Spontaneous Generation Unit 3. What is Spontaneous Generation?
Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid...
Transcript of Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid...
![Page 1: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/1.jpg)
Spontaneous droplet trampolining on rigid
superhydrophobic surfaces
Team 6:
Ching Him Leung
(Zeqian) Chris Li
Kuan-Sen Lin
Gengming Liu
Schutzius, T. M. et al. Nature 527, 82–85 (2015).
![Page 2: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/2.jpg)
Outline
• Engineering the surface: lesson from nature
• Experimental set up and results
• Driving force for the bouncing: vaporization
• Modeling
• Droplet freezing
• Further studies
• Summary and critiques
![Page 3: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/3.jpg)
Engineering the surface
• Surface morphology and chemistry → different surface property
• Liquid droplet behavior on the surface
• Application: ex. Self-cleaning
Hydrophobic/Hydrophilic/Superhdyrophobic
Superhydrophobic Surfaces: Hydrophobic
surface having nano-scale roughness.
water
superhydrophobic
Hydrophobic Surfaces: “Water-fearing surface”
Water tries to minimize contact with surface.
Examples: Teflon, oily surfaces
water
hydrophobic surface
Hydrophilic Surfaces: “Water-loving surface”
Water tries to maximize contact with surface.
Examples: Glass, rusted metal surfaces
water
hydrophilic surface
Hydrophobic/Hydrophilic/Superhdyrophobic
Superhydrophobic Surfaces: Hydrophobic
surface having nano-scale roughness.
water
superhydrophobic
Hydrophobic Surfaces: “Water-fearing surface”
Water tries to minimize contact with surface.
Examples: Teflon, oily surfaces
water
hydrophobic surface
Hydrophilic Surfaces: “Water-loving surface”
Water tries to maximize contact with surface.
Examples: Glass, rusted metal surfaces
water
hydrophilic surface
Hydrophobic/Hydrophilic/Superhdyrophobic
Superhydrophobic Surfaces: Hydrophobic
surface having nano-scale roughness.
water
superhydrophobic
Hydrophobic Surfaces: “Water-fearing surface”
Water tries to minimize contact with surface.
Examples: Teflon, oily surfaces
water
hydrophobic surface
Hydrophilic Surfaces: “Water-loving surface”
Water tries to maximize contact with surface.
Examples: Glass, rusted metal surfaces
water
hydrophilic surface
Roughness
![Page 4: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/4.jpg)
Can learn from Nature
• Lotus leaf
• When the leaf tilts a little bit the droplet will roll off.
Nature-Inspired Superhydrophobic Surfaces
SEM images of lotus leaf surface
Double roughening of a hydrophobic surface, on the submicron and nanometer
scale, creates superhydrophobicity!
Cheng, Y. T., et. al. Applied Physics Letters 2005, 87, 194112.
A water droplet beads up on a lotus
leaf due to the hydrophobic
nanostructures
http://www.pbase.com/yvesr
Nature-Inspired Superhydrophobic Surfaces
SEM images of lotus leaf surface
Double roughening of a hydrophobic surface, on the submicron and nanometer
scale, creates superhydrophobicity!
Cheng, Y. T., et. al. Applied Physics Letters 2005, 87, 194112.
A water droplet beads up on a lotus
leaf due to the hydrophobic
nanostructures
http://www.pbase.com/yvesr
Zoom in
Cheng, Y. T., et. al. Applied Physics Letters 2005, 87, 194112.
![Page 5: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/5.jpg)
Droplets levitate due to vaporization
https://commons.wikimedia.org/wiki/File:Leidenfrost_droplet.svg
http://www.irishmanabroad.com/2015/02/science-saturday-leidenfrost-effect-explained/
![Page 6: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/6.jpg)
In the work we are presenting…
• Combine super-hydrophobic surface + vaporization effect.
• Don’t rely on hot plate to create vapor.
• In special environment condition, single droplet can jump spontaneously.
![Page 7: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/7.jpg)
Experimental set up and results
![Page 8: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/8.jpg)
Setups and conditions
• Low ambient pressure (0.01 bar)
• Low environmental humidity
• Controllable water droplet sizes
• Silicon micropillar specifications
![Page 9: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/9.jpg)
Spontaneous Trampolining
![Page 10: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/10.jpg)
Characterizing Motion
![Page 11: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/11.jpg)
Hunting key Forces
Low pressure case
Normal Pressure case
![Page 12: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/12.jpg)
Continued
• Measure restitution coefficient
• Assume invariant mass to estimate the momentum change
• Then estimate average force
∆𝑃 = න0
∆𝑡𝑟
𝑓 𝑑𝑡 ≈ ሚ𝑓∆𝑡𝑟
𝜺 =𝒗𝟐𝒗𝟏
![Page 13: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/13.jpg)
Continued
• Then estimate average force
• Pressure = ሚ𝑓
𝐴𝑟𝑒𝑎= 2.2 ×
𝜎𝑅0
𝜋𝑅𝑀𝑎𝑥2
• Pressure ≈ 0.9 × (2𝜎
𝑅0)
ሚ𝑓 =∆𝑃
∆𝑡𝑟≈ 2.2 𝜎𝑅0
![Page 14: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/14.jpg)
Vaporization
![Page 15: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/15.jpg)
Can vaporization account for the driving force
• Vapor flow generate the force needed to accelerate the droplet
• At low pressure
high vaporization flux 𝐽
vapor can be trapped between the micropillar
Excess pressure between the droplet and the surface
![Page 16: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/16.jpg)
Measuring vaporization flux
• At pressure lower than 0.1bar, vaporization flux increases significantly
![Page 17: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/17.jpg)
Overpressure due to vaporization
• Overpressure Δ𝑃 ∝ 𝐽
• Using the measured vaporization flux, the maximum overpressure Δ𝑃 ≈4.7(2𝜎/𝑅)
• Since the pressure varies between 0 and 4.7(2𝜎/𝑅), the average pressure is ΔഥP ≈ 2.3(2𝜎/𝑅)
• From previous slides, ΔഥP ≈ 0.9(2𝜎/𝑅0)𝑅 is the contact radius𝑅0 is the radius of the droplet
![Page 18: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/18.jpg)
Modeling
![Page 19: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/19.jpg)
Modeling
• Toy model: forced, mass-spring-damper system.
𝑚𝑑2𝑦
𝑑𝑡2+ 𝑐
𝑑𝑦
𝑑𝑡+ 𝑓𝑘 𝑦 = 𝑓 𝑡 − 𝑚𝑔 𝑖𝑓 𝑦 < 0
𝑦 = 𝑦0 + 𝑣0𝑡 −1
2𝑔𝑡2 𝑖𝑓 𝑦 ≥ 0
𝑦 = 0 Spring: The droplet deforms like a spring when it impacts the surface.
(free fall)
![Page 20: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/20.jpg)
Modeling
• Toy model: forced, mass-spring-damper system.
𝑚𝑑2𝑦
𝑑𝑡2+ 𝑐
𝑑𝑦
𝑑𝑡+ 𝑓𝑘 𝑦 = 𝑓 𝑡 − 𝑚𝑔 𝑖𝑓 𝑦 < 0
𝑦 = 𝑦0 + 𝑣0𝑡 −1
2𝑔𝑡2 𝑖𝑓 𝑦 ≥ 0(free fall)
Spring: The droplet deforms like a spring when it impacts the surface.
Blue: experimentBlack: modeling
![Page 21: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/21.jpg)
Droplet freezing
![Page 22: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/22.jpg)
Droplet freezing and levitation
Aluminum surface, 24°𝐶, ~0.01bar, humidity<10%
Strong vaporization
Supercools to -20°𝐶
Recalescent freezing
• Sudden temperature increase: -20°𝐶 → 0°𝐶
• Sudden latent heat release
Explosive flux
Levitate
![Page 23: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/23.jpg)
Silicon micropillar surface; 25°𝐶, humidity<10%
Strong vaporization
Supercools to -20°𝐶
Recalescent freezing
• Sudden temperature increase: -20°𝐶 → 0°𝐶
• Sudden latent heat release
Explosive flux
Levitate
Droplet freezing and levitation
![Page 24: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/24.jpg)
Further studies
Pham, J. T., Paven, M., Wooh, S., Kajiya, T., Butt, H. J., & Vollmer, D. (2017). Spontaneous jumping, bouncing and trampolining of hydrogel drops on a heated plate. Nature communications, 8(1), 905.
• Hydrogel
• Heated surface
• Initial jump: massive water loss
• Trampolining after: same mechanism
![Page 25: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/25.jpg)
Summary
![Page 26: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/26.jpg)
High vaporization
Flux trapped in surface structure
Resonating force Trampolining
Allowed by second law!
How is this not violating the second law?
![Page 27: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/27.jpg)
Our critiques
• Pressure control?
![Page 28: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/28.jpg)
Our critiques
• Pressure control?
• The estimation of ΔഥP ≈ 2.3(2𝜎/𝑅) is too rough
• 0.9(2𝜎/𝑅0) and 2.3(2𝜎/𝑅) are not consistent as the authors claimed.
• It does not contain enough experimental trials to convince readers that the shown contact radius dynamics is a good representation of the general trend.
![Page 29: Spontaneous droplet trampolining on rigid …Spontaneous droplet trampolining on rigid superhydrophobic surfaces Team 6: Ching Him Leung (Zeqian) Chris Li Kuan-Sen Lin Gengming Liu](https://reader031.fdocuments.us/reader031/viewer/2022013022/5f39a6e0442d666e0f05fb31/html5/thumbnails/29.jpg)
Thanks!