Air film failure mechanisms of a drop impacting an inclined surface

Drop impact studies have applications in industrial, agricultural and natural settings. Two air film failure mechanisms for drop impact on horizontal lubricated surfaces have been reported. For intermediate We (~1<We<10) drop-film contact is initiated at the center due to the downward motion of the drop’s top surface from impact-induced capillary waves. For larger We (We>O(10)) increased air pressure under the drop causes air film failure to occur much earlier, at a location surrounding the center dimple where the air film is very thin and van der Waals interactions become important. This study examines the development of the air layer beneath a drop approaching an inclined and atomically smooth surface using high-speed total internal reflection microscopy integrated with side-view imaging. A thin film of high viscosity silicone oil was spin coated onto a glass slide to create an atomically smooth surface. Surface tilt angles ranging from 0º to 60º and We ranging from 1 – 100 were studied under various pressures. Both normal and tangential components of We were examined. By varying We, tilt angle, and ambient pressure, different impact regimes, air film failure patterns, and drop-film interactions are established, and results are compared with those of horizontal surfaces.