Many of water's peculiar physical properties are still not well understood, and one of the most important unresolved questions is its glass transition related dynamics. The consensus has been to accept a glass transition temperature (T(g)) around 136 K, but this value has been questioned and reassigned to about 165 K. We find evidence that the dielectric relaxation process of confined water that has been associated with the long accepted T(g) of water (130-140 K) must be a local process which is not related to the actual glass transition. Rather, our data indicate a glass transition at 160-165 K for bulk water and about 175 K for confined water (depending on the confining system).

The relaxation dynamics of dipropylene glycol and tripropylene glycol (nPG-n=2,3) water solutions on the nPG-rich side has been studied by broadband dielectric spectroscopy and differential scanning calorimetry in the temperature range of 130-280 K. Two relaxation processes are observed for all the hydration levels; the slower process (I) is related to the alpha relaxation of the solution whereas the faster one (II) is associated with the reorientation of water molecules in the mixture. Dielectric data for process (II) at temperatures between 150 and 200 K indicate the existence of a critical water concentration (x(c)) below which water mobility is highly restricted. Below x(c), nPG-water domains drive the dielectric signal whereas above x(c), water-water domains dominate the dielectric response at low temperatures. The results also show that process (II) at low temperatures is due to local motions of water molecules in the glassy frozen matrix. Additionally, we will show that the glass transition temperatures (T(g)) for aqueous PG, 2PG, and 3PG solutions do not extrapolate to approximately 136 K, regardless of the extrapolation method. Instead, we find that the extrapolated T(g) value for water from these solutions lies in the neighborhood of 165 K.

We provide a new approach to describe the component segmental dynamics of miscible polymer blends combining the concept of chain connectivity, expressed in terms of the self-concentration, and the Adam-Gibbs model. The results show an excellent agreement between the prediction of our approach and the experimental data. The self-concentrations obtained yield length scales between 1 and 3.2 nm depending on the temperature, the flexibility of the polymer, expressed in terms of the Kuhn segment, and its concentration in the blends, at temperatures above the glass transition range of the blend.

The effect of water content on silica nanoparticles was examined by thermogravimetry analysis (TGA), broadband dielectric spectroscopy (from 10 −2 to 10 7 Hz), and differential scanning calorimetry for a wide temperature range (110−250 K). Silica nanoparticles were dried and rehydrated at different water levels to determine the critical factors affecting the dielectric response. The dynamics of both hydration water and hydrated silanol groups were addressed. Whereas hydration water dynamics depend on the water content, the dynamics corresponding to hydrated silanol groups are almost water independent once the maximum hydroxylation level is reached. In addition, we determined that during hydration water molecules prefer to form clusters instead of filling a complete layer around the particles. Finally, we observed that contrary to other water containing systems, the corresponding relaxation times of water molecules do not show any crossover (from high-T super-Arrhenius to low-T Arrhenius behavior).