Activation energy of viscous flow

Caustic Waterflooding. In caustic waterflooding, the interfacial rheologic properties of a model crude oil-water system were studied in the presence of sodium hydroxide. The interfacial viscosity, the non-Newtonian flow behavior, and the activation energy of viscous flow were determined as a function of shear rate, alkali concentration, and aging time. The interfacial viscosity drastically... 

The viscosities of the membrane casting dopes were measured by a Hoeppler viscometer as previously described (6). The solution densities were obtained by the modified Gibson and Loeffler (,9) dllatometer. From these data the solution viscosities at different temperatures were calculated. The activation energies of viscous flow obtained from the logri-1/T plots were corrected by the corresponding values of the solvents used. 

Figure I. Effect of phosphoric acid concentration in additive on the activation energy of viscous flow of casting solutions...

The results of the calculations shown in Fig. 2.32 represent a complete quantitative solution of the problem, because they show the decrease in the induction period in non-isothermal curing when there is a temperature increase due to heat dissipation in the flow of the reactive mass. The case where = 0 is of particular interest. It is related to the experimental observation that shear stress is almost constant in the range t < t. In this situation the temperature dependence of the viscosity of the reactive mass can be neglected because of low values of the apparent activation energy of viscous flow E, and Eq. (2.73) leads to a linear time dependence of temperature ... 

Walter, R. H., and Sherman, R. M. (1981). Apparent activation energy of viscous flow in pectin jellies, f. Food Sci. 46 1223-1225. 

Ea apparent activation energy of viscous flow e base of natural logarithm (2.718)... 

Molar viscosity-temperature Hp M-Ep Activation energy of viscous flow E i- T)... 

In both the cases, the activation energy of the infiltration process (Fig. 1) is practically the same ( 40 kJ/mol) and close to that of the cobalt viscous flow (37.3 kJ/mol) [8], i.e. the observed variations in kinetics of the infiltration are caused by the difference between viscosities of cobalt and its alloys. According to [8] y= Aq exp(Ea/RT), where y is the kinematic viscosity, Aq is the constant, Ea is the activation energy of viscous flow, R is the universal gas constant, T is the absolute temperature. Correlating this formula with Eq. (2) and considering that q = py, where p is the density of the liquid, we have for k ... 

Williams, Ellard and Dawson92 have used the capillary method with 14C-labelled NMA to determine the self-diffusion coefficient of NMA. Values were found to range from 4.11 x 10-1° m2 sec-1 at 35 °C to 7.33 x 10-10 m2 sec-1 at 60 °C. The activation energy for the self-diffusion of NMA was calculated to be 19 kJ mol-1. This is quite close to the value of 19.2 kJ mol-1 calculated for the activation energy of viscous flow, thus suggesting the same rate controlling step for the two processes. 

The viscosities of the same two series of methylpolysiloxanes have been measured at several temperatures,11 and the logarithm of the absolute viscosity at any one temperature has been found to be a linear function of the logarithm of the number of units in either series. The activation energy of viscous flow may be expressed by an equation very similar to those just given for heat of vaporization ... 

Recently, contribution of dimethylsiloxane unit in the series of cyclic (D3 - Ds) and linear (D2 - Du) oligodimethylsiloxanes with various end groups was studied [1-4], It is indicated that absolute values of the activation energy of viscous flow of each cyclic compound are higher, compared with linear ones possessing the same number of dimethylsiloxane units in the molecule. 

A generalized kinetic model of cure is developed from the aspect of relaxation phenomena. The model not only can predict modulus and viscosity during the cure cycle under isothermal and non-isothermal cure conditions, but also takes into account filler effects on cure behavior. The increase of carbon black filler loading tends to accelerate the cure reaction and also broadens the relaxation spectrum. The presence of filler reduces the activation energy of viscous flow, but has little effect on the activation energy of the cure reaction. 

The activation energy of viscous flow will be decreased by an increase in filler loading and, therefore, the viscosity and modulus of filled polymer systems are less temperature dependent. On the other hand, filler loading has little effect on the activation energy of cure. 

Therefore, the study of rheological properties, the determination of the activation energy of viscous flow, composition-fluidity relationships, and key factor effects of the lubricity-promoting additive on the fluidity of oligoethylsiloxane-based compositions were of interest. 

Fig. 8. Activation energy of viscous flow. Data adapted from D. W. Van Krevelen, P. J. Hoftyzer, Properties of Polymers, Elsevier, 1976.

However, based on the validity of the Arrhenius equation for temperature dependence of viscosity and on the additivity of activation energies of viscous flow due to the general validity of Hess s law, the additivity of logarithms of viscosity could be accepted as the ideal behavior, e.g. for a ternary system at constant temperature, it may be written as... 

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