SelfAssembled Monolayers and Soft Lithography in High School Chemistry

1
Self-Assembled Monolayers and Soft Lithography
in High School Chemistry

• Jen Ehrlich
• UW-MRSEC RET
• Summer 2007

2
Water

• Polar
• Hydrogen bonding (very strong!)

3
Waters Unique Properties
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Surface Tension
http//www.chem1.com/acad/sci/aboutwater.html
Bulk Molecule Attracted to molecules in all
directions All forces balance each other out.
Surface Molecule Attracted to molecules next to
and below, but NOT above. So its pulled INTO the
liquid
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Surface tension is the enhancement of the
intermolecular attractive forces at the surface
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Have You Ever Seen a Square Water Droplet?

• Why Not?

To minimize surface and maximize volume, water
naturally forms a spherical shape
7
Astronaut Leroy Chiao, Expedition 10 commander
and NASA ISS science officer, watches a sphere of
water float between him and the camera, showing
his image refracted, on the International Space
Station.Image Credit NASA
8
How is surface tension affected by soap?
Soap breaks the Surface Tension! Why?
http//demo.physics.uiuc.edu/lectdemo/scripts/demo
_descript.idc?DemoID1144
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Hydrophobic
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Hydro phobic
water - fearing
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Hydrophobic materials
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What makes something hydrophobic?
Tristearin (beef fat, lard)
Carbon nanotubes, graphite
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Hydrophilic
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Hydro philic
water - loving
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Hydrophilic materials
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What makes something hydrophilic?
Ethanol
Acetic acid
http//www.erowid.org/chemicals/alcohol/alcohol_ch
emistry.shtml
http//www.bmrb.wisc.edu/metabolomics/gen_metab_su
mmary_5.php?molNameacetic_acid
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SoapHydrophobic or Hydrophilic?
Hydrophilic
http//chem.ufl.edu/itl/2045/lectures/lec_i.html
Hydrophobic
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Soap is a
act
ant
surf

• surface acting agent

http//wwwchem.csustan.edu/chem2000/Exp5/BKG.HTM
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Surfaces
Where do we change the surface of an object to
change its properties?
Galvanized Pipe
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WWWD? What would water do?
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http//www.eurekalert.org/multimedia/pub/3999.php?
from95205
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Student Lab

• Self Assembled Monolayer Role Play
• Silver Petri Dishes and Test Water on monolayers
  of Alkane Thiol, Acid Thiol, Ag
• Prepare PDMS Stamp
• Play-doh Analogy
• Stamp Ag with Alkane Thiol

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Self Assembly

• Classroom Role PlayPart 1
• Rules
• Your right hand can only touch someones back
• Your left hand can only touch someones right
  shoulder
• Teacher should limit space to a small enough area
  to get a mass of students

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Self Assembly

• Students will self-assemble themselves into a
  mono-layer

• Things to notice
• Students are so close to each other that they
  have essentially changed the make-up of the
  surface
• Students are strongly (covalently) bonded to the
  surface and weakly attracted
• (Van der Waals forces) to each other

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Self Assembly

• Classroom Role PlayPart 2
• Rules are the Same
• Your right hand can only touch someones back
• Your left hand can only touch someones right
  shoulder
• This time, the teacher should limit the space
  students can take up (i.e. they can only stand in
  these three rows or cover some tiles with
  chairs/colored paper so they are not accessible
  to students)

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Part 1
Part 2
Students are non-polar molecules Imagine
holding an umbrella to shield yourself from
water.
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What Is Self Assembly?

• When molecules organize themselves into patterns
  without any outside intervention
• Examples
• Formation of crystals
• Cell membrane formation (lipid bilayers)
• Schools of fish
• Self assembled monolayers

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What Self Assembly Is Not
X
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Self Assembled Monolayers (SAMs)

• Molecules arrange themselves spontaneously onto
  certain surfaces in a layer that is one molecule
  thick
• Surface properties of the material are changed,
  while bulk properties remain the same

2 nm tall
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WWWD? what would water do?
X
X
16-mercaptohexadecanoic acid SAM (Acidic Thiol)
Hexadecane thiol SAM
http//www.asemblon.com/node/240
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Student Lab

• Self Assembled Monolayer Role Play
• Silver Petri Dishes and Test Water on monolayers
  of Alkane Thiol, Acid Thiol, Ag
• Prepare PDMS Stamp
• Play-doh Analogy
• Stamp Ag with Alkane Thiol

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Prepare Petri Dishes for Silvering

• Wash plastic Petri dishes with dish washing
  detergent or laboratory detergent
• Add dilute tin (II) chloride solution to each
  Petri dish for 30 seconds.
• Rinse each Petri dish with distilled water.

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Preparation of Tollens Solution

• To 0.1 M silver nitrate, add concentrated aqueous
  ammonia dropwise, while stirring. At first, brown
  precipitate will form. Continue adding ammonia
  until the precipitate dissolves.

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Silvering Plastic Petri Dish

• Add Tollens solution to the Petri dish
• Add about 1 ml of 0.5 M glucose solution to the
  Petri dish.
• Rinse with distilled water, and dry with a blow
  dryer.

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Chemical reaction to form the silver?

• 2 Ag (aq) 2 OH- (aq) ? Ag2O (s) H2O (l)
• Ag2O (s) 4NH3 (aq) H2O (l) ? 2Ag(NH3)2
  (aq) 2 OH- (aq)
• Glucose is oxidized/Ag ion is reduced
• C6 H12 O6 Ag(NH3 )2 OH- ?

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Self Assembled Monolayers

• On the back of one Petri dish, use a permanent
  maker to divide it into three sections. Use tape
  to label the front of the Petri dish as shown.
• Add a few drops of HDT and Acid Thiol to their
  respective thirds and let dry

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WWWD? what would water do?
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• Tilt the Petri dish to almost a 90o angle and,
  from your pipet, let one drop of water fall onto
  a dry spot of each surface. Release as small a
  drop of water as possible. Record your
  observations

39
Student Lab

• Self Assembled Monolayer Role Play
• Silver Petri Dishes and Test Water on monolayers
  of Alkane Thiol, Acid Thiol, Ag
• Prepare PDMS Stamp
• Play-doh Analogy
• Stamp Ag with Alkane Thiol

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Making the PDMS Stamp

• Mix 10 parts Sylgard polymer base to 1 part
  curing agent crosslinker.
• Place an overhead transparency, with the
  patterned grid facing up, onto a metal plate and
  place the square metal tubing on top of the
  transparency.
• Pour the uncured PDMS mix over the transparency.
• Place the whole assembly in a toaster oven set at
  250oF for 20 minutes.

41
Student Lab

• Self Assembled Monolayer Role Play
• Silver Petri Dishes and Test Water on monolayers
  of Alkane Thiol, Acid Thiol, Ag
• Prepare PDMS Stamp
• Play-doh Analogy
• Stamp Ag with Alkane Thiol

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Macroscopic Model

• Station 1 Printing a Pattern

Petri dish (overhead transparency)
Solid shapes are glued onto Petri dish (ink from
laser printer)
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Macroscopic Model

• Station 2 Making the PDMS Mold

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Macroscopic Model

• Station 3 Coating stamp with alkanethiol

vegetable oil (alkanethiol)
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Macroscopic Model

• Station 4 Stamping the metallic surface

Paper Bag (Silver)
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Macroscopic Model

• Station 5 Applying water to stamped image

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Student Lab

• Self Assembled Monolayer Role Play
• Silver Petri Dishes and Test Water on monolayers
  of Alkane Thiol, Acid Thiol, Ag
• Prepare PDMS Stamp
• Play-doh Analogy
• Stamp Ag with Alkane Thiol

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WWWD? what would water do?
PDMS
overhead transparency with pattern
HDT
or
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Stamping

• Use a cotton swab to spread HDT on the surface of
  the PDMS stamp. Dry it with a blow dryer or wave
  it in the air. Repeat.
• Invert the stamp onto the surface of your
  silvered Petri dish.
• Cover the stamp with a 1kg mass or the equivalent
  for 2 minutes.
• Peel the stamp away from the silver.

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Exhale onto the silver to lightly mist the
surface with water vapor Drip about 0.5 1.0 ml
of water onto the surface. Agitate the Petri
dish to spread the water out and then tilt the
Petri dish and observe the movement of the water.
What shape does the water form?
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Alternative Use a 20uL micropette
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How is this Nanotechnology?

• We stamped nanometer sized molecules onto silver
  in such a way that the molecules cause water to
  form into shapes that they would not naturally
  form.

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Recall

• Floor ? Silver Surface
• Feet ? Sulfur atom
• Body ? Hydrophobic Carbon Chain 2 nm tall
• Arm to Back/Arm to Shoulder Connections
• ? Van der Waals Forces

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Steps of Soft Lithography
http//www.nanoterra.com/i/soft_lithography_diagra
m.jpg
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Why Use Microcontact Printing?

• Simple
• Quick
• Cost effective for making small high quality
  structures
• Can form a pattern on a non-planar surface
• Can be performed in a conventional chemistry lab
  (no clean room necessary)
• Stamps can be re-used and are durable

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Applications

• Surface Chemistry
• Study different surface characteristics i.e.
  roughness, wettability, reactivity
• Microelectronics
• SAMs can be used as nm size resists
• Protein Research
• SAMs used to control the adsorption of proteins
  onto a surface
• Patterns of proteins used for biosensors, cell
  biology research, tissue engineering
• Cell Biology
• How cells interact with different surfaces, how
  cell shape affects cell division
• DNA arraysfaster and less DNA needed
• Microfluidic Channels
• used to flow small volumes of protein solutions
  along a certain path

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Something to Look Into
www.radioshack.com
16 oz. PCB Etchant Solution
Model 276-1535  Catalog 276-1535 4.49
2-Sided Copper-Clad PC Board
Model 276-1499Catalog 276-1499 4.49
NNIN The Water Race Hydrophobic Hydrophilic
Surfaces
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Acknowledgements
George Lisensky
Wendy Crone
Mike Condren
Greta Zenner
University of Wisconsin-Madison
Katie Cadwell
Dana Horoszewski
Ken Gentry
Tony Antony
Farrell Rogers
Sue Whitsett
David Bergandine, University Laboratory High
School, Urbana, IL Aman Singh Ghotra and the
College Access Program Angela Johnson, IPSE
Intern Chris Johnson, Madison Memorial High
School Stephen Rudisill, Beloit College