Unique Properties At The Nanoscale


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Nanoscale physics

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Unique Properties At The Nanoscale

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