Large Slip of Aqueous Liquid Flow over a Nanoengineered Superhydrophobic Surface

Superhydrophobic drag reduction in laminar flows: a critical review

“…1b). Nevertheless, the slip enhancement was found significant compared with smooth surfaces (Watanabe et al 1999;Ou et al 2004;Choi and Kim 2006a;Choi et al 2006), propelling the superhydrophobic (SHPo) 1 surfaces of Fig. 1c as a potential dragreducing surface for fluidic systems above micrometers.…”

“…However, the numerous experimental studies in the literature have reported (many erroneously, as discussed in Sects. 3.2.5 and 3.3.5) a wide range of slip lengths spanning from tens of nanometers to even millimeters on SHPo surfaces consisting of regular (periodic) structures (Ou et al 2004;Ou and Rothstein 2005;Choi et al 2006;Davies et al 2006;Truesdell et al 2006;Maynes et al 2007;Steinberger et al 2007;Byun et al 2008;Lee et al 2008;Tsai et al 2009;Jung and Bhushan 2010;Lee and Kim 2011a;Kashaninejad et al 2012;Kim and Hidrovo 2012;Maali et al 2012;Karatay et al 2013;Bolognesi et al 2014;Lee and Kim 2014) or random structures (Watanabe et al 1999(Watanabe et al , 2003Gogte et al 2005;Choi and Kim 2006a;Joseph et al 2006;Bhushan et al 2009;Govardhan et al 2009;Shirtcliffe et al 2009;Wang et al 2009;Kim and Hwang 2010;Li et al 2010;Wang and Bhushan 2010;Ming et al 2011;Srinivasan et al 2013). Sometimes orders-of-magnitude differences in the measured slip lengths were reported even on structurally similar SHPo surfaces (e.g., Lee et al 2008vs.…”

“…Another indirect approach to slip measurement is to measure shear stress or frictional drag on a SHPo surface (Choi and Kim 2006a;Truesdell et al 2006;Steinberger et al 2007;Lee et al 2008;Bhushan et al 2009;Govardhan et al 2009;Wang et al 2009;Li et al 2010;Lee and Kim 2011a;Ming et al 2011;Maali et al 2012;Srinivasan et al 2013). Despite its relatively low accuracy (>1 µm in measurable slip length), the commercial rheometer has shown to be a convenient tool when measuring a (8) Q = − πr 4 8η dP dx 1 + 4δ r large slip length (e.g., >5 µm), as shown in Fig.…”

“…For example, the drag reduction (DR) by a liquid slip in Couette flow is calculated to be DR = 1/(1 + H/δ), where H is the gap distance between the slip surface and the opposing nonslip surface (Choi and Kim 2006a). A similar expression of DR = 3/(3 + H/δ) has been derived for Poiseuille flow (Ou Abstract A gas in between micro-or nanostructures on a submerged superhydrophobic (SHPo) surface allows the liquid on the structures to flow with an effective slip.…”

Using surface force apparatus, diffusion and velocimetry to measure slip lengths

“…Furthermore, recent theoretical predictions and experimental results have pointed to the possibility to create huge (more than 10 mm) slip lengths by the use of composite surfaces (Choi & Kim 2006;Ybert et al 2007). mPIV is a particularly appropriate method to measure the slippage on such surfaces, thanks to its ability to precisely reconstruct the speed profile with a submicrometre resolution, as has already been demonstrated on carbon nanotube-coated surfaces (Joseph et al 2006).…”