Revealing the natural surfaces demonstrating pronounced water repellence (the so-called ''lotus effect'' [5, 59]) stimulated extended theoretical and experimental research of wetting phenomena occurring on rough surfaces. It is already well understood that certain kinds of hierarchically rough reliefs supply extreme water repellency (superhydrophobicity) to interfaces [48, 78, 90, 91]. Superhydrophobic properties demonstrate plants, birds' wings, legs of water striders and other natural

Laboratory of Polymers, Ariel University Center of Samaria, Post Box 3, 40700 Ariel, Israel e-mail: [email protected]

M. Nosonovsky and B. Bhushan (eds.), Green Tribology,

Green Energy and Technology, DOI: 10.1007/978-3-642-23681-5_6,

© Springer-Verlag Berlin Heidelberg 2012

Fig. 6.1 8 il droplet deposited on the polymer superhydrophobic surface prepared as described by [12]

Fig. 6.1 8 il droplet deposited on the polymer superhydrophobic surface prepared as described by [12]

objects [9, 14, 40, 83]. Various sophisticated experimental techniques including UV-lithography and plasma etching were applied for manufacturing lotus-like biomimetic surfaces [8, 53]. Typical superhydrophobic wetting is shown in Fig. 6.1: an 8 il droplet is deposited on the polymer water-repellent surface. The detailed recent reviews of the state of art summarized the accumulated experience in the field [77, 84]. Superhydrophobic surfaces demonstrate a potential for a variety of green technologies, including energy conversion and conservation and environment-friendly self-cleaning underwater surfaces [33, 45, 77].

The wetting of rough surfaces is characterized by the apparent contact angle (APCA), which is different from the local contact angle given by Young's relation [68]. However, a high APCA does not necessarily guarantee true superhydrop-hobicity and self-cleaning properties. Moreover, high-stick surfaces demonstrating large APCA were reported recently [23, 28, 39]. Low contact angle hysteresis resulting in low sliding angles and high stability of "lotus-like" wetting state supply water repellent and self-cleaning properties to the surface [41, 42, 73]. Design of such surfaces allowing emerging green applications remains a challenging scientific and technological task.

The wetting of atomically smooth surfaces is characterized by the equilibrium or Young angle hY given by the well-known Young equation:

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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