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Carbon Nanotube and Paints

Nitin Raibole, 
The author is a Technical Office at Kansai Nerolac Paints

Carbon nanotube is tube-like structure that results from a special arrangement of carbon atoms. Specifically, they are fullerene-related structure that consists of grapheme cylinder close at either end with caps containing pentagonal ring.

In order to understand the structure of a nanotube, we start from the structure of grapheme, which consist of a layer of a carbon atom arranged in a hyneycomb structure. These honeycomb layers are stacked on top of each other. During the formation of graphite, sp2 hybridisation takes place where three hybrids sp orbital are formed at 120˚ to each other within the plane. The remaining P bond out of plane and much weaker than the in plane bond. Carbon nanotubes (CNs) represent attractive possibilities for developing new; strong composite materials in as much as different studies have demonstrated that both single walled nanotubes (SWNTs) and multiwall nanutubes (MWNTs) have outstanding high Young’s modulus, stiffness, and flexibility. However, despite the many reports published in CN composites with a polymeric matrix, only few papers have involved chemical groups to effectively improve the transfer o mechanical loads from the matrix to the nanotubes.

Structure of carbon nanotube

Carbon nanotubes have been fortuitously discovered in 1991 by Sumio Lijima who found it out between secondary products during fullerene synthesis. In fact carbon nanotubes are fullerene related structure which consist of graphene cylinder closed either end with a sort of semi-fullerene. Two categories of carbon nanotubes are usually considered single wall nanotubes; multiwall nanotubes.

In the Fig. shown single walled carbon nanotubes whereas at the second figure multi-walled carbon nano tubes with and without interaction between tubes actually carbon nanotubes structure has imperfection that deforms the structure (for example octagonal or pentagonal rings) range of single walled carbon nanotubes diametre is from 1 nm to 10 nm, but the greater number of nanotubes are about 2 nm. Nanotubes are characterized of high length/diameter ratio (10e4 10e5) give the typical great properties of the nano structure materials. Typical parameter of the carbon nanotubes are: diameter and helicities by the rolling vector (n, m)   nanotubes. Between the tubes of multi-walled carbon nanotubes there are weak interaction (lip-lip) seems stabilized growth of nanotubes during synthesis process. Diameter is greater than single walled nanotubes as far as in nm. Structure of multi-walled carbon nanotube has more imperfection than single walled carbon nanotubes. For these reasons single walled carbon nanotubes are considered as the product more valuable than multi walled nanotube and very difficult to synthesize.

The quantity and quality of the nanotubes obtained depend on various parameters such as the metal concentration, inert gas pressure, kind of gas, the current and system geometry. Usually the diameter is in the range of 1.2 to 1.4 nm.

Chemical Properties

  • Nanotubes are composed entirely of sp2 bonds,m similar to graphite.
  • Nanotubes naturally align themselves into “ropes” held together by Van der Waals forces.
  • Under high pressure, nanotubes can merge together.
  • Nanpolar properties: this nonpolarity enables the coupling of membrane-constituent lipids to the surface of the CNT probes.

Synthesis method of carbon nanotubes

There are three main synthesis methods. Obviously there are other techniques. Research centers are working hard to obtain sustainable (low cost) carbon nanotubes.

Carbon is generally produced by three main techniques, arc discharge, laser ablation and chemical vapour deposition. In arc discharge, a vapour is created by an arc discharge between two carbon electrodes with or without catalyst. Nanotubes self-assemble from the resulting carbon vapour. In the laser ablation technique, a high-power laser beam impinges on a volume of carbon – containing feedstock gas (method or carbon monoxide). At the moment, laser ablation produces a small amount of clean nanotubes, whereas arc discharge methods generally produce large quantities of impure material. In general, chemical vapour deposition (CVD) results in MWNTs or poor quality SENTs. The SWNTs produced with CVD have a large diameter range, which can be poorly controlled. But on the other hand, this method is very easy to scale up.

ARC Discharge

The carbon nanotubes were produced using the arc discharge evaporation method similar to that for the fullerene synthesis.

The carbon needles ranging from 4 to 30nm in the diameter and up to 1 mm in length, were grown on the negative end of the carbon electrode used for the direct current arc discharge evaporation of the carbon in an argon fuelled vessel.

Two carbon electrodes are used in the carbon arc-discharge technique to generate an arc by DC current. The electrodes are kept in a vacuum chamber and an inert gas is supplied to the chamber. The purpose of the inert gas is to increase the speed of carbon deposition. Initially, the two electrodes are kept independent. Once the pressure is stabilized, the power supply is turned on (about 20 V) and the positive electrode is then gradually brought closer to the negative electrode to strike the electric arc. On arcing, the electrodes become red hot and a plasma forms. Once the arc stabilizes, the rods are kept about a millimeter apart while the CNT deposits on the negative electrode. The power supply is cut-off and the machine be is left for cooling once a specific length is reached. Arc-discharge technique produces high quality CNTs. While SWNTs can only be grown in presence of a catalyst, MWNTs do not need a catalyst for growth. MWNTs can be obtained by controlling the pressure of inert gas in the discharge chamber and the arcing current. The byproducts are polyhedron shaped multi-layered graphitic particles in case of MWNTs. High quality MWNTs having diameters in the range of 2 to 20 nm and lengths of several microns at the gram level were synthesized for the first time by Ebbesen and Ajayan. A potential of approximately 18 V and a helium pressure of about 500 Torr was applied by them. Analysis by transmission electron microscopy (TEM) revealed that the nanotubes consisted of two or more carbon shells. The MWNTs produced by arc-discharge method were highly crystalline and were bound together by strong vander Waals forces. SWNTs with diameters 1 nm were synthesized by new functionalities like improved mechanical properties, anti-static behavior or electrical conductivity are desired. To achieve this several materials can be incorporated into the coating film. For enhanced electrical conductivity, substances like copper or silver particles, conductive organic polymers, or carbon black can be used. In many cases, such materials have to be used in the form of nanoparticles to achieve even distribution inside the film and low percolation thresholds.

There are several synthesis routed known to produce such nanoparticles, but they often result in either low yields or in materials that need further processing to show optimum performance. This can lead to high material prices, and in combination with increasing raw material costs, the overall costs can become prohibitive for some applications. An example of this would be the use of silver. The average price of silver has been steadily increasing during the last few years, and silver nanoparticles are even more expensive. For coatings applications, most companies now focus on non-metallic compounds, like carbon materials, achieve electrical conductivity.

Carbon exists as different allotropes, f dir example diamond, graphite, fullerenes and carbon nanotubes. While diamond consists of sp3 hybridized carbon with a cubic crystal lattice, all other known allotropic forms contain sp2 hybridized carbon atoms, and thus they are preferred for electrical conductivity. Since their observation in 1991 by lijma, carbon nanotubes have been the focus of considerable research. 1 Scientists have since reported remarkable physical and mechanical properties for this fascinating allotrope of carbon.

From unique electronic properties to mechanical properties that exceed any current material, carbon nanotubes offer tremendous opportunities for the development of new material systems. In particular, the excellent electrical conductivity of carbon nanotubes combined with their high aspect ratio offer potential for the development of functional coatings. This article reports on recent advances in using additives based on carbon nanotubes to enhance the electrical conductivity of several coating systems.

Recent development as an example in Nanotechnology

BIPHOR is a new family of aluminum phosphates or polyphosphates made by a patented wet chemistry process. It is a “green chemistry,” zero-effluent product made under mild temperature and pressure conditions that do not create any environmental problems during the fabrication process.

Due to its chemical nature, BIPHOR residues in the paint industry or in the final user location many be sadly discarded in the environment as a fertilizer component. It is produced as slurry as well as a dry powder. In both cases it is easily dispersed in water, forming stable dispersions that have stable rheological properties.

Following are some applications:

  • A pair of nanotubes can be used as tweezers to move nanoscale structures on surfaces.
  • Sheets of SWNTs can be used as electromechanical actuators, mimicking the actuator mechanism present in natural muscles.
  • SWNTs may be used as miniaturized chemical sensors. On exposure to environments, which contain No2, NH3 or O2, the electrical resistance changes.
  •        Interacting light element
  •        X-ray device
  •        Data storage (memory)
  •        Field emission display

Medical applications:

  • Drug delivery system
  • Artificial muscles

Other application

A new discovery in the world of nanotechnology led to the production of a hard wearing and fire proof paint, by replacing the soap used to stabilize latex emulsion paints with nanotech sized clay armor. Latex is used in paint because it solidifies by coalescence of the polymer particles as the water evaporates and therefore can form films without releasing potentially toxic organic solvents in the environment.

The method developed by researchers at the University of Warwick’s Department of Chemistry, replacing the traditional use of soap additions to overcome one major problem in latex paints, the polymer parts of the paint’s aversion to water.

The university of Warwick chemistry researchers led by Dr Stefan Bon created a new and simple technique for stabilizing the paint and making it work, by individually coating the polymer particles used in such paintings with a series of nanosized Laponite clay discs.

It’s these disks that create a layer of armor atop of the individual polymer latex group and they can be applied with presently available industrial paint manufacture equipment. Having a diameter of only 1 nanometer (a nanometer is one billionth of a meter), the clay disks are individually small but extremely resistant as an ensemble.

Another advantage of these Laponite clay disks, in addition to being an efficient alternative to soap, is their ability to produce highly wear-resistant and fire proof paints. The team envisions numerous industrial applications for their new process, like highly sensitive materials for sensors.

They say that they can burn away the polymer cores of the armored particles within a closely packed sample, to produce just a network of nanosized connected hollow spheres which provide an extremely useful surface area in a very small space.

This is exactly the characteristic required by compact but highly sensitive sensors to be produced in the near future.

Advantages of carbon nanotube in paints

  • The advantages of using carbon nanotube array as  dry adhesive material allowing reproducing biological adhesion structure and generate fairly strong adhesion strength.
  • If can bend repeatedly with large deflection without failure which makes them suitable as a reusable or re-attachable dry adhesive.
  • The carbon nanotube however acts as a quasi one dimensional path and possess no called bulk therefore power supply voltage can be reduced linearly as a function of channel length.
  • The carbon nanotube is versatile material with outstanding electrical properties that exceeds those of semiconducting silicon.
  • It requires less power, dissipate less heat, emerging at a faster rate and obtain enabling scalability.

Nanotechnology VOC free wall paints

The implementation of nanotechnology components into wall and façade coatings created some products which architects and building owners have been waiting for. These high-tech products make it possible, by simply replacing conventional wall paints, to achieve better energy ratings for buildings, better indoor air quality and fewer allergy-related illnesses.

Nanovations has teamed up with a leading paint manufacturer to bring to the Australian market multi functional coatings for buildings and constructions, producing intelligent coatings which meet the highest standards of quality and add real value and benefits for professional applicators and building owners and are now able to present functional coatings with exceptional properties and product characteristics that have not been possible before with the help of the carbon nanotubes.

The German manufacturer is uncompromisingly selecting the highest possible quality of raw materials while paying great attention to environmental issues.

Thanks to the joint venture with of a number of leading scientific institutes, the products represent the combination of proprietary knowledge and the latest scientific discoveries, in the field of nanotechnology and coating technology.

Conclusion

To increase the conductivity of coatings, carbon nanotubes can offer an interesting alternative to the classical conductive pigments like carbon black or metallic particles. To get the optimum benefit from this fascinating material they should be incorporated into the coating in the form of dispersions to guarantee optimum distribution. In addition, the right wetting and dispersing additives have to be used to enable percolation and compatibility with the coating matrix. Further investigations manufacturers to predict the interaction between coating ingredients and the carbon nanotubes and the resulting performance.


Nano Tv