2D materials shroud liquid droplets to exploit electronic properties

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Physicists at Sussex University have developed a method of wrapping 2D materials around liquid droplets to exploit their electronic properties, an advance with potential applications in printed electronics and healthcare wearables.

2D materials
Graphene-wrapped emulsion droplets deposited onto electrodes for single-droplet thin-film electronic device (Image: Sussex University Materials Physics group)

The scientists have built on their previous work to wrap emulsion droplets with graphene and other 2D materials by reducing the coatings down to atomically-thin nanosheet layers. In doing so they were able to create electrically-conducting liquid emulsions that are the lowest-loading graphene networks ever reported at 0.001 vol%.

According to Sussex University, this means that the subsequent liquid electronic technology –strain sensors to monitor physical performance and health, electronic devices printed from emulsion droplets, and even potentially more efficient and longer-lasting electric vehicle batteries - will be cheaper and more sustainable because they will require less graphene or other 2D nanosheets coating the droplets.

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Significantly, the scientists can now make these electronic droplet networks using any liquids (previous research focused on oils and water) because they have discovered how to control which liquid droplets are wrapped in graphene, so emulsions can be designed specifically to the desired application. The team’s findings are published in ACS Nano.

In a statement, Dr Sean Ogilvie, research fellow in material physics in Sussex University School of Mathematical and Physical Science and lead author of the paper, said: “The potential of 2D materials, such as graphene, is in their electronic properties and their processability; we developed a process to harness the surface area of our nanosheet dispersions to stabilise emulsion droplets with ultra-thin coatings.

"The tuneability of these emulsions allows us to wrap 2D materials around any liquid droplets to exploit their electronic properties.  This includes emulsion inks, in which, we've discovered that droplets can be deposited without the coffee ring effect which hinders printing of conventional functional inks, potentially enabling single-droplet films for printed transistors and other electronic devices.

“Another exciting development for our research group is that we can now also design and control our emulsions towards specific applications such as wrapping soft polymers such as silicone for wearable strain sensors that exhibit increased sensitivity at low graphene loading, and we are also investigating emulsion assembly of battery electrode materials to enhance the robustness of these energy storage devices.”