Unique Properties At The Nanoscale
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Unique Properties At The Nanoscale

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Nanoscale physics

Nanoscale physics

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    Unique Properties At The Nanoscale Unique Properties At The Nanoscale Presentation Transcript

    • Unique Properties at the Nanoscale The Science Behind Nanotechnology
    • 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
    • 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
    • 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
    • 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
    • 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!
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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