Capillary filling speed of water in nanochannels

The capillary filling speed of water in nanochannels with a rectangular cross section and a height on the order of 100 nm has been measured over a length of 1 cm. The measured position of the meniscus as a function of time qualitatively follows the Washburn model.. Quantitatively, however, there is a lower than expected filling speed, which we attribute to the electro-viscous effect. For demineralized water in equilibrium with air the elevation of the apparent viscosity amounts up to 24+/-11% in the smallest channels (53 nm height). When using a 0.1 M NaCl (aq) solution the elevation of the apparent viscosity is significantly reduced. (C) 2004 American Institute-of Physics.