On the thermodynamics of carbon nanotube single-file water loading: free energy, energy and entropy calculations.

Single-file water chains confined in carbon nanotubes have been extensively studied using molecular dynamics simulations. Specifically, the pore loading process of periodic (6,6) and (5,5) single-walled carbon nanotubes was thermodynamically characterized by means of free-energy calculations at every loading state and compared to bulk water employing thermodynamic cycles. Long simulations of each end-state allowed for the partitioning of the free energy into its energetic and entropic components. The calculations revealed that the initial loading states are dominated by entropic (both translational and rotational) components, whereas the latter stages are energetically driven by strong dipolar interactions among the water molecules in the file.