Showing papers on "Differential scanning calorimetry published in 1969"

Calorimetric evidence for the liquid-crystalline state of lipids in a biomembrane

Abstract: Both membranes of Mycoplasma laidlawii and water dispersions of protein-free membrane lipids exhibit thermal phase transitions that can be detected by differential scanning calorimetry. The transition temperatures are lowered by increased unsaturation in the fatty acid residues, but in each case they are the same for membranes and lipids. The transitions resemble those observed for synthetic lipids in the lamellar phase in water, which arise from melting of the hydrocarbon chains within the phospholipid bilayers. Such melts are cooperative phenomena and would be greatly perturbed by apolar binding to protein. Thus the identity of membrane and lipid transition temperatures suggests that in the membranes, as in water, the lipids are in the bilayer conformation in which the hydrocarbon chains associate with each other rather than with proteins. Observations of morphological changes indicate that osmotic imbalance occurs when the membrane transition temperature exceeds the growth temperature, and that for transport processes to function properly the hydrocarbon chains must be in a liquid-like state.

Specific Heat and Heat of Crystallization of Amorphous Germanium

Abstract: : The specific heat and heat of crystallization of vapor- and electro-deposited amorphous germanium were measured with a differential scanning calorimeter. The excess specific heat of the amorphous germanium over that of crystalline phase increased linearly with temperature over the temperature range from 215 to 460K. The heat of crystallization of the amorphous films was found to be about 2.75 k cal/gm-atom. The interpretation of the results in terms of the structure is discussed. The specific heat of crystalline germanium was also measured for the temperature range from 215 to 700K. (Author)

Rate effects in the measurement of polymer transitions by differential scanning calorimetry

Abstract: Depending on heating rate, differences as large as 15°C in polymer transition temperatures may be observed in DCS measurements. A heat transfer analysis of the method shows that this rate dependence is a result of a lag in the heat path to the test sample and lag in heat transfer within the sample. Experiments confirmed the analysis. Methods for obtaining the correct values of transition temperatures are given.

Liquid‐induced crystallization of poly(ethylene terephthalate)

Abstract: Amorphous unoriented poly(ethylene terephthalate) was crystallized at 25°C by various organic liquids. The crystalliznity induced in the amorphous polymer was measured by differential scanning calorimetry and infrared spectroscopy. The ability of liquids to interact with and induced crystallinity in the amorphous polymer was classified on the basis of their solubility parameters. Measurements of the density of liquid-crystallized 0.8-mil films of poly(ethylene terephthalate) indicated the presence of extensive internal voids in the semicrystalline polymer matrix. Comparison of differential scanning calorimetric thermograms and infared spectra of heat-crystalized and liquid-crystallized polymer indicated significant differences in the polymer morphologies induced by the two crystallization processes.

Transport in Molten Salts under Pressure. I. Glass‐Forming Nitrate Melts

Abstract: The electrical conductances of calcium nitrate–potassium nitrate solutions have been measured as a function of temperature to 200°C and pressure to 3000 atm, by imposing oil pressure directly on samples held within an externally heated bomb. Log (conductance) varies linearly with pressure at high temperatures, but curvilinearly at low temperatures, the “activation volume” appearing to increase with increasing pressure. “Activation volumes” increase rapidly with decreasing temperature. The observations may be accounted for if the “ideal glass transition temperature” T0 is taken to be the only pressure‐dependent variable in a simple equation previously found to describe temperature and composition‐dependent variations in conductance in this, and other, systems. Within uncertainty limits, T0 varies linearly with pressure and mole fraction, thus pressure equivalents of given composition changes can be simply stated. Using a thermodynamic relation applicable at the glass transition, the observed dependence of T0 on pressure is used to predict the change of heat capacity at the glass transition. The value is confirmed within error by direct measurements. Application of the Adam–Gibbs theory of relaxation processes leads to the derivation of approximate “constant (configurational) entropy” parameters, E (Sc), which exhibit qualitatively the properties of “constant volume” parameters, E(V), observed in studies of nonionic liquids.The electrical conductances of calcium nitrate–potassium nitrate solutions have been measured as a function of temperature to 200°C and pressure to 3000 atm, by imposing oil pressure directly on samples held within an externally heated bomb. Log (conductance) varies linearly with pressure at high temperatures, but curvilinearly at low temperatures, the “activation volume” appearing to increase with increasing pressure. “Activation volumes” increase rapidly with decreasing temperature. The observations may be accounted for if the “ideal glass transition temperature” T0 is taken to be the only pressure‐dependent variable in a simple equation previously found to describe temperature and composition‐dependent variations in conductance in this, and other, systems. Within uncertainty limits, T0 varies linearly with pressure and mole fraction, thus pressure equivalents of given composition changes can be simply stated. Using a thermodynamic relation applicable at the glass transition, the observed dependence of ...

Scanning Calorimetry of Aromatic, Difunctional, Unsaturated, and Substituted Acid Esters of Cholesterol

Abstract: Ten nonaliphatic esters of cholesterol, including three difunctional acid esters, have been studied by differential scanning calorimetry. The heats of transition for the smectic, cholesteric, and l...

Relaxation in Polyurethanes in the Glass Transition Region

Abstract: A study has been made of the relaxation phenomena in three series of polyurethanes in the neighborhood of their glass transition temperatures and above. The technique of dynamic mechanical relaxation was used in the investigation at various frequencies up to 110 Hz. Differential Scanning Calorimetry (DSC) was also used as a supplement to the mechanical measurements. The series are: (1) H series based on polymerization of hexamethylene diisocyanate and various diols, (2) DP series based on polymerization of 4,4′ diphenylmethane diisocyanate and various diols, and (3) 4M series based on polymerization of 4‐methyl meta phenylene diisocyanate and various diols. Four relaxation regions are discernible in the temperature range investigated and these are labelled β, α, αt and αc in order of increasing temperature. The following molecular mechanisms are associated with these relaxations: (1) The β relaxation (DP and 4M series only) arises from phenyl group motion in the chain backbone, (2) the α relaxation (all s...

Melting behavior of poly-4-methyl-pentene-1 single crystals

Abstract: The present study described an investigation on differential scanning calorimetry (DSC) for isotactic poly-4-methyl-pentene-1 (P4MP1) single crystals. DSC was carried out in the following three procedures: (a) The crystals grown isothermally at various temperatures in n-hexadecane. tetralin, p-xylene. and decalin were heated at a constant heating rate of 80°C/min; (b) Some samples of crystals were heated at four kinds of heating rate, 80, 40, 10, and 5°C/min; (c) The crystals used in the above experiment (b) were irradiated to 14 Mrads with60Co γ-ray. and these irradiated samples were heated at the same rate as in (b). Only the crystals from decalin revealed an endothermic peak in the vicinity of 80 °C (named as peak 1), which was concluded to originate from the solid-solid transition between two crystalline modifications. All crystals grown in various solvents gave a slightly observable endothermic peak in the vicinity of 125 °C (peak 2). The origin of peak 2, however, could not be determined whether it was based on a transition between crystalline modifications, or it merely reflected the abrupt change in the molecular motion at this temperature region. In high temperature region, two endothermic peaks that were inseparable from each other appeared (peak 3 and 4). The positions of peak 3 and 4, and the endothermic quantities of these peaks, from the above experiments (a). (b). and (c). were found to depend on crystallization condition and heating rate. These results could be explained well by considering that peak 3 corresponded to the melting of original single crystals, and peak 4 to the melting of the crystals with thicker lamellae that were formed in bulk during heating by partial melting and recrystallization. The introduction of the irradiation method helped us in investigating the origins of these four kinds of peak.

The measurement of fatty solids by differential scanning calorimetry

Abstract: A method has been developed for the measurement of the solids content of vegetable and animal fats by differential scanning calorimetry Although precision is about half that of existing dilatometric methods, this is a rapid procedure, designed for hydrogenation control Elapsed analysis time for the determination of solids at two temperatures is about 40 min, compared with 3 to 4 hr by dilatometry Procedures are outlined employing either of two commercially available instruments

Thermal Analysis of Organic Medicinals. I. Detection of the Molecular Compound Formation by the Differential Thermal Analysis and by the Differential Scanning Calorimetry

Abstract: The differential thermal analysis (DTA) and the differential scanning calorimetry (DSC) were carried out with various two-component mixtures of organic materials prepared by mechanical mixing, by solidification after fusion and by evaporation of the solution of components. As was expected, when the components did not form a molecular compound, no distinct difference in the thermograms were observed between the kinds of samples except that in the ones for the simple physical mixture, additional small peaks due to polymorphic transition appeared occasionally. On the contrary, the method of sample preparation exerted marked influence on the result, if the molecular compound was formed between components. Usually, the evaporated mixture solidifies in the state of stable equilibrium ; therefore, the DTA and DSC curves were the same as that for the mixture of the isolated compound and one of the components. In the case of the physical mixture which is in the metastable state, the curves showed characteristic peaks of the metastable fusion (endothermic), and of the subsequent compound formation and solidification (exothermic). Thus, by applying DTA or DSC to the physical mixture, a simple method was developed for detecting the molecular compound between organic materials. Also, the heat of formation of the molecular compound could be obtained by reducing the total area of the DSC peaks for the isolated compound from that for the corresponding physical mixture.

Thermodynamics of Mesophase Transitions from Calorimetric Measurements

Abstract: The increasing amount of research on mesophases (liquid crystals), the availability of differential scanning calorimetry for rapid, quantitative thermodynamic evaluation, and the availability of compounds in a number of homologous series of compounds have led to studies that attempt to interpret the nature of mesophase transitions. This paper collects and reviews data for two homologous series and provides the general conclusions which can be drawn from the therodynamics of mesophase formation.

Study of polyethylene blends by differential scanning calorimetry

Abstract: The melting behaviors of linear and branched polyethylene blends were studied using a Perkin-Elmer DSC-1B differential scanning calorimeter. Three endothermic peaks were occasionally observed in the DSC thermogram on polyethylene blends which had not been subjected to any isothermal annealing. The nature of the third intermediate temperature peak is discussed in relation to the prior cooling rate, the blend composition and the molecular structures of both components. The results appear to indicate that the intermediate peak is associated with the fusion of the hybrid crystallites of linear and branched polyethylenes. These hybrid crystallites seem to be formed on the rapid cooling of lean linear polyethylene blends. Blends containing low molecular weight branched polyethylene seem inclined to form the hybrid crystallites.

Apparent anomalous thermal behavior of polymers undergoing a glass transition

Abstract: Glass transitions in certain polymer samples were detected as a step change in a DTA trace in the exothermic sense. This anomaly is explained as a manifestation of the volume relaxation shown to occur at the glass transition in internally strained samples.

Glass transition temperatures of several fluorine‐containing polymers

Abstract: The glass transition temperatures Tg of several fluorine-containing polymers were determined by use of the differential scanning calorimeter. Values between −3 and 230°C were obtained. In polymers of α-olefins, Tg increases with the fluorine content of the backbone and the length of the n-perfluoroalkyl branch. In styrene polymers Tg also is higher if the backbone contains fluorine but nearly the same Tg's are found for polymers with phenyl and pentafluorophenyl groups. Saturated polymers of perfluoro-α,ω-dienes have lower Tg's than polyperfluoro-α-olefins. The Tg's of chloroperfluoropolymers are higher than those of perfluoropolymers. Polyperfluoropentadiene-1,3 has the lowest Tg of the polymers examined. Polyperfluoropentadiene-1,3 forms by 1,4-addition.

Thermodynamics of polymerisation of heterocyclic compounds. Part. III. The heat capacity, entropy, enthalpy, and free energy of tetroxan

Abstract: A precision, adiabatic vacuum calorimeter and a differential scanning calorimeter have been used to measure the heat capacity of tetroxan over the temperature range 80 to 420°K. An estimate has been made of heat capacity values below 80°K. Values of the heat capacity, entropy, enthalpy, and free energy are listed at 10° intervals. Values of 22.6 ± 0.4 kJ · mole−1 and 385 ± 1°K are obtained for the heat of fusion and melting temperature, respectively. The vapour pressure (P) of tetroxan has been measured over the temperature range 300–375°K. The results are summarized as The results have been used in conjunction with previously published data to evaluate the entropy changes occurring in the system formaldehyde ⇌ trioxan ⇌ tetroxan ⇌ polyoxymethylene.