Differential Scanning Calorimetry Heating Research Articles

Denaturation and aggregation processes in thermal gelation of whey proteins resolved by differential scanning calorimetry

Gelation of globular proteins on heating involves two separate stages. The first is partial unfolding (denaturation) of the native globular structure; the second is intermolecular aggregation. Denaturation involves dissociation of intramolecular bonds (non-covalent and, in some cases, disulfide) and is therefore an endothermic process. The aggregation step involves formation of new bonds between protein molecules, and would therefore be expected to give a differential scanning calorimetry (DSC) exotherm on heating, but numerous previous studies of the thermal gelation of whey proteins, carried out on conventional (fast scanning) DSC calorimeters (typical sample mass ∼15–50 mg), have shown only endothermic transitions. In the present work, however, we have observed the endothermic (denaturation) and exothermic (aggregation) processes in thermogelation of whey protein isolate (WPI) as separate transitions in DSC heating traces recorded on a Setaram microcalorimeter (sample mass ∼850 mg). Under conditions where aggregation occurs much more slowly than denaturation (low protein concentration; low ionic strength) the two transitions are well resolved, with the exotherm from aggregation following the endotherm from denaturation. The position of the exotherm, however, appears to be time-dependent rather than temperature-dependent. On reduction in heating rate, the apparent peak-maximum temperature of the aggregation exotherm decreases towards the (essentially constant) position of the denaturation endotherm, and, at sufficiently low scan rates, the exotherm becomes obscured by the more intense endotherm. Progressive displacement of the exotherm into the temperature range of the denaturation endotherm also occurs in response to changes that accelerate intermolecular aggregation and accompanying gelation (addition of salt; increasing protein concentration). The absence of a detectable exotherm in previous studies using conventional calorimeters is attributed to the much smaller sample mass than in the Setaram instrument, giving much faster heat transfer, which may cause the exothermic heat flow from the slow aggregation process to be swamped by the endothermic heat flow from the more rapid denaturation process.

Uniquely Broad Glass Transition Temperatures of Gradient Copolymers Relative to Random and Block Copolymers Containing Repulsive Comonomers

Nitroxide-mediated controlled radical polymerization is used to synthesize gradient and block copolymers of styrene (S) and 4-acetoxystyrene (AS), and conventional free radical polymerization is used to synthesize S/AS random copolymers. The S/AS copolymers are hydrolyzed to yield S/4-hydroxystyrene (HS) copolymers. Gel permeation chromatography and 1H NMR of aliquots taken during polymerization yield proof of the controlled nature of the gradient copolymer structures. The glass transition temperature (Tg) responses are compared using the derivative of differential scanning calorimetry heat curves, with the temperature range over which the derivative exceeds a base level being equated to the Tg breadth. A single, narrow Tg is obtained in each random copolymer, consistent with a single phase of limited compositional nanoheterogeneity. Two narrow Tgs are evident in each block copolymer, consistent with well-developed nanophases containing nearly pure S or nearly pure AS or HS units with a very narrow interp...

Effect of cooling rate on crystallization and magnetic properties of metallic Co43Fe20Ta5.5B31.5 glass

X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were employed to investigate the effect of cooling rate on both non-isothermal and isothermal crystallization behavior of metallic Co43Fe20Ta5.5B31.5 glass. It is found that all DSC traces of the metallic Co43Fe20Ta5.5B31.5 glasses under different cooling rates exhibit one exothermic peak, which indicates that the crystallization of metallic Co43Fe20Ta5.5B31.5 glass follows a one-stage process. The XRD patterns of the metallic Co43Fe20Ta5.5B31.5 glasses under different cooling rates after non-isothermal DSC up to 1150 K show that all melt-spun ribbons of Co43Fe20Ta5.5B31.5 alloys produced under different cooling rates have the same precipitation phases after crystallization in the continuous heating DSC. In the case of non-isothermal crystallization process, the thermodynamic parameters are not affected by the cooling rate. During the isothermal annealing, the cooling rate also does not change the crystallization kinetics of metallic Co43Fe20Ta5.5B31.5 glass, but the nucleation rate in the whole crystallization process. The magnetic hysteresis loops measuring indicates that the values of saturation moment and coercivity exhibit correlation with the cooling rate.

Cryoprotective Effects of Saccharides on the Freeze-Drying of Sonicated Vesicles of the Novel Lipid A Analog, E5531

A sonicated dispersion of the novel lipid A analog, E5531, was feeze-dried in the presence of various additives such as saccharides and polyalcohols, and their cryoprotective effects were investigated. Fusion of the vesicles was examined by measuring fluorescence energy transfer and size distribution. Cryoprotective ability differed among the addtive species. The addition of polyalcohols led to considerable fusion. Although monosaccharides, similar to disaccharides, completely prevented the fusion of the vesicles during lyophilization, they showed far less ability to retain the entrapped calcein in the vesicles compared to disaccharides. Differential scanning calorimetry heating profiles of vesicles that had been lyophilized with various additives were obtained. Disaccharides and monosaccharides again resulted in markedly different thermal properties of the vesicles. This variety in cryoprotective ability of saccharide species can be attributed to differences in their interaction with the E5531 head group.

Pressure Perturbation and Differential Scanning Calorimetric Studies of Bipolar Tetraether Liposomes Derived from the Thermoacidophilic Archaeon Sulfolobus acidocaldarius

Differential scanning calorimetry (DSC) and pressure perturbation calorimetry (PPC) were used to characterize thermal phase transitions, membrane packing, and volumetric properties in multilamellar vesicles (MLVs) composed of the polar lipid fraction E (PLFE) isolated from the thermoacidophilic archaeon Sulfolobus acidocaldarius grown at different temperatures. For PLFE MLVs derived from cells grown at 78°C, the first DSC heating scan exhibits an endothermic transition at 46.7°C, a small hump near 60°C, and a broad exothermic transition at 78.5°C, whereas the PPC scan reveals two transitions at ∼45°C and 60°C. The endothermic peak at 46.7°C is attributed to a lamellar-to-lamellar phase transition and has an unusually low Δ H (3.5 kJ/mol) and Δ V/ V (0.1%) value, as compared to those for the main phase transitions of saturated diacyl monopolar diester lipids. This result may arise from the restricted trans-gauche conformational changes in the dibiphytanyl chain due to the presence of cyclopentane rings and branched methyl groups and due to the spanning of the lipid molecules over the whole membrane. The exothermic peak at 78.5°C probably corresponds to a lamellar-to-cubic phase transition and exhibits a large and negative Δ H value (−23.2 kJ/mol), which is uncommon for normal lamellar-to-cubic phospholipid phase transformations. This exothermic transition disappears in the subsequent heating scans and thus may involve a metastable phase, which is irreversible at the scan rate used. Further, there is no distinct peak in the plot of the thermal expansion coefficient α versus temperature near 78.5°C, indicating that this lamellar-to-cubic phase transition is not accompanied by any significant volume change. For PLFE MLVs derived from cells grown at 65°C, similar DSC and PPC profiles and thermal history responses were obtained. However, the lower growth temperature yields a higher Δ V/ V (∼0.25%) and Δ H (14 kJ/mol) value for the lamellar-to-lamellar phase transition measured at the same pH (2.1). A lower growth temperature also generates a less negative temperature dependence of α. The changes in Δ V/ V, Δ H, and the temperature dependence of α can be attributed to the decrease in the number of cyclopentane rings in PLFE at the lower growth temperature. The relatively low Δ V/ V and small Δ H involved in the phase transitions help to explain why PLFE liposomes are remarkably thermally stable and also echo the proposal that PLFE liposomes are generally rigid and tightly packed. These results help us to understand why, despite the occurrence of thermal-induced phase transitions, PLFE liposomes exhibit a remarkably low temperature sensitivity of proton permeation and dye leakage.

Thermochemical Analysis of Venlafaxine Hydrochloride Polymorphs 1−5

Five polymorphs of the antidepressant drug venlafaxine hydrochloride (VenHCl) are reported. Forms 1 and 2 are crystalline modifications, form 3 is obtained by melting, form 4 is a hydrate/alcoholate, and form 5 is an amorphous, glassy phase from sublimation. These five polymorphs of VenHCl are characterized by differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and additionally structures of polymorphs 1 and 2 are confirmed by single-crystal XRD (Pca21 and P21/n). The endotherms for the melting transition of forms 1−4 appear at slightly different temperatures in different patents. Moreover, DSC thermograms of forms 1 and 2 (recorded at 10 K/min) are single, sharp peaks, and there is no discussion of phase transition other than melting. Our DSC profiles (recorded @ 2 K/min) show that both forms 1 and 2 undergo a phase transition just after the melting event in the temperature range 210−220 °C. Form 1 transforms to form 3 (phase from melting) and form 5 (phase from sublimation), whereas form 2 converts completely to form 5 in DSC heat−cool−heat cycles. These transitions are also examined under a hot stage microscope. Form 5 is not very stable and converts to form 1 (inert conditions) or hydrate form 4 (open air) in laboratory experiments. In the heating cycle of DSC (30−300 °C), both polymorphs 1 and 2 undergo sublimation to form 5, as characterized by thermogravimetry-infrared (TG-IR) spectroscopy of the evolved vapor. There is no interconversion between polymorphs 1 and 2 in the ambient-to-melting temperature range. Crystal lattice energy of polymorph 2 is lower than form 1 by 2.0 kcal/mol. However, form 1 is stable to ball mill grinding, whereas form 2 partially transforms to hydrate phase 4, suggesting that form 1 is perhaps more suitable in pharmaceutical formulations. With the identification of at least five different solid-state modifications, VenHCl belongs to the category of highly polymorphic drug substances.

Kinetics study on non-isothermal crystallization of the metallic Co 43Fe 20Ta 5.5B 31.5 glass

The crystallization kinetics of metallic Co 43Fe 20Ta 5.5B 31.5 glass has been studied by continuous heating differential scanning calorimetry. The DSC traces have been analyzed in terms of activation energy and kinetic model. It is found that all the DSC traces have a single exothermic peak which is asymmetrical, with a steeper leading edge and a long high temperature tail. The heating rate has a significant influence on the shape of the DSC curve, activation energy and transformation mechanism. The existence of a critical heating rate, β crit = 20 K min −1, is evident. The activation energy for crystallization are determined as 594.8 and 581.4 KJ mol −1 for the heating rates β = 5–20 K min −1, and 437.7 and 432 KJ mol −1 for the heating rates β = 25–65 K min −1, when using the Kissinger equation and the Ozawa equation, respectively. For the volume fraction crystallized, α, E c dependence was obtained by the general Ozawa's isoconversional method. Using the Suriñach curve fitting procedure, the kinetics was specified. Namely, the crystallization begins with the Johnson–Mehl–Avrami nucleation-and-growth mode and the mode which has been well described by the normal grain growth kinetic law. These two modes are mutually independent. The proportion between the JMA-like and the NGG-like modes is related to the heating rate. The JMA kinetics is manifested as a rule in the early stages of the crystallization. The JMA exponent, n, initially being larger than 4 and continuously decreases to 1.5 along with the development of crystallization. The NGG-like mode dominates in the advanced stages of the transformation with the NGG exponent, m = 0.5 and is the major and principal kinetic characteristics for heating rate, β > 25 K min −1.

Effect of relaxation and primary nanocrystallization on the mechanical properties of Cu 60Zr 22Ti 18 bulk metallic glass

The dependence of the microscopic and macroscopic mechanical response of a Cu-based bulk metallic glass (BMG) on the degree of thermal relaxation and different crystalline volume fractions has been studied. The samples were characterised by constant-rate heating differential scanning calorimetry (DSC), macroscopic compression and nanoindentation tests. Macroscopic compression tests revealed that the fracture strength and Young's modulus increase with increasing annealing time, and therefore, with increasing crystalline volume fraction. However, embrittlement of the material is also found for longer annealing treatments. A perfect solute mixture model of defect-free nanoparticles embedded in an amorphous matrix was used to account for the strengthening effect. Nanomechanical tests have contributed to the understanding of the mechanical behaviour of the heat-treated BMG states under investigation.

Glass transition in hyperquenched water?

It has been unclear whether amorphous glassy water heated to around 140-150 K remains glassy until it crystallizes or whether instead it turns into a supercooled and very viscous liquid. Yue and Angell compare the behaviour of glassy water under these conditions to that of hyperquenched inorganic glasses, and claim that water stays glassy as it heats up to its crystallization point; they also find a 'hidden' glass-to-liquid transition at about 169 K. Here we use differential scanning calorimetry (DSC) heating to show that hyperquenched water deposited at 140 K behaves as an ultraviscous liquid, the limiting structure of which depends on the cooling rate--as predicted by theoretical analysis of the liquid-to-glass transition. Our findings are consistent with a glass-to-liquid transition-onset temperature (T(g)) in the region of 136 K (refs 3,4), and they indicate that measurements of the liquid's properties may clarify the anomalous properties of supercooled water.

Comparative Investigation by Two Analytical Approaches of Enthalpy Relaxation for Glassy Glucose, Sucrose, Maltose, and Trehalose

In an effort to understand the stability of glassy sugars such as glucose, sucrose, maltose, and trehalose, the molecular mobility below the glass transition temperature (Tg) was investigated by an enthalpy relaxation measurement with differential scanning calorimetry (DSC). The glassy sample was aged over several days at (Tg - 10) K to (Tg - 30) K, before a DSC heating scan was taken. The relaxed enthalpy (deltaHrelax) was estimated from the endothermic peak area. The enthalpy relaxation time was analyzed from the time course of deltaHrelax using two different approaches; Kohlrausch-Williams-Watts (KWW) and extended Adam-Gibbs (exAG). TauKWW, which is defined as the mean average enthalpy relaxation time in a distribution, and tau(eff)0 and tau(eff)infinity, which correspond to the enthalpy relaxation time of the initial minimum and final maximum cooperative rearrangement region, were estimated by KWW and exAG, respectively. And three activation energies for enthalpy relaxation were calculated from the Arrhenius plot. Although these deltaEs originated from different theoretical backgrounds, almost the same trend was observed for a comparison of the values of the four sugars. The finding that the deltaEs of glassy trehalose were the largest among the four sugars may support the reason that glassy trehalose is an effective stabilizer.

Solid + Liquid Equilibria of Isotactic Poly(1-butene) + n-Alkanes by Differential Scanning Calorimetry and Dynamic Methods

Isotactic crystalline low-molecular-weight poly(1-butene), iPBu-1, was synthesized by using a metallocene catalyst. The molecular weight was determined by using gel permeation chromatography. The chemical structure of iPBu-1 was verified by using high-temperature 13C NMR spectroscopy and differential scanning calorimetry (DSC) methods. The solid + liquid phase equilibria (SLE) of iPBu-1 with three long-chain n-alkanes (n-tridecane, n-octadecane, and n-tricosane) were studied by DSC and dynamic methods. It was found that in the first and second heating runs of the mixture the multiple endotherms were detected on heating. This was attributed to the solid + liquid phase transition at melting temperature and to the solid + solid phase transitions of the well-known polymorphic forms, form I‘ → form II. After the next few heating runs of the mixture, one new endotherm for the same sample was detected. It was assumed that the new endotherm, being observed at higher temperature, was evidence of the transformation of iPBu-1 into the new high-temperature crystalline form of polymer, form I (twinned hexagonal). The same was observed over the systematic thermal conditioning after a few days. By the performance of DSC heating and dynamic method experiments over a large concentration range, the T−x phase diagrams of polymer−solvent systems could be constructed. From these diagrams, it was found that the solubility of iPBu-1 is the highest in n-tridecane and the lowest in n-tricosane in the mole fraction range measured. A similar conclusion was made from a dynamic method. The excess Gibbs energy models were used to describe the nonideal behavior of the liquid phase and to estimate the solubility of iPBu-1 in the whole mole fraction range.

Crystallization Kinetics of Zr<sub>65</sub>Ni<sub>25</sub>Ti<sub>10</sub> Metallic Glass Alloy

The crystallization reaction of Zr65Ni25Ti10 (at. %) metallic glass was studied by using differential scanning calorimetry (DSC) at constant heating rate. Two distinct exothermic peaks were observed from the continuous heating DSC curves, implying the crystallization process undergoes two different stages. The crystallization kinetic parameters, including activation energy (E), Avrami exponent (n) and frequency factor (K0), were determined with non-isothermal analysis method based on the DSC data. The values of E are 267.353 KJ/mol and 224.293 KJ/mol, n 4.0±0.1 and 6.8±0.1, K0 4.4±0.05E+20 and 2.0±0.08E+15, for the first and second crystallization stage, respectively. The results suggest that the crystallization mechanism is governed dominantly by interface controlled growth with constant nucleation rate for the first crystallization stage and with increasing nucleation rate for the second stage.

Intimate blending of binary polymer systems from their common cyclodextrin inclusion compounds

A procedure for the formation of intimate blends of three binary polymer systems polycarbonate (PC)/poly(methyl methacrylate) (PMMA), PC/poly(vinyl acetate) (PVAc) and PMMA/PVAc is described. PC/PMMA, PC/PVAc, and PMMA/PVAc pairs were included in γ-cyclodextrin (γ-CD) channels and were then simultaneously coalesced from their common γ-CD inclusion compounds (ICs) to obtain intimately mixed blends. The formation of ICs between polymer pairs and γ-CD were confirmed by wide-angle X-ray diffraction (WAXD), fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). It was observed [solution 1H nuclear magnetic resonance (NMR)] that the ratios of polymers in coalesced PC/PMMA and PC/PVAc binary blends are significantly different than the starting ratios, and PC was found to be preferentially included in γ-CD channels when compared with PMMA or PVAc. Physical mixtures of polymer pairs were also prepared by coprecipitation and solution casting methods for comparison. DSC, solid-state 1H NMR, thermogravimetric analysis (TGA), and direct insertion probe pyrolysis mass spectrometry (DIP-MS) data indicated that the PC/PMMA, PC/PVAc, and PMMA/PVAc binary polymer blends were homogeneously mixed when they were coalesced from their ICs. A single, common glass transition temperature (Tg) recorded by DSC heating scans strongly suggested the presence of a homogeneous amorphous phase in the coalesced binary polymer blends, which is retained after thermal cycling to 270 °C. The physical mixture samples showed two distinct Tgs and 1H T1ρ values for the polymer components, which indicated phase-separated blends with domain sizes above 5 nm, while the coalesced blends exhibited uniform 1H spin-lattice relaxation values, indicating intimate blending in the coalesced samples. The TGA results of coalesced and physical binary blends of PC/PMMA and PC/PVAc reveal that in the presence of PC, the thermal stability of both PMMA and PVAc increases. Yet, the presence of PMMA and PVAc decreases the thermal stability of PC itself. DIP-MS observations suggested that the degradation mechanisms of the polymers changed in the coalesced blends, which was attributed to the presence of molecular interactions between the well-mixed polymer components in the coalesced samples. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2578–2593, 2005

Development of freeze-dried injectable formulation for the novel lipid A analog, E5531

A sonicated dispersion of the novel lipid A analog, E5531, was feeze-dried in the presence of various additives such as saccharides and polyalcohols, and their cryoprotective effects were investigated. Fusion of the vesicles was examined by measuring fluorescence energy transfer and size distribution. The ability as cryoprotectants differed among the addtive species. The addition of polyalcohols led to considerable fusion. Although monosaccharides, similar to disaccharides, completely prevented the fusion of the vesicles during lyophilization, they showed far less ability to retain the entrapped calcein in the vesicles compared to disaccharides. Differential scanning calorimetry heating profiles of vesicles that had been lyophilized with various additives were obtained. Disaccharides and monosaccharides again resulted in markedly different thermal properties of the vesicles. This variety in cryoprotective ability of saccharide species can be attributed to differences in their interaction with the E5531 head group.

Development of Freeze-Dried Injectable Formulation for the Novel Lipid A Analog, E5531

A sonicated dispersion of the novel lipid A analog, E5531, was feeze-dried in the presence of various additives such as saccharides and polyalcohols, and their cryoprotective effects were investigated. Fusion of the vesicles was examined by measuring fluorescence energy transfer and size distribution. The ability as cryoprotectants differed among the addtive species. The addition of polyalcohols led to considerable fusion. Although monosaccharides, similar to disaccharides, completely prevented the fusion of the vesicles during lyophilization, they showed far less ability to retain the entrapped calcein in the vesicles compared to disaccharides. Differential scanning calorimetry heating profiles of vesicles that had been lyophilized with various additives were obtained. Disaccharides and monosaccharides again resulted in markedly different thermal properties of the vesicles. This variety in cryoprotective ability of saccharide species can be attributed to differences in their interaction with the E5531 head group.

Preparation and Enzymatic Degradation of Blends of Poly(L‐Lactic Acid) and Potentially Biodegradable Thermotropic Copolyester

Blend films of poly(L‐lactic acid) (PLLA) and potentially biodegradable thermotropic liquid crystalline (LC) copolyester (HBS) based on hydroquinone, p‐hydroxybenoic acid, and sebacic acid were prepared, using solution blending followed by melt‐pressing. All blend films were opaque, except a transparent, pure PLLA. The differential scanning calorimetry (DSC) heating curves showed the glass transition (T g), cold crystallization exotherm (T cc), and melting endotherm (T m) associated with PLLA, while the HBS transitions were not shown. The T ms were not affected by blending, indicating that these two polymers are immiscible. However, a slight shift T gs in the blends implied that these two polymers are partially miscible in the amorphous region. Degradation behaviors of the films were studied in a buffer solution containing proteinaze‐K at 37°C. The degradation rate of blend films was affected significantly by the blend composition. PLLA/HBS (90/10) and (80/20) films showed slightly higher degradation rates than that of pure PLLA, while the films containing more than 50 wt% of HBS showed little weight loss. Thermal stability of the blends was increased with increasing HBS content. Blends with 10 wt% of HBS showed the best tensile strength.

Thermodynamic aspects of the constitution, grain refining, and solidification enthalpies of Al-Ce-Si alloys

The ternary Al-Ce-Si phase equilibria were investigated using X-ray diffraction (XRD) methods, metallography, scanning electron microscopy with energy-dispersive X-ray analysis (SEM/EDX) and wavelength-dispersive X-ray microanalysis, and differential thermal analysis (DTA). The focus was on the Al-rich corner and the phases in equilibrium with (Al). Key experiments were selected by preliminary thermodynamic calculations. A consistent thermodynamic description was developed using the Calphad method incorporating all experimental data. A thermodynamic assessment for the binary Ce-Si system was also performed. Two ternary phases, Ce(Si1−xAlx)2 (τ1) and AlCeSi2 (τ2), were confirmed. The phase Al2CeSi2 (τ4) was sporadically observed, but is apparently metastable. The earlier reported phase Al4Ce3Si6 could not be confirmed. In addition, the enthalpy of solidification of five Al-rich ternary alloys was measured in a differential scanning calorimetry (DSC) heat flux calorimeter. The agreement with the thermodynamic enthalpy calculations is acceptable. The fundamental intricacies involved in calculating a “latent” heat for alloys with a freezing range are pointed out. Various phase diagrams of the Al-Ce-Si system were calculated based on the thermodynamic description. They were used to quantitatively identify possible contributions to the grain refinement potential of Ce in Al-Si alloys due to the phase equilibria.

Crystallization behavior and morphology of poly(ethylene‐co‐trimethylene terephthalate)s

AbstractThe melt crystallization behaviors and crystalline structures of poly(ethylene terephthalate) (PET), poly(trimethylene terephthalate), and poly(ethylene‐co‐trimethylene terephthalate) (PETT) were investigated with differential scanning calorimetry (DSC), polarized optical microscopy (POM), and X‐ray diffraction at various crystallization temperatures (Tcs). The PETT copolymers were synthesized via the polycondensation of terephthalate with ethylene glycol and trimethylene glycol (TG) in various compositions. The copolymers with 69.0 mol % or more TG or 31.0 mol % or less TG were crystallizable, but the other copolymers containing 34–56 mol % TG were amorphous. The DSC isothermal results revealed that the addition of a small amount of flexible TG (up to 21 mol %) to the PET structure slightly reduced the formation of three‐dimensional spherulites. A greater TG concentration (91–100%) in the copolyesters changed the crystal growth from two‐dimensional to three‐dimensional. The DSC heating scans after the completion of isothermal crystallization at various Tcs showed three melting endotherms for PET, PETT‐88, PETT‐84, and PETT‐79 and four melting endotherms for PETT‐9 and PETT. The presence of an additional melting endotherm could be attributed to the melting of thinner and imperfect copolyester crystallites. Analyses of the Lauritzen–Hoffman equation demonstrated that PETT‐88 had the highest values of the product of the lateral and folding surface free energies, and this suggested that the addition of small amounts of flexible trimethylene terephthalate segments to PET disturbed chain regularity, thus increasing molecular chain mobility. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4255–4271, 2004

A differential thermal analysis of the gelatinization and retrogradation of wheat starches with different amylopectin chain lengths

This paper reports on the influence of amylopectin chain length distributions on the gelatinization and retrogradation of starch. Wheat starch samples with different amylopectin chain length distributions were isolated, and the gelatinization and retrogradation phenomena of the samples were studied with differential scanning calorimetry (DSC). Wheat starch containing longer side chains of amylopectin (LCA) in higher ratios exhibited a sharper and deeper peak at higher temperatures in the heating DSC curve than did starch with low ratios. The retrogradation of starch was advanced with LCA. Although the re-gelatinization temperatures for retrograded starch varied slightly, the peak depth and enthalpy for re-gelatinization were higher with high ratios of LCA. For retrograded starch, each ordered region of amylopectin was not very different, however, more number of ordered regions was formed as the ratio of LCA of amylopectin increased.

An alternative treatment of non-isothermal heterogeneous transformations: Application to the crystallization of Ge 0.13Sb 0.23Se 0.64 alloy

Continuous heating differential scanning calorimetry is frequently employed to study the kinetics of transformation reactions and, in particular, the crystallization of the glassy alloys. Such data are analyzed by the Kissinger method, which was originally derived for the study of homogeneous reactions. Although the consensus in the literature, over several decades, was that such applications (i.e. to heterogeneous solid state transformations) of the Kissinger method are not valid, nevertheless, by assuming that the transformation products and mechanism do not change with temperature, it is possible a valid application of Kissinger method to non-isothermal heterogeneous transformations. In this work, the principal objections to these applications are addressed and bearing in mind the quoted assumptions alternative derivations of theoretical results are provided. These results demonstrate that the Kissinger method is valid for heterogeneous reactions of the type described by the Johnson–Mehl–Avrami–Kolomogoroff equation in the isothermal case. Isothermal and continuous heating data on the crystallization of Ge 0.13Sb 0.23Se 0.64 semiconducting alloy are presented. These experimental results and the discussion presented here help to clarify the effects of incubation time on the non-isothermal transformation kinetics and provide a further demonstration of the validity of the generalized Johnson–Mehl–Avrami–Kolomogoroff theory for the description of heterogeneous solid state transformations.