Dual scale roughness

N. J. Shirtcliffe, G. McHale, M. I. Newton, G. Chahrol, and C. C. Perry, Dual-scale roughness produces unusually water-repellent surfaces, Adv Mater., 16, 1929-1932 (2004). 

Lin, P.-C. Yang, S., Mechanically Switchable Wetting on Wrinkled Elastomers with Dual-Scale Roughness. Soft Matter 2009,5,1011-1018. 

As mentioned earlier, flame synthesized carbon nanostructures demonstrate superhydrophobicity due to inherent hydrophobicity of carbon as well as the formation of dual-scale roughness during deposition. However, their main drawback is that nanostructured carbon materials do not form a firm bond with the surface upon which they are assembled, considerably reducing their practical applications in liquid repellent surface... 

Shirtcliffe, N.J., McHale, G., Newton, M.I., ChabroL G., Perry, C., 2004b. Dual-scale roughness produces unusually water-repellent surfaces. Adv. Mater. 16,1929. 

One key to achieving the best combination of stencil profile and surface roughness lies in the selection of the stencil material. The right dual-cure emulsion must be selected for its wet-on-wet coating properties, solids content, and print definition. The fact is that you may have to accept a little give and take between print clarity and ink transfer. In photorealistic CID printing, Rz values for direct emulsion stencils generally are measured on a Rz scale from 4-10. 

In addition to its influence on surface reactivity, surface structure is also seen to affect wettability on the micrometer scale, as is best illustrated by the lotus effect (see Chapter 3b). The lotus leaf is superhydrophobic, i.e. has a water contact angle of about 160°, thanks to the combination of the waxes on the surface with a characteristic dual micrometer- and nanometer-scale surface topography. Without the structure, the wax chemistry would only impart mild hydrophobicity to the surface. Superhydrophobicity comes about only when a water droplet is in contact with a rough surface with a substantial enclosure of air beneath the drop (Figure 9). This is the so-called Cassie-Baxter state, named after the authors of the work that described the contact angle of water droplets in this state by means of the equation ... 

---