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Adhesion and Cohesion

Adhesion and Cohesion By definition, multicellular life does not exist without biological binding of the various components (see Biological Bonds). The modern world would fall apart literally if the mechanical interlocking (see Mechanical Bonds) is suddenly switched off. The crystal is held together in one piece by chemical bonds (see Chemical bonds). They become rocks and minerals via actions in nature.

Adhesion and cohesion are very general concepts to express whether the binding parts are different or similar (Figure 12-25d). The interface between water and solid is often used as example to illustrate binding in daily life. Due to the surface tension, a water droplet by itself is always in spherical shape. As shown by the various illustrations in Figure 12-25d, it more or less retains its round shape if the cohesion is strong; otherwise the liquid would spread out called wetting.

Figure 12-25d Adhesion and Cohesion [view large image]

The degree of wetting can be expressed roughly with the contact angle formed by the tangential at the edge. It is inversely proportional to wetting (see formulas in Figure 12-25d).

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