Electroosmotic flow in single PDMS nanochannels.

The electroosmotic flow (EOF) velocity in single PDMS nanochannels with dimensions as small as 20 nm is investigated systematically by the current slope method in this paper. A novel method for the fabrication of single nanochannels on PDMS surfaces is developed. The effects of channel size, ionic concentration of the electrolyte solution and electric field on the EOF velocity in single nanochannels are investigated. The results show that the EOF velocity in smaller nanochannels with overlapped electric double layers (EDL) is proportional to the applied electric field but is smaller than the EOF velocity in microchannels under the same applied electric field. The EOF velocity in relatively large nanochannels without the overlap of EDLs is independent of the channel size and is the same as that in microchannels under the same applied electric field. Furthermore, in smaller nanochannels with overlapped EDLs, the EOF velocity depends on the ionic concentration and also on the channel size. The experimental results reported in this paper are valuable for the future studies of electrokinetic nanofluidics.