Study of the rise time in electroosmotic flow within a microcapillary.

For the first time with a temporal resolution higher than 100 micros, we have successfully measured the risetime of electroosmotic flow (EOF) in a microcapillary using recently developed laser induced fluorescence photobleaching anemometer (LIFPA). Although there are some theoretical estimations in literature about the risetime in microcapillaries, to the best of our knowledge, this has never been experimentally validated in a microcapillary with inner diameter less than 100 microm. The LIFPA with high temporal and spatial resolution described in this paper is capable of measuring risetime distribution radially in a cylindrical microcapillary tube. The experimental results show that the risetime under a pulsed electric field decreases with the reduction of the inner diameter of a microcapillary, and the risetime also increases from the wall to the axis for a given microcapillary. These are qualitatively similar to the theoretical prediction. In addition, the initial pressure driven flow does not appear to affect risetime.