Unique Properties At The Nanoscale

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Nanoscale physics

Nanoscale physics

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  • 1. Unique Properties at the Nanoscale The Science Behind Nanotechnology
  • 2. What’s So Special About Nano?
    • Using new scientific tools, we have found that nanosized particles of a given substance exhibit different properties than larger particles of the same substance
    • As we study these materials at the nanoscale, we are
      • Learning more about the nature of matter
      • Developing new theories
      • Learning how to manipulate their properties to develop new products and technologies
  • 3. Size-Dependent Properties
    • Properties of a material
      • Describe how the material acts under certain conditions
      • Are often measured by looking at large (~ 10 23 ) aggregation of atoms or molecules
    • Types of properties that often change
      • Optical (e.g. color, transparency)
      • Electrical (e.g. conductivity)
      • Physical (e.g. hardness, boiling point)
      • Chemical (e.g. reactivity, reaction rates)
    Sources: http://www.bc.pitt.edu/prism/prism-logo.gif http://www.physics.umd.edu/lecdem/outreach/QOTW/pics/k3-06.gif
  • 4. Optical Properties Example – Gold
    • Bulk gold appears yellow in color
    • Nanosized gold appears red in color
      • The particles are so small that electrons are not free to move about as in bulk gold
      • Because this movement is restricted, the particles react differently with light
    Sources: http://www.sharps-jewellers.co.uk/rings/images/bien-hccncsq5.jpg http://www.foresight.org/Conferences/MNT7/Abstracts/Levi/ 12 nanometer gold particles look red “ Bulk” gold looks yellow
  • 5. Optical Properties Example – Zinc Oxide (ZnO)
    • Large ZnO particles
      • Block UV light
      • Scatter visible light
      • Appear white
    • Nanosized ZnO particles
      • Block UV light
      • So small compared to the wavelength of visible light that they don’t scatter it
      • Appear clear
    “ Traditional” ZnO sunscreen is white Zinc oxide nanoparticles Nanoscale ZnO sunscreen is clear Sources: http://www.apt powders.com/images/zno/im_zinc_oxide_particles.jpg http://www.abc.net.au/science/news/stories/s1165709.htm http://www.4girls.gov/body/sunscreen.jpg
  • 6. Meaningless Properties
    • At the nanoscale, some properties don’t make sense
    • One example is boiling temperature
      • Vapor pressure becomes less and less meaningful when you have smaller and smaller numbers of particles
      • When you have 50 molecules there are no bubbles!
  • 7. Why Do Properties Change?
    • Four important ways in which nanoscale materials may differ from macroscale materials
      • Gravitational forces become negligible and electromagnetic forces begin to dominate
      • Quantum mechanics is used to describe motion and energy instead of classical mechanics
      • Greater surface to volume ratios
      • Random molecular motion becomes more important
  • 8. Dominance of Electromagnetic Forces
    • Because the mass of nanoscale objects is so small, gravitational force becomes negligible
      • Gravitational force is a function of mass and is weak between nanosized particles
      • Electromagnetic forces are not affected by mass, so they can be very strong even when we have nanosized particles
      • Electromagnetic forces between two protons are 10 36 times stronger than gravitational forces
  • 9. Quantum Mechanical Model Needed
    • Classical mechanical models explain phenomena well at the macroscale level, but often break down at the nanoscale level
    • Four phenomena that quantum mechanical models can explain (but classical mechanical models cannot)
      • Discreteness of energy
      • The wave-particle duality of light and matter
      • Quantum tunneling
      • Uncertainty of measurement
  • 10. Surface to Volume Ratio Increases
    • As surface to volume ratio increases
      • A greater amount of a substance comes in contact with surrounding material
      • This results in better catalysts, since a greater proportion of the material is exposed for potential reaction
    Source: http://www.uwgb.edu/dutchs/GRAPHIC0/GEOMORPH/SurfaceVol0.gif
  • 11. Random Molecular Motion is Significant
    • Random motion at the macroscale
      • Small compared the size of the object
      • We can barely detect motion of dust particles on the surface of water
    • Random motion at the the nanoscale
      • Large when compared to the size of the object
      • The molecules that make up the dust particle are moving wildly compared with the size of the particle
    Source: http://galileo.phys.virginia.edu/classes/109N/ more_stuff/Applets/brownian/brownian.html
  • 12. What Does This All Mean?
    • The following factors are key for understanding nanoscale-related properties
      • Dominance of electromagnetic forces
      • Importance of quantum mechanical models
      • Higher surface to volume ratio
      • Random (Brownian) motion
    • It is important to understand these four factors when researching new materials and properties