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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 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.

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. Component of Coating

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. Nanocoating

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. Organic Coating --  Coating with organic binders (organic based materials- eg. Zinc epoxy based coating, zinc rich phenoxy, etc.) 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. 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. Self-cleaning Easy-to clean (anti- graffiti) Antifouling Soft feel Antibacterial DurabilityReproducibility Easy application and cost effectiveness Tailored surface morphology Environmental friendliness Expectations of functional coatings Examples of functional coating

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) Bulk film properties Film/ substrate interface properties Air/ Film interfaces properties

The use of a sacrificial anode such as zinc to protect steel is a long standing and well- known 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. 1) Sacrificial

 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. 2) Barrier effect

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. 3) Inhibition

 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. Silicon- containing 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.

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. 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.

a) Cracks form in the matrix wherever damage occurs. (b) The crack ruptures the microcapsules, releasing the healing agent into the crack plane through capillary action. (c) The healing agent contacts the catalyst, triggering polymerization that bonds the crack faces closed Crack Microcapsule Healing agent Polymerized healing agent

Self-cleaning II – photocatalytic nanotitanium dioxide (TiO 2 ) 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. 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 Produce pairs of electrons and holes. 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 negative- electron (e-) and positive- hole (h+) pair. 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) These photo- produced radicals are powerful oxidizing species and can cause the deterioration of organic contaminants or microbials pieces on the particle surface. MECHANISM of Self-cleaning photocatalytic nanotitanium dioxide (TiO 2 )

Titanium dioxide to reduce pollution and clean the air

Microorganisms represent potential threats for our modern hygienic lifestyle. Viruses Fungi Bacteria 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. Cause to Antibacterial Coatings

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. 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. 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

Auckland University have discovered that the fouling of vessels by marine creatures is greatly increased by the underwater sounds generated by the vessels themselves. Fouling of hulls is a major problem for world shipping. Application of antifouling paint to a ship hull

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. 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. Nanopolymer Coatings

Pregnancy test- Detects the hCG protein in urine. Glucose monitoring device (for diabetes patients)- Monitors the glucose level in the blood.

Self-assembled nanophase (SNAP) Coating

SNAP - potential replacement for chromate- based 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. SNAP - potential replacement for chromate- based 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 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). 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). BEFOREAFTER

Conventional Coating System

SNAP Coating System

Nanoparticle/Fillers For Coating A microscopic particle with at least one dimension less than 100nm. What is nanoparticle??

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 ) Method for Coating

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 3 samples containing different amount of clay (1.3 and 5%) were prepared 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 2. Epoxy-clay nanocomposite coating TiO2 Nanoparticle Dispersed In An Epoxy Resin (M.R.Bagherzadeh et al, 2007)

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 dispersion of nanoparticles in the films effects on the properties of resultant powder coatings was greatly This method can be a reference to make other kinds of nanoparticle modified powder coatings The tensile properties and neutral salt spray corrosion resistance of the modified coating was improved Method of in situ and inclusion polymerization is effective way to disperse nano-caco3 in the 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.

1. What are the differences between conventional coating and nanocoating? Q & A…… 2. What are the method used in the preparation of self-assembled nanophase coating?

Answer Question 1: Conventional Coating Vs Nanocoating Conventional coatingNanocoating 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

COATING APPLICATION Dip coating SNAP SOLUTION MIXING Cross-linking agentSurfactant SOL-GEL PROCESS Hydrolysis Condensation Answer Question 2: Preparation of SNAP (Self- Assembled Nanophase Protection)

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. SNAP Procedures

2.0 Coating technique 2.1 Processing or coating for organic coating Spray coating

Dip coating Stages of the dip coating process: dipping of the substrate into the coating solution, coating of substrate (wet layer ) by solvent evaporation Plastic dip coating Dipping Wet layer formation Solvent evaporation

Conductive nanocoating on textiles  atomic layer deposition(VCD) 2.2 Processing for inorganic and hard coating