title: Control of slippage with tunable bubble mattresses.
abstract: Tailoring the hydrodynamic boundary condition is essential for both applied and fundamental aspects of drag reduction. Hydrodynamic friction on superhydrophobic substrates providing gas-liquid interfaces can potentially be optimized by controlling the interface geometry. Therefore, establishing stable and optimal interfaces is crucial but rather challenging. Here we present unique superhydrophobic microfluidic devices that allow the presence of stable and controllable microbubbles at the boundary of microchannels. We experimentally and numerically examine the effect of microbubble geometry on the slippage at high resolution. The effective slip length is obtained for a wide range of protrusion angles, θ, of the microbubbles into the flow, using a microparticle image velocimetry technique. Our numerical results reveal a maximum effective slip length, corresponding to a 23% drag reduction at an optimal θ ≈ 10°. In agreement with the simulation results, our measurements correspond to up to 21% drag reduction when θ is in the range of -2° to 12°. The experimental and numerical results reveal a decrease in slip length with increasing protrusion angles when >/~ 10°. Such microfluidic devices with tunable slippage are essential for the amplified interfacial transport of fluids and particles.
authors: Soft Matter, Fluidics, and Interfaces Group, Mesa+ Institute for Nanotechnology, Department of Science and Technology, University of Twente, 7500 AE Enschede, The Netherlands.
authors: Elif
authors: E
authors: Karatay
authors: A Sander
authors: AS
authors: Haase
authors: Claas Willem
authors: CW
authors: Visser
authors: Chao
authors: C
authors: Sun
authors: Detlef
authors: D
authors: Lohse
authors: Peichun Amy
authors: PA
authors: Tsai
authors: Rob G H
authors: RG
authors: Lammertink
mesh_terms: D045423:Microbubbles; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation* / Q000379:methods*; D008962:Models, Theoretical
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