This article is part of a 5 article series ‘Scale up to Success’ published by the INSPIRED project. The series tracks the essential aspects of scale up for nanomaterials in printed electronics, and articles will be published every 2 weeks until the end of 2018. You can read articles published to date through the INSPIRED website.
Ensuring the Quality and Consistency of Nanomaterials to Achieve Commercial Success
Ensuring consistent quality in any synthetic process, scale-up process or formulation approach is key to building a loyal customer base. Purchasers, researchers or corporations need certainty that the material they are going to receive meets the required standards and be the same as their previous batch. Such challenges are currently widespread in global graphene supply and a barrier to successful market development.
Ensuring quality with nanomaterials is often more difficult than producing bulk chemicals. This can be due to several factors, including more complex fabrication/synthetic processes and spontaneity in the synthetic routes. These factors also have a knock-on effect in that synthetic processes become harder to control, resulting in a potentially costlier process and ultimately more challenging to scale-up a nanomaterial. Another aspect to consider is that many chemicals and processes have been optimised over many years. In comparison, the fabrication and quality control of nanomaterials is a relatively young area.
Whilst ensuring the quality of nanomaterials (overall) can be tricky enough, it becomes significantly more difficult when nanomaterials are formulated into functional inks. The INSPIRED project has been working to help companies scale up their production of nano-formulated inks, and this includes helping companies to ensure that these inks can be produced consistently and to the required quality.
Thomas Swan, from the UK, is one of the project partners of the INSPIRED project and focuses on scaling up graphene nanoplatelet production and subsequent formulation into functional inks. Although though there is often a trade-off between price and quality, one of the unique selling points (USPs) of Thomas Swan is that it prides itself on the delivery of consistent products.
However, delivering a consistent product is not without its challenges. During the INSPIRED project there were issues with not only trying to understand what properties the customers wanted from their ink formulations, but also from agglomeration and poor dispersion of nanoparticles within the formulations and nanosafety hazards.
Despite this, through efficient post-formulation quality control protocols, Thomas Swan was able to formulate nanomaterial-based inks with consistent properties to deliver a high-quality, cost-effective and safe product in line with its other nanomaterial product ranges. The INSPIRED project supported Thomas Swan by enabling Thomas Swan to test multiple ways of producing larger volumes of raw material and various formulations and, through collaboration with multiple external partner, combining expertise to realise consistent results and products.
Why are inks more challenging?
There are several answers to this question. Consistency must be ensured in at least two separate processes – in the fabrication of the nanomaterials themselves, and in the formulation of the inks. This can also extend out to a third process, providing a consistent printing process onto a given substrate. There are also different needs that must be met at each stage, so the same approach cannot be used for all the different stages.
In the production of the nanomaterial itself, be it copper, silver nanowires, graphene or other, consistent quality arises from the size distribution of the nanomaterial. This can take the form of polydispersity if the material is a nanoparticle, lateral dimensionality if it is a single layered material, or the number of layers in each sample if the material in question is layered. Regardless of the type, ensuring uniformity (there will always be some variation) within each sample (or batch) is key to ensuring a consistent quality in a production process. The main reason for this is that materials with significantly different dimensions act differently to each other, and if this is the case, the material will exhibit differing properties between batches.
Consistency also needs to be maintained in the formulation of the nanomaterial-based ink. There are many constituents in inks and uniform ratios must be achieved, otherwise intended properties could vary between batches. However, it is not just the ratio that should be considered. Many of these formulations have a potential end use as a conductive ink, and it is often the nanomaterial that provides the conductivity. Alongside consistent ratios, uniform distribution of the nanomaterial within the formulation needs to be addressed, because an aggregation of nanomaterials in one region of the ink will leave a nanomaterial gap within the ink, resulting in non-uniform conductivity across the ink. This may also affect the localised ink stability. For electronic applications, stability and uniform conductivity are key, and if these properties are not met, then their use as commercially-viable conductive inks will not be realised.
The final aspect for consideration is the printing process. Whilst it is important for the ink formulation to be uniform in its internal make-up, the printing of the ink also needs to be uniform. This relates closely to ensuring a consistent distribution over a wide area, but this time, the printing process needs to provide a uniform distribution of ink across the surface (i.e. the same thickness). This is to not only ensure an even distribution of conductivity, but to also ensure that there are no ‘bumps’, or ink-less regions, on the substrate.
Regardless of processes used to produce the nanomaterial and the formulated ink, whether batch or continuous methods, quality must be ensured at all points. For batches, this means that the end-user should get a material with the same structure, internal make-up and property if they bought more than one batch of product. For continuous processes, the production line always needs to be kept consistent (even after downtime has occurred).
Nanogap, from Spain, is another manufacturing partner in the INSPIRED project. Its focus is on developing new silver nanowires and their scale up and formulation into functional inks. While Nanogap has broad experience on developing new products and scaling up of process, the formulation was more challenging.
Throughout the INSPIRED project, Nanogap benefitted from the ability to collaborate with other project partners. NANOGAP provided samples to the partners in charge of printing trials and adjusted formulations according to the feedback received. For example, at the beginning of the project, Nanogap formulated and produced the inks itself, but due to issues surrounding the formulation during printing process, some parameters such as concentration, pre-filtration etc. were changed to improve the performances of the inks in printed processes.
For Nanogap, the major efforts were undertaken during the scale up process of silver nanowires, rather than their formulation into the inks. Whilst it was a challenge to reduce the diameter of the nanowires and to alter their aspect ratio (suitable for use in the ink products), by controlling and fixing specific synthetic parameters, Nanogap was able to provide a consistent nanomaterial to other partners.