Experimental Determination of the Effect of Disjoining Pressure on Shear in the Contact Line Region of a Moving Evaporating Thin Film

Abstract

The thickness and curvature profiles in the contact line region of a moving evaporating thin liquid film of pentane on a quartz substrate were measured for the thickness region, δ<2.5 μm. The critical region, δ<0.1 μm, was emphasized. The profiles were obtained using image-analyzing interferometry and an improved data analysis procedure. The precursor adsorbed film, the thickness, the curvature, and interfacial slope (variation of the local “apparent contact angle”) profiles were consistent with previous models based on interfacial concepts. Isothermal equilibrium conditions were used to verify the accuracy of the procedures and to evaluate the retarded dispersion constant in situ. The profiles give fundamental insight into the phenomena of phase change, pressure gradient, fluid flow, spreading, shear stress, and the physics of interfacial phenomena in the contact line region. The experimental results demonstrate explicitly, for the first time with microscopic detail, that the disjoining pressure controls fluid flow within an evaporating completely wetting thin curved film.