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Once dried the ink can be bent without losing conductivity

Hybrid ink allows electronic circuits to be drawn by hand

A hybrid ink composed of both organic and inorganic electronic materials has been developed that allows electronic circuits to be applied to paper directly from a pen.

To create the hybrid ink, research scientists at Leibniz Institute for New Materials (INM) in Germany coated nanoparticles made of metals with organic, conductive polymers and suspended them in mixtures of water and alcohol.

The mixture can then be directly applied to paper or foil using a pen and it dries without any further processing to form a functional electric circuit.

“Electrically conductive polymers are used in OLEDs, for example, which can also be manufactured on flexible substrates,” explains INM’s Tobias Kraus who worked on the project.

“The combination of metal and nano-particles that we introduce here combines mechanical flexibility with the robustness of a metal and increases the electrical conductivity”.

The developers combine the organic polymers with gold or silver nanoparticles with the organic compounds serving a multitude of functions in the mixture.

They work as ligands, neutral or negatively charged particles, that ensure the nanoparticles remain suspended in the liquid mixture; any agglomeration of particles would have a negative effect on the printing process.

They also ensure that the nanoparticles have a good arrangement when drying. Ultimately, the organic compounds act as 'hinges' - if the material is bent, they maintain the electrical conductivity.

In a layer of metal particles without the polymer sheath, the electrical conductivity would quickly be lost when the material is bent.

Due to the combination of both materials, when bent the electrical conductivity is significantly better than layers made solely from conductive polymers or metal nanoparticles.

“Metal nanoparticles with ligands are already printed to form electronics today,” Kraus said. “Our new hybrid inks are conductive as soon as they have dried. As well as being particularly mechanically flexible, they do not require sintering." Sintering is the process of compacting and forming a solid mass of material by heat or pressure without turning it into a liquid.

The hybrid ink could allow future electronic circuits to be easily printed as part of the manufacturing process or it could be incorporated into a 3D printer to allow consumers to print their own circuits.

Stretchable electronics were unveiled last month that can be stretched up to four times their original length and could be incorporated into artificial skin, body sensors and clothing.

A team from the American Chemical Society has also demonstrated self-propelled nanomotors that can seek out and repair tiny scratches to electronic systems that may be disrupting conductivity pathways.

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