Application of nanotechnology to specialty chemicals 20th May 2019
By Liam Critchley
Nanotechnology is no longer a niche area, says Liam Critchley. Many applications are already seeing the use of nanomaterials in en
Nanotechnology is no longer a niche area, says Liam Critchley. Many applications are already seeing the use of nanomaterials in end-user products, and their scope is only going to grow as more industries adopt them.
Nanotechnology’s application reach is vast. Nanomaterials are already here in many commercially available products, and this is only going to grow as more industries adopt them. In particular, nanomaterials are starting to find a lot of use in the speciality chemicals space, especially in coatings, paints, polymers and composites. This is because nanomaterials often have active surfaces and a very high relative surface area, which enable them to form strong bonds in coating mediums, composites and inks, as well as other dispersion mediums. In this article, we look at just a few examples of how the field is developing.
One of the most rapidly growing concepts, trialled applications and real-world uses for nanomaterials is barrier coatings. Many nanomaterials are inherently stable to moisture, humidity, high temperatures and pressures, abrasion, and various hazardous and corrosive chemicals. This makes them ideal for providing barrier properties. While it is uncommon to find a single nanomaterial that can protect against all of these – with the exception of graphene, depending on how it is formulated – many nanomaterials can provide a barrier to multiple stimuli. These range from 2D materials, to nanoclays and nanoceramics, to various nanocomposites. So, it should come as no surprise that there is a whole host of potential applications, from protecting ships against corrosion or aircraft engines from high temperatures, to protecting food from moisture or oilfield equipment from corrosive gases. Nanotechnology barrier coatings even extend to everyday technology, such as mobile phone displays, and this is being realised by companies such as NanoFixit from The Philippines.
Recent developments have also led to more environmentally friendly nanotechnology-based barrier coatings. This is an area that is growing commercially, especially when many companies need to think about their environmental impact. One of the main materials used in this way is nanocellulose, i.e. nanosized crystals or fibres of cellulose, with CelluForce from Canada leading the way in this area.
In some circumstances, it is more beneficial to formulate the nanomaterial into a dispersion, where it can be coated using conventional methods, such as spin coating. In other instances, nanomaterials can be formulated into an ink, and the coating can be ‘printed’ on the surface. Another common method is to formulate the nanomaterial into a polymer matrix and then coat the polymer-based nanocomposite onto a surface. In other scenarios, the nanomaterials can be directly applied to a surface through bottom-up nanofabrication methods, such as chemical vapour deposition (CVD), physical vapour deposition (PVD) or atomic layer deposition (ALD).
Each method has its own advantages and disadvantages, and the choice depends on how well the nanomaterial will formulate. Some are inherently hard to disperse into a liquid medium, so embedding them into a nanocomposite can be a better choice. Likewise, some don’t take to polymer matrices but can be dispersed in an ink or liquid medium. There are cases where it is hard to do either, so they need to be directly applied to the surface. But this again has its own drawbacks, such as the limited surface size that can be coated. Applying a nanomaterial-based barrier coating is often dependent on many factors, which is why many are still at trial stage, but it is an area that has a huge amount of potential across many applications and industries.
Another developing area, especially within electronics and textiles, is the use of conductive coatings. While there are different materials that can be used, graphene is by far the front-runner in this space and is being trialled at both an academic and industry level as a means for producing flexible and printable circuitry, as coatings in energy storage devices, and to provide a conductive pathway in electronic textiles (e-textiles) by coating the fibres (which turns the garment into a conductive medium for any embedded electronics – such as sensors and other monitoring devices).
Unlike barrier coatings, there are fewer fabrication and formulation methods for these applications. The main methods in the electronics space are inkjet printing and applying liquid-based coatings, whereas they can be dip-coated in textile applications.
In electronics, one of the key drivers for using graphene-based conductive coatings is to create wearable, flexible and printable electronics, so a lot of work is focussed on the optimal way of formulating graphene into an ink and the best ways of printing a uniform coating.
In the textile space, most graphene coatings are used to thermally dissipate heat (i.e. thermally conductive coatings). This had already been realised in a number of commercially available garments, but its use as a conductive medium in the textile space is relatively new. There is also a big drive to develop clothes that can sense and monitor various points on the body, so this is an area that is likely to grow. The partnership between Directa Plus and Deewear, both from Italy, has so far yielded one of the widest ranges of thermally regulating clothes, by using printed graphene-based coatings between textile layers.
As mentioned above, nanomaterials can be used in food packaging to provide a barrier to moisture. However, as well as simply reducing the humidity in the internal environment, there is another way in which nanomaterials can be used in food packaging. This is through using nanomaterial-based sensors, which are coated on the walls of the packaging.
Nanomaterials make very efficient sensors (this is another big application area for nanomaterials) because of their active surfaces. Nanomaterials can be formulated into polymer matrices and coated inside the packaging to detect when food has gone bad, usually by detecting the presence of chemicals or contaminants that induce a reaction with the nanomaterial. This can provide a visual sign that the food is not safe for consumption. It’s a niche area, but it’s one that is developing a lot of interest in the smart packaging industry.
Another area of smart coatings involves quantum dots. Quantum dots can be applied through a transparent coating or ink to products that are susceptible to counterfeiting (e.g. cigarette packets). The small size of quantum dots gives them unique fluorescence properties which cause them to emit light under ultraviolet (UV) light. Therefore, coating packaging with a specific array of quantum enables people to detect whether the product is a fake or not when shone with UV light. They can also be used to trace and identify products along the supply chain by putting a separate quantum dot pattern on each product to act as a ‘barcode’. This is again a niche area, but one which is being realized commercially by the likes of IQDEMY (Switzerland) and Dotz Nano (Australia).
While coatings are one the most promising areas in the realm of speciality chemicals, nanomaterials are also starting to show their worth in paint formulations. A few key nanoparticles are being used as additives to improve the properties of paints (alongside other common additives). Given that there are not many well-established nanoparticles yet, it makes it much easier to discuss the specific nanoparticles rather than the use of nanomaterials as a class of materials (which is the case for coatings).
In many commercial paints, titanium dioxide (TiO2) is one of the most widely used additives, so it may come as no surprise to learn that TiO2 nanoparticles are also the front-running nano-additive for paints. But it’s use is far different to that of its bulk additive counterpart. Whereas bulk TiO2 is used to whiten the paint formulation, TiO2 nanoparticles are being used to improve the self-healing, thermal insulating, anti-bacterial, UV resistance and fire resistance properties of paint.
Other nanoparticles being tested for use in paints include silicon dioxide, copper nanoparticles and silver nanoparticles. These have not been as well-documented, as many showcase the same effects as TiO2 (but are less beneficial overall). However, they can offer key added benefits such as antibacterial effects, improved barrier properties, improved wear resistance, and an improved resistance to water, graffiti, fire and high temperatures. Even AzkoNobel, who have been a leading figure in the paint industry for many years, are starting to develop paints that include nanomaterials.
Nanotechnology is making its way into many coatings, paints and other specialty chemical applications. One of the main drivers is their barrier properties, and their ability to stay embedded within a matrix. While migration is not an issue for some applications, for applications within the food industry it is of utmost importance, as no-one wants them entering their food.
There is a great deal of work being done in both industry and academia, and many applications are already being realised commercially. However, the area will continue to expand as more people start to the realise the vast potential of nanomaterials, and as scientists find more effective ways to formulate them. These developments should be watched carefully by anyone in the specialty chemicals space, as they are likely to impact on many sectors of industry, bringing new nano-opportunities on a potentially mega-scale.
With two master’s degrees in chemistry with nanotechnology (MChem) and chemical engineering (MSc by Research), Liam Critchley has written more than 500 articles on chemistry and nanotechnology. He holds two international advisory board positions for nanotechnology associations – the National Graphene Association (NGA) and Nanotechnology World Network (nWN) – as well as a trustee board position for the UK science charity GlamSci.