Contact of Liquids with Porous Solids and Powders

9 CONTACT OF LIQUIDS WITH POROUS SOLIDS AND POWDERS 

Any solid can be pulverized into particles of small size not all can be fabricated into the smooth supports we have discussed in this chapter. This consideration alone —not to mention the many practical applications of powdered solids —encourages us to look for a relationship that describes the junction of a liquid interface with such solids. One thought might be to compress the powder into a pellet and treat the surface of the pellet in the same way as we have treated other solid surfaces. On a fine scale the surface of such a pellet is rough, however, so hysteresis effects should be severe. Therefore we look for some alternative approach. 

Commercial instruments are available that carry out these operations under the control of a computer, which also analyzes the results. Let us consider the penetration of the liquid into the pores of the plug to see the basis for this analysis. 

In the capillary rise experiment p = Apgh, whereas p is the applied pressure in the case discussed in the present section. 

Now suppose a liquid is pushed through the plug that forms a contact angle of zero with the walls of the channels. Using the subscript 0 to represent this situation, Equation (86) becomes 

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Now we are better equipped to consider measurements of surface tension in detail. Section 6.8 describes the use of shapes of menisci, drops, and bubbles for such measurements, and Section 6.9 considers the practically important case of contact of liquids with porous solids and powders. 

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