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WELCOME TO
NANOCOATINGS
WORLD
Coating
A coating is
a covering that is
applied to the surface
of an object, usually
referred to as
the substrate.
In many cases coatings are
applied to improve surface
properties of the substrate,
such as appearance,
adhesion,
wettability, corrosion
resistance, wear resistance,
and scratch resistance
Coating
In other cases, in particular
in printing processes and
semiconductor device
fabrication (where the
substrate is a wafer), the
coating forms an essential
part of the finished
product.
Component of Coating
• Pigment – Pigment are used decoratively as colorant or
functional as anticorrosion or magnetic pigment.
• Binder – The binder bonds the pigment particles to each other
and to the substrate.
• Additives
- Substances added in small proportion to coating
composition to modify or improved properties
• Fillers - Mostly used to extend the volume (low price), to confer
or to improve technical properties.
• Solvent – Liquid consists of several components and dissolved
binders without chemical reaction.
Nanocoating
• Nanocoating are coating that produced by usage of some
components at nanoscale to obtain desired properties.
• Nanocoatings
can
be
categorized
as
nanocrystalline,
multilayer coatings with individual layer thickness of
nanometers, and nanocomposites.
• Nanostructured coatings offer great
potential for various
applications due to their superior characteristics that are not
typically found in conventional coatings.
Classification of
Coating
Properties
Functional
Coating
Self- Assembled
Nanophase
Coating
ORGANIC COATING
Organic: A molecule or compound
that come up with carbon. The
carbon are covalently bonded with
other atoms in the organic
compound. All organic compounds
contain carbon-hydrogen atoms or
C-H bonds.
INORGANIC COATING
Inorganic: A molecule or compound that
come up with no carbon. Some compounds
that contain carbon atom are also
considered as inorganic when they come up
with lack of carbon and hydrogen atoms or
when their carbon atoms are ionically
bonded to other atoms in the compound.
Example or inorganic compounds are
carbon dioxide, carbon monoxide, the
carbonates and cyanides.
Organic Coating -- Coating with
organic binders (organic based
materials- eg. Zinc epoxy based
coating, zinc rich phenoxy, etc.)
All the interesting allotropes of carbon such
as diamonds, graphite, buckyballs and
nanotubes are also considered as inorganic.
Inorganic Coating -- Coating with silicate
based materials (eg.- zinc silicate based
coating) or metal/ceramic based coating
(hard coating of Chromium, TiN, Si3N4,
alumina etc.)
FUNCTIONAL COATING
The term ‘functional coatings’ describes systems which represent other than
the classical properties of a coating (decoration and protection). Functional
coating come up with additional functionality. This functionality depend
upon the actual application of a coated substrate.
Examples of functional coating
Self-cleaning
Easy-to clean (antigraffiti)
Antifouling
Soft feel
Antibacterial
Expectations of functional coatings
Durability
Easy application
and cost
effectiveness
Reproducibility
Tailored surface
morphology
Environmental
friendliness
•
Functional coatings perform by means of physical, chemical, mechanical and
thermal properties.
•
Chemically active functional coatings perform their activities either at:
– Film–substrate interfaces (anticorrosive coatings),
– In the bulk of the film (fire-retardant or intumescent coatings)
– Air–film interfaces (antibacterial, self-cleaning)
Air/ Film interfaces
properties
Bulk film properties
Film/ substrate
interface properties
1) Sacrificial
The use of a sacrificial anode such as zinc to protect steel is a long standing and wellknown industrial practice. The zinc layer on galvanized steel degrades when exposed
to an adverse environment, and this protects the underneath surface. Using a
similar approach, both inorganic and organic resin based, zinc-rich coatings have
been developed to protect a variety of metal substrates.
2) Barrier effect
Polymeric coatings are applied to metallic substrates to provide a barrier against
corrosive species. They are not purely impermeable. Moreover, defects or damages in
the coating layer provide pathways by which the corrosive species may reach the metal
surface, whereupon localized corrosion can occur.
Pigments having lamellar or plate-like shapes (e.g., micaceous iron oxide and
aluminum flakes) are introduced to polymeric coatings; this not only increases the
length of the diffusion paths for the corrosive species but also decreases the corrosion.
The orientation of the pigments in the coating must be parallel to the surface, and they
should be highly compatible with the matrix resin to provide a good barrier effect.
Layered clay platelets such as montmorillonite may also be introduced into organic
resin systems to increase the barrier effect towards oxygen and water molecules,
thereby enhancing the anticorrosive performance of the coating.
3) Inhibition
Primers containing metallic phosphate, silicate, titanate or molybdate compounds
are available as compounds used as corrosion inhibitors to formulate anticorrosive
primers for metallic substrate.
These pigments form a protective oxide layer on the metallic substrates, and often
also form anticorrosive complexes with the binder.
 High thermal-resistant coatings are required for a wide variety of metallic
substrates, including nonstick cookware, barbecues and boilers.
 Fluorine or silicon-based products are used for the products. Fluorinated
coatings are not suitable for high-temperature applications as they
degrade above ~300 ºC and produce toxic by products. Siliconcontaining polymers offer better thermal resistance due to the high
energy required to cleave silicon bonds compared to carbon bonds in
analogous molecules.
 Phosphorus containing compounds function by forming a protective layer
as a glassy surface barrier.
 Expandable graphites also used as fire retardant; these contain chemical
compounds, including an acid, entrapped between the carbon layers.
Upon exposure to higher temperatures, exfoliation of the graphite takes
place and this provides an insulating layer to the substrate.
form an expanded carbonaceous layer
which acts as a protective barrier against heat transfer and hinders the
diffusion of combustible gases and melted polymer to the site of
combustion.
Figure: SEM micrograph of intumescent char obtained on an organic coating.
Consumer prefers to retain the aesthetic appearance of coated
materials and for this reason clear coats used on automobiles must
have good scratch and abrasion resistance.
Scratch resistance can be obtained by incorporating a greater number
of cross links in the coating’s binder but highly cross linked (hard) films
have poor impact resistance due to less flexibility. A less-cross linked
(softer) film will show better performance with regard to other
properties such as antifingerprint and impact resistance but will have
less scratch and abrasion resistance. Thus, correct combination of
hardness and flexibility is required.
Self Healing/Cleaning
Coatings
The recent research in self healing coatings is inspired
by natural healing processes. Self-cleaning coatings, as
the name suggests, have a special functional property,
and today the term Lotus effect. That is, the ability for
a surface to repair itself after naturally occurring or
biological systems.
(a) Scanning electron micrograph of lotus leaf. (b) Schematic depicting the relationship
between surface roughness and self-cleaning. (c) Mechanism of self-cleaning action.
In 1997, Barthelott and coworkers showed that the self-cleaning property of lotus
leaves was due to their specialized surface morphology and hydrophobicity.
This specialized morphology prevents dirt from forming an intimate contact with the
surface, while the high hydrophobicity makes the leaf water-repellent. Consequently,
as the water droplets roll onto the leaf surface, they carry along the contaminants.
Microcapsule
Crack
a) Cracks form in the matrix
wherever damage occurs.
Healing agent
(b) The crack ruptures the
microcapsules, releasing the
healing agent into the crack
plane through capillary action.
Polymerized healing
agent
(c) The healing agent
contacts the catalyst, triggering
polymerization that bonds
the crack faces closed
Self-cleaning II – photocatalytic
nanotitanium dioxide (TiO2)
• Probably the most wide-spread application
ascribed to nanotechnology in the construction
industry. There are already a great number of
buildings worldwide which have been treated
with it.
• Titanium dioxide is hydrophilic due to its high
surface energy, hence water does not form drops
on a surface coated with it, but a sealed water
film instead.
Photocatalyst TiO2 absorbs
UV radiation from
sunlight/fluorescent lamps
These photoproduced radicals
are powerful
oxidizing species and
can cause the
deterioration of
organic
contaminants or
microbials pieces on
the particle surface.
Produce pairs of
electrons and
holes.
The positive-hole of TiO2
breaks apart the water
molecule to form hydrogen
gas and hydroxyl radical.
The negative-electron
reacts with oxygen
molecule to form super
oxide anion. (Both known
as photo-produced
radicals)
Electron of the valence
band of titanium dioxide
becomes excited when
illuminated by light.
The excess energy of this
excited electron promoted
the electron to the
conduction band of
titanium dioxide therefore
creating the negativeelectron (e-) and positivehole (h+) pair.
MECHANISM of Self-cleaning photocatalytic
nanotitanium dioxide (TiO2)
Titanium dioxide to reduce
pollution and clean the air
Bacteria
Antibacterial
Coatings
Microorganisms represent
potential threats for our
modern hygienic lifestyle.
Cause to
Fungi
Viruses
1. Problems of aesthetics
(discoloration of the coating),
2. Risks to health and hygiene,
3. Biofilm development or microbial
corrosion in the case of metallic
substrates.
• The classical biocides function is to either by inhibit the growth of bacteria (biostatic) or
by kill them (biocidal).
• New legislations and the possibility of bacterial mutation have forced coating
manufacturers to seek new alternatives.
• Today, more emphasis is placed on the development of bio-repulsive (without killing)
antibacterial coatings. A wide variety of organic or inorganic biocides are available
commercially and these demonstrate a wide variety of biocidal and biostatic
mechanisms.
Schematic of biofilm formation by microorganisms.
Nitric oxide (NO)-releasing sol–gels as potential
antibacterial coatings for orthopedic devices. Bacterial
infection due to an implanted medical device is a
potentially serious complication, typically leading to
premature implant removal.
These coatings are intended for application onto
biomedical devices to prevent device-related infections
caused by bacterial biofilms.
Antifouling Coatings
Problem:
The microorganisms cause inconsistencies in the coating surface and create friction with
the water. This friction decreases the speed of the vessel and adds weight to the hull.
Both of these factors increase fuel consumption and inflate the cost of maintaining the
vessel. The ideal antifouling coating would prevent marine growth as well as maintain a
long performance life while keeping within strict environmental regulations.
There are two main types of underwater antifouling coatings. Chemical release coatings use biocides, or
chemical toxins that are released into the seawater and prevent marine organisms from attaching to the
surface. The toxins create a barrier that prevents the marine growth. In the past these coatings were
typically copper oxide. Some of the chemicals that give these products their toxic properties include;
cuprous oxide, mercury, copper, arsenic and tributyltin oxide (TBT). Any combination of these chemicals
provides a harmful biocide to the aquatic environment.
Another type of underwater hull coating is an ablative, self-polishing coating system. Ablative systems
prevent marine sea life from attaching sufficiently to the coating surface. The initial coating surface
steadily dissolves in the seawater. As the top layer dissolves, a new smooth layer is left behind to repeat
the process. The rate of replenishment is controlled and constant allowing a uniform transition through
each layer of the coating.
Schematic of critical biofouling stages
Fouling of hulls is a major problem for world shipping.
Auckland University have discovered that the fouling of vessels by marine
creatures is greatly increased by the underwater sounds generated by the
vessels themselves.
Application of antifouling paint to a ship hull
Nanopolymer Coatings
Conducting Polymer
A conductive polymer is an organic polymer semiconductor. They provide pathways for
electronic conduction by doping. Common classes of organic conductive polymers
include: Poly(acetylene)s, Poly(pyrrole)s, Poly (thiophene)s, Poly(aniline)s etc.
Biosensor- Biosensor is an analytical device which converts a biological response into
readable signal. Bio sensor comprises of three components: bioreceptor, transducer and
detector.
Polypyrrole nanocomposites with oxides, especially with Fe3O4 have prospects for use
in corrosion protection of iron.
Glucose monitoring device (for diabetes
patients)- Monitors the glucose level in the
blood.
Pregnancy test- Detects the hCG protein in
urine.
Self-assembled
nanophase
(SNAP) Coating
BEFORE
Conventional chromate conversion
coatings (CCC) work well for iron and
aluminum alloys in terms of their corrosion
protection performance. However, the
strong oxidation properties of chromates
make them a potential lung carcinogen
responsible for the DNA damage.
For primer coating applied sol–gel derived
thin films. Sol–gel films have good
adhesion to both metallic substrates and
organic top coats.
However, they result voids throughout the
solid gel after the drying procedure
(Evaporation process). Besides, they
cannot provide any active corrosion
protection or stop the propagation of
corrosion once corrosion is initiated
(Highly crack-forming potential).
AFTER
SNAP - potential replacement for chromatebased surface treatments on aircraft
aluminum alloys.
This Self-assembled Nanophase Particle
(SNAP) process can be used to form thin,
dense protective organic surface treatment
coatings on Al aerospace alloys. The ability to
design coating components from the
molecular level upward offers tremendous
potential for creating multifunctional
coatings.
The SNAP coating mostly be used as part of a
complete aircraft coating system designed to
protect the aircraft’s aluminum alloy from
corrosion. The coating steps include, in order
of application, surface preparation, surface
treatment (SNAP), primer and topcoat.
Conventional Coating System
SNAP Coating System
Nanoparticle/Fillers For Coating
What is
nanoparticle??
A microscopic particle
with at least one
dimension less than
100nm.
Method for Coating
TiO2 – nanoparticles dispersion in an epoxy
resin matrix
TiO2 – nanoparticles dispersed when sliding
against a smooth steel counterpart
The friction and wear behavior of
nanocomposits sensitive to the dispersion
states of the nanoparticles
The wear resistance could be increased if
the micro structural homogeneity was
improved
1. TiO2 Nanoparticle Dispersed In An Epoxy Resin (Min Zhi Rong et al, 2001 )
2. Epoxy-clay nanocomposite coating TiO2 Nanoparticle Dispersed In
An Epoxy Resin (M.R.Bagherzadeh et al, 2007)
3 samples containing different amount of clay (1.3 and 5%) were prepared
The desired amount of resin and nanoclay was mixed together and
performed in an oil bath (50-70 degree)
The mixture was subjected to sonication for 8-12h
Addition of some additives to epoxy –clay mixture
The stoichiometric amount of the hardener was added to mixture
The clay loading increases the barrier and anti-corrosive properties
increases
The best anti-corrosive performance of coatings was obtained at 3 and 5
wt % clay concentrations
Nanoparticles/Fillers For Coatings
Prepared nanosilica containing coatings by UV
curing of an epoxy system. They found that, surface
properties were modified with an increase on
hardness in the presence of filler.
Finally the strong decrease on water uptake in the
presence of SiO2 was noticed. These nanocomposite
materials can be a good choice for gas barrier
coatings applications.
3. Nano-CaCO3 Powder Coatings Using Epoxy Resin/NanoCaCO3
(H.J.Yu et al, 2006 )
Nano-CaCO3 modified powder coatings was prepared using epoxy
resin/NanoCaCO3 composite by in situ and inclusion
polymerization
Compared with unmodified powder coatings
The tensile properties and neutral salt spray corrosion resistance of
the modified coating was improved
The dispersion of nanoparticles in the films effects on the
properties of resultant powder coatings was greatly
Method of in situ and inclusion polymerization is effective way to
disperse nano-caco3 in the powder coatings
This method can be a reference to make other kinds of
nanoparticle modified powder coatings
Conclusion
Protective coatings perform important functions based on types
of coatings. The application of nanotechnology in the
corrosion protection of metal has recently gained momentum
as nanoscale materials have unique physical, chemical and
physicochemical properties, which may improve the corrosion
protection in comparison to bulk size materials. Significant
work on nanoscale coatings is underway globally in the area of
the area of nanocoating in the way of incorporating
nanoparticles in coating formulation that enhance specific
features.
Q & A……
1. What are the differences between
conventional coating and
nanocoating?
2. What are the method used in the
preparation of self-assembled
nanophase coating?
Answer Question 1: Conventional Coating Vs Nanocoating
Conventional coating
Nanocoating
Micron scale structure
Nanostructured materials
High contact tension between
water drop of and coating layer
Contact tension reduced (water
repellence)
Moisture can penetrate housing
Moisture penetration is minimized
Surface roughness is 5 μm due to
larger particle size
Surface roughness reduce to 1 nm
for better dirt repellence
Physical, chemical, mechanical and
thermal properties
Improved the properties of
conventional coating
Answer Question 2: Preparation of SNAP (SelfAssembled Nanophase Protection)
SOL-GEL PROCESS
Hydrolysis
Condensation
SNAP SOLUTION MIXING
Cross-linking agent
Surfactant
COATING APPLICATION
Dip coating
SNAP Procedures
1.
SNAP solutions were prepared by drop-wise addition of 42.8
glycidoxypropyltrimethoxysilane (GPTMS) and 8.9 ml
tetramethoxysilane (TMOS) to 64.8 ml solution of 0.05 M acetic
acid in doubly distilled deionized (DDI) water.
2.
The application solutions were prepared by diluting the aged
SNAP solution with water and subsequent addition of a
crosslinking agent (DETA) and surfactant.
3.
The final mixture was vigorously stirred and applied to the cleaned
aluminum alloy panels by dip-coating.
2.0 Coating technique
2.1 Processing or coating for
organic coating
Spray coating
Dip coating
Dipping
Wet layer
formation
Solvent
evaporation
Plastic dip coating
Stages of the dip coating process: dipping of the substrate into the coating
solution, coating of substrate (wet layer ) by solvent evaporation
2.2 Processing for inorganic and hard
coating
• Conductive nanocoating on textiles
 atomic layer deposition(VCD)