- Prepare PVA-clay microspheres.
- Run diffusion tests on hydrogels prepared on 2013/01/30 with Rhodamine 6G dye added on 2013/02/08.
- 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.
- The desired ratio of PVA and clay was measured out. The total mass was ~1g.
- 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.
- The magnetic stir bar was removed and 25mL of mineral oil was added to the beaker.
- 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.
- The blender was turned on a low setting for 7 minutes.
- The contents of the blender were poured into a beaker and the appropriate amount of DMSO/Rhodamine 6G solution was added.
- The microsphere solution was placed in a freezer at -20°C for 24 hours and then removed and allowed to thaw for 24 hours.
- Repeat this freeze-thaw cycle three times.
This procedure was adapted from 
Preparation of Microspheres:
- New calculations for the amount of DMSO/Rhodamine 6G to be added:
For a 90:10 ratio:
For a 50:50 ratio:
- Information about prepared microspheres:
|Prepared Clay-PVA(MW 146,000-186,000) microspheres
| Composition of hydrogel(ratio of PVA to clay)||Amount of PVA added(g)||Amount of clay added(g)||Concencentration of DMSO/dye stock solution added(μM)||Amount of DMSO/dye added(mL)
| 90:10 PVA:110% NaMT||0.9099||0.1045||92||0.272
| 50:50 PVA:110% NaMT||0.5076||0.4913||165||0.152
| 90:10 PVA:110% Lamponite||0.9010||0.0998||92||0.272
- 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.
- 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.
- Excess Rhodamine 6G sample still present in the beaker was removed.
- Hydrogel samples were removed from the beakers, pat dry with a paper towel, and placed in a new, clean beaker.
- 25mL distilled H2O were added to each beaker sample.
- A timer was started, and every 15 minutes, a sample of distilled H2O was removed from the beaker and placed in an unfrosted cuvette.
- The sample was discarded into a waste beaker.
- This process was repeated for 2 hours.
Figure 1. Diffusion test fluorescence spectra for 50:50 PVA MW 146,000-186,00: 50% NaMT hydrogel
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
- 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.