What is nanotechnology?


 
Hello, my name is Nina.

I have a PhD in environmental engineering, which makes me a certified know-it-all in all issues environmental. Right?

At least that’s what some of my friends and family seem to think when they approach me with questions ranging from global warming to BPA-free bottles. And I do feel the obligation to keep myself informed to be able to address those questions as well as possible, but no, not a certified know-it-all and very ignorant in many things.

In January 2013 I was hired into my current job, as associate director for the Virginia Tech Center for Sustainable Nanotechnology. I took my freshly earned PhD degree and happily embarked in this new adventure. So, it should not have surprised me when the first question I had to answer, from friends and co-workers alike, was, evidently: “What is sustainable nanotechnology?” Since this is a blog on sustainable nanotechnology, I saw it fitting to suggest our definition here, or at least start a discussion about it.

What we have here is a double-buzzworder (d-buzz for short?), and those tend to be tricky, especially since the definitions of both “sustainability” and “nanotechnology” are still under a bit of debate. So, I’m going to try to tackle this by parts, in a 2-part series of blog posts, starting with Nanotechnology.

 

Nanotechnology.

The prefix “nano” originates from the word νᾶνος, which is Greek for dwarf. So, in simple terms, it’s the technology of small things. One of the most widely acceptable definitions of nanotechnology is described by the National Science Foundation (NSF) as:

“Research and technology development at the atomic, molecular or macromolecular levels, in the length scale of approximately 1 – 100 nanometer range, to provide a fundamental understanding of phenomena and materials at the nanoscale and to create and use structures, devices and systems that have novel properties and functions because of their small and/or intermediate size. The novel and differentiating properties and functions are developed at a critical length scale of matter typically under 100 nm. Nanotechnology research and development includes manipulation under control of the nanoscale structures and their integration into larger material components, systems and architectures. Within these larger scale assemblies, the control and construction of their structures and components remains at the nanometer scale. In some particular cases, the critical length scale for novel properties and phenomena may be under 1 nm (e.g., manipulation of atoms at ~0.1 nm) or be larger than 100 nm (e.g., nanoparticle reinforced polymers have the unique feature at ~ 200-300 nm as a function of the local bridges or bonds between the nano particles and the polymer).”

This definition was actually developed by the Nanoscale Science, Engineering, and Technology (NSET) subcommittee of the National Nanotechnology Initiative.

In less complicated terms, nanotechnology deals with the manipulation of nanomaterials: materials that exhibit novel properties when they are made into very small particles. These particles are so small that they are at this point reaching the limits of being called a particle —or a solid— at all. Some examples of nanoscale properties follow:

Optical behavior. When these particles are suspended in liquid (including glass), they interact with light differently, depending on their size, which is actually how stained glass works. Some centuries-old cathedral windows are red because they were made with gold nanoparticles suspended into the glass. Nano-gold is not gold in color, as it transmits red light, but absorbs the other visible wavelengths.

Colloidal suspensions of metal particles (aka nanoparticles) were used centuries ago to make beautiful glass as seen on the Notre Dame cathedral, in Paris. Image source: http://www.therosewindow.com/
Colloidal suspensions of metal particles (aka nanoparticles) were used centuries ago to make beautiful glass as seen on the Notre Dame cathedral, in Paris.
Image source: http://www.therosewindow.com/

Electrical conductivity. Some semiconductive materials become conductive, or super conductive, at the nanoscale. Some materials that are not conductive at all, become semiconductive. Carbon nanotubes, for example, are extremely conductive.

Hardness and strength. Some nanomaterials are many orders of magnitude stronger than their larger counterparts (e.g., fullerenes and carbon nanotubes are much stronger than graphite and even diamond).

Enhanced solubility. Silver nanoparticles are known for their antimicrobial properties because they dissolve. As you know, silverware or your silver jewelry is not particularly soluble in water. Nanoscale silver, however, slowly releases silver ions in liquid. These ions are very reactive and particularly dangerous to bacteria and other microorganisms.

 

So, nanotechnology goes far beyond miniaturization. It’s not enough to make something really small. Nanomaterials must exhibit enhanced or novel properties at nano-size compared to their full-scale counterparts.

For most nanomaterials, novel properties like these appear in the 1 – 100 nanometer range, although many researchers debate this specific size range, because for some materials it is more like 1 – 30 nm or so.

Surfaces are at the heart of the super powers of nanomaterials. The atoms at the surface of a solid material are the ones in contact with its surrounding and are responsible for most of its reactivity. Many nanoscale properties are caused by the large amount of surface area that small particles have in comparison to larger particles, as demonstrated in this figure:

 

The surface area of a cube with 4-in sides is 96 inches. If you slice this cube into 4 smaller cubes in every direction, you end up with a total surface area four times higher than the original cube, even though the total mass of cubes is still the same. If you keep slicing up these cubes into smaller and smaller ones, until they are within nanoscale, their combined surface area will be about a million times higher than the original cube.
The surface area of a cube with 4-in sides is 96 inches. If you slice this cube into 4 smaller cubes in every direction, you end up with a total surface area four times higher than the original cube, even though the total mass of cubes is still the same. If you keep slicing up these cubes into smaller and smaller ones, until they are within nanoscale, their combined surface area will be about a million times higher than the original cube.

There’s also something called quantum confinement, a physics term to describe changes in fundamental properties of solid materials when those materials are so small that they cannot accommodate the normal wavelengths of the electrons in the band structure of the material . . . in other words, the electrons must seek new energy levels in very small materials because they don’t have room to operate as they normally do, and this changes the properties of that material.

The NNI definition of nanotechnology also includes the manipulation of materials within this scale of 1 – 100nm. Many modern electronic applications would fall under this description. But this part of the definition partly contradicts what we have been talking about, since making things that fall under the nanoscale (1-100nm) would be described as “nanotechnology, whether or not these materials have novel properties at nanoscale. In this case, the techniques used can be defined as “nanotechnology”, but what’s produced cannot necessarily be called a “nanomaterial”.

As you may have noticed, nanomaterials encompass more than particles. We can divide nanomaterials in 3 main categories based on their physical shape:

1-D nanomaterials: Very thin films or layers of atoms. These materials are nano-sized (<100nm) in one dimension (its thickness), but not in width or length.

2-D nanomaterials: Nanowires, nanotubes, nanowhiskers, nanorods, etc… These materials are nano-sized in two dimensions (thickness and width), but may be very long.

3-D nanomaterials: Nanoparticles, which can be spheres, cubes, pyramids, rods, etc… These materials are nano-sized in all three dimensions.

 

It’s worth mentioning here that although the term “nanotechnology” is somewhat new, research at nanoscale is not new at all. As I mentioned before, the stained glass cathedral windows have been here for centuries, although no one knew why small particles changed color until quite recently. In chemistry, it’s been long known that very small particles suspended in liquids behave in a special way. The study of these particles suspensions is called colloidal science and the suspensions, colloids. In atmospheric and aerosol science, particles in the 1 – 100 nm size range have also been long studied and referred to as “ultrafine aerosols”.

To learn more, check out this great video by the Nanoyou project: http://vimeo.com/9068558

 

Stay tuned for the next post, on Sustainable Nanotechnology.

 

About the Author: 

Nina Quadros is the Associate Director for VTSuN: Virginia Tech’s Center for Sustainable Nanotechnology and a postdoctoral associate of the Institute for Critical Technology and Applied Science (ICTAS) at Virginia Tech.

Update [2 Sep 2014] Nina Quadros has recently changed her name to Marina Vance

On twitter@marinavance


 

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