User:Mary Mendoza/Notebook/CHEM 581: Experimental Chemistry I/2014/10/31

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Continuation of Bead Synthesis Trials

  • The burette set-up utilized by Eleni, Melvin, and Becca's group will be used; details of their assembly can be found on Kalivas' entry for 10/29/2014.
  • The assembly was prepared as shown in the picture.
IMG 3226.JPG

Description

  1. A column was set up with glutaraldehyde and hexane. Air is being bubbled through the column to mix the two liquids.
  2. PVA-Clay will be dropped down the column

Hexane Trial

  • The PVA-Clay formed beads within the hexane and floated down the column. They did not cross-link fast enough if at all and they dissolved into the glutaraldehyde.

Organic-Glutaraldehyde Solution

  • We attempted to add acetone to glutaraldehyde and then add hexane to get rid of the solvent layers. The solution was not hydrophobic enough to form beads however. When only a slight layer of hexane and stirring were applied, it yielded no good results.
  1. We have decided to abandon the beads and begin synthesis of ribbons
    1. We filled a column with acetone and 1.5mL of Glutaraldehyde
    2. we then dropped in the PVA-Clay

Trial of Several Organic Solvents

  • I observed that as soon as the organic phase, formed bead comes into contact with the aqueous phase of the glutaraldehyde, the bead disperses into the aqueous solution. I decided to conduct my own trials and have my group members continue the burette-ribbon experiments.
  • I concluded that the dilemma in the formation of beads is the immiscibility of the organic phase which forms the beads and the aqueous phase that cross-links the beads.
  • Therefore, I thought, I can resolve this issue by choosing several organic solvents slightly miscible with water but hydrophobic enough to form the beads.
  • In an attempt to keep the reaction mixture homogenized, motion is required. Thus, the reaction should be kept stirring on a stir plate. Also, stirring prevents the formed beads from clumping together."
  • I used the solvent miscibility table provided by Dr. Hartings taken from chemical company, phenomenex, as shown in the picture.
Solvent miscibility chart.jpg

Acetonitrile Trial

  • A drop of the PVA-clay was added into 3 mL of acetonitrile contained in a 12x100 mm, 8 mL disposable test tube.
  • The PVA-clay did not form beads.
  • Acetonitrile was tested without the use of the solvent miscibility chart. Upon checking the chart, the solubility in water of acetonitrile (%w/w) is 100.

DMSO and Ethyl Acetate

  • Hence, I selected the top 5 least immiscible organic solvent according to their solubility in water (%w/w) as shown in the picture.
  • I first tested dimethyl sulfoxide (DMSO) and ethyl acetate. For DMSO, a quick formation of bead was observed but readily dispersed as it settled on the bottom of the tube. On the other hand, as the drop of PVA-clay-HCl passed through the ethyl acetate, the bead retained its shape for at least 5 to 7 seconds and gradually dispersed.
  • Without testing the remaining organic solvents, I chose ethyl acetate as my organic solvent. It had the suitable features such that it enables the bead formation and its slight immiscibility with water.
  • Next, it was time to test ethyl acetate with glutaraldehyde. The following amounts for the ethyl acetate trial were not exactly measured but made by approximation. I took a 50 mL beaker with a magnetic stir bar. I approximately added 15-20 mL of ethyl acetate. In a drop wise manner, I added my PVA-clay-HCl solution using a pasteur pipette. I added at least 500 uL of glutaraldehyde.
  • With this experimental set-up, I was able to form beads but had to resolve the ratio of materials I used since everything was performed by approximation.
Solvents.png