Thermodynamics and dielectrics of polymerization, crystallization and interfacial phenomena

Year: 1999

Authors: Tombari E., Ferrari C., Salvetti G., Johari G.P.

Autors Affiliation: Istituto Fisica Atomica e Molecolare del CNR, via del Giardino 7, 56127-Pisa, Italy; Department of Materials Science and Engineering, McMaster University, Hamilton, Ont. L8S 4L7, Canada

Abstract: Several types of dielectric and calorimetric measurements have been made simultaneously on chemically and physically changing systems, e.g., systems undergoing polymerization and crystallization, in real time using newly developed equipment. The relaxation times, tau(0), obtained at a certain degree of polymerization in the temperature modulation mode and the isothermal mode are the same, although the polymerization is slower in the former case. tau(0) and direct-current conductivity do not follow the same formalism, although both change upon polymerization as if the liquid was being cooled. The heat capacity decreases on polymerization and the original GHz-frequency dielectric relaxation becomes gradually extinct. The dynamics upon heating a partially polymerized sample is not determined by further polymerization. Calorimetry and dielectric data show that the diffusion control\’s onset occurs gradually and not at a particular value of tau(0). The crystallization and melting of poly(ethylene glycol) of molecular weight 3400 show substantial effects arising from interfacial polarization. Its equilibrium permittivity does not follow the law of mixtures, indicating substantial contributions from changes in the dipole moment at the solid/liquid interface.


Volume: 11 (10A)      Pages from: A317  to: A327

DOI: 10.1088/0953-8984/11/10A/029

Citations: 8
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