Abstract
The effect of the wall surface roughness on the zeta potential in a microchannel flow was investigated by micron-resolution particle image velocimetry combined with a confocal scanner (hereinafter called confocal micro-PIV). The nanoscale wall surface roughness of microchannel was modified by a cryogenic micromachining system that enables the formation of grooves in elastic materials such as polymers by applying cryogenic cooling. polymers change from a rubbery state to a glassy state below the glass transition temperature; for polydimethylsiloxane (PDMS), this transition occurs at -123 degrees centigrade. Prior to a set of experiments, the electrophoretic velocity of 1 micron diameter fluorescent particles at different pH was measured by current monitoring. The particle mobility near the PDMS wall at different wall roughness was measured by confocal micro-PIV. The electroosmotic velocity was calculated subtracting electrophoretic velocity from particle velocity. Finally the zata potential was obtained by the Helmholtz-Smoluchowski equation.
