High-Pressure Crystallization of Glass-Forming Liquids …
31
to characterize especially dynamics aspects related to the glass-formation and crystallization, dielectric spectroscopy emerges as a highly promising experimental tool
[44].
The principle idea of the dielectric relaxation relies on the interactions of the
molecules possessing a permanent dipole moment with an external electric field.
When a time-dependent electric field is applied it causes polarization of the dielectric material and by following time-dependent changes in the relaxation function one
gets information on certain molecular movements in the sample. Dielectric spectroscopy is a very powerful tool to study the molecular dynamics of supercooled
liquids and glasses in the broad range of characteristic relaxation times and temperature. It can also be used to detect phase transitions (e.g., in liquid crystals) and
follow the kinetics of the different processes (e.g., crystallization, polymerization,
mutarotation, isomerization, physical aging, etc.). In this chapter, dielectric studies
of crystallization are of primary importance. Therefore, we will limit further discussion only to those aspects of the dielectric response in glass-forming systems that
are related only to the crystallization event. For more detailed information on the
dielectric spectroscopy and its applicability in diverse fields of science and industry
the readers are referred to more specialized literature, e.g., [55–59].
In Fig. 3, we demonstrate typical dielectric response recorded for a glass-forming
liquid at some certain, fixed, temperature and pressure conditions. Panel (a) refers to
the real part while (b) to the imaginary part of the dielectric permittivity. The presence of the α-relaxation process—associated with cooperative movements of the
molecules—is signified in the dielectric spectra as a characteristic step in frequency
10
1
10
2
10
3
10
4
10
5
10
6
4
6
8
10
12
10
1
10
2
10
3
10
4
10
5
10
6
0.0
0.5
1.0
1.5
2.0
0
45000 90000 135000
0.00
0.25
0.50
0.75
1.00
ε'
Freq. / Hz
(a)
(b)
crystallization
ε"
Freq. / Hz
(T, p)
(T, p)
crystallization
ε'
N
Time[s]
Fig. 3 Time evolution of the real a and imaginary b parts of the dielectric permittivity for a typical
glass-forming liquid at a given (T, p) conditions as due to crystallization. The inset shows normalized
dielectric constant ε N
as a function of crystallization time
31
to characterize especially dynamics aspects related to the glass-formation and crystallization, dielectric spectroscopy emerges as a highly promising experimental tool
[44].
The principle idea of the dielectric relaxation relies on the interactions of the
molecules possessing a permanent dipole moment with an external electric field.
When a time-dependent electric field is applied it causes polarization of the dielectric material and by following time-dependent changes in the relaxation function one
gets information on certain molecular movements in the sample. Dielectric spectroscopy is a very powerful tool to study the molecular dynamics of supercooled
liquids and glasses in the broad range of characteristic relaxation times and temperature. It can also be used to detect phase transitions (e.g., in liquid crystals) and
follow the kinetics of the different processes (e.g., crystallization, polymerization,
mutarotation, isomerization, physical aging, etc.). In this chapter, dielectric studies
of crystallization are of primary importance. Therefore, we will limit further discussion only to those aspects of the dielectric response in glass-forming systems that
are related only to the crystallization event. For more detailed information on the
dielectric spectroscopy and its applicability in diverse fields of science and industry
the readers are referred to more specialized literature, e.g., [55–59].
In Fig. 3, we demonstrate typical dielectric response recorded for a glass-forming
liquid at some certain, fixed, temperature and pressure conditions. Panel (a) refers to
the real part while (b) to the imaginary part of the dielectric permittivity. The presence of the α-relaxation process—associated with cooperative movements of the
molecules—is signified in the dielectric spectra as a characteristic step in frequency
10
1
10
2
10
3
10
4
10
5
10
6
4
6
8
10
12
10
1
10
2
10
3
10
4
10
5
10
6
0.0
0.5
1.0
1.5
2.0
0
45000 90000 135000
0.00
0.25
0.50
0.75
1.00
ε'
Freq. / Hz
(a)
(b)
crystallization
ε"
Freq. / Hz
(T, p)
(T, p)
crystallization
ε'
N
Time[s]
Fig. 3 Time evolution of the real a and imaginary b parts of the dielectric permittivity for a typical
glass-forming liquid at a given (T, p) conditions as due to crystallization. The inset shows normalized
dielectric constant ε N
as a function of crystallization time