Structural Fluctuations at Nanoscale and Cooperative Molecular Dynamics in Bulk Water

The investigation of cooperative dynamics in H₂O, visible in coherent neutron scattering, has been hindered until now due to the very small signal. Using neutron polarization analysis, we were able, for the first time, to directly measure the coherent neutron scattering signal in light water with unprecedented accuracy. The observed coherent signal is enhanced in the intermediate Q range of 0.2 to 1 Å^-1, providing clear evidence that intermolecular interactions in water extend beyond the distances between nearest neighbors. Our study reveals the existence of a picosecond cooperative process in water, whose nature could be related to the cooperative rearrangements of several water molecules. This process may act as a precursor to large-scale transport related to viscosity. Our results help to improve the understanding of general transport mechanisms at the nanoscale, which can be useful for biomedical technologies or the development of nanofluidic devices.