Chemistry Lab Methods
Aluminium oxide columns are used to purify the styrene. They are realized in short pastor pipettes. To stop the aluminium oxide from falling out, use a small amount of quartz wool and push it to the tip of the pastor pipette. Use a small plastic tool to push it to the bottom of the pastor pipette. Do not push too hard, to avoid breaking the glass or the quartz wool fibres leaking into the styrene. After, use the appropriate funnel to fill the pastor pipette 3/4 of the way with aluminium oxide under the fume hood.
To safely dispose of it afterwards, clean the pastor pipette using the hexane wash bottle to fill the rest of the pastor pipette. Use the pipette bulb to push the hexane through. Repeat these steps twice. The hexane should be disposed of in the non-halogen bin. Leave the pastor pipette to dry under the fume hood. The aluminium oxide will now be easy to remove and then should be discarded in contaminated silica bin.
The density of styrene (0.909 g/mL) is used to make sure all the preforms made have the same volume. Use the air dial on the fume hood to remove any dust in the test tube. Place the test tube in an erlenmeyer as a support. Weigh out the test tube used for the preform with the analytical balance. Write down its weight to compare with the filled test tube later. Depending on how much styrene is required for the preform, calculate the styrene mass using its density. Take a beaker and fill it with approximately the quantity of styrene needed (based on the calculations).
A column can purify approximatif 15 mL of styrene. Push the pipette bulb on the aluminium oxide column’s pastor pipette all the way through so the top of the pastor pipette can be seen through the pipette bulb. Take a 20 mL syringe and place a pink 1 mm needle tip. Fill the syringe with 1 mL less than the required amount of styrene. The last 1 mL of styrene will be used later to incorporate the quantum dots and wash their container. Take a beaker to be used for the impure styrene disposal. Pierce through the centre of pipette bulb on the aluminium oxide column with the needle of the syringe containing the styrene. Slowly push the styrene into the aluminium oxide column. Discard the first few drops in the appropriate beaker. Then, slowly purify the rest of the styrene in the test tube.
Initiator needs to be added to the styrene to start the polymerization. Usually, 80 mg of benzoyl peroxide (Luperox) is used for 13 mL of styrene. Use a small waxed paper, folded in half to make the pouring easier, to weigh it on the analytical balance. Press zero on the analytical balance and add the benzoic peroxide on the waxed paper using a small metal spatula. When the required amount of benzoic peroxide is obtained, pour it into the test tube containing the styrene. The waxed paper can then be discarded in the garbage bin. The analytical balance can be wiped down with the brush provided for this purpose to clean it for future use.
The air displacement pipette is used to precisely measure the volume of the quantum dot solution. Using the 200 mL air displacement pipette will provide more accuracy in the measurement, if 20 to 200 mL of quantum dot solution is used. Use the 20 mL air displacement pipette, if 1 to 20 mL of quantum dot solution is used.
To use the air displacement pipette, first push the plunger button halfway down to create a vacuum. Second, put the air displacement pipette’s tip in the solution and release the plunger button to aspirate it. Third, move the air displacement pipette over the container where the measured solution needs to be moved and press the plunger button all the way down to release the solution.
To set the volume on the air displacement pipette, rotate the volume adjustment knob on the side until the digital volume indicator displays the desired number.
The quantum dot solution is not very viscous, thus it will leak out of the air displacement pipette’s tip if the manipulation is not done quickly. If you need to do this step multiple times, the disposable tip needs to be replaced every time, so that the concentration of quantum dots in the solution remains the same.
To change out the disposable tip, press the tip ejector button on the top of the air displacement pipette. The plastic disposable pipette tips should be placed in the red bin if they have been used with quantum dot solution.
The quantum dot solution should be treated in disposable containers, as they are easier to discard afterwards. The quantum dot solution is highly toxic and should be handled carefully.
The quantum dot solution is transferred into a disposable centrifuge container on a support designed for this purpose with the air displacement pipette. The disposable centrifuge container is filled to the 1 mL line with isopropanol, using the wash bottle.
The container is placed in the centrifuge to separate the quantum dots from the impurities. A weight (a centrifuge container filled with water) can be used if an odd number of solution needs to be centrifuged. The centrifuge containers should always be placed symmetrically from each other. The time dial is used to set the rotation time, usually 5 minutes. The RPM dial is used to set the speed of the rotations, usually 10 000 RPM. After being centrifuged, the quantum dots have stuck to the walls of the centrifuge container. The isopropanol, containing the impurities, can be discarded in the red bin.
The quantum dots are solubilized is the 1 mL preserved styrene. Add half (0.5 mL) to the centrifuge container with the air displacement pipette. Mix thoroughly using the ultrasonic bath. If the quantum dots do not dislodge, the metal basket in the ultrasonic bath can be removed.
Pour the quantum dot dissolved in styrene in the test tube. Aim for the centre of the test tube, so that all the quantum dots get into the styrene and do not stick to the side of the test tube.
Add the other half (0.5 mL) of the preserved styrene in the centrifuge container to clean it and solubilize the left over quantum dots. Pour it into the test tube.
To mix and remove the air bubbles from the quantum dot and styrene solution in the test tube, a stream of nitrogen gas is used. Add a piece of clear tape around the rubber septum and the test tube to prevent it from coming off. Under the fume hood, pierce the test tube’s rubber septum in the centre with the 10 mm metal needle connected to the nitrogen outlet. Add a pink 1 mm needle onto the side of the rubber septum to release the gas. Turn the white dial on the side of the fume hood to allow the nitrogen gas to flow. Use the timer to make sure the solution is mixed for five minutes. To remove the needle, hold the test tube far under the fume hood to protect yourself.
To prepare the ultrasonic bath, to start heating up the quantum dot and styrene solution, you need to pour hot tap water (approximately 60ºC) into the container.
To create a vacuum in the solution’s test tube, pierce the centre of the rubber septum with the 1 mm pink needle connected to the aspirator. Turn on the water with the green dial to start the aspirator. Move the test tube around in the ultrasonic bath to remove as many bubbles as possible.
To disperse the quantum dots in the styrene, leave the test tube in the ultrasonic bath with the vacuum for 7 hours.
Place the test tubes in the mineral oil beaker using the plastic support. Make sure they are perfectly straight and not touching any sides of the beaker. Place the beaker in the centre of the oven. Rotate the dial at 2.5 (approximately 90ºC).
Any object that has been in contact with quantum dots needs to be discarded in the red bins. If quantum dot solution gets on the gloves, dispose of then directly in the red bin and wash the skin that has been in contact. Any superfluous styrene needs to be disposed of in the non-halogen waste bin. The discarded hexane, used to wash the aluminium oxide column needs to be placed in the non-halogen bin. The aluminium oxide, used for the purification columns, needs to be disposed of in contaminated silica. Needles need to be placed back in their protective plastic septums and disposed of in the specific needle bin. The plastic disposable pipette tips should be placed in the red bin if they have been used with quantum dot solution. The pipette bulbs used for the styrene should be left under the fume hood to let the chemicals evaporate, then discarded in the regular bin. Any glassware should be rinsed with hexane, then acetone and left under the fume hood to dry. If the glassware is not disposable, it needs to be washed with soap and water, left to dry near the sink and then placed back on the shelves. If the glassware is disposable, it needs to be placed in the glass bin. The gloves should be thrown away in the regular bin, unless they have come into contact with the quantum dot solution, then they should be placed in the red bin.
After the preforms have polymerized for 48h, turn the oven off and let the preforms cool down in the oven. Ensure the oven door is closed until they reach room temperature, to prevent the glass test tubes from braking because of the thermal shock. If the main oven is still used for polymerizing other preforms, remove the mineral oil filled beaker containing the preforms from the oven carefully using gloves and place it in the secondary oven. Decrease the temperature over the course of the day to cool the preforms down to room temperature.
Take the test tubes out of the oil and set them on the test tube rack to be cleaned. Using isopropanol, clean the test tubes. Roll the preform in two sheets of brown paper. Use the handle of the screwdriver to carefully break the top of the test tube. Afterwards, remove the remaining glass off the preform. Use the tweezers if necessary. Wash the preform with soap and water, then wash it with isopropanol and dry it off with a lint-free tissue. Do not use any other solvent (i.e. hexane, acetone or ethanol), as they will dissolve the preform.