What's Unique About the Nanoscale?

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Scales

How “big” is “nano” ?

• The prefix “ nano” means “ one billionth”, or 10^-9.
• A nanometer (nm) is one billionth of a meter.
• Nanometers are typically used to define dimensions between 0.1 nm (10^-10 m) and 100 nm (10^-7m). 

Nanoscale

• Nanoscale:  Nanoscale is a scale of measurements that uses “nano” or “10^-9” as a multiplier to define its order of magnitude.
• Nanoscale measurements
  • Ex: Nanometers -> nano & meter
    • “ nano” defines the “scale” or “order of magnitude” of the unit of measurement.
    • “ meter” is the unit of measurement for linear dimensions (e.g., length).
  • It’s just like centimeter: where “centi” defines the order of magnitude 10^-2. 
• Nanomaterials are talked about in nanometers, but nanoscale can apply to any unit of measure:
  • Electrical current (nA: nanoamps).
  • Voltage (nV: nanovolts).
  • Time (ns: nanoseconds).
  • Concentration (nM: nanomolar).
  • Etc...

Visualize Nano

• We can try to visualize how small nano is by thinking about the various scales and powers of ten (10^x). 
• Try to relate them to things around you.

Nanomaterials on a dimensional scale

• Typical nanomaterials in the 1-100 nm scale are shown on the lower side of the dimensional scale. 
• The smallest nanomaterials are comparable in size to molecules, such as caffeine.
• Mid-size nanomaterials are comparable to biological macromolecules, such as nucleic acids and antibodies.
• Larger nanomaterials are comparable to viruses, and are still much smaller than any living entity (i.e., bacterial cells). 

Nanomaterials vs Bulk Materials

• Nanomaterials offer unique properties compared to “bulk” materials.
  • The uniqueness of nanomaterials and the ability to manipulate them is what makes nanotechnology so exciting and diverse.
• To understand just how unique nanomaterials are, let’s discuss characteristics of “non-nano” or bulk materials.
• Bulk materials:
  • the materials and items you are used to dealing with (larger than nanoscale).
  • intrinsic properties are generally fixed, regardless of their shape, size, etc...

Bulk materials have fixed properties 

• For example; the FIXED properties of gold in bulk. 
• A piece of gold in a coin, a nugget, or part of a printed circuit board, will have the same properties (aka they are fixed).
  • All bulk forms melt at same temp, have the same conductivity & density…

Bulk: different structure, different properties

• The only way to change the properties of bulk materials is to change its chemical composition or structure.
• For instance, to change the conductivity of iron, you must make an alloy with other elements.
  • You can see on the table how the conductivity changes as you combine iron with aluminum, silicon, carbon, etc.
• Another example is  if you want to change the color of a food dye molecule, you must completely change the chemical structure of the molecule.
   

 Conductivity of iron-based alloys                            Color of food dye molecules

Nanomaterials do not have fixed properties

Nanomaterials behave differently from the corresponding bulk scale material.

At the nanoscale, everything is changeable!

• For a given nanomaterial, the properties are not fixed, but determined by the size and shape of the material.
  • Not the chemical composition.
• This is one of the most important concepts of nanotechnology.
  • Characteristics of nanomaterials are dependent on structures, but strongly on size and shape.
  • The same material can display radically different properties due to varying sizes, shapes.

Properties at the nanoscale: changing shape

All the properties (electrical, mechanical, chemical, etc.) are dependent of the size and shape of the material.

• To illustrate this concept, we will examine optical properties (color).
• For example: Gold 
  • In BULK we know gold always has the same color no matter how it is shaped or the size of a gold object.

Properties at the nanoscale: changing shape

All the properties (electrical, mechanical, chemical, etc.) are dependent of the size and shape of the material.

• For example: Gold
  • At the NANOSCALE optical properties change as a function of size (diameter).
  • Gold nanoparticles are easily made in the 1-100 nm range; here we have varying diameters of gold nanoparticles dispersed in solution.
    • 100 nm gold nanoparticles are orange/brown, 10 nm gold nanoparticles are bright red, 1 nm nanoparticles are transparent.

Solutions on gold nanoparticles

Properties at the nanoscale: changing shape

• These are all gold atoms, but have very different properties!
• It is important to emphasize that the size and shape of these materials is more important than their chemical composition (which has not changed).
• Nanomaterial sizes range 2 orders of magnitude (1-100).

Bulk

Nano

Properties at the nanoscale: changing shape

• Example: Cadmium Selenide (CdSe)
  • In BULK (left) CdSe appears gray to the eye, like a gray slab/tombstone
  • At the NANOSCALE (right), the color of CdSe color is dependent on its diameter
• Very extreme example where a small variation in diameter results in a big change in color
  • The difference between 3 and 5.5 nm is only 1.5 nm -- TINY TINY TINY! (** remember, a single nucleotide is 1 nm!)

Nano

Bulk

Shape matters too!

Another look at how optical properties are changed, this time by shape.

• Here we examine nanoparticles of very similar sizes but with different crystalline structures -> therefore, different shapes.

    Different shape configurations of nanoparticles.

Size & Shape-dependent

• Silver nanoparticles change color with different sizes and shapes.
  • Great example of how size AND shape change the properties of a given nanomaterial.
  • Illustrates chemical composition is not as important to change properties of nanomaterials.

Example:  Al nanoparticles

• We took a look into the difference in optical properties between bulk and the nano equivalent of the same material.
• Remember, there are many other properties that change with size and shape of nanomaterials.
  • Not just optical properties/color.
• Aluminum for example…

Bulk Aluminum

Aluminum nanoparticles combust on contact with air!

Size and Shape-dependent

The chemical composition of the material is not as important as its size and shape for the resulting properties in nanomaterials.

• Nanomaterials can be tuned by various sizes or shapes
• “Custom made” to have specific, desired properties
  • Now we can use materials with tailored properties for different applications

In-Class Assignment

Using your own words:

1. List the following in order of increasing size: a buckyball, a soccer ball, a human red blood cell, a virus, an antibody, a molecule of insulin (a hormone), an E. coli cell, a molecule of methanol, and an 80-nm gold nanoparticle. 
   • Don’t know the size of something, look it up! 
2. Nanoscale refers to the magnitude 10^x; x =? 
3. What kind of properties are fixed in bulk materials that may be different at the nanoscale? Give 2 examples.
4. Properties of nanomaterials depend on their ___ and ___. 

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To learn more about nanotechnology, visit omninano.org​