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Type of Document Master's Thesis Author Wu, Qingfang Author's Email Address qwu1@lsu.edu URN etd-0411103-114830 Title A Disjoining Pressure for Small Contact Angles and Its Applications Degree Master of Science in Mechanical Engineering (M.S.M.E.) Department Mechanical Engineering Advisory Committee
Advisor Name Title Harris Wong Committee Chair Glenn Sinclair Committee Member Keith A. Gonthier Committee Member Keywords
- intermolecular forces
- disjoining pressure
- thin film
Date of Defense 2003-03-27 Availability unrestricted Abstract A thin liquid film experiences additional intermolecular forces when the film thickness h is less than roughly 100 nm. The effect of these intermolecular forces at the continuum level is captured by the disjoining pressure . Since dominates at small film thicknesses, it determines the stability and wettability of thin films. To leading order, a thin film can be treated as uniform and . This form, however, cannot be applied to films with non-zero contact angles. A recent ad-hoc derivation to include the slope leads to a that allows a contact line to move without slip. This work derives a new disjoining-pressure formula by minimizing the total energy of a drop on a solid substrate. The minimization yields an equilibrium equation that relates to an excess interaction potential . By considering a fluid wedge on a solid substrate, is found by pairwise summation of van der Walls potentials. This gives in the small-slope limit,
where is the contact angle and is a material constant. The term containing the curvature is new; it prevents a contact line from moving without slip. Equilibrium drop and meniscus profiles are calculated for different B. Evolution of a film step is solved by a finite-difference method with the new disjoining pressure included; it is found that at the contact line is sufficient to specify the contact angle.
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