Dielectric Study of Hydration
Water in Silica Nanoparticles
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Abstract
The effect of water content on silica nanoparticles was
examined
by thermogravimetry analysis (TGA), broadband dielectric spectroscopy
(from 10<sup>β2</sup> to 10<sup>7</sup> Hz), and differential
scanning calorimetry for a wide temperature range (110β250
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)