Polymer nanotube

Carbon nanotubes (NTC) as reinforcement of polymers have been the subject of countless investigations. Equally striking is the large number of research institutes that try to develop them. Spain is no exception.
Pascual Bolufer, Chemical Institute of Sarria (IQS)


The NTC is a ribbon of graphene rolled up to form the nanotube. When cutting a graphene sheet (pictured), will do an angle, ie attaching the NTC chirality. Depending on the angle of cut, the NTC shall become metallic or semiconducting.

Chemical Institute of Sarria (IQS) has since 1994 of the Laboratory of Materials Science, where Dr. Carles Colominas works with nanocomposites, coatings synthesized by chemical vapor deposition and sol-gel technique, wet, for obtain ultra hard materials, with hardness of 10 to 40 times higher than steel. The oldest center in nanomaterials is AIN (Navarre Industry Association) in Cordovil. Let us add the Institute of Science and Technology of Polymers (CSIC), Madrid, AIMPLAS (Institute of Polymer Technology), in Paterna (Valencia), and finally, let me quote a Nanospain (www.nanospain.org). Has 275 research groups and 1,200 researchers.

But industrial and commercial level, where we find a company doing business with nanotechnology? There is an exception that proves the rule. Pere Castell, Nanozar, says that the industry sees nanotechnology as a high risk market, not assumed by it, and that Spain suffers from a lack of highly qualified technical staff. The properties 'miracle' of nanomaterials are a reality, but turning them into industrial success is even more difficult. Progress will be steady but slow.

There are many kinds of nanomaterials, for example, nanoclays (an easy topic for reinforcement of polymers) and carbon nanotubes, one or many layers. The latter are very difficult to handle. Carbon hexagonal networks are curved and closed trivalent, which have a length of several microns. Their diameters range from 1 to 20 nanometers. They were discovered by S. Iijima, Japan in 1991. There are two types: single wall, or mono, and multi-walled, up to 100 layers.

To understand the problem, simply quote the NIMS (National Institute for Materials Science), Tsukuba, Japan. The research teams that have not any business can afford, or the international level. Only the state: high-voltage microscopy and electron synchrotron, among others.
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NTC Nano Tech Institute of the University of Texas.
The nano scale

The chemicals, through bottom-up strategies, have been synthesized molecular materials that have extremely interesting physical properties. The nanochemistry is an invaluable tool for developing even artificial molecular machines. So says Thomas Torres Barley, from their chemistry professor at the UAM. The chemist can offer electronics engineers assembled car systems, like bricks on a molecular scale to build transceivers electronic and electro-optical, much smaller than those of current in use.
The nanochemistry, which manipulates materials at the nanometer scale, between 1 and 100 nm, representing an impact of several orders of magnitude on submicrometer technology, which is the foundation of today's electronics

The nanochemistry manipulates materials at the nanometer, between 1-100 nm. Represents an impact of several orders of magnitude on submicrometer technology, which is the foundation of today's electronics. Their interest is obvious. It involves constructing, from pieces of matter such as atoms and molecules, supramolecular entities at the nanoscale with specific properties. Try to manipulate molecular scale structures and providing them with new properties, not found in conventional materials.

The molecular materials are synthesized separately and organized into some kind of condensed phase, capable of presenting unconventional physical properties. The properties of nanostructured materials depend on the size effects of dimensional changes of the system. Nanocrystalline materials usually consist of crystalline blocks and there is a marked difference with glasses and gels, which are microstructurally homogeneous.

The best energy to work at a molecular switch machine or are photons and electrons. A much-repeated phrase, that Richard Feynman gave on December 29, 1959: There's plenty of room in the bottom.

The strength or hardness of crystalline material, according to Hall-Petch effect depends on the grain size. At any pressure, as grain size decreases, the metal hardens. Young's modulus characterizes the elastic material behavior, according to the direction in which force is applied, and voltage values in the range of complete reversibility of deformation. The value of Young's modulus is defined by the ratio of the voltage applied to the material and the deformation caused. The smaller the grain, the higher the Young's modulus, the greater the force to be applied, so that the metal enters the zone of plasticity.

Shear modulus with the same thing happens: the smaller the grain, the greater the force that must be done to achieve a given deflection.
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NTC French CEA (Atomic Energy Commission).
Thermodynamics suggests that the nanostructures synthesized probably never get the uniformity and perfection of electronic circuits made with silicon crystals

The Hall-Petch effect holds for grains of a diameter greater than 12 nm. For smaller grains hardness decreases. There dislocations within a grain, which spread to nearby grain, and weaken the metal. A smaller, more difficult is the propagation of dislocation and the emergence of metal plasticity. But the practical results are not encouraging, do not confirm the theory. Thermodynamics suggests that the nanostructures synthesized probably never get the uniformity and perfection of electronic circuits made with silicon crystals obtained with conventional lithography. The mere size reduction, by itself, can not provide the expected increase in features.
Nanotubes National Microelectronics Center (CNM)

CNM works in the UK Dr. Adrian Bachtold, who has made some statements that try to summarize here. Try to clarify the quantum properties of the NTC and its behavior in applications. The center has the largest clean room in Spain and with international professional experience. They are concerned with mechanical and electrical properties of NTC. For example, how an electron flowing through the NTC, which is its vibration, or see if there are quantum phenomena and what type.

After the first logic circuit made from nanotubes, seems to have made little progress. More than two decades ago which spoke of the possibility of substituting silicon for NTC, to improve their performance. Until our work appeared in Science in 2001, it was not proven, you could build a logic circuit with a few molecules. That did not mean to appear shortly NTC based computers. NTC is now getting something simple and inexpensive, but its handling remains very complex. Moreover the NTC can behave as metals, semiconductors or superconductors. Recall here that the diamond is pure carbon insulation.
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Three of the four photos show the NTC linking electrodes. Donald Bethune of IBM.
The NTC can be a good option to replace silicon. The properties of NTC are clearly superior to the latter, in phenomena such as conductivity or transductancia

We do not have techniques to efficiently manipulate the NTC. In addition, a random feature on a surface, which forces discover, and it is not easy. The NTC should be in a precise position on the substrate (polymer), which reinforced.

The NTC can be a good option to replace silicon. The properties of NTC are clearly superior to those of the latter. For example, phenomena such as conductivity or transductancia. This is important so that the circuits operate at higher speeds, and therefore have better transistors. We must master the management of carbon atoms, that is what defines, if you are superconducting or not.

The NTC defines a rigid structure, strong and very light with mass, but we know very little about other mechanical properties: the vibration. Your understanding would open the door to many applications, from optimizing energy use in mobile telephony, the identification of weak forces (sensors very sensitive), or detect the mass of a single atom. It also expects a lot of quantum computing.

Before this, what really matters is the basic science that lies behind the NTC. For example, see how the NTC behave according to the principles of quantum mechanics. Also interested in their behavior as a function of temperature, or the fluctuation of atoms at that level.

The reality is we still do not understand well what happens at the nano scale. So far Dr. Adrian Bachtold, the CNM. If you can not measure at the nanoscale, one can not progress in nanoscience.

It's disappointing, after much research in molecular engineering of nanosystems, the lack of success in technological and commercial exploitation. The manipulation of molecular structures is a very difficult issue. And it is worth remembering that we have changed the structure of polymers, which are now everywhere. These are molecules that can be considered large.
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The photo has merit: insert at NTC hemispheres of Buckminster fullerenes. Dr. A. Yazdani, Science Photo Library - Institute of Physics, London 2007.
Production of NTC

The best known method for the production of NTC is the sublimation of carbon in an inert atmosphere. Also by electric arc discharge. It consists of generation of plasma through a current between two carbon electrodes, a distance of 1 mm in an inert atmosphere. The electrodes reach 3,500 ° C. The alignment, performance and quality of the NTC depend on the conditions of the arc and plasma stability. Other methods include laser ablation and catalytic decomposition of hydrocarbons.

The chirality is a property to be reckoned with in the NTC. A chiral object has no rotation axes. Chiral molecules have the ability to shift (rotate) the plane of polarized light that passes through them. The plane is diverted angle. If the light rotates clockwise, the molecule is dextrógena, swi is left is levorotatory.

In the NTC chirality corresponds to the direction in which rolls a sheet of graphite one atom thick to form the nanotube. Graphite sheet appears the tape, which wound into the NTC. It is easy to imagine that the tape can be cut from the sheet forming different angles, from 0 to 90 degrees. The chirality and therefore the properties of the NTC, depend on the angle of cut. NTC may not achieve the same chirality, because some are NTC hardware (drivers), and other semiconductors. All tubes are made by assembling hexagons, but the chirality varies. It's a mixture.
At Duke University seems to have managed to grow exclusively NTC type semiconductor. Its merit is to have achieved a precise combination of two alcohols with argon and hydrogen, with copper as catalyst
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The polymer sheet absorbed well the NTC. In the picture the NTC pull the organic film. Trinity College 2006.

The problem remains, as in monolayer tubes, which in the multilayer. Separate the NTC for chirality is not possible, because, due to attractive Van der Waals forces, the NTC tend to self-assemble to form fibers or meshes.

The news, last January, comes from Duke University. Jie Liu and Patricia Crawford say they have managed to grow exclusively NTC type semiconductor. Its merit is to have achieved a precise combination of two alcohols with argon and hydrogen, with copper as catalyst. We will have to confirm their method.

There NTC chirality zero: the nanotube shows a side view vertical rows of hexagons, parallel to the axis of the nanotube. The nanotubes with chirality have rows of hexagons, forming an angle with the axis of the NTC. The intertwining of the NTC, or when mixed with thermoplastic resins, greatly increases the viscosity.

The most practical method to select NTC is the chemical vapor deposition that is performed in the IQS, Barcelona. It is based on the decomposition of gaseous hydrocarbons (benzene or acetylene) precursor called on a graphite substrate covered by transition metals (cobalt, iron, nickel) that act as a catalyst. Temperatures range between 700 and 1,500 ° C. The NTC of this method are not straight but curved, forming a conglomerate contaminated with catalyst. The diameter of the NTC is quite uniform.

When the pyrolysis is conducted in the presence of organo-metallic compounds are obtained NTC aligned. The NTC growth is fast initially, but decreases greatly when the catalyst is encapsulated in the NTC. The density is very low compared with graphite, which is a great advantage for certain applications.

The theoretical mechanical properties of the NTC are fascinating, but in practice no such high values are achieved. Its characteristics depend largely on the high ratio radius / length and surface to volume ratio, which in turn implies a drastic increase in interfacial area.

They are also highly elastic, ie ideal candidates for reinforcement in polymers, comparing with traditional reinforcing. For its ability to withstand high strains offer a significant advantage over carbon fiber. The assumption has been achieved ideal dispersion in the polymer matrix. As the agglomerates present NTC is a challenge to achieve effective dispersion.

In fact, the dispersion is achieved in a mixed base, which acts as a shearing and breaking the NTC. If the mixing is energy, reduces the length of the NTC, which is not serious. In fact, the ratio radius / length of the NTC is still high, is reduced from 1,000 to 250.
Nanopolímero final properties depend on the degree of dispersion and alignment of the NTC
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The carbon nanotube is formed by trivalent.

It's the price we pay for achieving acceptable dispersion. Nanopolímero final properties depend on the degree of dispersion and alignment of the NTC. The direction and degree of alignment of the NTC are determined using TEM images and X-ray diffraction

The NTC provide the polymer not only greatly improved the mechanical properties but also electrical: conductivity, increased by 10 orders of magnitude, an advantage over conducting electrical charges.

The polystyrene acrilonitrito-butadiene-styrene (ABS) and polypropylene are used to form multi-component, where the dispersion of the NTC is carried out using a mixer. The dispersion achieved is analyzed by SEM and TEM techniques.

The charge transfer of the polymer matrix to the NTC is influenced by the interfacial binding by the molecular structure of the polymer and its ability to form helices arranged around the individual nanotube.

The uniform distribution is achieved with a concentration of NTC low, less than 1% by weight, at least in the case of PS and PMMA. Increasing the concentration to 2.5 or 10% changes the properties of charge, but the disadvantages outweigh the advantages.

The epoxy matrix can not be reinforced with NTC, due to weak interfacial bonds between the two phases. The NTC-polymer chemical bonds lead to a successful transfer.