# Structural Fluctuations at Nanoscale and Cooperative Molecular Dynamics in Bulk Water

## TL;DR

This study reveals a new cooperative process in water molecules that could influence transport mechanisms at the nanoscale.

## Contribution

First direct measurement of coherent neutron scattering in light water with high accuracy.

## Key findings

- Coherent signal is enhanced in the intermediate Q range, showing intermolecular interactions beyond nearest neighbors.
- A picosecond cooperative process in water is identified, possibly linked to molecular rearrangements.
- The process may act as a precursor to large-scale transport related to viscosity.

## Abstract

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.