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Abstract  

The relaxation map of highly concentrated sucrose water mixtures was built using mechanical and impedance spectroscopies. Data of - and -relaxation processes obtained with both techniques complete calorimetric and rheological measurements. The temperature evolutions of the relaxations were extrapolated using the measured data and the equations commonly used to describe the relaxations: Arrhenius and WLF behaviours for respectively the - and -relaxations. The temperature/frequency domain when and processes merge for 99% sucrose solution is discussed with respect to scenery proposed in the literature.

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Abstract  

The glass transition and relaxation processes in polystyrene resins with the number average molecular weight ranging from 7.0·102 to 9.8·104 were studied with the positron annihilation technique. The pick-off annihilation lifetime of ortho-positronium ( 3) and its intensity (I 3) were measured in the temperature range from 20 to 430 K. The glass transition temperature (T g) was determined as an onset temperature coefficient of 3.T g shows the molecular weight dependence in these samples. BelowT g, local motions were detected by measurements ofI 3. The local motions could be observed above 100 K in this experiment.I 3 show the minimum at around 250 K and it does not show molecular weight dependence.

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A new high molecular weight polyimide based on 4,4′-oxidiphthalic anhydride (ODPA) dianhydride and 2,2′-dimethyl-4,4′-diaminobiphenyl (DMB) diamine has been synthesizedvia a one-step polymerization method. This polyimide is soluble in phenolic solvents. Films from 7 to 30 μm thick were cast from the polymer solution and show in-plane orientation on a molecular scale detected by Fourier transform infrared spectroscopy experiments. This anisotropic structure leads to anisotropic optical properties arising from two different refractive indices along the inplane and out-of-plane directions. ODPA DMB possesses high thermal and thermo-oxidative stability. The glass transition temperature has been determined to be 298 °C. Dynamic mechanical analyses show two relaxation processes appearing above room temperature: the β- and the α-relaxation processes. The α-relaxation corresponds to the glass transition while the β-relaxation is a secondary relaxation process associated with the non-cooperative subsegmental motion.

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time-dependent changes in its structure [ 1 , 2 ]. The fundamental information that is inevitable for the evaluation of the relaxation process is obtained from experiments performed by thermal analysis methods such as DSC and TMA. In the glass

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model oligoester were studied by DMTA method. Activation energy for all identified relaxation processes was determined [ 15 ]. The description of relaxation processes of model oligoester can make it easier to interpret the dependence between the

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Journal of Thermal Analysis and Calorimetry
Authors: R. Golovchak, O. Shpotyuk, A. Kozdras, B. J. Riley, S. K. Sundaram, and J. S. McCloy

[ 4 , 5 ]. The related structural relaxation processes are the reason for uncontrolled drift in the exploitation characteristics of ChG-based devices and can have extended kinetics from few hours up to tens of years depending on the glass composition

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. Maneesha , G , Quamara , JK . Multiplicity relaxation processes in high-energy ion irradiated kapton-H polyimide: thermally stimulated depolarization current study . Nucl Instrum Methods Phys Res B 2006 246 : 355 – 363 10.1016/j.nimb.2006

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effect of rearranging regions is correlated with a thermodynamic behavior of glass transition. Therefore, the study of CRR could improve the understanding of the relaxation processes in amorphous materials at temperatures close to the T g value. Thus

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low temperature) and a broad α c relaxation (mainly assigned to the molecular motions within the crystalline structure, located at the high temperature) in the samples of low CTFE content. These two relaxation processes completely mixed together in

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Journal of Thermal Analysis and Calorimetry
Authors: Elodie Carsalade, Alain Bernès, Colette Lacabanne, Sophie Perraud, Michel Lafourcade, and Michel Savignac

Abstract  

The correlations between the transitions and the dielectric relaxation processes of the oriented poly(ethylene terephthalate) (PET) pre-impregnated of the polyester thermoplastic adhesive have been investigated by differential scanning calorimetry (DSC) and dynamic dielectric spectroscopy (DDS). The thermoplastic polyester adhesive and the oriented PET films have been studied as reference samples. This study evidences that the adhesive chain segments is responsible for the physical structure evolution in the PET-oriented film. The transitions and dielectric relaxation modes’ evolutions in the glass transition region appear characteristic of the interphase between adhesive and PET film, which is discussed in terms of molecular mobility. The storage at room temperature of the adhesive tape involves the heterogeneity of the physical structure, characterized by glass transition dissociation. Thus, the correlation between the transitions and the dielectric relaxation processes evidences a segregation of the amorphous phases. Therefore, the physical structure and the properties of the material have been linked to the chemical characteristics.

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