User:Moira M. Esson/Notebook/CHEM-581/2013/02/20

Objectives

1. Perform pressure tests on prepared hydrogels with Rhodamine 6G added.
2. Prepare microspheres using a new preparation method.

Microsphere preparation

• After viewing the microspheres prepared on 2013/02/15, it appears as if all prepared microspheres formed a layer at the bottom of the beaker, creating a textured film as opposed to microspheres. Complete separation of the aqueous and organic layer occurred. The emulsion and suspension of the microspheres did not occur, perhaps due to the high freezing point of mineral oil. As such, a new procedure was used for the preparation of microspheres. This procedure was adapted from [1].

General Protocol:

1. Measure out the desired mass of PVA and clay. The total mass should not exceed 1g.
2. Place the PVA and clay in a clean, 50mL beaker with a magnetic stir bar.
3. Add ~25mL distilled H₂O to the beaker. While stirring, heat the contents of the beaker to at least 100°C and allow the PVA/clay to completely dissolve. (Allow the contents to heat for at least 1 hour. If necessary, more distilled H₂O may be added. The exact amount of distilled H₂O should be recorded for future Rhodamine 6G addition).
4. After complete dissolution of PVA/clay, remove the magnetic stir bar and pour solution into a blender.
5. Add at least 35mL safflower oil to the blender. If more than 25mL distilled H₂O was added to the PVA and clay, then the same volume increase should used in the addition of safflower oil.
6. Blend the safflower oil and PVA/clay solution on high for 5 minutes.
7. Quickly pour the contents of the blender into 20mL glass vials.
8. Quickly freeze the PVA/clay and safflower oil emulsion in liquid nitrogen. The vial should be held in the liquid nitrogen until the sample is completely frozen throughout. If the sample has been sitting for a short period of time and it appears as if the microsphere particles are separating out of the organic layer, use a sonicator prior to freezing the sample to ensure that the microsphere particles are frozen in the organic layer.
9. Place the frozen samples in a freezer at -20°C for 24 hours. After 24 hours, remove the samples from the freezer and allow the samples to thaw for 24 hours.
10. Repeat step 9 three times.

Note: Extreme Caution: Liquid nitrogen is extremely cold. Extra care should be used when handling liquid nitrogen. Prepared Microspheres:

• 90:10 PVA MW 146,000-186,000:Lamponite microspheres were prepared. The sample was dissolved in 35mL distilled H₂O and 45mL safflower oil was added.
• Due to the dyes affinity for the organic layer, the Rhodamine 6G will be added at a later date.

Hydrogel Pressure testing