The Lotus Effect

1
The Lotus Effect

• Properties, Applications and Challenges.

2
Overview

• Lotus Flower
• What is the Lotus Effect?
• Physical and Chemical Properties
• Biomimicry
• Commercial and Technical Applications

3
The Lotus Flower

• Nelumbo nucifera
• National flower of India
• Aquatic Plant that can
• grow up to 8 feet high
• Leaves can grow up
• to 2 feet in diameter

4
What is the Lotus Effect?

• The Lotus Flower Its leaves
• have self-cleansing properties.
• Surface has the ability to
• make water bead off completely
• and wash off contamination,
• leaving the leaf clean and dry.
• First studied intensively by
• Barthlott and Nienhuis from University of Bonn
  in 1975.

5
SEM Analysis of Lotus Leaf

• SEM showed
• combination of nano
• and microstructures
• on surface of the leaves SEM Images
  of Lotus Leaf Surface
• Properties of the
• microstructures repel water while
• the nanostructures found on top
• are made of waxy materials which are badly
  wettable.

6
Contact Angle

• The angle at which the liquid/vapour interface
  comes in contact with a solid surface.
• Specific to individual systems
• Influenced by surface tension factors as well as
  surface properties such as adhesion factors and
  nano-scale roughness.

7
Adhesional Wetting

• A liquid, which is not is not in contact with the
• solid substrate, makes contact and some
  degree
• of adhesion occurs.
• The area of the liquid-gas interface decreases.
• The work of adhesion is given by the Dupré
  equation
• Wa ?Ga/A
• When combined with the equation for free energy
  of the system
• dG ? SLdA ? LGdAcos? - ? SGdA
• We get
• Wa ? LG (1 cos?)

8
Liquid Surface Interaction

• Hydrophilic Surface
• - polar H bonding
• - droplet spreads out
• - contact angle lt 90O
• Hydrophobic Surface
• -non-polar
• - droplet retains most of its shape
• - contact angle gt90o
• Superhydrophobic Surface
• - water is highly repelled
• - droplet retains shape
• - contact angle gt 150o

9
Roughness of Surface at the Micro-Particle Level

• The roughness of a surface decreases wettability
  for hydrophobic surfaces.
• Lowered contact area between liquid and solid
  Interface
• Result is a lowered contact angle.

Water
Water
10
Self- Cleaning Properties

• The lotus plants double structured surface can
  achieve a contact angle of 170o with the water
  droplet, leaving only 0.6 of the droplets area
  in contact with the leaf surface.
• This leads to a cleansing effect, as since as the
  water rolls off of the inclined leaves it
  collects with it dirt particles, bacteria, and
  other foreign materials as it rolls.

11
Video Demonstrating the Lotus Effect

• http//www.youtube.com/watch?vMe-h1LA9pm0feature
  related

12
Naturally Occurring Lotus Effect

• Other species of plants and
• animals demonstrate the benefits of
• Superhydrophobicity
• Pond Skimmer -nano-rough feet
• Wings of Butterfly
• Tulip Leaves

13
Biomimicry

• Biomimicry a relatively new science that
  studies nature, its models, systems, processes
  and elements and then imitates or takes creative
  inspiration from them to solve human problems
  sustainably.
• The Lotus effect is not limited to one species.
  Its effects in nature are found to be due to
  specific physical and chemical properties.

14
Smooth vs. Rough Surfaces

• At first, easy-to-clean surfaces were made
  using smooth surfaces
• By using the roughened surface, dirt particles
  are completely removed.

15
Technical and Commercial Applications

• Paint, roof tiles, fabrics, coatings and other
  surfaces have been developed that can stay dry
  and self-clean similarly to the lotus leaf.
• Hydrophobic
• Coating-gt

water
glass
16
Lotusan Paints

• Lotusan paints have been developed to have a
  surface almost identically to that of the lotus
  leaf at a nanoparticle level.
• Lotus Leaf Lotusan surface

17
High Water Repellency

• Reduced energy
• Consumption
• Less water resistance
• Energy saving through
• speed advantages
• Prevent buildup of rain, snow and ice

18
Superhydrophilic Surfaces

• New research to suggest that
• self-cleaning properties can be
• obtained through use of
• superhydrophilic surfaces.
• Contact angle will now be very small and as close
  to 0o as possible.
• Very thin layer of water will form, completely
  wetting the surface and thus prevent any dirt or
  dust from sticking to the surface

19
Summary

• Discovery and Discussion of Lotus Plant
  Properties
• Physical and Chemical Factors
• Similar Effects found in Nature
• Technical and Commercial Applications
• Superhydrophilicity

20
Questions?
21
References

• Dupont- Teflon Industrial. (2008) Oustanding
  Properties. Retrieved 1 November 2008.
  lthttp//www2.dupont.com/Teflon_Industrial/en_US/pr
  oducts/selection_guides/properties.htmlgt
• Evonik Industries. (2007) Easy to Clean surfaces
  and Underlying Nanoscale Materials. PDF.
  Author Klaessig, F.
• Lai, S. (2003) Mimicking nature Physical basis
  and artifiical synthesis of the Lotus Effect
  PDF lthttp//home.wanadoo.nl/scslai/lotus.pdfgt
• Lotus- Effect (2002) Micro- and nanostructured
  plant surfaces. Facts Sheet. Author Cerman. Z
• Science Daily (2007) Super Water Repellent Could
  Cause Big Wave in Market. lthttp//www.sciencedaily
  .com/releases/2007/11/071129142426.htmgt
• Shaw, D. (1992). Colloid and Surface Chemistry.
  Fourth Edition. Wiltshire Redwood Books
• UCLA Chemistry Department. (2008)
  Superhydrophobic Surfaces PDF

22
Teflon

• Fluropolymer product
  
• introduced by the Dupont Lab in 1938

Surfaces coated with Teflon 1) are both
oleophobic and hydrophobic, 2) And they are not
readily wetted. They therefore show some of the
similar non-stick, self-cleaning characteristics
demonstrated by the Lotus Leaf.