User:Moira M. Esson/Notebook/CHEM-581/2013/02/15

Objectives

1. Prepare PVA-clay microspheres.
2. Run diffusion tests on hydrogels prepared on 2013/01/30 with Rhodamine 6G dye added on 2013/02/08.

Microsphere Preparation

• Due to the relatively unsuccessful preparation of PVA/clay microspheres(the prepared spheres were either larger than a micrometer or did not appear at all), a new method was used for the preparation of PVA/clay microspheres.

General Protocol:

1. The desired ratio of PVA and clay was measured out. The total mass was ~1g.
2. The PVA/clay was placed in a 50mL beaker with a magnetic stir bar. 25mL distilled H₂O were added to the beaker and the solution was heated to ~100°C and allowed to stir until complete dissolution of PVA/clay.
3. The magnetic stir bar was removed and 25mL of mineral oil was added to the beaker.
4. The contents of the beaker were poured into a blender to homogenize the solution and create an emulsion of the aqueous and organic layer in the attempt to create a suspension of microspheres.
5. The blender was turned on a low setting for 7 minutes.
6. The contents of the blender were poured into a beaker and the appropriate amount of DMSO/Rhodamine 6G solution was added.
7. The microsphere solution was placed in a freezer at -20°C for 24 hours and then removed and allowed to thaw for 24 hours.
8. Repeat this freeze-thaw cycle three times.

This procedure was adapted from [1]
Preparation of Microspheres:

• New calculations for the amount of DMSO/Rhodamine 6G to be added:

For a 90:10 ratio:

 (25mL)(1μM)/(92μM)=0.272mL

For a 50:50 ratio:

 (25mL)(1μM)/(165μM)=0.152mL

• Information about prepared microspheres:

Observations:

• After the addition of dye/DMSO to the 110% Lamponite, the dye appeared to stick to very small spheres at the bottom of the beaker. Bright pink spheres immediately formed. This did not occur for the samples containing 110% NaMT.

Fluorescence

• The six hydrogel samples that were allowed to soak in Rhodamine 6G were tested for the rate of diffusion of Rhodamine 6G from the samples.

General Protocol:

1. Excess Rhodamine 6G sample still present in the beaker was removed.
2. Hydrogel samples were removed from the beakers, pat dry with a paper towel, and placed in a new, clean beaker.
3. 25mL distilled H₂O were added to each beaker sample.
4. A timer was started, and every 15 minutes, a sample of distilled H₂O was removed from the beaker and placed in an unfrosted cuvette.
5. The sample was discarded into a waste beaker.
6. This process was repeated for 2 hours.

Spectra:
Figure 1. Diffusion test fluorescence spectra for 50:50 PVA MW 146,000-186,00: 50% NaMT hydrogel
Correction: The x-axis should be labeled Wavelength(nm). The image will be corrected. Figure 2. Diffusion test fluorescence spectra for 50:50 PVA MW 146,000-186,000: NaMT hydrogel

Figure 3. Diffusion test fluorescence spectra for 90:10 ratio of PVA MW 146,000-186,000:Lamponite

Figure 4. Diffusion test fluorescence spectra for a 90:10 ratio of PVA MW 146,000-186,000:NaMT

Figure 5. Diffusion test fluorescence spectra for a 90:10 ratio of PVA MW 146,000-186,000:50% NaMT

• Correction: The x-axis should be labeled Wavelength(nm). The image will be corrected

Observations:

• Each of the samples had a very fast diffusion rate. If the spectra are viewed additively for each hydrogel sample, a significant amount of dye leaked out of the hydrogel sample in only 2 hours, in comparison to the hydrogels which remained in distilled H₂O for one week and had minimal dye diffusion. This indicates that the dye must be added prior to the freeze-thaw crosslinking method.
• Due to the fact that the dye did not immediately, completely diffuse out, the crosslinking of PVA/clay hydrogels slowed the diffusion rate of the dye.
• Comparing the 50:50 ratio of PVA:clay and the 90:10 ratio, the hydrogels with 50:50 ratio had more dye leak out of the hydrogel than the 90:10 ratio. Perhaps indicates a more effective pressure stimuli.
• In the future, when performing the diffusion tests, after taking a sample every fifteen minutes, the sample will be readded to the test beaker rather than discarded.