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

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

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)

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

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

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

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

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!

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

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

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

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

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

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

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

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

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