VYPT: Bouncing Drop
Water droplet before, during and after impacting with a super-hydrophobic material (in this case, a nanotube-covered substrate)
Image credit:
Applied Physics Letters
What is being investigated?
Investigate the motion of water droplets falling on a hydrophobic surface.
Image credit:
ANVER Corp.
Teflon tape is highly
hydrophobic
How can it be measured?
• Rebound height (vertical direction)
• Spread (horizontal direction)
Image credit:
Van Der Waals-Zeeman Institute
Spread
What factors might affect it?
• Height from which water droplet is released (which affects its impact speed)
• Size (or volume) of water droplet (determined by type of pipette used)
• Type of hydrophobic surface (e.g. normal vs super hydrophobic)
• Temperature of water droplet
• Tilt angle (i.e. at what angle does the water droplet make contact with the impacting surface)
How might these [factors] be measured?
• Height – measured with ruler
• Size of water droplet – measure droplet diameter(?)
• Temperature of water droplet – allow water to reach equilibrium, then measure temperature
• Tilt angle – measured using a protractor(?)
What equipment might be needed?
• Retort stand, boss head and clamp
• Pipette, eye dropper or similar mechanism of dispensing one drop at a time
• Vernier caliper for measuring outer diameter of pipette’s exit(?)
• Glass slide (biology-type)
• Teflon tape or Water Proofing Spray
• High speed camera (or video)
How could the experiment be setup?
• Coat microscope slide with soot from burning candle
• Apply several fine coats of water-repellant to soot-covered slide
• Pipette positioned directly above microscope slide
• Water droplet is released
• Measure/record water droplet velocity prior to impact, contact time with hydrophobic surface, and droplet deformation