Thermally stimulated depolarization currents and differential scanning calorimetry are performed on thermoplastic polyesters
to characterize both a and b relaxations. The influence on the different relaxations phenomena of the chemical structure (size
of the naphthalene groups, presence of cyclohexane, length of the aliphatic group, ...) as well as the influence of the crystallinity
are discussed. The three phases model with a crystalline part, a rigid amorphous part unable to relax and an amorphous phase
able to relax at various temperatures depending on the distribution of the relaxation times is used to explain the evolution
of the main α relaxation while the standard two-phases model is sufficient to explain the variations of the β relaxation mode.
Elementary analysis of both α and β relaxations show that the β relaxation characterized by a continuous variation of activation
energies as a function of temperature follows the activated state equation with a zero activation entropy while the cooperative
a relaxation exhibits a prominent maximum of the activation energies at the glass transition temperature.
A new method of calculation of parameters of enthalpy relaxation models is proposed. Regression analysis treatment compares the experimental and calculated values of relaxation enthalpy. The experimental values of relaxation enthalpy are obtained by numerical integration of the difference between the two DSC curves. Contrary to the overall shape of the DSC curve the integral values are not affected by particular heat flow conditions during the DSC experiment. The Narayanaswamy's numerical model based on the Kohlrausch—William—Watts relaxation function was used to calculate the theoretical values of relaxation enthalpy. The application of the proposed method on the DSC experimental data of enthalpy relaxation of As2Se3 is shown.
The amplitudes of the relaxation curves, as obtained by the Temperature-jump method have been used to measure simultaneously
equilibrium constant and enthalpy for the reaction of complex formation of Ni2+ ion by 2,6-dihydroxobenzoic acid in the presence of a buffer. The experiments have been performed by changing the concentration
of metal ion at constant ligand concentration andpH as in a complexometric titration. The points of such ‘dynamic titrations’ have been analysed by means of the concept of ‘normal
reactions’ which enabled us to transform a set of coupled individual steps into a set of kinetically independent reactions.
The potentialities of the dynamic titrations are discussed.
The enthalpic relaxation of the title glasses, studied by differential scanning calorimetry, is well described by a mathematical
model based on the stretched exponential relaxation function with the relaxation time proportional to the actual viscosity.
The dependence of viscosity on temperature and the fictive temperature was expressed by Mazurin's approximation. The relaxation
parameters obtained correlated significantly with the glass composition, indicating the changes in the structural of the TiO2 role near a TiO2 content of 3–4 mol%.
Authors:Tiziana Cardinali and Nikolaos Papageorgiou
In this paper we study the relaxation of optimal control problems monitored by subdifferential evolution inclusions. First
under appropriate convexity conditions, we establish an existence result. Then we introduce the relaxed problem and show that
it always has a solution under fairly general hypotheses on the data. Subsequently we examine when the relaxation is admissible.
So we show that every relaxed trajectory can be approximated by extremal original ones (i.e. original trajectories generated
by bang-bang controls) and that the values of the original and relaxed problems are equal. Some examples are also presented.
Authors:Y. Matsuda, C. Matsui, Y. Ike, M. Kodama, and S. Kojima
heat capacity, Cp*=Cp'–iCp'',
of lithium borate glasses xLi2O(1–x)B2O3
(molar fraction x=0.00–0.30) has
been investigated by Modulated DSC. We have analyzed the shape of Cp*
by the Cole-Cole plot, performed fitting by the Havriliak-Negami equation,
and then determined the parameters related to the non-Debye nature of thermal
relaxation. Moreover, the concentration dependence of the thermal properties
has been investigated. Glass transition temperatures become higher with the
increase of molar fraction of Li2O and shows the board
peak around x=0.26. Temperature ranges
of glass transitions become narrower with the increase of Li2O
Authors:M. Chromčíková, M. Rodová, K. Nitsch, and M. Liška
Glasses prepared by quenching of the melt do not reach any equilibrium state but they seek to attain it. The process the glass undergoes to reach this state is called structural relaxation and it is connected with
Authors:Bhupendra Singh Rathore, Mulayam Singh Gaur, and Kripa Shanker Singh
crystalline solids, polymer nanocomposites, bio material, cells, tissues, [ 13 ] etc. The effects of dipolar, direct current (dc), and space charge relaxations are closely linked to the temperature-dependent mobility of molecules, their fragments, protons