Live from the small bang
A lift for nanos
There are two different approaches to nanotechnologies: top-down and bottom-up. The first, top-down, is based on miniaturisation, starting with blocks of material that are divided as many times as possible to obtain an object of nanometric size. This process uses techniques derived from the lithographic processes used in microelectronics to produce printed circuits.
The second approach, bottom-up, is based on the self-assembly of atoms or molecules, similar to the process at work in nature. This supramolecular chemistry has its architects who are able to create nanostructured polymers by manipulating the building blocks of matter at an infinitesimally small scale.
Winning combinations with hybrid polymers
In order to obtain a copolymer, it is necessary to combine different monomers, but never different polymers. Although there are a few exceptions, most are not miscible on a molecular scale. They cannot, therefore, simply be mixed any old how. Doing so could lead them to organise themselves into heterogeneous networks - into a conglomerate of a lower quality than the original polymers.
For twenty years now, alloys can be created from different polymers. Called block polymers, they are obtained by exploiting certain covalent bonds present in molecular chains as anchor points around which, for instance, a polymer can be grafted to another, or several polymers can restructure themselves without losing their properties.
The Arkema Company develops several such hybrid copolymers, such as the Apolhya range of materials obtained by continuously grafting a polyamide onto the chain of a polyolefin through reactive extrusion. This nanostructuring enables the plastic's mechanical performance to be improved above 150°C, the highest temperature for most polyolefins. It also improves their transparency but, first and foremost, makes them compatible with other polyolefins and polyamides.
Another type of nanostructured copolymers, Nanostrength, combines two rigid blocks of methyl methacrylate (PMMA) around a flexible central block of polybutyl acrylate. By modifying the proportions of either component in the chain of the hybrid polymer, it is possible to combine their individual properties.
When carbon flies solo
It is a well-known fact that carbon has an affinity with many elements; it is at the origin of many organic compounds present in natural or synthetic polymers. Yet, although it plays an essential role in team efforts to create these combinations, number six on the periodic table also excels in solo efforts, at the nanoscale.
In addition to the carbon black particles that abound in rubbers and inks, and the rarer diamond particles used to optimise anti-tumour radiation therapies, the carbons derived from the graphite used in pencils form the basis of three nanomaterials with a high potential.
First in order of appearance, fullerenes have been the object of growing interest since they were first discovered in 1985 by three future Nobel Prize-winners, Harold Kroto, Robert Curl and Richard Smalley.
Their spherical structure consisting of a hexagonal mesh of 60 carbon atoms provides solid anchor points on which it is possible to graft highly resistant polymers or polymers with magnetic, optical and electrical properties which are currently paving the way for "all plastic" photovoltaic panels that are less expensive and more efficient.
Great success for nanotubes
The same type of mesh led to the creation of carbon nanotubes organised into simple or nested cylinders, closed at each extremity by domes similar to those found in fullerenes. Since their discovery in 1991 by Sumio Iijima from Japan, and the discovery of their extraordinary mechanical and electrical performance, these nanomaterials have met with increasing popularity, thanks to their electrical properties in particular.
They vary according to the orientation of the meshes, the way they were coiled, and the number of layers. Some nanotubes are insulators, others are semiconductors, and others still are metallic conductors. Among its strong points is the fact that it enables carbon black to be replaced, in infinitesimally smaller proportions, to manufacture antistatic plastics and paints resistant to fire hazards.
Their performance is no less impressive when it comes to resistance: six times lighter than steel, they are ten times stronger and are much more elastic. This makes them highly sought-after reinforcements for many polymer matrixes, in equipment with a composite structure such as bicycle frames, high-end bodywork and, increasingly, aerospace parts.
A prodigy for the nanocomposites of the future
The latest in the family, appearing in 2004 thanks to the work of two future Nobel Prize winners (2010), André Geim and Konstantin Novoselov, graphene nourishes the wildest ambitions. Thanks to its honeycomb structure, it is the thinnest material. And it is the champion of superlatives: 200 times stronger than steel, a superconductor more efficient than copper, the most transparent material, and the most impermeable to liquid and gas alike.
Given its properties, graphene appears to be the best candidate to replace silicon or to produce nanocomposites adapted to all applications where transparency and resistance are required: ultra-thin flexible screens, packaging and optical equipment fitted with electronic circuits, ultra-resistant glass, and more.
