Viscosity glass-forming liquids

The solidity of gel electrolytes results from chain entanglements. At high temperatures they flow like liquids, but on cooling they show a small increase in the shear modulus at temperatures well above T. This is the liquid-to-rubber transition. The values of shear modulus and viscosity for rubbery solids are considerably lower than those for glass forming liquids at an equivalent structural relaxation time. The local or microscopic viscosity relaxation time of the rubbery material, which is reflected in the 7], obeys a VTF equation with a pre-exponential factor equivalent to that for small-molecule liquids. Above the liquid-to-rubber transition, the VTF equation is also obeyed but the pre-exponential term for viscosity is much larger than is typical for small-molecule liquids and is dependent on the polymer molecular weight. 

Glass-Forming Liquids II. Detailed Comparison of Dielectric Relaxation, DC-Conductivity and Viscosity Data. 

Figure 4.5 Viscosity versus inverse temperature for glass-forming liquids, showing behavior classified as strong, typified by open tetrahedral networks, to fragile, typical of ionic and molecular liquids. Here Tg is defined by the criterion that nlT ) = 10 P. For most of the liquids, the viscosities seem to extrapolate to a common value of around 10" P at high temperatures, corresponding to a fundamental molecular vibrational frequency of around 10 sec-i. (Reprinted from J. Non-Cryst. -Solids, 73 1, Angell (1985), with kind permission from Elsevier Science—NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands.)...

The narrow transformation range commonly referred to as the glass transition is the temperature interval where the characteristic molecular relaxation time becomes of the order of 100 s (the laboratory time scale). The viscosities of several glass-forming liquids are shown in Fig. 3 as a... 

Figure 2.18 Variation of logarithmic viscosity as a function of inverse temperature for a simple glass forming liquid (schematic), r] is in Poises.

Roessler, E., Hess, K.-U., and Novikov, V. N. (1998) Universal representation of viscosity in glass forming liquids, J. Non-Cryst. Solids 223, 207-222. 

The functional dependence of viscosity on temperature has been measured in a large number of glass-forming liquids, and phenomenologically it has been... 

Fig. 5. Plots of log viscosity versus reduced inverse temperature for various glass forming liquids (Mackenzie et al. 1987).

At low viscosities, glass forming melts usually behave as Newtonian liquids which immediately relax to relieve an applied stress. At extremely high viscosities, however, these liquids respond to the rapid application of a stress as if they were actually elastic materials. It follows that there must exist an intermediate range of viscosities where the response of these melts to application of a stress is intermediate between the behavior of a pure liquid and that of an elastic solid. Since this behavior has aspects of both viscous flow and elastic response, it is known as viscoelasticity, or viscoelastic behavior. 

Stickel, F, Fischer, E. W., and Richer , R., Dynamics of glass-forming liquids 11. Detailed comparison of dielectric relaxation, dc-conductivity, and viscosity data, J. Chem. Phys., 104, 2043-2055 (1996). 

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