The effect of gamma irradiation on the pressure dependence of the room temperature transition in PTFE

Some of the effect of gamma irradiation on the pneumatic pressure dependence of the well established room temperature transition (ca. 19 °C) in polytetra(fluoroethylene) are described. The experiments, conducted up to a maximum gamma dosage of 60 Mrad and a superimposed nitrogen pressure of 48.3 MPa indicate a significant reduction in the room temperature transition as well as its pressure dependence with the increasing of the gamma dosage. These data, combined with the observed and reported reduction in the free volume (actually net volume) are consistent with the proposition that irradiation process results in a reduction in the ‘effective internal pressure’ due to extensive bond scission. The latter process is manifested in an observed dramatic decrease in the molecular weight. Data on the compressibility and coefficient of thermal expansion, accompanied by thermodynamic arguments, indicate that the room temperature transition more closely resembles a second order transition as gamma dosage increases. This is consistent with a change in system behaviour progressing from a viscoelastic to that of a brittle glassy polymer as confirmed by monitoring the polymer creep behaviour following rapid pressurisation. Data for the ‘freshly’ irradiated specimens indicate highly transient post-irradiation induced changes in the polymer morphology.     

On anomalies of generalized susceptibilities at phase transitions described by several order parameters

For a model potential in which the third-order interaction of order parameters is the lowest allowed by symmetry, behaviour of generalized susceptibilities is described along all characteristic thermodynamic paths. A set of numerically calculated susceptibility curves is presented, illustrating diverse manifestation of possible phase transition types.     

Glass transition and exclusion model in crystallization of polyether-polyester block copolymers with amide linkages

Polyether-polyester block copolymers having various polyetheramide contents were synthesized. Single glass transition intermediated in temperature between the glass transition temperatures of polyester and polyetheramide components was found for all of polyether-polyesters. The compositional variation of glass transition exhibited a similar trend to the predicted result of thermodynamic theory for compatible polymer blends. The incompatible pair of homopolyester and homopolyether was forced to be compatible after copolymerization. A modified theoretical prediction for the glass transition of copolymers based on the thermodynamic theory is proposed. Consistent results between theoretical prediction and experimental measurements were found. Unlike homopolyesters, the glass transition temperature of copolymer amorphous domains gradually decreases with crystallization time. An exclusion model for the crystallization of polyester segments in copolymers is proposed. The temperature width of the glass transition increases with crystallization time. The broadening towards the low temperature side in glass transition is interpreted as the evidence of crystallization-induced partial phase separation. Instead of forming macroscopic segregation, the excluded polyether segments resided in-between crystalline polyester lamellae and mix with amorphous polyesters to generate amorphous domains exhibiting concentration gradient along the lamellar basal surface normal. Further increasing the polyetheramide segment content brings the excluded polyetheramide segments to form domains among the crystallized polyester spherulites so as to inhibit the occurrence of spherulitic impingement.     

On the melting behaviour of calcium monoxide under different atmospheres: A laser heating study

The melting behaviour of calcium monoxide has been revisited by quasi-containerless laser heating under controlled atmosphere. The current results suggest that the large discrepancy in the literature data for the melting temperature of CaO is probably linked to the influence of the environmental oxidising/reducing conditions. The CaO solidification point measured in this work is (3222 ± 25) K in an oxidising environment, in agreement with previous research performed under similar conditions. In a reducing atmosphere, the liquid/solid transition occurs at a slightly, but systematically lower, less accurately reproducible temperature, (3192 ± 40) K. These phase transition temperatures are not depending on the external pressure, up to 0.3 MPa. In the latter case, radiance and optical spectroscopy measurements revealed a more abundant formation of colour centres, i.e. a higher concentration of oxygen defects in the material, which can affect the thermodynamic stability of the solid at very high temperatures. A similar behaviour may be expected to occur in multi-component material systems including CaO.     

A comment on the phase transition in Quasi-One-Dimensional system CSH2(D2)PO4

We propose an explanation of the unusual behaviour of thermodynamic quantities near the phase transition in quasi-one-dimensional system CsH₂(D₂)PO₄.     

Theoretical Investigation for the Active-to-Passive Transition in the Oxidation of Silicon Carbide

The oxidation of silicon carbide at high temperatures from 673.15 to 2173.15 K is investigated by using thermodynamic equilibrium calculations and a mass transfer model. The dominant reaction of the active-to-passive transition and five other dominant reactions, which are in six different temperature regions, have been determined according to the main equilibrium products. Then, a modified Wagner's model has been developed to determine the active-to-passive transition boundary by combining mass transport and thermodynamic calculations. The present theoretical calculations satisfactorily explained the reported experimental and theoretical data. The influence of flow rate on the active-to-passive transition boundary has been explained using our model. The rate controlling mechanism of the oxidation at the active-to-passive transition point is proposed.     

Generic Phenomenological Theory of Vitrification

In the framework of the thermodynamics of irreversible processes and using a graphical approach based on the simple theorems of differential geometry, a generic phenomenological treatment of the glass transition is developed. A thermodynamic derivation of the basic kinetic condition for vitrification—the Frenkel–Kobeko–Reiner equation—is given in a new generalized form. The temperature course of the thermodynamic functions and the kinetic characteristics of vitrifying systems are constructed using one of the general principles of irreversible thermodynamics. The results thus obtained underline the substantial differences and formal similarities between vitrification, considered as a diffuse kinetic transition and thermodynamic phase transformations. A general reconsideration of the axiomatics of the thermodynamics and kinetics and kinetics of glass transition and relaxation is attempted.     

Solubility behaviour of polystyrene: thermodynamic studies using gas chromatography

Studies of thermodynamic parameters and solution properties of polystyrene with various solvents have been performed by gas-liquid chromatography (g.l.c.). A range of solvents has been selected for this purpose. Experiments were performed at 162.31°C, 171.84°C, 219.77°C and 229.43°C. From the chromatographic retention data obtained at these temperatures, the solubility behaviour of polystyrene with each of the solvents selected has been observed and the Flory-Huggins interaction parameters, infinite dilution activity coefficients and heats of solution were determined. The glass transition temperature of polystyrene was determined experimentally.     

Solvent dependence of the viscous and viscoelastic properties of a high molecular weight polystyrene in moderately concentrated solution

The steady-flow viscosity and viscoelastic behaviour of two solutions of a sensibly monodisperse polystyrene of high molecular weight (M_w = 498 000) have been measured over a temperature range of 100°C for identical concentrations of 20.55 wt.%. Toluene and methyl ethyl ketone were chosen as the two low viscosity solvents having, respectively, good and marginal thermodynamic affinities. Dynamic viscoelastic measurements were made at a frequency of 41 kHz using travelling torsional waves. At this frequency, both solutions exhibit behaviour characteristic of the rubbery region, and the ratio of the dynamic viscosity normalised by dividing by the corresponding solvent viscosity is independent of the solvent until the onset of the glass transition region with decreasing temperature. The storage shear modulus of the toluene solution in the rubbery region is higher than for the MEK solution, indicating a higher entanglement density in the better solvent and a larger polymer radius. Some features of the results in the poor solvent (MEK) appear to indicate that, as the temperature decreases, partial exclusion of the solvent leads to the formation both of stronger entanglements and of macromolecular aggregates or bundles, as suggested by Dreval and others^6–8,11,22.     

Chemical equilibrium analysis of silicon carbide oxidation in oxygen and air

Due to their refractory nature and oxidation resistance, Ultra-High Temperature Ceramic materials, including silicon carbide, are of interest in hypersonic aerospace applications. To analyze the thermodynamic behavior of silicon carbide during transition between passive and active oxidation states, chemical equilibrium calculations are performed. The predicted oxygen pressures for passive-to-active transition show improved agreement up to an order of magnitude with experimental transition data in the literature, compared with Wagner's model. Both oxygen and air environments are examined, and a 3% difference in transition temperature is observed. Material response analysis demonstrates that a surface temperature jump occurs during thermal oxidation of silicon carbide, corresponding to passive-to-active transition.     

Elastic, dielectric and electromechanical nonlinearities of rochelle salt at the ferroelectric phase transition

The temperature dependence of nonlinear elastic, dielectric and electromechanical coefficients near the upper ferroelectric phase transition is determined by means of resonance methods. The results fit the thermodynamic theory.     

Miscibility and thermal and dynamic mechanical behaviour of semi‐interpenetrating polymer networks based on polyurethane and poly(hydroxyethyl methacrylate)

The thermodynamic miscibility and thermal and dynamic mechanical behaviour of semi‐interpenetrating polymer networks (semi‐IPNs) of crosslinked polyurethane (PU) and linear poly(hydroxyethyl methacrylate) (PHEMA) have been investigated. The free energies of mixing of the semi‐IPN components have been determined by the vapour sorption method and it was established that the parameters are positive and depend on the amount of PHEMA in the semi‐IPN samples. Thermal analyses glass transition temperatures evidenced two in the semi‐IPNs in accordance with the investigation of the thermodynamic miscibility of these systems. Dynamic mechanical analysis revealed a pronounced change in the viscoelastic properties of the PU‐based semi‐IPNs with different amounts of PHEMA in the samples. The semi‐IPNs have two distinct tan δ maxima related to the relaxations of the two polymers in their glass temperature domains. The temperature position of PU relaxation maximum tan δ is invariable but its amplitude decreases in the semi‐IPNs with increasing amount of PHEMA in the systems. The tan δ maximum of PHEMA is shifted to a lower temperature and its amplitude decreases with increasing amount of PU in the semi‐IPNs. The segregation degree of components α was calculated using the viscoelastic properties of semi‐IPNs. It was concluded that the studied semi‐IPNs are two‐phase systems with incomplete phase separation. The different levels of immiscibility lead to the different degree of phase separation in the semi‐IPNs with compositions. Copyright © 2004 Society of Chemical Industry     

Intracellular Thermometry at the Micro-/Nanoscale and its Potential Application to Study Protein Aggregation Related to Neurodegenerative Diseases

Temperature is a fundamental physical parameter that influences biological processes in living cells. Hence, intracellular temperature mapping can be used to derive useful information reflective of thermodynamic properties and cellular behaviour. Herein, existing publications on different thermometry systems, focusing on those that employ fluorescence-based techniques, are reviewed. From developments based on fluorescent proteins and inorganic molecules to metal nanoclusters and fluorescent polymers, the general findings of intracellular measurements from different research groups are discussed. Furthermore, the contradiction of mitochondrial thermogenesis and nuclear-cytoplasmic temperature differences to current thermodynamic understanding are highlighted. Lastly, intracellular thermometry is proposed as a tool to quantify the energy flow and cost associated with amyloid-β42 (Aβ42) aggregation, a hallmark of Alzheimer's disease.     

Glass transition temperature in nylons

The determination of the glass transition temperature of semi-crystalline polymers is a controversial problem in the literature, because of the complexity of the phenomenon and of the different methods used for its measurement. In this work the glass transition temperatures of five commercial nylons (nylon-6, nylon-6,6, nylon-6,10, nylon-11, nylon-12) have been measured by both thermal and mechanical methods. The behaviour observed during thermal measurements is analogous to that observed by Gordon, who found that the transition detected in the heating cycle disappeared in the subsequent cooling cycle and appeared again only after a sufficient rest period of the samples, and at a temperature different from the initially measured one. He attributed this behaviour to the structure of the amorphous regions of the material, where the hydrogen bonding groups form an irregular network. The delay in reforming the above mentioned network is the main cause of the dependency of the observed transition on the thermal history imposed on the samples. Mechanical measurements give results that are quite insensitive to the thermal treatment of the materials, and thus provide very reproducible values of the transition. This feature allows the possibility of attributing to the transition obtained the character of a true glass transition where the main cause of the phenomenon is the increased mobility of the chain backbone in the amorphous regions of the materials with increasing temperature. This character was also confirmed by dilatometry, with results in agreement with Boyer's criteria for a true glass transition temperature.     

Starch gelatinization

The dependence of the melting temperature of starch on its concentration in a polymerdiluent mixture was determined. The resultant data were analysed by application of the thermodynamic equations appropriate to a first-order phase transition. It is suggested that this analysis may be used to explain certain features of starch gelatinization.     

Immiscibility in the CoO-NiO System

The thermodynamic properties of the solid CoO-NiO solution have been assessed in terms of a thermodynamic model including a contribution from the magnetic transition. The parameters in the model have been adjusted to fit emf measurements in the literature. The miscibility gap at low temperatures is calculated and compared to the gap proposed by Kinoshita, Kingery, and Bowen from their TEM studies. A very severe discrepancy between experimental maximum temperature (760°C) and the calculated one (185°C) is found. Various reasons for the descrepancy are discussed.     

Gas - liquid equilibrium of aqueous salted solutions under high pressure and temperature

In several countries, geothermal resources have great potential for an economic production of energy. Mineral salts and/or desalted water can be valuable by-products in several cases.The knowledge of the thermodynamic behaviour of geothermal fluids, characterised by the presence in solution of salts and gases at high pressure and temperature, can be useful for optimal design , control and optimal ranning of large scale industrial plants.However, because of substantial deviations from ideal behaviour of these two phase multicomponent mixtures, particular problems are encountered in modelling their thermodynamic properties with the required degree of accuracy and generality. Furthermore, since hot geothermal fluids are available at high pressure, we have to account for the influence of the pressure on both the liquid and the vapour phase.We have developed a general analytical procedure based on the SRK equation of state by which it is possible to correlate and predict the thermodynamic behaviour of any kind of natural geothermal fluids under high pressure. Available experimental information for the pure components of natural geothermal fluids as well as for the sub-binaries are used for the parametrization of the model.The comparison between experimental and calculated results for the system water-carbon dioxide-sodium chloride shows that the model has satisfactory correlation and predictive capabilities.     

Effects of crystallinity and stress state on the yield strain of polyethylene

The yield strain has been measured over a wide range of temperatures for four polyethylene grades which differ with respect to both their short chain branch content and their molecular weight. The results have shown that all the materials exhibit a transition in their mechanical behaviour at sub-ambient temperatures. The transition temperature is shown to increase as the crystallinity is increased. It is proposed that this transition temperature is related to an interlamellar shear process. The yield strain measured over a range of temperatures generally increases as the crystallinity is reduced.     

Longitudinal ultrasonic wave propagation along X-axis in KDP near it's ferroelectric phase transition temperature

We have examined the propagation behaviour of longitudinal ultrasonic wave along the X-axis near the ferroelectric phase transition temperature of KDP. We find the propagation behaviour is similar in nature to that along the Z-axis (polarization axis).