Dynamics of wetting and dewetting

The model of Girifalco, Good, and Fowkes has been extended to other interactions. For example, if we assume that the surface energies are the sum of van der Waals (dispersive) and polar interactions, one often uses the equation [272] 

Several experimental arrangements are used to measure and analyze the wetting of liquids on solid surfaces. Typical geometries are a spreading drop on a solid surface, liquid-fluid displacement through a capillary tube, steady immersion or withdrawal of fibers, plates or tapes from a pool of liquid, and the rotation of a horizontal cylinder in a liquid (Fig. 7.12). 

Experiments on forced wetting showed that, in general, the apparent contact angle depends not only on the speed v but also on the viscosity 77, and the surface tension 7l of the liquid. 

Often these are correlated and the contact angle is affected only by one parameter, the so called capillary number  

Especially for low capillary numbers the apparent contact angle is a function of Ca only [277]. For this reason, results on dynamic wetting are usually plotted with respect to the capillary number. 

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