Controlled adsorption of droplets onto anti-nodes of an ultrasonically vibrating needle

We show that droplets adsorb onto the anti-nodes of a stainless needle in flexural vibration when the needle is lifted from a layer of liquid thin film. The adsorbed liquid includes water, saline and olive oil, which cannot adsorb onto a stainless surface if the surface does not vibrate. The adsorbed droplets take on the shape of ellipsoid when the needle vibration is large enough. A physical model based on the hypothesis that sound pressure decreases the cohesive force among molecules of liquid has been proposed, which can well explain the experimental phenomena.