Structural fluctuations at nanoscale and cooperative molecular dynamics in bulk water

Abstract

The investigation of cooperative dynamics in H2O, visible in the coherent neutron scattering, has been hindered up to now due to the very small signal. Using a novel approach with employing of 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 at intermediate Q range of 0.2-1 Å -1 which is clear evidence that intermolecular interactions in water spread beyond distances between two nearest neighbours. Our study reveals the existence of a picosecond cooperative process in water, whose nature could be related to the cooperative rearrangements between several water molecules. This process serves as a precursor to the large-scale transport related to the viscosity. Our results help to understand the general transport mechanism at nanoscale which can be useful for biomedical technologies or the development of nanofluidic devices.