Ice-Like Dynamics of Water Clusters

Understanding certain behaviors of water, e.g., its dynamics, is extremely important in various fields. Recently, using ¹H nuclear magnetic resonance spectroscopy, we have identified a metastable state of water molecules, i.e., water clusters, in hydrophobic solvents in addition to dissolved water molecules and a small bulk water domain. However, the low abundance of water clusters made observing their dynamics challenging. In this study, the dynamics of water clusters in benzene-d₆ were investigated by quasi-elastic neutron scattering measurements using the AGNES time-of-flight spectrometer of the Japan Research Reactor JRR-3. The diffusion dynamics of the hydrogen atoms were much slower than those of bulk water (with a self-diffusion coefficient of 1.15 × 10^-9 m²/s at 273 K) and even slower than the upper-limit dynamics at the observable scale (10^-10 m²/s). The dynamics of water clusters are slow, "like ice", even at 283-303 K, which is above the freezing point of water (273 K).