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Nanoparticles, and nanomaterials in general, have become one of the new active materials being put into ink formulations to make the ink conductive. There are many reasons why this is being done, with the most common being that some nanomaterials have extremely high electrically conductive properties that can be utilized in an ink formulation. Here, we look at these conductive inks in a bit more detail and how they are helping to realize printable electronics.
End-user companies that operate within the electronics space are always trying to bring down the size of their components and circuitry to make the overall device smaller. In many cases, this reduction in size needs to be accompanied with a performance that is just as good, if not better, than the bulkier technology. So, one way that has emerged to achieve this is by formulating nanoparticles into ink formulations, followed by printing these inks on to a substrate to act as a conductive medium—i.e. a printed electronic circuit. Aside from making devices smaller, they are often more flexible than bulk circuitry, so have also gained a lot of interest in the wearable and flexible electronics application space as well.
Nanomaterials in Ink Formulations
So, why nanoparticles? There are many reasons why. There are many different nanomaterials out there, such as graphene, silver nanoparticles and silver nanowires, that are highly conductive. Moreover, it is often the case that only a few wt% is only required in a formulation to make it conductive, meaning that they are not as expensive as many might think. Because nanomaterials are being formulated, rather than bulk materials, the ink can be printed in a very thin layer on top a substrate. The application process can also be as simple or as complex as required. There are cases where companies use specific additive manufacturing methods (and associated software) to produce conductive pathways, but other companies simply print these conductive networks using an inkjet printer.
The key for any nanoparticle ink to be successful relies on uniformity across all the different stages. First off, the nanomaterials used need to be uniform (or as uniform as possible), in terms of size, composition, surface functionalization, and active properties. Secondly, how the nanomaterial is dispersed within the formulation is key, as the formulation needs to be as monodisperse as possible. If not, there will be regions within the ink that have a large concentration of nanoparticles, and areas without any at all, which would lead to highly conductive and insulating regions, respectively, which would affect the conductive performance of the ink. Finally, the printing of the ink itself needs to be uniform, otherwise you can end up with areas with no ink and areas with too much ink, which again, can affect the performance of the printed circuit—which is not an ideal scenario for any electronic device application.
Uses of Ink Formulations
So, many might wonder what happens when you print an ink, can they be encased with protective, insulating materials when they are so thin? While it is trickier than the normal coating, molding and potting methods used in many consumer electronics, there are also ink formulations out there which are dielectric in nature. These ink formulations act as an insulator and can be used in the same way as insulating materials are used in electronics, with the difference being that they can be printed. These formulations usually take the form of polymer-based inks which provide a protective, insulating barrier to the conductive medium, while ensuring that the device can remain thin and flexible.
On-Going Research on Nano-Conductive Inks
However, it’s an area that’s not without its challenges. Formulating an ink is not the easiest task at the best of times, never mind when nanomaterials are involved—which can be tricky to formulate in their own right. Luckily, there is a lot of work being done in this space to learn how to better formulate these inks into end-user products. This is not only being done by companies, but through EU-funded projects such as INdustrial Scale Production of Innovative nanomateRials for Printed Devices (INSPIRED). Projects such as INSPIRED have been looking at how to improve the production capacity of nano-conductive inks, to help bring the price down to a level where it is more realistic from a commercial perspective. On the other hand, it has also looked at the safety of these nanomaterial inks—from raw handling to end-user product—to ensure that consumer safety is not going to be an issue for nanomaterial-based inks, as well as looking at how to reduce waste associated within the production process. While these areas may not be as exciting as the finished product, they are steps which are necessary if the technology is to mature and be used globally, and projects such as INSPIRED, alongside the work done by companies, has given nanomaterial-based inks a great platform to build on.
The utilization of nanoparticle conductive inks is no longer a technology that is confined to the academic lab, as there are companies out there who are creating these formulations and using them in real-world products. As scientists find new and more efficient ways of dispersing and formulating nanomaterials into inks, it is an industry that is certain to grow, as the consumer demand is there for the types of devices that these inks will help to create.
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