서강대학교

초록/요약

The no-slip boundary condition for liquid flows in microchannel has been applied successfully although it has no theoretical foundation. Liquid molecules, however, can slip at the liquid-solid interfaces if the liquid has a lower wettability. The velocity slip at the solid wall, called the Navier slip, is proportional to the velocity gradient at the wall for given wall physicochemical properties. Since the electroosmotic flow has a sharp velocity variation at the wall, the Navier slip of electroosmotic °ow can be appreciable in a microchannel where there may be negligible Navier slip for a purely pressure-driven flow which has a smooth velocity variation at the wall. The Navier slip affects the volumetric rate significantly in electrokinetic flows and, therefore, one must be cautions about the possible occurrence of Navier slip in the design and operation of various micro fluidic devices. In the present work, we have devised a simple method of estimating both Navier slip coefficient and zeta potential, which can be applied to any rectangular microchannels regardless of Navier slip, by measuring streaming potential and volumetric flow rate under a given pressure gradient. The method relies on a semi-analytic formula derived in the present work, which allows evaluation of streaming potential and volumetric flow rate without the necessity of numerical solution of nonlinear partial differential equations. The present method is found to estimate both slip coefficient and zeta potential reasonably accurately even using contaminated experimental data.