Coexistence of slow and fast dynamics in interfacial water around a carbon nanotube

We investigated the dynamics of water molecules in the interfacial water around a carbon nanotube (CNT) by analyzing the rotational autocorrelation function (RACF) for water molecules using molecular dynamics simulations. We found that the function undergoes a gradual crossover with temperature for the interfacial water with double-molecular-layer structure around the CNT, in contrast to bulk water, which shows a discontinuous change in the RACF at 0 °C. This is consistent with recent experimental results showing that interfacial water does not exhibit a solid-liquid phase transition. In addition, the RACF results can be fitted by exponential functions with two different time constants, indicating that the proportion of disordered structures relative to ordered structures, in which water molecules have more restricted rotation, increases continuously with temperature. The continuous structural change yields the gradual solid-liquid crossover.