Drag reduction for viscous laminar flow on spray-coated non-wetting surfacesElectronic supplementary information (ESI) available: Viscosity and torque measurements of n-decane calibration liquid, side view of pinned liquid meniscus, array of confocal microscopy images at various depths, schematic of imaging setup, dynamic force trace of spray-coated mesh from tensiometry. See DOI: 10.1039/c3sm50445j

• Main Authors: Srinivasan, Siddarth, Choi, Wonjae, Park, Kyoo-Chul, Chhatre, Shreerang S, Cohen, Robert E, McKinley, Gareth H
• Format: Journal Article
• Language: English
• Published: 29.05.2013
• ISSN: 1744-683X; 1744-6848
• DOI: 10.1039/c3sm50445j

We estimate the effective Navier-slip length for flow over a spray-fabricated liquid-repellent surface which supports a composite solidairliquid interface or CassieBaxter state. The morphology of the coated substrate consists of randomly distributed corpuscular microstructures which encapsulate a film of trapped air (or plastron) upon contact with liquid. The reduction in viscous skin friction due to the plastron is evaluated using torque measurements in a parallel plate rheometer resulting in a measured slip length of b slip 39 m, comparable to the mean periodicity of the microstructure evaluated from confocal fluorescence microscopy. The introduction of a large primary length-scale using dual-textured spray-coated meshes increases the magnitude of the effective slip length to values in the range 94 m b slip 213 m depending on the geometric features of the mesh. The wetted solid fractions on each mesh are calculated from free surface simulations on model sinusoidal mesh geometries. The trend in measured values of b slip with the mesh periodicity L and the computed wetted solid-fraction r s are found to be consistent with existing analytic predictions. We estimate the effective Navier-slip length for flow over a spray-fabricated liquid-repellent surface which supports a composite solidairliquid interface or CassieBaxter state.