Liquid crystals based on [60] fullerene

Liquid crystals based on [60] fullerene

Over the last decade, [60] fullerene Has attracted considerable attention in materials science.Notably, Several Efforts Have Been Aimed at Producing liquid-crystalline C60-based materials for value added in the form of INcreased Processability, film formation, and self-control over assembly. Examples of C ₆₀ derivatives Possessing a high character SC (bearing more Than Two anisotropic moieties per C ₆₀ via polyaddition dendritic gold approach) showed a transient Either nematic, chiral nematic has, or has smectic A phase. "Gaol cells, the properties of the materials Were Mostly Dominated By The anisotropic moieties, due to dilution of the C ₆₀ unit.As [60] fullerene can Be regarded as a versatile building block for hard dendritic systems due to ITS tunable core Valency (1 to 6) and regioselective polyaddition We Were intéressée Further to look "at its use as a template to build multicomponent supermolecule. Applying the "orthogonal transposition" described by B. Krautler And The Diederich's method of "tether directed remote functionalization" for Specifying multifunctionnalized [60] fullerenes, it would Be possible to regioselectively prepare new Three dimensionally structured molecules and Malthus new structural motives impossible to Obtain starting from Other cores SUCH've silsesquioxanes gold gold nanoparticles .
The work described "Is a first Step Towards o Attempt to Reach and to control and Ordered arrays containing [60] fullerene. Hexaaddition On The carbonated polyhedron Has Allowed the preparation, in high yield of An enantiotropic, room temperature nematic material, despite the absence of mesomorphism of the malonate side-group promoters. It Subsequent heating-cooling cycles, a stable and Reproducible behavior Took up with the reversible sequence Glass (G) 13 Nematic (N) 60 Isotropic (I).
Here, we show Specifying That the architecture of the nematic phase has hexakisadduct inducer with unusual features. The Highly symmetric [sixty] fullerene accordingly Represents a particularly versatile scaffold for the regioselective covalent assembly of a Variety of regular Three dimensionally structured molecules, Which May enlarge sacrifice part of the Existing directory of programmed molecular components for the construction of Useful Ordered materials.
Figure 1. (A) Chemical structure of hexa-adduct of [60] fullerene. (B) micrograph in polarized light (POM) obtained at 55 ° C after cooling from the isotropic.
 Figure 2. X-ray pattern obtained at 50 ° C for the hexa-adduct of C _60. Top: snapshot oriented in a magnetic field (right) and representation of the three reflections (left). Bottom: Profile 2θ. Inset: profile 2θ obtained for a distance greater film sample (328.0 mm).

Des nanotubes pour filtrer les ondes parasites

A manufacturer of injection nozzle used carbon nanotubes to develop a nuclear radiation detector of small, accurate and reliable. This tool will detect radiation through a scintillator, a crystalline material which emits light when exposed to radiation.
To prevent the scintillator to respond to other sources of radiation (eg electromagnetic) the opening is covered by a layer of plastic was mixed carbon nanotubes the thickness of a sheet of paper.
This layer will help to block radio waves, visible light and other sources of electromagnetic wave so that the scintillator does not perceive that nuclear radiation.

The methods of observation of nanotubes Transmission Microscopy

The methods of observation of nanotubes

 Transmission Microscopy

The essential tool to observe the nano structure is transmission electron microscopy. The operating principle is quite simple, we will send radiation on the object to observe and build the image using a microscope (lens system for focusing the radiation used.)
The resulting image will be directly related to the radiation that is going to send, this radiation is a wave whose power of resolution (minimum size objects observable) will depend on the wavelength of the radiation sent.
Example: Photons of visible light:
 = 400nm, R = 1 micron (R is the resolution)
Thus we see, albeit with a beam of visible light it is not possible to observe structures at atomic dimensions.
The solution to be able to observe nanostructures has been found by E. Ruska 1937 who designed the first microscope in transmission using high-energy electrons  0.001 nm.
The general lines of transmission microscope is constructed as an optical microscope but here we will be interactions between the electrons and the material used so that you can get different types of information as possible:

• Morphologies and microstructures of micron nm

• Arrangement of atoms: crystal structure and defects

• Spatial distribution of chemical elements (spectroscopy) (mapping and chemical profiles)

However, one must always remember that the images obtained with a microscope transmission are the result of a projection along the direction of beam propagation and the depart of a 3D structure yields a structure (2D)

And here is the type of image one gets when considering such a multiwalled nanotube:

TEM image obtained







When viewing tube is made perpendicular to the axis, the image is a set of equidistant lines corresponding to the projection of rows of tubes. This method allows to study in detail the architecture of interlacing bundles and tube connections, but does not determine their helicity.
5.2 Surface Microscopy
This technique relies on using the microscope scanning tunneling (STM scanning tunneling microscopy. This technique was developed in the early 1980s by Gerd Binnig and Heinrich Roher at IBM Zurich and earned them the Nobel Prize is 1986.Elle bringing a metallic tip (made of platinum and iridium) consisting of only a few atoms at its end, very very close to a conductive surface and apply a few volts potential between the tip and the surface. The lack of contact directly between the tip and the surface forces the electrons to traverse the void to establish the current between two conductors. This remarkable property called tunneling is very sensitive to the separation between the tip and the surface, the tunneling current exponentially with decreasing distance. piezoelectric reader, a measuring instrument, assesses the least variation with an accuracy of 0.1angstrom, smaller than an atom! The system is connected to a computer that reconstructs the information and gives an image of the surface. This technique, for example, characterized at the atomic scale topography of a metal surface by analyzing when scanning the surface vertical displacement of the point required for the measurement of a constant current.

Tunneling microscope
6 Applications
Miniaturization is a goal constantly searching the man. But also because at this scale nanotubes have physical and chemical properties that can be very different from those we know. Nanobiotechnology, medicine (pharmaceuticals), space activities, environment, industry, construction, various industries (textile packaging etc..) Computer.
6.1 Nanobiotechnology

Carbon nanotubes are insoluble in organic solvents and water, which restricts, at present, considerably their field of use. However, when carbon nanotubes are mixed and stirred with a detergent, they disperse and form stable suspensions. The detergent molecules stick together on the surface of the nanotubes self-organize in the form of rings or spirals. But the stability of these assemblies, however, remains limited.
Afin de voir si d'autres molécules lipidiques pouvaient s'adsorber et s'auto-organiser sur les nanotubes de carbone en formant des assemblages plus stables, les chercheurs ont conçu et synthétisé de nouveaux réactifs. Ces derniers forment des « bagues » lipidiques constituées de structures supramoléculaires hemi-cylindriques. Leur stabilité dépend de la longueur et du nombre de chaînes carbonées des réactifs lipidiques qui les constituent. Ces bagues permettent également de fixer des protéines à la surface des nanotubes. Un tel assemblage organique stable constitue une méthode simple et efficace pour rendre fonctionnel des nanotubes par des réactifs chimiques. La structure supramoléculaire ainsi obtenue permet d'envisager de nombreuses applications dans le domaine des nanobiotechnologies: elle pourrait servir à l'élaboration de détecteurs moléculaires pour le dosage des molécules de l'organisme. Elle pourrait également permettre la fabrication de nouveaux vecteurs de composés hydrophobes, notamment de médicaments complexes. D'autres utilisations sont aussi envisagées comme par exemple une nanoboîte pour transporter un médicament, remplacer certains tissus, nanosondes, etc..

• Informatique

Des chercheurs se sont aperçus que des molécules avaient les propriétés de certains éléments de circuit. En fait un nanotube de carbone peut se comporter comme un transistor. L'intérêt, et un des défauts de ces éléments, est que contrairement aux matériaux de plus grande taille, leurs propriétés varient de façon non-linéaire, mais tout de même régulière. Autrement dit, le nombre d'atomes qui compose la macromolécule détermine si le matériau est conducteur ou non ou le simple fait de le plier légèrement influencera de beaucoup ses propriétés. Cela découle du fait que ces nanotubes sont soumis aux lois de la mécanique quantique. Les nanotubes sont fabriqués en brûlant du carbone à très haute température et en faisant baisser, par la suite, la température et la pression de façon brutale. Ce procédé produit des feuilles qui sont roulées pour faire de petits tubes. Cela est rendu possible par le fait que le carbone sous la forme de graphite est constitué de minces couches d'atomes disposés en hexagone et que ces couches glissent facilement les unes par rapport aux autres. Ces nanotubes sont perçus comme les remplaçants du transistor, car ils sont environ 100 fois plus rigides que l'acier et que leurs propriétés conductrices varient de conducteur à semi-conducteur. Les nanotubes de carbone ne sont évidemment qu'une des applications de l'électronique moléculaire. Des composants autres que les transistors peuvent être reproduits à l'échelle moléculaire, comme des diodes, des interrupteurs, etc. Les applications en informatique de cette technologie sont évidentes. Le transistor composé d'un nanotube de carbone permet d'économiser beaucoup d'espace, consomme moins d'énergie et l'information y circule beaucoup plus rapidement étant donné sa petite taille.

• le microscope à effet tunnel et l'optique

Le microscope à effet tunnel a beaucoup contribué à étudier le nanotube de carbone. On déplace une pointe très fine au-dessus de la surface à analyser. Les images sont générées par les électrons qui passent de la pointe à la surface. La pointe est sensible au changement de la surface et on peut aisément distinguer les changements de surface et les défauts de celle-ci. Cette technologie a beaucoup évolué dernièrement et permet maintenant de déplacer des atomes et de briser les liaisons entre ceux-ci.

Des applications optiques se sont aussi développées telles que les nanofeuilles de verre envisagés dans le domaine des disques optiques. La densité d'informations pourrait être multipliée par 4, mettant en œuvre le dépôt d'oxyde de cobalt sur la surface du disque. Il ya aussi les nano-cristal avec des propriétés optiques particulières, etc..

roperties amazing MWNT

Researchers from the CNRS, in collaboration with a British team showed that carbon nanotubes with double walls exhibited novel properties of resistance to high pressures. Their results, published in the journal Physical Review Letters, have important applications in various fields.
The scientists have sought to understand the mechanical behavior of the sheets relative to each other. They subjected carbon nanotubes with double walls to hydrostatic pressure of 10,000 to 100,000 times atmospheric pressure, and analyzed their behavior by an optical technique for probing the mechanical properties of materials through their vibrations. They show that the two sides of the nanotubes did not behave the same way under the pressure, while the outer wall behaves like a single wall nanotubes single wall, the wall seems to undergo internal part of pressure. These experiments prove that the various walls of carbon nanotubes are not in strong interaction and behave in a mechanical point of view independently of one another. This behavior is specific to carbon nanotubes and is not in the graphite, which is the macroscopic equivalent. This fundamental research on nanotubes with double walls, the easiest system to understand the mechanical behavior of layers relative to each other, is an important step in modeling the mechanical properties of multi-walled nanotubes. Their great strength is the ideal tool for applications in certain areas of nanotechnology that involve the use of high pressure. double-walled nanotubes represent a high security since the accidental breaking of an inner wall is not necessarily transmitted to all walls of the nanotube, as would likely occur if all the leaves were also sensitive to pressure.

• Important Note:

French and U.S. physicists have discovered beads hanging on carbon nanotubes, like beads of dew on a cobweb. They show the role of liquid carbon nanotube growth in the hitherto assumed to be formed from carbon vapor.
So far, all the mechanisms put forward involves a vapor phase: we imagined that the carbon anode is vaporized under the effect of arc (5000 ° C) and was crystallized at the cathode. In the study published by Science, the scientists showed that the formation mechanism of carbon nanotubes involves melted. The chemical composition analysis revealed that this was pure carbon ion and amorphous. In addition, the ball looked like leftover liquid.
Through this work, the researchers had the opportunity to study the behavior of liquid carbon (very poorly known because it evaporates very quickly) and see that it is comparable to that of other liquids.Under the scenario they have developed, the nanotubes are formed, like most of the crystals from a liquid phase cooling. The arc creates a drop in the carbon anode, which evaporates until the pressure of gas leaving the carbon drop equals the helium pressure in the oven, thus stabilizing the liquid carbon. The drop then continues to cool by convection and its edges become more and more viscous. Inside, the liquid cools slowly. Nanotubes crystallize it, by sticking to each other to form a needle. Carbon viscous, which covers the needle nanotubes, then formed glass beads on carbon nanotubes.

Channels of possible synthesis of nanotubes

Channels of possible synthesis of nanotubes

  4.1 Method of electric arc:
It consists of an arc discharge between two graphite electrodes in a chamber filled with helium. One of the two graphite electrodes, the anode, is associated with a few percent of a metal such as Co, Fe and Ni. The anode will be consumed to form a plasma whose temperature can reach 6000 ° C
(Note: A plasma is an ionized gas where the atoms are broken down into positively and negatively charged ions. For example, our universe is composed of 99% plasma.).
The plasma condenses on the other electrode, the cathode, a rubbery and stringy deposit containing nanotubes. This method is very simple realization was quickly implemented throughout the world, only here, the processes occurring during the synthesis are very complex and that makes it virtually uncontrollable.
A variant of the technique known as arc discharge is the synthesis from solar energy. The graphite-catalyst mixture is sprayed in this case using a concentrated radiation solar furnace


Method of electric arc

4.2 Laser ablation
It is to destroy a composite graphite electrode-metal transition with laser radiation of high energy pulsed or continuous. The graphite is then vaporized in an argon atmosphere and give the nanotubes. The main advantage of this method is the limited number of control parameters, which makes possible the study of synthesis conditions, although this process is very expensive
Note
We have synthesized different behaviors when the laser is pulsed (it emits a certain amount of photon has a well-defined frequency) or when it is continuous.
Here we have shown what we call synthetic routes to high temperature. There are others to develop carbon nanotubes at lower temperatures.

• The catalytic decomposition of a gas

  The principle of these methods is to decompose a carbon containing gas to the surface of particles of metal catalyst in a furnace heated to a temperature between 500 ° C and 1100 ° C.


The carbon atoms released by thermal decomposition of gas will then precipitate on the catalyst surface leads to the condensation growth of tubular structures graphitized. This technique has already led to other types of nano structures (filaments, nano fiber, ...).
The first gas used was acetylene, using as a catalyst of fine particles of iron, but also cobalt and nickel. Benzene has been in the same way as methane as a carbon source. An alternative to acetylene is the carbon monoxide that Smalley and her team used by said mutation on molybdenum at 1200 ° C.
Note: The pro mutation is a redox reaction between two molecules of a compound, an oxidant and the other being reduced by it.
The oxidation number of the item, identical in the two molecules of departure is increased in one and reduced in another.
Example: Cannizzaro reaction

However there is a major drawback to this method of manufacture, the difficulty lies in the construction and control the size of catalyst particles. Their sizes to be of the order of few nm for the synthesis of nanotubes. The particles are obtained by reduction of an organometallic compound (such as ferrocene) and are either deposited on a ceramic support material (silica, alumina) is broken down into the reaction chamber where the reaction takes place with the gas carbon.
The nanotubes obtained by these methods are less good qualities they exhibit geometric characteristics (length, diameter) much more uniform, which is an advantage. It is possible to orient tube growth in a synthetic catalysts on blocks arranged on a support according to a defined geometry.
This possibility opens up exciting prospects for certain uses. In addition, the average temperature processes can be designed to obtain the means of large-scale production like carbon fiber, which is much more difficult to envisage ways to high temperature.

• The different modes of assembly of carbon nanotubes
• The single-wall nanotubes (SWNT Single Wall Nanotubes)

The SWNT are found mostly in the form of bundles (bundles), also called clusters. In each bundle, the tubes stacked in a compact and form a periodic arrangement of triangular symmetry. Their number may reach several tens in a bundle and their diameter varies between synthesis conditions of 0.6 to 1.5 nm.
S ructure of a SWNT

Cross section of a SWNT

• Multiwalled nanotubes (MWNTs Multi Wall Nanotubes) 6199

Two configurations are possible for this type of nanotube or tubes nested one inside the other like Russian dolls (a) or when the structure is constructed by wrapping a single sheet of grapheme (b).



Structure of multiwalled nanotubes

In both types of assembly, the distance between two adjacent tubes is about equal distance between two planes of grapheme, meaning that the assembly of the tubes do not change the nature of chemical bonds that are identical to what 'they are in graphite.
The two assembly modes are mutually exclusive and are obtained for the other synthesis conditions radically different. On tracks high temperature, obtaining beams monotube requires the use of a metal catalyst that is mixed up a few percent to the graphite powder.
The catalyst is a transition metal, Ni, Co, Pd, Pt nanotubes multi layer formed directly in the vapor phase at a temperature of at least 3000 ° C. Conversely, the single nanotube layer formed in a colder zone between 800 and 1400 ° C.
On tracks average temperature, the nature of the assembly is controlled by temperature and size of catalyst particles. If these conditions of synthesis are now well established, it remains that the mechanisms that control the formation and growth of the tubes are still very poorly understood and much remains to be done before we know drive the synthesis of a tube a given configuration.

The physical properties of carbon nanotubes

• Mechanical Properties

Because of its structural anisotropy (that is to say that the material does not exhibit the same properties in the directions of space), graphite presents a tensile modulus (modulus which measures the resistance to deformation) very important in terms of hexagons and much lower out of the plane. The nanotube has the mechanical strength of the grapheme and even amplify it. It combines the resistance to deformation at a very high flexibility. Various experiments have shown that the nanotube has an incredible ease to bend up to angles very important to warp and twist along its axis. The boron nitride nanotubes have mechanical properties similar to those of carbon nanotubes in particular a high strength and greater rigidity. These nanotubes are pledged to cover a wide scope in many areas complementary to those discussed for carbon nanotubes. Carbon nanotubes used to make transistors a level of miniaturization reached until now. IBM researchers have already managed to create a nanotube transistor. Carbon nanotubes could also allow issuers to make fields (of electrons, in other words) at the nanoscale. Carbon nanotubes are superconducting at low temperature.
3.2 Properties of electrical conduction
Graphite is a poor conductor, however, cargo capacity is very sensitive to electrical disturbances such as chemical or geometric distortions, or doping (adding impurities to semiconductor increases the electrical conductivity of the body). With the nanotube disruption comes from the curvature effect. The consequence is that following its elicited a nanotube is a good or a bad driver. One third of the tubes the tubes 'chair' has a metallic character. This important property has been calculated theoretically and verified experimentally. In addition a number of phenomena related to the reduced dimensionality have been highlighted on the guide tubes. These phenomena of quantum origin are generally difficult to study because they could not have suitable physical systems. Simplicity Structural and chemical stability of the nanotube are metallic object model of molecular quantum wire.

• Chemical Properties

The nanotubes have chemical properties very attractive: as shown in the figure, it is possible to fill them by capillary action with fullerene molecules or crystalline compounds in order to obtain nano encapsulated son. These compounds may be metals, sulfides and metal chlorides.
  

Nanotube filled with fullerene