40
K. Adrjanowicz
obtained dependences look very much the same. Moreover, it was found that the
value of the Avrami parameter—providing information on the dimensionality of the
growing crystals—shows very weak variation with temperature and pressure. In the
considered T-p range, which covers a change of temperature by more than 50 K and
1 GPa in pressure, it varies around 3. From that, it can be concluded that the changes
in the density of the supercooled PC do not affect in any way the morphology of the
growing crystalline phase.
Summarizing, we have demonstrated that the glass-forming/crystallization
tendency of the molecular liquids can be controlled not only by changing the rate
of cooling/heating at constant pressure but also compression/decompression rate
under isothermal conditions. The results also suggest that when it comes to crystallization increasing pressure, to some extent, produces a similar effect as lowering
the temperature. Interestingly, within studied T-p range crystallization time and the
dimensionality of growing crystals do no depend significantly on whether temperature or pressure is used as the control thermodynamic variable. Thus, we can transfer
to high-pressure research the formalism used so far to describe the overall crystallization behavior of the glass-forming systems as a function of temperature. In line
with this, we constructed TPT/CDT diagrams as the pressure analogs of TTT/CHT
diagrams. The applicability of such diagrams to describe crystallization/vitrification
tendencies of the molecular systems upon non-isothermal or non-isobaric conditions
covers not only numerous research investigations but also industrial processing.
2.2 The Effect of Path Dependence on the Crystallization
Tendency of Glass-forming Liquids
The motivation for this research was to examine the effect of path dependence on
the crystallization of the molecular glass-formers [72]. Because of the experimental
difficulties arising when using high-pressure, it is typically more important to focus
on a particular feature of the studied material at a given (T, p) conditions rather than
analyze in detail the way how new thermodynamic state was approached. Compression at a fixed temperature is more convenient because the stabilization of pressure
usually takes less time than the temperature. This is not a big issue when considering
dynamics of liquids far above the glass transition temperature, because molecular
motions in the liquid state are always much faster the time needed for adjusting
new (T, p) conditions. On the other hand, when the liquid becomes more viscous
and reaches the glassy state molecular movements drastically slow down and the
thermal history aspect becomes extremely important. In such a case, the choice of
the thermodynamic path to attain the same final state point results in obtaining glassy
materials of different density and local relaxation dynamics [73, 74].
Intuitively, we can expect that the effect of path dependence is important not only
in the context of the glass transition but also such multivariable-dependent process
K. Adrjanowicz
obtained dependences look very much the same. Moreover, it was found that the
value of the Avrami parameter—providing information on the dimensionality of the
growing crystals—shows very weak variation with temperature and pressure. In the
considered T-p range, which covers a change of temperature by more than 50 K and
1 GPa in pressure, it varies around 3. From that, it can be concluded that the changes
in the density of the supercooled PC do not affect in any way the morphology of the
growing crystalline phase.
Summarizing, we have demonstrated that the glass-forming/crystallization
tendency of the molecular liquids can be controlled not only by changing the rate
of cooling/heating at constant pressure but also compression/decompression rate
under isothermal conditions. The results also suggest that when it comes to crystallization increasing pressure, to some extent, produces a similar effect as lowering
the temperature. Interestingly, within studied T-p range crystallization time and the
dimensionality of growing crystals do no depend significantly on whether temperature or pressure is used as the control thermodynamic variable. Thus, we can transfer
to high-pressure research the formalism used so far to describe the overall crystallization behavior of the glass-forming systems as a function of temperature. In line
with this, we constructed TPT/CDT diagrams as the pressure analogs of TTT/CHT
diagrams. The applicability of such diagrams to describe crystallization/vitrification
tendencies of the molecular systems upon non-isothermal or non-isobaric conditions
covers not only numerous research investigations but also industrial processing.
2.2 The Effect of Path Dependence on the Crystallization
Tendency of Glass-forming Liquids
The motivation for this research was to examine the effect of path dependence on
the crystallization of the molecular glass-formers [72]. Because of the experimental
difficulties arising when using high-pressure, it is typically more important to focus
on a particular feature of the studied material at a given (T, p) conditions rather than
analyze in detail the way how new thermodynamic state was approached. Compression at a fixed temperature is more convenient because the stabilization of pressure
usually takes less time than the temperature. This is not a big issue when considering
dynamics of liquids far above the glass transition temperature, because molecular
motions in the liquid state are always much faster the time needed for adjusting
new (T, p) conditions. On the other hand, when the liquid becomes more viscous
and reaches the glassy state molecular movements drastically slow down and the
thermal history aspect becomes extremely important. In such a case, the choice of
the thermodynamic path to attain the same final state point results in obtaining glassy
materials of different density and local relaxation dynamics [73, 74].
Intuitively, we can expect that the effect of path dependence is important not only
in the context of the glass transition but also such multivariable-dependent process