On the Generation and Spreading of ‘Finger’ Instabilities in Film Coating Processes
Spreading viscous films are of considerable interest in industrial applications, especially in coating processes, where, in general, a uniform quality of the final coating is preferred. Experiments show that the contact-line of, in this case, liquid films driven down an inclined plane through gravity, rapidly destabilizes, forming either sawtooth or finger patterns. For the latter situation, portions of the contact-line may stop to move at all, leaving uncovered regions on the plane. Theoretical investigations using linear stability analysis for the lubrication approximation are in good agreement with experimental results for large to moderate inclination angles [2,4,8,12]. However, for small inclination angles, they predict stability in contrast to experimental observations.
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