Translation from 'Handelsblatt', Dec 20th 1995
Bernhard Wessling
Zipperling Kessler & Co., Germany
Organic metals - a new family of materials with a broad scope of application potential
A totally new family of materials is on the way to contribute important aspects to solving many different technical and ecological problems - the organic metals. The first commercially available member of this new materials group, polyaniline, ORMECON, is actually being introduced into the market by a medium sized independent company, Zipperling Kessler & Co.
The company is located in Ahrensburg near Hamburg in Germany and has 270 people. Zipperling conducted basic research for over 14 years in several areas, including "conductive polymers", which enabled it now to introduce PAni as the first into the world market.
Some first commercial applications have been developed in the last years and have been stabilized since 1995.
The organic metal polyaniline has some properties which sound strange for the expert:
it is an organic polymer, but totally unmoldable and insoluble
it is a metal, i.e, it has free electrons in a metallic "conduction band" (but: the conduction band is "only" extending over about 10 nanometers, which is the reason, why this metal is to be named as mesoscopic metal and behaves as other mesoscopic metals (copper, silver, etc, when being prepared in colloidal particles size below 1 micron) behave.
it is a salt (more exactly: a poly-radical-cationic salt)
it is redox active and can exist in at least 3 oxidation states (of which only one is metallic), but does not change its macroscopic form during reversible oxidation or reduction (hence can act as a "redoc catalyst")
2 of 3 oxidation states are stable under "normal" conditions (air, ambient temperature up to over 200 deg.C, ...)
it is "electro-chromic", i.e., it changes colour upon oxidation or reduction (the stable metal is green, the stable oxidized or neutralized form is blue, the reduced form - readily reoxidized to the green or blue form - is pale yellow)
in thin layers, it is transparent (but coloured)
Dispersion as the key for applications
First commercial applications have therefore been realized in relatively obvious like transparent (green) antistatic or conductive coatings of plastics. But not at all easy: how to make this organic metal, being insoluble and not moldable, processable and applicable onto plastic (or other) surfaces, leading to a thin transparent layer?
The solution to this task - dispersion of polyaniline - is the technology which represents the company's lead in this one-and-a-half decades lasting research competition. Zipperling realized the dispersion by 2 supplementing steps:
first a completely new polymerization procedure for the whole class of materials leading to a measurable dispersability
parallel to this extremely performing dispersion techniques were developed, because also the best dispersible organic metals belong to the "hardest to disperse materials" in the world - by far harder than any "hard-to-disperse" pigment.
With the strategy "dispersion", Zipperling has opened and practiced a way which is surprinsingly still not accepted in the research community. But we think, the success - equally visible in well performing products as in basic new scientific results (including a new non-equilibrium thermodynamics theory for polymer systems) cannot be overlooked any more.
A very helpful and funny new tool is a computer simulation of structure formation, which we performed recently and will be published soon - months after being available on the world wide web:
These structures are responsible for conductivity and other phenomena (like melt viscosity or impact strength).
A coating of only a few micrometres thickness allows for designing the surface resistivity between 103 and 109 Ohms/sq which reveal no particles visible by eye or microscope.
And this technology now opens a range of high tech possibilities of various kinds: you can coat glasses and (with a special design) change the optical and IR transparency properties electrochemically - the "smart window"; such a project is actively being pursued by us with a customer in pre-industrial scale.
Printed Circuit Boards Production
With coating formulations of specifically designed properties we suceeded - together with a circuit board technology company - to replace an inefficient production step in the circuit board production, which is considered by experts being a revolution in this field. We will disclose details later, after broader introduction of the product into the industry. Actually an industrial production test is successfully ongoing and the boards are working in real world end-products.
It is to be expected that the technology will become regularly commercial in 1996 and will be used world-wide very quickly. Other applications in this field are under development.
Also for optoelectronics applications might be found in future.
Corrosion protection
Probably the least obvious and scientifically and technically most complicate application of the organic metal polyaniline is the corrosion protection. It was before 1987 that we made first discoveries according to which polyanilin containg coatings on metals were showing some improved corrosion protection. But despite continuous intensive research it took until 1993 that we found out about the principles of the effect:
Polyaniline behaves like a noble metal thanks to ist redox potential being close to silver, therefore it ennobles the surface of conventional metals; moreover it transforms the surface of the metal to be protected into a thin but dense metal oxide layer. It passivates metals.
During a complex reaction mechanism, which we were able to reveal recently, iron (in simple or in stainless steel) is converted to Fe203 quite in analogy to the passivation of aluminum to Al203 by air. We assume that such a reaction occurs also with other metals like copper, aluminum or zink which are all ennobled by PAni .
In contrast to "rust" (which is a wild mixture from various iron oxides and hydroxides with salt inclusions) Fe203 does not build ever new surfaces for corrosion attack of offer iron cations able to autocatalytically enhance corrosion velocity.
The new coating is shifting the corrosion potential by up to 800 mV (for iron and steel) and more than 2 V for copper. This leads to a dramatic decrease of the corrosion velocity under certain corrosion environments. The new coatings are being offered as primers or concentrates for the development and production of primers.
An efficient corrosion coating system with PAni includes the ennobling primer and a suitable ("sealing") top coat. We have gathered a lot of and positive results of official test institutes up to now, but many more questions have to be answered with thourough research and development and further practical testing, to which we invite all interested companies.
There is actually also a product named "CORREPAIR" which is designed for the "do-it-yourself" expert who has to repair corroded metal products at home. Zipperling gathered very good results in a first test market phase.
