Electrokinetic flow imaging in well-designed microfluidic channels to analyze hydrodynamic slip behavior
- Electrokinetic flow imaging in well-designed microfluidic channels to analyze hydrodynamic slip behavior
- 김광석; 전지훈; 전명석
- hydrodynamic slip; slip length; hydrophobicity; shear rate; particle streak velocimetry; fluorescent microscope
- Issue Date
- 10th ELKIN 2012
- VOL 10, 124-124
- Hydrodynamic fluid slippage at the hydrophobic stationary interface can be interpreted in terms of the
continuity of shear stress and the interfacial friction [Navier, Mem. Acad. Sci. Inst. Fr., 1823; Joly et
al., J. Chem. Phys., 2006]. The slip length is the local equivalent distance below the solid surface at
which the no-slip boundary condition would be satisfied if the flow fields were extended linearly outside
of the physical domain [Lauga and Stone, J. Fluid Mech., 2003; Lim and Chun, Phys. Fluids,
2011]. Particle streak imaging by fluorescent microscope (shown in Fig. 1) can be applied to obtain
electrokinetic velocity profile and fluid slip, as reported earlier [Chun and Lee, Colloids Surf. A, 2005].
Moving submicron-sized fluorescent polystyrene latex beads results in image streaks, where the dispersion
concentration is sufficiently dilute underlying the condition of simple fluid. The local velocity
was determined in terms of a ratio of the real distance to the number of pixels. For the purpose of fast
and accurate measurements of slip lengths at different shear rates and channel widths, we fabricated a
branched multi-channel type PDMS (polydimethylsiloxane) microfluidic chip that contains two main
streams. The test fluid that enters the first stream undergoes a series of step reductions of shear rate,
while the fluid that enters the second stream experiences a series of different channel widths, as displayed
in Fig. 1. On-chip switching valve is also designed for the test fluid to enter only one specified
stream. We observed that, in Fig. 2, the slip length is nearly constant in the range of shear rate less
than about 100 s–1, but increases with the shear rate above 100 s–1.
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