180
S. Cerveny and J. Swenson
3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5
-9
-6
-3
0
3
PVP - c w = 40 wt%
Fast solvent
Slow Solvent
α-relaxation
log (τ [s])
1000/T [K
-1
]
Fig. 7 Temperature dependences of the relaxation times for PVP aqueous solutions with 40 wt% of
water in the temperature range where water is amorphous. The straight lines below T g represent fits
to the experimental data by the Arrhenius equation, whereas above T g full lines represent VFT-fits
to the experimental data. Adapted from Ref. [45] with permission
about 10 K), it is possible to observe a single water relaxation with the characteristics
discussed above.
Different to PVME or 3PG solutions, PVP solutions show a different dynamical
behavior. For PVP solutions (Fig. 7), we observe three relaxations [44]: the slowest
is related to the α-relaxation of the solute and the two fastest are due to motions
of water molecules [44]. It is important to note that in our previous works of PVP
aqueous solutions [46–48], these two water relaxations were not reported (only the
fast relaxation was included). In Fig. 7, we show the temperature dependence of
the relaxation time of each relaxation process for PVP with 40 wt% of water. It is
evident that the relaxation times of the slow solvent process and the solute exhibit
the same temperature dependence in the high temperature range above T g . Note that
this slow solvent relaxation is not observed for 3PG or for PVME. In addition, for
these solutions, the fast solvent relaxation shows a completely different temperature
dependence than the solute relaxation (Fig. 7).
5 The Dynamics of Solutions During Isothermal
Crystallization
There is quite a lot of information about the water dynamics in solutions when water
remains amorphous at all temperatures. However, there is little information about the
dynamical changes of the water during and after isothermal crystallization. Therefore, in this section, we address the dynamics of water in semi-crystalline solutions.
BDS is a good technique to follow the dynamics of the amorphous solutions and
S. Cerveny and J. Swenson
3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5
-9
-6
-3
0
3
PVP - c w = 40 wt%
Fast solvent
Slow Solvent
α-relaxation
log (τ [s])
1000/T [K
-1
]
Fig. 7 Temperature dependences of the relaxation times for PVP aqueous solutions with 40 wt% of
water in the temperature range where water is amorphous. The straight lines below T g represent fits
to the experimental data by the Arrhenius equation, whereas above T g full lines represent VFT-fits
to the experimental data. Adapted from Ref. [45] with permission
about 10 K), it is possible to observe a single water relaxation with the characteristics
discussed above.
Different to PVME or 3PG solutions, PVP solutions show a different dynamical
behavior. For PVP solutions (Fig. 7), we observe three relaxations [44]: the slowest
is related to the α-relaxation of the solute and the two fastest are due to motions
of water molecules [44]. It is important to note that in our previous works of PVP
aqueous solutions [46–48], these two water relaxations were not reported (only the
fast relaxation was included). In Fig. 7, we show the temperature dependence of
the relaxation time of each relaxation process for PVP with 40 wt% of water. It is
evident that the relaxation times of the slow solvent process and the solute exhibit
the same temperature dependence in the high temperature range above T g . Note that
this slow solvent relaxation is not observed for 3PG or for PVME. In addition, for
these solutions, the fast solvent relaxation shows a completely different temperature
dependence than the solute relaxation (Fig. 7).
5 The Dynamics of Solutions During Isothermal
Crystallization
There is quite a lot of information about the water dynamics in solutions when water
remains amorphous at all temperatures. However, there is little information about the
dynamical changes of the water during and after isothermal crystallization. Therefore, in this section, we address the dynamics of water in semi-crystalline solutions.
BDS is a good technique to follow the dynamics of the amorphous solutions and