SelfCleaning Surfaces

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Self-Cleaning Surfaces
By Stevie Jew, Veena Pathiparampil, Jimmy Teo,
and Jennifer Wong
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How Nanobumps were Developed

• Scientists developed nanobumps from lotus leaves
  which are known to repel water very well

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How Nanobumps Work

• Nanobumps are only a few micrometers across and
  packed very closely together
• Bumps are too small to pierce the surface tension
  of a water drop
• Bumps are hydrophobic so that water is even more
  repelled
• This keeps water from sticking to the surface
• Help with car windshields
• It is transparent, and so the glass looks the
  same.

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Lotus Nanobumps
Scanning electron micrograph image of the surface
of a lotus leaf. Ohio State University
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Problems and Development

• At close to horizontal angles the water drops do
  not slide off because they balance on the
  nanobumps
• Scientists still need to develop what size and
  shape nanobumps are most effective
• Nanobump design depends on sliding water drops to
  clean off dirt, does not repel dirt directly
• Leaves spots and streaks

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Titanium Dioxide

• Window glass would be coated with a thin layer of
  titanium dioxide while still molten
• Titanium dioxide is a photocatalyst which will
  oxidize dirt particles when Ultra-Violet rays
  shines on it
• Titanium Dioxide is Hydrophilic
• Water will spread out evenly on surface, so it
  will sheet off instead of beading up
• Water will dry evenly leaving no spots or streaks

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TiO2 is a Photocatalyst

• TiO2 is a semiconductor
• That means that it has an empty conduction band,
  but a small band gap (3.2 eV)
• Energy from ultraviolet light excites electrons
  to the conduction band

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Redox

• Electrons (e-) in the conduction band can be
  donated to dirt molecules (Reduction)
• Positively charged holes (h) in the valence band
  can accept electrons from dirt molecules
  (Oxidation)
• Products of the Redox reactions are often H2O and
  CO2 which can be washed away
• NO2 H2O ? H NO3-
• H CO32- ? H2O CO2

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Drawbacks

• Depends on Ultra-violet rays from the sun
• Cannot be used on interior glass surfaces such as
  mirrors or shower doors
• If too much dirt builds up, it can block the
  Ultra-violet rays

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Importance

• Spray-on self-cleaning surfaces wear off
• Nanosurfaces would be built into the material and
  last the lifetime of the surface
• Nanosurfaces can also be used as lubricating
  surfaces in microbots which are too small for
  liquid lubricants and where friction is a huge
  problem

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Photocatalysis Applications of Titanium Dioxide
Ti02.titaniumart.com.lthttp//www.titaniumart.com
/photocatalysis-ti02.htmlgt.   Azom.com. CERAM
Research Ltd.lthttp//www.azom.com/details.asp?Art
icleID1179gt.   Benedix, Roland, et al.
Application of Titanium DioxidePhotocatalysis to
Create Self-Cleaning Building Materials.lthttp//w
ww.uni-leipzig.de/massivb/institut/lacer/lacer05/
l05_19.pdfgt.   clarkpublicutilities.com.lthttp//w
ww.clarkpublicutilities.com/Residential/TheEnergyA
dviser/Archives2004/04_10_17gt.
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Dye, Lee. Abc News. Ohio State.lthttp//abcnews.go
.com/Technology/DyeHard/story?id440893page1gt.  
Nano Tsunami.lthttp//www.voyle.net/Future20Tech
nology202005/future202005-0006.htmgt.   Ozone
Lite. lthttp//www.ozonelite.com/otheruses.htmlgt.  
world changing another world is
here.lthttp//www.worldchanging.com/archives/00084
4.htmlgt.