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we have used the viscosity value at a common shear stress of
0.7 Pa, i.e. at flow conditions closest to Newtonian.
3.2. Constant-shear viscosities before
after thermal preload
The viscosity of the emulsions was strongly affected by their
fabrication temperature TF.
Fig.1(A,B) shows the effect of TF on the dependencies of vis-
cosity at a constant shear stress (0.7 N/m
2
) on the flow (measure-
ment) temperature, for the wa-
ter/crude oil emulsions (A) and for the
bitumen emulsions (B). Note, that the
viscosity values are plotted on a log-
scale. The data denoted by circles were
obtained after fabrication at room
temperature (TF=24°C), without
thermal preload. Squares and trian-
gles denote the results for TF=36°C
and TF=45°C, respectively. In all
cases the viscosity decreases with in-
creasing flow temperature due to the
enhanced thermal mobility of the mo-
lecular, aggregate and colloidal spe-
cies. However, the rate of this de-
crease (as well as the viscosity value at any flow temperature)
shows a strong non-monotonic dependence on the fabrication tem-
perature.
For the water-crude oil emulsions (Fig.1 A), a moderate ther-
mal preload (TF=36°C) leads to a large increase of viscosities as
compared to emulsions, fabricated at room temperature. At flow
temperature of 10°C this increase is almost four-fold – from
372 mPa⋅s to 1440 mPa⋅s. A somewhat stronger thermal preload
(TF=45°C) causes a qualitatively opposite effect of decreasing the
viscosities as compared to the RT data. At flow temperature of
10°C the decrease is from 372 mPa⋅s to 116 mPa⋅s. For W/O emul-
29
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