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S. Cerveny and J. Swenson
This implies that the “universal” water relaxation we observed is not only the same
for bulk water, but it also has the characteristics of a local reorientational motion in
amorphous ice, i.e., the water we observe below the crossover temperature at about
180 K should be considered as amorphous ice rather than as a supercooled liquid
[23].
9 Conclusion
In this chapter, we have presented old and new experimental data on the dynamics of
water in semi-crystalline environments and we have compared with the dynamics of
water in the amorphous state. By using broadband dielectric spectroscopy, we have
analyzed the dynamics during and after crystallization at different crystallization
temperatures and times. The dynamical behavior of both the solute and the remaining
non-crystalline water is remarkably affected by the crystallization temperature. At
a low crystallization temperature (just above T g ), there is basically no changes of
the glass transition and its related structural relaxation or the low-temperature water
relaxation, suggesting that some of the amorphous water transforms to crystalline
water without affecting the overall structure of the solution or the hydration of the
solute molecules. However, at a high crystallization temperature, the dynamics of
both the solute (and therefore also the glass transition temperature) and the water is
slowed down by the partial crystallization of the water. This is the typical behavior
of freeze-concentrated solutions when the amorphous part of the solution is “dried
out” by a micro-phase separation into ice regions and freeze-concentrated amorphous
regions.
The differences in the dynamics described above for low and high crystallization temperatures occur for “ordinary” aqueous solutions exhibiting only one water
relaxation. However, for solutions exhibiting two water relaxations, as commonly
observed for biological systems and solutes for which the addition of water has a
dramatic effect on T g [44, 45], yet another dynamical behavior is observed. In this
case, partial crystallization of the water does increase the glass transition temperature,
as typical for freeze-concentrated solutions, but nevertheless the low-temperature
water relaxation is not affected. This indicates that the fast water relaxation in this
type of solutions may be considered as an intrinsic water relaxation. This conclusion is furthermore supported by the fact that an almost identical water relaxation
is observed for both bulk water (or rather low-density amorphous ice) [57] and
water confined in hard confinements with or without ice. Thus, there is no reason
to believe that this common water relaxation should not have the same origin in the
three mentioned types of systems. The “universality” of this water relaxation gives
also further evidence for that it is of local character, in contrast to the viscosity related
structural (α) relaxation.
S. Cerveny and J. Swenson
This implies that the “universal” water relaxation we observed is not only the same
for bulk water, but it also has the characteristics of a local reorientational motion in
amorphous ice, i.e., the water we observe below the crossover temperature at about
180 K should be considered as amorphous ice rather than as a supercooled liquid
[23].
9 Conclusion
In this chapter, we have presented old and new experimental data on the dynamics of
water in semi-crystalline environments and we have compared with the dynamics of
water in the amorphous state. By using broadband dielectric spectroscopy, we have
analyzed the dynamics during and after crystallization at different crystallization
temperatures and times. The dynamical behavior of both the solute and the remaining
non-crystalline water is remarkably affected by the crystallization temperature. At
a low crystallization temperature (just above T g ), there is basically no changes of
the glass transition and its related structural relaxation or the low-temperature water
relaxation, suggesting that some of the amorphous water transforms to crystalline
water without affecting the overall structure of the solution or the hydration of the
solute molecules. However, at a high crystallization temperature, the dynamics of
both the solute (and therefore also the glass transition temperature) and the water is
slowed down by the partial crystallization of the water. This is the typical behavior
of freeze-concentrated solutions when the amorphous part of the solution is “dried
out” by a micro-phase separation into ice regions and freeze-concentrated amorphous
regions.
The differences in the dynamics described above for low and high crystallization temperatures occur for “ordinary” aqueous solutions exhibiting only one water
relaxation. However, for solutions exhibiting two water relaxations, as commonly
observed for biological systems and solutes for which the addition of water has a
dramatic effect on T g [44, 45], yet another dynamical behavior is observed. In this
case, partial crystallization of the water does increase the glass transition temperature,
as typical for freeze-concentrated solutions, but nevertheless the low-temperature
water relaxation is not affected. This indicates that the fast water relaxation in this
type of solutions may be considered as an intrinsic water relaxation. This conclusion is furthermore supported by the fact that an almost identical water relaxation
is observed for both bulk water (or rather low-density amorphous ice) [57] and
water confined in hard confinements with or without ice. Thus, there is no reason
to believe that this common water relaxation should not have the same origin in the
three mentioned types of systems. The “universality” of this water relaxation gives
also further evidence for that it is of local character, in contrast to the viscosity related
structural (α) relaxation.