The “Coffee Ring Effect”: Inspiring the Design of Self-Assembling Conductive Circuits

Thousands of conductive circuit arrays are self-assembled in just one minute by utilizing the coffee ring effect.

Large-scale conductive networks are desirable for a multitude of fields such as optoelectronics and biomedical devices. Currently, these are limited by low efficiency fabrication methods and unreliable pattern control, using complex set-ups and multiple fabrication steps.

Now, researchers from Massachusetts Institute of Technology and Harvard University, and Huazhong University of Science and Technology (China), have reported in Advanced Functional Materials their simple, one-step method for rapid fabrication of thousands of conductive circuit arrays with different, completely predictable geometries and dimensions that are self-assembled simultaneously over a large area (75 mm × 50 mm) in 1 minute.

The whole procedure is enticingly simple. A gold nanoparticle solution is pipetted onto a glass substrate that is patterned with a polydimethylsiloxane (PDMS) nanofilm. The nanoparticles then self-assemble into 1D wires, according to the PDMS pattern, as their solvent evaporates and the “coffee ring effect” takes hold.

When combined with a PDMS elastomer, the self-assembled circuit can be used for flexible electronic devices. Furthermore, this technique can be applied to numerous other nanoparticles, e.g., quantum dots or polystyrene, for a variety of functional applications.

With some more practice, the researchers propose that their reproducible patterns could be scaled-up by machinery to achieve high-throughput, precisely patterned electronics.

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