Sierra Castillo: Team Second; Water Droplets on a Hydrophobic Surface

Sierra Castillo: Team Second; Water Droplets on a Hydrophobic Surface

Music: Yellow Taxi Under a Blue Sky by Mindseye

Team 2nd Photo

Sierra Castillo

Introduction

Flow visualization give insight to how flow phenomena operates in our surroundings. For this assignment, teams were tasked with photographing these phenomena. Team 2 consists of Sierra Castillo, David Leng, and Katie Gresh. The team worked with a high speed camera operated by Professor Tad Truscott to visualize the water droplets falling on a hydrophobic surface. These surfaces allow water droplets to have high contact angles, resulting in spherical or semi-spherical droplets. Additionally, the droplets are able to bounce off of the surface without wetting. Using a Goretex rain jacket made by Marmot, the team dropped several water droplets on the surface and photographed the results with a high speed camera.

Apparatus

All of the photography completed for this assignment was captured in Prof. Hertzberg’s lab. The team laid the jacket across a cart such that the surface in the FOV for the camera was relatively flat. Next, the team set up a tripod over the surface to regulate the drop height and ensure that the drops would splash in the same spot (using reference tape) on the jacket to preserve the focus of the camera. Lighting was achieved through 2 sources; one lamp to the left of the apparatus at 120 degrees behind the drop zone and one held by a team member on the right close to the drop zone from 120 degrees in the back. For my submission, a cardboard box was placed under the jacket and angled to 45 degrees to achieve rolling droplets. Figure 1 shows the setup of the apparatus. Figure 2 is a picture of the tripod with a dime for scale. Figure 3 shows the setup before the tripod is added.

finalapp

Figure 1: Apparatus used to capture videos using a high speed camera.

presetup

Figure 2: Dime placed on surface for scale.

dime

Figure 3: Apparatus before tripod was added.

Fluid Physics

The physics of a hydrophobic surface are related to the microstructure of the surface. A detailed explanation of hydrophobic surfaces is presented in the report for the first team assignment found here. The distinction between a hydrophobic and superhydrophobic surface resides in the contact angles of the drops. Hydrophobic surfaces exert contact angles of 90 to 150 degrees. In this case, the contact angle is difficult to estimate due to the downward motion of the droplets. The surface is assumed to be hydrophobic as little to no wetting occurs.

Another interesting aspect of this video is the upward bounce of the droplet. The droplet bounces perpendicular to the surface, even though it is tilted at an angle. This is interesting as intuition tells us that the drop should bounce perpendicular to the ground or gravity. Unfortunately, these physics are widely unexplored and I could not find a decent reference to explain why this might happen. My best guess is that the droplet is behaving as a solid object. To explain, if you bounce a ball on an angled surface, it will bounce perpendicular to where it hit (depending on the material properties of the surface). This is one possible explanation of why the water droplets behave similarly, even though it is a fluid.

Photographic Technique

The camera used to complete this assignment was the Phantom V2511 high speed camera, operated by Professor Tad Truscott. The specifications are tabulated below.

Frames per Second 4000
Field of View ~4”
Distance: Obj to Lens ~6”
Resolution 1280×800
Pixels 12-bit, 28 microns

Once the images were compiled, very few edits were made to the video. I adjusted the contrast slightly and sped up the video. Additionally, I added background music of a snippet of “Yellow Taxi Under a Blue Sky” by Mindseye, found here. This artist employs a Creative Commons license, the details of which can be found here.

Conclusion

The outcome of the footage using the high speed camera was exciting and gave insight to the intermediate steps of what the naked eye can perceive and what actually happens when a drop of water falls on a hydrophobic surface. Overall, I am very pleased with my submission. The drops of water take on an almost animalistic life that reminds me of the movie Flubber. It almost looks like they are marching down a mountain.

References

[1] Youtube.  https://www.youtube.com/watch?v=HCGiwSghrqQ.  [Online]. [Accessed: 10- Oct-   2016].
[2] Cheng, Y. T. Superhydrophobic Surfaces. et. al. Applied Physics Letters 2005, 87, 194112. [Online]. [Accessed: 20- Oct- 2016].
https://vimeo.com/189707236/settings

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15 Comments. Leave new

  • Daniel Baker
    Nov 9, 2016 12:13

    This is some of the funniest droplet flow I have seen yet. The music syncs up quite well with how the droplets leap over one another. If I had to see one nitpick about this video, and this is really just a small nitpick, I wish the video was a bit longer. The video has a lot of potential to be cinematic, but I love what’s there. The red layout is what catches thee ye, and the fluorescent gleam of the water are what keeps it at attention. Well done.

    Reply
  • Kate Gresh
    Nov 9, 2016 12:08

    1. The video is artistically fantastic and the hopping of the droplets is very interesting and matches the upbeat mood of the music.
    2. The fluid physics are well demonstrated.
    3. The video has great focus and lighting. The music is on point for the dynamic nature of the droplet movement.

    Reply
  • Mark Noel
    Nov 9, 2016 12:06

    Fun video! great contrast and the focus is great! Just need credits

    Reply
  • Peter Brunsgaard
    Nov 9, 2016 12:05

    The lighting is well done on the video. I really like the texture of the backdrop and the leap frog effect captured from the slope.

    Reply
  • Zachary Cymanski
    Nov 9, 2016 12:05

    The bouncing of the water droplets is awesome! Especially how the second one jumps the small droplet left behind. Cool video

    Reply
  • Stephanie Mora
    Nov 9, 2016 12:05

    This video is so cute, the music gives it a really playful feel. Especially since it looks like the droplets are playing leapfrog. Great focus, very crisp video and perfect lighting.

    Reply
  • Michael Waterhouse
    Nov 9, 2016 12:05

    Very cool how the water droplet jumps over the other. Great detail and focus. Good lighting. I like how you used a different angle to test how the droplets change trajectory.

    Reply
  • Harrison Lien
    Nov 9, 2016 12:05

    I like your video, the music is nice, cool fluid physics. Nice lighting!

    Reply
  • Really cool to see the dropplets jumping over eachother on the sloped surface. Cool to see the ring spread out on impact.

    Reply
  • Branden Goldenberg
    Nov 9, 2016 12:04

    Great focus in the video. Love the leapfrogging phenomenon of the droplets. The physics displayed are very interesting.

    Reply
  • Daniel Luber
    Nov 9, 2016 12:04

    Very cool. Good job capturing a unique flow from your team mates. I really like the added effect that the inclined plane brought to the video and flow. I really like the uniqueness of the leap frogging of the drops.

    Reply
  • Sean Harrison
    Nov 9, 2016 12:03

    Well focused on the droplets and well lit. Really fun to see these droplets in slow motion. I liked the happy music that is in the video.

    Reply
  • Ryan Daniel
    Nov 9, 2016 12:03

    This high speed video is really interesting to watch! There is so much more going on here when slowed down to these extremes, it’s like a whole new world!

    Reply
  • Alexander Rosenberry
    Nov 9, 2016 12:03

    It’s really cool how tight the depth of field is on this shot, and that you got the drop to stay in focus the whole way. Really interesting effects too. Also great music choice, matched the tone of the video and it was a nice change from the classical music we’ve been hearing.

    Reply
  • Joseph Straccia
    Nov 9, 2016 04:15

    Nice video of an everyday event which we can’t fully appreciate with the naked eye. I enjoy watching the water drops jump over and onto each other and seeing how the impact with an inclined surface imparts rotation to the water drop. Focus and lighting are good.

    Reply

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