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 100nm has been measured over a length of 1cm. 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 (53nm height). When using a 0.1M NaCl (aq) solution the elevation of the apparent viscosity is significantly reduced.