Glass Transition Process Research Articles

Synthesis and Properties of Poly(ketone‐co‐alcohol) Materials: Shape Memory Thermoplastic Elastomers by Control of the Glass Transition Process

AbstractSummary: The well‐controlled reduction of polyketone carbonyl functional group was performed without chain degradation by using NaBH4 in tetrahydrofuran (THF)/MeOH solvent mixtures. Three different families of flexible polyketones (alternating propene/CO “PCO”, hex‐1‐ene/CO “HxCO” copolymers, and “pulse feed” alternating olefin/CO terpolymers from ethene and propene “EPCO”) were investigated to achieve either a partial reduction, leading to poly(ketone‐co‐alcohol)s of corresponding composition, or a complete conversion into polyalcohols. Increasing the ratio of [OH]/[CO] functions allows continuous change of the Tg of the resulting polymers from below room temperature to about 75 °C. Properties of the synthesized materials, like thermal decomposition, glass transition temperature, surface tension, and mechanical performance, are described depending on the degree of reduction. Thermoplastic elastomers with an interesting “shape memory” effect result from the partially reduced, elastic EPCO terpolymers.Stress‐strain curves for ethylene‐propylene/CO copolymers reduced to different extents.imageStress‐strain curves for ethylene‐propylene/CO copolymers reduced to different extents.

Sorption isotherms and the state diagram for evaluating stability criteria of abalone

Water adsorption isotherms and the state diagram of abalone were developed to further investigate the connection between the two distinct criteria of food stability. The isotherms were measured at 23, 40 and 60 °C using an isopiestic method and they were treated with appropriate models available in the literature. The state diagram was developed using freezing points, as derived by the cooling curve method, and glass transition temperatures were measured by dynamic oscillation on shear. The limited glass transition process of the abalone network necessitated derivation of the mechanical glass transition temperature, since the transition could not be detected using MDSC. Results indicate that there is a considerable discrepancy in the temperature-related stability criteria predicted by the concepts of water activity ( a w) and the glass phenomenon ( T g). In contrast to the progressive deviation between a w and T g with increasing molecular weight reported earlier for a homologous family of materials, the effect of rising temperature produces a constant index of comparison between the two concepts.

Glass transition kinetic property of novel bulk Zr-Al-Ni-Cu (Nb,Ti) amorphous alloy*

The kinetic property during the glass transition process of Zr_Al_Ni_Cu (Nb,Ti) amorphous alloys was systematically investigated by differential scanning calorimetry method. The activation energy (ΔE) at the glass transition temperature was much smaller than tradition amorphous alloys and have different magnitude compared to ΔEvalue at Tx. These reveal that the bulk amorphous alloys show special structure characteristics and that is the reason of its big glass_forming ability. The Vogel_Fulcher_Tammann fits to the experimenta l data are given by the full curves and the fragility parameter mvalue was calculated to be about 30, reflecting its “strong" liquid property in deep_unde rcooled region. The B value of Lasocka function，atom activation energy and glass fragility parameter reveal a close relationship between kinetic behavior at glass transition and the glass_forming ability. So it could be used as an impor tant judgment for glass_forming ability.

Thermodynamic investigation on the azeotropic mixture composed of water + n-propanol + benzene

Molar heat capacity of the azeotropic mixture composed of water, n-propanol, and benzene was measured by an adiabatic calorimeter from 79 to 320K. The glass transition and melting processes of the mixture were determined based on the curve of the heat capacity with respect to temperature. The glass transition occurred at 101.920K. The melting processes took place in temperature ranges 258–268 and 268–279K. The corresponding melting enthalpies and entropies were calculated to be 1.474kJmol−1, 5.508JK−1mol−1; 6.144kJmol−1, 22.28JK−1mol−1, respectively. The thermodynamic functions and the excess thermodynamic functions of the mixture relative to temperature 298.15K were derived based on the relationships of the thermodynamic functions and the function of the measured heat capacity with respect to temperature.

Pressure effect on glass transition in a Zr65Al7.5Cu27.5 metallic glass

By means of the enthalpy recovery experiments in a Zr65Al7.5Cu27.5 metallic glass, the glass transition process was found to correlate with an obvious variation of enthalpy change with the annealing temperature. With this correlation, we developed an approach to determine the pressure effect on the glass transition temperature (Tg), and a drastic increment of Tg up to 50 K was observed in this glass when a hydrostatic pressure of 5 GPa was applied. It is much smaller than that observed in nonmetallic glasses, which is attributed to smaller activation volume of the relaxation in metallic glasses.

Calorimetric glass transition in bulk metallic glass forming Zr-Ti-Cu-Ni-Be alloys as a free-volume-related kinetic phenomenon

The change of the calorimetric glass transition in ${\mathrm{Zr}}_{46.25}{\mathrm{Ti}}_{8.25}{\mathrm{Cu}}_{7.5}{\mathrm{Ni}}_{10}{\mathrm{Be}}_{27.5}$ (vit4) bulk metallic glass during differential scanning calorimetry experiments was simulated with the free-volume theory. With the kinetics of the free-volume annihilation and production, calculations carried out on this basis are in good agreement with available experiment data in vit4 alloy both on structural relaxation and the glass transition. The change of the glass transition process is dependent upon the reduced free volume remained in the specimens. The structural relaxation occurring during annealing below the calorimetric glass transition temperature for different times is relative to the annihilation of the excess free volume. The results support that the calorimetric glass transition is a mainly kinetic process.

THE RELATIONSHIP BETWEEN THE SCALING PARAMETER AND RELAXATION TIME FOR NON-EXPONENTIAL RELAXATION IN DISORDERED SYSTEMS

A memory function equation and scaling relationships were used for the physical interpretation of the Cole-Cole exponent. The correspondence between the relaxation time, the geometrical properties, the self-diffusion coefficient and the Cole-Cole exponent was established. Using this approach the dielectric relaxation spectra of the polymer-water mixtures and the glass transition process in the nylon 6,6 quenched, crystalline and micro-composite samples were analyzed.

Characterization of Transition Temperatures of a Langmuir—Blodgett Film of Poly(tert-butyl Methacrylate) by Two-Dimensional Correlation Spectroscopy and Principal Component Analysis

External reflection FT-IR spectra of a Langmuir–Blodgett (LB) film of poly( tert-butyl methacrylate) (PtBMA) were measured at temperatures ranging from 26 to 136 °C. The glass transition temperature ( Tg) was determined from a two-dimensional (2D) mapping of the first derivative spectra of absorbance values against temperature over the wavenumber range 1100–1300 cm−1, which contains spectral features that are very sensitive to conformational changes. This mapping provides a surprisingly simple and direct method for detecting the value of Tg. The glass transition temperature determined from the 2D map was approximately 84 °C. Another transition at 103 °C, corresponding to the glass transition temperature of bulk PtBMA, was also detected from the 2D map. Principal component analysis (PCA) was employed to analyze the temperature-dependent FT-IR spectra. The glass transition temperatures (80 °C; 100 °C) of the PtBMA LB film determined by the score plot of PCA are consistent with those determined by the 2D map. Additionally, the loading vectors of PCA were found to give valuable insight into the molecular-level phenomena associated with the glass transition process. To gain more details about the polymer chain mobility, two-dimensional (2D) correlation analysis was performed on two sets of FT-IR spectra collected above and below Tg. In the synchronous 2D correlation spectrum obtained below the glass transition temperature (26–66 °C), the observation that the strongest intensity change occurs at 1137 cm−1 indicates that the reorganization of the bending mode of the bbC–C–O and bbC–C=O bonds connected to the backbone (bb) chain and coupled to the C–O stretching mode of the tert-butoxy group is potentially the mechanism underlying the β-transition. This result is in good agreement with the presence of a transition (β-transition) at approximately 43 °C obtained from the band around at 1137 cm−1 in the 2D mapping data.

High-frequency dynamics of the glass former dibutylphthalate under pressure

The high-frequency dynamics of a fragile molecular glass former (dibutylphthalate) was studied through inelastic x-ray scattering (IXS), as a function of pressure and temperature. The mesoscopic structural arrest associated with the glass transition process was tracked by following upon cooling the inelastic excitations at fixed Q points in the dispersion curves, at ambient pressure and 2 kbar. The application of pressure to this system induces an offset between the macroscopic glass transition temperature T(g) and the mesoscopic glass transition temperature, as determined from IXS. The concomitant fragility decrease of dibutylphthalate under pressure unveils that the stronger the glass former is, the more its mesoscopic dynamics differ from the macroscopic regime. This trend is interpreted as the signature of a nanoscopic inhomogeneous elastic network. Further aspects of this system are obtained when studying the temperature dependence of its nonergodicity factor f(Q)(T). The chemical specificity of the molecule is suggested to be responsible for the nonobservation of a critical temperature T(c) in dibutylphthalate up to approximately 300 K.

The apparent activation energy and relaxation volume from the point of view ofAdam–Gibbs theory

The temperature and pressure dependence of the glass-transition process isdiscussed on the basis of the molecular Adam–Gibbs equation for the relaxationtime. An equation for measuring the temperature and pressure dependence of theAdam–Gibbs size of the cooperative rearranging region is suggested. The apparentactivation energy and the apparent relaxation volume by this equationare presented as the product of the activation energy and the activationvolume per basic molecular kinetic unit respectively with the size of thecooperative unit to the second power. In this way, for the first time, anequation for measuring the activation volume of a basic molecular kineticunit involved in the cooperative molecular dynamics is obtained. Theisobaric and the isothermal activation volume of a basic molecular species(BMS) measured by this equation correlate with the molar volume ofthe liquid. From the experimental results it follows that the size of thecooperatively rearranging region at isothermal conditions increases withpressure until at the glass-transition pressures it reaches an apparent limit.On the basis of the activation volume measured per BMS, a method forevaluating their volume in liquids and their number in molecules or inrepeated units in polymers is suggested. By this method, for the first time,from a relaxation experiment, the basic kinetic units in several molecularglass-forming liquids are found to be close to the fragments of the monomersegments or molecules known in thermodynamics as Wunderlich’s beads.

Novel approach to the analysis of the non-Debye dielectric spectrum broadening

The memory function approach and scaling relationships were used as a basis for the dynamic model of symmetric dielectric spectrum broadening. For the first time the correspondence between the relaxation time, the geometrical properties, the self-diffusion coefficient and the exponent of power-law wings was established. Using this model the dielectric spectra of the glass-transition process in quenched, crystalline and micro-composite samples of nylon 6,6 were discussed.

Mechanical and thermodynamic properties of infrared transparent low melting chalcogenide glass

The properties of infrared (IR) transparent chalcogenide glass Se 57I 20As 18Te 3Sb 2 have been studied for the first time by dynamic mechanical analysis (DMA). This glass demonstrates both high transparency in a broad IR band (1–12 μm) and a particularly low softening point (near 50 °C). It is known as one of the best adhesives intended for the binding of IR optics elements. The DMA method gives valuable information about the complex Young’s modulus of the glass in its softening region. In parallel with the study of mechanical properties of the glass the character of its glass transition process has been investigated. Our results of DMA were then compared with our thermodynamic data obtained by scanning calorimetry. The peak of mechanical losses in DMA appears to be situated considerably higher than the calorimetrically determined glass transition temperature.

Formal determination of the nucleation probabilities in binary alloys: A hyperfinite approach and thermodynamic justification of the lattice models

We obtained an equation of the Burgers type modeling the glass transition process in binary alloys with inhomogeneous inclusions. The proposed equation is thermodynamically justified; conditions are indicated under which this equation converts into the classical Cahn–Hillard equation.

Influence of Moisture on the Glass Transition of A Spray-Dried Compound Using the Isosteptm Method

The interaction among moisture content, solvent loss and glass transition temperature is relevant for processing of spray-dried pharmaceuticals, since the glass transition temperature determines the application range of a compound. Conventional Differential Scanning Calorimetry (DSC) does usually not allow to separate glass transitions from common kinetic effects like evaporation or crystallization. Based on classical DSC methods, the IsoStepTM method allows the independent determination of heat capacities and kinetic effects, and thus, the separation of kinetic effects from effects arising from heat capacity changes. This technique is used to separate glass transition and evaporation processes, and to find the relation between moisture content and glass transition temperature for a pharmaceutical sample based on a modified Gordon–Taylor equation.

Mistura PAni.DBSA/SBS Obtida por Polimerização "In Situ": Propriedades Elétrica, Dielétrica e Dinâmico-Mecânica

Misturas elastoméricas condutoras de eletricidade envolvendo copolímero tribloco poli(estireno-b-butadieno-b-estireno) (SBS) e polianilina dopada com ácido dodecilbenzenosulfônico (Pani.DBSA) foram obtidas por polimerização "in situ". Os filmes obtidos por moldagem por compressão mostraram baixo limiar de percolação, apresentando valores de condutividade semelhantes aos encontrados para o polímero condutor puro com cerca de 20 % em massa de Pani.DBSA. A caracterização das misturas por análise termodinâmico-mecânica (DMTA) evidenciou uma ligeira interação da Pani.DBSA com ambas fases do copolímero SBS. Na região borrachosa, o módulo da mistura aumenta com o aumento do conteúdo de Pani. No entanto, existe uma progressiva queda no fator de amortecimento ("damping") com o aumento da concentração de Pani. A energia de ativação, Ea, do processo de transição vítreo-borrachoso de ambas fases do SBS foi calculada, utilizando a equação de Arrhenius com os dados obtidos tanto por DMTA como por análise termodielétrica (DETA). A caracterização dielétrica não proporcionou informações a respeito da localização da Pani.DBSA na matriz de SBS. No entanto, observou-se o fenômeno de polarização interfacial entre a Pani e o SBS. Uma morfologia do tipo microtubos foi observada para Pani.DBSA na mistura SBS/Pani.DBSA, utilizando-se a técnica de microscopia eletrônica de varredura.

Dynamics of alpha and beta processes in thin polymer films: poly(vinyl acetate) and poly(methyl methacrylate).

Dynamics of thin films of poly(vinyl acetate) (PVAc) and poly(methyl methacrylate) (PMMA) have been investigated by dielectric relaxation spectroscopy in the frequency range from 0.1 Hz to 1 MHz at temperatures from 263 to 423 K. The alpha process, the key process of glass transition, is observed for thin films of PVAc and PMMA as a dielectric loss peak at a temperature T(alpha) in temperature domain with a fixed frequency. For PMMA, the beta process is also observed at a temperature T(beta). For PVAc, T(alpha) decreases gradually with decreasing thickness, and the thickness dependence of T(alpha) is almost independent of the molecular weight (Mw< or =2.4x10(5)). For PMMA, T(alpha) remains almost constant as thickness decreases down to a critical thickness dc, at which point it begins to decrease with decreasing thickness. Contrastingly, T(beta) decreases gradually as thickness decreases to dc, and below dc it decreases drastically. For both PVAc and PMMA, the broadening of the distribution of the relaxation times in thinner films is observed and this broadening is more pronounced for the alpha process than for the beta process. It is also observed that the relaxation strength is depressed as the thickness decreases for both the polymers.

The dielectric properties of glass-fibre-reinforced epoxy resin during polymerisation

The change in dielectric properties of thermosets between 10 Hz and 1 MHz allows us to monitor the cure of these materials. During the first heating phase at 80°C the resin conductivity (which is correlated with the Newtonian viscosity by a power law) decreases by several decades. In the subsequent heating phase at 140°C, the glass transition process is observed as a broad maximum of the dielectric loss factor at 30 kHz. The shift of the loss factor peak to lower frequencies with cure time marks the increasing relaxation time of the curing system. The relaxation time and the conductivity are indicators for cure monitoring that do not depend on frequency. So they are suitable for a comparison with other methods like DSC, FTIR and rheometry. The glass transition is analysed in the complex plane with a skewed arc function proposed by Havriliak and Negami (Havriliak S, Negami S. A complex plane analuysis of α-dispersions in some polymer systems. J Pol Sci C 1966;14:99–117). There is no significant change in the shape of the dielectric complex-plane plot during curing. The cure-monitoring parameters conductivity and relaxation time are not much affected by glass-fibre reinforcement. Only the relaxation strength and the maximum value of the loss factor are reduced as a result of the low loss factor of the glass fibres.

Dynamical properties in dense triblock copolymer micellar system

We present results of analyses of an extensive set of dynamic light scattering (PCS) and viscoelastic (frequency dependent complex moduli) measurements in concentrated aqueous solutions of a triblock copolymer L64 (PEO 13PPO 30PEO 13) micellar system at different temperatures. In particular we study the system dynamical properties in a region of the phase diagram characterized by the existence of a percolation process and a kinetic glass transition. Both the processes, temperature and concentration dependent, are related with adhesive interaction between micelles. The intermediate scattering function (ISF) shows an ergodic to non-ergodic transition on crossing a temperature and concentration dependent line. Viscoelasticity data, determined by means of frequency-dependent complex moduli, satisfy the scaling relations predicted by the scalar elasticity percolation theory and well account for the glass transition process, give indication that percolation and the ergodic non-ergodic transitions take places in separate regions of the phase diagram. Detailed analysis of ISF and rheological data, conducted in terms of the mode coupling theory (MCT) gives evidence of a logarithmic decay on the density fluctuations, which could be attributed to a higher order singularity, followed by a power-law behavior.

Kinetics of the glass-transition and crystallization process of Fe72−xNbxAl5Ga2P11C6B4 (x=0, 2) metallic glasses

The kinetics of the glass-transition and the crystallization process of multicomponent ferromagnetic Fe72−xNbxAl5Ga2P11C6B4 (x=0, 2) metallic glasses have been investigated by constant-rate heating differential scanning calorimetry at different heating rates. The glass-transition temperature Tg and the crystallization peak temperature Tp shift to higher temperatures with increasing heating rate. The apparent activation energy and the frequency factor are evaluated by the Kissinger method, and the rate constant of the crystallization process is estimated by an Arrhenius law. The kinetics of the glass-transition process have been analyzed in terms of a Vogel–Fulcher–Tammann equation describing the heating rate dependence of the glass-transition temperature. The effect of the niobium addition on the glass-forming ability has been investigated with respect to the glass-transition and crystallization kinetics, revealing that substitution of Nb for Fe does not improve the glass-forming ability and it lowers the thermal stability of the material.

Characteristics of the glass transition and supercooled liquid state of theZr41Ti14Cu12.5Ni10Be22.5bulk metallic glass

Acoustic velocities and their temperature dependence of ${\mathrm{Zr}}_{41}{\mathrm{Ti}}_{14}{\mathrm{Cu}}_{12.5}{\mathrm{Ni}}_{10}{\mathrm{Be}}_{22.5}$ bulk metallic glass (BMG) have been measured up to 773 K by using an ultrasonic pulse-echo overlap method. The temperature dependence of density, Vicker's hardness, elastic constants, and thermodynamic parameters of the BMG are determined. A rapid change of the density, acoustic velocities, elastic constants, and Debye temperature near the glass transition temperature, and anomalous density, acoustic and elastic behaviors in the supercooled liquid region are observed. A striking softening of long-wavelength transverse acoustic phonons in the glassy state relative to the supercooled liquid state is found. The glass transition process is delayed to high temperature with an increase of heating rate. Our results provide evidence that the glass transition in the BMG can be regarded as a kinetically modified thermodynamic phase transformation.