A Nanoscale Thin Film ActivityA Nanoscale Thin Film Activityfor thefor the

Middle and High School STEM CurriculumMiddle and High School STEM Curriculum

Rob SnyderRob SnyderUniversity of Massachusetts AmherstUniversity of Massachusetts Amherst

Thin films with nanoscale dimensions improve many products.

Gold-coated plastic can be used as insulation.

Nanoscale thin films on glass make windows more energy efficient.

Nanofilm on plastic Nanofilm on glass

Nanoscale thin films are being developed to make flexible sheets of solar panels.

Nanoscale thin films on eyeglasses and camera lenses can make them water-repellent, antireflective, self-cleaning,

resistant to ultraviolet or infrared light and scratch-resistant.

A nanoscale structure has a length, width, diameter and/or thickness of between 1 and 100 nanometers.

1 nanometer = 1 billionth of a meteror

1 nanometer = 0.000000001 metersor

1 nanometer = 1 x 10-9 meters

nano.gov

Today’s ActivityToday’s Activity• Learn that Ben Franklin experimented with making a thin Learn that Ben Franklin experimented with making a thin

film of oil that had a nanoscale dimension.film of oil that had a nanoscale dimension.• Use graduated cylinders to make a very dilute solution of Use graduated cylinders to make a very dilute solution of

oleic acid. Household oils can also be used.oleic acid. Household oils can also be used.• Put a very small volume of oleic acid onto the surface of Put a very small volume of oleic acid onto the surface of

water.water.• Make measurements of a circular area of a thin film of Make measurements of a circular area of a thin film of

oleic acid.oleic acid. • Use the formula for the volume of a disc to calculate the

thickness of a thin film of oleic acid.• Learn why oleic acid molecules form a very thin film.• Discover that your may have measured the length of a

molecule.• Be introduced to the Be introduced to the Big Ideas Big Ideas of a nanoscale process of a nanoscale process

called Self-Assemblycalled Self-Assembly

Was Ben Franklin an Early NanoscientistWas Ben Franklin an Early Nanoscientist??

Excerpt from Letter of Benjamin Franklin to William Brownrig (Excerpt from Letter of Benjamin Franklin to William Brownrig (Nov. 7, 1773) Nov. 7, 1773)

...At length being at Clapham, where there is, on the Common, a large ...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 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 saw it spread itself with surprising Swiftness upon the Surface ... the Oil tho' not more than a Tea Spoonful ... which spread amazingly, and tho' not more than a Tea Spoonful ... which spread amazingly, and extended itself gradually till it reached the Lee Side, making all that 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 Quarter of the Pond, perhaps half an Acre, as smooth as a Looking Glass....Glass....

... 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)

If: V = A T

V = 1 teaspoonful

A = 0.5 acre

~ 2 cm3

~ 2,000 m2

Then: T = _V_ A

20,000,000 cm2

T = 2 cm3

20,000,000 cm2

T = 0.0000001 cm T = 1 x 10-7 cm T = 1 x 10-9 m T = 1 nanometer

It would be difficult to produce a thin film on the UMass Amherst campus pond..

Different sizes and shapes of plastic tray can be Different sizes and shapes of plastic tray can be used to experiment with thin films. However, you used to experiment with thin films. However, you need to use much less than a teaspoon of oil.need to use much less than a teaspoon of oil.

Results from groups using large and small trays can be compared.

Thin Film Documents

• A student document with directions for both a small tray and a large tray of water.

• A calculations worksheet. One side has hints for making calculations.

• Sample calculations that can be provided for students who are having difficulty.

• A teacher’s guide with a sample calculation

You will form a thin film of oleic acid on the surface of water. Oleic acid is one of the liquids in olive oil.

• Water is in a small or large tray. Water is in a small or large tray. • Make a Make a double dilutedouble dilute solution of oleic acid in alcohol. solution of oleic acid in alcohol.• Determine Determine how many drops of a very dilute solution are in of a very dilute solution are in

one cm3 of the of the second dilute solution. dilute solution.• Evenly sprinkle a layer of baby powder or lycopodium sprinkle a layer of baby powder or lycopodium

powder across the surface of the water.powder across the surface of the water.• Let one drop of the very dilute solution of oleic acid Let one drop of the very dilute solution of oleic acid

spread across the surface of the water. spread across the surface of the water. • The alcohol solvent will dissolve in water leaving a thin The alcohol solvent will dissolve in water leaving a thin

film of oleic acid solute on the surfacefilm of oleic acid solute on the surface• Measure the average diameter of the somewhat circular Measure the average diameter of the somewhat circular

layer of oleic acid.layer of oleic acid.

A thin film usually does not form a perfect disc shape. But you can calculate the area of a somewhat circular

thin film by determining its average radius.

These are the first four steps of a calculation of the thickness of a thin film of oleic acid.

These first four steps correspond to the sequence These first four steps correspond to the sequence of of calculationscalculations on the on the calculationcalculation worksheet. worksheet.

Step 1: The volume fraction = 1 / 25Step 1: The volume fraction = 1 / 25

Step 2: 0.04 cmStep 2: 0.04 cm33

Step 3: 0.04 cmStep 3: 0.04 cm33 / 25 = 0.0016 cm / 25 = 0.0016 cm33

A group determined that 40 drops of the second A group determined that 40 drops of the second dilute solution = 1.0 cmdilute solution = 1.0 cm33..

Step 4: If a group determined that 40 drops of the Step 4: If a group determined that 40 drops of the second solution of oleic acid had a volume of 1.0 second solution of oleic acid had a volume of 1.0 cmcm33; Then 0.0016 cm; Then 0.0016 cm33 / 40 = 0.00004 cm / 40 = 0.00004 cm33..

A group recorded the average radius as 7.25 cm

This sample calculation reveals that the thin This sample calculation reveals that the thin layer of oleic acid had a nanoscale dimension.layer of oleic acid had a nanoscale dimension.

Step 5: Area = 3.14 x RStep 5: Area = 3.14 x R22 The area of a thin film with a The area of a thin film with a radius of 7.25 cm film is 165.05 cmradius of 7.25 cm film is 165.05 cm22

Step 6: Step 6: If Volume = Area x Depth; If Volume = Area x Depth; Then: Depth = Volume / Area and the thickness of Then: Depth = Volume / Area and the thickness of

the example group’s film would be 2.42 x 10the example group’s film would be 2.42 x 10-7-7 cm. cm.

Step 7: 2.42 x 10Step 7: 2.42 x 10-9-9 meters meters

Step 8: 2.42 x 10Step 8: 2.42 x 10-9-9 m = 2.42 nanometers m = 2.42 nanometers

You experimented with three different molecules.

What two roles did alcohol play so that you could form a thin film of oleic acid?

Oleic acid

Isopropyl Alcohol Water

A polar end of an oleic acid molecule is hydrophilic.

The hydrogen atom at one end of the oleic acid molecule is more positive

than the rest of the molecule.

The region around the oxygen end of a water molecule is more negative than the rest of the molecule

When you poured a small amount of oleic acid onto the When you poured a small amount of oleic acid onto the surface of water, electric interactions caused the oleic surface of water, electric interactions caused the oleic

acid molecules to “self-assemble” into a thin layer.acid molecules to “self-assemble” into a thin layer.

- Charge on an oxygen atom in each water molecule

+ charge on a hydrogen atom in each oleic acid molecule

Water molecules in a tray.

Weak van der Walls forces describe the attraction between Weak van der Walls forces describe the attraction between adjacent hydrocarbon chains. They are strong enough for the thin adjacent hydrocarbon chains. They are strong enough for the thin

film to maintain its integrity as it spreads across the water.film to maintain its integrity as it spreads across the water.

In your In your oneone small drop of oleic acid there many small drop of oleic acid there many billionsbillions of of oleic acid molecules that stood up like blades of grass on oleic acid molecules that stood up like blades of grass on

the surface of waterthe 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. Multiple layers of oleic acid can sometimes form on the

surface of water.

Non-polar ends of oleic acid

A Few QuestionsA Few Questions

• What measurement skills were required to What measurement skills were required to do this activity?do this activity?

• What math skills were required to do this What math skills were required to do this activity? activity?

• What might be some sources of error when What might be some sources of error when calculating the thickness of a thin film of calculating the thickness of a thin film of oleic acid?oleic acid?

• How could the sources of error be How could the sources of error be minimized?minimized?

The Big Ideas in Nanoscale Self-AssemblyThe Big Ideas in Nanoscale Self-Assembly

• Structural components are Structural components are mobilemobile. . • The goal is a The goal is a low energy equilibriumlow energy equilibrium state. state.• Ordered structuresOrdered structures result from a less ordered result from a less ordered

system.system.• Assembly is a result of Assembly is a result of attractive or attractive or

repulsive forcesrepulsive forces between the components. between the components.• An An environment is selectedenvironment is selected to induce to induce

designed interaction.designed interaction.• Components Components retain physical identityretain physical identity through through

and after.and after.

• The process is The process is reversible or adjustablereversible or adjustable..Whitesides & Boncheva (2002)