Hitech polymers: US on flow speed, conductivity, Denmark has software and Belgium bids photonic

Wednesday 6th February 2008
Confocal microscope image of a carbon nanotube/polypropylene composite. Small concentrations of carbon nanotubes--one percent by mass--can change the polymer electrical properties dramatically. NIST

New measurements by scientists at the National Institute of Standards and Technology (NIST) have uncovered an intriguing wrinkle. For a given CNT concentration, the electrical properties of the composite can be tuned from being a conductor to a non-conductor simply by changing processing conditions, basically how fast the polymer flows.
Denmark offers Computer Aided Polymer Design (CAPD which analyses the user's required target properties and gives output in terms of the required polymer units and their number, in addition to branch details including length and molecular weight.
From Belgium, the developed lanthanide complex doped polymers are capable of emitting in the infrared region by photoluminescence (PL) and possibly electroluminescence (EL) processes.
In both processes there is light emission due to either photon absorption or an electrical field/current passing through.

One of the immediate applications of carbon nanotubes (CNT) is as an additive to polymers to create electrically conducting plastics a relatively low CNT concentration can dramatically change the polymer electrical conductivity by orders of magnitude, from an insulator to a conductor.

Carbon nanotubes—sheets of graphite rolled up into nanoscale hollow cylinders—are under intense scrutiny for a wide range of materials applications. The NIST study shows how the conductivity and dielectric properties of these mixtures depend on flow and how they change once flow has stopped. Property changes have relevance to the process design of these materials in a long list of potential applications for conducting plastics including transparent electrodes, antennas, electronic packaging, sensors, automotive paint, anti-static fuel hoses and aircraft components.

The NIST researchers augmented a standard instrument, a shear rheometer, normally used for viscosity measurements, to simultaneously measure conductivity and dielectric properties Using this “rheo-dielectric spectrometer,” they discovered that the conductivity of the nanocomposite dramatically decreases with increasing flow rate, effectively changing the material from a conductor to an insulator.

This extraordinary sensitivity of the conductivity (and other properties) to flow is prevalent near a characteristic CNT concentration where an interpenetrating CNT network first forms. Surprisingly, once the flow is removed, they found that the nanocomposite reverts back to its original conductivity.

Based on these measurements, the NIST team proposed a theoretical model that successfully accounts for these dramatic effects. This model quantitatively predicts the observed conductor-insulator transition and is useful for optimizing and controlling the properties of these new polymer-nanotube composites.

Denmark develops software tools for picking polymers
Polymers forms the backbone of manufacturing industry due to their multifunctional nature. A team of scientists in Denmark ,has devised a software package whereby the type of polymer can be predicted based on the designer's required properties.

The range of polymers in relation to structure and function is seemingly infinite, from synthetic hair to heat-resistant cookware through to waste pipes. Macro properties of the polymer reflect the changes undergone when the material is subjected to pressure, temperature, light, electrical and magnetic forces.  Included also are its behaviour when dissolved in a solvent or its chemical reactivity. To vary these properties, the chemical engineer has many means including changes in monomer identity, chain length, branching and composition of branch, as well as in the degree of crystallinity.

The European project PMILS set about to make the life of the industrial polymer user easier. Partners designed modelling tools whereby the performance of polymers and the mechanisms involved can be predicted through the advanced software tools. More specifically, a team of scientists within the project designed the Computer Aided Polymer Design (CAPD).

As such, it gives the production engineer a list of candidate polymers that can then be tested to identify the final choice of polymer. Two tools were developed, one for generating property predictions and another for generating the molecular structures of the chemicals. The CAPD tool is user-friendly being Windows-based and has an interface which is easy to use.

The CAPD tool is capable of assisting in polymer product development by allowing the designer to concentrate on the most promising candidates for a successful product. Further development of this technology could refine the tool further for a more specifically defined output and collaboration is sought for further R&D

Photonic technology platforms   
In Belgium, the OPAMD project has developed novel lanthanide complexes for cost-effective and eco-friendly infra-red semiconductor applications. Compared to its existing inorganic counterparts, polymer-based technology has been considered as more environment-friendly.

Due to its excellent performance coupled with inexpensive production and ease of manufacture, this technology is highly suitable for use in data, telecommunication and optical computing applications. Motivated by this, the OPAMD project focused on the fabrication of new polymer based-materials and devices for further deployment in photonic technology platforms. Research work resulted in two families of materials emitting in the visible and infrared along with device demonstrators for further commercial exploitation.

One of the key project results involved novel lanthanide complexes of sandwich type and perhalogenated sandwich type erbium. For the synthesis of these innovative complexes a wide range of compounds was developed. This range included quinolinate, betadiketonate and sulfonyl imide as well as other complexes of mainly erbium, neodymium and ytterbium ions for applications in the near infrared spectrum.Their primary applications include infrared Light-Emitting Diode (LED) applications and collaboration is sought for further research or development support.

Sources: http://www.nist.gov/public_affairs/techbeat




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