Simultaneous dielectric spectroscopy and calorimetry of the dynamics during a macromolecules growth
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A method and an instrument has been developed for measuring almost simultaneously and continuously in time three different quantities: i) the heat evolved during the course of exothermic reactions, ii) the heat capacity and iii) the dielectric spectra of a liquid or solid sample. By using this instrument, we have studied the decrease in the d.c. conductivity and the increase in the relaxation time as molecules in an isothermally kept liquid chemically react to produce, irreversibly, a macromolecular structure until the liquid vitrifies and becomes rigid. The number of covalent bonds formed in the structure,n, has been calculated and the dielectric relaxation time, τ, is related ton. This τ increases progressively more rapidly withn, and decreases, of course, on increasing the temperature. A compensation between these two effects determines the dynamic behaviour observed during rate heating. The effect of temperature is found to predominate. Such observations have been made possible by means of the new instrument.
PACS 64.70.PfGlass transitions
PACS 77.22.GmDielectric loss and relaxation
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