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