Activation energy for viscous flow

Melt Viscosity. As shown in Tables 2 and 3, the melt viscosity of an acid copolymer increases dramatically as the fraction of neutralization is increased. The relationship for sodium ionomers is shown in Figure 4 (6). Melt viscosities for a series of sodium ionomers derived from an ethylene—3.5 mol % methacrylic acid polymer show that the increase is most pronounced at low shear rates and that the ionomers become increasingly non-Newtonian with increasing neutralization (9). The activation energy for viscous flow has been reported to be somewhat higher in ionomers than in related acidic... 

In connection with the earlier consideration of diffusion in liquids using tire Stokes-Einstein equation, it can be concluded that the temperature dependence of the diffusion coefficient on the temperature should be T(exp(—Qvis/RT)) according to this equation, if the activation energy for viscous flow is included. 

The viscosity of liquid silicates such as drose containing barium oxide and silica show a rapid fall between pure silica and 20 mole per cent of metal oxide of nearly an order of magnitude at 2000 K, followed by a slower decrease as more metal oxide is added. The viscosity then decreases by a factor of two between 20 and 40 mole per cent. The activation energy for viscous flow decreases from 560 kJ in pure silica to 160-180kJmol as the network is broken up by metal oxide addition. The introduction of CaFa into a silicate melt reduces the viscosity markedly, typically by about a factor of drree. There is a rapid increase in the thermal expansivity coefficient as the network is dispersed, from practically zero in solid silica to around 40 cm moP in a typical soda-lime glass. 

Under stress conditions similar to those arising in the extrusion or pressure molding processes, the activation energy for viscous flow of systems with PMF is little different from that for the matrix [163, 164,209, 344, 345], This means that the secondary network of the materia has been destroyed [69]. 

A variation of Equation 4-9 is to approximate the many terms in it by viscosity Tj (Kirkpatrick, 1975). Assuming that the activation energy for viscous flow is the same as that for nucleation, then p =A exp[E/(RT)] where A is a constant. Substituting it into Equation 4-9 leads to... 

Accordingly the increase in excimer/molecular fluorescence yield ratio with temperature in this region (Fig. 9) reflects the corresponding increase in encounter frequency dm[M] of excited and unexcited molecules if t/([M]rP)/ dT 0, and the temperature coefficient is related to the activation energy for viscous flow of the solvent Ed. 

The activation energy for viscous flow, 7/ x, for normal metals is... 

Figure 4.1 Dependence of activation energy for viscous flow on melting point for normal metals and semi-metals. Reprinted, by permission, from T. lida and R. I. L. Guthrie, The Physical Properties of Liquid Metals, p. 187. Copyright 1988 by Oxford University Press.

Since the activation energy for ionic recombination is mainly due to viscosity we use the activation energy for viscous flow (10kJ.mol l). AH ] and 3 were determined from conductance as 44.2kJ.mol and 11,4kJ.mol From the data presented in Table III it is clear that the temperature dependence of the slope is very satisfactorily described by A% +l/2(AHd-AH3). Another, and rather critical, test for the applicability of eq. 14b is the effect of pressure since the slope of eq. 14b is largely pressure independent so that we ask here for a compensation of rather large effects. From Table III we Indeed see an excellent accordance between the experimental value and the pressure-dependence calculated from the activation volume of viscous flow (+20.3 ctPmol ), AVd (-57.3 cnAnol" ) and (-13.9 cnAnol ) the difference between the small experimental and calculated values is entirely with the uncertainties of compressibility - corrections and experimental errors. 

B — Constant R — gas constant T — absolute temperature E = activation energy for viscous flow. 

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