High-Pressure Crystallization of Glass-Forming Liquids …
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(RS)-ketoprofen
(S)-ketoprofen
t
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[hours]
pressure [MPa]
k/s
-1
pressure [MPa]
Avrami n
pressure [MPa]
Fig. 16 Pressure evolution of the crystallization half-time (main panel), overall crystallization rate
(lower inset), and Avrami parameter (upper inset) for S-ketoprofen and RS-ketoprofen crystallized along the same isochrone. Adapted with permission from [65]. Copyright (2015) American
Chemical Society
while for S-ketoprofen (314 K, 5 MPa), (324 K, 41 MPa), (343 K, 126 MPa), (384 K,
342 MPa).
Changes in the overall crystallization rate and Avrami parameter for all studied
(T, p) points located on the same isochrone are shown in the insets of Fig. 16.
The former one provides information about the rate of transformation, while the
latter one depends on the growth mechanisms and crystal shape. It is evident that
when moving along an isochrone toward higher pressures, the crystallization of RSketoprofen slows down with increasing compression, while for S-ibuprofen it speeds
up. These differences are even more straightforward when the crystallization halftime (i.e., time after which changes in the crystallinity of the sample reaches 50%) is
considered. For example, for the racemic sample kept at 345 MPa and 384 K t 1/2 is
almost 5 times longer when compared to its ambient pressure value. Meanwhile, the
evolution of the Avrami exponent for racemic sample seems to be almost temperature
and pressure invariant. In contrast, for S-enantiomer crystallization along the same
isochrone speeds up with increasing pressure and half-time decreases. We found it
very surprising that the crystallization tendencies of the racemic mixture and pure
isomer are much different already at low pressure. For RS-ketoprofen, it proceeds
faster (t 1/2 ∼ = 4 h) than for its pure enantiomer (t 1/2 ∼ = 10 h). This trend, however,
changes completely on increased pressure. At around 345 MPa t 1/2 ∼ = 46 h for RS
while for the pure S form t 1/2 ∼ = 1.5 h. As we suppose, at much higher pressure
this may result in complete inhibition of the crystallization progress for the racemic
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10
-5
10
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100 200 300 400
1.5
2.0
2.5
(RS)-ketoprofen
(S)-ketoprofen
t
1/2
[hours]
pressure [MPa]
k/s
-1
pressure [MPa]
Avrami n
pressure [MPa]
Fig. 16 Pressure evolution of the crystallization half-time (main panel), overall crystallization rate
(lower inset), and Avrami parameter (upper inset) for S-ketoprofen and RS-ketoprofen crystallized along the same isochrone. Adapted with permission from [65]. Copyright (2015) American
Chemical Society
while for S-ketoprofen (314 K, 5 MPa), (324 K, 41 MPa), (343 K, 126 MPa), (384 K,
342 MPa).
Changes in the overall crystallization rate and Avrami parameter for all studied
(T, p) points located on the same isochrone are shown in the insets of Fig. 16.
The former one provides information about the rate of transformation, while the
latter one depends on the growth mechanisms and crystal shape. It is evident that
when moving along an isochrone toward higher pressures, the crystallization of RSketoprofen slows down with increasing compression, while for S-ibuprofen it speeds
up. These differences are even more straightforward when the crystallization halftime (i.e., time after which changes in the crystallinity of the sample reaches 50%) is
considered. For example, for the racemic sample kept at 345 MPa and 384 K t 1/2 is
almost 5 times longer when compared to its ambient pressure value. Meanwhile, the
evolution of the Avrami exponent for racemic sample seems to be almost temperature
and pressure invariant. In contrast, for S-enantiomer crystallization along the same
isochrone speeds up with increasing pressure and half-time decreases. We found it
very surprising that the crystallization tendencies of the racemic mixture and pure
isomer are much different already at low pressure. For RS-ketoprofen, it proceeds
faster (t 1/2 ∼ = 4 h) than for its pure enantiomer (t 1/2 ∼ = 10 h). This trend, however,
changes completely on increased pressure. At around 345 MPa t 1/2 ∼ = 46 h for RS
while for the pure S form t 1/2 ∼ = 1.5 h. As we suppose, at much higher pressure
this may result in complete inhibition of the crystallization progress for the racemic