Sugar Cube Falling

A World of small things: Introduction to Nanotechnology

Nanotechnology deals with the science of building small, but why do we talk about such small things?

Well, they ultimately constitute the world we live in and we can explore fascinating things with them, literally, it can shape the world around us. Properties of materials change due to quantum effects when they are made small, really small at a scale range of 1-100nm (1 nm is $10^{-9}$m) called nanoscale.

Human hair measures around 75000nm, so imagine how small is the nanoworld!. It is possible to change the properties of materials like electrical conductivity, chemical reactivity, magnetic properties such as magnetic phase transitions, saturation magnetization, magnetic permeability, and so on.

Such tunability of properties at nanoscale made the world shrink, shrink in the sense, replacement of heavy objects in day to day life with smaller components, for instance, spare parts in cars, airplanes, and spacecraft with lightweight nanomaterials, small computer chips with large memory capacity and so on.

Remember the scenario 40 years back, a computer of very slow running capacity and slow memory was occupying a big room and now we are easily traveling with our lightweight laptops anywhere in the world. Magnetic tunnel junctions and transistors at the nanoscale range made it possible.

The applications of nanotechnology extend from smart electronic devices to nanomedicines as well as to find the solution to environmental pollutions. Yes, nanotechnology can really do great things not only to the human race but to the whole universe itself. It is a promising science to a better world, A small beautiful better world.

As professor Norio Taniguchi rightly pointed out, nanotechnology consists of the processing of separation, consolidation, and deformation of materials by one atom or molecule, i.e it vests on the manipulation of individual atoms.

How Physical and chemical properties of material change at the nanoscale? 

The significant essence of excitement in nanotechnology lies in the fact that nanoparticles exhibit unique properties that are different from the macroparticles of the same material. The larger surface to volume ratio exhibited by nanoparticles is the solid reason behind such changes in properties.

Large surface area means a quite large number of the particles on the surface can actively participate in a reaction. As the size gets reduced, the surface area increases, 

Let’s consider a sphere of radius $a$
The volume of the sphere is $\frac{4}{3}\pi a^3$ and the surface area is $4 \pi a^2$
Hence the surface to volume ratio is proportional to $\frac{3}{a}$

This tells the ratio of surface area to volume increases when the radius decreases. You might have observed a solid cube of sugar take a longer time to dissolve in a tea/coffee compared to a packet of sugar with finely powdered sugar content.

This is because when the particle size is smaller, a greater number of particles are on the surface to participate in a reaction (here dissolving into the solute tea/coffee) which enhances the reaction rate. This increase in the exposed surface area when particles are made at the nanoscale range allows the reaction to be faster compared to their bigger counterpart.

A bulk material which is inert can be made reactive by changing it to its nanoparticles and which realizes the famous lecture of Richard Feynman titled “ There’s plenty of rooms at the bottom: An invitation to enter a new world of physics”.

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