The final pancake

A being a Hamaker constant. For more complex fluids, such as water, the exact structure of P(e) is not fully understood at present, but there exist some reliable data for certain solid substrates (Pashley, 1980). 

Consider now a macroscopic droplet which has spread out and covered an area /has two antagonist terms 

The resulting e(S) is a decreasing function of S. For instance, in Van der Waals case (equation (3)) 

If S/y l equation (6) gives a thickness comparable to a, in agreement with the common creed. But if S/y 1 we do expect a relatively thick pancake (c 100A). This has many implications. 

These considerations are important for a discussion of dry spreading on a random surface (i.e., when 5 is slightly modulated from point to point) for more details see de Gennes (1985b) and Joanny (1985). 

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Fig. 3.1. The final pancake profile in dry spreading The thickness e(S) is constant except in an edge region of width i,.

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