Nonmonotonic behavior of a contact angle on approaching critical end points

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Abstract
We study the behavior of the contact angle of a middle-phase pendant drop at an oil-water interface in an amphiphilic system. A Landau theory with a one-component order parameter is employed. We find that as a weak amphiphilic system departs from its balanced state, the contact angle decreases monotonically to zero at a wetting transition as a critical end point is approached. In a stronger system, the angle initially increases with this departure before ultimately falling to zero. For a very strong system, the angle can increase to 180° before falling to zero. In such a case, three wetting transitions would be encountered.