Showing papers on "Differential scanning calorimetry published in 1974"
TL;DR: Differential scanning calorimetry has been applied to the study of some simple model biomembranes and the endothermic phase transitions which they exhibit when transforming from the gel to liquid crystal phase have been studied, showing that clusters of gel and liquid crystalline lipids can coexist within this temperature range.
409 citations
TL;DR: The shifts of transition temperature caused by the morphine drugs appeared to be quite sensitive to their precise structure, some drugs more markedly than others.
135 citations
TL;DR: The phase behavior of bovine brain sphingomyelin in water has been determined by polarizing light microscopy, differential scanning calorimetry, and X-ray diffraction.
127 citations
TL;DR: Particle aggregation, induced by lipid phase transition, could also be observed in Streptococcus faecalis membranes, but no aggregation was seen in the fracture faces of some Bacillus species and Staphylococcus aureus, and the non-appearance of aggregation could be explained by the presence of branched-chain fatty acids in the membrane lipids of these bacteria.
122 citations
TL;DR: In this article, a phase diagram of polyethylene/1,2,4,5-tetrachlorobenzene and hexamethyl-benzene was calculated for χ = 0.37, which gave a eutectic temperature of 135°C.
112 citations
TL;DR: In this article, a thermal degradation of low-density polyethylene, free from additives, were heated at temperatures between 284° and 355°C under high-purity nitrogen.
Abstract: Samples of low-density polyethylene, free from additives, were heated at temperatures between 284° and 355°C under high-purity nitrogen. Changes in molecular weight distribution (MWD), molecular weight averages, and degree of long-chain branching (LCB) were followed by gel chromatography (GPC) and viscosity measurements. Other structural changes were investigated by infrared spectroscopy and differential scanning calorimetry (DSC). At 284° and 315°C, the MWD's were shifted toward higher molecular weights and the Mw values increased. At 333° and 355°C, the MWD's shift toward lower molecular weight, but the high molecular weight, tail is largely retained. Mw decreases slowly at 333°C. At 355°C, Mw undergoes a rapid initial drop which levels off. Mw/Mn and the degree of LCB increase with heating time and temperature. Olefinic unsaturation increases. The vinyl groups show a larger relative increase than do the trans-vinylene and vinylidene groups. At 355°C, the peak of the unimodal DSC thermogram is shifted to ∼3°C higher temperature. A lower melting peak then develops, and after 72 and 90 min the two peaks are about equal in size. The density increases from 0.922 g/cm3 to 0.930 g/cm3 for samples heated at 355°C, and the weight loss was 1.5% after 90 min. A reaction scheme for the thermal degradation of polyethylene is discussed. Initiation is suggested to be accomplished by scission of allylic CC bonds. Propagation proceeds by both intra- and intermolecular hydrogen abstraction, followed by β-scission. Termination can occur by both combination and disproportionation. Combination reactions are suggested to account for the observed formation of LCB and high molecular weight material. Due to changes in the degree of LCB during the degradation, viscometry alone will not give a proper measure of the changes in molecular weight.
104 citations
TL;DR: In this paper, the influence of molecular weight on the glass transition temperature of low polydispersity polystyrene (anionically prepared) has been studied by differential scanning calorimet...
Abstract: The influence of molecular weight (900 to 1.8 × 106) on the glass transition temperature of low polydispersity polystyrene (anionically prepared) has been studied by differential scanning calorimet...
96 citations
TL;DR: In this article, a nonlinearity in the changes of viscosity with temperature was found in sonicated human erythrocyte membranes at 18-19 °C, and it was inferred that the break observed in the membranes correspond to the transition temperature of the lipids.
88 citations
TL;DR: A differential scanning calorimeter was used to determine quantitatively the concentration of dispersed progesterone and cholesterol in a silicone rubber matrix and the heat of mixing and the solubility of the drug at the drug melting point.
87 citations
TL;DR: In this article, simple theory and techniques are explored and developed to utilize the dif-ferential scanning calorimeter for the determination of heat capacities, glass transition and enthalpies of transition between two thermodynamic states of substances.
79 citations
TL;DR: Pressure and temperature data obtained, taken together with the literature value for the bilayer volume expansion during solid-fluid phase transition, and inserted into the Clausius-Clapeyron equation yield a ΔH value of 8.8 kcal/mole, which is within experimental error of the ΔHvalue obtained from differential scanning calorimetry and serves to support the validity of the data and the experimental technique.
TL;DR: The effect of increasing concentrations of lysolecithin (1,2-dipalmitoyl-sn-glycerol-3-phosphorylcholine) on the gel → liquid crystal thermal transition was studied by differential scanning calorimetry (DSC) as discussed by the authors.
TL;DR: In this paper, the heat capacities at constant pressure were measured at temperatures above 273.15 K. The polymorphism of 1-tridecanol and 1-hexadecanol were studied and elucidated.
TL;DR: In this article, the chemical structure and cure characteristics of a group of phenolic resole resins were studied by means of three major analytical techniques: Gel permeation chromatography, NMR and differential scanning calorimetry.
Abstract: The chemical structure and cure characteristics of a group of phenolic resole resins were studied by means of three major analytical techniques. In particular, the effects on structure and reactivity of formaldehyde/phenol ratio and the type of reaction catalyst used were studied. Gel permeation chromatography was used to determine resin molecular weight distributions, and NMR, to determine chemical structural features. In this connection a selective oxidation procedure, converting free methylol groups to adehydes, has allowed unambiguous determination of methylene ether bridge structures to be made from the NMR data. The F/P ratio in a resole largely determines the type of molecular structures which are formed. However, triethylamine as a catalysts tends to favor methylene ether bridge formation, whereas sodium hydroxide favors methylene bridges. The rate and direction of subsequent thermal cure of the resoles prepared is shown by differential scanning calorimetry to depend markedly on the type of catalyst present during the curing stage. The DSC curing curves are interpreted in the light of the structural information provided by NMR.
TL;DR: In this paper, the equilibrium penetrant content of polystyrene, poly(phenylene oxide), and blends of these homopolymers was studied over a significant range of penetrant activity and temperature.
Abstract: The equilibrium sorption of n-hexane vapor and n-hexane liquid in solution cast films of polystyrene, poly(phenylene oxide), and blends of these homopolymers was studied over a significant range of penetrant activity and temperature. These equilibrium sorption measurements were supplemented by density determinations, refractive index measurements, differential scanning calorimetry and differential thermal analysis. A seemingly complicated pattern of results emerged when the equilibrium penetrant content was plotted as a function of blend composition. At relatively low activity and temperature the equilibrium concentration of n-hexane in these films monotonically increased with poly(phenylene oxide) content in the blend. Conversely, at high activities and in unit activity liquid, the equilibrium penetrant concentration exhibited a distinct minimum when plotted as a function of blend composition. At higher activities, solvent induced crazing accompanied the sorption of penetrant. These results were explained consistently by considering the nature of the sorption isotherm over an activity range sufficient to lower the glass transition temperature, of the equilibrated and swollen blend, below the temperature of the sorption experiment. Most importantly, the interpretation and explanation of these data are based upon phenomena common to all glassy polymer-organic penetrant systems and no special properties of this blend system were included in the analysis. The results, therefore, reflect the apparent homogeneity of polystyrene-poly (phenylene oxide) blends and are useful in considering the equilibrium of penetrant sorption in glassy polymers as a general class of materials.
TL;DR: In this paper, structural and thermal properties have been examined as a function of composition throughout the glass forming region of the AsTe binary system, and evidence is presented to support the conclusion that a new face-centered cubic crystalline structure has the binary stoichiometry AsTe.
TL;DR: The kinetic parameters of the complex reaction between phenol and formaldehyde in the presence of sodium hydroxide (NaOH) have been obtained by differential scanning calorimetry (DSC).
TL;DR: In this article, a combined static and dynamic temperature calibration is described, where the static calibration corrects the instrumental dial temperature reading and the dynamic calibration has instrumental and material components and therefore varies from specimen to specimen.
Abstract: A combined static and dynamic temperature calibration is described. The static calibration corrects the instrumental dial temperature reading. The dynamic calibration has instrumental and material components and therefore varies from specimen to specimen. It is obtained from individual DSC curves and so removes uncertainties in sample temperature due to varying mass, geometry, and heating rate. The instrumental performance is improved and specific heats may be obtained to an accuracy of ±1%.
TL;DR: In this article, the glass transition temperatures of linear and four-and six-branched regular star polystyrenes are measured by penetration, differential scanning calorimetry, and a density gradient technique.
Abstract: The glass transition temperatures of linear and four- and six-branched regular star polystyrenes are measured by penetration, differential scanning calorimetry, and a density gradient technique. The results of the three methods show that the glass transition temperature depends on the concentration of chain ends in the polymer sample. An attempt is made to assess the influence of the presence of the branch point on the glass transition temperature using a series of four-branched polystyrenes containing varying amounts of isoprene near the branch point. However, any effect of the central branch point on the glass transition temperature is obscured by plastification of polystyrene by polyisoprene.
TL;DR: In this article, the curing reaction of bisphenol A diglycidylether with 4,4′-diaminodiphenylmethane (DDM) was studied by thermoanalytical methods.
Abstract: The curing reaction of bisphenol A diglycidylether with 4,4′-diaminodiphenylmethane (DDM) was studied by thermoanalytical methods. The overall reaction was monitored through the exothermic heat of reaction by differential scanning calorimetry (DSC), and a method is developed for predicting isothermal conversion-time curves over a wide temperature range from the results of two dynamic DSC scans. The reaction mechanism is not specified but it is assumed not to change with conversion, and the rate is assumed to be controlled by a single rate constant of the Arrhenius form. A series of fully cured resins prepared with varying DDM concentration is characterized by penetrometer, thermal expansion, and DSC methods. The Tg's of these resins are compared with those obtained using the stoichiometric quantity of DDM and reacted to different calorimetric degrees of cure. The Tg of the resin increases by about 70[ddot];C in the final 10% of the curing reaction where ΔH measurements are least sensitive, so tha...
TL;DR: In this article, three halogen-containing poly-p-xylylenes were characterized by thermogravimetry and differential scanning calorimetry to determine their relative thermal stabilities in nitrogen and air.
Abstract: Poly-p-xylylene and three halogen-containing poly-p-xylylenes prepared by the Gorham method from purified dimers were characterized by thermogravimetry and differential scanning calorimetry to determine their relative thermal stabilities in nitrogen and air. As judged by these techniques, thermal stability in nitrogen is not greatly changed by halogenation of the cyclic dimer from which polymer is made. However, thermal oxidative stability depends on the type and degree of halogenation. Aliphatic fluorine atoms greatly improved upon the thermal oxidative stability of poly-p-xylylene. To a lesser but significant degree, two aromatic chlorine atoms, poly(dichloro-p-xylylene), also improved upon the thermal oxidative stability of poly-p-xylylene or poly-(chloro-p-xylylene). Oxidative degradation caused a rapid exothermic weight loss near 300°C for poly(dichloro-p-xylylene) and near 250°C for poly-p-xylylene and poly(chloro-p-xylylene) when films were heated at 10°C/min. Poly(dichloro-p-xylylene) maintained a constant weight during an induction period before it started to lose weight when it was heated isothermally at temperatures below 300°C. However, poly-p-xylylene and poly(chloro-p-xylylene) gained weight during oxidation before they lost weight when heated isothermally below 250°C.
TL;DR: In this article, a direct gas chromatographic resolution of enantiomers on optically active mesophases has been achieved using mesomorphic chiral carbonyl-bis-(amino acid esters).
TL;DR: In this article, the existence of a first-order phase transition, characterized by a separation temperature Ts, is verified and found to be predictable by the model, and details of morphology, including transitions in microstructure in certain temperature ranges, are also reported and shown to be consistent with the theory.
Abstract: The predictions of a model presented previously are tested with data on five styrenebutadiene–styrene copolymers. Differential scanning calorimetry and laser light transmission are the primary tools, spanning 180–630°K, with some evidence supplied also by electron microscopy and mechanical properties. The existence of a first-order phase transition, characterized by a separation temperature Ts, is verified and found to be predictable by the model. Details of morphology, including transitions in microstructure in certain temperature ranges, are also reported and shown to be consistent with the theory.
TL;DR: Differential scanning calorimetry has been applied to a study of elemental sulphur in this paper, where the thermal curves have been interpreted on the basis of allotropic conversions and melting points.
TL;DR: In this paper, the first estimated PtC bond strength for platinum-trimethylene complexes has been reported, where the authors used differential scanning calorimetry and thermogravimetric analysis.
TL;DR: In this paper, a model for the gel state of crosslinked potato starch was proposed, and it was concluded that the entropy of melting is the determining factor in establishing the temperature of gelatinization.
Abstract: Samples of epichlorohydrin crosslinked potato starch were prepared by using a high ratio of starch to water and alkali concentration below the gelatinization level. This yielded crosslinked samples that were partially crystalline, and where the number of crosslinks could be varied between 1 and 20 crosslinks per 100 anhydroglucose units. The degree of swelling varied regularly with degree of crosslinking, and the molecular weight between crosslinks Mc as derived from swelling data in a good swelling agent compared favorably with Mc derived from chemical analysis.
From the heat of gelatinization of the crosslinked starches, as observed in a differential scanning calorimeter, for gelatinization in glycerol, water, and dimethylsulfoxide, a model for the gel state of the crosslinked starch is proposed. It is concluded that the entropy of melting is the determining factor in establishing the temperature of gelatinization.
TL;DR: In this article, the authors measured changes in microhardness, small-angle X-ray scattering and heat capacity with time of annealing at several temperatures ranging from room temperature to 413 K.
Abstract: The heats of formation of amorphous (1− x )As 2 Se 3 · x Sb 2 Se 3 ( x = 0 to 0.4) referred to crystalline As 2 Se 3 and Sb 2 Se 3 were measured by liquid metal solution calorimetry. The values of heats of formation of amorphous (1− x )As 2 Se 3 · x Sb 2 Se 3 decreased from 1.39 ± 0.03 kcal · (g-at) −1 at x = 0 to 1.27 ± 0.04 kcal · (g-at) −1 at x = 0.4. The glass transition temperature and the temperatures of the maximum rates of crystallization and fusion were measured by differential scanning calorimetry. The glass transition temperature increased and the temperatures of the maximum rates of crystallization and fusion decreased with increasing Sb 2 Se 3 content. The relaxation process in amorphous (1− x )As 2 Se 3 · x Sb 2 Se ( x = 0.3) was investigated by measuring changes in microhardness, small-angle X-ray scattering and heat capacity with time of annealing at several temperatures ranging from room temperature to 413 K. With increasing annealing time the microhardness, the height and the temperature of the glass transition peak increased whereas the intensity of small-angle X-ray scattering decreased. These changes reflect relaxation towards a more stable structure of smaller molecular mobility. The changes in the enthalpy with annealing time and the activation energy spectra for relaxation were derived from the heat capacity data. The effects of temperature and time of annealing on the various properties are explained in terms of structural changes and relaxation kinetics.
TL;DR: In this article, an inhibitor-free styrene was polymerized by benzoyl peroxide and a copolymer was used as an intiator for 24 hours through the styrene.
Abstract: Burning rate, heat of combustion, flame temperature, and surface temperature of the two composites have been measured. Studies on thermal degradation kinetics and differential scanning calorimetry (DSC) of the propellants have also been made. The inhibitor-free styrene was polymerized by benzoyl peroxide. To prepare the oxygen-styrene copolymer, azobis isobutyronitrile was used as the intiator and oxygen was passed at 1 atm pressure for 24 hr through the styrene. The reaction was completed by adding benzoyl peroxide and maintaining the solution in thermostat at 50°C for another 24 hr until it became sufficiently viscous. The yield of styrene peroxide was of the order of 21-22%. Styrene peroxide was characterized by microanalysis and infrared spectroscopy. Infrared spectra have weak characteristic absorption bands at 7.42 // and 11.15 n and a broad absorption band at 9.75 \i characteristic of peroxide linkage. Burning rate was measured in a manner described earlier. The products of combustion were analyzed by an Orsat Gas Analyzer. The heat of combustion of the PS and copolymer propellant was determined by a Parr Bomb Calorimeter. Thermal degradation of the propellants was determined by the weight-loss method. The flame temperature was measured by the sodium-line reversal technique. The stray light incident on the spectroscope was minimized by putting a diaphragm between the flame and the lens. The measured temperature was corrected for a shift in wavelength on account of the red filter in the pyrometer which was used for calibration. For the polystyrene +70% AP propellant, the flame temperature was found to be 1550±30°C whereas for the corresponding copolymer propellant, the value was 1850±30°C. The surface temperature of the PS and copolymer propellants during burning was determined by using a Pt-Pt (Rh 10%) thermocouple (0.45-mm-diam). The hot junction was kept touching the surface by putting a load of 60-80 g. The cold junction was kept in water at room temperature. The thermocouple was calibrated beforehand by taking measurements on the melting points of silver nitrate, potassium dichromate, and
TL;DR: In this paper, the solid phase heat capacities of a number of hydrocarbon containing salts have been determined in the temperature range 273 to 373 K using a differential scanning calorimeter.
TL;DR: The x, T-phase diagram of the binary system Na2WO4Na2MoO4 has been redetermined at ambient pressure, taking into account the influence of hysteresis effects as discussed by the authors.