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This indicates that some long-lived extended molecular struc-
tures appeared in the emulsions after the fabrication processes at
“critical” temperatures (the effect of long-term “thermal memory”).
In the matrix crude oil phase, this “thermal memory” was found to
extend for a period of at least four months.
2. Activation energies of the viscous flow
Activation energies were determined from the dependencies of
the logarithm of viscosity on the reciprocal flow temperature, by
fitting straight line approximations (the Arrhenius plots) between
the consecutive experimental points. To reduce a random scatter,
the obtained sets of activation energies were smoothed with a
three-point sliding data window. The results of these calculations
are presented in Figure 2 for (1) the bitumen emulsions; (2) the
water/crude oil emulsions; (3) the water-free crude oil.
The left part of
Figure 2 shows the
dependencies of
activation energies
on the flow (measu-
rement) tempera-
ture for samples,
subjected to room
temperature forma-
tion (TF=20°C).
The notable feature is a virtual coincidence of activation ener-
gies for all studied samples. For flow temperatures decreasing from
30°C down to 20°C all activation energies remain fairly constant,
slowly increasing within the limits of 8.5–10.5 kcal/mol
(≈36–44 kJ/mol).
At temperatures close to 20°C there is a step-like increase of
the activation energies to a new level of 22–29 kcal/mol (≈92–121
kJ/mol). Below 10-12
0
C the activation energies show the tendency
of decreasing, so the shape of the curves in the range of 8–20°C
may be described as a “flat maximum”.
20
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