Indian scientists use tiny bubbles to draw plastic circuits

In a first, Indian scientists have found a way to use micro-bubbles to draw complex plastic circuits with lasers, an advance that may lead to low-cost flexible electronic devices.
Solution-printed electronics is one of the fastest growing areas in the industry primarily due to its very low cost and flexibility, researchers from the Indian Institute of Science Education and Research (IISER) in Kolkata said.
It is mostly based on conducting plastics, that are doped to increase conductivity.
The process of synthesising, doping and designing circuits separately is often complex and time consuming.
For the first time, scientists led by Ayan Banerjee and Soumyajit Roy from IISER Kolkata, have developed a simple and inexpensive technique to simultaneously synthesise and pattern conductive polymers on a glass surface in a matter of minutes.

They exposed a solution of charged metal oxide, known as soft oxometalate (SOM) and organic molecules in a glass chamber to optical tweezers - a tightly focused laser.

Absorbing the beam, oxometalate stuck to the chamber surface to form a micro-bubble around which the metal oxide and organic molecules assembled themselves to form conductive polymers.
"This patterning technique was discovered somewhat serendipitously when one of my graduate students was working with SOMs in optical tweezers and noticed these bubbles grow unexpectedly," Banerjee, associate professor at IISER Kolkata, told PTI.
Bubbles in optical tweezers often occur when the tightly focused laser hits some accumulated material which partially absorbs the light, so that the local temperature increases very rapidly.

However, these also can be dispensed easily by just redirecting the laser or shutting it off.
"In the case with the SOMs, the student observed that when he tried to move the laser away, the bubble followed it, and in the process generated a pattern in its wake," Banerjee said.
"We then proceeded to unravel this mystery, and in the process understood the phenomenon, which took more than a year," he said.
"The research revealed fascinating explanations, which then led to us think of various applications," he added.
This method can be used for complex electronic circuits which are useful for fabricating electronic devices such as micro-capacitors.

According to Roy, associate professor at IISER Kolkata, the method is cheaper and much easier than several existing technologies.
"The method can even be used to make biodegradable flexible plastic circuits," Roy said.
The research was published in the Journal of Materials Chemistry C.