Suppression of terahertz collective motion of water confined in nanogaps

Water confined within nanostructures has been the subject of extensive investigation across various systems, revealing a diminished permittivity under static conditions. However, the exploration of their dynamics, especially in the terahertz (THz) range where hydrogen bond dynamics predominate due to elongated wavelengths, has been largely overlooked. We report the THz complex refractive index of water confined within gold gaps ranging from 2 to 20 nanometers in width. Notably, under stringent confinement conditions, we observed a suppression of long-range correlation dynamics in hydrogen bond networks, particularly within the THz frequency range. This suppression led to a substantial decrease in the terahertz permittivity of water, even in regions not directly interfacing with the confinement surfaces. Insights gained from this platform are instrumental in comprehending the collective dynamics of water molecules over long distances, which are pivotal for elucidating processes like protein folding, formation of lipid rafts, and molecular recognition facilitated by water.