Superhydrophobic surface

The authors thank the following Union College students for photographs used in this chapter Emily Green, Jason Melville, and Caleb Wattley. Our own work with aerogels has 

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Fotmdation. 

Briones, Y J, Wolfe, R L, Carroll, M K, Bakrania, S D, Mandel, S G, Anderson, A M (2004) Aerogel-platform optical sensors for oxygen gas. J Non-Cryst Solids 350 326-335. 

Fesmire, J (2006) Aerogel insulation systems for space launch applications. Cryogenics 46(2-3) 111-117. Gougas, A, lUe, D, lUe, S, Pojidaev, V (1999) Behavior of hydrophobic aerogel used as a Cherenkov medium. Nucl Instrum Methods Phys Res, Sect A 421(1-2) 249-255. 

Branson, E D, Malanoski, A P, Watkins, E B (2(X)5) Investigating the interface of superhydrophobic surfaces in contact with water. Langmuir 21(17) 7805-7811. 

In the case of an uncharged gas interface (qi = qg, qi = 0), we predict the simple Smoluchowski formula. In other words, there is no EO flow enhancement, and the flow is isotropic despite 

In the case of a charged gas interface (only) a considerable enhancement of electro-osmotic flow is possible. For a uniformly charged (qi = q2 = qo) anisotropic superhydrophobic surface, the expression for electro-osmotic flow can be transformed to  

An interesting scenario is expected for oppositely charged solid and gas sectors. In this case Eq. 2.31 transforms to  

The calculation results for this situation are also included in Fig. 2.19 and suggest a very rich fluid behavior. We see, in particular, that an inhomogeneous surface charge can induce EO flow along and opposite the field, depending on the fraction of the slipping area. 

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Fig. 3.18 Schematic of the near-wall and cavity regions for liquid flow over a superhydrophobic surface exhibiting micro-rib structures and flow perpendicular to the ribs...

In optical tweezer experiments, the optical scattering force is used to trap particles, but the force can also be used to control the shape of liquid droplets26. An infrared laser with 43-mW power focused onto a microdroplet on a superhydrophobic surface enabled up to 40% reversible tuning of the equatorial diameter of the droplet26. Such effects must naturally also be taken into account when exciting laser modes in droplets in experiments with levitated drops. 

Sennaroglu, A. Kiraz, A. Dundar, M. A. Kurt, A. Demirel, A. L., Raman lasing near 630 nm from stationary glycerol water microdroplets on a superhydrophobic surface, Opt. Lett. 2007, 32,2197 2199... 

Figure 7.9 Water drop on a superhydrophobic surface showing a high apparent contact angle app- The combined effect of hydrophobicity and roughness on the right length scale, causes the Lotus effect.

Furstner R, Barthlott W, Neinhuis C, Walzel P (2005) Wetting and self-cleaning properties of artificial superhydrophobic surfaces. Langmuir 21 956-961... 

Superhydrophilic and superhydrophobic surfaces are more effective at stabilizing two-phase microflows. These surfaces can be obtained by creating roughness utilizing titanium nanoparticles. Titanium modification of a microchannel yields nanometer-scale surface roughness, and subsequent... 

The problems of supramolecular organization and distribution of bonded molecules are of great importance not only for the materials with a low surface coverage. These are also important for the preparation of the most dense bonded layers with the maximum shielding of the surface. Indeed, the complete modification of silica with alkylsilanes and preparation of superhydrophobic surfaces [44,45] are only possible under the conditions of island-like coverage of the surface with a. modifier. 

Nosonovsky M, Bhushan B (2005) Roughness optimization for biomimetic superhydrophobic surfaces. Microsyst. Tecfmol. 11 535—549. 

Figure 16.15 Superhydrophobic surfaces in biology the lichen Lecanora conizaeoides showing high roughness with inset showing water drop 155 4°. (Reprinted with permission from Journal of Plant Physiology, A lichen protected by a super-hydrophobic and breathable structure by N.J. Shirtcliffe, F. B. Pyatt, M.l. Newton and C. McHale, 163, 1193-1197. Copyright (2006) Elsevier Ltd)...

The lotus effect has inspired scientists to design superhydrophobic surfaces for applications such as self-cleaning windows and water-repellent clothing. To understand the lotus effect and other phenomena involving liquids and solids, we must understand intermoiecuiar forces, the forces that exist between molecules. Only by understanding the nature and strength of these forces can we understand how the composition and structure of a substance are related to its physical properties in the liquid or solid state. 

Latthe, S.S., Terashima, C., Nakata, K., Fujishima, A., 2014. Superhydrophobic surfaces developed by mimicking hierarchical surface morphology of lotus leaf— review. Molecules 19, 4256-1283. 

The contact angle is 0ca < 90° when the solid is hydrophilic (so-called high energy solid) and the water wets such a solid well it is usually < 30° and approaches zero when the water completely spreads over the solid. For hydrophobic solids (so-called low energy solids) 0ca > 90° and may have values up to 150° for so-called superhydrophobic surfaces such as specially prepared (non-wettable) fluorohydrocarbons. There exists some hysteresis (amounting typically up to 10°) between the contact... 

P. Tsai, S. Pacheco, C. Pirat, L. Lefferts, D. Lohse Drop impact upon micro- and nanos-tractured superhydrophobic surfaces, Langmuir, 25, 12293-12298 (2009). 

The wettability of solid surfaces is a veiy important properly of surface chemistiy, which is controlled by both the chemical composition and the geometrical microsttuc-ture of surface [21-23], When a liquid droplet contacts a solid surface, it will sptead or remain as droplet with the formation of angle between the liquid and solid phases. Contact angle (CA) measurements are widely used to characterize the wettability of solid surface. Surface with a water CA greater than 150° is usually called superhydrophobic surface. On the other hand, when the CA is lower than 5°, it is called superhy-drophilic surface. Fabrication of these surfaces has attracted considerable interest for both fundamental research and practical studies [23-25]. 

Y.H. Kim, D.K. Yoon, H.S. Jeong, J.H. Kim, E.K Yoon, FLT. Jung, Fabrication of a superhydrophobic surface from a smectic liquid-crystal defect array. Adv. FuncL Mater. 19, 3008-3013 (2009)... 

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