Nanoworld deals with matter at very small scale. Our daily life experience is made of matter in bulk. For instance every letter you are reading here can fit in 50 million carbon atoms, a sheet of paper has about 1023 atoms, a 70 kg human has 7 x 1027 atoms etc.
We experience the world composed of atoms at bulk-level. If you zoom in and zoom in and zoom in to the material to say to the level of 100 atoms or 10 atoms, matter behave very differently. This means the properties of matter depend on the sizes at which they are grouped together.
Nanoscience is all about understanding matter to such 10 atoms-level or 100-atoms level.
- The understanding of properties that are size-dependent is the science of nano and our ability to use and manipulate these properties by fabricating matter at this level to make useful products is called nanotechnology.
- Nanoparticles have been in use even before we understood anything about it. Colloidal materials (very fine particles of one substance are mixed with another bulk material) were 1st made by faraday, damscus sword had nanowires and nanotubes, wootz steel had carbon nanotubes etc.
Imagining the Nano
- Nanometer (10-9 m) is a measure of objects in the nano world.
- Imagine the size of earth and a marble that is the comparison of a meter and a nanometer.
- Keep 10 hydrogen atoms together, you get a nanometer.
- A glucose molecule is less than a nanometer
- The diameter of protein or a virus is around 10 nm.
- Width of DNA molecule is nearly 2.5nm.
- The size of blue light (wavelength) nearly 400nm, that of red is 700nm.
Behaviour of Material with Size
(I) At 50nm – Properties similar to bulk material
(II) At 10-50-nm – Properties change linearly
(III) Below 10nm – New properties emerge
How to make nanomaterials?
There are two approaches to make nanomaterial.
- Top-down: Bulk material is powdered or cut or broken into smaller and smaller pieces using grinders or lasers.
- Bottom-up: Material made atom by atom or molecule by molecule.
- The main feature of nanomaterial is that it is the size that determines its property.
- If you take iron that is magnetic and keep reducing its size they will lose magnetic property at small scale.
- Gold in bulk is metal but gold particle with 1nm dia is not metallic.
- Cadmium Selenide
- Other nano particles
- Nano porous solids, nanocapsules and DNA chips
- Nano wires are 10 times thicker than nanotubes are easy for mass production. Nanowires of silicon, indium phosphide and gallium nitride are made.
- Nanowires are used to make transistors for memory devices.
- Nanocrystalline material show both strength and ductility at the same time (which is rare)
- Nanopipes are used in making bio-sensors.
- Silicon when made into nano-sized clumps of 2nm emit visible light. However silicon is not biocompatible. Silicon-nano porous particles are used to monitor drug performance inside the body.
TYPES OF NANOMATERIALS
Nanoparticles or Nanocrystals
- Nanoparticles are material that is nano-sized in all 3 dimensions. These are called quantum dots. Nanoparticles of metals, metal oxides, semiconductors, magnetic materials are all prepared to harness their properties.
- They may be of different shapes like spherical, triangular, square etc.
- Are nano-sized in one dimension. In other dimensions they could be long.
- Nanowires and nanotubes belong to this category.
- Nanowires and nanotubes of metals, oxides and other material are made
- Carbon nanotube is an example
- These nanomaterials extend into two-dimensions like a sheet of paper.
- Examples: Nanofilms, Nanosheets & Nanowalls.