Wed April 17th 2024
16:00 – 17:00
Seminar From rebound to bound: droplet impact and the wetting transition
John Kolinski


Droplet impact is a ubiquitous phenomenon in our daily experience, from droplets splashing in the sink to precision inkjet printing systems. Using a nanometer-sensitive 3D implementation of frustrated Total Internal Reflection (TIR) microscopy, we probe the final instants preceding droplet contact on a smooth, solid surface in an ensemble of experimental configurations. We find that the air plays a critical role in mediating the transition to contact, as it typically forms a large-aspect ratio, lubricating film of air. Measurements with a carefully calibrated fTIR set-up reveal a characteristic height at which the air film ruptures above atomically smooth mica surfaces. Surprisingly, the statistics of contact for water are significantly different than those of oil droplets of the same size; these observations may suggest a non-trivial role of electrostatics in the air film rupture process that we are probing in ongoing experimental work. I conclude with perspectives on how this work might fit into the broader context of propagating singularities, which our group explores with experiments on both contact initiation and the fracture of brittle hydrogels.
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