Nanocoatings Noraiham Mohamad, PhD Faculty of Manufacturing Engineering, Universiti Teknikal Malaysia Melaka

What is 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.

Coating  Coatings are usually applied as multi-layered systems that are composed of primer and topcoat. However, in some cases – for example automotive coating systems, this may vary from four to six layers.  Each coating layer is applied to perform certain specific functions, though its activities are influenced by the other layers in the system.  The interactions among different layers and the interfacial phenomenon play an important role in the overall performance of the multi-coat systems

Type of coating  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.)  Organic Coating- Coating with organic binders (organic based materials- eg. Zinc epoxy based coating, zinc rich phenoxy, etc.)

Inorganic Coating  Silicone (polysiloxane) hard coatings are finishes of superior abrasion resistance and inertness to hostile chemical and environmental conditions.  They consist of several monomers and other ingredients, and the makeup of the formulations varies from manufacturer to manufacturer.  Among the highly varied components are monomeric silanes, dimerized silanes, silane hydrozylates, silaceous materials, leveling agents, flow control agents, cross-linking agents, and catalysts of various types.  Silicone coatings are solvent-borne coatings. Some of the possible solvents are alcohols and glycol ethers. This includes such alcohols as isopropanol, propanol, ethanol, n-butanol, isobutanol, and methanol.

Inorganic Coating  Polysiloxane coatings are applicable to many substrates, but the majority of applications are on nonmetallic surfaces, especially plastics.  Silicone coatings can be dyed or pigmented, but for the most part these coatings are used as clear top coatings.  They have excellent light transmission and actually improve the optical properties of the material that is coated.  Some of the plastics that are used with polysiloxane coatings are polycarbonate, acrylic, polyarylate, polysulfone, vinyls, nylons, polyester, cellulose acetate, cellulose acetate-butyrate, and polyolefins, etc.

Inorganic Coating  Hard silicone coatings are useful as antifog, antistatic photochromic, color-dyed, pigmented, UV absorbing, UV stabilized for exterior exposure, chemical resistance, 5-min curing, and tinted coatings.  Many of these properties can be combined in one coating.  The coatings are used in such diverse areas as the automotive, electronic, computer hardware, architectural and architectural glazing, recreation, sporting goods, protective eyewear, safety, and optical industries.

Organic Coating  Organic coatings are essentially pigment dispersed in a solution of a binding medium.  Binding medium or resin - decide the basic physical and chemical properties of the coating but these will be modified by the nature and proportion of pigments present.  Sole function of volatile component -to control the viscosity of the paint for ease of manufacture and for subsequent application.  Not possible to forecast -what combination of properties a particular formulation will possess and the formulation of paints for specific purpose remain very much a technological art.

Nanomaterials in Coating  The appearance and appliance of nanomaterials brings new opportunities to the coating industry.  Addition of nano-materials to the coatings improves the properties of the conventional coatings and produces new multi-functional coating due to their tiny particle size.

Category of Coating  Coatings are mainly applied on surfaces for decorative, protective or functional purposes, but in most cases it is a combination of these.  3 category:  Decorative Coating  Functional coating  Self-Assembled Nanophase Coating

Functional coating  Functional coatings- systems which possess, besides the classical properties of a coating (i.e., decoration and protection), an additional functionality  This additional functionality may be diverse, and depend upon the actual application of a coated substrate.  Typical examples of functional coatings are:  self-cleaning  easy-to clean (anti-graffiti)  antifouling  soft feel  antibacterial

Functional coating  Typical expectations of functional coatings include:  durability  reproducibility  easy application and cost effectiveness  tailored surface morphology  environmental friendliness

Functional coating  Functional coatings perform by means of physical, chemical, mechanical, thermal and 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), or  at air–film interfaces (antibacterial, self- cleaning)

Coating Techniques

Processing for Inorganic Coating & Hard Coating

Processing for Organic Coating

Sol-Gel Coating (Organic or Inorganic)

Nanoparticles in Sol-Gel  Possible to increase the coating thickness, without increasing the sintering temperature.  Eg. Electrophoreticdeposition of commercial SiO sol on AISI 304 stainless steel substrates leads to coatings as thick as 5 mm with good corrosion resistance  Incorporation of nanoparticles in the hybrid sol–gel systems increases the corrosion protection properties due to lower porosity and lower cracking potential  Can be a way to insert corrosion inhibitors, preparing inhibitor nano reservoirs for self repairing pretreatments with controlled release properties

Example of Nanoparticles in Sol-Gel  Studies showed that sol–gel films containing zirconia nanoparticles present improved barrier properties.  Doping this hybrid nanostructured sol–gel coating with cerium nitrate brings additional improvement to corrosion protection.  Zirconia particles present in the sol–gel matrix act as nano reservoirs providing a prolonged release of the cerium ions  The recent discovery of a method of forming functionalized silica nanoparticles in situ in an aqueous sol–gel process, and then cross linking the nanoparticles to form a thin film

Coating Applications