1) The document discusses superhydrophobic surfaces and coatings that repel water due to their microscale roughness and low surface energy. 2) These coatings are inspired by the self-cleaning properties of lotus leaves, which stay clean due to the water droplets rolling off and dragging dirt particles. 3) Potential applications of superhydrophobic coatings include water repellent clothing and surfaces, self-cleaning windows, drag reduction on boats, and anti-corrosion and anti-icing coatings.

1. TSSM’s BHIVRABAI SAWANT COLLEGE OF ENGINEERING
AND RESEARCH, NARHE-PUNE
SELF CLEANING-SUPERHYDROPHOBIC SURFACES
PRESENTATION ON
BY :
GAVHALE SWAPNIL S
GUIDED BY :
PROF.TAWARE

2. • Some of the common natural
Hydrophobic materials are waxes, oil
and fats.
Hydrophobicity comes also from the Greek word Hydro(water) and
Phobicity (fear) it refers to the physical property of a material that repels a
mass of water.
INTRODUCTION
• The evaluation of hydrophobicity is
made through water contact angle
measurements.
• A water droplet would be spherical
so the water contact angle will be
significantly high.

3. SUPER HYDROPHOBIC COATING
• Super hydrophobic technology makes water bounce, it stops it, rolls it off the
surface.
• The process of coating the surface of a material with hydrophobic property
material in order to avoid sticking of liquids on that surface.
• This is absolutely unique way of coating unlike conventional which shrink
continuously during drying to produce low porosity films.

4. - Surfaces can be classified depending on their contact angle as illustrated in the
Table.
- Contact angle is a measurement of the interaction energy between the surface
and the liquid.
Contact angle
value
Type of surface Example
~0 Super-hydrophilic UV irradiated TiO2
> 30 Hydrophilic Glass
30-90 Intermediate* Aluminium
90-140 Hydrophobic Plastic
140+ Superhydrophobic Lotus leaf
-There are some natural materials that have superhydrophobic properties,
such as the Lotus leaf, and the legs of the water strider
- Another plant that has superhydrophobic leaves is Nasturtium
continued…

5. SELF-CLEANING: HOW DOES IT WORK?
→The consequence is that water droplets roll off
the leaf surface and in doing so it drag dirt
away from it. This effect, called “self-cleaning”
renders the Lotus leaf clean and resistant to dirt.
→ Contaminants on the surface rest on the tips
of the rough surface. When a water droplet rolls
over the contaminant, the droplet removes the
particle from the surface of the leaf.
Figure:. (Top) Diagram summarising the connection
between roughening and self-cleaning: in the top image
a droplet of water removes dirt from a surface thanks to
the Lotus effect (bottom): Graphical representation of
contaminants and water droplets on a lotus leaf (Image
credits: see slide 16)

6. HOW IS THIS “NANO”?
 The Lotus-effect has revealed the presence of wax nanocrystals on the
leaf surface.
 These crystals provide a water-repellent layer, which is enhanced by the
roughness of the surface, making it a superhydrophobic surface, with a
contact angle of about 150.
 Water droplets interfacing with the leaf are in contact with a large
fraction of air. This forces the water to bead and roll off. The image
below shows the progressive magnification of a Nasturium leaf.
A B C D
nanocrystals few tens of
nanometres
Figure . Micro and nanostructure of a nasturtium leaf

7. MATERIALS USED

8. APPLICATIONS
With the recent advances in durable superhydrophobic surfaces and coatings, there
will soon be a large number of existing products converted into superhydrophobic
products .
 1. Water Repellency :
Water repellency is the most obvious application of superhydrophobic coatings and
surfaces. The complete list of possible water repellency applications would be extensive .
A partial list includes clothing that will be both breathable and water repellant, umbrellas
that stayed completely dry, building materials, paints, epoxies, and silicones,boats,mobile
phones, automobiles etc. Figure below shows a water drop being repelled and beading up
by a superhydrophobic volumetric painted surface.

9. 2. Self-cleaning Optical Windows And Lenses :
Optically clear superhydrophobic coatings on glasses, windows, and optical
lenses will make seeing in foul weather much easier and cleaning windows will be
as simple as spraying them with water. Figure 2.1 below shows a periscope
window that first had its right side coated with an optical superhydrophobic thin
film and then mud was applied to the entire window. The superhydrophobic area
of the window (right side) repelled the mud and stayed clean, while the untreated
side (left side) gets covered with mud.
Fig 2.1 Periscope window Fig 2.2 Car windshield and windows

10. 3. Viscous Drag Reduction :
Superhydrophobic paints and epoxies could greatly reduce the cost of
transporting goods by ships and improve the efficiency of water craft of all kinds
due to the reduction of water drag on the watercrafts hull. Figure 3.1 (left and
right) shows a toy boat with and without a thin superhydrophobic coating on its
hull. Notice how high in the water the left boat sits when its treated with a
superhydrophobic coating. While the buoyancy increase produced by coating toy
boats with superhydrophobic paint doesn’t scale to large watercraft, there can still
be a relatively large viscous water drag reduction due to the large slip length
produced by the pinned layer of air. The use of riblets on watercraft is a well-
established drag reduction mechanism.
Figure 3.1 Left: SH coated boat (notice how high the waterline is now), Right: uncoated top boat (note
the waterline location)

11. 4.Anti-corrosion:
As an example, figure 4.1 shows two plates, one coated with an epoxy paint
and one coated with the same epoxy paint which has been modified to be
volumetrically superhydrophobic. Both plates were placed into a salt-fog chamber
and subjected to a salt fog for 1000 h. While the standard epoxy paint coating
showed heavy corrosion, the volumetric superhydrophobic epoxy coating showed
no corrosion.
Figure 31. Two 6″ × 8″ plates subjected to 1000 h of salt fog chamber testing. Left: shows an
epoxy coated plate reference, Right: shows the same type of plate and coating with a volumetric
porous superhydrophobic topcoat.

12. 5.Anti Icing:
Superhydrophobic coatings and oil-modified superhydrophobic coatings
could greatly reduce or even eliminate many of the effects of ice storms and
aircraft icing.
Figure 5.1. SH Coated Power Lines In Simulated Ice Storm Chamber. Figure 5.2 Aircraft SH Coating Against Icing

13. CONCLUSION
 Smart self-cleaning coatings are those which respond to external influences such as electric
field, temperature, and light.
 Self-cleaning, basically comprising hydrophobic and hydrophilic coatings, has been reviewed.
It is already being reaected in our daily life in applications such as silver nano-coated clothes,
waterproof paints, shoes, and umbrellas. In TiO2-based photocatalytic–hydrophilic coatings,
further research should focus on broadening the absorption wavelength range of the
photocatalysts since the photocatalytic effect of the TiO2 coatings is UV light-based, which
only represents 4% of the solar spectrum; hence, the efficiency of the photocatalytic effect is
minimum.
 Other areas of investigation will probably be the study of toxicity of such coatings, so that they
can be applied safely in real-life applications such as water purification membranes, and self-
repair, self-healing and self-lubricating coatings. Currently, although research studies are
focused on the fabrication of such coatings, novel synthesis routes need to be developed that
are cost-effective without compromising on the quality.