Nanoscience


Definition

Nanoscience is the name given to the wide range of interdisciplinary science that is exploring the special phenomena that occur when objects are of a size between 1 and 100 nanometers in at least one dimension. This work is on the cutting edge of scientific research and is expanding the limits of our collective scientific knowledge.

Examples

Examples of nanosized objects include: a virus, the diameter of a DNA strand, a ribosome, hemoglobin, a sucrose molecule, the diameter of a carbon nanotube, buckyballs, some enzymes, some molecular motors, the photosynthetic machinery in plants and bacteria. Some objects are smaller than nanosized, such as water molecules, atoms and sub-atomic particles. Other objects are larger than nanosized but are not visible with the unaided eye, such as: bacteria, amoeba, human egg cell, human sperm cell, red blood cell.

Material Properties

Intensive properties (color, odor, luster, malleability, ductility, conductivity, hardness, melting/freezing point, boiling point, and density) are only independent of the size of the sample of the substance at the macroscale. When sizes get very small, properties change.

Some properties are "surface dominated", that is, they change when the surface area to volume ratio changes. These properties include: chemical reactivity, melting, dissolving, adhesion, and absorption. Other properties are "size dominated", they change with the size of the object. Size dominated properties include: electron structure and malleability or hardness.

Unique Properties

Unique phenomena that occur at the nanoscale can be categorized as: optical properties, electrical properties, and chemical properties.

Optical properties observed at the nanoscale include changes in color. For example, bulk gold appears yellow in color, but nanosized gold appears red. Changes in color of gold are related to quantum mechanics. As amounts of substances become nano-sized, electrons are confined to a smaller number of energy states and these energy states determine the color we see. Another example is zinc oxide, the chemical in sunscreen that appears white on the skin. Nanosized zinc oxide appears clear because it is smaller than the wavelength of visible light and does not reflect light.

Electrical properties observed at the nanoscale include changes in conductivity. Carbon nanotubes vary in conductivity depending on diameter, twist, and number of walls. Some materials have different physical properties such as density and boiling point at the nanoscale. Nanoparticles have lower melting and boiling points because there is a greater percentage of atoms at the surface, thus, less energy is required to overcome intermolecular attractions. When size gets extremely small, the concepts of melting and boiling are do not make any sense.

Chemical property changes observed at the nanoscale include greater chemical reactivities and reaction rates. Nanoparticles have a greater percentage of atoms at the surface and thus greater reactivities.

Scientific Models

Four general reasons describe why properties of nanosized objects can be different than those of the same materials at the bulk scale: (1) dominance of electromagnetic forces, (2) quantum effects, (3) surface to volume ratio, and (4) random molecular motion.

Electromagnetic forces dominate at the nanoscale because the gravitational force depends on mass and is weak between nanosized particles. The electromagnetic force depends on charge and can be very strong even when particles are small. At the nanoscale, classic mechanical models that worked at the macroscale no longer work. At the nanoscale, probability concepts explain phenomena such as quantum tunneling, where an electron can pass through a barrier. As surface to volume ratio increases, a greater amount of the substance is in contact with the surrounding material which increases reaction rates. Random molecular motion (the vibration, rotation and motion of molecules) occurs in all substances, but at the nanoscale this motion is as large as the size of the particles and becomes an important influence on how nanoparticles behave, especially in phenomena such as self-assembly.

"Seeing" at the Nanoscale

Visible light cannot be used to see objects at the nanoscale because the objects we want to see are smaller than the wavelength of light. The tools used to “see” objects at the nanoscale use other kinds of interactions, such as electrical and magnetic forces, to create a representation of the object. These technology tools include the atomic force microscope and the scanning tunneling microscope. The atomic force microscope uses a tiny tip that responds to the electromagnetic forces between the atoms on the surface of the object and the tip. The scanning tunneling microscope uses electrical current to create a topographical image of the object.

Applications

Existing applications of nanotechnology include:
  • Stain resistant clothes – fine fibers, or nanowhiskers act like peach fuzz to create a cushion of air around the fabric so that liquids bead up and roll off.
  • Nano solar cells – a new kind of solar cell that uses nanoparticles of TiO2 coated with dye molecules to capture the energy of visible light and convert it into electricity. These cells are less expensive to produce.
  • Clear sunscreen – ZnO and TiO2 nanoparticles provide the same sun protection as their normal sized counterparts but are so small that they do not scatter visible light and appear clear on the skin.
  • Building smaller devices and chips – a technique called nanolithography allows microchips to be made much smaller.
  • Health monitoring – nano-devices are being developed to keep track of daily changes in patients’ glucose and cholesterol levels.
  • Water Treatment - special filters that can remove objects as tiny as viruses from water
  • Antimicrobial Clothing - nanoparticles of silver are embedded into fibers

Potential applications include:
  • Paint that cleans the air
  • Paint on solar cells
  • Drug delivery systems
  • Clean energy
  • Detecting disease with quantum dots

Implications

Nanotechnology holds the promise of great benefits to society, but at what cost? The toxicity of nanoparticles is relatively unknown and there are ethical considerations for the introduction of nanosized monitoring devices. Students will explore the risks and benefits of nanotechnology in this unit using learning strategies such as: critical thinking, creative thinking, problem solving, and inquiry.



Website by Lori Andersen, 2012