Water superhydrophobic

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.

The linear correlation between BCF and Kow apparently breaks down for chemicals with a log Kow greater than approximately 6 (Figure 9.4), resulting in a "parabolic" or "bilinear" type relationship between the BCF and Kow (Bintein 1993, Meylan et al., 1999). For these superhydrophobic chemicals, the BCF appears to be much lower than expected from the chemical s octanol-water partition coefficient. A loss of linear correlation between the BCF and Kow can be caused by a number of experimental artifacts (described in section 9.4.3) and physiological processes, including metabolic transformation, fecal egestion, and growth. 

Equation (645) shows that contact angle is a thermodynamic quantity, which can be related to the work of adhesion and interfacial free energy terms. When 6 values are small, the work of adhesion is high and considerable energy must be spent to separate the solid from the liquid. If 0 = 0°, then W L = 2yv if 0 = 90°, then W L = yLV, and if 0 = 180°, then W1L = 0, which means that no work needs to be done to separate a completely spherical mercury drop from a solid surface (or a water drop from a superhydrophobic polymer surface), and indeed these drops roll down very easily even with a 1° inclination angle of the flat substrate. 

Stratakis E, Mateescu A, Barberoglou M, Vamvakaki M, Fotakis C, Anastasiadis SH. From superhydrophobicity and water repellency to superhydrophilicity smart polymer-functionalized surfaces. Chem Commun 2010 46(23) 4136—8. 

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)...

Singh S, Houston J, van Swol F, Blinker CJ (2006) Superhydrophobicity drying transition of confined water. Nature 442 526... 

One major challenge that has attracted many research efforts in recent years is the development of durable water repellent (superhydrophobic) treatments (Zimmermann et al., 2008 Xue and Ma, 2013). A further issue is the eco-friendliness of such treatments, as there are ecological concerns about the classical treatments, which are based on fluorinated compounds. 

THE LOTUS PLANT GROWS in aquatic environments. In order to thrive in such an environment the surface of a lotus leaf is highly water repellent. Scientists call surfaces with this property superhydrophobic. The superhydrophobic character of the lotus leaf not only allows it to float on water but also causes... 

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. 

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... 

Ferrari M, Ravera F (2010) Surfactants and wetting at superhydrophobic smfaces water solutions and non aqueous liquids. Adv Coll Interf Sci 161 22-28 Freitas AA, Quina FH, CarroU FA (1997) Estimation of water-organic interfacial tensions. A linear free energy relationship analysis of interfacial adhesion. J Phys Chem B 101 7488-7493 Guerrero MI, Davis HT (1980) Gradient theory of surface tension of water. Ind Eng Chem Fund 19 309-311... 

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]. 

Figure 8.3 The PS fibrous mats containing 14.3 wt% silica nanoparticles showed a stable superhydrophobicity with a water contact angle as 157.2°. Reprinted with permission from Ref. 221, Copyright 2011, Royal Society of Chemistry.

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