Reference no: EM132303162

Assignment - Need help in fixing lab report. Attached the lab manual, need to make lab report on it./

LAB MANUAL - NANOCOMPOSITES

Based on "Take-Home Nanochemistry: Fabrication of Gold- or Silver- Containing Cling Film, Campbell, D. et al. JChemEd, 89, pp.1312-15, 2012

The purpose of this laboratory experiment is to introduce aspects of nanocomposites using a polymer matrix and developing gold nano-reinforcement in situ within the polymer. There are essentially two ways to incorporate metal nanoparticles into a polymer matrix, in situ; where the metal nanoparticles are formed in the matrix and ex situ; where metal nanoparticles are added to the polymer. Both have advantages/disadvantages and will be discussed in lectures later in the semester.

The matrix material, polydimethylsiloxane (PDMS) can be produced as a colourless, transparent elastomer that is used for a variety of applications, such as encapsulation of electronic components to protect them from moisture and dirt.

When the liquid kit components are mixed together (Fig 1- attached) silicon-hydrogen bonds attached to PDMS oligomers (species 2) oxidatively add to a platinum catalyst (possibly Karstedt's catalyst formed by the reaction of chloroplatinic acid, H₂PtCl₆, and divinyltetramethyldisiloxane). The carbon-carbon double bonds, attached to short polymer chains (Species 1), react with the silicon-hydrogen single bonds attached to other short polymer chains (Species 2). Vinyl groups attached to PDMS oligomers (species 1) insert into the platinum-hydride bond and then the alkyl and silyl groups reductively eliminate to produce -Si-CH₂-CH₂-Si- cross-links within the PDMS.

After the cross-linking is essentially complete, however, some of the leftover silicon-hydrogen bonds can still reduce some metal-containing ions, such as tetrachloroaurate- (III), tetrachloropalladate(II), tetrachloroplatinate(II), and silver(I), that are carried into the elastomer by organic solvents. The metallic particles produced by this reduction reaction are embedded within the polymer matrix, which restricts particle aggregation. The PDMS is transparent to visible light wavelengths, so the colours of the nanoparticles can be examined both by the eye and by visible light spectroscopy.

Part A: Casting a thick sheet of polydimethylsiloxane (PDMS)

1) Obtain a plastic Petri dish from your lab instructor. This dish will be a mould for making a disk-shaped PDMS window cling.

2) You can use dry-erase markers to mark the inside bottom edge of the dish to identify your group. Do not cover the whole surface as we need to do UV-VIS on the sample later on.

NOTE: Any written markings that transfer from the dish to the PDMS will be reversed (a mirror image).

3) Weigh 3.0 g (no more than 4.0 g) of PDMS base into a plastic weigh boat. Use a disposable plastic pipette with the tip cut away to dispense the viscous liquid. Clean up any spills with paper towels immediately.

4) Weigh 0.3 g (no more than 0.4 g) of PDMS curing agent into the same plastic weigh boat. Use a different disposable plastic pipette with the tip NOT cut away to dispense this less-viscous liquid. Clean up any spills with paper towels immediately. DO NOT place the pipette back into the curing agent, you will need it for the next step.

5) Mix the PDMS precursors together thoroughly in the weigh boat using the plastic pipette from the previous step. Stir for at least 100 strokes.

6) Pour the mixed PDMS into the Petri dish so that the entire bottom of the dish is covered. Use the plastic pipette to scrape as much of the PDMS from the weigh boat into the Petri dish as possible.

7) Let the mixed polymer stand in the dish for at least 15 minutes to allow some of the trapped air bubbles to rise to the surface of the polymer. These bubbles can be popped by gently blowing on the surface of the mixed PDMS.

8) Place the Petri dish on a bench as instructed by the demonstrator. The films will be dried in a drying oven set to at least an hour and be ready for you next lab session.

Part B: Growth of gold or silver nanoparticles within the PDMS

1) Remove the cross-linked PDMS from the Petri dish without tearing the elastomer. This is best accomplished by inserting a spatula between the PDMS and the edge of the dish. Carefully move the spatula around the inside edge of the dish, the PDMS should release from the dish relatively easily. When this is accomplished, carefully use the spatula to pry the PDMS away from the bottom of the dish. The dry-erase marker markings should have been encapsulated into the elastomer. You now have a PDMS window cling!

2) Place the cross-linked PDMS into a soaking solution of 1 mM sodium tetrachloroaurate(III), Na[AuCl4], dissolved in ethyl acetate in a beaker for one hour. Place aluminium foil over and around the beaker to minimize evaporative losses and photoreduction of the metal species in solution.

3) After an hour the PDMS will have swollen due to the absorbed ethyl acetate. In the Na[AuCl₄] solution the polymer will have taken on a pinkish-purple tint. Gently remove the PDMS sample from the soaking solution with a forceps, dip it in clean ethyl acetate to rinse it, and then place it between two sheets of aluminium foil to dry in a fume hood. Leave the PDMS in the fume hood at least overnight.

Part C: Optical characterization of gold nanoparticles within the PDMS

1) Place the PDMS in the light beam of the visible light spectrometer. As mentioned above, the valence electrons in each metal nanoparticle collectively absorb light (via plasmon resonance). The specific wavelengths of light that each particle absorbs depend on such factors as particle size, shape, and composition. To obtain the best spectrum from the nanoparticles in PDMS, avoid shining the beam through the ink markings at the surface of the polymer. Record the wavelength corresponding to the maximum absorbance of the nanoparticles in your sample. The absorption of light due to the gold nanoparticles should have a maximum absorbance wavelength between 500 and 600 nm.

Questions -

1) Write the redox reaction between the silicon-hydrogen bonds in polydimethylsiloxane and the metal compound. Which is the oxidizing agent?

2) The redox reaction within the PDMS has also been used to produce gold and silver nanoparticles from ionic species, but not nickel or iron nanoparticles from their metal ions. Would you expect PDMS to be used to produce zinc nanoparticles from zinc(II) ions? Why or why not?

3) Na[AuCl₄] and AgBF₄ dissolve readily in water. Why was ethyl acetate used as a solvent to carry these species into the PDMS instead of water?

4) What is the wavelength of the maximum absorbance of the nanoparticles? To what colour of visible light does this correspond? Estimate a size for the gold nanoparticles formed.

5) The absorption of light by the collective oscillation of the gold or silver nanoparticles is referred to as plasmon resonance. What type of bonding exists between gold or silver atoms in these particles?

6) Palladium and platinum nanoparticles have been also been grown in PDMS. These nanoparticles have been shown to act as catalysts to accelerate chemical reactions. What advantages and disadvantages might there be to having the palladium and platinum particles trapped within the PDMS matrix?

Advice on lab reports -

Three basic principles

(1) Be clear.

(2) Be reasonably thorough.

(3) Write for someone who doesn't know what you know now.

Strategies

• Use a logical progression. At the very least follow a similar progression to your instructions - the marker will be looking for information in that order. Generally information should flow from old to new. A useful model is the formal scientific report, which usually has:

We need to write these below highlighted things in the lab report:

- Introduction (background and why you are doing it) AIM, OBJECTIVE

- Methods (what you did)- No need to duplicate this in your report, just refer to the lab manual unless you varied the procedure for some reason!

- Results (what you found)

- Analysis of Results (formulae, calculations and graphs)

- Discussion (what the results mean, answers to questions, your own thoughts and comments)

- Conclusions (what the IMPLICATIONSare).

-  Answers to the questions of lab manual at the end.

You will not have time to write a large amount in your lab report, and doing so is not really necessary (e.g. the introduction is mostly given by your instructions, which can be condensed). However, it is a good idea to briefly to cover most of the items above.

• Use efficient structures. Make the information easy to find and read. Use appropriate headings. Group related information together. Readers tend to focus on graphical features, so include important information there.
• Be selective. Aim for short reports. It may not be necessary to include everything in the main report. When writing a formal report, if you have a section that is significant in size and may be of interest, but is not central to the message, then consider using an appendix.
• Label your graphs fully. - Title, x-axis, y-axis, line-labels, any special notes. Write a short but self-contained caption that explains the graph.
• Record "everything". Obviously this has to be balanced against the the need to be clear and concise, but many important discoveries rely on recording details that did not seem important at the time. You may need that information to answer a question later!
• Explain context. Try to make the report stand on its' own. When you're answering questions, try to paraphrase the question in your answer, so it is clear what you are talking about. In a log, use short sentences to explain what you are writing and why you are writing it. In formal reports the standard structure is designed with this idea in mind.
• What would you need to know? Imagine someone is going to ask you questions about your experiments in a few months time. Save time later by recording it now.

Attachment:- Assignment Files.rar