Sticking Non-stick Surfaces Together

Polymers made up of non-polar, or only very slightly polar, functional groups are said to have low surface energy and poor adsorption which means that the surfaces are not "sticky".
Teflon (polytetrafluoroethylene or PTFE) is an example of a polymer with a very low surface energy, so low that it is used to provide non-stick coatings to things like pots and pans.
Silicones (polysiloxanes), with the general formula [R₂SiO]_n in which R is an organic group such as a methyl or ethyl group, also tend to have low surface energies. Because most materials do not adhere to, or stick to, silicones, silicones have become widely used to make flexible "rubber" molds.

So, how do you join together materials like these that are not "sticky"?

This is the question that scientists at Kiel University in Germany have been studying, and the solution they have devised is to use nano-scaled crystal linkers as internal staples. These staples are made of zinc oxide in which the crystals are shaped like tetrapods, that is, each staple has 4 legs. Zinc oxide crystals are sprinkled evenly onto a heated layer of teflon. Then a layer of silicone is poured on top. The material is then heated to 100^oC for less than an hour in order to join the materials firmly together.When the zinc oxide crystals are heated, the tetrapods pierce the teflon and silicone materials, sink into them and get anchored.
Peeling the teflon layer off the silicone layer held together by the tetrapod staples is about the same as peeling sticky tape off glass.

Reference:
X. Jin, J. Strueben, L. Heepe, A. Kovalev, Y.K. Mishra, R. Adelung, S.N. Gorb, A. Staubitz. Joining the un-joinable: Adhesion between low surface energy polymers using tetrapodal ZnO linkers. Advances Materials, 2012 DOI: 10.1002/adma201201780

Further Reading
Polymers and Polymerization
Functional Groups
Molecule Polarity

Suggested Study Questions:

1. Define the term polymer
2. Give two examples of polymers that are commonly used in households.
3. Define the term functional group and give three exaples.
4. Explain what is meant by a polar functional group and a non-polar functional group.
5. Give the structural formula for the monomer that can be used to form teflon.
6. Are the bonds in the monomer you have drawn in question 5 polar or non-polar bonds. Explain your answer.
7. Is the molecule that is the monomer in question 5 polar or non-polar. Explain your answer.
8. Given the general formula for silicones provided in the article, write the formula for:
   • polydimethylsiloxane
   • polydiethylsiloxane
9. Give a possible structural formula for the monomer used to produce each of the silicone polymers in question 8.

New Electrochemistry Resources

AUS-e-TUTE has just updated its Faraday's Laws of Electrolysis and added new resources for Q = It and E=QV calculations.

A "draft" of the VCE 2013-16 chemistry syllabus study guide has also been added.

Visit http://www.ausetute.com.au to view these resources.

New Electrochemistry Resources

AUS-e-TUTE has been updating its electrochemistry section.
The latest additions have been tutorials, games, tests, exams and drills on the following topics:

• Strength of Electrolytes
• Galvanic (Voltaic) Cell Diagrams
• Electroplating Concepts

Periodic Table Teaching Resources

AUS-e-TUTE has downloadable resources related to the teaching and learning of Periodic Table concepts.

Visit http://ausetute.com.au/downloads.html to download:

• Interactive Periodic Table (only for Windows)
• Lesson Outlines for teaching Periodic Table concepts (designed to be used with AUS-e-TUTE's interactive Periodic Table)

AUS-e-TUTE Update July 2012

AUS-e-TUTE's electrochemistry resources are currently being updated.

This has resulted in a major revision of most of the resources relating to the concepts of electrochemistry.

Below is a list of the new and updated resources that have recently been added to AUS-e-TUTE.

Links to all of these resources can be found in the Test Centre :

• Oxidation and Reduction Concepts: (tutorial, game, test, drill)
• Oxidation Numbers (States): (tutorial, game, tests, exams)
• Writing Half-equations (simple ions): (tutorial, game, test, drill)
• Writing Half-equations (aqueous solutions): (tutorial, game, test, exam)
• Redox Reaction Concepts: (tutorial, game, test, exams)
• Writing Redox Reaction Equations: (tutorial, game, test, exams)
• Spontaneous and Non-spontaneous Redox Reactions: (tutorial, game, test, exam)
• Displacement Reactions: (tutorial, game, tests, exam)          

Visit www.ausetute.com.au for more information

Olympic Medal Metals

Metallic medals have been awarded to 1^st, 2^nd and 3^rd place Olympic athletes since the 1900 Paris Olympic Games. The medals awarded at the 2012 London Olympic Games are 7mm thick, 85 mm in diameter, and, weigh 400g.
While we happily refer to these olympic medals as gold, silver and bronze, is this chemically accurate?

"Bronze medals" are often made of bronze, an alloy of copper and tin.
At the 2012 London Olympic Games, the bronze medals are made up of a mixture of 97% copper, 2.5% zinc and 0.5% tin. This composition is actually much closer to the composition of brass which is the term used to refer to an alloy of copper and zinc.

"Silver medals" contain at least 92.5% silver. The silver medals awarded in the 2012 Olympic Games were composed of 92.5% silver and 7.5% copper.

"Gold medals" must also contain at least 92.5% silver, but they are plated with at least 6g of gold so they look like "gold" medals. The 2012 Olympic gold medals are made up of 92.5% silver, 6.16% copper and 1.34% gold.

Reference

www.olympic.org/Assets/OSC%20Section/pdf/QR_1E.pdf

Further Reading
Periodic Table
Percentage Composition
Mass-mole Calculations
Moles-Number of Particle Calculations
Density Calculations

Suggested Study Questions

1. Give the chemical symbol for each of the following elements:
   • gold
   • silver
   • copper
   • tin
   • zinc
2. Explain why chemists refer to bronze and brass as alloys.
3. Calculate the mass of each element present in the bronze olympic medals awarded in 2012.
4. Calculate the mole of each element present.
5. For the 2012 Olympic gold medal, calculate the mass of silver present.
6. Calculate the number of silver atoms present in a 2012 olympic gold medal.
7. Calculate the mass of gold present in a 2012 olympic gold medal.
8. Calculate the volume of an olympic medal and use this to calculate the density of an olympic medal.
9. Calculate the surface area of a 2012 Olympic gold medal.
10. Assuming the 2012 gold medal is coated evenly with gold, what thickness is the layer of gold?

Sulfur Cycle

Sulfur, an element found in proteins, is cycled through the Earth's atmosphere, oceans and land, and, as it does, it undergoes chemical changes.
Most of the sulfur found on Earth is found in seawater and in rocks, in particular sedimentary rocks like shales containing pyrite (iron(II) sulfide or iron disulfide) and  in evaporite rocks containing anhydrite (anhydrous calcium sulfate), baryte (barium sulfate) and gypsum (hydrated calcium sulfate). The amount of mobile sulfur is continuously increasing due its release during volcanic activity. Human activities such as the burning of fossil fuels including coal and natural gas are also increasing the amount of mobile sulfur on Earth because fossil fuels contain sulfur as an impurity.

The sulfur cycle can be represented by the following 4 steps:

1. The incorporation of sulfur from organic (carbon) compounds like proteins, into elemental sulfur and inorganic compounds such as hydrogen sulfide, and the sulfide minerals such as pyrite (iron pyrite or fool's gold).
2. Oxidation of hydrogen sulfide, elemental sulfur and inorganic sulfides into sulfate ions.
3. Reduction of sulfate ions to sulfide ions.
4. Incorporation of the sulfur from sulfide ions into organic compounds (including organic compounds that contain metal atoms), such as proteins.

The oxidation of sulfur (step 2 in the cycle above) plays a part in removing oxygen from the atmosphere by incorporating oxygen into sulfate ions. Scientists have thought for a long time that the contribution of the sulfur cycle in removing atmospheric oxygen  is not nearly as important as the role of the carbon cycle in removing atmospheric oxygen. New research is suggesting that the weathering of pyrite and its burial may be more important than originally thought in regards to regulating oxygen.

Reference:
Halevy, S. E. Peters, W. W. Fischer. Sulfate Burial Constraints on the Phanerozoic Sulfur Cycle. Science, 2012; 337 (6092): 331 DOI: 10.1126/science.1220224

Further Reading:
Writing Ionic Formulae
Naming and Writing Formulae for Covalent Compounds
Oxidation Number (oxidation state)
Writing Precipitation Reaction Equations
Balancing Molecular Equations
Oxidation and Reduction Concepts
Carbon Cycle

Suggested Study Questions:

1. Write the chemical formula for each of the following:
   • elemental sulfur
   • hydrogen sulfide
   • iron(II) sulfide (iron disulfide)
   • calcium sulfate
   • barium sulfate
   • sulfate ion
   • sulfide ion
2. Give the oxidation number (oxidation state) for sulfur in each of the following:
   • S₈
   • H₂S
   • CaSO₄
   • BaSO₄
   • CaSO₄.2H₂O
3. Seawater is an aqueous solution which contains ions such as, barium, calcium, and sulfate. As seawater evaporates, calcium sulfate and barium sulfate precipitate out of the solution. Write a balanced molecular equation for:
   • precipitation of barium sulfate from seawater
   • precipitation of calcium sulfate from seawater
4. Write balanced chemical equations for each of the following:
   • combustion of carbon in coal to form carbon dioxide
   • combustion of sulfur in coal to form sulfur dioxide
   • combustion of methane (natural gas) to form carbon dioxide
5. Consider this equation for the oxidation of elemental sulfur :
   2S + 2H₂O + 3O₂ → 2H₂SO₄
   • Determine the oxidation number (oxidation state) of sulfur in elemental sulfur and in H₂SO₄
   • Use this information to explain why this equation can be said to represent an oxidation of sulfur.
   • Identify a species that is being reduced. Explain why this species can be said to be undergoing reduction.
   • Explain why it is appropriate to refer to the equation above as a redox (oxidation-reduction) reaction
   • For the reaction given above give the formula for the oxidant (oxidizing agent) and for the reductant (reducing agent).