Neutron scattering investigation of liquid–liquid transition in confined water

Pioneering quasi-elastic neutron scattering (or QENS) studies have revealed an exotic phase transition, known as a liquid-to-liquid crossover in supercooled water—in which the hydrogen bond network goes from a ’fragile’ high-density state at room temperature to a ’strong’ low-density phase at lower temperatures. Various research groups have since attempted to independently confirm the existence of this transition and elucidate the mechanism behind it, but obtained conflicting results. The present study uses deep inelastic neutron scattering (DINS) to investigate the proton momentum distribution n(p) and the average proton kinetic energy ⟨KE⟩ between the two phases. The measurements show a relative increase of ⟨KE⟩ as the temperature is lowered across the transition, suggesting a stiffer inter-molecular potential below TLL, in agreement with recent DINS studies of water confined in nanoporous Xerogel. Graphical abstract