Video from the paper "Bouncing Water Droplet on a Superhydrophobic Carbon Nanotube Array," authored by Adrianus I. Aria, Morteza Gharib, published online on ArXiv, Submitted on 7 Oct 2010: http://arxiv.org/abs/1010.1351
The first two parts of the video show the impact dynamic of 30 microliters water
droplet at different impact velocity. At low impact velocity of 1.03 m/s, the water droplet deforms upon impact and eventually bounces off completely of the surface of the array. At higher impact velocity of 2.21 m/s, the droplet breaks up into many smaller droplets and eventually bounces off completely
of the surface of the array.
The coefficient of restitution of water droplet at very low impact velocity can be seen clearly by dropping a water droplet on a slightly tilted carbon nanotube array. At tilt angle of 2.5 degrees the droplet skips off of the surface of
the array multiple times without showing any sign of pinning on the surface
of the array, as demonstrated in the third part of the video. The fourth
part of the video shows the sliding/rolling behavior of the droplet along the
surface of a U-shaped carbon nanotube array. The fifth part of the video
shows the impact of two identical 14 microliters water droplets to one another on a U-shaped carbon nanotube arrays. Upon impact, these two water droplets, which come from the opposite direction, merge to form one larger droplet.
All parts of the video were captured by high speed camera operated at
various frame rates. The droplet was illuminated from behind with a diffuse
halogen light. The droplet was dropped on the surface by at-tipped needle
and the volume of the droplet was controlled precisely by syringe pump.
This work was supported by The Charyk Foundation and The Fletcher Jones Foundation.