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

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  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:


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.

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 2 hr diffusion test 50 MW 146 50% NaMT correct.png
Figure 2. Diffusion test fluorescence spectra for 50:50 PVA MW 146,000-186,000: NaMT hydrogel 2 hr diffusion test 50 MW 146 NaMT.png
Figure 3. Diffusion test fluorescence spectra for 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.