Wetting on Flat and Smooth Surfaces

Wetting on Flat and Smooth Surfaces ---------------- Contact Angle... 

In the wetting and dewetting kinetics studies described earlier, the solid substrate was a flat and smooth surface. However, the sohd deformation due to the action of the vertical component of the hquid surface tension may be expected to act in any geometry. For example, viscoelastic braking is involved in the sliding of a liquid drop on a tilted rubber track [32],... 

At present, many authors I20-I26 follow another concept From the plot of pj p [M /t) versus the surface tension of the liquids, the geometric factor K is calculated for those liquids that should wet the solid completely. By inserting this K value and [t]/p- ] M2/t for these liquids into Eq. (13). their contact angles 0 are calculated and used for the interpretation of the solid-vapor surface tension of the porous material. This procedure is dubious, because it can be expected that the contact angles, calculated from the Washburn equation, are affected by roughness and porosity. If we apply this procedure to the PTFE powder for hexadecane, a contact tingle 0 = 88 would be obtained. However, it is well known that the contact angle of hexadecane on a flat and smooth... 

Sodium chloride can be easily polished between use. The crystal is sanded flat with a flnegrade sandpaper if it is freshly cleaved, scratched, or damaged by water. Two polishing laps are prepared. There are different types, but the wet lap can be simply two thicknesses of fine nylon cloth stretched over a flat surface. The wet lap is wetted with water and sprinkled with a little fine polishing powder such as aluminum oxide or cerium oxide. This is rubbed smooth and all excess water is wiped off. The flat salt plate is mbbed about 20 strokes on the wet lap and then, without delay, is buffed about 7 strokes on the dry lap, which can be simply a layer of diaper cloth held flat. Cesium bromide... 

Suppose that water is not originally in contact with the solid surface and adheres to it (i.e., adhesional wetting). When the drop of water is laid on a flat, smooth, solid surface, three forces are at work surface tension between the solid and air, ySA interfacial tension between the solid and water, ysw and surface tension between water and air, yWA. Incorporating only the horizontal components of these forces leads to ... 

Consider a vertical flat plate exposed to a condensable vapor. If the temperature of the plate is below the saturation temperature of the vapor, condensate will form on the surface and under the action of gravity will flow down the plate. If the liquid wets the surface, a smooth film is formed, and the process is called film condensation. If the liquid does not wet the surface, droplets are formed which fall down the surface in some random fashion. This process is called dropwise condensation. In the film-condensation process the surface is blanketed by the film, which grows in thickness as it moves down the plate. A temperature gradient exists in the film, and the film represents a thermal resistance to heat transfer. In dropwise condensation a large portion of the area... 

In systems where A G - A G < 0, the solid is not completely wetted by the liquid but a sessile drop of L is formed on S. Such a drop on a flat, smooth, and horizontally positioned solid surface is depicted in Rgure 8.1. The shape of the drop or, more precisely, the contact angle 0 with the solid is determined by the balance of interfacial tensions. In equilibrium... 

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