer Systems.
Abstract: 1. 13C NMR Spectroscopy of Polymers.- 2. Mass Spectrometry.- 3. High Performance Gel Permeation Chromatography.- 4. Light Scattering in Synthetic Polymer Systems.- 5. Molecular Dimensions of Amorphous Polymers by Neutron Scattering.- 6. Recent Advances in the Study of Polymers by Small Angle X-ray Scattering.- 7. Quantitative Differential Scanning Calorimetry.- 8. Microscopy of Polymer Surfaces.
TL;DR: It is from workers in the field of thermal analysis and differential scanning calorimetry that the study of non-isothermal kinetics has received impetus as discussed by the authors, and it is from them that the work of as discussed by the authors was initiated.
Abstract: It is from workers in the field of thermal analysis and differential scanning calorimetry that the study of non-isothermal kinetics has received impetus.
TL;DR: Differential scanning calorimetry has been used to study several structural transitions of the human erythrocyte membrane and it is shown that two of the other transitions (B and C) exhibit a high sensitivity to a local anesthetic, benzyl alcohol.
TL;DR: In this article, two non-crystalline alloys, Cu-50 at% Zr and Cu-54 at % Zr, were splat quenched using a piston and anvil device, and the glass transition and crystallization temperatures were measured using differential scanning calorimetry of as-splat specimens and specimens aged below Tg.
Abstract: Two CuZr alloys, Cu-50 at% Zr and Cu-54 at% Zr, were splat quenched to the non-crystalline state using a piston and anvil device. The glass transition and crystallization temperatures, as well as the enthalpy releases observed during crystallization were measured using differential scanning calorimetry of as-splat specimens and specimens aged below Tg. Transmission electron microscopy and X-ray diffraction experiments were utilized to monitor phase and structural changes in the alloys as they were transformed to the crystalline state.
The results of the investigation indicated that the non-crystalline to crystalline transformation of these two alloys in constant heating rate experiments above Tg was a two-step process. The initial step, which is associated with a large exothermic reaction, results in the appearance of crystallites in a matrix of non-crystalline material. The final step, associated with a smaller exothermic reaction, results in the total transformation of glass to the crystalline state and the formation of the equilibium crystalline phases.
The effect of aging these splat-quenched non-crystalline alloys at temperatures below Tg was also investigated. It was determined from these experiments that crystallization does occur when the non-crystalline alloys are aged ∼ 15°C below Tg. However, the incubation time for crystalline nucleus formation was found to be substantially greater for the Cu50Zr50 glass. Finally, it was determined that the thermal stability of the aged glass relative to the spontaneous crystallization observed during the constant heating rate experiments above Tg decreases as a function of aging time.
01 Jan 1978
TL;DR: In this paper, the authors provide a detailed account of solid-state transition behavior of poly (2, 6-dimethylphenylene oxide)-polystyrene blends and PPO-poly-chloro-structure blends.
Abstract: Publisher Summary This chapter focusses on the solid-state transition behavior of blends. It discusses the criteria for miscibility and briefly reviews the widely used methods of glass transition temperature (Tg) measurement in polymer blends with respect to their advantages and limitations in the study of polymer compatibility. The methods by which Tg of polymers may be determined are differential thermal analysis (DTA), thermal optical analysis (TOA), probe penetration thermo-mechanical analysis (TMS), differential scanning calorimetry (DSC), dynamic mechanical and dielectric measurements, and dilatometry. DSC has been widely used in the study of blend compatibility and in the determination of crystallinity in crystalline-amorphous polymer blends. DSC thermograms are plots of heat capacity (Cp) versus temperature. Apart from rapidity of measurement, the principal advantages of DSC in the study of polymer blends are that only small (typically 5–30 mg) samples are required and the available rapid temperature scan permits the study of heat sensitive polymers such as PVC without the addition of stabilizers. Dynamic mechanical measurements are widely used in the study of polymer compatibility. With this technique, a dynamic modulus can be measured as a function of temperature over a range of frequencies. From traditional torsion pendulum measurements, the dynamic shear loss modulus (G") and the dynamic shear storage modulus (G') can be obtained as a function of temperature at a nominal frequency in the vicinity of 1 Hz. The chapter provides a detailed account of solid-state transition behavior of poly (2, 6-dimethylphenylene oxide)-polystyrene blends and PPO- poly-chloro-styrene blends.
TL;DR: Using both differential scanning calorimetry (DSC) and differential thermal analysis (DTA), the kinetics of the transformation upon heating of the metastable tin-nickel alloy were studied as discussed by the authors.
Abstract: Using both differential scanning calorimetry (DSC) and differential thermal analysis (DTA), the kinetics of the transformation upon heating of the metastable tin‐nickel alloy were studied The solid‐state reaction proceeds according to a classical Avrami equation The parameters of the reaction equation were determined, and it is shown that the metastable alloy will not revert to the stable state, for all practical purpose, if kept at temperatures below 100°C Variations of the kinetic parameters were observed which can explain most of the different stability evaluations reported by different authors
TL;DR: In this paper, DSC measurements were applied to sodium sulfate decahydrate, paraffin wax, urea, and phthalimide to investigate the behavior of materials that store energy by melting or by undergoing solid state transitions.
TL;DR: The high-temperature phase behavior of RbH 2 PO 4 and CsH 2PO 4 has been studied in this article, where a single quasi-irreversible phase transition with an enthalpy of 4.665 kJ mol −1 was found to occur over the temperature range 86-111°C.
TL;DR: In this article, the thermodynamic state of densified glasses is discussed and the authors make use of differential scanning calorimetry (d.s.c.) and specific volume measurements on polystyrene glasses formed by cooling from the melt under pressure.
TL;DR: In this article, high-molecular-weight alternating copolymers of propylene and ethyl acrylate were prepared by using boron trifluoride to complex the acrylated ester.
Abstract: High-molecular-weight alternating and acrylate-rich copolymers of propylene and ethyl acrylate were prepared by using boron trifluoride to complex the acrylate ester. The polymerizations were run at room temperature and autogeneous pressures with free-radical initiation. The polymers were characterized by their nuclear magnetic resonance (NMR) and infrared (IR) spectra, differential scanning calorimetry, and gel permeation chromatography. The proton and 13C NMR spectra show that the equimolar copolymers are alternating to a high degree.
TL;DR: In this paper, the influence of two nucleating agents on the crystallization parameters of 6-polyamide was investigated by differential scanning calorimetry and some substantial differences for the crystallisation rate of the examined polymers were determined.
Abstract: The influence of two nucleating agents on the crystallization parameters of 6-Polyamide was investigated by differential scanning calorimetry and some substantial differences for the crystallization rate of the examined polymers were determined. The induction times ti, the semicrystallization times t1/2, the crystallization rate constants k, and the Avrami n coefficients were measured and related to the different characteristics and morphology of the specimens. The experimental data are represented in form of various plots and the microscopic examination of thin sections of the polymers allows to extend the study, showing remarkable differences in specimens morphology in correspondence of the nucleation effect.
TL;DR: It is concluded that the ability of gramicidin to form conducting channels in a gel state bilayer depends on the thickness of the paraffin core.
TL;DR: In this paper, the thermal decomposition of N-methylformamide intercalate was studied by differential scanning calorimetry (DSC) and it was shown that the decomposition starts at 355 K, finishes at 450 K and follows Avrami-Erofeev kinetics for α = 0.04-0.96.
Abstract: The thermal decomposition of the kaolinite: N-methylformamide intercalate [Al2Si2O5(OH)4·HCONHCH3] has been studied by differential scanning calorimetry (DSC). The decomposition starts at 355 K, finishes at 450 K and follows Avrami-Erofeev kinetics for α = 0.04–0.96. ΔH for the loss of organic is 19 ± 2 kJ mol−1; the activation energy for the reaction is 30 ± 3 kJ mol−1.
TL;DR: In this paper, a model successfully applied to explain the volumetric relaxation of amorphous polymers near the glass transition has been used to predict the behavior in a scanning calorimeter of polymers annealed or aged below their glass transition.
Abstract: A model successfully applied to explain the volumetric relaxation of amorphous polymers near the glass transition has been used to predict the behavior in a scanning calorimeter of amorphous polymers annealed or aged below their glass transition. Although the predictions are incomplete because of the uncertainty of several critical parameters, the calculations indicate that caution is needed in interpreting scanning calorimeter data. Possible problems interpreting such data include (1) underestimation of the conformational heat capacity, (2) incorrect comparison of specimens aged at different temperatures, and (3) uncertain energy of the quenched state, against which aging is often compared.
TL;DR: In this article, the melting behavior of polynuclear aromatic hydrocarbons and hydrocarbon free radicals was studied with differential scanning calorimetry and hot-stage microscopy.
TL;DR: No indication of a temperature-dependent conformational transition is obtained by using a differential scanning calorimeter having a sensitivity considerably in excess of that required to detect such a transition, and the implications of this discrepancy are discussed.
Abstract: A number of authors have reported observations on D-amino acid oxidase [D-amino acid: O2 oxidoreductase (deaminating), EC 1.4.3.3.] that they have interpreted in terms of a temperature-dependent conformational transition having a van't Hoff enthalpy amounting to more than 1 cal per g of protein (1 cal = 4.184J). No indication of this transition is obtained by using a differential scanning calorimeter having a sensitivity considerably in excess of that required to detect such a transition. The implications of this discrepancy are discussed.
TL;DR: In this article, a differential scanning calorimeter is used to monitor the number of reactive sites present in the prepolymer, thus achieving a degree of control on the ultimate properties of the cured film.
Abstract: Modification of a standard differential scanning calorimeter to allow irradiation of the sample material with ultraviolet light allows one to follow the course of polymerization of photocurable polymer systems. The rate and heat of polymerization are readily determined by this technique which gives it a number of very useful applications. As a quality control tool, one can use the heat of polymerization to monitor the number of reactive sites present in the prepolymer thus achieving a degree of control on the ultimate properties of the cured film. Similarly, analysis of a cured film will indicate the presence of any uncured material, thus allowing one to adjust curing conditions accordingly. The technique has numerous other applications in the study of photocurable resins, such as evaluation of initiator efficiencies, optimization of curing parameters (initiator concentration, lamp design), and the sensitivity of prepolymers to oxygen and wavelength.
TL;DR: In this paper, a "theoretical" shape for the thermogram of a first-order phase transition such as melting is constructed, and then it is shown how that shape should be analyzed to obtain an accurate value for the heat of transition.
Abstract: Commencing with the usual first-order approximate descriptions of radiative heat-transfer processes, and assuming uniformity of temperature across the cells of a differential scanning calorimeter, a 'theoretical' shape for the thermogram of a first-order phase transition such as melting is constructed, and then it is shown how that shape should be analysed to obtain an accurate value for the heat of transition.