Nanotechnology makes plastics smarter
Nanoadditives offer the potential for developing novel products and processes, since the characteristics of engineering materials may change fundamentally at the nanometer scale.
Optical effects of polymer nanocompounds
Certain optical and electronic characteristics cannot be achieved at the micrometer scale, confirms Dr. Walter Caseri from the Swiss Federal Institute of Technology (ETH) in Zurich. A professor at the Institute for Polymers, he develops nanocompounds by adding inorganic particles to polymers in order to improve their optical and electrical properties. Due to the high surface tension of inorganic solids, the colloids will frequently lump together. Such agglomerated nanoparticles will increase light scatter, even if the particle size is much smaller than the wavelength of the incident light. Caseri explains that this aspect is of interest to optics. In this connection, also the refractive index is crucial. The refractive index of most organic polymers lies in the narrow range between 1.3 and 1.7, whereas that of inorganic solids may be far below 1 or above 4. The introduction of inorganic nanoparticles in organic polymers allows refractive indexes to be achieved that are outside the typical range of organic polymers. For example, using gold particles, indexes of refraction as low as 1.0 or as high as 2.5 were achieved with polymer compounds. The addition of colored nanoparticles may allow nanocompounds to serve as colorants, for instance with metallic nanoparticles for coloring glass. Dichroic nanocompounds have been known for over 100 years, which are based on natural polymers plus gold and silver nanoparticles. This dichroism is believed to stem from uniaxially oriented, longish particle accumulations. Optical applications include UV protection and lenses plus optical waveguides, color images, and two-colored materials.
Nanotechnology prevents cable fires
For years now, the cable manufacturer "Kabelwerk EUPEN" has been using nanocompounds for protecting cables from flames. For this purpose, flame-retardant nanocompounds are synthesized by melt-mixing ethylene vinyl acetate copolymers with modified layered silicates as nanofillers. Dr. Günter Beyer says that when the nanocomposite catches fire, an insulating and non-combustible layer is created that reduces the emission of the volatile products of polymer decomposition. Beyer won the Jack Spergel Memorial Award in 2003 for his research into nanocomposites as a flame retardant for polymers. This reduces the maximum temperature as well as the height of the flames. The subject is of high current interest, for the EU FIPEC (Fire Performance of Electrical Cables) study is giving rise to a new directive on cable installations inside buildings, regulating their heat discharge and flame propagation.
Carbon nanotubes – from laboratory to commercial scale
To develop new nanocompounds, Dr. Volker Abetz from the GKSI Research Centre Geesthacht GmbH relies on carbon nanotubes – so-called Multiwall Carbon Nanotubes. He applies a very loose network of these MWNTs with lengths ranging from 1 to 10 microns and diameters from 10 to 20 nanometers in the matrix of thermoplastic polymers. In order to prevent the problematic agglomeration of the nanoparticles, which would produce a heterogeneous distribution, he first functionalizes the tubes. For this purpose, he treats them with nitric acid. The acid breaks down the graphene structure, creating carboxylic acid groups on the MWNT as a function of time, acid concentration, and reaction temperature. The more powerful this effect, the better the dispersion of the tubes in the solution. The distribution of the MWNT to a large extent determines the mechanical properties. According to Abetz, the commercial potential of thermoplastic elastomers and materials is likely to increase as the price of MWNT drops. Large-scale production will enable further modification and functionalization, leading to adaptable reinforcing fillers or to the introduction of conductibility in novel nanocompounds.
Organic electronics with reduced energy consumption Organic transistors are components of choice for roll-up display screens, sensors for humanoid robot skin, or radio-frequency identification tags. However, they still require operating voltages of 15 to 30 V, consuming large amounts of valuable energy. Dr.Marcus Halik, professor of materials science at the University of Erlangen-Nürnberg, is taking a new approach: His organic circuit runs for several years on a 1.5 V battery. The transistor is produced with the aid of an organic insulator with a thickness of 1 molecule in conjunction with a complementary circuit design. Halik says that the energy consumption is reduced by several orders of magnitude to less than 1 nW per logic gate compared with traditional organic circuits. For electric devices with functions at the molecular scale, he works with arrangements of functional molecules on selected surfaces. The challenge lies in the stable interlinking of the molecules and a useful packing density in order to implement fully integrated devices. He believes the most promising approach is the self-organization of organic molecules with anchoring groups that are chemically attracted by the desired surfaces. The application of molecular gate dialectrics in organic film transistors allows outstanding performance to be achieved while minimizing the required supply voltages. The commercial opportunities are considerable. He explains that NanoMarkets market researchers believe that organic electronics will generate sales revenues of almost 2 billion U.S. dollars by the year 2012 if current restraints such as life expectancy and energy requirement are eliminated.
Gluing from the inside
Sophisticated adhesive technology allows today’s automobile industry to bond materials with different properties such as metals and plastics. This enables the design of light-weight cars and thus reduces fuel consumption. However, to date it was necessary to expose the components to be bonded to several minutes of heating in special equipment. This slowed down the production process and required very much energy. Researchers from Degussa and their colleagues from the Fraunhofer Institute for Manufacturing Technology and Materials Research IFAM sought to correct this situation. They coated iron oxide particles with silicon dioxide and included these super-paramagnetic nanoparticles – called MagSilica – in a conventional adhesive or polymer. When they expose these materials to rapidly alternating magnetic fields, the iron oxide particles start to oscillate. Heat is generated inside the adhesive, causing it to cure within a short time. Since it is no longer necessary to heat individual components, the production process is accelerated. In addition, the energy requirement drops drastically. Dr. Markus Pridöhl, research manager with Advanced Nanomaterials at Degussa, says that theSiO2 coating ensures a good dispersion of the MagSilica powder throughout the plastic or polymer and separates the iron oxide domains. This – in conjunction with the wide surface range of the particles – results in a uniform heat distribution and prevents local overheating. Nanotechnology enables MagSilica to reach the required strength about ten times faster, and the material exhibits better mechanical properties. Even thermally sensitive polymers can be bonded above the melting point. Moreover, selective heating also allows non-destructive separation of objects that have been previously bonded, and this with a lower energy requirement.
Nanotechnology is highly multidisciplinary and interdisciplinary and combines basic and applied research. On the one hand, the goal is to shed light on fundamental issues concerning "nanophenomena." On the other hand, industries are approaching researchers with current problems. Knowledge hubs such as the NanoEurope offer all players in the nanoscene an excellent opportunity to exchange ideas and to seek partners for joint projects.
Following last year's successful event, which was attended by some 3,500 visitors from over 40 countries, the NanoEurope will once again this year provide a meeting platform for the interested specialist public. The event in 2008 offers businesses and managers from industry and research institutions a forum for exchanging information on commercialization strategies and investment know-how. In addition, the participants will learn more about the following focal subjects: Multifunc-tional Textiles, Nanobased Electronic and Sensor Systems, and Systems with Functionalized Sur-faces and Structures. Lastly, for the fourth time now, the internationally renowned "NanoRegulation Conference" on voluntary measures in Nano Risk Governance including an international Nano Stakeholder Dialog will be organized as part of the NanoEurope 2008.
At a glance: NanoEurope 2008
Date: September 16 – 17, 2008
Venue: Olma Messen St.Gallen, St.Gallen, Switzerland
Exhibition: Hall 9.1; Congress: Halls 9.1.2, 9.2, and 2.1.
Registration: Via OnlineTicket at www.nanoeurope.com