Fine Structure of the Triple Line

In a partial wetting regime and in the immediate vicinity of the triple line, the profile of the liquid can deviate from the constant slope (tan ) described by Young s equation. A legitimate question to ask then is whether long-range forces can cause visible deformations of the profile. The relevant spatial scale is typically a few nanometers, which is a challenge to observe. 

A discussion of such profiles is particularly interesting when the contact angle is small. 

This equation expresses the fact that the Laplace pressure and the disjoining pressure are in equilibrium. A first integration gives [see equation (1.34)]  

The integration constant 7 e/2 ensures that at large distances u — oo) we end up with dufdx = 0, which is consistent with P u) 0. 

With this formula, we can determine the function P u)—as long as we know the profile of the wedge—by measuring the local slope dujdx. 

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Bormashenko E, Bormashenko Y, Stein T, Whyman G, Pogreb R, Barkay Z. (2007) Environmental scanning electron microscope study of the fine structure of the triple line and Cassie Wenzel wetting transition for sessile drops deposited on rough polymer substrates. Langmuir Li 4378 382. 

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