学术报告：Carbon nanostructure based mechano-nanofluidics
报告题目：Carbon nanostructure based mechano-nanofluidics
This presentation reports some recent advances about carbon nanostructure based mechano-nanofluidics of the authors. These include the transport of water in carbon nanotubes and diffusion of water nanodroplets on graphene. Theoretical as well as numerical approaches are adopted, and the results are compared with existing experimental measurements.
The emergence of the field of nanofluidics in the last decade has led to the development of important applications such as water desalination, ultrafiltration and osmotic energy conversion. Most applications make use of carbon nanotubes, boron nitride nanotubes, graphene and graphene oxide. In particular, understanding water transport in carbon nanotubes is key for designing ultrafiltration devices and energy efficient water filters. However, although theoretical studies based on molecular dynamics (MD) simulations have revealed many mechanistic features of water transport at the molecular level, further advances in this direction are limited by the fact that the lowest flow velocities accessible by simulations are orders of magnitude higher than those measured experimentally.
Here, we extend MD studies of water transport through carbon nanotubes to flow velocities comparable with the experimental ones using massive crowdsourced computing power. We observe previously undetected oscillations in the friction force between water and carbon nanotubes and show that these oscillations result from the coupling between confined water molecules and the longitudinal phonon modes of the nanotube. This coupling can enhance the diffusion of confined water by more than 300%.
Besides water transport in CNTs, we have also studied the diffusion of water nanodroplet on graphene. Using molecular dynamics, we show that a layered material such as graphene opens up a new mechanism for surface diffusion whereby adsorbates are carried by propagating ripples via a motion similar to surfing. For water nanodroplets, we demonstrate that the mechanism leads to exceedingly fast diffusion that is 2-3 orders of magnitude faster than the self-diffusion of water molecules in liquid water. We also reveal the underlying principles that regulate this new mechanism for diffusion and show how it also applies to adsorbates other than water, thus opening up the prospect of achieving fast and controllable motion of adsorbates across material surfaces more generally.
 M. Ma, F. Grey, L.M. Shen, M. Urbakh, S. Wu, J.Z. Liu, Y.L. Liu, Q.S. Zheng, Water transport inside carbon nanotubes mediated by phonon-induced oscillating friction, Nature Nanotech., 10 (2015) 692-695.
 M. Ma, G. Tocci, A. Michaelides, G. Aeppli, Fast diffusion of water nanodroplets on graphene, Nature Mater., 15 (2016) 66-71.