Suction Experiments on Drops

Suppose we deposit a drop on a porous surface. We can force it to drain itself into the interior of the porous medium in one of two ways  

We can start with a dry substrate, which will spontaneously draw the liquid if jso Isl] 

Or we can start with an already saturated substrate and apply to it a mechanical suction inducing a liquid flow J (volume drawn per unit area and per unit time) directed toward the interior. 

The two cases are not fundamentally different. In case 1, a flow J t) is set up, which is described by Washburn s law (chapter 5) and varies as In case 2, The flow J is independent of time, which simplifies things. In this section, we shall discuss primarily case 2. 

Combining equations (9.27) and (9.28) leads to a linear decrease of 6 t) in time, which has recently been verified experimentally.  

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