Selective interaction water-hydrophilic/hydrophobic impurities observed by four-photon Brillouin spectroscopy

The four-photon scattering spectra of water in the aqueous solution/suspension of various hydrophilic/hydrophobic impurities in the range ±3 cm^?1 (±90 GHz) have been observed. We have found the strong dependence of the Brillouin resonance frequency upon the connectivity of the impurities and water molecules. The Brillouin shift is attributed to the local restructuring of the hydrogen bond network in water inside the interface layer that is sensitive to the hydrophilic/hydrophobic properties. In fact, it results in variations in the isothermal compressibility and sound velocity.