Spontaneous Spatiotemporal Ordering of Single-File Water Flow in Narrow Nanotubes

Self-organization is usually observed in two- or three-dimensional nonequilibrium processes, where an ordered pattern spontaneously emerges in an initial disordered system. Since spontaneous ordering is not prohibited in one dimension, it is interesting to investigate the ordering behavior in the quasi-one-dimensional nanofluids such as a single-file chain of water molecules. In this paper, we show that spatiotemporal ordering of the single-file water, in the form of collective oscillating unidirectional flows, spontaneously emerges inside a narrow nanotube between two independently heated water reservoirs by molecular dynamics simulations. The spatiotemporal ordering of the single-file water induces a low-frequency coupling and a unidirectional duration time up to nanoseconds and also low-configuration entropy in the flow pattern that separates itself from the chaotic motion of water molecules. Mass density fluctuation plays a critical role in the ordered flow pattern formation, and its crossover from an exponential to a power-law decay decides the disappearance of the ordered flow pattern. We further find that spatiotemporal ordering induces high heat-transfer enhancement that is comparable to thermal conductivity of gaseous water. Our result reveals a peculiar self-organization phenomenon and entirely different dynamics in the single-file water that departs from macroscopic flows in the continuum limit.