Metrologically based procedures for the temperature, heat and heat flow rate calibration of DSC

Metrologically based measuring procedures and evaluation methods are recommended as guidance for practical temperature, heat and heat flow rate calibration of DSC instruments which are largely independent of instrumental, test and sample parameters. The relevant terms are defined, the measuring procedures and evaluation methods described, calibration materials and their characteristic data stated and guidance for the sample handling provided. Reference is made to three extended papers on calibration. The recommendations were developed by the working group Calibration of Scanning Calorimeters of the German Society of Thermal Analysis (GEFTA).Recommendation of the working group Calibration of scanning calorimeters of the Gesellschaft für Thermische Analyse e.V. (GEFTA)     

Volumes,heat capacities,and compressibilities of the mixtures of acetonitrile and 2-methoxyethanol

Heat capacities and speed of sound of (acetonitrile + 2-methoxyethanol) mixtures at 298.15 K and the densities of the same mixtures at T = (308.15 and 318.15) K were determined over the whole composition range. The excess of molar volume and isobaric heat capacity of the mixture, the partial molar volumes and heat capacities of both components of the mixture as well as the adiabatic and isothermal coefficients of compressibility and their excess were calculated from the obtained experimental data. The internal pressure of the examined system was also calculated. The results of investigations were analyzed and discussed. The behavior of the analyzed functions is similar to that observed in the case of the mixtures of acetonitrile with some aprotic solvents examined earlier.     

Concentration,temperature, and isotopy effects on the heat capacity of aqueous urea

Relations for the apparent molar heat capacity ?_c of urea in an aqueous solution depending on the molality m and temperature were obtained. A transition to the relations ?_c(m,T) for D₂O-(ND₂)₂CO and T₂O-(NT₂)₂CO systems was effected by temperature scaling. At low temperatures, the isotherms of the molar heat capacity C _p(m) of the protium and deuterium systems have minima shifted to more dilute solutions at elevated temperatures. At m = 1, C _p of a solution does not depend on temperature in both systems. The dependences C _p(T) also have minima at constant concentrations. The temperature of the minimum heat capacity is most effectively lowered by small additions of urea. For m = 0.25, T _min is 7.5 K lower than T _min of pure water, and its heat capacity is 0.08 J/(mol K) higher. A transition from m = 1.5 to m = 2 lowers the temperature of the minimum heat capacity by 3.6 K; thus, the heat capacity of solutions differs by 0.02 J/(mol K) only.     

Heat and concentration effects on the small heat shock protein, alpha-crystallin

alpha-Crystallin, a major protein of the mammalian lens, plays a vital role in maintaining the structural stability and transparency of the lens. It performs this function through chaperone-like activity; it has recently been reported that heating alpha-crystallin enhances this ability. The present studies, using both time-resolved and steady-state fluorescence methods, were carried out to compare the conformational changes that result from heating with those that result from increasing protein concentration (up to 70 mg/mL). The relative fluorescence quantum yield from tryptophan (Trp) present in alpha-crystallin increases and then decreases with a concomitant shift of the emission maximum to longer wavelengths when either heating times or protein concentrations are increased. The time profile of fluorescence decay was resolved into three components with lifetimes of ca 0.5, 3 and 7 ns and emission maxima of ca 340, 342 and 350 nm, respectively. With longer heating time or increasing concentrations the contribution from the longer-lived component increases at the expense of the shorter-lived species. These data indicate that with heating or at higher concentrations the internal Trp residues move to the surface of the protein giving a more hydrophobic exterior and possibly explain the reported increased chaperone activity upon heating. As a result of the concentration studies, alpha-crystallin may be more efficient in its chaperone activity in vivo than has been determined by in vitro experiments.     

The enthalpy and heat capacity characteristics of the water-N,N-dimethylpropyleneurea system

A variable-temperature isothermic-shell calorimeter was used to measure the heat effects of dissolution of N,N-dimethylpropyleneurea (DMPU) in the water-N,N-dimethylpropyleneurea system at 298 and 313 K over the interval of compositions x ₂ = 0−0.1 mole fractions. The partial molar enthalpies of mixture components and the enthalpies and heat capacities of mixing were calculated. The results were compared with the data on water-amide systems. The exothermic effect of mixing of nonelectrolytes with water was found to increase in the series dimethylformamide < dimethylacetamide ∼ DMPU < hexamethylphosphorotriamide (HMPT). The McMillan-Mayer formalism was used to determine the enthalpy and heat capacity parameters of pair and three-particle interactions between DMPU molecules in water. The behavior of DMPU in water was to a substantial extent determined by hydrophobic interactions between nonpolar molecule moieties. This interaction was, however, noticeably weaker than in solutions of HMPT.     

ViscosityB-coefficients,structural entropies and heat capacities,and the effects of ions on the structure of water

The water-structural contributions to the entropies and heat capacities of hydration of over 120 ions and the viscosity B-coefficients of nearly 80 aqueous ions are tabulated and correlated. B-coefficients for many more ions are predicted from this relationship and from their dependence on ionic size and charge. The structural entropies determine a unique scale of water structure making and breaking by the ions.     

Research progress in the heat resistance,toughening and filling modification of PLA

Due to its high strength, high modulus, excellent clarity, good biodegradability and biocompatibility, poly(lactic acid) (PLA), a bio-based thermoplastic polyester, has evolved into a competitive commodity material with potential to replace conventional petrochemical-based polymers. However, the wide applications of PLA have been hampered by its native drawbacks, such as low heat distortion temperature (HDT), inherent brittleness and relatively high cost. In recent years, researchers have devoted to breaking above-mentioned bottleneck and attempted to extend the application of PLA. This review will summarize recent work about the modification of PLA, especially focusing on enhancing HDT, toughening and reducing cost.     

Pressure dependence of the thermal conductivity,thermal diffusivity,and specific heat of some polymers

The pressure dependence of the specific heat of poly(methyl methacrylate), polystyrene, and atactic and isotactic polypropylene was determined from simultaneous measurements of thermal conductivity and diffusivity in a cylindrical geometry at 300°K and in the pressure range 0–37 kbar. The thermal conductivity and the diffusivity both increase strongly with pressure, while the specific heat decreases. The pressure dependencies are most pronounced at low pressures. The results are compared with other experimental results and with theoretical calculations.     

Temperature dependence of the heat capacities in the solid state of 18 mono-, di-, and poly-saccharides

The temperature dependence of the heat capacities in solid state C_p(T) of 18 mono-, di-, and poly-saccharides has been determined using a power-compensation differential scanning calorimeter. The saccharides were α-d-xylose, d-ribose, 2-deoxy-d-ribose, methyl-β-d-ribose, α-d-glucose, 2-deoxy-d-glucose, α-d-mannose, β-d-fructose, α-d-galactose, methyl-α-d-glucose, sucrose, maltose monohydrate, α-lactose monohydrate, cellobiose, maltotriose, N-acetyl-d-glucosamine, α-cyclodextrin, and β-cyclodextrin. The measurements were carried out at atmospheric pressure and from T = (288.15 to 358.15) K for 15 saccharides and from T = (288.15 to 328.15) K for d-ribose, 2-deoxy-d-ribose, and methyl-β-d-ribose. The present results are compared against literature values both at single temperatures, where most of the data are available, and throughout a range of temperatures, i.e., for C_p(T). The predictions of a recently published correlation for organic solids are briefly discussed. By grouping saccharides in subsets, our present results can be used to compare amongst saccharide isomers and to assess the effect of different chemical groups and molecular size.     

Modeling the heat flow and heat capacity of modulated differential scanning calorimetry

Modulated differential scanning calorimetry (MDSC) uses an abbreviated Fourier transformation ?r the data analysis and separation of the reversing component of the heat flow and temperature signals. In this paper a simple spread-sheet analysis will be presented that can be used to better understand and explore the effects observed in MDSC and their link to actual changes in the instrument and sample. The analysis assumes that instrument lags and other kinetic effects are either avoided or corrected for.     

Calculation of the formation enthalpies,standard entropies,and standard heat capacities of alkali and alkaline-earth germanates

The formation enthalpies, standard entropies, and standard heat capacities of alkali and alkaline-earth germanates were determined by regression analysis with allowance for error in the initial data (weights). The potentialities of the presented method of calculation appreciably grew due to the possibility to enhance the array of initial data independently of the crystal structure of compounds. The thermodynamic properties of alkali germanates were estimated for the first time and could be used in the physicochemical models of magmatic melts.     

Theory of the kinetics of adsorption taking into account heat evolution,where the rate of the process is limited by external mass and heat transfer

Conclusions The problem of the nonisothermal kinetics of adsorption for a granule of arbitrary shape, where the rate of the process is limited by external mass and heat transfer, was examined.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2831–2833, December, 1970.     

Determination of the purity,melting point and heat of melting of cyclic polyethers

Conclusions Differential scanning calorimeter was used to determine the thermal stability, purity, melting point, and heat of melting of benzo-15-crown-5, dibenzo-18-crown-6, and dibenzo-24-crown-8. These crown ethers have relatively high heats of melting.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 691–692, March, 1986.     

Thermophysical properties of binary liquid mixtures of polyether and n-alkane at 298.15 and 323.15 K: heat of mixing,heat capacity,viscosity, density and thermal conductivity

An apparatus for a rapid and simultaneous determination of the thermophysical properties excess enthalpy, isobaric heat capacity, kinematic viscosity, density and thermal conductivity has been developed. The experimental setup is subject of this paper. At 298.15 and 323.15 K, the systems ethylene glycol dimethyl ether–n-dodecane, diethylene glycol dimethyl ether–n-dodecane, triethylene glycol dimethyl ether–n-dodecane, tetraethylene glycol dimethyl ether–n-dodecane and diethylene glycol dibutyl ether–n-dodecane have been investigated. The experimental results are correlated and the macroscopic properties are interpreted.     

Determination of the Flory–Huggins χ parameter,the heat of dilution,and the excess heat capacity of some alkanes in polydimethylsiloxane by gas chromatography

The change in standard chemical potential of a number of alkanes on PDMS going from dilute solution to the perfect vapor Δ? was measured by gas chromatography over a large range of temperatures. The change in standard chemical potential of the alkane going from the pure liquid to the perfect vapor Δ? was calculated from fugacity data. These data were fitted separately to three Taylor's series expansions wherein the (partial) heat capacity of vaporization is zero, constant, and linearly dependent on temperature, respectively. On the basis of statistical and physical arguments it was concluded that the partial excess functions determined by gas chromatography should be described with a temperature-independent partial excess heat capacity.     

Effect of heat treatment on the morphology and structure of crystals,powders, and fibers of polyacrylonitrile and saran

As part of a study of chemical and physical changes accompanying the formation of carbons by the pyrolysis of polymers, conventional electron microscopy, electron diffraction, and scanning electron microscopy techniques have been used to examine structural and morphological features of polyacrylonitrile (PAN) crystals, powder, and fibers, and of Saran and poly(vinylidene chloride) (PVDC) powder. Changes accompanying the heating of these polymers in air and in nitrogen have been investigated. PAN crystals grown from propylene carbonate were similar to those obtained by Klement and Geil. When heated in air at 220°C they retained their morphology, and electron diffraction gave the same reflections as PAN. On further heating to 400°C in nitrogen the morphology was retained, but the diffraction was lost. Crystals treated in nitrogen alone at 200°C showed morphology similar to that of the polymer. PAN powders and fibers retained discernable external features of their morphology on heating to 800°C. These results are discussed with reference to changes which take place when poly(vinylidene chloride) and Saran are heated in the range 150–180°C, which results in the loss of one hydrogen chloride per monomer unit, and are subsequently carbonized at 800°C. The development of pore structure and the adsorptive properties of Saran carbons are also discussed.     

Effect of hydrolysis on heat capacity, thermodynamic functions, and the relaxation transition of crab chitin and chitosan

The heat capacity of crab chitin and chitosan is measured in a vacuum adiabatic calorimeter at 10–330 K. The thermodynamic characteristics (enthalpy, entropy, and Gibbs function) are calculated at T → 0 K to 330 K. Differential thermal analysis is used to calculate the relaxation transitions and thermal degradation of chitin and chitosan at 80–600 K. Acid hydrolysis is performed and its effect on the physicochemical properties and thermodynamic functions of chitin and chitosan is studied.