Energy activation, viscous flow

Table 1. Activation energies and ratios of the preexponential factors to the radiative rate constants (A/kp) for the photoisomcrization of BMPC in several solvents. Solvent dielectric constants at room temperature, e [65], and viscous flow activation energies, Eri [66], are shown too.

Rheological properties of the oligoethylsiloxane-based compositions with additives are of vital importance for the selection of maintenance conditions of various items, but they have not been studied yet. No data on such composition-fluidity relationships (unconfined fluctuating free volume and viscous flow activation energy values) are available. 

Another key feature of the fluid is the design parameter B (see Table 3), obtained by differentiation of the Falcher-Tamman equation [3], which is proportional to the viscous flow activation energy ... 

Additive content increase in the compositions results in a regular increase in the value of Bt and the values of the viscous flow activation energy at 20 °C (see Table 3). 

Thus, the conducted research showed that absolute reaction rate theory is not applicable to the explanation of the composition s viscosity-temperature relationship. It was found that the fi e volume theory allows us to describe the viscosity-temperature relationship with satisfactory accuracy within the studied temperature range from nunus -20 to 50 C. Parts of the fi ee fluctuation volume and viscous flow activation energy values determining fluids properties were calculated. 

It was found that introduction of dimethylsiloxane units into an oligodiethylsiloxane chain leads to an insignificant drop in the viscous flow activation energy from 23.3 to 22.6 kJ/mol, and an increase in trifunctional unit content leads to the growth of probability of intermolecular contacts due to molecule branch interactions this results in viscous flow activation energy growth to 25.5 kJ/mol. 

Polyvinyl acetate Apparent viscosity, viscous flow activation energy Viscometry 128... 

The temperature dependence of viscosity follows the Arrhenius equation. The flow activation energy (J/mol), E, for viscous flow can be measured from log(apparent viscosity) vs. 1/T plots, where T is the absolute temperature (K). The activation energy of viscous flow is found to decrease with increase in shear rate (Figure 3). But it can be seen that the viscosity of molten PES has a weak dependence on temperature, obviously due to the fairly lower viscous flow activation energy it has. 

Figure 3. Variation of viscous flow activation energies with shear rate.

Figure 11.29 shows that the slope of log tiq versus 1/T plot is almost the same for both PS and PMMA, meaning that the viscous flow activation energy E in the Arrhenius expression, t]Q viscosity ratio, t]Q ps/>lo pmmA expected to be virtually independent of temperature. 

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