  Developing 'smart' membranes that allow precise and reversible control of
molecular permeation using external stimuli would be of intense interest for
many areas of science: from physics and chemistry to life-sciences. In
particular, electrical control of water permeation through membranes is a
long-sought objective and is of crucial importance for healthcare and related
areas. Currently, such adjustable membranes are limited to the modulation of
wetting of the membranes and controlled ion transport, but not the controlled
mass flow of water. Despite intensive theoretical work yielding conflicting
results, the experimental realisation of electrically controlled water
permeation has not yet been achieved. Here we report electrically controlled
water permeation through micrometre-thick graphene oxide (GO) membranes. By
controllable electric breakdown, conductive filaments are created in the GO
membrane. The electric field concentrated around such current carrying
filaments leads to controllable ionisation of water molecules in graphene
capillaries, allowing precise control of water permeation: from ultrafast
permeation to complete blocking. Our work opens up an avenue for developing
smart membrane technologies and can revolutionize the field of artificial
biological systems, tissue engineering and filtration.
