“Blackest Black” to Date Developed by MIT Engineers
Renee Shaine R. Balanay
The “blackest black” is a constantly moving target. Someone will find a blacker material, and eventually we’ll understand all the underlying mechanisms, and we will be able to properly engineer the ultimate black.
The pursuit of the darkest material has long traversed the world of art. “Vantablack” is an extremely dark paint material that has developed controversy in the field and is owned by artist Anish Kapoor. To rival Vantablack, artist Stuart Semple created an acrylic paint called “Black 3.0”. This has sparked the interest of MIT engineers and has led them to develop a material that is 10 times darker than anything that has been previously synthesized.
Brian Wardle, a professor of aeronautics and astronautics at the Massachusetts Institute of Technology, along with a team of MIT researchers created the coating while they were finding new methods to grow carbon nanotubes on aluminum to increase its conductivity.
The coating is made from vertically-aligned carbon nanotubes grown on chlorine-etched aluminum foil and is reported to have the ability to absorb 99.995% of visible light. To bear comparison, Vantablack, the coating created by Surrey NanoSystems, only absorbs up to 99.96% of visible light.
Carbon nanotubes, or CNTs for short, are cylindrical molecules that are comprised on rolled-up sheets of single-layer carbon atoms called graphene. CNTs are chemically bonded with sp2 bonds, which is a very formidable molecular interaction. Carbon nanotubes have a natural inclination to link together through Van Der Waals interactions, forming an avenue to develop lightweight and strong materials that are electrically and thermally conductive.
The process of developing the “blackest black” material did not actually start with the intention of creating the darkest color; the research strictly considered the thermal and electrical properties of the material.
While attempting to grow CNTs on aluminum, the researchers found that a layer of oxide coats the aluminum when exposed to air, creating a layer of insulation as opposed to the initial intention of developing a conductor.
The aluminum foil was soaked in salt water to extract the oxide layer. Then, the foil was transferred to an oxygen-free environment to avoid reoxidation from taking place. Finally, the etched aluminum was placed in an oven and techniques to grow CNTs were conducted; this process is known as chemical vapor deposition.
Kehang Cui, one of the MIT researchers, mentioned that they noticed an initial black color when they began experimentation, but they observed that the addition of carbon nanotubes formed an even darker color. This observation led them to analyze the optical reflectance of the sample, obtaining the data of 99.995% absorbed visible light.
Carbon nanotubes contain miniscule clusters that can trap light and convert most incoming light to heat. However, Wardle stated that the reason for CNTs being extremely black still needs more mechanistic understanding and study in the future.
The material has attracted interest from the aerospace industry since it has the potential capacity to reduce unwanted glare for instruments such as telescopes and cameras as well as withstand the harsh conditions of outer space. Further developments with this material can surely be expected.
The researchers published their findings in the journal ACS-Applied Materials and Interfaces. The MIT team also collaborated with Diemut Strebe, a resident artist in MIT Center for Art, Science, and Technology, to showcase the material in an art piece called “Redemption of Vanity”; Strebe coated a $2,000,000 yellow diamond with the “blackest black” material, making the brilliant gem look like a floating black void.
Wardle mentioned that the “blackest black” is a constantly moving target. “Someone will find a blacker material, and eventually we’ll understand all the underlying mechanisms, and we will be able to properly engineer the ultimate black”, he adds.
