Ice to vapor: Dynamics of confined water in carbon nanotube manipulated by terahertz waves

Single-file water chains, as a unique form of existence, play a significant role in nature. In this study, molecular dynamics simulations were employed to investigate the static and dynamic properties of water molecules confined within carbon nanotubes (CNTs) under the influence of terahertz (THz) waves. We found that water behavior can be significantly modulated by electric fields of varying orientations, i.e. water molecules can undergo ice-like to liquid and ultimately to vapor-like phase transitions within the CNT under the modulation of different THz waves. To be more specific, the parallel field disrupts the hydrogen bond structure and causes the vapor-like state, while the vertical field strengthens the hydrogen bond structure and creates the ice-like state. Our analyses on the translation diffusion coefficient, axial density profile and distribution of the dipole angle prove this phenomenon. The ice-like phase exhibits a low diffusion coefficient, periodically oscillating density distribution and single-peak dipole angle orientation. In contrast, the vapor-like phase exhibits high diffusion coefficient, a relatively flat density distribution and highly disordered dipole angle orientation. These findings provide novel insights into the dynamic modulation of confined water while demonstrating the potential of THz electric fields as a tool for tuning nanoscale water properties with implications for nanofluidics.