Form a Nanoscale Thin FilmForm a Nanoscale Thin Film

Rob Snyder snyder@umassk12.net

Mort Sternheim mort@umassk12.net

STEM Education Institute

University of Massachusetts Amherst

Today’s ActivityToday’s Activity

• Learn about Ben Franklin’s Observation of a Learn about Ben Franklin’s Observation of a very thin film.very thin film.

• Create a very thin film with a very dilute Create a very thin film with a very dilute solution of oleic acidsolution of oleic acid

• Use scientific notation to calculate the Use scientific notation to calculate the thickness of the thin film of oleic acidthickness of the thin film of oleic acid

• Describe chemical interactions between Describe chemical interactions between Oleic Acid, Alcohol and WaterOleic Acid, Alcohol and Water

• Be introduced to the Big Ideas of Nanoscale Be introduced to the Big Ideas of Nanoscale Self-AssemblySelf-Assembly

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

Excerpt from Letter of Benjamin Franklin to William Brownrigg (Excerpt from Letter of Benjamin Franklin to William Brownrigg (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)

V = A T

V = 1 teaspoonful

A = 0.5 acre

~ 2 cm3

~ 2,000 m2

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 conduct a thin film It would be difficult to conduct a thin film experiment on the UMass Amherst experiment on the UMass Amherst

campus pond.campus pond.

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

Today, we will compare results from groups using large trays and small trays or plates.

There are three molecular substances used in this activity.

Oleic acid

Isopropyl Alcohol Water

You will form a thin film of oleic acid You will form a thin film of oleic acid on the surface of water. on the surface of water.

Oleic acid is one of olive oil’s ingredients.Oleic acid is one of olive oil’s ingredients.

You will need to make a double You will need to make a double dilute solution of oleic acid.dilute solution of oleic acid.

• Water is in each plastic tray. Water is in each plastic tray. • Make a double dilute solution of oleic acid in alcohol.Make a double dilute solution of oleic acid in alcohol.• Determine how many drops of a very dilute solution Determine how many drops of a very dilute solution

are in one cmare in one cm33 of the second dilute solution. of the second dilute solution.• Evenly sprinkle a layer of baby powder or Evenly sprinkle a layer of baby powder or

lycopodium powder across the surface of the water.lycopodium 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 The alcohol solvent will dissolve in water leaving a

thin film of oleic acid solute on the surfacethin film of oleic acid solute on the surface• Measure the average diameter of the circular layer of Measure the average diameter of the circular layer of

oleic acid.oleic acid.

You need to estimate the area of the thin film.

Sample CalculationsSample Calculations

The following steps correspond to the sequence of The following steps correspond to the sequence of calculations on your calculation worksheet.calculations on your calculation 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

A sample calculation of the A sample calculation of the thickness of the oleic acid filmthickness of the oleic acid film

Step 5: Area = 3.14 x RStep 5: Area = 3.14 x R22 The area of a thin with a The area of a thin 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

Why did oleic acid form a thin film?Why did oleic acid form a thin film?

Oleic acid molecules have a polar ends Oleic acid molecules have a polar ends that are attracted to polar water that are attracted to polar water molecules.molecules.

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.

Weak van der Walls forces were strong enough for the film to Weak van der Walls forces were strong enough for the film to

maintain its integrity as the oleic acid spread across the water.maintain its integrity as the oleic acid spread across the water.

If you formed a monolayer, the 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.

What two roles did alcohol play in the activity?

Oleic acid

Isopropyl Alcohol Water

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

water

hydrophobic end

hydrophilic end

A Few QuestionsA Few Questions What might be some sources of error What might be some sources of error

when calculating the thickness of a layer when calculating the thickness of a layer of oleic acid?of oleic acid?

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

What would be some challenges when What would be some challenges when using a tray the size of a dinner plate?using a tray the size of a dinner plate?

The Big Ideas in Self-AssemblyThe Big Ideas in Self-Assembly• Structural components are mobile. Structural components are mobile. • The goal is a low energy equilibrium state.The goal is a low energy equilibrium state.• Ordered structures result from a less Ordered structures result from a less

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

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

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

through and after.through and after.

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

UMass Amherst NanotechnologyCurriculum Resources are available at

http://umassk12.net/nano/

Examples of Activities, Teacher Guides, Worksheets, Multimedia Module and PowerPoints Include:

This Oleic Acid Thin Film ActivityNanoscale ElectrodepositionA Fine Measurement Machine as a model of an

Atomic Force MicroscopeGel DiffusionThe Nanotechnology of SunscreenNanoscale Powers of Ten