Super-Black Coatings

In the last 20 years, carbon nanotubes (CNTs) have come into their own in all sorts of applications including the coatings industry.  In a very simplistic way they can be described as graphene sheets rolled into tubes. However, their unique properties and learning how to use them is a science in itself.  Within the coatings industry we know they are used in conductive, corrosion control, flame retardant, and camouflage coatings as well as for biofoulant applications.   I wish we would see more articles and presentations dealing with the use of CNTs in coatings.  I thought the following (taken from their website and press release) was interesting and aptly illustrates one of the many CNT uses.

Surrey NanoSystems, a ten year old UK-based company, was founded as a spinout from the University of Surrey. As their name implies they have focused on the development and commercialization of nanomaterials and, in fact, started out in support of the semi-conductor industry.  Their R&D efforts led them to develop super-black coatings to enhance optical imaging systems; these coatings were introduced as Vantablack®.

Vantablack is a super-black coating that set a world record for absorption of light at 99.965%; it is made up of light-absorbing carbon nanotubes, and is applied to surfaces via a chemical vapor deposition process. It was originally developed for satellite-borne blackbody calibration systems, where it increased instrument sensitivity by improving absorption of stray ultraviolet, visible and infrared light. Since then, many other applications have emerged, including solar-energy collector elements, functional surfaces in buildings and architecture, cinematographic projectors, high-performance baffles and lenses, and scientific instruments.  Its ability to deceive the eye also opens-up a range of design possibilities to enhance styling and appearance in luxury goods and jewelry.  Its unique physical and optical properties have resulted in it finding widespread application.

Vantablack absorbs virtually all incident light, making it ideally suited to addressing a host of light-suppression and light-management problems. It reflects so little light that it is often described as the closest thing to a black hole we’ll ever see. With such exceptionally low levels of reflectance, Vantablack produces some startling optical effects; when it’s applied to a three-dimensional object, Vantablack is so black that it becomes extremely difficult to discern any surface features, and three-dimensional objects appear to become two-dimensional.  

To enhance the flexibility of applying super-black coatings, Surrey NanoSystems developed a spray-on version called Vantablack S-VIS  with a reflectance of typically 0.2% in the visible spectrum (@700 nm). This allows super-black coatings to be applied to almost any stable material surface – such as polymers – as well as to large and complex shapes (objects just need to be able to fit into a spray painting booth). The application process is much more flexible than original Vantablack, which is applied in a vacuum chamber using low-temperature chemical vapor deposition (CVD).
Vantablack S-VIS spray paint is manufactured from CNTs (carbon nanotubes) and other organic materials dispersed in a carrier solution. As the solution evaporates, it leaves behind a structured coating that is then subjected to further processing steps. This process functionalizes and binds the coating structure together while forming optical cavities which trap light in a similar way to Vantablack.  Vantablack S-VIS is so effective that its reflectance performance far outstrips any other known paint or super-black coating – and it offers the second-lowest level of reflectance available today, second only to the original Vantablack.

Obviously this use is for specialized applications and needs, but it serves to illustrate the unique opportunities that the CNTs offer in today’s formulations.  I suspect we have but begun to tap their diversified applications. If you have an application paper on the use of CNTs in coatings send it to us to review for possible publication.  The applications are out there, but not much has been in print.