Physics of Fluids · 2006 · 455 citations · 42 references
EngineeringMaterials EngineeringMaterials ScienceFluid DynamicsSurface EngineeringSurface ScienceFlow ResistanceMicrofluidic DevicesNanomechanicsNanoporous MaterialsSurface HydrophilicitySurface HydrophobicityFriction Coefficient ReductionFriction ReductionLiquid FlowMicrochannel FlowPressure DropSlipSuperhydrophobic SurfacesSuperhydrophobicity
This study reports the first use of nanoscale nanograted surfaces to measure their effect on liquid slip and friction reduction in microchannels, enabled by a fabrication technology that creates well‑defined nanogrates over a large area. Using a fabrication technology that creates dense (∼230 nm pitch) and deep (∼500 nm) nanogrates over a 2 × 2 cm² area, the study maintains air in the troughs under hydrophobic conditions and pressurized flow (>1 bar) to investigate liquid slip and friction reduction in microchannels. A noticeable slip length of 100–200 nm (20–30 % pressure‑drop reduction in a ∼3 µm high channel) is observed for water flowing parallel over the hydrophobic nanogrates, with larger slip in the parallel direction than transverse, indicating directional control of slip and friction reduction.
Enabled by a technology to fabricate well-defined nanogrates over a large area (2×2cm2), we report the effect of such a surface, in both hydrophilic and hydrophobic conditions, on liquid slip and the corresponding friction reduction in microchannels. The grates are designed to be dense (∼230nm pitch) but deep (∼500nm) in order to sustain a large amount of air in the troughs when the grates are hydrophobic, even under pressurized liquid flow conditions (e.g., more than 1bar). A noticeable slip (i.e., slip length of 100–200nm, corresponding to 20%–30% reduction of pressure drop in a ∼3μm high channel) is observed for water flowing parallel over the hydrophobic nanogrates; this is believed to be an “effective” slip generated by the nanostrips of air in the grate troughs under the liquid. The effective slip is clearer and larger in flows parallel to the nanograting patterns than in transverse, suggesting that the nanograted superhydrophobic surfaces would not only reduce friction in liquid flows under pressure but also enable directional control of the slip. This paper is the first to use nanoscale grating patterns and to measure their effect on liquid flows in microchannels.
42
A general boundary condition for liquid flow at solid surfaces
Peter A. Thompson, Sandra M. Troian · Nature · 1997 · 1.2K citations
Engineering, Physics, Fluid Dynamics +15
Apparent fluid slip at hydrophobic microchannel walls
Derek C. Tretheway, Carl Meinhart · Physics of Fluids · 2002 · 998 citations