Abstract
The following flow equations are discussed and analysed in detail in this paper: Bottinga's non-Newtonian flow equation based on configurational entropy theory, which shows a dependence of the reduced viscosity on the square of the applied stress, and Graessley's non-Newtonian flow equation derived from the molecular entanglement theory. The comparison between these two equations and the phenomenological equations recently proposed by the present authors are made with respect to experimental results of various silicate glass melts and various amorphous polymers at different temperatures, obtained with the cylinder compression method [R. Brückner, Y. Yue and A. Habeck, Glastechn. Ber. Glass Sci. Technol. 67 (1994) 114], fiber elongation method [S.L. Webb and D.B. Dingwell, Phys, Chem. Miner. 17 (1990) 125] and rotation method [D.P. Wyman, L.J. Elyash and W.J. Frazer, J. Polm. Sci. A3 (1965) 681]. It is demonstrated that the equations proposed by the present authors describe best the experimental values not only for non-Newtonian flow behaviour but also for the ‘gross’ or ‘bruto’ shear thinning effect which includes the viscous heating effect. The existence of parameters such as the ultimate Binghamian viscosity, η∞, and stress limit under steady-state condition, σ lim, as observed in our measurements, can be predicted and interpreted with these equations. The concepts of changes of isotropic and anisotropic configurational entropy are introduced in the present paper, which correspond to isotropic and anisotropic changes of a glass liquid structure. In addition, the balance of dissipation heat in the sample were taken into account. Graessley's equation based on entanglement theory depicts the ‘gross’ or ‘bruto’ shear thinning effect of amorphous polymers. The decrease in density of entanglement of the molecular chains in organic polymers is not the unique dominating origin of the non-Newtonian flow behaviour of inorganic glass melts.
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