Portland, Ore. A conductive plastic that mixes electronics functions into the material before it is cured could make possible products ranging from disposable e-newspapers to large-scale organic LEDs that can be sprayed on walls.
The patented plastic, Oligotron, was developed by TDA Research Inc. (Wheat Ridge, Colo.) under a National Science Foundation contract. Unlike earlier materials, it uses noncorrosive solvents to manufacture products.
"Before Oligotron the best choice for organic electronics, like OLED [organic light-emitting diode] displays, was water-soluble Pedot," or polyethylenedioxythiophene, said Brian Elliott, principal investigator at TDA. "But water corrodes organics, making Pedot hard [to use] to manufacture devices."
In contrast, he said, by adding two nonconducting molecules to the normal Pedot conducting core, Oligotron not only dissolves in convenient solvents but specialized molecules can be attached to its ends for specific electronics applications. Elliott identified the solvents as propylene carbonate, acetone and nitromethane.
Plastics are popular in every segment of product manufacturing because of their convenient solubility in a variety of inexpensive solvents, enabling plastics to be formed into a final shape like a soda bottle while still a liquid that then becomes solid and insoluble after curing.
Unfortunately, conductive plastics traditionally have been insoluble in nearly everything, making them difficult to fabricate. Pedot, being water soluble, helped but since water (along with oxygen and many other elements in our natural environment) is corrosive to organic electronics, researchers have sought a better solution.
"Many different groups are working on soluble conductive polymers, but we think that TDA Research has a unique solution with its Oligotron material," said National Science Foundation (NSF) program officer Winslow Sargeant. "We are very excited about the easy functionalizing for specific applications, and the easy lithographic methods you can use to fabricate devices with it. This material could be the enabler for large-scale wall-size displays."
TDA Research has just finished phase one of its NSF contract to invent Oligotron. In phase two, which is just starting, it will perfect the dispersion capabilities that enable the material to fabricate various electronic devices. Oligotron is also being made available to other researchers through standard distributors from which they already order supplies.
"We want to beta-test Oligotron by making it available to other researchers through a standard laboratory supplier. We are just chemists, but we hope that electronics experts will experiment with the material and give us suggestions for how to improve it further," Elliott said.
Oligotron, which adds nonconducting molecules to the ends of a conducting Pedot molecule, can be "fuctionalized" by attaching, for instance, transducing molecules to the nonconducting ends. For instance, attaching photosensitive molecules could enable plastic solar cells.
Technically, Oligotron is a soluble and highly conductive multiblock co-polymer, able to be photo-crosslinked to produce printable conducting polymer circuitry.
During manufacturing, Oligotron is mixed with a solvent that permits it to be inkjet-printed into the shape of a circuit. Alternatively, a laser-printed mask on an overhead transparency can be made with the clear part in the shape of the circuit. In either case, ultraviolet (UV) light cures the material, making it solid and insoluble.
In a demonstration for the NSF, a laser printer produced a negative image of the letters (the letters "NSF" were clear on a black background). Then Oligotron was evenly coated on a glass substrate atop which the mask was laid. After exposing the sandwich to UV light, the letters solidified and the rest of the Oligotron was washed from the glass with the solvent.
"We added photosensitive end groups to the Oligotron to create a material that could be printed using an ultraviolet light source to pattern an image that conducts electricity," said Elliott.
TDA hopes that other scientists will synthesize new molecules that build other functions into the basic Oligotron molecule. It was developed under an NSF Small Business Innovation Research contract. NSF has an annual budget of over $5.5 billion from which it makes about 11,000 new funding awards each year (from about 40,000 requests for funding).