2. Nanotechnology-A Boon

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Nanotechnology in High Performance Paint Coatings

A.S. KhannaCorrosion Science and Engineering

Indian Institute of Technology,Bombay, India

Abstract : There is hardly any technology that has attracted an immense interest in a shortestspell of a few years. Whether it is materials development, chemistry, physics or engineeringsciences, there are ample examples where nano-science or technology has created sign of

positive developments. Chemical Industry has played a very important role in developing notonly nano-materials but also make use of them in various applications. One field wherenanotechnology has created a ripple is the paint coatings. Whether it is the improvement ofchemical resistance, erosion and abrasion resistance, resistance to U.V. light, anti-foulingproperties, nano-modified paints have shown great potential in several industrial applications.

Key words : Nano-modified paints, Anti-fouling properties, High performance paint coatings

Introduction :

Small is beautiful is very famousstatement of past but now it has to bemodified by small is not only beautiful butpowerful too. It is an age of nanotechnologywhere every thing is going smaller and smallerto create big impression. Nanotechnology isone of hottest field which is able to drawattention from all over the world, and it haspotential to outdate most of the technology

existing today. Because of its great applicationin future, chemists, physicists, biologist andall other scientist from renowned fields areputting their heads together, and targetingwhat promises to be a new IndustrialRevolution. Nanotechnology will leavevirtually no business untouched. The potentialof creation of materials from building blocksthe size comparable to virus will havetremendous potential. Whether Autos orairplanes, computers or chips, medicines or

cosmetics, chemicals or coatings,construction and energy all of theseindustrial sectors, and many more, are facing

the heat of nanotechnology and going tobenefit immensely from its application.

What is Nanotechnology?

Nanotechnology refers a wide rangeof scientific or technological phenomena thatfocus on the properties of the nanometerscale (around 0.1-100 nm). It is the scienceof developing materials by controllingindividual atoms and molecules to create

devices that are thousands of times smallerthan current technologies permit in order toimpart them with special electrical andchemical properties. The basis of thistechnology is to change the inherentproperties of material like color, abrasion,conductivity etc by reducing its size withoutchanging its chemical composition.Nanotechnology is expected to make asignificant contribution to the fields ofcomputer storage, semiconductors,biotechnology, manufacturing , energy,

chemical and coating industry.

In coming future, this highly potenttechnology will allow us to arrange atoms

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and molecules in most of the ways permittedby physical law. It exploits characteristiceffect, which occurs in the transition zonebetween the atomic and microscopic level.

It will give us a ability to completely controlthe structure of materials and developingcomplex objects with molecular accuracy.The best part of nanotechnology is that itmakes it possible to manipulate individualatoms on surfaces using a variant of theatomic force microscope along withinfluencing wave like properties of electroninside matter by varying nanometer scale. Allproducts are made from atoms and theirproperties depend on the arrangement of

atoms. In future, it will be possible tomanufacture products which are ultimate inprecision; the finest features will be madefrom individual atoms and molecules. Thediversity of products will be mind blowingand it will be possible to make almost anyarrangement of atoms consistent with basicprinciples and laws.

Unique Properties of Nanoparticles

Size of nano particles are smaller towave length of visible light.

Forces like Vander wall, electronresistance and magnetic force play moredominant role than gravitational force orinertia.

One of the most critical characteristics ofnanoparticles is their very high surface-to-volume ratio, i.e. large fractions ofsurface atoms and thus surfaceproperties dominate bulk properties.

Nanoparticles improves many of desired

properties like chemical and heatresistance, reduction in weight andopacity.

Nanotechnology in Coating Industry

Coating industry is growing day by dayin India and around the globe. Today, coatingnot only serves the purpose of beautificationbut also a means to protect valuable metalsand buildings from corrosion, which almostaccounts for 4% of worlds GNP. All majorpaint and coating companies are investinghuge amounts on their research anddevelopment sector to formulate paints,which is compatible and suitable for todaysaggressive environment. Although, many newformulations of paints and coating have cometo light in recent years, but none is able tofullfull all the requirements in a single

formulation. For example, a coating systemhaving good chemical properties may behandicapped by poor weathering propertiesor flexibility, or one with good flexibility maynot have good thermal stability and marresistance property. Hence, it would be agreat achievement to develop a paintformulation satisfying many of suchconditions. Nanotechnology in paint coatingspromises to fulfill this desire.

Nano coating

Nano-coatings are materials that areproduced by shrinking the material at themolecular level to form a denser product. Theappearance and usefulness of nanoparticlesbrings many advantages and opportunities topaint and coating industry. Coating industryis among the first to tap the potential ofnanotechnology. Addition of nanoparticles tocoatings can upgrade many properties ofcoating system and can producemultipurpose coatings with a little cost

difference. Such coatings, sometimes madeof self-assembling monolayers are applicablein many ways : from scratch resistant

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coatings on glass to self-cleaning surfaces tomoisture absorbing to anti-graffiti andcorrosion resistance coatings. Further, uniquecomposition, better strength and flexibility

along with excellent gloss and transparencymakes nano-coatings even more effective.Many of the nanoparticles like nano- ZnOare non-toxic in nature and thus add anotheradvantage to coating industry.

Nano-coating can be applied in manyways including chemical vapor phasedeposition, physical vapor phase deposition.Electrochemical deposition. Sol-gel methods,electro-spark deposition, and laser beamsurface treatment.

Main Advantage of Nano-coating

Some of the main advantages of nano-coating are:

Better surface appearance.

Good chemical resistance.

Decrease in permeability to corrosiveenvironment and hence better corrosionproperties.

Optical clarity.

Increase in modulus and thermal stability. Easy to clean surface.

Anti-skid, anti-fogging, anti-fouling andanti-graffiti properties.

Better thermal and electrical conductivity.

Better retention of gloss and othermechanical properties like scratchresistance.

Anti-reflective in nature

Chromate and lead free

Good adherence on different type ofmaterials

Scratch Resistance

Many coating surfaces possess lowscratch and abrasion resistance and have tobe modified with scratch resistant additives

to maintain an attractive appearance overlong periods of time. As a result, interest increating protective organic coatings isgrowing.

Scratch resistance of coating can beimproved by using micron sized inorganicfillers, but they cause matt or semi-mattappearance to coating by scattering visiblelight. However, by using nanoparticles,scattering of light can be reduced significantly.Nano powders of particle size around 40 to

60 nm are effective fillers. Nanoparticlessuch as ZrO

2,AlOOH,

SiO

2have been

embedded in UV-curable lacquers, resultingin improved abrasion resistanceNanoparticles have been shown to improvethe mechanical properties even at lowloadings and due to their small particle size,they do not affect the transparency of clearcoats. Scratch resistance also improvedfurther due to homogeneous distribution ofnano particles in polymers. Even a small

amount can retain the appearance of surfacewithout any negative impact on coating andits gloss.

To evaluate the performance of aluminananoparticles as scratch-resistant fillers in atransparent coating, a nanocomposite wasprepared with Nano-alumina dispersed in aUV-curable coating formulation at 30 wt%,with variable levels of alumina particlesbetween 0.2 and 2.0 wt%. Thesecomposites were subjected to a scratch test

by measuring the increase in haze due to thescratches. The performance of the alumina-containing composite coatings was compared



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with the neat coating without aluminaparticles. The results of this scratch study areshown in Figure 1.

The performance of the alumina

nanoparticles in Figure 1 is expressed as Xtimes improvement in scratch resistancecompared with the neat coating. It is evidentthe alumina nanoparticles significantlyimprove the performance of the UV-curablecoating, up to a nine-fold improvement, evenwith very low levels of alumina incorporatedin the composite.

UV Resistance

Photochemical degradation caused byUV rays are common mode of failures of

most of the coating systems. It causes theoxidation and decomposition of polymer filmsalong with inorganic or organic pigments.Organic UV stabilizers also undergodeterioration after certain periods. Usingnanoparticles like titania or zinc oxideimprove UV resistance property by not onlyabsorbing but also reflecting those harmfulrays. Also, they are not easily destroyed by

UV rays and hence can increase the life spanand weather resistance of paints

Hydrophobic and Oil RepellentNature

At present, water and oil repellentsurfaces are being explored due to their self-cleaning properties as they can have widerange of applications like automobile andgreen house glass, bathroom mirrors andbuilding materials too. These kinds of surfacescan be prepared by a combination ofoptimum surface roughening and lowering ofsurface energy. Addition of nanoparticles tocoating systems increases its surface areaand pore volume, which in turn increases the

surface roughness of a surface.Increase in roughness increases the

contact angle of water and other solventssignificantly and hence decreasing the surfacetensions of a surface. Fig. 2 shows, theexcellent water and oil repellency of asurface, coated with nanoparticles incombination with fluoromethyl group.

Fig. 1 : Scratch-resistance performance of NanoDur alumina particles in a UV-curable transparentcoating.



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Fire Resistant Property

Most of the flame retardant coating likeammonium polyphosphate and melamineloose their effectiveness as fire resistant

because of their reduced mechanicalproperties and reduced char formation in fireand hence get easily detached from thesubstrate. Mechanical and chemicalproperties of flame retardant coating can beimproved by incorporating nano-concentrates like nano sized magnesiumaluminum layered double hydroxides (LDH)to different flame retardant coating system.Also, specific amount of nano LDH improvethe fire resistant and char formationproperties of flame retardant coating. Nano

LDH absorbs the heat and send out waterand carbon dioxide when burns and hencelowers the temperature of substrate alongwith enhancement in char formation.

Time period in which back tempratureof the test plate got to 300o C is known asfire resistant time. It is apparent from Figure3 that coating with 1.5% of nano LDH haveincreased fire resistant time significantly .However, limited addition of nano LDHshould be done, otherwise it will start

showing negative results as shown in figurebecause large amount of nano particles canmake strong cross linking network and resultin lamp wick influence. Coating with 3%

nano particle has shown this lamp wickeffect as shown below.

Anti-corrosive Property

Corrosion resistance of a coating getinfluenced by P/B (pigment-binder) ratio. Itis one important factor by which propertiesof coating can be determined and is relatedto transportation of harmful corrosivespecies in electrolyte through the coatingsystem.

Plotting the low frequency Rf with

respect to P/B ratio for different coatingsystems can gives clear picture of relativecorrosion properties at different P/Bloadings.

According to Figure 4 anticorrosiveproperties of coating with optimum level ofnanoparticles show far better results thanconventional coating. Highest value ofR

ffor

nano-coating was at P/B ratio of 0.3 andfor conventional coating, corresponding valueis 1.0, which is much lower from the former.

Fig. 2 : Photographs of water and oil droplets on nanoparticle coated panel



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Fig. 3 : Heat insulation graphs of film retardant coating with different content of nano- LDHs

Because of greater surface activity ofnano particles they can absorb more resinscompared to conventional pigments and thusreduce the free space between the pigmentand the resin. Thus, incorporation ofnanoparticles increase the density of coating,reduces the transport path of corrosive

species and enhance the protectiveperformance. Only optimum amount ofnanoparticles should be added to the coatingsystem to get maximum benefits. Excess ofnanoparticles should not be used as pigmentsas the amount of resin may not be enough towet all the nano-pigments, which may resultin the formation of discontinuous film and inturn give rise to defects in the coating systems.

High Performance Coating

Using nanotechnolgy, it is possible tocreate better pigments and coating systems

that can give UV alternation, transparency tovisible light according to need, along withdifferent colors. Nano-coating can be in

great demand for automobile industry.Arrangement of nano pigments can bechanged in paints by altering electrical field.Thus, paints can change its color as a functionof voltage. This concept can be highlyapplicable for automobile sector. Nano-sizedpigments particle having narrow particle size

distribution packed well at the surface of thefilm resulting in a uniform surface finish. Thisuniform surface complemented by highscattering power of nanoparticles givesexcellent gloss properties to coating systems.

Self-Cleaning

Otus effect (self cleaning surface )ispopular in nano-coating. They check evenvery fine dirt or droplets from beingaccumulated on surface. If nano-coating isapplied to glass surface, nanoparticles willinteract with ultra violet rays, loose down the

dirt particles and than using water, dirt willbe distributed across the surface. So, in suchglasses dirt can easily be washed off.



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Fig. 4 : Coating resistance of coatings vs. P/B after exposure to 3.5%of NaCl for 1000 hours

Fig. 5 : Calculated capacitance of ZnO ( micro and nano sized) based coatings vs. P/B after exposure to3.5%of NaCl for 1000 hours



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Anti-fouling

Nano-coating inhibits the adhesion ofmicrobes and marine fouling organisms.Establishment of nano-structure results in

appreciable reduction in interaction betweengerms and surface. Nano-coating helps inreduction of germs, virus, algae byoligodynamic effect of metal component.

Anti fingerprints Coating

It involves establishment of surface withlow surface free energy followed byestablishing extremely flat surface usingnanoparticles. This kind of surfacesignificantly reduces fingerprints and othercontaminants. As adhesion of fingerprints is

reduced, oxidation will not take place andhence increases durability. Also, time toclean the surface will reduce significantly.

Hydrophilic Surface

Nano particles may increase surfacefree energy and thus improve the wettingbehavior of water and other solvents. Theyresults in antifog effect due to maximumspreading of water droplets. They also affectcapillary flow in microstructure

Main Issues in Nano-Coating

Main problem in using nano particles forcoating purpose is dispersion and stabilityof nanoparticles. Agglomeration maytake place because of high surfaceenergy possessed by nanoparticles dueto their large surface area.

Pigments may lose their color onreducing their size to nano level andhence will loose their opacity.

Stable binder is required to inhibitphotocatalytic activities of nano TiO

2.

Hardening problems of ultrafine powder.

Extensive use of nanoparticles may givebirth to new type of environmentalproblems, such as newer type of toxic

materials and other environmentalhazards. Ultrafine particles can catalyzechemical reactions inside body whichmight be dangerous.

Future of Nano-coating.Future of nano-coating is looking very

bright. Advancement in nano-technology willimprove the properties of nano-coating evenfurther. Automobile sector is going to get lotof benefits from nano coating. Goal for futurenano-coating would be to formulate such asystem in which center will have one set ofproperties and exterior will have other set ofproperties.

We have to make coating systems

where nanoparticles are soluble even at veryhigh concentration without increasing theviscosity of system. Making hybrid coatingusing nanoparticles may have most of theproperties required for effective coatingsystem to sustain various environmentalimpacts and others too.

Conclusion

Application of nanotechnology in thefield of coating can facelift the coatingindustry. Properties like corrosion resistance,flame resistant, UV stability, gloss retention,

chemical and mechanical properties areimproved significantly using nanoparticles.Hybrid coating has many properties in singlecoating system and hence can give corrosionprotection without affecting its gloss andappearance. However, nano-coating alsohave some limitations, like agglomeration ofnanoparticles, hardening of ultra fine particlesetc. However, benefits of nano-coating out-weigh its drawbacks. Our aim, therefore,should be to overcome these drawbacksand make even more effective coatingsystems.


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