Wet deposition of carbon nanotube black coatings for stray light reduction in optical systems

• Simple and low cost method proposed for producing non-reflective, high light-absorbing coatings
• Super-black coating for stray light reduction in optical systems
• Method based on wet deposition of carbon nanotube formulations
• Suitable for coating large areas and 3D structures
• Coating performance can be controlled by the MWCNT/binder concentration.

Stray light, also known as optical noise, affects the performance of many optical devices. It can be reduced to a tolerable level by well-designed and well-baffled system or/and by using functional black coatings that are fabricated in a complex and costly process. Carbon nanotubes (CNTs) absorb light strongly, making them an ideal candidate for realizing a super black coating. CNT coatings were formed by spraying formulations composed of a silicon binder and low cost multiwalled CNTs on a pre-heated aluminum plate. The diffuse reflectance of the coatings in the VIS range (350–800 nm) was in the range of 2.6–5.11%, depending on the MWCNT concentration in the coating. In the NIR range (850–2400 nm), the reflectance values were in the range of 4–6.5%, however the dependence on MWCNT concentration was not very significant. Excellent adhesion to the aluminum substrates was achieved, for coatings with CNT concentration below 15%, while still having very low reflectance, even at temperature cycling between 200 °C and − 196 °C. The proposed coating formulations enable simple and low cost approach for producing high light-absorbing coating of complex 3D structures within a very short time by wet deposition of CNTs.