Part 1. General introduction to nanoscience and commonly used terms explained

Doc Brown's Chemistry Revision Notes

NANOCHEMISTRY - Nanoscience - Nanotechnology - Nanostructures

Alphabetical keyword index for the nanoscience pages : Index of nanoscience pages : boron nitride * Buckminsterfullerenes-bucky balls * carbon nanotubes * fat nanoparticles * fluorographene * fullerenes * graphene * health and safety issues * liposomes * nanochemistry * nanomaterials * nanoparticles * nanoscale * nanoscience * nanosized-particles * nanostructures * nanotechnology * nanotubes * problems in nanomaterial use * silver nanoparticles * safety issues * sunscreens-sunblockers * titanium dioxide

Part 1. General introduction to nanoscience, nanoparticles and commonly used terms explained

• The prefix 'nano' in the context of the definitions-descriptions given below, and used on this webpage, usually refers to dimensions-size of 1 - 100 nm. i.e. of nanoscale (1 x 10^-9 m to 1 x 10^-7 m)

  • nm is the accepted abbreviation for nanometre (nanometre) - more on the relative size of molecules and bigger particles is given further down in a size comparison data table to put the nanoscale 'scene' in perspective.

  • For some ideas on scales and particle sizes, and the table of examples further down the page.

  • Scale units for nanometres,1 nm = 1 x 10^-9 m = 1 x 10^-12 mm, so 1 nm is a millionth millionth of a millimetre!

  • Most atoms have a diameter of around 0.1 to 0.2 nm and compare this with some examples of larger 'particles'.

  • Nanoparticles may contain just a few hundred atoms, they are very very small ! Nanoparticles range in size from 10^-9 m to 10^-7 m (1 nm to 100 nm).

  •  Fine particles (PM_2.5), are larger than nanoparticles, and have diameters between 1 x 10^-7 m and 2.5 x 10^-6 m (100 and 2500 nm).

  • Coarse particles (PM₁₀), are larger than fine particles with diameters from 2.5 x 10^-6 m to 1 x 10^-5 m (2 500 nm to 10 000 nm), course particles are often referred to as fine dust particles.

    • You need to appreciate all examples in at least two units e.g. nm and m

  • Typical nanoparticles are roughly spherical in shape, but the surface area to volume ratio is extremely important.

  • If you think of a simple cube, if the side is decreased by a factor of 10, the surface to volume ratio increases by 10.

    • See APPENDIX 1 for some simple calculations to emphasise this point.

  • So nanoparticles have a very high surface area to volume ratio and this gives them special properties different from larger particles of other bulk material e.g.

    • This difference in surface area / volume ratio for the particles of the material give nanoparticles extra chemical reactivity compared to the bulk material.

    • In nanoparticles, far more atoms on their surface are able to interact with other atoms, either reactant molecules or part of some fabricated mixture - see carbon nanotubes.

    • It means less of a nanomaterial like a catalyst is needed in a chemical process, so catalysts based on nanoparticles are more efficient than those based on bulk material catalysts.

• What is Nanoscience?

  • Nanoscience is the branch of science concerned with the development and production and uses of materials whose basic components are of nanoscale size, i.e. ~1 - 100 nm in size. Other more specific terms which come under the general term 'nanoscience' are described in more detail, particularly the term nanochemistry.

• What is Nanotechnology?

  • Nanotechnology involves methods for transforming matter, energy and information based on nanometre scale (nanosized) components with particular defined molecular features and prescribed physical and chemical properties.

  • It involves techniques that produces materials with characteristic features with particle sizes of ~1 - 100 nm and involves advanced microfabrication techniques.

  • Nanotechnology is still based on manufacturing processes that use typical chemical and mechanical principles BUT in novel and unfamiliar situations (at least to those of us who were graduate students in the late 60s!).

  • Nanotechnology creates and uses structures that have novel properties because of their nanoscale small size.

  • Nanotechnology is developing from the ability to control and manipulate at the atomic scale, which essentially means controlling situations at the atomic and molecular level, far removed from normal processing of bulk materials in a typical laboratory or industrial process.

  • The use of the scanning tunnelling microscope allows us to 'see' individual atoms in an atomic or molecular lattice in a way that was inconceivable a 100 years ago when the principles of atomic and molecular structure were being discovered.

    • So, it is now possible to see and investigate nanoscale structures at the atomic-molecular level and this 'feedback' enables you to compare the actual structure with the desired designed structure which eventually you would hope to have the prescribed desirable properties.

    • Does this advanced technology blur the distinction between computer simulation and reality?

    • We are now well into CAD (computer aided design) at the molecular level and there doesn't seem to any limit (within the laws and principles of chemistry) as to what structures we can build.

  • The many applications of nanotechnology include the use of semi-conductors that only conduct electricity in specific conditions and allows the design of much very tiny 'devices' normal scale conductors, so the final product can be much smaller, enabling the design and use of faster smaller computers working at the molecular level. It will be/is? possible to make very tiny mechanical devices to perform some task in otherwise inaccessible situations.

• What are Nanostructures?

  • Nanostructures are material structures assembled from layers or clusters of atoms of nanoscale size i.e. ~1-100 nanometre. By controlling the size and assembling of nanoscale constituents it is possible to alter and control the structure and properties of the final nanostructure. The advantage of these new materials is that they can be designed and built from the atomic level upwards to have specific properties of great use to material scientists, a good example is the ongoing development in the design and use carbon nanotubes.

  • Nanocrystals may consist of over 1000 atoms but it can be quite variable within the 1-100 nm range.

  • The wide applications of such nanostructures includes semi-conductor devices, strained-layer lattices, magnetic multilayers.

  • Nanostructures are built up from atomic or molecular precursors and processed via chemical deposition or physical vapour deposition, gas condensation, chemical precipitation, aerosol reactions and biological templating - a wide range of methods of assembling arrays of atoms.

  • Note that some nanoparticles are created naturally e.g.

    • Very finely suspended mineral particles in water - the tiniest of colloidal particles act as nanoparticles.

    • During inefficient combustion of organic molecules e.g. fossil fuels or plastics, nanosized particles of soot (mainly carbon) are formed.

    • Evaporated seaspray can produce nanoscale salt particles.

• What are Nanomaterials?

  • Nanomaterials is a general word for any material that has a composition based on nanoparticle units e.g. nanoparticles of silver, carbon nanotubes, inorganic ceramic materials etc. more examples

• NANOPARTICLES

  • As already mentioned nanoparticles are usually in the size range of 1 to 100 nm, described as being of nanoscale

  • Nanoparticles can be made of elements, organic molecules, inorganic compounds, inorganic cluster compounds or metallic/semi-conductor (maybe ~'semi-metal') particles.

  • Nanoparticles have a high surface to volume ratio which has a dramatic effect on their properties compared to non-nanoscale forms of the same material.

  • As a point of comparison, since nanoparticles are in the size range 1 - 100 nm, a human hair is 0.05 to 0.1 mm (50000 -100000 nm) in diameter, in other words nanoparticles are usually 500 - 100000 times 'thinner' than a human hair!

  • 1 nanometre (US nanometre), 1 nm = 10^-9 of a metre (0.000 000 001 m, pretty small!)

    • Compared to other units:

      • 1 cm = 10^-2 m  (1 cm = 10000000 nm)

      • 1 mm = 10^-3 m  (1 millimetre = 1000000 nm)

      • 1 μm = 10^-6 m  (1 micrometre = 1000 nm)

      • 1 nm = 10^-9 m

      • 1 pm = 10^-12 m  (1 picometre = 0.001 nm)

  • So, when talking nanoscale science, we are talking about pretty small structures!

  • More 'chemical structure' points of comparison are given in the table below.

  • To put nanoparticles in 'size' or 'dimension' perspective, consider the table below of 'materials' - pure elements, pure compounds and other more complex materials etc.

  • To put nanoparticles in 'perspective' i.e. what 'scale' are we talking about, I've put together a size comparison table of various 'particles' in its broadest sense. add DNA?

• Notes on the table
  • na = not applicable i.e. no simple formula or representation possible
  • n = a large number of atoms or molecules
  • Need diameter x length if possible and revision of some of the data in the table above (microns?)
    1. Carbon is the basic atom or unit of carbon nanotubes.
    2. Sulfur is a typical non-metal atom.
    3. Water is a relatively small molecule, one of the smallest in fact.
    4. Silver is typical metallic lattice or huge array of atoms, titanium dioxide is a giant lattice ionic lattice.
    5. Glucose is a molecule of 24 combined atoms of carbon, hydrogen and oxygen atoms.
    6. Fullerene-60, a 'bucky ball', is the precursor structure on which carbon nanotubes are based.
    7. A simple protein is a polymer of alpha-amino acids [H₂HCH(R)COOH]_n where R is of variable structure, n is a large number of peptide units-residues.
    8. Assume silver or titanium dioxide nanoparticles are ~spherical
    9. A virus is a very simple organism, the simplest of which consists of a strand of RNA in a protein sheath.
    10. A typical carbon nanotube might have a radius of 3 nm and up to 100 nm long.
    11. The wavelengths of visible light are typically 4 to 700 times bigger than most nanoparticles!
    12. A bacterium is a usually a single celled cellular micro-organism and can contain over 5000 different molecules and ions.
    13. A eukaryotic cell is what all multi-celled higher organisms are made up of.
    14. The human hair is easily recognised as strands of a pretty thin material.
    15. Very fine dust particles have typical particle diameter sizes of 1 x 10^-5 m to 2.5 x 10^-6 m

APPENDIX 1 An arithmetical investigation of the relationship between surface area and volume

Its effectively an exercise in looking at one of the most important properties of nanoparticle materials, namely, their very high surface area to volume ratio.

APPENDIX 1a

APPENDIX 1b

Another approach to this kind of arithmetical exercise is to derive a simple equation from the geometrical equations for a sphere.

This is a better approach than above as nanoparticles are more likely to be nearer a spherical shape than a simple cube, though many textbooks use the cube to illustrate the idea (because its simpler maths I suppose). So, using r as the radius of the spherical particle, the final equation is very simple!

surface area of a sphere = 4πr²

volume of sphere = ⁴/₃πr³

surface area / volume ratio = 4πr² / ⁴/₃πr³ = ³/_r

(π, 4 and r² all cancel out, 3 goes to top line, leaving 3/r)

So, you can clearly see that as r gets smaller, the surface area to volume ratio increases.

Same result as in 1b: The smaller the particles the greater their surface area to volume ratio.

TOP OF PAGE

WHERE NEXT?

NANOSCIENCE - NANOCHEMISTRY INDEX

Website content © Dr Phil Brown 2000+. All copyrights reserved on revision notes, images, quizzes, worksheets etc. Copying of website material is NOT permitted. Exam revision summaries & references to science course specifications are unofficial.

 Doc Brown's Chemistry 

*