I noticed an issue with the water evaporation rate from the sample chambers after the first trial. At first it wasn’t so bad, but got progressively worse. When the second trial came there was a heat wave in the lab (chiller went down for a week), and the evaporation rate increased. I discarded the results anyways because the heat affected the seed growth, but the evaporation rate would have ruined the experiment regardless.
Now I’m investigating the best way to seal the chamber while affecting the sample as little as possible. This is important because deuterium/hydrogen exchange could be a major source of experimental error and right now I have no real way of measuring this effect so it may be best to avoid it at all costs. I have purchased/selected sealants based on this. Also, based on the figure to the left, you can see it isn’t very easy to fit many things into that gap created by the top and bottom of the analyslide. The space there is 1/8″ so whatever I use has to either mold to the shape or be small. That is why I chose the following sealants:
- no sealant (control)
- glue/plastic from glue gun (I don’t know what the material is, donated by girlfriend)
- silicon o-ring purchased from amazon
- rubber band (had in the lab)
- parafilm “M”
- Vaseline (donated by me)
- Dupont Krytox Grease (borrowed from CHTM machine shop)
- DOW Corning Vacuum Grease, purchased from amazon
I filled 8 samples with exactly 6mL of DI water. I place the tops of the analyslides carefully on the slide portions and pushed them together slowly so as not to spill any water. I put pressure only on the walls and not the middle of the sample. I then put each sealant around the rim of the analyslide. For the vaseline, Krytox, and DOW Grease I used the giant q-tip seen in the picture to the left to spread the sealant around the area where the lid and the slide meet. For the o-ring and the rubber band I used a clean forceps to move the rubber over the same area. The glue gun glue filled the area between the lip on the top and the slide quite easily. For the parafilm, I cut a small strip (slightly larger than 1/8″ and stretched and wrapped it around the opening. I used to strips in hopes of ensuring a decent seal.
I chose these sealants for various reasons. I was looking for non-reactive “liquids” or suitable solids that could present the least amount of contact/transfer with water. Vaseline, Krytox, and DOW are all nonreactive (maybe not the Vaseline) and hydrophobic. Parafilm is waxy as well but is also a suitable solid. The rubber band and the o-ring were solid enough that I could place them wherever I wanted. The glue gun had the benefit of being a liquid at one point and a solid after cooling.
I was worried that the glue gun would heat the sample considerably but that wasn’t that big a deal. There was some sample heating but it wasn’t very much (although I didn’t measure the exact amount), and the glue cooled quickly.
My guess is the greases and the vaseline will work the best, but they are all the messiest. I don’t think the o-ring will work at all because it never seemed to make contact with the proper edges of the sample. But I have a feeling the rubber band may work well enough.
The experiment results can be seen “live” here.