Activation energy, for viscosity

Other aspects of transport phenomena including activation energies for viscosity parameters and Washburn transport numbers (Feakins, 1974a Feakins and Lorimer, 1974) have also been measured to probe ion-solvent interactions in mixed solvent systems. 

In order to rationalize this result for PE, a simple calculation of the energy required for scission of main-chain bonds (E c c) the frictional dissipation between chains due to mechanical action was performed. The latter was calculated from the activation energy for viscosity of the monomer repeat unit, E, determined from a low-molar-mass analogue of polyethylene. This was then used to determine the number of repeat units, n, necessary to exceed the C-C bond energy of 349 kJ/mol. From the value of 4.22 kJ/mol for E, an estimate for n of 83 was made, which was considered a good approximation to the experimental result of 100 (Sohma, 1989b). However, such a simple approach is not amenable to extension to systems of structural complexity such as chain scission during the mastication of rubber. 

The activation energy for viscosity of pure silica drops from 565 to 163 kJ/mol upon the addition of 0.5 mol fraction MgO or CaO. The addition of alkali oxides has an even more dramatic effect, lowering the activation energy to 96 kJ/mol for 0.5 mol fraction additions. Explain, using sketches, why this is so. 

The viscosity parameters for a borosUicate glass are softening point, 794 °C annealing point, 574 °C strain point, 530 °C. Estimate the activation energy for viscosity. 

Figure 6. Dependence of the homogeneous nucleation rate, J, upon the extent of supercooling, e = T/Tm, where Tm is the equilibrium crystallization temperature. Numbers on the curves are values of c F (see Equation 68). E is the activation energy for viscosity normalized by kT ,. N,ot kT/h = 1Q35 -3 -1 5 ...

In these simple molecules, the dielectric relaxation curves conform to the simple Debye form and hence it is relatively straightforward to determine activation energies from the variation of the relaxation frequency with temperature (Table 4.1). A surprising feature of the rotator phase is that in certain cases the activation for dipolar relaxation is smaller in the solid than it is in the liquid phase, when the solid conforms to a face-centred cubic lattice. When the solid melts, the local force field loses its symmetrical form and the result is that the activation energy for free rotation is observed to increase slightly (Figure 4.5). For most polar liquids, the activation energy for viscosity flow and for dipole... 

---