Thermal behavior of blends based on a thermoplastic-modified epoxy resin with a crosslinking density variation

The thermal behavior of blends based on a polystyrene (PS) and several epoxy-amine systems where amino groups were provided by a monoamine (MA) and a diamine (DA) mixed in different proportions was investigated. This way, the crosslinking density of epoxy-amine polymer was controlled and continuously changed from a linear polymer (epoxy-MA) to a highly crosslinked polymer (epoxy-DA). The effect of the MA–DA proportion and PS modifier on the thermal stability, glass transition, and polymerization reaction was studied by differential scanning calorimetry and thermogravimetric analysis. The MA–DA ratio and modifier proportion did not affect the reaction heat but affected the reactivity. The thermal stability and glass transition temperature increased by increasing the DA proportion in the blend as a result of the higher degree of crosslinking. A study of miscibility of blends based on glass transitions was performed. The thermoplastic-modified materials generally showed two glass transitions with values close to the those of the pure materials, indicating that the mixtures were separated into phases.     

Thermodynamic properties of the binary mixture of water and <Emphasis Type="Italic">n</Emphasis>-butanol

The molar heat capacities of the binary mixture composed of water and n-butanol were measured with an adiabatic calorimeter in the temperature range 78–320 K. The functions of the heat capacity with respect to thermodynamic temperature were established. A glass transition, solid–solid phase transition and solid–liquid phase transition were observed. The corresponding enthalpy and entropy of the solid–liquid phase transition were calculated, respectively. The thermodynamic functions relative to a temperature of 298.15 K were derived based on the relationships of the thermodynamic functions and the function of the measured heat capacity with respect to temperature.     

Thermodynamic properties of the azeotropic mixture of acetone and methanol

The molar heat capacities of the pure samples of acetone and methanol, and the azeotropic mixture composed of acetone and methanol were measured with an adiabatic calorimeter in the temperature range 78–320 K. The solid–solid and solid–liquid phase transitions of the pure samples and the mixture were determined based on the curve of the heat capacity with respect to temperature. The phase transitions took place at 126.16±0.68 and 178.96±1.47 K for the sample of acetone, 157.79±0.95 and 175.93±0.95 K for methanol, which were corresponding to the solid–solid and the solid–liquid phase transitions of the acetone and the methanol, respectively. And the phase transitions occurred at 126.58±0.24, 157.16±0.42, 175.50±0.46 and 179.74±0.89 K corresponding to the solid–solid and the solid–liquid phase transitions of the acetone and the methanol in the mixture, respectively. The thermodynamic functions and the excess thermodynamic functions of the mixture relative to standard temperature 298.15 K were derived based on the relationships of the thermodynamic functions and the function of the measured heat capacity with respect to temperature.     

Effect of gamma-irradiation on morphology of copolymer of tetrafluoroethylene with hexafluoropropylene as revealed by thermomechanical analysis and radiothermoluminescence

The morphologies of different commercial forms of the copolymer of tetrafluoroethylene with hexafluoropropylene (FEP) were investigated by thermomechanical analysis. Both granules and powders of FEPs have similar morphologies, but different temperatures for phase transitions. Irradiation reduces the crystallinity of the FEPs and results in a transformation from the crystalline to the amorphous form. After heating of various forms of FEP irradiated at 77 K, there are three intense maxima of radiothermoluminescence in the temperature ranges: 150–144, 174–167, and 210–206 K. The nature of the radiothermoluminescence and the phase transitions of the FEPs as a result of gamma—irradiation are discussed.     

Phase separation and morphology development in a thermoplastic-modified toughened epoxy

The morphologies developed by blends based on a polystyrene modifier and an epoxy system polymerized with a monoamine and a diamine mixed in different proportions that are phase separated during the polymerization, were studied. The proportion of monoamine–diamine in the system affects the crosslinking degree of the material, which was controlled and continuously modified from a linear polymer to a highly crosslinked polymer. The effect of modifier proportion, polymerization temperature, and monoamine–diamine ratio on the final morphology was investigated. Different types of morphologies were developed depending mainly on the composition of modifier in the blend. The nature of the separated phases in the different types of morphologies was investigated and confirmed by experiments with a solvent and elemental analysis. Explanations for the developed morphologies as a function of the variables were proposed and discussed in detail.     

Simulation of molecular fractionation and species distributions in phase separation of polystyrene-modified epoxy/monoamine–diamine blends

Molecular fractionation occurred at the beginning of phase separation in blends based on a polystyrene modifier and an epoxy system undergoing polymerization with a monoamine and a diamine mixed in different proportions was studied thermodynamically. The study was conducted by simulating in each separated phase the species distributions of components of the blend, the stoichiometric ratio, and the proportion of monoamine–diamine at cloud-point conditions. A model based on Flory–Huggins theory described in a previous paper Rico et al. [1] where the interaction parameters were dependent on temperature, composition, and conversion, χ(T,?,p), and where the polydispersity of the components was taken into account, was used for simulation. The effect of modifier proportion, monoamine–diamine ratio and polymerization temperature on molecular fractionation and species distribution was determined and analyzed. Explanations of the estimated trends were given on the basis of the thermodynamic model used.     

Optimization and Calculation of the EuCl<Subscript>3</Subscript>–MCl (M = Na,K, Rb,Cs) Phase Diagrams

By using the CALPHAD technique, an optimization of the binary EuCl₃–MCl (M = Na, K, Rb, Cs) systems has been carried out. To describe the Gibbs energies of liquid phases in these systems the new modified quasi-chemical model was used in the pair-approximation for short-range ordering. From the measured phase equilibrium data and the experimental thermo-chemical properties, the EuCl₃–MCl phase diagrams were optimized and calculated. A set of thermodynamic functions has been optimized based on an interactive computer-assisted analysis. The calculated phase diagrams and thermodynamic data are self-consistent.     

Thermally-induced dielectric relaxation spectra in three aldohexose monosaccharides

Three aldohexose monosaccharides, d-glucose, d-mannose, and d-galactose, were examined by scanning temperature dielectric analysis (DEA) from ambient temperatures through their melts. Phase transitions, including glass transition (T _g) and melting temperature (T _m), were evaluated by differential scanning calorimetry (DSC). The monosaccharides were found to exhibit thermally-induced dielectric loss spectra in their amorphous-solid phase before melting. Activation energies for electrical charging of each of the monosaccharides were calculated from an Arrhenius plot of the tan delta (e″/e′, dielectric loss factor/relative permittivity) peak frequency versus reciprocal temperature in Kelvin. The DEA profiles were also correlated with the DSC phase diagrams, showing the changes in electrical behavior associated with solid–solid and solid–liquid transitions.     

Predicting the phase behaviour of solvent-modified epoxy resins

 The Flory–Huggins equation has been used to model the equilibrium phase behaviour of a solvent-modified epoxy resin intended for the fabrication of porous components by chemically induced phase separation followed by evacuation of the solvent after curing. Points in composition–temperature space corresponding to a transition from homogeneous to heterogeneous postcuring microstructures have been identified for a variety of solvents using a thermal gradient oven. Assuming this transition to coincide with the cloud-point curve corresponding to the gel point of the resin, the data were used in conjunction with the predictions of the Flory–Huggins equation to estimate the interaction parameter and its temperature dependence for each solvent. Phase diagrams in composition–conversion space were then calculated for a range of curing temperatures. Received: 20 September 1999 Accepted: 21 December 1999     

Thermodynamics of alternating copolymer of propylene and CO in the 0–550 K region

The temperature dependences of the heat capacity and the temperatures and enthalpies of physical transitions of the alternating copolymer of propylene and CO were studied in the 5–550 K region by adiabatic vacuum and dynamic calorimetry techniques. The heat of combustion of the copolymer was measured at 298.15 K in a calorimeter with a static bomb and an isothermal shield. The thermodynamic parameters of glass transition and fusing were estimated. The thermodynamic functions in the 0–450 K region and the thermodynamic characteristics of the formation of the copolymer from simple substances atT=298.15 K andp=101.325 kPa were calculated. The thermodynamic parameters of the alternating copolymerization of bulk propylene and CO were calculated in the 0–450 K region at standard pressure.     

Contribution to the thermodynamics of the molybdenum — Oxygen — Chlorine system

Starting from tabulated thermodynamic data of stable compounds in the Mo−O−Cl system, phase diagrams for the Mo−O−Cl system were developed on the basis of GIBBS' phase law by means of thermodynamic calculations. The behaviour of molybdenum trioxide in a temperature gradient tube was investigated experimentally under chlorinating conditions, using⁹⁹Mo as indicator. The thermochromatografically separated compounds were characterized by their deposition temperature in the temperature gradient tube and by an activation analytical determination of their Mo/Cl ratio. The experimental results were compared with the calculated phase diagram.     

Thermal analysis of the structure of segmented polyurethane elastomers

Polyurethanes were prepared from 4,4′-methylenebis (phenyl isocyanate) (MDI), 1,4-butanediol (BD), and poly(tetrahydrofurane) polyether polyol (PTHF) by melt polymerization. The –OH functional group ratio of polyol/total diol was kept constant at 0.4, while the ratio of the isocyanate and hydroxyl groups (NCO/OH) changed between 0.940 and 1.150. The thermal analysis of the polymers by DSC and DMTA measurements indicated several transitions. The three glass transition temperatures observed were assigned to the relaxation of the aliphatic –CH₂– groups of the polyol, and to that of the soft and hard segments, respectively. The glass transition temperature of the soft and hard phase changed with the NCO/OH ratio indicating changes in phase structure and composition confirmed also by the maximum in the number of relaxing soft segments. Changes in the relatively small number of end-groups result in considerable modification of mechanical properties. Strength is determined by molecular mass and interactions, while stiffness depends mainly on phase structure. Surprisingly enough, –OH excess yields stiffer polymers, since the interaction of the –OH groups results in a decrease in the amount of the soft phase. A unique correlation was found between tensile modulus and the number of relaxing soft segments.     

乙醇和甲苯组成的最低共沸混合物热力学性质的研究

The molar heat capacity of the azeotropic mixture composed of ethanol and toluene was measured by a high precision adiabatic calorimeter from 80 to 320 K. The glass transition and phase transitions of the azeotropic mixture were determined based on the heat capacity measurements. A glass transition at 103.350 K was found. A solid-solid phase transition at 127.282 K, two solid-liquid phase transitions at 153.612 and 160.584 K were observed, which correspond to the transition of metastable crystal to stable crystal of ethanol and the melting of ethanol and toluene, respectively. The thermodynamic functions and the excess ones of the mixture relative to the standard temperature 298.15 K were derived based on the relationships of the thermodynamic functions and the function of the measured heat capacity with respect to temperature.     

Comparative Thermodynamic Investigation of the Bi–GaSb System

Results of the thermodynamic investigations in the Bi–GaSb system are presented in this paper. Thermodynamic characteristics experimentally determined by Oelsen's calorimetric method were compared with values predicted by different thermodynamic predicting methods (general solution model, Kohler, Muggianu, Toop, Hillert) at the temperature of 1073 K. Also, based on the obtained cooling curves and microstructure analysis of the investigated samples by optical microscopy, phase diagram of the Bi–GaSb system was investigated and compared with literature data. This revised version was published online in July 2006 with corrections to the Cover Date.     

Experimental investigation and thermodynamic modeling of the Au–Ge–Ni system

Abstract  

Phase equilibria in the Au–Ge–Ni ternary system were studied by means of scanning electron microscopy, electron probe microanalysis, X-ray diffraction, and differential scanning calorimetry. The phase relations in the solid state at 600 °C as well as a vertical section at Au₇₂Ge₂₈–Ni were established. No ternary compound was found at 600 °C. On the basis of the experimental phase equilibria data, a thermodynamic model of the Au–Ge–Ni ternary system was developed using the CALPHAD method. Thermodynamically calculated phase diagrams are shown at 600 °C, in two vertical sections and the liquidus projection. Reasonable agreement between the calculations and the experimental results was achieved.     

水与正丁醇二元体系最低共沸混合物的热容

Molar heat capacities of n-butanol and the azeotropic mixture in the binary system [water （x=0.716） plus n-butanol （x=0.284）] were measured with an adiabatic calorimeter in a temperature range from 78 to 320 K. The functions of the heat capacity with respect to thermodynamic temperature were estabhshed for the azeotropic mixture. A glass transition was observed at （111.9±1.2） K. The phase transitions took place at （179.26±0.77） and （269.69±0.14） K corresponding to the solid-hquid phase transitions of n-butanol and water, respectively. The phase-transition enthalpy and entropy of water were calculated. A thermodynamic function of excess molar heat capacity with respect to temperature was estabhshed, which took account of physical mixing, destructions of self-association and cross-association for n-butanol and water, respectively. The thermodynamic functions and the excess thermodynamic ones of the binary systems relative to 298.15 K were derived based on the relationships of the thermodynamic functions and the function of the measured heat capacity and the calculated excess heat capacity with respect to temperature.     

Equilibrium of two liquid phases and critical phenomena in a ternary system of cyclohexane-pyridine-acetic acid in the 10–55°C range

A visual polythermal method is used to study the mutual solubility of components and critical phenomena in a ternary system of cyclohexane-pyridine-acetic acid in the 10.0–55.0°C range. It is noted that the isothermal solubility diagrams of the system in the 10.0–52.5°C range is characterized by the occurrence of a closed separation region. A temperature dependence of the mixture composition, which corresponds to the critical point of solubility, is determined. It is found that with the increase in the temperature a two-liquid phase region disappears through a non-critical point.     

Heat capacity and thermodynamic functions of cadmium fluoride

Adiabatic calorimetry was used to measure heat capacities of cadmium fluoride in the range 5–340 K. Spline smoothing of the heat capacity versus temperature data allowed thermodynamic functions to be calculated within the range of the measurement temperatures. The thermal behavior of CdF₂ was studied and showed no phase transitions within 300–723 K.     

Thermal analysis of protein–metallic ion systems

Advanced thermal analysis methods, such as temperature modulated DSC (differential scanning calorimetry) and quasi-isothermal TMDSC were used to analyze the protein–metallic ion interactions in silk fibroin proteins. The precise heat capacities were measured and theoretically predicted in this study. To remove bound water and simplify the system, a thermal cycling treatment through both standard DSC and TMDSC was used to detect the underlying heat capacity and reveal the phase transitions of the silk–metallic salts system. Results show that K⁺ metallic salts play the role of plasticizer in silk fibroin proteins, which reduces the glass transition (T_g) of the pure silk protein and negatively affects its structural thermal stability. On the other hand, Ca²⁺ metallic salts act as an anti-plasticizer, and increase the glass transition and the thermal stability of the silk protein structure. This indicates that the thermal analysis methods offer a new pathway to study protein–metallic ion systems, yielding very fruitful information for the study of protein structures in the future.