첨가물 ≫ 색소 ≫

세상에서 가장 검은 색, 밴타블랙  

구조색
- Shape : 형태가 기능이다
- 전반사 = White : Cloudy, 안개, 산호
- 회절격자
- 다층박막
- 구조와 색 : 꽃잎 색상의 물리학
- 구조와 색 : 세상에서 가장 검은 색

세상에서 가장 검은색 ‘밴타블랙’
빛흡수율 99.96% '블랙홀 만큼 검다'

사이언스타임즈 김준래 객원기자 stimes@naver.com

앞이 캄캄하여 아무 것도 보이지 않을 때, ‘칠흑(漆黑)같이 어두운 밤이다’라는 표현을 쓴다. 칠흑이란 옻칠처럼 짙고 검은 색을 말하는데, 최근 이 보다도 훨씬 검은 ‘세상에서 가장 검은 색’이 등장하여 과학계의 관심이 모아지고 있다. 바로 ‘밴타블랙(Vantablack)’이다.

 
밴타블랙은 현존하는 가장 검은색 물질이다 ⓒ SurreyNanoSystems

첨단 생산기술 전문 매체인 ‘매뉴팩쳐링넷’(Manufacturing.net)은 빛을 거의 완벽하게 흡수하여 우주의 블랙홀만큼이나 검게 보이는 ‘밴타블랙’이라는 신물질이 주목을 끌고 있다고 보도하면서, 앞으로 우주관측 및 국방 분야에서 유용하게 사용될 것으로 보인다고 전망했다. (관련 기사 링크)

현존하는 가장 검은 색인 밴타블랙

밴타블랙은 영국의 나노테크 전문기업인 서리나노시스템즈(Surrey NanoSystems)가 개발한 물질이다. 탄소나노튜브를 제조하는 저온 공정을 통해 만들어진 이 물질은, 현존하는 색들 중 가장 검은 것으로 밝혀졌다. 탄소나노튜브는 머리카락 1만분의 1 크기에 불과한 작은 물질이다.
얼마나 검기에 세상에서 가장 검은 색이라고 할까? 밴타블랙의 가시광선 흡수율은 99.96%인 것으로 측정되었는데, 보통 검은색의 흡수율이 95∼98% 정도인 것을 감안하면 밴타블랙의 색도가 얼마나 검은지를 짐작할 수 있다.
이론적인 설명이 피부에 잘 와닿지 않을 때는, 아래의 사진을 참조하면 어느 정도 궁금증을 해소할 수 있다. 런던의 과학박물관에 전시된 2개의 얼굴 조각상인데, 밴타블랙이 칠해져 있는 한 쪽 조각상은 굴곡이 있음에도 불구하고 마치 평면처럼 보인다는 것을 알 수 있다.


 
밴타블랙으로 코팅된 조각상은 평면처럼 보인다 ⓒ SurreyNanoSystems

사람의 눈은 빛의 반사에 의해 물체의 요철을 구분한다. 반사율이 높은 밝은 색일수록 요철을 확연하게 구분할 수 있는 반면에, 반사율이 낮은 어두운 색일수록 요철을 구분하기가 쉽지 않다. 따라서 어떤 물체에 완벽한 검은 색이 칠해져 있다면, 그 물건에 요철이 있다 하더라도 평면처럼 보이게 될 것이다.
서리나노시스템즈의 최고기술책임자(CTO)인 벤 젠슨(Ben Jensen)은 “밴타블랙의 색이 얼마나 검은지, 구겨진 은박지도 밴타블랙이 칠해지면 질감이 전혀 느껴지지 않을 정도”라고 전하며 “이 같은 현상은 기계도 마찬가지여서, 흡수하는 빛의 스펙트럼을 계측하는 분광기(spectrometer)로도 측정할 수 없다”라고 소개했다.
그는 “밴타블랙이 눈에 보이는 가시광선뿐 아니라 적외선 영역까지 흡수하기 때문에 이 같은 현상이 발생한다”라고 설명하며 “레이저포인터의 빛마저 밴타블랙을 만나면 사라질 정도로, 이 초미세 탄소 구조체는 거의 모든 빛을 빨아들인다”라고 덧붙였다.
의류 제작에 활용될 가능성을 묻는 질문에 대해 젠슨 이사는 “만일 밴타블랙으로 옷을 만들게 되면 레이스 부분이나 실밥처럼 눈에 띌 만한 특징까지 모두 보이지 않게 될 것”이라고 예상하며 “드레스를 입은 사람의 머리와 손발이 마치 검은 구멍에서 나온 것처럼 기괴하게 보일 수도 있다”라고 답변했다.

우주관측 및 군사위성 등에 활용

과학계가 밴타블랙의 탄생에 관심을 기울이는 이유는 그 용도가 실로 무궁무진하기 때문이다. 우선 천체 관측을 하는 망원경에 적용되면, 지금까지 해결하지 못했던 난반사 문제를 일거에 해결할 수 있을 것으로 기대를 모으고 있다.
멀리 떨어진 별을 관측할 때 가장 큰 장애물은 주변 빛에 의한 난반사다. 이런 문제를 해결하기 위해 망원경 내부에 검은색을 칠하여 불필요한 빛을 흡수하는 조치를 취했지만 한계가 있었다.
난반사에 따른 빛의 반사율이 국내 망원경은 7% 정도이고, 미 항공우주국(NASA)의 망원경도 1% 수준에 머무르고 있다. 하지만 밴타블랙을 사용하면 반사율이 0.04% 정도로 줄일 수 있다는 것이 대다수 전문가들의 의견이다.
우주관측 외에 밴타블랙의 활약이 기대되는 분야는 바로 군사무기를 개발하는 국방분야다. 군사전문가들은 첩보 위성의 표면을 밴타블랙으로 칠하면, 적의 눈에 띄지 않으면서 완벽한 첩보업무 수행을 할 수 있을 것으로 예상하고 있다.
이 밖에도 밴타블랙은 높은 열전도율과 인장력을 갖추고 있다. 따라서 구리보다 7.5배에 이르는 효율로 열을 전달할 수 있고, 강철보다 10배나 높게 늘어날 수 있다.
젠슨 이사는 “밴타블랙의 이런 특성 덕에 실제로 발견할 수 없는 수준의 가스 입자 이탈을 방지하고, 먼지를 없애는 데에도 도움이 될 수 있다”라고 강조하며 “물론 부품 등을 코팅 처리하는 데에도 활용될 수 있을 것”이라고 기대했다.



So why IS Vantablack so incredibly dark?
In order to understand exactly how dark this material is, we have to go back to this idea of carbon nanotubes. Growing carbon nanotubes is not a new technology, and have been proposed for potential use in situations like cleaning oil spills and boosting solar energy storage due to its amazing structural makeup.

A visualization of the material; to give you an idea of scale, this material is almost 50,000 times smaller than a human hair.
The material is 200 times stronger than steel, 1000 times more conductive than copper, and almost half the density of aluminum (an important point that we'll revisit). According to the inventors of Vantablack, Surrey Nanosystems, when light interacts with this incredibly low density material it "is rapidly absorbed as it 'bounces' from tube to tube and simply cannot escape as the tubes are so long in relation to their diameter and the space between them. The near total lack of reflectance creates an almost perfect black surface."

 

6 Facts About Vantablack, the Darkest Material Ever Made

Jessica Hullinger

In the Antenna wing of the Science Museum in London, a bronze bust of a man sits behind a wall of glass. The face, which belongs to BBC presenter Marty Jopson, isn’t very big—maybe 6 or 7 inches tall. It’s highly textured, and light catches in its rivets and dimples. Aside from the playfully upturned edges of Jopson’s mustache, there’s nothing particularly remarkable about this bust. But next to it sits an identical bust that absolutely boggles the mind. It looks like someone has cut a hole in the air in the shape of Jopson’s head, leaving only a gaping, empty blackness. The texture of the face disappears into a velvety mass; only from the side is it possible to tell that the bust has any dimension at all.  
This visual magic is the work of Vantablack, the darkest material ever made by man. The ominously named coating, which absorbs virtually all light, was created by British company Surrey NanoSystems to help eliminate stray light in satellites and telescopes. It has since gathered a rabid following of artists, designers, and other curious creatives desperate to get their hands on the stuff. But despite its popularity, there’s still a lot of confusion about what this mysterious material actually is and how it can be used. mental_floss recently spoke with Surrey NanoSystem’s Steve Northam to find out about all things Vantablack; here's what we learned.

 

1. IT'S NOT ACTUALLY A COLOR.

Let’s get technical for a minute. Color, as we humans know it, is the result of the way light is reflected off of an object and into our eyes. Different light frequencies translate into different colors. Vantablack isn't a color, but a material. It’s made of a “forest” of tiny, hollow carbon tubes, each the width of a single atom. According to the Surrey NanoSystems website, “a surface area of [1 centimeter squared] would contain around 1000 million nanotubes.” When light hits the tubes, it’s absorbed and cannot escape—which means that actually, Vantablack is the absence of color.


2. YOU CAN'T BUY IT.

Because it’s not a pigment or a paint, you can’t just buy a bucket of it and dip a brush in and slather it onto your walls. The nanotubes that make up Vantablack must be grown in the Surrey NanoSystems lab using a complicated (and patented) process involving several machines, a few layers of different substances, and some extreme heat. From start to finish, applying Vantablack to an object can take up to two days, according to Northam. “I had an inquiry yesterday asking how much would it cost for a kilo of Vantablack pigment,” Northam says. “First of all, I can’t sell you a bucket of Vantablack, but if I could, I don’t think there’d be much on the planet that would be more expensive.” He says that, ounce for ounce, Vantablack is a lot more expensive than both diamond and gold.


3. IT DOESN'T FEEL THE WAY IT LOOKS.

“One of the things that people often say is ‘Can I touch it?’” Northam says. “They expect it to feel like a warm velvet.” Though Vantablack does have a sort of soft, velvety look to it, Northam says that doesn’t translate to physical sensation. When you touch Vantablack, it just feels like a smooth surface. That’s because the nanotubes are so small and thin, they simply collapse under the weight of human touch. Here’s how Northam describes it: “Imagine you have a field of wheat, and instead of the wheat being 3 or 4 feet high, it’s about 1000 feet tall. That is the equivalent scale that we’re talking about for nanotubes. The reason they work is they’re very, very long compared to their diameter. It will stay upright and not blow away in the wind, but if you then try and land a plane on it, you’ll make a dent.” So, Vantablack is pretty susceptible to damage, which is why it can’t yet be applied to unprotected surfaces like cars or high-end gowns—one brush of a hand and the material would lose its magic.


4. IT HAS ALMOST NO MASS.

While Vantablack is sensitive to touch, it’s super robust against other forces, like shock and vibration. This is due to the fact that each carbon nanotube is individual, and has almost no mass at all. Plus, most of the material is air. “If there’s no mass, there’s no force during acceleration,” Northam says. This makes Vantablack ideal for protected objects that might have to endure a bumpy ride, like a space launch, for example.


5. IT COULD HAVE A NUMBER OF USES BEYOND ITS ORIGINAL APPLICATION.

The material was originally designed for super technical fields, like space equipment, where its ability to limit stray light makes it ideal for the inside of telescopes. But it could be applied in more everyday objects if the conditions are right. Northam says Surrey NanoSystems has already been approached by a handful of luxury watchmakers interested in incorporating Vantablack into their wrist candy, and high-end car manufacturers want to use it in their dashboard displays for stunning visual appearance. Northam says they also have a few smartphone makers knocking on their door.
Artists are also clamoring to get their hands on Vantablack and make some crazy, mind-boggling works of art. But for now, much to the chagrin of thousands of creatives, only one artist is allowed to work with the material, and that’s sculptor Anish Kapoor. Surrey NanoSystems gave Kapoor the exclusive rights to using Vantablack in “creative arts,” which Northam says translates into anything that’s meant to be observed purely as a work of art. He says the company will continuously reassess this agreement, but as Vantablack is still such a new material, it makes sense that they’d want to have some control over how it’s being used. “I do understand that people would wanna get their hands on this stuff,” Northam says. “But I suspect many would not want to pay the prices for it.”


6. IT WILL BE A WHILE BEFORE IT'S USED ON CLOTHES.

Vantablack could take the “little black dress” to a whole new level if it can successfully be applied to fabric without compromising its physical properties. Northam says the company is working with fabric, but Vantablack’s foray into fashion is probably a long way off. “I wouldn’t be surprised if at some point we see something along the lines of a black dress,” he says, optimistically, “but we won’t see people walking down the street in it any time soon.”



Cloud gate
 

anish kapoor 가 vantablack을 칠하기만 했는데 입체가 사라졌다