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8/23/2019 Ravi Self Cleaning
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Self cleaning smart coating
Ravindra Marathe
M.Sc M.Tech
Under the Guidance of
Dr. V.V.Gite
M.Sc. Ph.D
School of Chemical Science,
North Maharashtra University, Jalgaon,
Maharashtra- 425001
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Introduction Many technologies existing in todays world have been derived
from nature. Self-cleaning is one amongst them.
Many surfaces in nature exhibit self-cleaning properties. E.g.
The wings of butterflies and the leaves of plants, such as
cabbage and lotus.
this technology received a great deal of attention during the
late 20th century
E.g. window glass cleaning, solar panel cleaning and cements to Thetextiles
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Aim & objective of self cleaning coatings
Develop highly efficient and durable self-cleaning coating
surfaces with enhanced optical qualities.
which include reduction in maintenance cost.
elimination of tedious manual effort
reduction in the time spent in cleaning work.
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Why self cleaning surface to clean surface of buildingmaterials causes ?
Considerable trouble.
High consumption of energy.
Chemical detergents High costs
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Classification of self cleaning coatingsClassified into two major group
hydrophilic
hydrophobic.
Both of the categories clean themselves by the action of water.
In a hydrophilic coating- the water is made to spread (sheeting of
water) over the surfaces, which carries away the dirt and other
impurities.
In hydrophobic technique- the water droplets slide and roll over
the surfaces thereby cleaning them.
E.g. metal Oxide
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What is self cleaning effect?
The self-cleaning phenomenon is related to the surface contactangle. It is the angle formed at the three phase boundary (solid/
liquid/vapour) between the surfaces of the liquid drop to the
surface of the solid. In general, if the contact angle is 90, the surface is defined as a hydrophobic surface.
Similarly, a surface with a water contact angle approaching zero is
classified as ultra (super) hydrophilic and a surface with a contactangle >150 is usually categorized as ultra (super) hydrophobic
Fig. 1 A schematic representation of hydrophilic, hydrophobic and ultra (super) hydrophobic surfaces.
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Hydrophobic coatings Nature is the source of inspiration for many around the world to
develop aesthetic self-cleaning functional systems.
e.g. lotus flower
The mystery behind this mechanism was unfolded after the invention
of the SEM in mid 1960s.
Studies made using SEM revealed that the lotus surfaces --macroscopically smooth,
-Exhibit microscopic roughness on different scale lengths.-Epicuticular wax crystalloids, make the leaves super-hydrophobic.
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there are two major types of surface in plant leaves withsuperhydrophobicity:
(i) hierarchical micro and nanostructures.
(ii) unitary micro-line structures.
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Plant leaves with hierarchical structure
Fig. a and b are SEM images of lotus leaf
surface
-Flanges 310 mm sized.
-valleys tinted with a 70
100 nm sized
wax like material.
-(Fig. a). A lot of nanorod like structures
with an average diameter of about 50 nm
-The water contact angle observed is
around 162.
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Fig. c and d show the SEM images ofrice leaf.
-The top surface of the leaf posses thepapillae
-Average diameter of about 58 mm
-they are arranged in one-dimensional order
Fig. d) The sub layer of the surface
consists of
- Nanopins that are proportionally well
distributed to the air trapping mechanism
in the surface
-(Fig.d). The water contact angle of
surface is 157
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Plant leaves with unitary structure.
This unique structure is also found on the surfaces of Chinese
watermelon shown in Fig. c and d. Surprisingly, the surface
morphologies of ramee leaf and Chinese watermelon are fibers and
both exhibit a WCA of 159
Fig. shows the SEM images of unitary structures exhibited by different plant leaves.
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Materials and mechanism to produce self cleaning coatings
Inspired by the self cleaning coating exhibited by nature, researchers
around the world started working on developing technologies to produce
surfaces with extremely low surface energies and also to control the
morphology of the surface on a micron and nano-metre scale. This ideaof controlling surface morphology opens up many possibilities for
developing a variety of engineered surfaces.
Techniques to produce hydrophobic and super-hydrophobic surfaces
classified into following categories:
a) making a rough surface from a low surface energy material;
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Roughening the surface of low surface energymaterialSilicones
Fluorocarbons
Organic materials
In-Organic materials
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Making a rough surface and modifying the surface withmaterial of low surface energy
In the past few years to fabricate rough surfaces and subsequently
modifying the surface chemistry to produce super-hydrophobic
membranes.
1. Wet chemical reaction and hydrothermal reaction.2. Electrochemical deposition.
3.Lithography.
4.Self-assembly and layer-by-layer (LBL) methods.
5.Electro-spinning technique.
6.Etching and chemical vapour deposition.
7.Solgel method and polymerization reaction
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Hydrophilic photo-catalytic coatings
Unlike hydrophobic/super-hydrophobic surfaces that rely solely on the
flow of water to clean the surface, hydrophilic coatings chemically
break down dirt and other impurities when exposed to sunlight.
This process is called photo-catalysis. The technique is basically
inspired from the process of the green leaves, which uses sunlight to
drive the chemistry.
Although a few products that work on the principle of hydrophilicity
are, this field is far from attaining maturity. Research works are under
way in developing hydrophilic self-cleaning coatings and there are
regular publications in this field.
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Functions of hydrophobic surfaces
Fig. Functions of super-hydrophobic surfaces.
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Characterization techniques
UV
TEM
FTIR
X-ray analyzes
(FE-SEM)
contact angle Goniometer
Atomic force microscopy (AFM)
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Applications of self-cleaning coatings
Textile industry (self-cleaning clothing).
Automobile industry (self-cleaning windshield glass, car bodies
and mirrors).
Optical industry (cameras, sensors, lenses and).
Marine industry (anticorrosion protection).
Aerospace industry (non sticky surfaces).
Self-cleaning coatings can also be used in windows (windowcoatings).
Solar modules (self-cleaning coatings for solar modules).
paints (exterior paints with self-cleaning).
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Conclusion The self cleaning surface on naturally occurring leaves and wings
of certain insects is multipurpose in achieving self-cleaning, anti-
reflective, and various other functionalities which has got
researchers across the globe take stock and attempt to mimic.
Though the self cleaning surfaces by them are yet to match
their naturally occurring, the fabrication techniques have indeed
evolved into more environmentally compatible and cost-effective.
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Reference
1 http://www.activglass.com/index_eng.htm. http://www.ppg.com/. A. Marmur, Langmuir, 2004, 20, 3517. A review on self-cleaning coatings. Hemant Kumar Raut, A. Sreekumaran
Nair and Seeram Ramakrishna V. Anand Ganesh, Cite this: J. Mater.
Chem., 2011, 21, 16304 Z. Cerman, A. Solga, B. F. Striffler, M. Spaeth and W. Barthlott,
Bioinspir. Biomimetics, 2007, 2, S126134. U. Mock, W. Menz and J. Ruhe, J. Phys.: Condens. Matter, 2005, 17, 595605.
Otten and S. Herminghaus, Langmuir, 2004, 20, 24052408. M. H. Sun, C. X. Luo, L. P. Xu, H. Ji, Q. Ouyang, D. P. Yu and Y. Chen, Langmuir, 2005, 21, 8978.
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