The wise man warns me that life is but a dewdrop on the lotus leaf - Tagore

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The wise man warns me that life is but a dewdrop
on the lotus leaf - Tagore
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Biomimicry of the Lotus Effect

• By Ankit Modi
• Parag Surana

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The Idea

• Lotus leaf has a remarkable self cleaning effect
  due to its superhydrophobic surface.
• It is free of dust and also of contamination from
  microbes.
• It has inspired many attempts to mimic the self
  cleaning effect by man-made materials.
• Few examples the lotusan paint, bioseperation,
  snow removal, anti fogging surfaces.
• It could throw the whole detergent industry out
  of business !!!

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Orientation

• The physical basis.
• Structural properties of lotus leaf at micro and
  nano level.
• The mechanism of self cleaning.
• Few examples of similar kind in other body
  designs.
• Biomimetics of lotus effect

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Physical Basis Surface Tension

• Causes the suface layer of liquid to behave as an
  elastic sheet.
• Bulk A Molecule is pulled equally in all
  directions by neighboring liquid molecules. Net
  force 0
• Surface The inward force of molecular
  attraction is balanced by the resistance to
  compression.
• Tendency to minimize surface energy by reducing
  surface area.

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Contact Angle

• cos ? (ss ?sl)/ sl
• If (ss ?sl) is larger than sl, the drop tends
  to spread, i.e. ? 0
• If (ss ?sl) is a lot smaller than sl, the drop
  is spherical, i.e. ? 180.

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Sliding Angle

• The minimum angle (T) of the surface tilt, for
  the drop to flow.
• T (Ta Tr)
• The flow of drops is determined by the sliding
  angle.
• Sliding angle of lotus leaf 2-4o !

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Lotus Leaf Surface
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Bar 20 µm
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Facts

• Contact Angle - 161.0 2.7
• Sliding Angle 2 to 4o
• The papillae is made of epicuticula wax.
• Nano fibres on the papillae

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Self Cleaning Effect
The decreased contact area between a particle and
a rough surface. Particle is cushioned by air.
Decreased contact area between liquid and surface
and air is enclosed.
Particles adhere to the surface of the droplet
and are removed from the leaf when the droplet
rolls off.
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Mechanism
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Points to remember

• Very small interfacial area between particle and
  rough surface.
• Adhesion is minimized.
• Particle is captured'' by the water droplet and
  removed from the leaf.
• Leaf surface is not only free from dust but also
  free of contamination from microbes.

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Similar surfaces in Nature

• Water Striders also have the typical micro and
  nano level hierarchy to produce high contact
  angles.
• The dimple generates the tensile force to balance
  the weight.
• Other examples rice leaf, wings of cicada.

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Biomimetics of the Lotus Effect

• The Process

Nano particles
TiO2 surface
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The Results!!!
Lotusan Paint
Self Cleaning Textile
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Thank You