Processus de l'ecoulement visqueux des hauts polymères

Two recent theories concerning the viscosity of high polymers are summarized: the first one, by Bueche, is based on a complex activation process; the other one, established by Cohen and Turnbull to explain the empirical equation of Williams, Landel, and Ferry, is based on the value of the free volume. The discrepancies with the experimental values are emphasized. A mechanism of deformation is proposed which implies that the displacement of a segment of a macromolecule requires the localization of no holes, at least, in a volume which contains No segments Then, the variation of the number of holes with the temperature is computed, with account of the flex energy of the backbone chain and the formation energy of holes (like Flory, and Gibbs and di Marzio). The theoretical results are in good agreement with the experimental values of the variation of the viscosity with the temperature, the second‐order transitions (thermal expansion and heat capacity), and the variation of the glass temperature with the molecular weight. A simple activation process can also produce the deformation and has the most important contribution at low temperature. It is believed that similar mechanism of diffusion of holes can also explain the viscosity of mineral glasses.