A new study from physicists at the University of Sussex will “significantly advance” the new technology domain of liquid electronics, improving the functionality and sustainability of probable applications in wearable health monitors, printed electronics and even batteries.
Graphene-wrapped emulsion droplets deposited onto electrodes for single-droplet thin-film electronic devices. Image Credit: University of Sussex.
In their research article published in ACS Nano, the Sussex researchers have added to their earlier work to cover emulsion droplets with graphene and other 2D materials by decreasing the coatings down to atomically-thin nanosheet layers.
By doing so, they could develop electrically-conducting liquid emulsions that are the lowest-loading graphene networks ever recorded — just 0.001 vol%.
This means that the ensuing liquid electronic technology — whether that might be electronic devices printed from emulsion droplets, strain sensors to track physical performance and health, and even possibly more efficient and longer-lasting electric vehicle batteries — will be both inexpensive and more sustainable as they will need less graphene or other 2D nanosheets coating the droplets.
Another important development was that the researchers can, at present, make these electronic droplet networks using any liquids — whereas earlier research concentrated on conventional oils and water — as they have learned how to regulate which liquid droplets are covered in graphene, meaning that they can engineer the emulsions precisely to the preferred application.
Research Fellow in Material Physics in the University of Sussex School of Mathematical and Physical Science and lead author of the study, Dr. Sean Ogilvie explains the science behind the development: “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.
Dr. Sean Ogilvie, Study Lead Author and Research Fellow in Material Physics, School of Mathematical and Physical Science, University of Sussex
“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,” Dr. Ogilvie added.
Alan Dalton, a professor of Experimental Physics at the University of Sussex, was first stimulated by the making of a salad dressing to investigate the potential of incorporating graphene into liquid emulsions.
In bringing the graphene coatings of the liquid droplets down to atomically-thin layers and in opening wide the potential for real-world applications by being able to do so with any liquid material, this research development will significantly advance the emerging and scientifically exciting field of liquid electronics.
Alan Dalton, Professor of Experimental Physics, University of Sussex
Journal Reference:
Ogilvie, S.P., et al. (2022) Nanosheet-Stabilized Emulsions: Near-Minimum Loading and Surface Energy Design of Conductive Networks. ACS Nano. doi.org/10.1021/acsnano.1c06519.