21 May 2015

Nanotechnology: An Introduction

Nanotechnology! Nowadays, almost any student claims to have an interest in becoming a scientist, working in laboratories, playing with atoms, fiddling with molecules, and on and on. Well, let me tell you one thing. If you fall in that 'almost any kid' category, then you might just end up finding nanotechnology exciting.

Nowadays in nanotechnology, things that were only “dreamt of”, are turning into a reality. But before we delve into the science of nanotechnology, let me point to you some exciting ways in which nanotechnology is being used today.

Have you ever “dreamt of” an invisibility cloak? Well if you have, then I suggest you stop dreaming because now invisibility cloaks have become a reality.

One other recent cutting edge invention is the “Ultra Ever Dry” product. And what this does, is that it does not allow any liquid irrespective of its viscosity to stain a substance on which the product has been sprayed on. The “Ultra Ever Dry” coating, creates a thin barrier of air at the nano scale, which prevents the coated substance from getting wet or dirty. And to see this mind-boggling product in action, you can take a look at:

Apart from this, there is also some interesting work going on in the field of medicine involving nanotechnology, where medical researchers are on the verge of creating an almost harmless cancer therapy which could possibly become a substitute to the standard chemotherapy.

There has been a quantum leap in the development of nanotechnology in the last five years. And from here, things only get better.

So let's get started with nanotechnology.

What is nanotechnology?

At a very high level, I would take nanotechnology as the science, engineering and technology practiced at the atomic or molecular level.

But going slightly deeper, it is a branch of science, which involves the manipulation of at least one dimension of a substance within the nano scale range of 1 to 100 nanometers (1 nanometer = 10-9 meters).

What is unique about nanotechnology?

There are many things that are unique to nanotechnology, though I feel the truly convincing answer to this, lies in the unusual behavioral-changes of substances at the nano scale.

What I mean by this is that substances show rather abnormal properties at the nano scale, which violate the norms of the Physics that we know so well as Classical Physics. We will understand and discuss this in greater detail a bit later.

Interesting concepts in nanotechnology

With this much of a background, I think we all are quite ready to take a look at some of the interesting concepts of nanotechnology!

Two main concepts are:
• Simple to Complex
• Larger to Smaller

Simple to Complex--

One of the most mind blowing concepts in which extensive research is being carried out is the ‘Simple to Complex’ also known as the ‘bottom-up approach’ concept. This concept involves molecular self assembly. In other words, scientists are trying to make molecules automatically arrange themselves into a desirable system.

Some of the fields where this is trying to be developed, is in the field of synthetic chemistry where scientists are trying to achieve self assembly of molecules into substances such as polymers, micro-computing where scientists are almost at the brink of having self assembled microcomputers and biology where substances like enzymes have already been self created!

Two main advantages of developing this Simple to Complex concept are:
• Production will become faster and more efficient.
• Both the purchasers as well as manufacturers will incur less cost.

Larger to Smaller--

As we had discussed earlier, the physical properties of substances begin to be different as the size of these substances start to enter the nano scale. These include differences in mechanical, thermal, electronic and catalytic properties of the substances. These changes, which occur in substances as their sizes are brought down from the macroscopic to the nano scale, constitute the major part of the ‘Larger to Smaller’ concept.

Some examples to give you a flavour of these ‘abnormal phenomena’, which occur among substances at the nano scale are:
• Plastic at the nano scale conducts electricity,
• Gold particles begin to appear red and purple,
• Particles of certain substances turn spontaneously from solid to liquid,
• Copper turns transparent,
• Platinum and Gold become catalysts, and so much more.

Why do substances begin to show these aberrant properties?

This can be explained by the drastic increase in the surface area to volume ratio, which exists at the nano scale. For example let us take a cube of side 8 units, which we will reduce thrice consecutively to an edge length of 6, 4 and then 2 units, and then observe the surface area to volume ratio. Then—

Edge length Surface Area Volume S.A. to V ratio
8 units 384 units2 512 units3 3/4 = 0.75 units-1
6 units 216 units2 216 units3 3/3 = 1 units-1
4 units 96 units2 64 units3 3/2 = 1.5 units-1
2 units 24 units2 8 units3 3/1 = 3 units-1

Now we can clearly see, that by reducing the dimensions of the cube, the surface area to volume ratio is increasing. This is also the case with any other three dimensional object. May it be a sphere, cylinder or cone. But, the more relevant question is how does the surface area to volume ratio cause an alteration in the behaviour of particles at the nano scale?

To understand this, let us continue with the example of a cube. If we take two identical sugar cubes of side = 10 units, and divide one of them into a 1000 equal blocks of 1 unit3 each, and leave the other one untouched, then the volume of the uncut and cut sugar cubes will remain the same. But, the surface area of the cut cube will be clearly larger than the surface area of the uncut cube. Now, if we were to dissolve both the cut and uncut sugar cubes, then the cut cubes will definitely dissolve quicker, as they share a greater contact area with the water as compared to the uncut cube.

It is this same kind of change that takes place in nanoparticles too, but the changes are much more drastic as the surface area to volume ratio in nanoparticles is much larger. Just for example’s sake, let us take a cube of side = 10-9metres or 1 nanometer. Then—

Surface Area = (10-9)2 x 6
=> (6 x 10-18)nm2

Volume = (10-9)3
=> 10-27nm3

Therefore the surface area to volume ratio = 6 x (10(-18)/10(-27))
=> 6 x 10(-18+27)
=> 6 x 109
=> 6,000,000,000 or Six billion nm-1!

And it is this huge surface to volume ratio, which causes abnormal properties in nanoparticles.

All of this is just the beginning of our understanding of the fast evolving field of nanotechnology. Some of the references I have provided below can help you understand more about this exciting field. If you have found anything interesting in the space and would like to share it, post a comment!

1. http://www.nano.gov/nanotech-101/what/definition
2. http://science.howstuffworks.com/nanotechnology.htm
3. http://www.livescience.com/33816-quantum-mechanics- explanation.html
4. http://www.gizmag.com/invisibility-cloak-hides-macroscopic-objects/37542/
5. http://www.nano.gov/nanotech-101/special

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