Research
K. H. Kang	Research	Publications	Life Style
Electroosmotic flows at an interior corner Kwan Hyoung Kang and In Seok Kang† Department of Mechanical Engineering and Department of Chemical Engineering,† Pohang University of Science and Technology, San 31, Hyoja-dong, Pohang 790-784, Republic of Korea (To be submitted to the J. Colloids Interface Sci.) The liquid handling method relying on the electroosmotic flow (EOF) has been widely adopted in modern microfluidic devices. It has some advantage over other methods in that its inherent plug-type velocity profile minimizes unwanted mixing of species, and it is favorable to interface with other microfluidic components. Numerous theoretical investigations have been performed concerning the characteristics of EOF; such as the flow inside the cylindrical capillary, the two-dimensional slit, and the rectangular channel. Numerical analyses have recently been performed by many investigators in various aspects for the complex microchannel geometries. This includes the three-dimensional flow in cross channel, and transient and developing flow in channel. There exist corner regions in any polygonal cross section (Fig. 1a) and intersection of channel sections (see Fig. 1b). Near the sharp corner, the potential distribution becomes very different from that of the plane electrical double layer due to the interaction of the electrical double layers. Besides, at the intersecting point of two channels in Fig. 1b, the electrostatic field originating from the externally applied voltage is singular. Fig. 1 (a) Rectangular cross section. (b) Intersection of channels (T-channel). (c) Coordinate system For a complete understanding of EOF inside a channel, an analytical solution including the corner region is desirable. Hitherto there appears no theoretical investigation which addresses the flow characteristics in the corner region has been reported. As a first attempt for that, in this work, a local solution of the flow in the corner region is obtained for the fully-developed flow along the corner (such as the case of Fig. 1a). To obtain the flow field, either for the longitudinal or the channel intersections (Fig. 1b), the potential distribution due to the electrical double layer around the corner should be known. The potential distribution is analyzed by using the linearized Poisson–Boltzmann equation under the constant zeta-potential condition throughout the channel wall. An equation which relates arbitrary surface potentials to the flow field is obtained. Then, the theoretical formulas assessing the excess charge due to double layer interaction and the excess volumetric flux caused by the corner are obtained. Lastly Modified in October 13, 2003