1. NATURAL
NANOMATERIALS

2. What is a natural nanomaterial?
Belonging to
natural world
Remarkable
No human
properties due
modification or
to inherent
processing
nanostructures

3. BIOMIMICRY
“The examination of nature, its models, systems,
processes, and elements to emulate or take
inspiration from in order to solve human
problems.”
◦ Basically scientists see something really cool in
nature and try and copy it.
◦ Lets get to some examples!!!!

4. Biomimetic material Inspired from
Adhesives Gecko’s feet
High tensile strength fibre Spider silk
Dirt and water resistant paint Lotus leaf
IMOD Display technology Butterfly wings
Reduced drag suits for athletes Shark skin
Structural elements Wood, ligaments and bone
Aerospace and automotive
Toucan’s beak
applications

5. Lotus leaf

6. • Clean leaves in muddy habitat
• Superhydrophobicity
• Water droplets roll off dragging dirt along with it
• ‘Self Cleaning effect’

7. How is this ‘Nano’?
• “Lotus effect”
• Self-cleaning properties of the lotus plant
are the combination of the micro-structure
of the leaves and of the epidermal cells on
its rough surface, which are covered with
wax crystals

9. Self Cleaning effect ?
• Large contact angle due to epicuticula wax and micrometer-
scale bumps on the leaf
• The epicuticula wax provides the low surface free energy, and the
micrometer-scale bumps brings a large extent of air trapping when
contacting with water, which is essential for superhydrophobicity.

10. (a) SEM micrographs (shown at three magnifications) of lotus (N. nucifera) leaf surface, which
consists of microstructure formed by papillose epidermal cells covered with epicuticular wax
tubules on the surface, which create nanostructure (Bhushan et al. in...
Bhushan B Phil. Trans. R. Soc. A 2009;367:1445-1486

11. Diagram summarizing the connection between roughening and
self cleaning. While on smooth surfaces the particles are mainly
redistributed by water (bottom), they adhere to the droplet
surfaces and are removed from the leaves when the droplets roll
off

12. Technical Applications
• Treatments, coatings, paints, roof tiles, fabrics and other
surfaces that can stay dry and clean themselves in the same
way as the lotus leaf.
• Super-hydrophobic coatings comprising Teflon
microparticles have been used on medical diagnostic slides.
• Self-cleaning glasses installed in the sensors of traffic
control units.
• Lotus effect superhydrophobic coatings applied to
microwave antennas can significantly reduce rain fade and
the buildup of ice and snow.

13. Gecko’s Sticky Feet
• Geckos are lizards belonging to the
infraorder gekkota.
• Can cling to any surface at any orientation
• Can walk on smooth and rough surfaces
• Upside down on a glass surface
• Walk on a dirty or wet surface maintaining
full contact

14. What makes it possible?
• At the initial study people thought that
friction and glue are the reasons.
• Geckos lack glandular tissue on their toes,
so sticky secretions were ruled out early in
the study of gecko adhesion.
• The friction hypothesis was also dismissed
quickly because, by definition, friction only
acts in shear; therefore, it cannot in itself
explain the adhesive capabilities of geckos
on inverted surfaces.

15. • Anton Haase first suggested that geckos stick by intermolecular
forces.
• Remarkable toes.
• Gecko toe is crossed by ridges covered with hair like stalks
called Setae , which branch into hundreds of tiny endings called
spatulae.

17. Small ridges called ‘Scansors’
◦ Numerous ‘Setae’ projections
◦ Setae - 100 µm long, 5 µm diameter
◦ Spatulae (200nm wide projections)
◦ These structures provide essential shear force
and adhesive force.
◦ So, In order to study scientists used a newly
developed microsensor to measure the
adhesive force (which resists pulling) and
shear force (which resists sliding) of an
isolated gecko seta.

19. • When they first tried to measure these forces,
the resistance to sliding was not more than
what they expected from plain friction.
• It wasn't until they oriented the seta correctly
that they discovered the importance of specific
motions in getting the seta to stick.
• Slightly pressing the seta against the surface
yielded a shear force of about 40 micro
newtons. Combining the preload with 5
micrometers of displacement (drag) gave an
even larger shear force.

20. • Around 6.5 million setae on a gecko feet could
generate 1,300 newtons of shear force enough
to support the weight of two medium-sized
people based on measurements from single
setae. These numbers suggest that a gecko is
only attaching 3 percent of its setae in
generating the strongest force (20 newtons)
measured in whole-animal experiments.
• But gecko is only attaching 3 percent of its
setae in generating force.

21. • Geckos could use it to withstand tropical storms,
resist predator attack or recover their grip after
a drop.

23. • A few years ago, they observed that simply
increasing the angle between the seta shaft
and the substrate to 30 degrees causes
detachment. As this angle increases , the
increased stress at the trailing edge of the seta
causes the bonds between seta and substrate
to break.
• In this way attachment and detachment
process occurs and it moves fastly.

24. • Using this technology scientists are trying to
create artificial, gecko like adhesives.
• They made good progress toward fabricating
synthetic spatulae.But if we compare it with
gecko standards still they are primitive.

25. Water Striders
Water striders able to walk on water for a
number reasons like
• Surface area
• Gravitational forces
• Surface forces(van der waals forces)
• A waxy(hydrophobic) surface on their legs
• Most importantly micro hairs on their feet
are ‘nano-groovy’.

26. • A large water-repellent force was produced
by nanostructures on the water strider’s
leg.

27. Butterfly Wings
Nature uses light on Nano scale

28. What makes colour ?
Three possible reasons for colour :
1. Pigment : If colour is due to pigment , it never changes. For
eg . a plant leaf.
2. Scattering of light.
3. Iridescence.
Chemical Colour and structural colour.

29. Case of Butterfly
The wings of Butterflies often display extra ordinary colours which
are a consequence of the wings’ surface and its interaction with
light.
It also exhibits the phenomenon of IRIDESCENCE.

30. IRIDESCENCE
• Physical Colour
• Interaction of light with physical structure of the surface.
• Structures must be nanosized . ( Visible light : between 300-
700 nm.)
• This interaction of light with nano-rough surface can lead to
constructive or destructive interference.

31. IRIDESCENCE
• Colour , intensity and angles of iridescence depends on
thickness and refractive index of the substrate, and on the
incident angle and frequency of incident light.
• Opals : Natural iridescence : packed silica spheres in the nm
range, uniform in size and arranged in layers ( appropriate
conditions for interference.)

32. Phenomenon of
iridescence in butterflies
• Wings : rows of scales arranged like tiles in a roof.
• Each scale is about 70*200 micrometer wide
• Smaller structure on its surface : very intricate and highly ordered nm
organisation of ridges
• Each ridge is about 800 nm wide
• The spaces between them form natural photonic crystal that can
generate cons/dest interference.

33. SEM Analysis of Wings
• Shows even more intricate structure called
SETAE : looks like fir trees
• About 400 nm long, responsible for producing
constructive interference in blue wavelengths
which generates strong blue colour.

34. Super hydrophobicity and
Self cleaning property
• The morpho butterfly’s wing structure also exhibits
another“remarkable” nano-phenomenon— it is waterproof.
• super-hydrophobic - minimization of contact rendered by the
apices of the triangular ridges and that the chitin material
is hydrophobic.
• Roughened hydrophobic surfaces have air filling the
interstitial spaces thereby reducing the liquid-to-solid
contact area.
• Water then tends to attract each other better forming larger
and larger droplets
• Roughened hydrophilic surfaces act in an opposite way: they
enhance water adsorption.

36. Applications
• Production of photonic crystals.
• Wrapping foils, decoration paper, hair sprays and, nail
polish as well as thin films for light emitting diodes and
photonic crystal lasers .
• Textile Industry : to create a new pale blue iridescent fabric.
The fabric is a multi-layer construction containing similar
refractive indices: 61 layers of nylon 6 (n=1.60) and
polyester (n=1.55), each with a thickness of about 70-90 nm).
• These applications may even find that “photonic crystal
diodes and transistors will eventually enable the
construction of an all-optical computer”

37. Toucan’s Beak: Strong a
and light
• Despite its large size (a third of the length
of the bird) and considerable strength, the
toucan beak comprises only one twentieth
the bird’s mass.
• While the large strong beak is useful in
foraging, defense and attracting mates, its
low density is essential for the toucan to
retain its ability to fly.

38. The exterior of the beak is made up of overlapping tiles of keratin, the
sulfur-containing fibrous protein that makes up hair, fingernails, and
horn.

39. The interior of the beak is constructed of a rigid foam made of a
network of calcium-rich bony fibers connected by membranes. The
membranes are similar in composition to keratin

40. Applications
• Automotive panels that could protect passengers in crashes.
(as the beak's sandwich structure also behaves as a high
energy impact-absorption system.)
• Construction of ultra light aircraft components.