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next temperature was set virtually at random in the range of
11–40°C. Hence, in continuing experiments, the state of our model
oil acquired more and more complicated thermal history.
Results and Discussion
Deposition Data
The results of a series of deposition experiments are shown in
Fig. 4. Open squares denote the data set for an “equilibrium” state
of the model oil, which in its thermal history has never been
heated above 28°C (cf. Introduction). The apparent property of an
“equilibrium” state (1) is an increase in the mass of deposits with
increasing temperature up to ≈20°C, followed by a decrease of M at
higher T .
Filled circles in Fig. 3 denote the data for the model oil with
thermal histories including a structural transition at ≈28°C. A new
state of the oil, induced by this transition, is distinguished by a no-
table increase in the mass of deposits at any measurement’s tem-
perature (e.g. ≈25% at 20°C). A prevailing tendency in this state (2)
is a continuing increase of deposits with increasing temperature.
The thermally transformed oil is apparently in an “equilibrium”
state (energetically preferable one) at 28–40°C, while below 28°C
this state should be regarded as a metastable (transient) one.
The month-long experiments have shown that the discussed
metastable state is fairly long-lived. E.g., in measurements at
17–27°C we never observed a relaxation of the oil to the low-
temperature “equilibrium” state (denoted as “1” in Fig.4). In meas-
urements at 11–16°C such relaxation occurred only in 40% of sam-
ples (cf. the respective bifurcation of data points in Fig.4). More-
over, at 20°C we have tested the thermally transformed model oil
after six months storage at RT (18–20°C) and still observed a mass
of deposits characteristic for a metastable (transient) state.
Viscosity Data
Some of the deposition experiments have been supplemented
by measurements of viscosity in the model oil with the same ther-
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