172
S. Cerveny and J. Swenson
dependence, typical for ionic and van der Waals systems, whereas a strong supercooled liquid shows a temperature dependence close to the Arrhenius law, which
is typical for materials with strong (commonly covalent) bonds forming a network
structure. It is well-established that: (1) water above approximately 233 K is one
of the most fragile liquids studied [25] and (2) the temperature dependence of its
viscosity (or structural relaxation time) seems to follow a power law diverging [26]
at about 228 K. Therefore, a glass-transition temperature, T g , substantially lower
than 228 K can be obtained only if the fragile behavior above 233 K changes to a
stronger Arrhenius-like temperature dependence slightly below 233 K. This is the
reason why it has been proposed that supercooled water undergoes a fragile-to-strong
(FS) transition around 228 K [25].
In fact, confined water (in hard- or soft- confinement systems) shows a similar
dynamic crossover in a temperature range between 180 and 220 K depending on
the system and experimental technique [22]. However, the origin of this dynamic
crossover and its relation to bulk water is a subject of controversial discussions. Some
studies indicate that the crossover is due to the existence of a fragile-to-strong transition at about 225 K, related to a transition from a high-temperature high density liquid
(HDL) to a low-temperature low density liquid (LDL) [27]. Other studies attributed
this dynamic crossover (sometimes observed at lower temperatures) to finite-size
effects [28, 29], where the low temperature relaxation (below the crossover temperature) represents a local relaxation (β-relaxation) of the confined water molecules
[24]. Lately, it has been proposed that the dynamical behavior changes in response
to fractional freezing of the confined water [30–33]. In this chapter, we are interested
in understanding the origin of a similar crossover in water solutions (i.e., in so-called
soft confinement systems), and how it is affected by a partial crystallization of the
water.
In this chapter, we are first reviewing some early work in this field and thereafter,
we are providing new experimental results on partial crystallization of water in solutions of some polymers and liquids. We analyze the impact of crystallization temperature and time on the glass transition of the solutions by calorimetric measurements.
Then, we are discussing the dynamics of amorphous water in solutions as seen by
broadband dielectric spectroscopy. We elucidate how the dynamical behavior of the
water is altered both during and after isothermal crystallization. Finally, we provide
implications of these results on the behavior of bulk water.
2 Experimental Section
2.1 Calorimetric Experiments
The DSC measurements described in this chapter were performed using a DSC Q2000
from TA Instruments in both standard and temperature-modulated (TMDSC) modes.
In the TMDSC mode, a periodic temperature perturbation is superimposed on a linear
S. Cerveny and J. Swenson
dependence, typical for ionic and van der Waals systems, whereas a strong supercooled liquid shows a temperature dependence close to the Arrhenius law, which
is typical for materials with strong (commonly covalent) bonds forming a network
structure. It is well-established that: (1) water above approximately 233 K is one
of the most fragile liquids studied [25] and (2) the temperature dependence of its
viscosity (or structural relaxation time) seems to follow a power law diverging [26]
at about 228 K. Therefore, a glass-transition temperature, T g , substantially lower
than 228 K can be obtained only if the fragile behavior above 233 K changes to a
stronger Arrhenius-like temperature dependence slightly below 233 K. This is the
reason why it has been proposed that supercooled water undergoes a fragile-to-strong
(FS) transition around 228 K [25].
In fact, confined water (in hard- or soft- confinement systems) shows a similar
dynamic crossover in a temperature range between 180 and 220 K depending on
the system and experimental technique [22]. However, the origin of this dynamic
crossover and its relation to bulk water is a subject of controversial discussions. Some
studies indicate that the crossover is due to the existence of a fragile-to-strong transition at about 225 K, related to a transition from a high-temperature high density liquid
(HDL) to a low-temperature low density liquid (LDL) [27]. Other studies attributed
this dynamic crossover (sometimes observed at lower temperatures) to finite-size
effects [28, 29], where the low temperature relaxation (below the crossover temperature) represents a local relaxation (β-relaxation) of the confined water molecules
[24]. Lately, it has been proposed that the dynamical behavior changes in response
to fractional freezing of the confined water [30–33]. In this chapter, we are interested
in understanding the origin of a similar crossover in water solutions (i.e., in so-called
soft confinement systems), and how it is affected by a partial crystallization of the
water.
In this chapter, we are first reviewing some early work in this field and thereafter,
we are providing new experimental results on partial crystallization of water in solutions of some polymers and liquids. We analyze the impact of crystallization temperature and time on the glass transition of the solutions by calorimetric measurements.
Then, we are discussing the dynamics of amorphous water in solutions as seen by
broadband dielectric spectroscopy. We elucidate how the dynamical behavior of the
water is altered both during and after isothermal crystallization. Finally, we provide
implications of these results on the behavior of bulk water.
2 Experimental Section
2.1 Calorimetric Experiments
The DSC measurements described in this chapter were performed using a DSC Q2000
from TA Instruments in both standard and temperature-modulated (TMDSC) modes.
In the TMDSC mode, a periodic temperature perturbation is superimposed on a linear