Ultrafast ballistic diffusion of nanotubular water shells in carbon nanotubes. Direct experimental evidence with two-dimensional (D-T2) NMR

Water when confined at the nanoscale acquires extraordinary transport properties. And yet there is no direct experimental evidence of these properties at nanoscale resolution. Here, by using 2D NMR diffusion-relaxation (D-T2)spectroscopy, we acquire the diffusion profile of water in single and double-walled carbon nanotubes (CNTs). Remarkably, in double-walled CNTs water is shown to split in two axial components with the inner one acquiring astonishing flow properties: high fragility, ultra-high self-diffusion coefficient, and "rigid" molecular environment, revealing a nonuniform ballistic mechanism underlying fast diffusion in hydrophobic nanochannels.