High-Pressure Crystallization of Glass-Forming Liquids …
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Formation of the crystalline phase is of great interest from both, scientific point
of view and technological applications. Crystallization underlies natural phenomena
such as biomineralization, honey granulation, natural rocks, and cave calcites
creation. On the other hand, artificial crystallization has been applied in various
areas of science and industrial processing for chemical synthesis, purification, and
selective fabrication of organic as well as inorganic materials with preferable physicochemical features. Because of the fundamental significance, the interest in the crystallization last endlessly for decades and continues to excite a large spectrum of
research activities [4–7].
Crystallization is essentially well studied, but not necessarily well-understood
phenomenon. Surprisingly, despite years of intensive studies, there are numerous
aspects related to the crystallization process which are being poorly recognized or
still intriguing in their nature. For example, it is by no means easy to understand
why some of the liquids are not prone to crystallize on cooling (even if a very slow
cooling rate is applied), whereas undercooling of the other ones require a tremendous effort [8, 9]. Some of the glassy materials can be physically stable for years,
while the other ones recrystallize within a few minutes or hours. A complete and
consistent description of the glass transition and crystallization phenomena constitute an enormous challenge in the field of modern condensed matter physics. This
includes for example explanation why on approaching the glass transition relatively
small changes in temperature affect the dynamic features of supercooled liquids
(viscosity, relaxation time or diffusion coefficient) by several orders of magnitude
[10–12]. There have been efforts in both, theory and experiment to provide a physical
understanding of the vitrification process which is predominantly discussed in the
context of its intimate link to crystallization [13]. Recent studies have also revealed
that the formation of the nuclei might follow a two-step mechanism, which in many
cases accounts better for the experimentally determined kinetic dependencies than
the predictions of the classical theory [14, 15].
There is a tremendous interest in manipulating and controlling crystallization
behavior of complex systems (i.e., supercooled liquids, polymer melts, liquid crystals or bio-fluids) which is an important aspect in the field of material physics,
chemical engineering, food, and pharmaceutical developments. For example, in the
pharmaceutical formulation, the disordered phase is usually more preferable than
crystalline one because of improved solubility and bioavailability [16]. However,
this can be difficult to achieve as thermodynamic instability prompt the amorphous
system to spontaneous recrystallization beginning just after a few hours, days, or
months after preparation. In some other cases, it is highly desirable to control in a
selective way formation of different polymorphic forms of the same compound as to
be able to affect its solid-state features (stability, dissolution rate, biological activity,
optical, and mechanical properties) [17, 18]. Because of that reason identification
and understanding, the critical factors that can influence the crystallization progress
are of great practical importance.
One of the most interesting strategies that can be employed to modify the crystallization behavior of glass-forming liquids is compression. Experimental studies
25
Formation of the crystalline phase is of great interest from both, scientific point
of view and technological applications. Crystallization underlies natural phenomena
such as biomineralization, honey granulation, natural rocks, and cave calcites
creation. On the other hand, artificial crystallization has been applied in various
areas of science and industrial processing for chemical synthesis, purification, and
selective fabrication of organic as well as inorganic materials with preferable physicochemical features. Because of the fundamental significance, the interest in the crystallization last endlessly for decades and continues to excite a large spectrum of
research activities [4–7].
Crystallization is essentially well studied, but not necessarily well-understood
phenomenon. Surprisingly, despite years of intensive studies, there are numerous
aspects related to the crystallization process which are being poorly recognized or
still intriguing in their nature. For example, it is by no means easy to understand
why some of the liquids are not prone to crystallize on cooling (even if a very slow
cooling rate is applied), whereas undercooling of the other ones require a tremendous effort [8, 9]. Some of the glassy materials can be physically stable for years,
while the other ones recrystallize within a few minutes or hours. A complete and
consistent description of the glass transition and crystallization phenomena constitute an enormous challenge in the field of modern condensed matter physics. This
includes for example explanation why on approaching the glass transition relatively
small changes in temperature affect the dynamic features of supercooled liquids
(viscosity, relaxation time or diffusion coefficient) by several orders of magnitude
[10–12]. There have been efforts in both, theory and experiment to provide a physical
understanding of the vitrification process which is predominantly discussed in the
context of its intimate link to crystallization [13]. Recent studies have also revealed
that the formation of the nuclei might follow a two-step mechanism, which in many
cases accounts better for the experimentally determined kinetic dependencies than
the predictions of the classical theory [14, 15].
There is a tremendous interest in manipulating and controlling crystallization
behavior of complex systems (i.e., supercooled liquids, polymer melts, liquid crystals or bio-fluids) which is an important aspect in the field of material physics,
chemical engineering, food, and pharmaceutical developments. For example, in the
pharmaceutical formulation, the disordered phase is usually more preferable than
crystalline one because of improved solubility and bioavailability [16]. However,
this can be difficult to achieve as thermodynamic instability prompt the amorphous
system to spontaneous recrystallization beginning just after a few hours, days, or
months after preparation. In some other cases, it is highly desirable to control in a
selective way formation of different polymorphic forms of the same compound as to
be able to affect its solid-state features (stability, dissolution rate, biological activity,
optical, and mechanical properties) [17, 18]. Because of that reason identification
and understanding, the critical factors that can influence the crystallization progress
are of great practical importance.
One of the most interesting strategies that can be employed to modify the crystallization behavior of glass-forming liquids is compression. Experimental studies