Showing papers on "Differential scanning calorimetry published in 1977"
TL;DR: In this article, the activation energy, the pre-exponential factor and the kinetic order of a thermoluminescence (TL) curve are evaluated for a series of related thermally stimulated phenomena which are governed by similar differential equations.
939 citations
TL;DR: In this article, isotactic polypropylene (PP) was zone-solidified in temperature gradients up to 300°C/cm at growth rates down to 3 μm/min.
Abstract: Samples of isotactic polypropylene (PP) were zone-solidified in temperature gradients up to 300°C/cm at growth rates down to 3 μm/min. Oriented α-type spherulites were obtained only by nucleation. While β nucleation is extremely rare, the β phase is easily initiated by growth transformations along the oriented α front. Since the β phase was found to grow considerably faster than the α phase, the α-to-β transformation points diverge across the sample, interrupting growth of the oriented α fibrils. This causes subsequent nucleation to yield teardrop-shaped α spherulites.
Differential scanning calorimetry (DSC) studies of zone-solidified PP show the β-phase to be favored by slow growth rates, high temperature gradients, and large degrees of superheat in the melt—all of which tend to suppress nucleation. Differential thermograms of largely β-PP obtained at a heating rate of 1°C/min show the actual melting and recrystallization of the β spherulites into the α form.
378 citations
TL;DR: Comparison with the purified proteins or fractions indicated that these transitions corresponded to denaturation of myosin, sarcoplasmic proteins and actin respectively, and the evidence suggested that this transition was closely linked with the process of contraction.
Abstract: Rabbit muscle and its constituent proteins were investigated by differential scanning calorimetry (d.s.c.). Post-rigor muscle yielded a complex thermogram comprising at least three endothermic transitions with Tmax values of 60, 67 and 80°C. Comparison with the purified proteins or fractions indicated that these transitions corresponded to denaturation of myosin, sarcoplasmic proteins and actin respectively. In addition to these endothermic transitions, pre-rigor muscle produced a single large exotherm of Tmax 54°C. The evidence suggested that this transition was closely linked with the process of contraction.
310 citations
TL;DR: Differential scanning calorimetry (DSC) was used to study thermal transitions of the following whey proteins and enzymes in milk ultrafiltrate solution: β-Lactoglobulin, α-lactalbumin, serum albumin, γ-globulin this paper.
Abstract: Differential scanning calorimetry (DSC) was used to study thermal transitions of the following whey proteins and enzymes in milk ultrafiltrate solution: β-lactoglobulin, α-lactalbumin, serum albumin, γ-globulin, apo- and Fe-lactoferrin, lysozyme, ribonuclease, α-chymotrypsin and xanthine oxidase. Denaturation enthalpies (ΔHD), denaturation temperatures (TD) and the half width of the denaturation peaks in DSC thermograms (ΔT½D) were determined and the degree of renaturation was estimated by rescanning previously denatured samples. A fair correlation between the results obtained by DSC and other more classical methods was found in general. However, for some proteins (α-lactalbumin, lysozyme, ribonuclease and xanthine oxidase), which have so far been considered relatively thermostable, calorimetry reveals conformational changes starting at temperatures as low as about 45 °C. In these cases thermostability observed after heat treatment of milk should be interpreted in terms of renaturation and not of high temperatures of denaturation.
246 citations
TL;DR: The interactions between myoglobin and bovine serum albumin and the anionic polysaccharides, pectate, alginate and carboxymethyl cellulose suggest that the interactions are primarily electrostatic in nature and increase as the net positive charge on the protein increases.
Abstract: The interactions between myoglobin and bovine serum albumin and the anionic polysaccharides, pectate, alginate and carboxymethyl cellulose, have been studied by differential scanning calorimetry (d.s.c), absorption spectrophotometry and Sephadex chromatography. At pH 6.0 the effect of the polysaccharides on the native proteins is merely to perturb the structure, causing spectral changes in myoglobin and decreased thermal stability in both myoglobin and bovine serum albumin. However, following heat denaturation at this pH much stronger interactions are formed giving rise to stable high molecular weight complexes which inhibit protein-protein aggregation and hence precipitation. The response of these systems to changes in ionic strength and pH suggest that the interactions are primarily electrostatic in nature and increase as the net positive charge on the protein increases.
194 citations
TL;DR: Water deuteron NMR spectra studied for the system dipalmitoyllecithin (DPL)-heavy water (D2O) at different compositions and temperatures show evidence that the "pretransition" observed by differential scanning calorimetry is caused by a crossing of a three-phase line.
Abstract: Water deuteron NMR spectra have been studied for the system dipalmitoyllecithin (DPL)-heavy water (D2O) at different compositions and temperatures. From an analysis of the spectra in terms of quadrupole splittings, a phase diagram has been constructed for the temperature range 25-60 degrees C and the composition range 4-15 mol of D2O/mol of DPL. Evidence is given that the "pretransition" observed by differential scanning calorimetry is caused by a crossing of a three-phase line. Strong support for a specific hydration of about 11 water molecules per lecithin molecule in the phase between the pretransition and main transition is also found.
143 citations
TL;DR: From data obtained by differential scanning calorimetry phase diagrams, phase diagrams were constructed, using a thermodynamically based fitting method, to study binary mixtures of phosphatidylcholines in water.
142 citations
TL;DR: Electron microscopic studies on freez-fractured dispersions of phosphatidylcholine-water-salt systems show that with some salts the typical rippled surface observed with L-alpha-dimyristoyl phosphatids, when in the gel state, is replaced by a smooth surface.
138 citations
TL;DR: The solid states formed by vitrified and frozen aqueous solutions of some hydrophilic polymers, able to act as biological cryoprotectants, have been studied by differential scanning calorimetry and freeze fracture electron microscopy.
Abstract: The solid states formed by vitrified and frozen aqueous solutions of some hydrophilic polymers, able to act as biological cryoprotectants, have been studied by differential scanning calorimetry and freeze fracture electron microscopy. Glass transitions, devitrification, recrystallization and melting behaviour of aqueous solutions of polyvinylpyrrolidone, hydroxyethyl starch and dextran have been established. The vitrified polymer solutions exhibit a characteristic microspheral morphology which is not induced by the quench cooling process but is an inherent feature of the solutions themselves.
130 citations
TL;DR: Differential scanning calorimetry was used to detect phase separation induced by hydrophobic myelin protein, lipophilin, in a mixture of phosphatidylserine and DPPC, and it can be estimated that for an equimolar mixture of PS andDPPC, the boundary layer contains only PS, although for higher DPPC contents, some DPPC can also be found in the boundary layers.
Abstract: Differential scanning calorimetry (DSC) was used to detect phase separation induced by hydrophobic myelin protein, lipophilin, in a mixture of phosphatidylserine (PS) and dipalmitoylphosphatidylcholine (DPPC). Preferential binding of PS to the boundary layer of lipophilin causes a decrease in the PS content of the remaining lamellar phase with a resultant shift in the phase-transition temperature to a higher temperature. The phase diagram for this mixture in the presence and absence of lipophilin is presented. From the phase diagram, it can be estimated that for an equimolar mixture of PS and DPPC, the boundary layer contains only PS, although for higher DPPC contents, some DPPC can also be found in the boundary layer. In the case where partial phase separation in induced in this mixture by Ca2+ alone, lipophilin increases the phase separation indicating that it also binds PS preferentially in the presence of Ca2+. Preferential binding of two other acidic lipids, phosphatidic acid and phosphatidyl-glycerol, to the boundary layer was also found, including a mixture where the acidic lipid was the higher melting component in the mixture.
123 citations
TL;DR: The melting behavior of drawn poly(ethylene terephthalate) bristles has been studied by means of differential scanning calorimetry as discussed by the authors, and the wide-angle X-ray diffraction pattern was analyzed.
TL;DR: In this article, the authors used differential scanning calorimetry to study the isothermal crystallisation of an Fe80P13C7 metallic glass with additions of Ti and Cr. Between 768 and 781 K the crystallisation occurs in a single stage, the kinetics of which fit an Avrami-Johnson-Mehl relationship with exponent n = 5.1 ± 0.
TL;DR: In this paper, differential scanning calorimetry (DSC) and hot stage transmission electron microscopy were used to characterize the solid state reactions accompanying heating of the highest strength (T651) and overaged (T7351) tempers of 7075 aluminum alloy.
Abstract: Both differential scanning calorimetry (DSC) and hot stage transmission electron microscopy were used to characterize the solid state reactions accompanying heating of the highest strength (T651) and overaged (T7351) tempers of 7075 aluminum alloy. Each of the observed endothermic or exothermic reactions that occurs over the 20 to 500°C temperature range has been ascribed to the dissolution or formation of a specific precipitate. The dissolution of each matrix phase,i.e., GP zones, ή and ή, can be characterized by a distinguishable dissolution temperature, dissolution enthalpy, activation energy, and activation entropy. The values of activation energy and activation entropy for the dissolution of the initial matrix precipitate of these phases indicate that the relative stability of the matrix precipitates is primarily influenced by the entropy rather than the energy term. This investigation provides a basis for the use of DSC analysis in the rapid, quantitative identification of the matrix microstructure of 7075 aluminum alloy as well as in the characterization of the matrix microstructure of other 7000 series aluminum alloys.
Journal Article•
TL;DR: In this paper, a correlation between differential scanning calorimetry and high temperature transmission electron microscopy for the characterization of preexisting matrix precipitates in the highest-strength and overaged tempers of 7075 aluminum was demonstrated.
Abstract: Correlation between differential scanning calorimetry and high temperature transmission electron microscopy for the characterization of preexisting matrix precipitates in the highest-strength and overaged tempers of 7075 aluminum was demonstrated. The solid state reactions undergone by these tempers in the 20-500 C temperature range were elucidated and expressed in terms of thermodynamic and kinetic parameters. The dissolution parameters for each phase are distinguishable and serve as guidelines for a rapid characterization of the matrix microstructure of these alloys.
TL;DR: In this article, a new method was presented to obtain the differential scanning calorimetry (DSC) curve associated with the growth and melting of the original crystals, and that with recrystallization and final melting process separately.
Abstract: The differential scanning calorimetry (DSC) melting curves of drawn nylon 6 were studied from the standpoint of reorganization of the crystals during the heating process. A new method was presented to obtain the DSC curve associated with the growth and melting of the original crystals, and that with the recrystallization and final melting process, separately. The results obtained show that, in the case of a heating rate of 10°C/min, the original crystals in the sample start perfecting themselves at temperatures far below their initial melting temperature and melt out below 222°C, recrystallization starts at about 210°C, and the newly emerged crystals melt out at 228°C. The superposition of two such constructed DSC curves reproduces the observed DSC curve well. Therefore, the double melting peaks of the sample are considered to be the result of superposition of three processes which occur successively during heating; perfection of the original crystals, melting of the perfected crystals concurrently with recrystallization, and melting of the recrystallized crystals.
TL;DR: The kinetic parameters of the polymerization of diglycidyl ether of bisphenol A with hexahydrophthalic anhydride and benzyldimethylamine as catalyst were determined using differential scanning calorimetry as mentioned in this paper.
Abstract: The kinetic parameters of the polymerization of diglycidyl ether of bisphenol A with hexahydrophthalic anhydride and benzyldimethylamine as catalyst were determined using differential scanning calorimetry. The reaction was found to be first order with some variation with temperature, and the activation energy and natural log of the frequency factor were 25 kcal/mole and ∼25 sec−1, respectively. These results are discussed with respect to a steady-state mechanism of the polymerization and compared with results reported for other epoxide–anhydride reactions.
TL;DR: Hydrated bovine brain gangliosides, although membrane lipid components, have physical characteristics which are very different from those of the membrane phospholipids.
TL;DR: The high temperature behavior of HDL indicates that apop protein A-1 is less important than apoprotein A-2 in maintaining the HDL apolar lipids in the form of a stable miroemulsion.
TL;DR: In this article, the phase diagram indicates the existence of a eutectic at a temperature TmE = 314°K and for a polymer volume fraction ϕ2E = 0.70, values close to those predicated by the Flory-Huggins theory.
Abstract: Binary mixtures of a linear polyester (poly(ϵ-caprolactone)) and a crystallizable monomer (trioxane) have been investigated by means of differential scanning calorimetry and optical and electron microscopy. The phase diagram indicates the existence of a eutectic at a temperature TmE = 314°K and for a polymer volume fraction ϕ2E = 0.70, values close to those predicated by the Flory–Huggins theory (using χ = 0.3). Microscopic studies reveal unusual morphologies: (1) In hypoeutectic mixtures, at room temperature, the solvent crystallizes as highly ramified or branched needles. When the remaining melt reaches the eutectic composition, transcrystallization of the polymer is induced by the epitaxial deposition (as established by electron diffraction) of polycaprolactone on the existing trioxane crystals, and leads to highly ordered structures. (2) In hypereutectic mixtures a predominantly spherulitic texture is observed. Blends of trioxane and several other linear polyesters are found to exhibit similar behavior.
TL;DR: In this paper, a dynamic mechanical study of four blends of PVdF and PMMA plus the constituent homopolymers indicates that these two polymers are partly compatible, but that a crystalline PVdf phase also exists.
TL;DR: The compatibility of random copolymers of para-chlorostyrene and ortho -chlorostyrerene with poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) has been studied by differential scanning calorimetry as mentioned in this paper.
TL;DR: The reversible denaturation of both apo and apophosphoryl derivatives of the dimeric ZnY+ metalloenzyme alkaline phosphatase can be described as a four-state process and the thermodynamic parameters characterizing the native and intermediate states relative to the unfolded state have been determined.
TL;DR: In this paper, differential scanning calorimetry has been used to characterize moisture transitions in paper and cellulose, including free water incorporation point (0.05 g/g), total bound water, fiber saturation point, and fiber saturation points.
Abstract: The association of water with cellulose is of significant technological importance. It forms the basis for the manufacturability of paper and ultimately controls, either directly or indirectly, mechanical, electrical, thermal, and optical properties. Differential scanning calorimetry has been used to characterize moisture transitions in these materials. Total bound water contents have been determined. Specific transitions for the model system, cotton linters, have been identified including free water incorporation point (0.05 g/g), total bound water (0.18 g/g), and fiber saturation point (0.05 g/g). Results are compared to those found in a pulsed nuclear magnetic resonance study in which a moisture distribution model was generated; free water point (0.046 g/g) and total bound water (0.19 g/g). The differential scanning calorimetry technique can provide a more readily available, less expensive, and simpler technique for paper/cellulose characterization and study.
ARCO1
TL;DR: In this paper, the α-form was the only crystalline polymorph present in the crystallized samples and the results were analyzed in terms of the Avrami equation, showing that the rates of crystallization depend upon the undercooling and the data agree with a growth of spherulites controlled by a secondary surface coherent nucleation mechanism.
TL;DR: The superior interfacial respreading found for the DPPC-analog indicates that its bulk phase liquid-crystalline transition temperature is not as directly related to its surface properties as it is in the case of DPPC.
TL;DR: In this article, the effects of substituent groups on the disordered phase behavior of these molecules are discussed, and the effect of substitution groups on disorder transitions in 1- and 2-methyladamantane, 1,3-dimethyladamide, 1-3,5-trimethyladamantsane, and 1-halogenoadamantanes have been investigated by differential scanning calorimetry.
Abstract: Order–disorder transitions in 1- and 2-methyladamantane, 1,3-dimethyladamantane, 1,3,5-trimethyladamantane, 1,3,5,7-tetramethyladamantane and in the 1-halogenoadamantanes have been investigated by differential scanning calorimetry. The effects of substituent groups on the disordered phase behaviour of these molecules are discussed.
TL;DR: In this paper, the evolution of enthalpy of As2Se3 glass during structural relaxation in the glass transition region was measured via differential scanning calorimetry for two types of time-temperature programs: rate-heating at 10 K/min following a cool at a constant rate (-20 to -0.31 k/min).
Abstract: The evolution of enthalpy of As2Se3 glass during structural relaxation in the glass transition region was measured via differential scanning calorimetry for two types of time-temperature programs: rate-heating at 10 K/min following a cool at a constant rate (-20 to -0.31 K/min) and isothermal annealing following a temperature step from an equilibrium state. The rate-heating data yield kinetic parameters for the structural relaxation which predict accurately the evolution of the enthalpy during isothermal annealing. The glass heat capacities were independent of cooling rate within experimental precision (≤0.2%). In this respect, As2Se3 is unlike previously studied glasses whose heat capacities are more dependent on thermal history.
TL;DR: These results represent the first direct determination of this important parameter for a ribo-oligonucleotide and are considerably lower than any of the previously published van't Hoff enthalpies but is consistent with values that can be derived from other calorimetric data.
TL;DR: Comparison between the lipid transition observed in whole cells, membrane vesicles, and extracted lipids enriched in elaidate reveal some basic similarities.
TL;DR: The results demonstrate that the heat capacity of single‐stranded polynucleotides is greater than that of the double-stranded forms and this increased heat capacity is mainly the result of the temperature dependence of the base‐stacking interactions in the single‐ Stranded form.
Abstract: The heat capacities of the single-stranded and double-stranded forms of polyadenylic acid, polyuridylic acid, and poly(uridylic and adenylic acid) were determined with a drop heat capacity calorimeter In addition, the temperature dependence of the apparent partial heat capacity (ϕCp) was measured with a newly developed differential scanning calorimeter The calculated ΔCp at 28°C for the transition poly(A)·poly(A) ⇄ 2 poly(A) was found to be 165 ± 24 cal/Kmol-base pair, compared with a value of 140 ± 28 for the transition poly(A)·poly(U) ⇄ poly(A) + poly(U) The temperature dependence of ϕCp of single-stranded poly(U) was consistent with the conclusion that it is totally unstacked at temperatures above 15°C The temperature dependence of ϕCp of single-stranded poly(A) was used to determine the base-stacking parameters for poly(A) The experimental results are consistent with a stacking enthalpy change of −85 ± 01 kcal/mol bases and a cooperativity parameter σ of 057 ± 003 for the stacking of adenine bases These results demonstrate that the heat capacity of single-stranded polynucleotides is greater than that of the double-stranded forms This increased heat capacity is mainly the result of the temperature dependence of the base-stacking interactions in the single-stranded form