Surface Between Water and a Solid

An extensive literature exists regarding the interface between water and solids, and only the main concepts are dealt with here. Two situations may be distinguished regarding the surface between water and a solid in one case a gaseous phase (vapor and/or air) is also present, as when a drop of water is located on a solid support, and the other case is at a submerged solid in the water (or an aqueous solution), e.g., at an electrode. 

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 

Vogler (1999) defined a transition region between hydrophobic and hydrophilic surfaces at contact angles between 74 and 56°, and distinguished two types of biological response to such surfaces. On hydrophobic surfaces the structure of the water is more nearly tetrahedral and open, whereas on the more hydrophilic surfaces it is more compact. 

The surface energetics of wetting of solid substrates by water was discussed by Tarasevich (2008). When water is sorbed from the vapor on a vacuum-degassed solid 

The structure of the water in the double layer at the electrode surface was reviewed by Henderson (2002) and by Ito (2008). The orientation of the water dipoles and then-ordering depends on the potential imposed on the electrode/solution interface. 

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