Bottle of graphene-wrapped emulsion droplets which can be used as a functional ink or assembled into conductive networks and sensors
New research from physicists at the University of Sussex will ‘significantly advance’ the new technology area of liquid electronics, enhancing the functionality and sustainability of potential applications in printed electronics, wearable health monitors and even batteries.
In their research paper published in ACS Nano, the Sussex 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 – just 0.001 vol%.
This means that the subsequent liquid electronic technology – whether that might be 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 both cheaper and more sustainable because they will require less graphene or other 2D nanosheets coating the droplets.
Another significant development was that the scientists can now make these electronic droplet networks using any liquids – whereas previous research focused on conventional oils and water – because they have discovered how to control which liquid droplets are wrapped in graphene, meaning thatthey can design the emulsions specifically to the desired application.
Research Fellow in Material Physics in the University of Sussex School of Mathematical and Physical Science and lead author of the paper, 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.
“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.”
Professor of Experimental Physics at the University of Sussex, Alan Dalton, who was first inspired by the making of a salad dressing to explore the potential of adding graphene to liquid emulsions, explains why this development is exciting: “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.”
The research paper ‘Nanosheet-Stabilized Emulsions: Near-Minimum Loading and Surface Energy Design of Conductive Networks’ can be accessed here.
Nanosheet-stabilised Emulsions: A Route Towards Single-droplet Devices
Our work on nanosheet-stabilised emulsions demonstrates that 2D materials (including graphene and molybdenum disulfide) confer emulsion stability and network conductivity at volume fractions as low as 10⁻⁵. Emulsions can be deposited as inks for functional thin films which preserve droplet structure and eliminate the notorious coffee ring effect, highlighting the potential for printed single-droplet devices.
Did you know that nitrogen dioxide (NO2) levels in Brighton are among the highest in the UK? NO2 is an air pollutant that originates from combustion engines and industrial processes. Long-term exposure to NO2 can cause respiratory issues, which can be particularly severe and even life-threatening for babies and asthma sufferers. We have developed a laser deposited carbon aerogel gas sensor with exceptional selectivity towards NO2.
Using a combination of graphene and silver nanowires we have developed an optically transparent, flexible touchscreen technology, eliminating the need for glass smartphone screens. Current touchscreen technology requires rare-earth alloys which are extracted by mining, making them unsustainable and expensive. This graphene technology would significantly reduce the cost of smartphone screens while improving their durability and flexibility.
We have developed highly sensitive breathing monitors out of a simple mixture of oil, water and graphene. These are a cheap, non-intrusive alternative to the current technology, with potential to alert parents of any change to their child’s breathing via their smartphone, potentially preventing seizures and cot death, which sadly affect hundreds of families each year.