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									Self-Assembled Monolayers
    and Soft Lithography
 in High School Chemistry

        Jen Ehrlich
      UW-MRSEC RET
       Summer 2007
                                   Water



           http://www.ktf-split.hr/glossary/image/hydrogen_bond.gif



• Polar
• Hydrogen bonding (very strong!)
Water’s Unique Properties




       http://musicsojourn.com/AR/AmbN/img/s/Surface10/SurfaceTensions_300.jpg
                         Surface Tension



                                http://www.chem1.com/acad/sci/aboutwater.html

Bulk Molecule:                                                         Surface Molecule:

Attracted to molecules in all directions                               Attracted to molecules next to and
All forces balance each other out.                                     below, but NOT above.
                                                                       So it’s pulled INTO the liquid
  Surface tension is the enhancement of the
intermolecular attractive forces at the surface
Have You Ever Seen a Square
      Water Droplet?



               Why Not?


To minimize surface and maximize volume,
 water naturally forms a spherical shape
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
    How is surface tension affected by soap?
       Soap breaks the Surface Tension! Why?




http://demo.physics.uiuc.edu/lectdemo/scripts/demo_descript.idc?DemoID=1144
Hydrophobic
Hydro phobic




 water - fearing
Hydrophobic materials
What makes something hydrophobic?


  Tristearin (beef fat, lard)   Carbon nanotubes, graphite
Hydrophilic
Hydro philic




 water - loving
Hydrophilic materials
              What makes something hydrophilic?


                      Ethanol                                                  Acetic acid




http://www.erowid.org/chemicals/alcohol/alcohol_chemistry.shtml   http://www.bmrb.wisc.edu/metabolomics/gen_metab_summary_5.php?molName=acetic_acid
          Soap—
  Hydrophobic or Hydrophilic?
                                                                  Hydrophilic




http://chem.ufl.edu/~itl/2045/lectures/lec_i.html




                                                    Hydrophobic
Soap is a surfactant

surface acting agent




 http://wwwchem.csustan.edu/chem2000/Exp5/BKG.HTM
                           Surfaces
  Where do we change the surface of an object to change its properties?




Galvanized Pipe
WWWD? – What would water do?



        X

                X
http://www.eurekalert.org/multimedia/pub/3999.php?from=95205
               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
             Self Assembly
• Classroom Role Play—Part 1
  – Rules:
    • Your right hand can only touch someone’s back
    • Your left hand can only touch someone’s right
      shoulder
  – Teacher should limit space to a small enough
    area to get a “mass” of students
                       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
             Self Assembly
• Classroom Role Play—Part 2
  – Rules are the Same:
    • Your right hand can only touch someone’s back
    • Your left hand can only touch someone’s 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)
Part 1
                Part 2

         Students are non-polar molecules
         “Imagine holding an umbrella to shield
         yourself from water.”
     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
What Self Assembly Is Not




            X
              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




            SSSSSSS SS S
WWWD? – what would water do?

                                                            X
X

                           16-mercaptohexadecanoic acid SAM
    Hexadecane thiol SAM   (Acidic Thiol)




                              http://www.asemblon.com/node/240
               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
        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.
 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.
        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.
     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
                                           Ag



                                –   CH3           –   COOH



                     Back                 Front
WWWD? – what would water do?
•   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
               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
         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.
               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
         Macroscopic Model
• Station 1: Printing a Pattern


                             Petri dish (overhead transparency)


                   Solid shapes are glued onto Petri dish
                   (ink from laser printer)
        Macroscopic Model
• Station 2: Making the PDMS Mold
         Macroscopic Model
• Station 3: Coating stamp with alkanethiol


                    vegetable oil (alkanethiol)
         Macroscopic Model
• Station 4: Stamping the metallic surface

                              Paper Bag (Silver)
         Macroscopic Model
• Station 5: Applying water to stamped image
               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
WWWD? – what would water do?

                    PDMS
       overhead transparency with pattern


                      HDT




                      or
                           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.
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?
     Alternative:
Use a 20uL micropette
  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.
                 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
Steps of Soft Lithography




http://www.nanoterra.com/i/soft_lithography_diagram.jpg
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
                             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 arrays—faster and less DNA needed

Microfluidic Channels
   used to flow small volumes of protein solutions along a certain path
          Something to Look Into…
                                www.radioshack.com




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            NNIN: The Water Race: Hydrophobic & Hydrophilic Surfaces
                           Acknowledgements
                       Wendy          Greta         Mike          George
                       Crone         Zenner        Condren        Lisensky



                                                                             University of Wisconsin-Madison

                                          Dana            Katie
                        Ken
                                       Horoszewski       Cadwell
                       Gentry




                          Tony           Farrell          Sue
                         Antony          Rogers          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

								
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