Structures with a nanoscale dimension Structures with a nanoscale dimension. Rob Snyder Mark Tuominen University of Massachusetts Amherst

Today’s Activity Learn about Ben Franklin’s observations of a thin film that had a nanoscale dimension. Create a very thin film with a very dilute solution of oleic acid. Use data you collect to determine if a thin film with a nanoscale dimension formed on the surface of water. Be introduced to the Big Ideas of Nanoscale Self-Assembly

Was Ben Franklin an Early Nanoscientist?

Excerpt from Letter of Benjamin Franklin to William Brownrig (Nov ...At length being at Clapham, where there is, on the Common, a large Pond ... I fetched out a Cruet of Oil, and dropt a little of it on the Water. I saw it spread itself with surprising Swiftness upon the Surface ... the Oil tho' not more than a Tea Spoonful ... which spread amazingly, and extended itself gradually till it reached the Lee Side, making all that Quarter of the Pond, perhaps half an Acre, as smooth as a Looking Glass....

CHALLENGE: How thick was the film of Ben Franklin’s oil? ... the Oil tho' not more than a Tea Spoonful ... ... perhaps half an Acre CHALLENGE: How thick was the film of Ben Franklin’s oil? Volume = (Area)(Thickness) V = A T T = V/A T = 2 cm3 20,000,000 cm2 This is how Ben Franklin would have calculated the thickness of a thin film of oil on water. This is also how you will calculate the thickness of a thin film. V = 1 teaspoonful A = 0.5 acre ~ 2 cm3 ~ 2,000 m2 T = 0.0000001 cm T = 1 x 10-7 cm T = 1 x 10-9 m T = 1 nanometer 20,000,000 cm2

How big are nanoscale structures? DNA 3 nanometers 6,000 nanometers Hair . 100,000 nanometers

Examples of Nanoscale Thin Films Nanofilm on glass Nanofilm on plastic Gold-coated plastic for insulation purposes "Low-E" windows: a thin metal layer on glass: blocks UV and IR light

It would be difficult to conduct a thin film experiment on the UMass Amherst campus pond. We can’t use the campus pond. Discuss several reason why.

Results from groups using large and small trays can be compared. Different sizes and shapes of plastic tray can be used to experiment with thin films. However, you need to use much less than a teaspoon of oil. We can, however, use a large plastic tray as a model of a pond. Results from groups using large and small trays can be compared.

You will form a thin film of oleic acid on the surface of water You will form a thin film of oleic acid on the surface of water. Oleic acid is one of olive oil’s ingredients. You will make a solution of one of the ingredients in olive oil.

You will need to make a double dilute solution of oleic acid. Water is in either a small or large tray. Make a double dilute solution of oleic acid in alcohol. Determine how many drops of a very dilute solution are in one cm3 of the second dilute solution. Evenly sprinkle a layer of baby powder or lycopodium powder across the surface of the water. Let one drop of the very dilute solution of oleic acid spread across the surface of the water. The alcohol solvent will dissolve in water leaving a thin film of oleic acid solute on the surface Measure the average diameter of the somewhat circular layer of oleic acid.

Thin films of oleic acid will have many shapes and require more than one measurement of diameters.

A Sample Calculation A group recorded the average radius as 7.25 cm These steps correspond to the sequence of calculations on the calculation worksheet. Step 1: The volume fraction = 1 / 25 Step 2: 0.04 cm3 Step 3: 0.04 cm3 / 25 = 0.0016 cm3 A group determined that 40 drops of the second dilute solution = 1.0 cm3. Step 4: If a group determined that 40 drops of the second solution of oleic acid had a volume of 1.0 cm3; Then 0.0016 cm3 / 40 = 0.00004 cm3. A group recorded the average radius as 7.25 cm

Does the film have a nanoscale dimension? Step 5: Area = 3.14 x R2 The area of a thin film with a radius of 7.25 cm film is 165.05 cm2 Step 6: If Volume = Area x Depth; Then: Depth = Volume / Area and the thickness of the example group’s film would be 2.42 x 10-7 cm. Step 7: 2.42 x 10-9 meters Step 8: 2.42 x 10-9 m = 2.42 nanometers

Why did oleic acid form a thin film? Do you see the two red spheres at one end of the oleic acid molecule? The red spheres represent oxygen atoms. Oxygen atoms will have a slightly negative charge so that end of the molecule is polar. Oleic acid molecules have a polar ends that are attracted to polar water molecules.

Water molecules in a tray. When you poured a small amount of oleic acid onto the surface of water, electric interactions caused the oleic acid molecules to “self-assemble” into a thin layer. + charge on a hydrogen atom - Charge on an oxygen atom Water molecules in a tray.

Weak van der Walls forces describe the attraction between adjacent hydrocarbon chains. They are strong enough for the thin film to maintain its integrity as it spreads across the water.

In a small drop of oleic acid there are billions of oleic acid molecules that will stand up like blades of grass on the surface of water. If you formed a monolayer, then you also calculated the length of an oleic acid molecule. The generally accepted value for the length of an oleic acid molecules 1.97 nanometers.

Perhaps you did not form a monolayer Perhaps you did not form a monolayer. Multiple layers of oleic acid can form on the surface of water. Non-polar ends of oleic acid

Three molecular substances were used in this activity Three molecular substances were used in this activity. What two roles did alcohol play? Isopropyl Alcohol Water Oleic acid

The thin film of oleic acid forms a Langmuir Film The thin film of oleic acid forms a Langmuir Film. The thin film can be confined to a specific area with a barrier. You used baby powder as a confining barrier. hydrophobic end water hydrophilic end

A Few Questions What might be some sources of error when calculating the thickness of a thin film of oleic acid? How could the sources of error be minimized? In what ways in this activity an example of nanoscale self-assembly?

Some Examples of Self Assembly

The Big Ideas in Nanoscale Self-Assembly Structural components are mobile. The goal is a low energy equilibrium state. Ordered structures result from a less ordered system. Assembly is a result of attractive or repulsive forces between the components. An environment is selected to induce designed interaction. Components retain physical identity through and after. The process is reversible or adjustable. Whitesides & Boncheva (2002)

A Few More Questions How many ways can the oleic acid thin film activity be seamlessly integrated into the K-12 STEM Curriculum? What essential knowledge is associated with this activity? What essential skills are associated with this activity?

UMass Amherst Nanotechnology Curriculum Resources are available at http://umassk12.net/nano/ Materials include student activity documents, teacher guides that include sample calculations, worksheets (with and without hints for making calculations), multimedia modules that enrich what students learn doing an activity and PowerPoints presentations.

K-12 Curriculum Materials are also available at the Center for Hierarchical Manufacturing’s web site. http://chm.pse.umass.edu/education_outreach/instructional