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Adapted from Nanosense

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Presentation on theme: "Adapted from Nanosense"— Presentation transcript:

1 Adapted from Nanosense
STEM ED/CHM Nanotechnology 2007 Why Size Matters Adapted from Nanosense

2 Relative sizes Atomic nuclei ~ 10-15 meters = 10-5 nanometers
Atoms ~ meters = 0.1 nanometers Nanoscale ~ 1 to 100 nanometers Everyday world ~ 1 meter = nanometers

3 The Basic Physics At the atomic and molecular level, quantum mechanics is needed to describe phenomena and properties Discrete energy levels, tunneling At the everyday scale, Newton’s laws (classical physics) work fine Nanomaterials are in a borderline region where either or both approaches may be appropriate

4 The Basic Forces Strong Nuclear Force – huge, hold nuclei together; act only at nuclear distances, 10-5 nm Weak Nuclear Force – small, responsible for nuclear beta decay, act only at nuclear distances, 10-5 nm Electric and Magnetic – dominant at atomic and nanotech scales; 1039 × gravitational forces; long ranged, 1/r2 Gravitational – long ranged, 1/r2; dominant at everyday world scale, since most objects lack a substantial net electrical charge

5 Properties of a Material
A property describes how a material acts under certain conditions Types of properties Optical (e.g. color, transparency) Electrical (e.g. conductivity) Physical (e.g. hardness, melting point, diffusion rate) Chemical (e.g. reactivity, reaction rates) Properties are usually measured by looking at large (~1023) aggregations of atoms or molecules

6 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 12 nanometer gold particles look red “Bulk” gold looks yellow Sources:

7 Optical Properties Example: Zinc Oxide (ZnO)
Large ZnO particles Block UV light Scatter visible light Appear white Nanosized ZnO particles So small compared to the wavelength of visible light that they don’t scatter it Appear clear Application to sunscreen Nanoscale ZnO sunscreen is clear “Traditional” ZnO sunscreen is white Zinc oxide nanoparticles Sources:

8 Physical Properties: Diffusion
Small particles (molecules in suspensions, dust particles in air) move randomly in zigzag paths (Brownian motion) due to collisions Particles spread out (diffuse) when introduced into a medium at one point Perfume in a room Average kinetic energy ½ mv2 ~ temperature Average particle speeds decrease as mass increases, so more massive particles diffuse more slowly We explore this phenomenon with the gelatin diffusion experiment

9 Electrical Properties Example: Conductivity of Nanotubes
Nanotubes are long, thin cylinders of carbon They are 100 times stronger than steel, very flexible, and have unique electrical properties Their electrical properties change with diameter, “twist”, and number of walls They can be either conducting or semi-conducting in their electrical behavior Electric current varies by tube structure Multi-walled Source:

10 Physical Properties Change: Melting Point of a Substance
Melting Point (Microscopic Definition) Temperature at which the atoms, ions, or molecules in a substance have enough energy to overcome the intermolecular forces that hold the them in a “fixed” position in a solid Surface atoms require less energy to move because they are in contact with fewer atoms of the substance In contact with 3 atoms In contact with 7 atoms Sources: and image adapted from

11 Physical Properties Example: Melting Point of a Substance
At the macroscale At the nanoscale The majority of the atoms are… …almost all on the inside of the object …split between the inside and the surface of the object Changing an object’s size… …has a very small effect on the percentage of atoms on the surface …has a big effect on the percentage of atoms on the surface The melting point… …doesn’t depend on size … is lower for smaller particles

12 Surface to Volume Ratio Experiments
As a sample is made larger, a smaller fraction of the atoms (or molecules) are on the surface Atoms on the surface have fewer neighbors than those on the interior Students at the edge of the classroom have fewer neighbors than those in the center Explore this with two activities – cards, blocks Only atoms on the surface can interact with another material and take part in a chemical reaction Explore this with Alka Seltzer tablets and powder

13 Size Matters in Biology
Metabolism (heat generation) is limited by the number of cells, or volume, L3 Heat loss to the environment is proportional to the surface area, L2 As we look at smaller and smaller organisms, the surface to volume ratio L2/ L3 = 1/L gets larger and larger, making it harder to maintain body temperature Smallest warm blooded organisms are hummingbirds and a small mouse-like mammal

14 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 area to volume ratio Random (Brownian) motion It is important to understand these four factors when researching new materials and properties

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