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Abstract  

The activation energy associated with the glass transition relaxation of an epoxy system has been determined by using the three-point bending clamp provided in the recently introduced TA Instruments DMA 2980 dynamic mechanical analyzer. A mathematical expression showing the dependency of modulus measurements on the sample properties and test conditions has also been derived. The experimental results showed that the evaluation of activation energy is affected by the heating rate and test frequency, as well as the criterion by which the glass transition temperature (T g) is established. It has been found that the activation energy based on the loss tangent (tanδ) peak is more reliable than on the loss modulus (E 2) peak, as long as the dynamic test conditions do not cause excessive thermal lags.

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states have recently been re-examined and previous attempts to trace the distinction revised [ 5 , 6 ]. Currently, Queiroz et al. [ 7 ] considered thermodynamic aspects of glasses focusing to their behavior in glass-transition region (GTR). Suñol et al

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XRD patterns), colorless and transparent samples were obtained. The obtained glasses were annealed for 1 h at temperature near their glass-transition temperature ( T g ). Fig. 1 Synthesized sample of system Ga 2

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selecting a composite material for design engineering and manufacture of products. The HDT can be basically correlated with the glass-transition temperature of the matrix polymer. The effect of the type and quantity of the reinforcing material on

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motion and heat capacity in the melting [ 3 ] and glass-transition regions [ 4 ]. One of these students was Prof. Michael Jaffe, whom we honor in this symposium. After this early work at Cornell University, he became one of my first graduate students at

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incompatible contaminations; in particular polyolefines diminish the mechanical properties. The polyethylene as a polymer of low glass-transition temperature should be a good impact modifier of PVC but the incompatibility makes its application seemingly

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Abstract  

Crystallization and glass-transition phenomena were studied for amorphous chlorobenzene (CB)/toluene (TL) binary systems as the function of composition. Samples were prepared by vapor-deposition onto cold substrates, and their structural changes due to temperature elevation were monitored with Raman scattering and light transmission. It was found that the crystallization temperature (T c) of CB-rich amorphous samples increases as the TL concentration is increased. This is similar to the linear dependence of glass-transition temperatures (T g) of many organic compounds on the concentration of additive. Also found was that T c of TL-rich supercooled-liquids decrease as the CB concentration is increased. Issues related to the two kinds of T c are discussed briefly.

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Journal of Thermal Analysis and Calorimetry
Authors: Carmen Rodríguez-Tenreiro, Carmen Alvarez-Lorenzo, Ángel Concheiro, and J. Torres-Labandeira

Abstract  

The interactions between Carbopol and β-cyclodextrin (BCD) or hydroxypropyl-β-cyclodextrin (HPBCD) were studied by differential scanning calorimetry (DSC) and FTIR spectroscopy. Aqueous solutions of both components were desiccated by freeze-drying or heating in an oven (films) at various temperatures. The use of different drying procedures allowed their influence on the interactions to be studied. The evolution of the Carbopol glass-transition was also evaluated by DSC using first heating runs up to different temperatures. Disappearance of the Carbopol glass-transition was observed in the freeze-dried systems prepared with either of the cyclodextrins and in the films that contained HPBCD. The changes in the FTIR band of Carbopol at 1700 cm-1 confirmed the existence of interactions with both cyclodextrins, especially with HPBCD. This information may be useful for optimising the solubilizing capacity and controlled release performance of aqueous Carbopol-cyclodextrin systems.

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Copolymers of styrene and maleic anhydride prepared by a charge transfer mechanism have been studied thermally by thermogravimetry and differential scanning calorimetry. The copolymers degrade in two stages; the first stage accounts for about 85% of the degradation. Incorporation of maleic anhydride to styrene decreases the thermal stability of the later. Differential scanning calorimetric studies show two exotherms between 300° to 500 °C. Glass-transition temperatures for the copolymers are lower than that of polystyrene.

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Abstract  

The fragility of ethylene glycol and glucose aqueous solution systems has been investigated by temperature-modulated differential scanning calorimetry (TMDSC). The frequency and temperature dependences of complex specific heat have been observed in the vicinity of a glass-transition temperature T g . It is shown that the value of the fragility index m can be determined from the temperature dependence of the α-relaxation times observed by TMDSC. We have also studied the elastic properties of these aqueous solutions by micro-Brillouin scattering, and determined these relaxation times of elastic properties in the gigahertz range.

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