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Why Are Carbon Nanotubes Fast Transporters of Water?

Summary: Why Are Carbon Nanotubes Fast
Transporters of Water?
Sony Joseph and N. R. Aluru*
Department of Mechanical Science and Engineering, Beckman Institute for AdVanced
Science and Technology, UniVersity of Illinois at Urbana-Champaign,
Urbana, Illinois 61801
Received September 17, 2007; Revised Manuscript Received December 11, 2007
Extraordinarily fast transport of water in carbon nanotubes (CNTs) in recent experiments has been generally attributed to the smoothness of
the CNT surface. Using molecular dynamics simulations we investigate water flow in (16,16) CNTs and show that the enhanced flow rates over
Hagen-Poiseuille flow arise from a velocity "jump" in a depletion region at the water nanotube interface and that the water orientations and
hydrogen bonding at the interface significantly affect the flow rates. For nanotube with the same smooth wall structure but with more hydrophilic
Lennard-Jones (LJ) parameters of silicon, the enhancement is greatly reduced because it does not have "free" OH bonds pointing to the wall
as in CNTs that would reduce the number of hydrogen bonds in the depletion layer. Roughness in the tube walls causes strong hydrogen-
bonding network and no significant flow enhancement is attained in rough tubes.
Dramatic enhancement of pressure driven flows of water
through carbon nanotubes as compared to other porous
materials has gained considerable attention recently due to
its potential applications in drug delivery, biomimetic selec-
tive transport of ions, etc. Pressure driven flow velocities of


Source: Aluru, Narayana R. - Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign


Collections: Engineering; Materials Science