Molecular transport through capillaries made with atomic-scale precision
Authors: B. Radha, A. Esfandiar, F. C. Wang, A. P. Rooney, K. Gopinadhan, A. Keerthi, A. Mishchenko, A. Janardanan, P. Blake, L. Fumagalli, M. Lozada-Hidalgo, S. Garaj, S. J. Haigh, I. V. Grigorieva, H. A. Wu, A. K. Geim
Publication Date: 06 September, 2016
Unexpectedly fast flow through nanocapillaries
Water transport is fundamental to life on earth and to a vast number of industrial applications including desalination, healthcare and drug delivery. In particular, the movement of water through nanometre sized channels is an essential step in many such processes but there is still great controversy over its behaviour when confined at the nanometre scale. Traditional transport studies based on lithographically processed structures suffer from problems due to surface roughness, which makes it challenging to produce capillaries with precisely controlled dimensions at this spatial scale. Now researchers at the University of Manchester have overcome these limitations by fabrication of the first narrow and smooth capillaries through graphite. These structures can be viewed as if individual atomic planes had been removed from a bulk crystal to leave behind flat voids of a height chosen with atomic precision. Water transport through the channels, ranging in height from one to several dozen atomic planes, is characterized by unexpectedly fast flow (up to 1 metre per second) that is attributed to high capillary pressures (about 1,000 bar) and large slip lengths. For channels that accommodate only a few layers of water, the flow exhibits a marked enhancement that is associated with an increased structural order in nanoconfined water. The work opens up a new route to making capillaries and cavities with sizes tunable to sub-nanometre precision.