Research Colloquium — Wednesday, October 4, 2006

A liquid film of thickness h < 100 nm is subject to additional intermolecular forces, which are collectively called disjoining pressure &Pi . Since &Pi dominates at small film thicknesses, it determines the stability and wettability of thin films. Current theory derived for uniform films gives &Pi = &Pi(h). This solution has been applied recently to non-uniform films and becomes unbounded near a contact line as h approaches 0. Consequently, many different effects have been considered to eliminate or circumvent this singularity. In this talk, I will present a mean-field theory of &Pi that depends on the slope h_x as well as the height h of the film. When this theory is implemented for Lennard-Jones liquid films, the new &Pi = &Pi(h,h_x) is bounded near a contact line as h approaches 0. Thus, the singularity in &Pi(h) is artificial because it results from extending a theory beyond its range of validity. The new &Pi can capture all three regimes of drop behavior (complete wetting, partial wetting, and pseudo partial wetting) without altering the signs of the long and short-range interactions. A linear stability analysis shows that a drop with an unbounded precursor film is linearly stable.