Ice-like structure of the hydrate shell of quartz nanoparticles in an aqueous suspension

Spectroscopy experiments of the inelastic scattering of laser pulses in an aqueous suspension of silicon dioxide (SiO2) nanoparticles at room temperature have revealed for the first time that the centroid of the OH Raman scattering band is shifted to the pump line up to 10 cm$^{-1}$ and two components of stimulated backward and forward Brillouin scattering with frequency shifts of $\sim$7.5 and $\sim$14.3 GHz are simultaneously generated. The frequency shift 7.5 GHz corresponds to the Stokes component of Brillouin scattering in water (speed of sound of $\sim$1490 m/s), while the 14.3 GHz shift component corresponds to the speed of sound of $\sim$2900 m/s; i.e., this component falls within the range of speeds of sound in ice at room temperature. In our opinion, the results of these experiments indicate both the formation of hydrate layers with an ice-like hydrogen bonding structure around SiO$_2$ nanoparticles and a decrease in the volumetric thermal expansion coefficient of the aqueous suspension.