domingo, 31 de enero de 2010

What are Nanocomposites?


What’s Nanotechnology?

This world as we are living now is getting synthesized smaller each day. The word which was described impossible is becoming possible now. Let me thank those mighty brains before I begin this short summary on nanocomposites. Nano technology is a very interesting subject which governs the human mind now. From smaller devices like IC’s to big buildings nanotechnology has spread its influence. Nanotechnology is the construction and use of functional structures designed from atomic or molecular scale with at least one characteristic dimension measured in nanometers. Their size allows them to exhibit novel and significantly improved physical, chemical, and biological properties, phenomena, and processes because of their size. When characteristic structural features are intermediate between isolated atoms and bulk materials in the range of about one to 100 nanometers, the objects often display physical attributes substantially different from those displayed by either atoms or bulk materials. Thanks for Richard “Rick” Errett Smalley, best known for co-discovering the soccer ball-shaped “buckyball” molecule, died of leukemia on October 28, 2005, at the age of 62. He was a leading advocate of nanotechnology and its many applications, including its use in creating strong but lightweight materials as well as its potential to fight cancer. Upon his passing, the US Senate passed a resolution to honor Smalley, crediting him as the “Father of Nanotechnology.”

Nobelist Rick Smalley. Courtesy Rice University

Nanotechnology indeed has many superior levels of classification. One of a kind is nanocomposites. Let’s now discuss what the nanocomposites materials are and what its controversial application is.


Nano composites as the name indicate is a multiphase material which has solid particles in its composition within its structure. The dimension wise size will be less than 100nm and also have nano-scale repeating units. They may have compositions of colloids, gels and copolymers. The properties including mechanical, electrical and thermal may differ depending upon the composition of the materials used for the synthesis of the composites. A simple example of a normal composite can be considered – we do have concrete for our houses. What exactly is this concrete? It’s a blend of cement, sand, and metal rod. These composition changes the total property of the material used. It becomes so hard that it can withstand tonnes of weight equally. It’s from this concept we device the idea about the nano composites.

SEM image of nGimat’s typical nanocomposites thin film coating on copper foil for printed wiring board applications.

There are certain size effects which govern the property of these materials:
• Less than 5nm for catalytic activities.
• Less than 20nm for making hard magnetic materials.
• Less than 50nm for refractive index changes.
• Less than 100nm for achieving super magnetism, mechanical strengthening or restricting matrix dislocation movement.

Nano composites are naturally found in nature too. It’s found in abalone (small or very large-sized edible sea snail) and bones.

Advantage of using the nanocomposites:

• Greater tensile and flexural strength for the same dimension of plastic part
• Reduced weight for the same performance
• Increased dimensional stability
• Improved gas barrier properties for the same film thickness
• Flame retardant properties
• Improved mechanical strength
• Higher electrical conductivity
• Higher chemical resistance

Classification of nanocomposites:

There are basically two modes of classification for nanocomposites. They are the organic and inorganic nanocomposites. So many efforts are taken by the research people to take control over nanostructures by synthetic approaches. The properties of the nano composites not only depend upon the individual parent compositions but also on their morphology and interfacial characteristic.

As we have discussed above on the classification of the nanocomposites the inorganic components can be 3 dimensional framework systems such as zeolites ; two dimensional layered materials such as clays, metal oxides, metal phosphates, chalcogenides and even one-dimensional and zero-dimensional materials, such as (Mo3Se3-)n, chains and clusters.

Industry Applications for Nanocomposites

Experimental work has generally shown that virtually all types and classes of nanocomposite materials lead to new and improved properties, when compared to their macrocomposite counterparts. Therefore, nanocomposites promise new applications in many fields such as mechanically-reinforced lightweight components, non-linear optics, battery cathodes and ionics, nanowires, sensors and other systems.
Organic/Inorganic Nanocomposites and Lamellar Nanocomposites

The general class of organic/inorganic nanocomposites may also be of relevance to issues of bio-ceramics and biomineralization, in which in-situ growth and polymerization of biopolymer and inorganic matrix is occurring. Finally, lamellar nanocomposites represent an extreme case of a composite in which interface interactions between the two phases are maximized.

Benefits of Studying the Interactions of Nanocomposites

Since the remarkable properties of conventional composites are mainly due to interface interactions, the materials dealt with here could provide good model systems in which such interactions can be studied in detail using conventional bulk sample (as opposed to surface) techniques. By judiciously engineering the polymer-host interactions, nanocomposites may be produced with a broad range of properties.
The Two Types of Lamellar Nanocomposites: Intercalated Nanocomposites and Exfoliated Nanocomposites
Lamellar nanocomposites can be divided into two distinct classes, intercalated and exfoliated. In the former, the polymer chains alternate with the inorganic layers in a fixed compositional ratio and have a well defined number of polymer layers in the intralamellar space. In exfoliated nanocomposites, the number of polymer chains between the layers is almost continuously variable and the layers stand >100 Å apart. The intercalated nanocomposites are also more compound-like because of the fixed polymer/layer ratio, and they are interesting for their electronic and charge transport properties. On the other hand, exfoliated nanocomposites are more interesting for their superior mechanical properties.

Applications of nanocomposites and some case studies

Now let’s discuss some brief applications of nanocomposites in the real field.

1. Aerospace application for Epoxy Layered-Silicate Nanocomposites

Researchers have made relatively awesome discoveries on nanocomposites over the last decade, ever since the pioneering work on nanocaly by the company Toyota. The dispersion of the silicate nanolayer with its high aspect ratio, large surface area, and high stiffness within a polymer matrix results in significant improvement of the properties of polymeric materials, including mechanical properties, barrier properties, resistance to solvent swelling, ablation performance, thermal stability, fire retardancy, controlled release of drugs, anisotropic electrical conductivity, and photo activity.

Layered-silicate nanocomposites have great applications, ranging from automotive and aerospace to food packaging and tissue engineering. Epoxy materials are widely used in adhesives, coatings, composites and electronics. These are also used in designing of aircraft parts too. The aerospace epoxy used in the study is made from Shell Epon 862 with Epi-Cure curing agent W.

This epoxy system has a high glass transition temperature (Tg), good mechanical and physical performance characteristics, and low viscosity, and involves non-4, 4’-methylenedianiline aromatic amines. The properties of the developed composites were studied through SEM and TEM.

In addition, epoxy nanocomposites as primer layer for aircraft coatings for improved anticorrosion properties are used.

Researchers are going on in the field of aircraft industry too. High performance composites are used in fuselage sinks in aircrafts. This technology was readily tested on the aircraft named Cirrus Aircraft SR22.

These were the design results they formulated.

Design Results:

• A decision to retool provides the opportunity to redesign parts for more streamlined processing.
• When laminate and core schemes are re-engineered, more consistent layups result.

Parts consolidation and greater functionality in the fuselage skins significantly reduce overall fabrication time.
The fuselage skins were a target for the company’s redesign decisions. In their earliest form, all Cirrus fuselages were produced in two halves, left and right, via wet layup. The fuselages included the vertical tail fin. According to Bergen, the left/right split simplified both tool and part construction: “The lengthwise split puts the bond joint at the middle of the windshield, which is not great, but integrates the vertical stabilizer into the skin moulds, which simplified tooling.” A top/bottom split would have put the bond joint through the door openings, significantly complicating door details.

The company named OEM Israel Aerospace Industries and North Coast Composites have used composite materials for the rudder of such aircraft for making it more stable. The figure below show the rudder developed by these company for the aircraft.

This screen shot of a rudder mold tool shows one stage of the deflection analysis completed during early mold design stages. NCTM determined to machine the primary tools from 6-inch/152.4 mm minimum-steel plate, a design decision that, under 240,000 lb (108,862 kg) of injection pressure (from injection), would limit mold deflection under pressure to less than 0.0025 inch (0.064 mm). Source: North Coast Composites.

2. Application of nanocomposites in electronics

High conductivity nanocomposites have been developed by research people now. The scientist from Iran and Azerbaijani were under this. TEHRAN (INIC)- The Iranian Researchers in cooperation with their colleagues from Azerbaijan Republic, managed to synthesize highly conductive nanocomposites broadly used in the production of toxic gases' sensors and radar wave absorbing coatings. Mohammad Reza Saboktakin, an Iranian researcher synthesised nanocomposites by a specified chemical method with good efficiency. The advantage of the developed material was said that it has the ability of absorbing electromagnetic waves of different frequencies by metallic nanoparticles.

The possibility of synthesizing conductive polymers with diverse melting points for which there was no chance of synthesis by the previous methods, placing of metallic nanoparticles into the polymer structure instead of its surface, the chance of using different polymers as carrier polymer and adherence increase, mechanical and thermal resistance of synthesized nanocomposite, and the easy and cheap preparation of raw materials.
Conductive nanocomposites are capable of conducting electric current well owing to the electric charges in their structure. This phenomenon is called 'doping phenomenon'.

Polyaniline, polythiophene, polypyrrole, similar heterocycles and common polymers, which can be used for making conductive nanocomposites, are of most importance in this research.

Saboktakin stressed that the product has applications in the production of toxic gases' sensors in petroleum, gas, and petrochemical industries, the production of wave absorbing coatings especially radar wave ones and the production of conductive coatings etc.

Polycarbonates which is an insulator can be made conductive

Polycarbonates, the inexpensive plastics known for their excellent optical and mechanical properties, could in future, find applications into newer and more important horizons. Polycarbonates are tagged as poor electrical conductors, but a research team from University of Houston (UH) has altered this very property by adding carbon nanotubes to them thereby resulting in highly conductive nanocomposites.

The team has come up with a strategy to achieve higher conductivities using carbon nanotubes in plastic hosts than what has been currently achieved. By combining nanotubes with polycarbonates, the team was able to reach a milestone of creating nanocomposites with ultra-high conductive properties. Shay Curran, associate professor of physics at UH demonstrated ultra-high electrical conductive properties in these plastics by mixing them with just the right amount and type of carbon nanotubes. As a result, the inexpensive plastic used to make optical discs will feature in high-end military aircrafts to shield them against build up of electrical charges and pulses which can lead to significant failures. Additionally, by modifying the amount of carbon nanotubes added to the polycarbonate-nanotube mix, the electrical conductivity of the nanocomposite could be changed from that of silicon to a few orders below what is achieved by metals.

This feat achieved by UH team perfectly lays groundwork for further things to come. The next step of this research is to develop ink formulations to paint these polycarbonate nanocomposites onto various electrical components. Generally, metal plates are used to dissipate electrical charge in aircrafts. The development of polycarbonate-CNT composite paintable ink could replace metal plates owing to its lightweight properties. This will finally lead to a much lighter aircraft requiring comparatively lesser fuel. Another key component of this latest research is that pristine nanotubes disbursed in this polycarbonate were found to possess an even higher conductivity than acid-treated carbon nanotubes. Traditionally, the tubes are solicited, or treated with acid, to clean them and remove soot to get a higher conductivity. This, however, damages the tubes and exposes them to defects. Instead, Curran and his group were able to centrifuge, or swirl them. This takes a little longer, but increases the potential to have higher conductivities.

While using metal plates for electrostatic dissipation in aircrafts and other electronic devices certainly adds weight and increases costs while remaining rigid. Taking this into perspective, the development of paintable ink formulations of polycarbonate-nanotubes nanocomposites could be well greeted by the industry due to its obvious benefits of low cost, weight reduction and higher efficiency.

Nanocomposites applications in displays and electronics

We have two main classifications of nanocomposites.
• Structural
• Pressure sensitive
To form a firm bond the structural nanocomposites harden via processes such as evaporation of solvent or water (white glue), reaction with radiation (dental adhesives), chemical reaction (two part epoxy), or cooling (hot melt). The pressure sensitive adhesives (PSAs) form a bond simply by the application of light pressure to attach the adhesive to the adherents.

PSAs adhere instantly and firmly to nearly any surface under the application of light pressure, without covalent bonding or activation. Waterborne pressure-sensitive adhesives solve the problem of meeting environmental regulations that forbid the emission of volatile organic compounds in manufacturing. However, often waterborne PSAs have poor adhesive performance.

Another problem, particularly relevant to display technologies, is how to make an electrically-conducting material that is also flexible and optically transparent. Indium tin oxide is commonly used as a transparent electrode in displays, but it is brittle and prone to mechanical failure or scratching. Adhesives can be made electrically conductive through the addition of metal particles, but then they lose optical transparency, and their adhesiveness is diminished. New research shows that waterborne PSAs containing single-wall carbon nanotubes (SWNTs) meet the requirements of environmental regulations while improving the adhesive performance. The resulting unprecedented combination of adhesion and conductivity properties holds enormous potential for demanding applications in displays and electronics.

To achieve the maximum tack energy (i.e. energy for de-bonding), a PSA must dissipate a large amount of energy on deformation, but it must not have an elastic modulus, E, that is too high. Recent work has shown that using nanocomposite polymer films opens the door to fabricating high performance PSAs.

The adhesives are optically transparent, as shown here. Looking through an adhesive film, the grass looks just as green! The adhesives have a high adhesion energy, while also being electrically conductive. (Image: T. Wang, University of Surrey)

The blending of colloidal polymer particles and carbon nanotubes enables good mixing at the nanometer length scale. The processing is simpler yet more effective than other methods of making nanocomposites. Typically, one must use aggressive sonic agitation and work at low weight fractions to disperse nanotubes finely enough to obtain homogeneous composites.

"Our colloidal methodology allows for a facile, non-destructive method to create composites with weight fractions as high as 20 wt. %, if required" says Keddie's colleague Dr. Alan Dalton, who leads the Nanostructured and Molecular Materials Group at the University of Surrey.

Previous research has described nanocomposite polymer films made from blends of polymer colloids (i.e. latex) and carbon nanotubes. In some cases, the improvements to mechanical properties were minimal because good dispersion of CNTs was not achieved.

"We dispersed the CNTs in water by grafting a hydrophilic polymer (poly(vinyl alcohol)) onto their surface" says Keddie. "They provide a unique combination of properties. The PSAs are optically transparent while also having electrical conductivity (with a value comparable to germanium) plus high adhesion energy in comparison to the polymer alone."

In a probe-tack experiment (left), a spherical (or cylindrical) probe in contact with the PSA surface is removed at a constant velocity. The force to de-bond the probe from the surface is measured. The area under the resulting nominal stress/strain curves (right) indicate the total energy of adhesion. PSAs that contain PVA-SWNTs (blue line) have higher tack energies compared to the pure polymer (pink line). The plateau in the curves corresponds to when there is extensive fibrillation during de-bonding. It is apparent that PVA-SWNTs increase the amount of fibrillation. (Graphics: T. Wang, University of Surrey

3. Nanocomposites in automobiles

The basic idea in implementing the nanocomposites in mechanical stream is the resistant to fracture and the often occurrence of wear and tear of the machine parts. CTN’S used as a blend against plastics can be used for strengthening the portions of the automobiles where higher efficiency is required. As the world is affected by the term pollution the automobile industry are in the idea of developing such a technology which controls the same cost effectively. They make the use of nanocomposites in automobile industry for achieving their so called goals. This gave them idea in going for polymeric nanocomposites.

Owing to their polymeric nature, polymers nanocomposites fit this description. Polymeric nanocomposites are a relatively new class of materials with ultra-fine phase dimensions, typically of the order of few nanometers. Because of their nanometer size features, polymeric nanocomposites possess unique properties, such as enhanced mechanical, impact, barrier and heat resistant properties, compared to other composites.
Combining the unique properties of nanocomposite and recyclable polymers to produce light-weight recyclable and biodegradable polymer/nanocomposite is a great challenge. These compositions were widely used for making the body parts of the automobiles. The industry was mainly concerned over the following aspects

• Weight reduction
• Improved performance
• Aesthetics
• And recyclability

Nanotechnology is already driving changes throughout this industry at nearly every level involving material, components, and systems. Nearly every car produced in the U.S. is said to contain some nanocomposite material, most typically carbon nanotube in nylon blend for use the fuel system to protect against static electricity. Hyperion Catalysis now plans to introduce nanotubes into other resins used in auto fuel systems. A new fluoropolymer/nanotube compound is being used to make O-rings for auto fuel connectors.
An Iranian company managed to utilize PP nanocomposites in four parts of a car, including bumper, hub cap, dashboard, and steering wheel frame. Pishgaman Fanavari Asia Company was inaugurated in 2001 with a pure nanotechnology approach and is one of the first companies involved in this field. One of the products of the company is nanocomposites used in auto industry.

Researchers at Iran Khodro Company (IKCO) in collaboration with their colleagues at SAPCO, two of the largest car producers in Iran, pursue replacing ordinary auto parts with nanotechnology-based ones in order to improve the qualities and reduce costs.

Their nominated parts for modification include windscreen, body paint, interior composite parts, various plastic parts, seat covers, dashboard, and gas tank.

It is proved that such modifications would provide easier and better hygiene level for the internal part of the car.