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Calcium silicate hydrates are members of a large family of minerals with layered structures containing pendant CaOH and SiOH groups that interact with confined water molecules. To rationalize the impact of the local chemical environment on the dynamics of water, SiOH‐ and CaOH‐rich model nanocrystals were synthesized by using the continuous supercritical hydrothermal method and then systematically studied by a combination of spectroscopic techniques. In our comprehensive analysis, the ultrafast relaxation dynamics of hanging hydroxy groups can be univocally assigned to CaOH or SiOH environments, and the local chemical environment largely affects the H‐bond network of the solvation water. Interestingly, the ordered "ice‐like" solvation water found in the SiOH‐rich environments is converted to a disordered "liquid‐like" distribution in the CaOH‐rich environment. This refined picture of the dynamics of confined water and hydroxy groups in calcium silicate hydrates can also be applied to other water‐containing materials, with a significant impact in many fields of materials science. [ABSTRACT FROM AUTHOR]

Calcium silicate, chemical environment, dielectric spectroscopy, nanoconfined water, nanominerals, supercritical fluids Keywords: calcium silicate; chemical environment; dielectric spectroscopy; nanoconfined water; nanominerals; supercritical fluids EN calcium silicate chemical environment dielectric spectroscopy nanoconfined water nanominerals supercritical fluids 11234 11234 1 08/07/21 20210805 NES 210805 B The ultra-fast synthesis of calcium silicate hydrates b was performed in supercritical water that acts as a solvent for mimicking the natural conditions at high pressure and high temperature of the geological process. [Extracted from the article]