Authors:J. Mano, S. Lanceros-Méndez, A. Nunes and M. Dionísio
Dielectric experiments are often performed in non-isothermal conditions. Thus, there is a difference between the temperature of the sample and the sensor temperature. In this work we propose and compare three temperature calibration methods based on the detection of transitions or relaxations: i) the melting of high-purity metallic standards (indium and tin), ii) the 2nd order phase transition of a ferroelectric crystal (TGS); iii) the -relaxation of an amorphous polymer (poly(carbonate)). The results obtained from the three different methods were used to construct a calibration curve for a given heating rate.
Triglycine sulfate [(NH 2 CH 2 COOH) 3 · H 2 SO 4 ] (TGS) is an interesting material for its wide range of applications and has an excellent pyroelectric and ferroelectric properties [ 1 ]. This crystal is
To study the corrosion resistance of metals and alloys,
an analysis system needs to be able to simulate the harsh environments to
which these materials are subjected. The system must also collect data from
metal and alloy samples at elevated temperatures over long periods of time
(typically days). Thermogravimetric analyzers (TGs) are well accepted systems
for both corrosion studies and long-term elevated temperature studies. However,
until now, TGs could conduct either corrosion studies or long-term studies,
but not both. This paper presents a TG system specifically designed to satisfy
the requirements of long-term corrosion resistance studies of metals and alloys.
An inherent challenge with polymer blends is the difficulty in resolving the glass transition, Tg, for the smaller mass fraction component. The objective of this work was to determine the practical scanning conditions for
identifying the dual Tg’s for a 75:25 polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) blend using a thermomechanical analyzer (TMA). Scanning
rates up to 20°C min−1 using dilatometer and expansion modes were studied. Heating and cooling rates were found to affect both Tg values but the effects were not simple relationships. Tg values could either increase or decrease depending on the scanning rate applied. Higher rates resulted in large thermal lags
which opened the accuracy of measurements to question. Generally, higher rates tended to display only one Tg but the duality of Tg’s can be detected with scanning rates between 0.5 and 5°C min−1 for both modes.
Authors:Y. Tsujimi, M. Kobayashi, H. Furuta and T. Yagi
The ultra-slow modes with a relaxation time much longer than 1 ns are discovered by a time-resolved spectroscopy in uniaxial ferroelectric (NH2CH2COOH)3H2SO4 (TGS) and in glass-former HOCH2(CHOH)4CH2OH (D-sorbitol). A mode discovered in TGS is a thermal relaxational mode and is proved to be the physical origin of the central peak found by Brillouin scattering. Two modes are discovered in D-sorbitol. One is a thermal relaxational mode. The other is a mode characterized by the Kohlraush-Williams-Watts function with a relaxation time
R. A remarkable result is that
R indicates a critical behavior not at the liquid-glass transition temperature Tg =–7°C but at the ergodic to nonergodic transition temperature Tc=33°C.
The effect of excipients on the secondary structure of lyophilized proteins was studied through second-derivative Fourier
transform infrared (FTIR) spectroscopic analysis. The glass transition temperature (Tg), denaturation temperature (Td) and moisture content were determined by differential scanning calorimetry (DSC) and thermogravimetry (TG). Tg, Td and the preservation of protein secondary structure were found to be dependent upon the type and amount of the excipient
included in the formulation. Meanwhile, the lyophilized proteins easily adsorbed amounts of moisture during storage to reduce
their Tgs and stability.
Authors:Marta Sánchez-Cabezudo, Margarita Prolongo, Catalina Salom and Rosa Masegosa
The cure kinetics
and morphology of diglycidyl ether of bisphenol A (DGEBA) modified with polyvinyl
acetate (PVAc) using diaminodiphenylmethane (DDM) as hardener were investigated
through differential scanning calorimetry (DSC) and environmental scanning
electron microscopy (ESEM). Isothermal curing measurements were carried out
at 150, 120 and 80C. The kinetic parameters were obtained using the general
autocatalytic chemically controlled model. The comparison of the kinetic data
indicates that the presence of PVAc does not change the autocatalytic nature
of the cure reaction. Two Tg’s
were observed in the fully cured samples of the modified systems. ESEM micrographies
confirm the biphasic morphology.
Authors:Y. Li, N. Obando, F. Tschen and R. J. Morgan
Thermal analysis of phenylethynyl end-capped imide oligomer AFR-PEPA-4
was performed to characterize cure reaction, thermal stabilities and semicrystalline
behavior of AFR-PEPA-4 oligomer and its cured polyimide. Cured AFR-PEPA-4
polyimide showed high Tgs
up to 418C. Both AFR-PEPA-4 oligomer and polyimide exhibit excellent
thermal stabilities comparable to PETI-5 polyimides. AFR-PEPA-4 imide oligomer
has a Tm of 330C
and exhibits spherulite crystalline morphology in the film. The crystallinity
in AFR-PEPA-4 films could not be regenerated under any annealing conditions
after the initial melt.
Complex mixtures of long chain organic compounds often show overlapping glass transition temperatures (Tgs) when analyzed by differential scanning calorimetry (DSC) or modulated DSC (MDSC). In such cases, subjective and inconsistent
smoothing of data acquired under different conditions can lead to the misinterpretation of results. A quantitative method
for the selection of smoothing factors for the analysis and comparison of (M)DSC results is presented. The method is most
useful for the analysis of the derivative of the heat capacity, dCp/dt or dCp/dT, plots which best highlight overlapping Tgs. Four equations are shown to relate the heating rate and the smoothing factor. The equations allow a comparison of data
acquired i) at different heating rates and plotted vs. temperature, ii) at a single heating rate and plotted vs. both time and temperature, i.e., dCp/dt vs. dCp/dT, iii) at different heating rates and plotted vs. both time and temperature, and iv) at different heating rates, and shown exclusively in the time domain. Examples of the use of the equations are provided
for the analysis of bitumen, a complex mixture of natural origin.
Authors:Margarita Prolongo, C. Arribas, Catalina Salom and Rosa Masegosa
ether of bisfenol-A (DGEBA)/poly(vinyl acetate) (PVAc)/poly(4-vinyl phenol)
brominated (PVPhBr) ternary blends cured with 4,4’-diaminodiphenylmethane
(DDM) were investigated by differential scanning calorimetry (DSC), dynamic
mechanical thermal analysis (DMTA) and scanning electron microscopy (SEM).
Homogeneous (DGEBA+DDM)/PVPhBr networks with a unique Tg
are generated. Ternary blends (DGEBA+DDM)/PVAc/PVPhBr are initially miscible
and phase separate upon curing arising two Tgs
that correspond to a PVAc-rich phase and to epoxy network phase. Increasing
the PVPhBr content the Tgof
the PVAc phase move to higher temperatures as a consequence of the PVAc-PVPhBr
interactions. Different morphologies are generated as a function of the blend