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EMS525U Functional Materials

Experimental Coursework 2. Tuesdays, 14^th(group B), 21^st (group A) and 28^th March (group C) and 4^th April (for technical failure and students with approved EC). Students might be split in 2 group of 3 students each. Each group carries out their own set of experiments.

Time 9.30am – 2pm (possibly run till 3pm). Intro starts strictly at 9.30am at G29

CW2 Title. Preparation of magnetic microcapsules.

The work is divided in two parts: preparation of magnetic nanoparticles and preparation of multilayer microcapsules. At later stages the magnetic nanoparticles are to be incorporated within polyelectrolyte multilayers. Preparation of magnetic nanoparticles are recommended to be done while adsorbing layers on calcium carbonate core (see below).

1. Preparation of magnetic nanoparticles.

Reagents: FeCl₂∙4 H₂O, FeCl₃∙6 H₂O and NaOH.

Preparation of Fe₃O₄ particles:  Iron oxide particles can be obtained by co-precipitation of water-soluble iron (II, III) salts (at a molar ratio of 1:2) in an alkaline medium of sodium hydroxide. The process of formation of magnetite (black precipitate) can be presented according to the reaction:

FeCl₂ + 2FeCl₃ + 8NaOH → Fe₃O₄↓ + 8NaCl + 4H₂O

0.43 g of FeCl₂∙4 H₂O and 1.17 g of FeCl₃∙6 H₂O are dissolved in 30 ml of deionized water. Then 10 ml of an aqueous solution of sodium hydroxide (containing 0.75 g of NaOH) is quickly added to a solution of iron salts with vigorous stirring on a magnetic stirrer. The colour of the solution changes from yellow to black. The magnetite suspension is allowed to stir for 10 minutes at room temperature. Then resulting particles of Fe₃O₄ are collected with a permanent magnet and washed several times with deionized water. Check that the particles are collected by applying magnet to the tube with particles suspension.

2. Preparation of microcapsules

The target of your work is to create hollow polymeric microcapsules. To do this you will create a template (CaCO₃ particles), then coat it with polyelectrolyte layers and then dissolve the cores to get hollow spheres.

The chemicals you will need for the process:

1. CaCO₃ particles preparation:

CaCl₂ + Na₂CO₃ → CaCO₃ + NaCl

You will use C_molar = 0.33 M solutions of CaCl₂ and Na₂CO₃ in deionised water.

You will need about 3 ml of each solution.

M_w(CaCl₂) = M_w(Ca) + 2*M_w(Cl) =

m(CaCl₂) = C_molar*M_w(CaCl₂)*V =

2. Depositing of layers :

You will use positively-charged Poly(allylamine hydrochloride) (PAH) and negatively charged Poly(styrene sulfonate) (PSS) polyelectrolytes 2 mg/ml solutions in 0.5 M solution of NaCl in deionised water. You should deposit at least 5 layers of polyelectrolytes, which leads to approx. 8 ml of each polyelectrolyte. As last layer, adsorb suspension of magnetic nanoparticles (MNPs) from part 1. (take 1 ml of the suspension after intensive shaking)

3. Cores dissolution

You will use Ethylenediaminetetraacetic acid (EDTA) 0.2 M solution in deionised water to dissolve the cores. You will need about 10 ml of the solution.

Procedures.

1. CaCO₃ particles preparation:

Introduce rapidly Na₂CO₃ solution into the CaCl₂ solution while stirring vigorously. The mixture should become white. Stir for about 30 s and then stop stirring.

After that put the solution into the tubes and wash them 3 times with deionised water. For this you will centrifuge the solutions at 5000 rpm for 30 s, remove the supernatant and refill the tube with deionised water.

2. Deposition of layers

For layer deposition you introduce polyelectrolyte solutions to the cores after removing the supernatant and stir for 10-15 minutes. After this, wash 3 times to remove excess polyelectrolyte. Then, the next layer is deposited. Positive and negative layers should alternate.

So, you will create a polyelectrolytic shell with structure:

PSS w w w/PAH w w w/PSS w w w/PAH w w w/PSS w w w/MNPs w w   (w – means “wash”).

3. Dissolving the core

To dissolve the core, you introduce 1 ml of EDTA solution to your covered particles after removing supernatant from them and leave to stir for 7 minutes. Then you introduce another 1 ml of EDTA and leave for incubation for another 7 minutes. After that, you apply 3 washing steps with EDTA and 3 washing steps with water, centrifugating at 4000 rpm for 2 minutes.

Warning! When EDTA reacts with CaCO₃, the gas (CO₂) is coming out, so there is a pressure inside the tube, which can open the cap and explode your capsules from the tube.

After completing these procedures you should get some more or less round capsules, which can be seen in the microscope.

Apply the magnet and see that the capsules are collected to the side by the magnet. Take a photo.

Recommended reading: see uploaded papers on QM+ on magnetic capsules

Marking scheme:

Preparation (e.g. response to questions about the techniques employed), work in lab, commitment to conduct experiments, effectiveness, working with other group members. (assessed by TA; absence from the labs will result in 0 marks)  5 marks

Abstract. Adequate summary covering whole report 2 marks

Introduction. Given background of magnetic materials for delivery, magnetic nanoparticles and polyelectrolyte capsules and its properties and application as outlined from cited papers   5 marks

Experimental details. All materials, procedures and methods are described in sufficient detail.   4 marks

Results and Discussion.  Illustrative and correct presentation of graphs and photos, 5 marks

Proper description of data and comparison with work of others (in cited papers) 6 marks

Conclusion. Adequate description of what student learnt in CW, what skills gained and what data produced    3 marks

References. 3 marks (12 relevant references means full mark for that)

All together CW worth 33 marks