Составители:
works by other strong surfactants introduced into the concentrated
product.
4.4. Interpretation of the activation energies
The means by which asphaltenes, resins and waxes interact to
exist in petroleum remains the subject of speculation but associa-
tion by hydrogen bonding and by formation of charge-transfer
π–π complexes have been cited as the causative mechanisms (12).
Through these noncovalent interactions, asphaltene molecules may
influence the structure of emulsions by forming a mechanical bar-
rier around the water droplets (13).
The strength of intermolecular bonds may be evaluated from
the changes in activation energies of the viscous flow, as shown by
viscosity studies in solutions of coal macromolecules, including as-
phaltenes (14). The removal (by chemical additives) of hydrogen
bonds and of π interactions decreased activation energies by
33 kJ/mol and by 30 kJ/mol, respectively. These results are close to
the bond strengths in coal solutions directly determined by IR-
spectroscopy (15). The IR average strengths of hydrogen bonds
were 30–50 kJ/mol, while some individual bonds had the strengths
of up to 70 kJ/mol.
Our measurements after RT formation (Fig.3A) show a step-
like decrease of activation energies by 50–60 kJ/mol for flow tem-
peratures exceeding 20°C. In view of the above arguments, this de-
crease may be attributed to a (reversible) thermally-induced break-
up of intermolecular hydrogen and/or π-bonds in the asphaltene
subsystems of the studied emulsions. Accordingly, an overall de-
crease of activation energies after the strong thermal preload
(TF=45°C, Fig.3C) should be due to an irreversible removal of non-
covalent bonds present in the RT-formed samples.
Finally, formation of emulsions in the “critical” temperature
range (TF=36°C, Fig.3B) induces the structural changes, charac-
terised by a large increase of activation energies of up to
300–380 kJ/mol, indicative of a possible covalent bonding. Namely,
this increase is close to the energies (≈380–420 kJ/mol) of unacti-
36
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